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1 The Scientific Basis for Prevention of Anterior Cruciate Ligament Injury Nagano, Yasuharu

2 ACL

3 ACL Point Cluster Technique

4 1

5 1 21 ( ACL) ACL 1 20 ACL 20 ACL ACL 20 ACL ACL van Mechelen [1] 4 4 ACL ACL

6 2 1 ACL ACL ACL 8 10[2] [3] ACL 2 8 [2-10][4, 6, 8-10] [4, 6, 9][7] ACL [11] ACL 70%[2, 3] 70%[3, 4, 12]ACL [3, 12, 13]ACL 2 ACL ACL

7 2 ACL ACL ACL ACL ACL 3 ACL ACL ACL ACL ACL ACL ACL ACL ACL ACL ACL 4 [7, 12, 14, 15] McNair [14] 20 Boden [12] 70% Myklebust [7] Olsen [15]

8 32 20 ACL ACL 4 [12, 15-17]Teitz [16] Boden [12] 23 Olsen [15] Krosshaug [17] 28 17ms 50ms 2 [18] Krosshaug [19]

9 ACLMRI (bone bruise)acl MRI [20-24]Mink [20] T2 ACL 72% Rosen [21] ACL 85%83%Graf [22] 1/3 ACL Kaplan [23] 215 MRI ACL Viskontas [24] ACL MRI ACLCipolla [25] ACL 1103 ACL ACL Bellabarba [26] ACL 20 ACL Nishimori [27]ACL ACL

10 ACL ACL ACL ACL (strain)(force) ACL 1980 Arms [28] ACL ACL Berns [29] ACL Markolf [30] ACL 10 ACL ACL Kanamori [31] pivot shift () ACL ACL 30 ACL [32] ACL ACL Renstrom [33] in-vitro ACL ACL 45 ACL Durselen [34] ACL ACL

11 Li [35] ACL 0 30 ACL ACL ACL ACL ACL ACL ACL Withrow [36-38] ACL ACL [36] ACL [37] ACL 30%[38]Weinhold [39] ACL ACL ACL ACL ACL Henning [40] ACL 22 ACL Beynnon [41] ACL ACL ACL Fleming ACL [42][42-44]

12 Closed Kinetic Chain ACL 15 ACL ACL Cerulli [45] ACL ACL MRI ACL Li [46]Li [46]ACL ACL ACL ACL ACL ACL ACL ACL ACL Q Q

13 [47]Q [47-50]Q [51] Q Q ACL ACL ACL Navicular drop [52](calcaneal angle) Navicular drop ACL Navicular drop [53-55]Smith [56]ACL ACL [56][54]ACL Nguyen [50]Navicular drop ACL Yoshioka [57] Braten [58] Nguyen [50] Craig ACL Dejour [59] Meister [60]ACL

14 Brandon [61]ACL Stijak [62] ACL ACL ACL ACL 1980 Notch width index [11] Notch width index [63-67] [68-70]ACL Notch width index [68, 71, 72][73, 74] ACL ACL [71, 72]ACL ACL [75][50] [76]Ramesh [77] ACL ACL Uhorchak [71] ACL ACL Myer [78] ACL ACL [79] ACL

15 Q ACL ACL ACL ACL ACL Huston [80] ACL Chu [81] ACL ACL Dyhre-Poulsen [82]ACL 90ms ACL 100ms [17, 45] 40ms [82] ACL 1970 Markolf [83] (stiffness) 2

16 4 Lloyd [84] Wojtys [85][86] [85, 86] ACL ACL ACL ACL Colby [87] ACL ACL Fagenbaum[88] Cowling [89] Sell [90] Chappell [91] ACL Sell [92]

17 ACL Sigward [93] Landry [94] [95] ACL Kellis [96] Fagenbaum [88] Sigward [97] ACL ACL ACL ACL [3, 12, 13]

18 [12, 15-17] ACL ACL ACL Grood [98] Wu [99] [ ] [103][ ] [ ] McLean [105] Salci [102] Ford [104]McLean [105][103, 105] [105] [103, 105] [102, 103] [105] [103]Hewett [107] ACL ACL

19 ACL [108, 109][88] [89, 106, 110] [106, 110]Lephart [108] [89, 110, 111] [106, 110][111] Hewett [111] Lephart[108] [106, 109]Pappas [106] ACL 40

20 Jacobs [112] ACL ACL Chappell [113] [91] [114] ACL [39]Sell [90]

21 [114] ACL ACL ACL ACL 45 [ ] [93-95, ] McLean [121] ACL ACL [ ][119, 120, 122] McLean [116] McLean [117]Pollard [120] Sigward [93] [93][94, 95, 116, 117]

22 [95, 117] [116, 120] [117, 120] [94, 116] [117][95, 118, 119] [122][94, 120][95] [120] [93, 94] [95, 123] [94, 95] [120] Hawkins [124] ACL

23 ACL [96, 110, 125] [110][110, 112, 125][112] [88] McLean [105] Moran [126] Chappell [127] ACL ACL Borotikar [128] ACL [3] (Maturation) ACL

24 Hewett [129] (1214 ) (15 ) Quatman [130] Yu [131] 12 ACL Hewett [129] ACL ACL Houck [132] Dempsey [133]

25 [134][135] Chaudhari [136] ACL ACL McLean [137] (r 2 =0.58, r 2 =0.64) McLean Noyes [138] Barber-Westin 9 10 [139]9 17

26 [140] Noyes ACL

27 3 ACL ACL ACL ACL 1 ACL ACL 1990 Henning [141] [ ] 4 1 ACL ACL ACL ACL ACL Bencke [153] Hewett [154] Chimera [155] Lephart

28 [156] Hurd [157] Wojtys [158] ACL Lephart [156] Pollard [122] Hewett [154] Noyes [138] Irmischer [159] Myer [160]

29 Myer [161] ACL [162][156] [154, 163, 164] [163][165] [162, 166] ACL

30 3 ACL ACL ACL 4 [1] 2 ACL 3 ACL 1 2 ACL ACL 1 ACL 2 1 ACL ACL

31 7 (Knee rotation)(tibial rotation)

32 2

33 1 1 ACL 2 8 [2-4, 7] ACL 70%[3, 4, 12] [3] ACL ACL [167] [8, 10]

34 2 13 (W 8 W1 5 ) ( ) ( ) Injury Report Form ( 1: IRF) Exposure Sheet ( 1) Injury Report Form () Exposure Sheet 15 Injury Report Form Exposure Sheet Player-Hours Player-Hours( PH)()[10] 1000PH ACL ()

35 PH PH( 1059PH) PH( 2809PH) PH( PH 3868PH) /1000PH /1000PH Table () Table ACL () Table ACL ACL

36 Table Injury location by incidence and injury risk Location Incidence (%) Injury risk Ankle, foot 76 (35.3) Knee 46 (21.4) Low Back 28 (13.0) Thigh 21(9.8) Upper limb 13 (6.0) Shank 10 (4.7) Shoulder 7 (3.3) Head 7 (3.3) Neck 3 (1.4) etc. 4 (1.9) Injury risk are presented by incidence/1000 Player-hours Table Injury diagnosis by incidence and injury risk Diagnosis Incidence (%) Injury risk Ankle lateral sprain 50 (23.3) Low back pain 18 (8.4) ACL injury 12 (5.6) Hamstrings strain 9 (4.2) Achilles tendinitis 4 (1.9) Low back sprain 4 (1.9) Contusion 4 (1.9) Medial meniscus injury 4 (1.9) Metatarsal stress fracture 4 (1.9) Elbow MCL injury 4 (1.9) Ankle medial sprain 3 (1.4) Ankle sprain etc. 3 (1.4) Femoral cartilage damage 3 (1.4) Adductor muscle strain 3 (1.4) Lateral meniscus injury 3 (1.4) Injury risk are presented by incidence/1000 Player-hours

37 Table ACL injury by incidence and injury risk Injury situation Incidence Injury risk ACL injury contact non-contact (game) contact non-contact Injury risk are presented by incidence/1000 Player-hours

38 4 Player-hours(PH) PH Athlete Exposure 1 PH /1000PH /1000PH Messina [10] 3.6 /1000PH 16.0 /1000PH Deitch [8] WNBA WNBA Messina [10] Fong [168] () ACL Deitch [8] WNBA 12.7% 3.6%ACL

39 0.9% WNBA [8] ACL WNBA ACL 6 ACL 12 ACL Messina [10]ACL 0.09 /1000PH 0.09 /1000PH[169] 0.31 /1000PH [7] ACL 83%(12 10 )[3, 4, 12] 70% ACL ACL /1000PH

40 3

41 1 1 ACL ACL 1 [3, 4, 12]ACL 2~8 [2-4, 6, 147] ACL ACL [7, 12, 14] Olsen [15] ACL [104, 107, 113, 115, 116, 119] ACL [87, 100, 101, 115, 116]ACL [116] [93, 120] [170]() ACL [33, 171] [115][91][93, 115] ACL

42 ACL ACL ACL

43 2 18 (19.8± ±7.6cm68.7±16.2kg; ±) 19 (19.4± ±7.5cm59.8±7.5kg) (Figure 3-1-1) 30cm 30cm (Figure 3-1-2) 3

44 30cm Figure Landing position and arrangement of makers Subjects performed a single limb landing from a 30cm platform. Twenty four reflective markers of 9 mm diameter were secured to the limb. Figure Experiment setup and test task Subjects landed with their right foot 30cm away from the platform. A seven camera VICON 370 motion analysis system was used.

45 (Figure 3-1-1)[170] Point Cluster Technique(PCT)[170]PCT PCT Andriacchi [170] 7 (VICON 370; Oxford Metrics Ink., Oxford, UK) 200Hz 1000Hz PCT [170] (PCT 2 )PCT 10 6 Grood [98] (DelSys Bagnoli-8 EMG system) 1/3 1/3

46 1000Hz (Intraclass correlation coefficients; ICC)(1, 3) Root Mean Square (RMS) RMS %MVC (Hamstrings Quadriceps Ratio: HQR)HQR [153] %MVC 50ms 50ms 50ms 50ms [172] 50ms [153] 46ms [173] 3 t U 5%

47 3 ICC(1, 3) ms Figure3-1-3 Table3-1-1 Table3-1-2 (p<0.05) (p<0.01; male 38.1±7.6ms, female 43.7 ±8.1ms) Table Mean (SD) of knee position at foot contact Position at foot contact Flexion (deg) Adduction (deg) External tibial rot. (deg) Ant. translation (mm) Males 15.9 (6.4) 2.0 (2.9) 1.2 (6.0) 2.0 (4.9) Females 18.0 (6.3) 1.8 (2.7) 2.2 (6.0) 3.2 (5.7) Table Mean (SD) of knee motion during at landing Degree or displacement during the landing Flexion (deg) Adduction (deg) Abduction (deg) Internal tibial rot. (deg) Ant. translation (mm) Males 27.8 (7.2) 1.4 (1.3) 1.7 (1.4) 9.4 (3.7)* 5.9 (2.3) Females 31.2 (6.5) 1.6 (1.1) 2.3 (1.7) 12.6 (5.1)* 7.5 (3.8) *: p < 0.05 between males and females

48 Figure Gender-based comparisons of joint motion and GRF data (Mean and SD) Data are presented for Knee Flexion (a), Knee Abduction (b), Internal Tibial Rotation (c), Anterior Tibial Translation (d), and GRF (e).

49 Figure3-1-4HQR Figure ms (p<0.001, Figure3-1-4a) 50ms (Figure3-1-4b)HQR 50ms (p<0.001, Figure3-1-5a) 50ms (Figure3-1-5b) Figure %MVC of the rectus femoris (RF) and the hamstrings (Ham) during the 50 ms time period before foot contact (a), and during the 50 ms time period after foot contact (b) Boxes denote the middle 50% of the range and the median. The whiskers show the extent of the rest of the data. ***p<0.001 between males and females.

50 Figure Ham/quad-ratio (HQR) before foot contact (a), and after foot contact (b) Boxes denote the middle 50% of the range and the median. The whiskers show the extent of the rest of data. ***p<0.001 between males and females

51 4 ACL [3, 12] ACL ACL ACL ACL ACL ACL Cerulli [45] ACL ACL PCT Andriacchi [170] PCT Lafortune [174] PCT [174] 2 PCT Andriacchi [170] ACL [28, 29][30, 32] Graf [22] ACL MRI 1/3 ACL ACL [26]

52 Waite [175] PCT ACL ACL ACL Screw home mechanism Asano [176] Screw home mechanism 30 Screw home mechanism Asano [176] Asano [176] ACL (stiffness)wojtys [86] HQR [91, 93, 115] [177] [178, 179]. [173]

53 ACL ACL ACL [104, 107, 115, 118, 119] 2 PCT ACL [30, 31] ACL [101, 115, 116][88][118] ACL [116, 180]PCT PCT [170, 181]

54 [174] ACL ACL ACL

55 2 ACL 1 ACL ACL ACL [12, 15-17]Olsen [15]ACL ACL ACL ACL ACL ACL ACL [12]- [15]Sell [90] -ACL - ACL Pappas [106] ACL Olsen [15]ACL ACL

56 ACL ACL -ACL ACL

57 2 24 (21.1± ±8.3cm59.3±8.2kg; ±) (Figure 3-2-1a)30cm 30cm 3 -(Figure 3-2-1b) 30cm (Figure 3-2-1c)

58

59 Figure Sequential photographs of experimental tasks: Single-limb landing (a), plant and cutting (b), and both-limb jump landing.

60 (Hawk; Motion Analysis Corp., Santa Rosa, CA, USA) 200Hz 1000Hz PCT [170] 200ms 3 ICC(1, 3) Bonferroni 5%

61 3 ICC(1, 3) ms Figure3-2-2 Table (p<0.01)- (p<0.01) - ( p<0.01) (p<0.05)- - ( p<0.01) (p<0.01) Table Mean (SD) for tasks of joint angle at the time of foot contact. Knee flexion Knee abduction Internal tibial rotation Single limb landing 15.8 (5.0) -4.0 (2.6) -9.0 (3.4) Plant and cutting 19.2 (7.0) -8.2 (3.1) (4.3) Both limb jump landing 32.8 (7.1) -2.2 (3.4) 3.0 (5.2) *; p <0.05, ; p <0.01 Table (p<0.05) - (p<0.01p<0.05)- - (p<0.05p<0.01) Table Mean (SD) for tasks of peak joint angle. Knee flexion Knee abduction Internal tibial rotation Single limb landing 72.5 (6.7) -1.2 (5.2) 12.3 (5.5) Plant and cutting 70.4 (8.5) -2.6 (6.1) 14.4 (6.0) Both limb jump landing 80.3 (16.4) 7.1 (5.5) 14.9 (5.5) *; p <0.05, ; p <0.01

62 Table ( p<0.01) - ( p<0.01) (p<0.01)- ( p<0.01) Table Mean (SD) for angular excursion (deg) and rate of excursion (deg/ms). Knee abduction Internal tibial rotation Excursion Rate Excursion Rate Single limb landing 6.6 (3.6) 0.12 (0.05) 21.4 (6.4) 0.15 (0.06) Plant and cutting 9.8 (3.8) 0.13 (0.04) 26.8 (6.8) 0.22 (0.07) Both limb jump landing 11.2 (3.6) 0.14 (0.05) 12.1 (4.9) 0.14 (0.05) *; p <0.05, ; p <0.01

63 Figure Task-based comparisons of joint motion Data are presented for Knee Flexion (a), Knee Abduction (b), and Internal Tibial Rotation (c).

64 4 ACL [90, 113, 182] ACL Chappell [113] Sell [90] ACL ACLBesier[182] ACL ACL - - [28, 29][30, 32] ACL

65 - ACL ACL [12, 15-17]ACL [90, 113, 182] ACL ACL [38] ACL ACL [30, 32] ACL - - ACL ACL [104, 105, 129] ACL [107][138, 139] Pappas [106] ACL ACL ACL [106]Pappas

66 ACL ACL [28, 33, 41]ACL ACL ACL ACL ACL ACL ACL [17] ACL ACL [139, 140] PCT ACL

67 - ACL PCT ACL -ACL ACL ACL ACL

68 3 1 ACL [4] [15] ACL [100, 101, 108, 115, 116][104, 105, 129] McLean [123]Sigward [183] ACL ACL [16]Zazulak [184][185] Houck [132]45 Blackburn [134] ACL ACL

69 ACL 1 ACL ACL

70 2 10 (20.7± ±5.4cm66.9±6.2kg; ±) 10 (20.1± ±5.5cm56.8±7.4kg;) (Shuttle run cutting) 1 5m 180 5m (Figure 3-3-1) 3

71 z y x Foot contact 5m Original motion direction Figure Shuttle run cutting Subjects ran straight ahead for five meters, planted their cutting foot vertically and then changed direction to move 180 degrees to their original direction of motion.

72 [136, 170] 2 8 (Hawk; Motion Analysis Corp., USA) 200Hz Point Cluster [136, 170] x z ()(+: -: )y z (+: -: ) Andriacchi [170] Grood [98] 50ms 150ms 75ms150ms 150ms 3 ICC(1, 3)

73 t 5%

74 3 ICC(1, 3) ms ms Figure Table (p<0.05) 75ms (p<0.05) (p<0.05) 75ms 150ms (p<0.05p<0.01p<0.05) (p<0.05) 75ms (p<0.01p<0.01)

75 Figure Comparisons of joint motion Data are presented for Knee Flexion/Extension (a), Knee Abduction/Adduction (b), Internal/Internal Tibial Rotation (c), Trunk Forward/Backward Inclination (d), and Trunk Lateral Inclination (e)

76 Table Mean (SD) of knee motion and trunk inclination (deg) Knee flexion Trunk forward inclination Trunk lateral inclination a Males Females Males Females Males Females Foot contact 37.5 (10.5) 29.2 (8.0) 38.4 (6.8)* 31.2 (4.8)* 7.3 (6.9)** -5.2 (9.2)** 75ms 56.0 (7.8)* 47.7 (6.4)* 45.1 (8.3)** 35.5 (5.4)** 8.3 (10.8)** -5.6 (9.9)** 150ms 66.5 (9.0) 58.9 (8.5) 51.5 (10.5)* 41.1 (6.4)* 7.8 (16.5) -5.4 (11.3) Excursion 29.0 (5.1) 29.6 (7.7) 13.1 (7.4) 9.9 (3.6) 0.5 (11.1) -0.2 (4.7) Males Females Males Females Foot contact 4.8 (3.7) 5.0 (4.3) 7.8 (5.2) 8.8 (6.8) Minimum peak 3.3 (4.4) -0.6 (5.2) 3.8 (5.6) 0.1 (5.4) Maximum peak 12.9 (5.3) 9.3 (6.7) 19.0 (5.3) 18.6 (4.2) Excursion 9.6 (2.3) 10.0 (3.7) 15.2 (5.9) 18.6 (5.8) a : positive value indicate the direction of original motion *: p < 0.05 between males and females **: p < 0.01 between males and females Knee abduction Internal tibial rotation

77 Table ms 150ms (r= ; p<0.01; Figure 3-3-3: ) 75ms 150ms (r= ; p<0.05) 75ms 150ms (r= ; p<0.01, p<0.01, p<0.05; Figure 3-3-4: ) 150ms (r=-0.49, -0.49; p<0.05; Figure 3-3-5:) (r=-0.48; p<0.05; Figure 3-3-6: )

78 Table r values for the association with trunk inclination and knee motion Knee flexion Knee abduction Trunk forward inclination FC b 75ms 150ms Exc. c FC b Min peak Max peak Exc. c FC b Min peak Internal tibial rotation Foot contact 0.76** 0.78** 0.65** * ** 75ms 0.72** 0.79** 0.64** * ** 150ms 0.64** 0.73** 0.60** * * Excursion Max peak Exc. c Trunk lateral inclination a FC b 75ms 150ms Exc. c FC b Min peak Max peak Exc. c FC b Min peak Foot contact * * 75ms ms Excursion -0.49* * a : positive value indicate the direction of original motion, b : foot contact, c : excursion *: p < 0.05, **: p < 0.01 Max peak Exc. c

79 60 Knee flexion at foot contact (deg) R = Trunk forward inclination at foot contact (deg) Figure Associations between trunk forward inclination at foot contact and knee flexion at foot contact 30 Excursion of internal tibial rotation (deg) R = Trunk forward inclination at foot contact (deg) Figure Associations between trunk forward inclination at foot contact and excursion of internal tibial rotation

80 60 Knee flexion at foot contact (deg) R = Excursion of trunk lateral inclination (deg) Figure Associations between excursion of trunk lateral inclination and knee flexion at foot contact Excursion of internal tibial rotation (deg) R = Trunk lateral inclination at foot contact (deg) Figure Associations between trunk lateral inclination at foot contact and excursion of internal tibial rotation

81 4 ACL ACL ACL ACL Blackburn [134] Farrokhi [186] Farrokhi [186] ACL Olsen [15] ACL ACL

82 ACL Boden [12] ACL ACL 30 ACL [33, 41] ACL [28]Kanamori [32] ACL ACL [115, 116] Chappell [91] ACL ACL [4] ACL [4] ACL

83 () ACL ACL ACL Point Cluster Technique [170]

84 1 1 ACL

85 4

86 1 1 ACL ACL [107]ACL ACL [121] ACL [104, 115, 119] ACL [30, 31][29] ACL [147, 148, 152] ACL ACL [138, 139, 187] McLean [137]

87 McLean [137] [107, 131, 138]

88 2 28 (20.9± ±7.8cm58.8±7.7kg; ±) (Figure 4-1-1) 5 (continuous jump test: )

89 Figure Continuous jump test All subjects performed five vertical jumps with maximum effort using both legs and landing.

90 (Hawk; Motion Analysis Corp., Santa Rosa, CA, USA) 200Hz 1000Hz PCT [170] 3 1.8cm () (30Hz; Sony Product, Japan) 3.8m (Dartfish software, Dartfish Japan Co., Ltd. Japan) (Figure 4-1-2)

91 Knee valgus angle Figure Measurement of knee valgus using the 2D method The angle between the line formed from the marker on the ASIS to the mid point of the patella and that formed from the mid point of the patella to the midpoint of the ankle joint was recorded as the knee valgus angle.

92 y = a + b x y = a + b x + c x y = a + b ln(x) 2 3 LSD Coorevits [188] (1, 2) 5%

93 3 (1, 2) (: r 2 =0.34, p<0.01; Figure 4-1-3A, : r 2 =0.40, p=0.01; Figure 4-1-3B, : r 2 =0.41, p<0.01; Figure 4-1-3C) (Figure 4-1-4)

94 r 2 r 2 r 2 Figure Associations between 2D valgus and 3D knee abduction during the continuous jump test for the linear model (A), the quadratic model (B), and the logarithmic model (C) The R2 values of all models between 2D valgus and 3D knee abduction were significantly different from zero.

95 Figure Associations between 2D valgus and 3D internal tibial rotation during the continuous jump test The R2 values of all models between 2D valgus and 3D internal tibial rotation were not significantly different from zero.

96 4 ACL ACL McLean [137]( ) McLean [137] McLean [137] ACL ACL Hewett [107]ACL 7.6 ACL Hewett [107]ACL

97 9 ACL 35%30%30% 0%10%10% ACL ACL ACL

98 ACL [29][30, 32] ACL ACL ACL

99 2 1 ACL ACL [12, 15, 16] ACL [107] ACL ACL ACL [143, 145, 147, 148] Plisky [189] ACL ACL ACL ACL Navicular drop [54, 56, 190](calcaneal angle) [54, 56]ACL Q ACL [191]

100

101 (19.4± ±6.6cm62.8±6.5kg; ± ) 5 (continuous jump test: )(Figure 4-2-1)() cm () (30 Hz; Panasonic Inc., Japan) 3.5m ( 55cm)(Figure 4-2-2) (Dartfish software, Dartfish Japan Co., Ltd. Japan) 4 1

102

103 Figure Continuous jump test All subjects performed five vertical jumps with maximum effort using both legs and landing. Figure Setting for continuous jump test The trial was recorded using digital video cameras from the frontal plane and sagittal plane. Each digital camera was placed 3.5 m distant from the landing point at the knee joint height.

104 Plisky [189]Star Excursion Balance Test (Figure 4-2-3) [192] ()3 3 3 ( )

105 Figure Star Excursion Balance Test procedure While maintaining a single-leg stance, the player was asked to reach with the free limb in the anterior, posteromedial, and posterolateral directions in relation to the stance foot. The device comprises a footplate and three measure cords with a slider spreading to anterior, posteromedial, and posterolateral directions.

106 Q Navicular drop Leg heel Q Q [47] 90 (Figure 4-2-4)(Multi Level A-300; Shinwa Sokutei K.K., Japan) 1/3 (mid-point of hip rotation: MPR) MPR = ( IR ER) 2(deg) MPR

107 Figure Measurement of hip rotation In the prone position with knee flexed 90 deg, the angle between the tibia and the vertical was measured using an inclinometer.

108 Denegar [193] 1/3 0 Navicular drop Navicular drop [194] Brody [52] (mm) Leg heel Leg heel Woodford-Rogers [54] 1/3 Leg heel ()() Pearson (F=2.0)

109 5%

110 ± ±7.7 r Table Navicular drop (p < 0.05)(p < 0.05)MPRNavicular drop Leg heel (p < 0.01, p < 0.05, p < 0.01, p < 0.01, p < 0.05) Table Navicular drop Navicular drop (p < 0.01) r Table Navicular drop Navicular drop (p < 0.01) r (r = 0.340, 0.258, p < 0.01)

111 Table Mean (SD) of lower limb alignment (deg or mm) and balance abilities (% leg length), and r values for the association with knee valgus angle and knee flexion angle Q-angle Hip IR Hip ER Mid point Ankle DF Navicular ROM ROM of rotation ROM drop Mean (SD) 20.1 (4.6) 49.9 (10.5) 33.5 (8.4) 8.2 (7.4) 34.5 (8.7) 5.7 (3.7) Knee valgus r * * Knee flex r ** * 0.42** 0.29** LH-angle AT Bal. PM Bal. PL Bal. 5.2 (4.5) 72.6 (5.7) (7.2) (9.2) Composite Balance 96.9 (6.1) Mean (SD) Knee valgus r Knee flex r 0.19* 0.35** *: p<0.05, **: p<0.01 AT bal., anterior balance; PM bal., posteromedial balance; PL bal., posterolateral balance

112 Table Results of step-wise regression model for peak knee valgus angle Model r r 2 Adj. r 2 SE of Est Equation 1: Knee valgus = 0.043(IR ROM) Equation 2: Knee valgus = 0.044(IR ROM) (ND) IR ROM, ROM of hip internal rotation; ND, navicular drop Table Results of step-wise regression model for peak knee flexion angle Model r r 2 Adj. r 2 SE of Est Equation 1: Knee flexion = 0.375(DF ROM) Equation 2: Knee flexion = 0.347(DF ROM) (ND) Knee flexion = 0.282(DF ROM) (ND) (AT) Equation 3: Knee flexion = 0.261(DF ROM) (ND) (AT) Equation 4: (IR ROM) DF ROM, ROM of ankle dorsiflexion; ND, navicular drop; AT, anterior balance; IR ROM, ROM of hip internal rotation

113 4 ACL [12, 15, 16] ACL [107] ACL ACL [12, 15, 16] ACL [28, 33, 41] ACL

114 [189] Navicular drop ACL ACL Cincinnati Sportsmetrics [145]PEP [148]Myklebust [147] ACL ACL ACL

115 ACL

116 5

117 1 ACL 1 ACL ACL ACL

118 2 ACL Pubmed ACLPrevention 251 ( ) ACL ACL [ ]12 ACL 10

119 3 12 Henning ACL Henning [200]Henning Quad-cruciate interaction () ACL ACL ACL ACL 0.33 / 0.25 / Henning ACL Vermont Vermont [142] ACL ACL ACL Phantom-foot 1 2 1) 2) 3) 4) 5)

120 20 ( 4700 )( 4000 ) ACL 2 ACL ACL 2 (26.6 / 10 /) Caraffa Caraffa [143] ACL ( ) 0.15 /season/team ( ) 1.15 /season/team [143] Cincinnati Sportsmetrics Hewett [145] Cincinnati Sportsmetrics Technique phasefundamentals phase Performance phasetechnique phase Fundamentals phase Performance phase ACL

121 ACL (463 ) 0.12 /1000Athlete exposure(ah)(366 ) 0.43 /1000AE 0.09 /1000AH [145] [154] ACL [138] Dynamic Neuromuscular Analysis (DNA) Hewett [152, 201, 202] Sportsmetrics Training Dynamic Neuromuscular Analysis program( DNA ) Ligament dominancequadriceps dominanceleg dominance 3 Ligament dominance ACL [154]31 wall-jumptuck-jumpbroad-jump and hold180jumpsingle-leg hop-and-hold Quadriceps dominance [101, 108]

122 ACL [80] 55 Quadriceps dominance squat-jump broad-jump and hold Leg dominance X-hop DNA ACL DNA ACL Hewett [161, 203]DNA 3 Soderman Soderman [144] [144] ACL (: 4 : 1 )ACL (0.12/1000Play Hours (PH) 1.36/1000 PH, RR: 10.96) (62 ) Frappier Acceleration Training

123 Heidt [146]Frappier Acceleration Frappier Acceleration Trainng 7 (258 ) 33.7%(42 ) 14.3%ACL 3.0% 2.4% [146] Myklebust Myklebust [147] ACL ACL ( ) 2 [147] ACL 0.09 /1000PH, 0.14 /1000PH ( (OR): 0.64) (OR: 0.37)

124 (OR: 0.06) [162] Prevent Injury, Enhance Performance (PEP) Mandelbaum [148] ACL Prevent Injury, Enhance Performance ( PEP)PEP 20 (without side to side movement) (soft landing) (opposed to landing with a flat foot) ACL (1041/844 ) 0.09 /1000AH (1902/1913 : 00/01) 0.49 /1000AH ACL [148] Olsen Olsen[149] 20 (Knee over toe) ( ) 6.9%( ) 13.1%(RR: 0.51)

125 3 (ACL 3 ) 14 (ACL 10 PCL 3 MCL 1 )(RR: 0.20) Petersen Petersen [150] Myklebust. [147] knee over toe 3 1 ACL ACL (134 ) 0.04/1000AH (142 ) 0.21/1000AH ACL (OR: 0.17) Knee Ligament Injnury Prevention (KLIP) Pfeiffer [151] Knee Ligament Injury Prevention ( KLIP) 4 Hewett [145]20 KLIP [159] ACL 2 ACL KLIP (577 ) 0.167/1000exposure(862 ) 0.078/1000exposure (OR: 2.05)[151]

126

127 4 ACL 12 ACL 10 ACL Table

128 Table Details and effects of the 10 ACL prevention programs Year Author Sports Strength Flexibility Agility Jump Balance Feedback 1995 Ettlinger et al. Ski 1996 Caraffa et al Hewett et al Soderman et al Heidt et al Myklebust et al Mandelbaum et al. Male soccer Female basketball, volleyball, soccer Female soccer Female soccer Female handball Female soccer PNF) treadmill 2005 Olsen et al. Handball Effects (control vs intervention) 26.6 vs 10/season a 1.15 vs 0.15/team/season 0.43 vs 0.12/1000AE b 1 vs 4 injuries (ACL) 0.12 vs 1.36/1000PH cd 3.0% vs 2.4% 0.14 vs 0.09/1000PH d (OR e : 0.64), (OR e : 0.37) f 0.49 vs 0.09/1000AE (RR g : 0.18) 14 vs 3 injuries RR g : 0.20 h a 2005 Petersen et al Pfeiffer et al. Female handball Female basketball, volleyball, soccer vs 0.167/1000AE b (OR e : 2.05) vs past 2 years b AE: Athlete Exposure c Severe knee injury d PH: Play Hour e OR: Odds Ratio f in top league g RR: Rerative Risk Including 3 PCL injuries and 1 MCL injury in control h 0.21 vs 0.04/1000AE b (OR e : 0.17)

129 ACL (Feedback) 6 ACL 1990 Ettlinger [142] Caraffa [143] Soderman [144] Hewett [145] [ ] 7 [ ] Heidt [146] 6 ACL [12]ACL Hewett [145]

130 7 4 Mandelbaum [148] Olsen [149] ACL ACL 3 [145, 147, 151]Hewett [145] [154]Myklebust [147] 1 35 [162]Pfeiffer [151] [159] ACL

131 Randomized control trial ( RCT) (Prospective cohort study: PCS) 10 RCT Olsen [149] Soderman [144] 2 Olsen [149]RCT Soderman [144] PCS [142, 143, 145, 146][142, 143, 145, 148] [146, 150] ACL Olsen [149] RCT Olsen [149] PCS [145, 147, 148, 150] Caraffa [143]Soderman [144] [147, 149, 150] Heidt [146]Pfeiffer [151]ACL

132 ACL ACL ACL ACL

133 2 1 ACL ACL 1 [204] [205] ACL ACL ACL [145, ] ACL [145, ] ACL ACL [122, 156, 160, 206] [156, 160][160][206] Myer [160] [122, 156] ()() ACL ACL [15] [153, 155, 156] [153, 155, 156]

134 DeMorat [207] ACL Colby [87] ACL ACL ACL

135 2 8 (19.4± ±4.9cm64.1±7.8kg; ±) ( 3 1 ) 3 1 (Pre-tarining1)5 2 (Pre-training2) (Post-training) 3 1 ( 3 1 ) [147, 154, 201, 202](Table 5-2-1) (1) (2) (3) 2

136 Table Jump and balance training Exercise Time or Repetitions Exercise Time or Repetitions Phase1: Technique Phase2 :Performance 1. Squat jumps 20sec 1. Squat jumps 20sec jumps 20sec 2. Scissors jumps 20sec 3. Single leg balance 20sec 3. Single leg balance and pass 20sec 4. Hop jump (both leg) 20sec 4. Hop jump (single leg) 20sec 5. Broad jump and hold 28m 5. Single-leg hop and hold 14m/leg 6. Crossover hop, hop, hop, stick 28m 6. Crossover hop, hop, hop, stick 28m Squat jumps: Drop into deep knee, hip, and ankle flexion and then take off into a maximal vertical jump. On landing, immediately return to the starting position and repeat the initial jump. 180 jumps : Initiates a 2-footed jump with a direct vertical motion combined with a 180 rotation in midair, keeping arms away from the body to help maintain balance. When landing, immediately reverses this jump to the opposite direction. Single-leg balance (and pass): This drill is performed on a balance device that provides an unstable surface. Begin by stanging on one foot on the device. After the subject has improved, the training drills can incorporate ball catches and passes. Hop jumps: Start by standing next to a small square balance board. Hop onto the board and then hop off on the opposite side. Repeat hopping on and off the board. Broad jump and hold: Begin by swinging arms forward and jumping horizontally and vertically at approximately a 45 angle to achieve a maximum horizontal distance. The athlete lands with her knees flexed to approximately 90. Crossover hop, hop, hop, stick: Start on a single limb and jump at a diagonal across the body landing on the opposite limb with the foot pointing straight ahead and immediately redirect the jump in the opposite diagonal direction. Scissors jumps: Start in a stride position with one foot well in front of other. Jump up, alternating foot positions in midair. Single-leg hop and hold: Initiate the jump by swinging the arms forward while simultaneously extending at the hips and knees. The jump should carry the athlete up at an angle of approximately 45 and attain maximal distance for a single-leg landing. The subject is instructed to land on the jumping leg in deep knee flexion.

137 3 1 ( 3 1 ) 50ms 50ms (%MVC)(Hamstrings Quadriceps Ratio: HQR) 3 Bonferroni Friedman Wilcoxon Pre-training1 Pre-training2 Pre-training2 Post-training 5%

138 3 60ms Figure Table Pre-training2 Post-training (p<0.01) Pre-training1 Pre-training2 Pre-training2 Post-training (p<0.01, p<0.05) Table Pre-training2 Post-training (p<0.001) Table Mean (SD) of knee position at foot contact Position at foot contact Flexion (deg) Adduction (deg) External tibial rot. (deg) Ant. translation (mm) Pre-training (7.3) 1.3 (2.7) 1.9 (5.3) 0.9 (5.5) Pre-training (7.0) 0.1 (3.3) 0.6 (7.1) 5.0 (3.9) ** ** Post-training 24.4 (5.9) 0.6 (3.2) 1.1 (5.7) 1.6 (5.0) * *: p < 0.05, **: p < 0.01 Table Mean (SD) of knee motion during at landing Degree or displacement during the landing Flexion (deg) Adduction (deg) Abduction (deg) Internal tibial rot. (deg) Ant. translation (mm) Pre-training (7.3) 1.5 (1.0) 2.8 (2.0) 12.3 (3.8) 9.4 (3.2) Pre-training (7.1) 1.3 (0.8) 3.7 (2.0) 13.8 (5.1) 9.2 (4.2) Post-training 40.3 (5.4) *** 1.3 (1.1) 4.1 (1.7) 13.3 (5.6) 9.1 (3.6) ***: p < 0.001

139 Figure Mean joint motion during the single limb drop landing for pre-training 1, pre-training 2, and post-training. Data are presented for knee flexion (a), internal tibial rotation (b), knee valgus (c) and anterior tibial translation (d).

140 Figure 5-2-2HQR Figure ms Pre-training2 Post-training (p<0.05, Figure 5-2-2a) 50ms (Figure 5-2-2b)HQR 50ms 50ms (Figure 5-2-3) Figure %MVC of the rectus femoris (RF) and the hamstrings (Ham) for the 50ms before foot contact (a), and for the 50ms after foot contact (b) Boxes denote the middle 50% of the range and the median. The whiskers show the extent of the rest of the data. * p < 0.05 from the previous test

141 Figure Ham/Quad-ratio (HQR) before foot contact (a), and after foot contact (b) Boxes denote the middle 50% of the range and the median. The whiskers show the extent of the rest of data.

142 4 ACL ACL [145, ] ACL (Figure 5-2-1) [156, 160, 206][122, 156] [160]ACL ACL ACL [12, 15, 16] ACL

143 [30, 32] ACL ACL ACL ACL ACL ACL Onate [206] ACL [208] [178, 179, 209, 210] (Pre activation)[153, 155]

144 (electromechanical delay) 50ms [172] [210] [211, 212] [173, 213] ACL ACL ACL 30 ACL [28, 33, 41] [33, 214] 60 ACL [41][177] [179] ACL ACL 3 1 5

145 ACL

146 6

147 ACL 4 [1] 4 2 ACL ACL ACL ACL ACL ACL ACL ACL 3 ACL Bahr [215] ACL ACL ACL ACL ACL

148 3 1 PCT ACL ACL 2 - ACL - ACL ACL ACL 3 ACL ACL 3 ACL 4 4 ACL ACL

149 ACL 4 1 ACL 2 ACL ACL 5 ACL ACL 1 ACL ACL ACL 2 1 ACL 3 ACL () ACL ACL

150 ACL ACL ACL ACL ACL ACL ACL ACL [216, 217] ACL 3 ACL 5 ACL 4

151 7

152 ACL ACL ACL ACL ACL ACL ACL - ACL ACL ACL ACL

153 ACL ACL ACL

154 1 Injury Report Form

155 Exposure Sheet

156 2 Point Cluster Technique PCT Andriacchi [170] PCT PCT I (( p i, y ) 2 + ( p i,z ) 2 ) m i p i,x p i, y ( m i ) p i,z p i,x ( m i ) i i i I = p i,x p i, y ( m i ) (( p i,z ) 2 + ( p i,x ) 2 ) m i p i, y p i,z ( m i ) i i i p i,z p i,x ( m i ) p i, y p i,z ( m i ) (( p i,x ) 2 + ( p i, y ) 2 ) m i i i i (1) p i i m i 3 3 R R = ( E 1, E 2, E 3 ) (2) E j j E j = ( e j,x,e j, y,e j,z ) T (3) PCT (2) R (2) R Grood [98] ()( )

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178 1 Y Nagano, H. Ida, M Akai, and T. Fukubayashi: 2007 Gender differences in knee kinematics and muscle activity during single limb drop landing. Knee, Vol.14, p Y Nagano, M Sakagami, H Ida, M Akai, and T Fukubayashi: 2008 Statistical Modeling of Knee Valgus during a Continuous Jump Test. Sports Biomechanics, Vol.7, p Y Nagano, H. Ida, M Akai, and T. Fukubayashi: 2008 Biomechanical characteristics of the knee joint in female athletes during tasks associated with Anterior Cruciate Ligament injury. Knee, in press. 4 Y Nagano, M Fukano, K Itagaki, S Li, S Miyakawa, and T. Fukubayashi: 2008 Influence of Balance Ability and Lower Limb Characteristics on Knee Motion during a Continuous Jump Test. Sports Medicine, Arthroscopy, Rehabilitation, Therapy & Technology, submitted. 5. Y Nagano, H. Ida, M Akai, and T. Fukubayashi: Effects of Jump and Balance Training on Knee Kinematics and Electromyography of Female Basketball Athletes during a Single Limb Drop Landing: 2008 Sports Medicine, Arthroscopy, Rehabilitation, Therapy & Technology, submitted. 6. : Point Cluster -, Vol24, , 7. : 2008 ACL - () Sports Physical Therapy Seminar Series ACL

179 1. Y Nagano, H Ida, M Akai, and T Fukubayashi: GENDER DIFFERENCES ASSOCIATED WITH THE RISK OF NON-CONTACT ACL INJURY -KINEMATICS DURING A SINGLE LIMB DROP LANDING-. International Symposium on Ligaments & Tendons-, Washington DC, February, Y Nagano, H Ida, M Akai, and T Fukubayashi: THE EFFECTS OF JUMP AND BALACE TRAINING ON KNEE KINEMATICS DURING SINGLE LEG LANDING. Orthopaedic Research Society 52nd Annual Meeting, Chicago, March, Y Nagano, M Sakagami, H Ida, M Akai, S Miyagawa and T Fukubayashi: THE CONTINUOUS JUMP TEST CAN SCREEN FOR ANTERIOR CRUCIATE LIGAMENT INJURY. Orthopaedic Research Society 53nd Annual Meeting, San Diego, February, Y Nagano, H Ida, M Akai, and T Fukubayashi: DIFFERENCES IN KNEE KINEMATICS DURING SINGLE AND BOTH LIMB ATHLETIC TASKS. American College of Sports Medicine 54th Annual Meeting, New Orleans, May, Y Nagano, H Ida, M Akai, and T Fukubayashi: EFFECTS OF PREVENTION TRAINING FOR ANTERIOR CRUCIATE LIGAMENT INJURY DURING SINGLE LIMB DROP LANDING IN FEMALE BASKETBALL ATHLETES. 15th Triennial Congress of Asia Pacific Orthopaedic Association, Seoul Korea, September, Y Nagano, S Kaneko, E Iwata, H Ida, M Akai, and T Fukubayashi: GENDER DIFFERENCES IN KNEE AND TRUNK MOTION DURING SSHUTTLE RUN CUTTING. Orthopaedic Research Society 54th Annual Meeting, San Francisco, March, Y Nagano, H Miki, K Tsuda, Y Shimizu, Y Nou, T Fukubayashi.: THE INCIDENCE OF INJURY FOR THE JAPANESE TOP LEVEL FEMALE BASKETBALL LEAGUE. 2nd World Congress on Sports Injury Prevention, Tromso, June, 2008.

180 Point Cluster Technique

181 The Knee 14 (2007) Gender differences in knee kinematics and muscle activity during single limb drop landing Yasuharu Nagano a,, Hirofumi Ida b, Masami Akai c, Toru Fukubayashi d a Waseda University Graduate School of Sports Sciences, Sports Orthopedic Laboratory, Mikajima , Tokorozawa, Saitama , Japan b Kanagawa Institute of Technology, Kanagawa, Japan c National Rehabilitation Center for Persons with Disabilities, Saitama, Japan d Waseda University Faculty of Sports Sciences, Saitama, Japan Received 13 August 2006; received in revised form 14 November 2006; accepted 19 November 2006 Abstract The likelihood of sustaining an ACL injury in a noncontact situation is two to eight times greater for females than for males. However, the mechanism and risk factors of ACL injury are still unknown. We compared knee kinematics as well as electromyographic activity during landing between male and female athletes. Eighteen male athletes and nineteen female athletes participated in the experiment. The angular displacements of flexion/extension, valgus/varus, and internal/external tibial rotation, as well as the translational displacements of anterior/posterior tibial translation during single limb drop landing were calculated. Simultaneous electromyographical activity of the rectus femoris (RF) and hamstrings (Ham) was taken. During landing, internal tibial rotation of the females was significantly larger than that of the males, while differences were not observed in flexion, varus, valgus, and anterior tibial translation. Hamstrings/quadriceps ratio (HQR) for the 50 ms time period before foot contact was greater in males than in females. The mechanism of noncontact ACL injury during a single limb drop landing would be internal tibial rotation combined with valgus rotation of the knee. Increased internal tibial rotation combined with greater quadriceps activity and a low HQR could be one reason female athletes have a higher incidence of noncontact ACL injuries Elsevier B.V. All rights reserved. Keywords: ACL injury; Risk factor; Tibial rotation; Hamstrings/quadriceps ratio 1. Introduction In sports science, many researchers have studied the mechanism as well as the risk factors of anterior cruciate ligament (ACL) injury. ACL injury is one of the most common injuries in sports activities and often occurs in noncontact situations [1 3]. The likelihood of sustaining an ACL injury is two to eight times greater for females than for males [1,3 6]. Corresponding author. Tel./fax: address: [email protected] (Y. Nagano). According to questionnaire and video analyses [2,7 9], a large portion of ACL injuries occur in the noncontact situation at the time of foot strike during sudden stopping, cutting or landing. The position of the knee at the time of injury is in slight flexion and valgus with the tibia in internal or external rotation [9]. In biomechanical studies, increased knee valgus and high abduction loads increased the risk of ACL injury during athletic tasks [10 16]. The angle of knee flexion was also a factor during ACL injury [11,14,17 19]. Furthermore, Wojtys et al. reported that female athletes have greater internal tibial rotation during external loading. However, the relationship between rotation of the tibia and the risk of ACL /$ - see front matter 2006 Elsevier B.V. All rights reserved. doi: /j.knee

182 Y. Nagano et al. / The Knee 14 (2007) injury during the high risk maneuver (i.e., landing, cutting) are still unknown. The purpose of this study was to analyze the 3-D in vivo kinematics of the knee including tibial rotation during a single limb drop landing. Moreover, we compared knee kinematics as well as electromyographic activity of the quadriceps and hamstrings between male and female athletes to examine the risk factors of ACL injury. Our hypothesis was that female athletes have greater internal tibial rotation also during landing and therefore have greater risk for ACL injury. 2. Materials and methods 2.1. Subjects Eighteen male athletes and nineteen female athletes who attend Waseda University and were free of musculoskeletal ailment participated in the experiment. The average age of the male subjects was 19.8 (4.6) yrs. (Mean (SD)), the average height was 1.77 (0.4) m, the average weight was 68.7 (16.2) kg and the average BMI was 21.9 (0.9). The average age of the female subjects was 19.4 (0.9) yrs., the average height was 1.66 (0.1) m, the average weight was 60.0 (7.5) kg and the average BMI was 21.6 (1.6). Ten male and eleven female subjects were basketball players, while the remaining eight male and eight female subjects were tennis players. Subjects who played different sports were recruited to examine the difference between genders that is not influenced by a particular sports activity. Subjects signed an informed consent document approved by Waseda University Experimental task All subjects performed a single limb drop landing from a 30 cm platform (Fig. 1). The subjects were instructed to put their hands on their lower torso, stand on their right foot, and jump 30 cm away from the platform. The Fig. 1. Landing position and arrangement of makers. Subjects performed a single limb drop landing from a 30 cm platform. Twenty four reflective markers of 9 mm diameter were secured to the limb. Fig. 2. Experiment setup and task. Subjects landed on their right foot 30 cm away from the platform. A seven camera VICON 370 motion analysis system was used. subjects were to land on their right foot with their foot in a neutral position (Fig. 2). Upon landing, each subject was instructed to place their center of mass as far forward as possible in an attempt to limit horizontal motion and land without jumping up. Throughout the experiment, the subjects were barefoot. The subjects were allowed several preparation trials. Measurement was continued until three successful trials were accomplished consecutively Data collection All experiments took place at the National Rehabilitation Center for Persons with Disabilities in Saitama, Japan. A seven camera VICON 370 motion analysis system (Oxford Metrics Ink., Oxford, UK) was used to record the 3-D movements of the lower limb (Fig. 2). The laboratory was equipped with six force plates (9287A, Kistler Japan Co., Ltd., Tokyo, Japan). The motion and force data were recorded at 200 Hz and 1000 Hz, respectively. For each subject, twenty four reflective markers of 9 mm diameter were secured to the lower limb using double-sided adhesive tape (Fig. 1). The markers were used to implement the Point Cluster Technique (PCT) [20]. The PCT provides a minimally invasive estimation of the in vivo motion of the knee. By using a cluster system of skin markers on a limb segment, the PCT assumes to cancel out the noise resulted from skin deformation. We developed our algorithm of the PCT following the procedure described by Andriacchi et al. [20]. We calculated the knee kinematics using the Joint Coordinate System proposed by Grood and Suntay [21]. In the PCT, the skin markers are classified into two groups: a cluster of points representing a segment and points representing bony landmarks. For a cluster of points, ten and six markers were attached on the thigh and shank segment, respectively. The bony landmarks were the great trochanter, the lateral and medial epicondyles of the femur, the lateral and medial edges of the tibia plateau, the lateral (fibula) and medial malleoli and the fifth metatarsophalangeal joint. Simultaneous electromyographical activity of the rectus femoris (RF), biceps femoris (BF) and semimembranosus (SM) were measured. Amplified surface electrodes (DelSys, Inc., Boston, USA) were used to detect muscular activity. Preamplification was equal to 1000, while the common mode rejection rate was 92 db. Double-sided adhesive strips were used to adhere the electrodes to the subject's skin. Additionally, surgical tape (NICHIBAN Co., Ltd. Tokyo, Japan) was placed over the electrodes as well as around the thigh and shank to retard movement of the electrodes on the skin that would cause movement artifacts. Surface EMG electrodes were placed at the midpoint of the top of the patella to the posterior superior iliac spine over the muscle belly of the RF and distally one-third of the distance from the knee joint space to the ischial tuberosity over the muscle bellies of the BF and the SM. The reference electrode was placed on the head of the fibula. We recorded the EMG data at 1000 Hz.

183 220 Y. Nagano et al. / The Knee 14 (2007) s to record a static trial, and then performed the task that was previously described Data analysis The coordinate data obtained from the markers were not smoothed because of the expected noise-canceling property of the PCT. In each trial, we calculated the angular displacements of flexion/extension, valgus/varus, and internal/external tibial rotation, as well as the translational displacements of anterior/posterior tibial translation using the PCT. The reference position for these measurements was obtained during the static trial. We analyzed these data at the time of foot contact and at the time when the vertical ground reaction force (GRF) peaked after foot contact (i.e., during the landing). During the landing, the angular displacements of flexion/extension, valgus/ varus, and internal/external tibial rotation as well as the anterior/posterior tibial translation were calculated. Additionally, we calculated the time of the peak vertical GRF. The root mean square (RMS) of the EMG data was calculated for each trial. The EMG activities of the two hamstrings muscle were averaged together to represent the whole activity of the hamstrings (Ham). For the maximum voluntary contraction, the RMS of the EMG data was calculated and the mean RMS of the middle one second was used to normalize the dynamic contraction recorded during the landing (%MVC). The hamstrings/quadriceps (quadriceps refers to the rectus femoris in this experiment) ratio (HQR) was calculated to define the flexor muscle activation relative to the extensor muscle activation. The HQR was calculated according to procedures outline by Bencke et al. [22]. Average %MVC (RF and Ham) and HQR data output was computed during each of the following time frames: 1) 50 ms before foot contact with the ground, and 2) 50 ms immediately after foot contact. The time period 50 ms before foot contact indicates preactivity of these muscles. Considering an electromechanical delay of about 50 ms [23], the preactivation force corresponds to the time before foot contact. The time period 50 ms after foot contact was chosen since a previous study found that the activity of the knee extensors peaked at approximately 46 ms after toe contact while the knee flexors showed a minimum EMG activity [22]. It is thought that these activities include spinal reflexive neuromuscular activities [24]. To compare between males and females, a student's T-test was performed on the kinematics data, and a Mann Whitney U-test was performed on the EMG data. All statistical comparison was performed with the level of significance set at pb Results 3.1. Kinematics data Fig. 3 illustrates the mean time course comparisons across genders for the three angular displacements (Flexion/Extension, Internal/External tibial rotation, and Valgus/Varus), the translational displacement of anterior tibial translation, and the GRF data during the single limb drop landing. At the time of foot contact, the position of landing was in slight flexion, external tibial rotation, and varus angulation. After foot contact, the magnitude of knee flexion and internal tibial rotation increased with time for all subjects. On Fig. 3. Gender-based comparisons of joint motion and GRF data (Mean and SD). Data are presented for knee flexion (a), internal tibial rotation (b), knee valgus (c), anterior tibial translation (d), and GRF (e). The EMG data were recorded when the subject performed a maximum voluntary knee flexion and extension at 60 of knee flexion against a manual resistance for three seconds. The subject remained in a standing position for Table 1 Mean (SE) of knee motion at foot contact Position at foot contact Flexion (degree) External tibial rot. (degree) Varus (degree) Ant. translation (mm) Males 15.9 (1.5) 1.2 (1.4) 2.0 (0.7) 2.0 (1.2) Females 18.0 (1.5) 2.2 (1.4) 1.8 (0.6) 3.2 (1.3)

184 Y. Nagano et al. / The Knee 14 (2007) Table 2 Mean (SE) of knee motion at landing Degree or displacement during the landing Flexion (degree) Internal tibial rot. (degree) Varus (degree) Valgus (degree) Ant. translation (mm) Males 27.8 (1.7) 9.4 (0.9) 1.4 (0.3) 1.7 (0.3) 5.9 (0.5) Females 31.2 (1.5) 12.6 (1.2) 1.6 (0.3) 2.3 (0.3) 7.5 (0.9) pb0.05 between males and females. the other hand, knee varus increased slightly with time, and then valgus increased with time. Anterior tibial translation got peak at approximately 20 ms, and then decreased to the level it was at the time of foot contact. GRF increased with time and got peak force occurred at approximately 40 ms. It was found that knee motion between genders at the time of foot contact were not significantly different (Table 1). During landing, internal tibial rotation was significantly larger for females compared to males ( p b 0.05), while significant differences could not be determined in flexion, varus, valgus, and anterior tibial translation (Table 2). The time of maximum vertical GRF after the time of foot contact for males was significantly faster than that for females ( pb0.01; male 38.1 (7.6) ms, female 43.7 (8.1) ms; Mean (SE)) Electromyographical data Before foot contact, the %MVC of the Ham was not significantly different between genders, however the %MVC of the RF was significantly greater in females ( pb0.001) (Fig. 4a). On the other Fig. 5. Ham/quad-ratio (HQR) before foot contact (a), and after foot contact (b). Boxes denote the middle 50% of the range and the median. The whiskers show the extent of the rest of data. pb0.001 between males and females. hand, during the 50 ms period immediately after foot contact, the % MVC of the RF and the Ham were not significantly different between genders (Fig. 4b). HQR during the 50 ms time period before foot contact was greater in males than in females ( p b 0.001) (Fig. 5a), while there were no differences in the HQR during the 50 ms time period immediately after foot contact (Fig. 5b). 4. Discussion Fig. 4. %MVC of the rectus femoris (RF) and the hamstrings (Ham) during the 50 ms time period before foot contact (a), and during the 50 ms time period after foot contact (b), Boxes denote the middle 50% of the range and the median. The whiskers show the extent of the rest of the data. pb0.001 between males and females. The primary purpose of this study was to analyze and compare knee kinematics between females and males during a single limb drop landing. A single limb drop landing is a common maneuver during which noncontact ACL injury occurs [2,3]. The analysis of this maneuver is beneficial to ensure the mechanism of ACL injury. Additionally, comparison across genders can provide insight as to the reason why females display a higher incidence of injury as compared to males. When examining the mechanism of ACL injury, the exact time when the ACL is ruptured is unknown. Cerulli et al. [25] reported that ACL strain begins to increase prior to landing and reaches a peak that corresponds to the peak ground reaction force. Therefore, the position of the knee at foot contact and the displacement of the tibia between the time of toe contact and the time of the peak ground reaction force may be important when considering ACL injury.

185 222 Y. Nagano et al. / The Knee 14 (2007) The result of this study showed that internal tibial rotation occurred after toe contact during a single limb drop landing. In cadaver studies, increased internal tibial rotation combined with knee valgus lead to increased strain [26,27] and increased force [28,29] in the ACL. Furthermore, bone bruises most often occur in the middle third of the lateral femoral condyle and the posterior third of the lateral tibial plateau [30]. In addition, a predominance of lateral meniscal tears was observed with acute ACL rupture [31]. Considering these observations combined with the results of this study, it is thought that internal tibial rotation may occur at the time of ACL injury. In another study that used the PCT, internal tibial rotation was also observed when walking [32]. Waite et al. [33] examined ACL-deficient knee kinematics during running and cutting using the PCT. Their data indicated that while tibiofemoral translation in the anteroposterior plane is controlled to within normal limits, coronal translation and rotation are poorly controlled. Their data suggested that the ACL may restrict coronal translation. In other words, coronal translation during athletic tasks may load the ACL. In the normal knee, it is commonly thought that internal tibial rotation accompanies knee flexion, i.e., the screw home mechanism. Asano et al. [34] reported that the screw home mechanism was noticeable when the knee flexion angle was less than 30 in vivo under weightbearing conditions. In this study, however, the internal tibial rotation was observed when the knee flexion angle was approximately between 20 and 40. During the time when the vertical GRF peaked after foot contact, the knee flexion angle was approximately between 15 and 30 and the angular displacements of internal tibial rotation were greater than the results of a previous study [34]. Thus, internal tibial rotation during landing is thought to be important. From the results of this study, internal tibial rotation was greater in females than in males. It is thought that this difference is caused by knee stiffness and electromyographic activities. Wojtys et al. [35] examined the torsional knee stiffness provided by passive and active restraints (ligament and muscle contraction). They reported that maximal tibial rotations were greater in females than in males in response to a passive load (12.5 (2.8) and 10.8 (2.2), respectively). Moreover, the female athletes exhibited a smaller volitional increase in apparent torsional stiffness of the knee under internal rotation loading than did the matched male athletes. As for electromyographic activity, the results of this study indicated greater quadriceps activation and a lower HQR in females than in males before foot contact. This result is supported by previous studies [11,17]. Quadriceps contraction can result in significant anterior tibial displacement and internal tibial rotation [36]. Coactivation of the hamstrings and quadriceps contribute to the stability of the knee joint [37,38]. Moreover, preactivation is necessary to restrain the knee [24]. It is suggested that these factors contribute to greater internal tibial rotation seen among female athletes during the single limb landing. Several researchers reported that females tend to land and remain with their knee in a more femorotibial valgus position during athletic tasks [10,11,13 15]. In this study, after toe contact, varus angulation of the tibia increased with time until it reached a maximum, and then valgus rotation increased with time. There were no differences in knee varus and valgus between males and females, while there was a difference in internal tibial rotation between females and males. The reason for the differences in the results of femorotibial valgus between this study and previous studies may be due to the selected tasks. While previous studies often selected cutting and both leg landing for analyses, this study selected a single limb landing since ACL injury often occurs during these maneuvers. It is thought that the proportion of valgus rotation and tibial rotation depends on the selected tasks. In the future, the relationship between knee valgus and internal tibial rotation should be examined. In this study, there were no differences in the knee flexion angle at the time of foot contact or at the time of the peak GRF. Some researchers previously reported that females tend to land with their knee in less flexion than males [11,14,18], while others reported that females land with their knee in greater flexion [39] and another study found no difference between genders [15]. However, previous studies report these findings during landing and cutting, while our study focused on single limb drop landing. Thus, it is thought that the knee flexion angle may depend on the level of activity or the testing task. Otherwise, in this study, females took a longer time to reach the peak GRF after the time of foot contact than males. Female also required a longer time to achieve the same knee flexion angle. There may be a risk to receive a disturbance with the knee flexed at a lower flexion angle. There are some limitations to this study. Influences of the hip and ankle have been recently suggested [14,40], however this study analyzed the kinematics of the knee only. Moreover, although we considered muscle activation; we did not consider differences in muscle mass, i.e., males have greater muscle mass than females. Additionally, analyses of risk maneuvers causing greater knee valgus are required to examine precisely the mechanism of ACL injury. In the future, a relationship between the kinematic data and the electromyographic data should be studied to identify athletes who might be at risk for ACL injury. 5. Conclusion The results of this study indicated that the mechanism of noncontact ACL injury during the single limb drop landing was internal tibial rotation combined with valgus rotation of the knee. Increased internal tibial rotation combined with greater quadriceps activity and a low HQR could be one reason female athletes have a higher incidence of noncontact ACL injuries. For prevention of ACL injury, identifying athletes who have these risky characteristics may be important.

186 Y. Nagano et al. / The Knee 14 (2007) Acknowledgment This work was supported by Grant-in-Aid for Scientific Research (C) ( ) in 2004 and References [1] Agel J, Arendt EA, Bershadsky B. Anterior cruciate ligament injury in national collegiate athletic association basketball and soccer: a 13-year review. Am J Sports Med 2005;33: [2] Boden BP, Dean GS, Feagin Jr JA, Garrett Jr WE. Mechanisms of anterior cruciate ligament injury. Orthopedics 2000;23: [3] Griffin LY, Agel J, Albohm MJ, Arendt EA, Dick RW, Garrett WE, et al. Noncontact anterior cruciate ligament injuries: risk factors and prevention strategies. J Am Acad Orthop Surg 2000;8: [4] Arendt EA. Anterior cruciate ligament injury patterns among collegiate men and women. J Athl Train 1999;34: [5] Miyasaka KC, Daniel DM, Stone ML. The incidence of knee ligament injuries in the general population. Am J Knee Surg 1991;4:3 8. [6] Myklebust G, Engebretsen L, Braekken IH, Skjolberg A, Olsen OE, Bahr R. 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187 Sports Biomechanics September 2008; 7(3): Statistical modelling of knee valgus during a continuous jump test Y. NAGANO 1, M. SAKAGAMI 1,H.IDA 2, M. AKAI 3, & T. FUKUBAYASHI 4 1 Graduate School of Sports Science, Waseda University, Saitama, Japan, 2 Kanagawa Institute of Technology, Kanagawa, 3 National Rehabilitation Center for Persons with Disabilities, Saitama, Japan, and 4 Faculty of Sports Sciences, Waseda University, Saitama, Japan (Received 25 November 2007; revised 9 May 2008; accepted 21 May 2008) Abstract Landing with the knee in a valgus position is recognized as a risk factor for anterior cruciate ligament (ACL) injury. Using linear and non-linear regression analyses, the purpose of this study was to examine the correlation between two-dimensional (2D) knee valgus and three-dimensional (3D) knee kinematics measured during a jump landing task. Twenty-eight female collegiate athletes participated. All participants were required to perform a continuous jump test. The average maximum angles of abduction and internal tibial rotation during landing were measured using the Point Cluster Technique. Average peak knee valgus angle was measured using a 2D approach. Linear and non-linear regression analyses between 2D valgus and 3D knee abduction, and between 2D valgus and 3D internal tibial rotation, were performed. The R 2 value between 2D valgus and 3D knee abduction was significantly different from zero and had a moderate correlation for all models, whereas the R 2 value between 2D valgus and 3D internal tibial rotation was not significantly different from zero. The 2D approach could be used to screen a specific group of individuals for risk of ACL injury; however, using frontal plane 2D analysis of valgus motion to evaluate internal tibial rotation is not advised. Keywords: Injury, kinematics, knee, landing, motion analysis Introduction Acute knee injuries, especially those to the anterior cruciate ligament (ACL), often occur during landing. Krosshaug and colleagues (2007) examined the mechanism of ACL injuries that occur while playing basketball and found that the most common manoeuvre at the time of injury is landing. Accordingly, many studies have focused on landing to examine the mechanism and risk of ACL injury. Recently, knee valgus at the time of landing has been recognized as a risk factor of ACL injury. In a prospective study (Hewett et al., 2005), female athletes with increased dynamic valgus and a high abduction load during a jump-landing task were at increased risk of ACL injury. In a biomechanical study, valgus torque and internal tibial rotation in combination with anterior force resulted in a significantly larger strain to the ACL (Berns et al., 1992). Correspondence: Y. Nagano, Sports Orthopedic Laboratory, Graduate School of Sports Science, Waseda University, Mikajima , Tokorozawa, Saitama , Japan. [email protected] ISSN print/issn online q 2008 Taylor & Francis DOI: /

188 Statistical modelling of knee valgus 343 Using a model-based investigation to examine injury causing kinematics, McLean et al. (2004) found that valgus loading is a likely injury mechanism, especially in females. Several researchers have reported that females tend to land and remain in a more valgus position than males (McLean et al., 1999; Malinzak et al., 2001; Ford et al., 2003). In programmes designed to help prevent ACL injury (Hewett et al., 2001; Myklebust et al., 2003; Mandelbaum et al., 2005), athletes are instructed to avoid knee valgus during landing. Consequently, it is important to determine the amount of knee valgus during athletic tasks to screen individuals at risk of injury as well as to evaluate prevention programmes. In biomechanical studies, three-dimensional (3D) motion analysis has been considered the standard method to measure the valgus angle of the knee during athletic tasks. Although this method provides reliable data, 3D motion analysis has spatial and temporal costs that prevent large screenings and evaluations to determine successful ACL injury prevention programmes. On the other hand, measuring frontal plane knee motion with a twodimensional (2D) approach using a standard video camera is a concise and versatile procedure. Recently, some studies have successfully used the 2D approach (Barber-Westin et al., 2005; Noyes et al., 2005; Willson et al., 2006). However, the valgus angle of the knee evaluated using a 2D approach is influenced by hip internal rotation, ankle eversion, and knee flexion. Moreover, knee valgus evaluated using a 2D approach includes not only knee abduction, but also tibial rotation. Using linear regression analysis, McLean et al. (2005) reported the potential of the 2D approach for screening knee valgus. While McLean et al. studied tasks that have high demands on the frontal plane (e.g. the side jump and sidestep), many researchers have examined landing tasks that have a high demand on the sagittal plane (e.g. the drop vertical jump, drop landings, etc.) (Hewett et al., 2005; Noyes et al., 2005; Yu et al., 2005). To our knowledge, no study has performed regression analyses using both linear and non-linear methods between 2D knee valgus and 3D knee kinematics data obtained during tasks that involve large movements in the sattigal plane. Most jump landing tasks are a one-shot trial with the possibility that the landing motion would include trial bias and feed-forward control. In contrast, individuals perform the continuous jump test without stopping after each landing task. Based on this characteristic, trial bias and feed-forward control should have less influence on the landing motion than one-shot tasks. The aims of this study were to examine the regression between 2D knee valgus and 3D knee kinematics (both knee abduction and internal tibial rotation) and to determine which statistical model linear, quadratic or logarithmic best describes the 3D knee kinematics measured during the continuous jump test. We hypothesized that there would be a significant correlation between 2D knee valgus and 3D knee abduction in all regression models and the non-linear model would better describe the 3D kinematics than the linear model. Furthermore, since knee valgus rotation is a movement that occurs mostly in the frontal plane and tibial rotation is a movement that occurs mostly in the horizontal plane, we assumed it would be difficult for a 2D approach using kinematics from the frontal plane to evaluate movement in the horizontal plane. Therefore, we further hypothesized that there would not be a significant correlation between 2D knee valgus and 3D internal tibial rotation for all models. Methods Participants Twenty-eight female collegiate basketball and lacrosse athletes gave their written informed consent to participate in the study. Approval for the study was obtained from the institutional

189 344 Y. Nagano et al. review board of the National Rehabilitation Center for Persons with Disabilities. Exclusion criteria included a history of lower limb injury and or any musculoskeletal injury in the previous 6 months that prohibited an individual from playing sports. The mean physical characteristics of the participants were as follows: age 21 ^ 1 years, height 1.66 ^ 0.8 m, and body mass 58.8 ^ 7.7 kg. Continuous jump test All testing took place at the National Rehabilitation Center for Persons with Disabilities in Saitama, Japan. The participants were measured in a static standing position. While barefoot, the participants performed five vertical jumps continuously (i.e. without resting between jumps) using both legs with maximum effort (Figure 1). They were instructed to place their hands on their lower torso, stand with their feet shoulder-width apart, and face the frontal plane during testing. A research assistant demonstrated the continuous jump test; however, the assistant did not provide any verbal instructions regarding landing or jumping technique. The participants were allowed several preparation trials. Measurement of the landing of the dominant limb from the second to the fourth jump was used for analysis. Analysis of the 3D data A six-camera motion analysis system (Motion Analysis Corp., California, USA) was used to record the 3D movements of the lower limb. The motion and force data were recorded at 200 Hz. For each participant, 24 reflective markers of 9 mm diameter were secured to the lower limb using double-sided adhesive tape as described previously (Nagano et al., 2007). From the coordinate system data obtained, the angular displacements of knee abduction/adduction and internal/external tibial rotation were calculated for each landing. The knee kinematics were calculated using the Point Cluster Technique (Andriacchi et al., 1998) and the Joint Coordinate System proposed by Grood and Suntay (1983). For this algorithm, the reference zero position for these measurements was obtained during the static standing trial. The angular displacements in each trial were indicated as a variation from the position in the static standing trial. The average maximum angle during landing from the static standing position was measured as knee abduction and internal tibial rotation. Figure 1. Continuous jump test. All participants performed five vertical jumps with maximum effort using both legs and landing.

190 Statistical modelling of knee valgus 345 Analysis of the 2D data Each trial was recorded from the frontal plane using a digital video camera (30 Hz; Sony Product, Japan). The camera was placed 3.8 m from the landing point at the height of the knee joint. For each participant, 3 square plastic tape markers with an area of 3.24 cm 2 were secured to the lower limb. Markers were placed at the anterior superior iliac spine (ASIS), the midpoint of the patella, and the midpoint of the ankle joint. Captured images were imported into a digitizing software program (Dartfish, Dartfish Japan Co., Ltd., Japan). The angle between the lines formed from the marker on the ASIS to the midpoint of the patella and that formed from the midpoint of the patella to the midpoint of the ankle joint was recorded as the knee valgus angle (Figure 2). The average peak 2D knee valgus angle from the static position was measured for analysis. As the purpose of this study was to screen for knee valgus, when participants showed knee varus during landing, these data were excluded from analysis. Statistical analyses Linear and non-linear regression analyses between 2D valgus and 3D knee abduction, and between 2D valgus and 3D internal tibial rotation, were performed to identify the model with the best fit. The models were expressed by the following equations: Linear model: y ¼ a þ bx Quadratic model: y ¼ a þ bxþ cx 2 Logarithmic model: y ¼ a þ b lnðxþ The coefficient of determination (R 2 value) for each model was calculated and tested for statistical significance. When the R 2 value for all three models was significant, an analysis of Figure 2. Measurement of knee valgus using the 2D method. The angle between the line formed from the marker on the anterior superior iliac spine (ASIS) to the midpoint of the patella and that formed from the midpoint of the patella to the midpoint of the ankle joint was recorded as the knee valgus angle.

191 346 Y. Nagano et al. variance (ANOVA) together with a post-hoc LSD test was conducted to investigate the effect of each model (linear, quadratic or logarithmic) on the R 2 value. These statistical analyses were referred to in a previous study of similar design (Coorevits et al., 2005) and conducted using the statistical software package SPSS (v. 11.0, SPSS Inc., Chicago, IL). Statistical significance was set at P, Based on the R 2 value calculated from a pilot study (0.36) and the power of 0.80, a sample size calculation revealed that 19 participants were required to have sufficient power to test the regression analysis. Results When measuring 2D valgus during the continuous jump test, eight participants showed knee varus. Therefore, the data for only 20 participants were analysed in this study. No significant differences were observed in age, height or body mass between those participants included in and excluded from the analysis. For the test retest trial, the intraclass correlation for the 2D valgus was 0.73, demonstrating substantial reliability of the videographic test and software capturing procedures. For all models, the R 2 value between 2D valgus and 3D knee abduction was significantly different from zero: linear model (R 2 ¼ 0.34, P, 0.01) (Figure 3A), quadratic model (R 2 ¼ 0.40, P ¼ 0.01) (Figure 3B), and logarithmic model (R 2 ¼ 0.41, P, 0.01) (Figure 3C). Regarding the results of the ANOVA tests, no significant differences were observed between three models based on the R 2 values. For all models, the R 2 value between 2D valgus and 3D internal tibial rotation was not significantly different from zero (Figure 4). Discussion and implications The present study used regression analysis to examine the potential of a 2D approach using a standard video camera to evaluate 3D kinematics. We also examined the best fit statistical model to describe 3D kinematics. By developing a regression relationship between 2D valgus and 3D knee kinematics, a 2D approach was able to be used to screen participants at risk for ACL injury as well as to evaluate prevention training programmes that attempt to reduce ACL injury rates. Additionally, researchers, coaches, and trainers should be able to conduct adequate evaluation without having to use a complicated 3D approach, since the continuous jump test procedure has substantial reliability and requires simple equipment. The results of this study showed that there was a moderate correlation between 2D valgus and 3D knee abduction in all regression models. McLean et al. (2005) used a linear regression analysis to show a correlation between 2D analysis of valgus and 3D analysis of valgus during frontal plane athletic tasks. The R 2 values in the present study were significant, but lower than those reported by McLean and colleagues. When the hip joint is internally rotated, the knee flexion angle is projected onto the frontal plane as a 2D valgus angle. Stance width and ankle eversion/inversion also contribute to the 2D valgus angle. The jump-landing task examined in the present study is more easily influenced by these other factors than the tasks examined in McLean s study, which have a high demand on the frontal plane. Therefore, the correlation for this study would naturally be lower. To determine whether the 2D valgus angles measured during the continuous jump test can be used to screen for individuals who are at risk for ACL injury, the following error analysis was performed. In the correlation plots of this study, the maximum residual error was 7.038, 6.768, and for the linear, quadratic, and logarithmic model, respectively.

192 Statistical modelling of knee valgus 347 Figure 3. Associations between 2D valgus and 3D knee abduction during the continuous jump test for the linear model (A), the quadratic model (B), and the logarithmic model (C). The R 2 values of all models between 2D valgus and 3D knee abduction were significantly different from zero. Figure 4. Associations between 2D valgus and 3D internal tibial rotation during the continuous jump test. The R 2 values of all models between 2D valgus and 3D internal tibial rotation were not significantly different from zero.

193 348 Y. Nagano et al. According to a prospective study (Hewett et al., 2005), individuals who went on to have an ACL injury had a 7.68 greater knee abduction angle at landing than those who did not get injured. Although a different movement task was studied, 98 of injured knee-abduction angle (Hewett et al., 2005) could be used to determine the accuracy of the regression models. By doing so, the false-negative rate was 35%, 30%, and 30% for the linear, quadratic, and logarithmic model, respectively. The false-positive rate was 0%, 10%, and 10% for the linear, quadratic, and logarithmic model, respectively. Thus, these regression models could be used as one screening tool to assess the risk of ACL injury during landing. However, the false-negative rates were slightly high. Therefore, other screening tools [i.e. lower limb strength (Barber-Westin et al., 2006) and joint laxity (Myer et al., 2008)] should be used in addition to these regression models to introduce athletes who are at risk for ACL injury to prevention training. Since there was no significant difference between the three models based on the R 2 values, any of the models can be used to evaluate knee valgus. However, the data points scatter around the regression curves, especially between 108 and 158 of 2D valgus. In this area, other factors contributing to the 2D valgus angle (i.e. hip rotation, ankle eversion/inversion, stance width, etc.) vary between individuals in a way that is not correlated with knee valgus. Although this occurrence is a fundamental limitation of the regression model approach, the non-linear regression models take into account the scatter in this area better than the linear model. Therefore, we suggest that the logarithmic regression model, which has a damping behaviour, has most suitable to evaluate knee valgus. On the other hand, data points above 158 of 2D valgus fit well with the regression curves. In this area, the regression model can be used to screen individuals at risk for ACL injury, since the knee abduction angle is relatively large. In this study, participants who showed knee varus during landing were excluded. In theory, the correlation should hold whether valgus or varus was measured. However, there was no significant correlation when those who showed varus landing were included. The 2D measurement of varus/valgus angle is affected by many factors including hip rotation, ankle eversion/inversion, foot position, and knee flexion. This result shows that the contributions of these factors may be different between 2D valgus and 2D varus. Since most female athletes show valgus landing and valgus landing is related to risk of ACL injury, we decided in this study to screen for valgus only. A significant regression relationship between 2D valgus and 3D internal tibial rotation could not be determined. Increased internal tibial rotation combined with knee valgus leads to increased strain (Berns et al., 1992) and increased force (Markolf et al., 1995; Kanamori et al., 2002) in the ACL. Therefore, evaluation of internal tibial rotation during landing has benefits for screening and identifying risk of ACL injury. However, from the results of this study, using frontal plane 2D analysis of valgus motion to evaluate internal tibial rotation is not advised. It may be necessary for other parameters (e.g. foot position) to be examined or 3D analysis should be used to measure tibial rotation. There are some limitations to this study. First, it is unclear whether the statistical regression model in this study could be applied to other athletic populations or to male athletes. Furthermore, since the participants in this study were barefoot, the effect of wearing shoes could have an influence on the results. There is also a fundamental limitation of the regression model approach. As mentioned earlier, hip internal rotation and other variables are correlated to 2D knee valgus; however, at times these factors vary among individuals in a way that does not correlate with 2D knee valgus and thus contributes to scatter within the data. Lastly, the power of this test to make comparisons among regression models was low (0.18). To examine which statistical model best describes the 3D knee kinematics, a larger sample size is needed.

194 Statistical modelling of knee valgus 349 Conclusion We examined the reliability of a 2D approach to screen individuals for risk of ACL injury during a jump landing task. The results suggest that not only the linear model, but the quadratic and logarithmic models, show a moderate association between the 2D and 3D methods to measure knee abduction. The 2D approach could be used to screen a specific group of individuals who have greater 2D valgus and 3D knee abduction. However, the use of frontal plane 2D analysis of valgus motion to evaluate internal tibial rotation is not advised. Acknowledgement This work was funded by Grant-in-Aid for Scientific Research #B References Andriacchi, T. P., Alexander, E. J., Toney, M. K., Dyrby, C., and Sum, J. (1998). A point cluster method for in vivo motion analysis: Applied to a study of knee kinematics. Journal of Biomechanical Engineering, 120, Barber-Westin, S. D., Galloway, M., Noyes, F. R., Corbett, G., and Walsh, C. (2005). Assessment of lower limb neuromuscular control in prepubescent athletes. American Journal of Sports Medicine, 33, Barber-Westin, S. D., Noyes, F. R., and Galloway, M. (2006). Jump land characteristics and muscle strength development in young athletes: A gender comparison of 1140 athletes 9 to 17 years of age. American Journal of Sports Medicine, 34, Berns, G. S., Hull, M. L., and Patterson, H. A. (1992). Strain in the anteromedial bundle of the anterior cruciate ligament under combination loading. Journal of Orthopedic Research, 10, Coorevits, P. L., Danneels, L. A., Ramon, H., Van Audekercke, R., Cambier, D. C., and Vanderstraeten, G. G. (2005). Statistical modelling of fatigue-related electromyographic median frequency characteristics of back and hip muscles during a standardized isometric back extension test. Journal of Electromyography and Kinesiology, 15, Ford, K. R., Myer, G. D., and Hewett, T. E. (2003). Valgus knee motion during landing in high school female and male basketball players. Medicine and Science in Sports and Exercise, 35, Grood, E. S., and Suntay, W. J. (1983). A joint coordinate system for the clinical description of three-dimensional motions: Application to the knee. Journal of Biomechanical Engineering, 105, Hewett, T. E., Myer, G. D., and Ford, K. R. (2001). Prevention of anterior cruciate ligament injuries. Current Women s Health Reports, 1, Hewett, T. E., Myer, G. D., Ford, K. R., Heidt, Jr, R. S., Colosimo, A. J., McLean, S. G. et al. (2005). Biomechanical measures of neuromuscular control and valgus loading of the knee predict anterior cruciate ligament injury risk in female aathletes. American Journal of Sports Medicine, 33, Kanamori, A., Zeminski, J., Rudy, T. W., Li, G., Fu, F. H., and Woo, S. L. (2002). The effect of axial tibial torque on the function of the anterior cruciate ligament: A biomechanical study of a simulated pivot shift test. Arthroscopy, 18, Krosshaug, T., Nakamae, A., Boden, B. P., Engebretsen, L., Smith, G., Slauterbeck, J. R. et al. (2007). Mechanisms of anterior cruciate ligament injury in basketball: Video analysis of 39 cases. American Journal of Sports Medicine, 35, Malinzak, R. A., Colby, S. M., Kirkendall, D. T., Yu, B., and Garrett, W. E. (2001). A comparison of knee joint motion patterns between men and women in selected athletic tasks. Clinical Biomechanics, 16, Mandelbaum, B. R., Silvers, H. J., Watanabe, D. S., Knarr, J. F., Thomas, S. D., Griffin, L. Y. et al. (2005). Effectiveness of a neuromuscular and proprioceptive training program in preventing anterior cruciate ligament injuries in female athletes: 2-year follow-up. American Journal of Sports Medicine, 33, Markolf, K. L., Burchfield, D. M., Shapiro, M. M., Shepard, M. F., Finerman, G. A., and Slauterbeck, J. L. (1995). Combined knee loading states that generate high anterior cruciate ligament forces. Journal of Orthopedic Research, 13, McLean, S. G., Huang, X., Su, A., and Van Den Bogert, A. J. (2004). Sagittal plane biomechanics cannot injure the ACL during sidestep cutting. Clinical Biomechanics, 19, McLean, S. G., Neal, R. J., Myers, P. T., and Walters, M. R. (1999). Knee joint kinematics during the sidestep cutting maneuver: Potential for injury in women. Medicine and Science in Sports and Exercise, 31,

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196 THEKNE-01139; No of Pages 6 ARTICLE IN PRESS The Knee xxx (2008) xxx xxx Contents lists available at ScienceDirect The Knee Biomechanical characteristics of the knee joint in female athletes during tasks associated with anterior cruciate ligament injury Yasuharu Nagano a,, Hirofumi Ida b, Masami Akai c, Toru Fukubayashi d a Waseda University Graduate School of Sports Sciences, Saitama, Japan b Kanagawa Institute of Technology, Kanagawa, Japan c National Rehabilitation Center for Persons with Disabilities, Saitama, Japan d Waseda University Faculty of Sports Sciences, Saitama, Japan article info abstract Article history: Received 22 May 2008 Received in revised form 20 October 2008 Accepted 26 October 2008 Available online xxxx Keywords: ACL injury Risk factor Knee kinematics Injury mechanism Prevention This study was designed to compare biomechanical characteristics of the knee joint for several athletic tasks to elucidate their effects and to examine what tasks pose a risk for ACL injury. Three athletic tasks were performed by 24 female athletes: single-limb landing, plant and cutting, and bothlimb jump landing. Angular displacements of flexion/extension, abduction/adduction, and external/internal tibial rotation were calculated. Angular excursion and the rate of excursion of abduction and internal tibial rotation were also calculated. During plant and cutting, from foot contact, subjects rotated the tibia more rapidly and to a greater degree toward internal tibial rotation. Moreover, excursion of knee abduction is greater than that during single-limb landing. During both-limb jump landing, the knee flexion at foot contact was greater than for either singlelimb landing or plant and cutting; peak knee abduction was greater than for either single-limb landing or plant and cutting. In plant and cutting, the risk of ACL injury is increased by greater excursion and more rapid knee abduction than that which occurs in single-limb landing, in addition to greater internal tibial rotation. Although singlelimb tasks apparently pose a greater risk for ACL injury than bilateral landings, both-limb landing with greater knee abduction might also risk ACL injury Elsevier B.V. All rights reserved. 1. Introduction Anterior cruciate ligament (ACL) injury is a serious injury in sports activities. After ACL injury, most athletes must undergo ligament reconstruction and continue rehabilitation for 6 months to a year before returning to sports activities [1]. The rate of ACL injury is reportedly much higher for female athletes than for males [2,3]. Additionally, almost 70% of situations causing ACL injury are noncontact situations: landing from a jump, stopping after fast running, and cutting to a different direction [2,4]. Understanding the mechanisms of ACL injury is important for its prevention. Olsen et al. [5] described ACL injury mechanisms from viewing videotapes of ACL injuries. They concluded that the main injury mechanism for ACL injuries is a forceful valgus collapse with the knee close to full extension, combined with external or internal rotation of the tibia. However, ACL injuries occur rapidly during games and practice sessions. In most cases, it is difficult to determine the mechanisms of ACL injury from videotapes or pictures recording the Corresponding author. Yasuharu Nagano, Waseda University Graduate School of Sports Sciences, Sports Orthopedic Lab Mikajima , Tokorozawa, Saitama , Japan. Tel.: ; fax: address: [email protected] (Y. Nagano). injury situation because of the image quality. Therefore, many researchers have examined injury mechanisms from motion capture images taken in laboratory conditions. Numerous studies using motion capture systems have examined the mechanism and risk factors of ACL injury during athletic tasks according to gender differences. As described previously, female athletes are more prone to sustaining ACL injury than male athletes. Therefore, female characteristic kinematics and kinetics are thought to be risk factors related to ACL injury mechanisms. Earlier studies have shown that female athletes demonstrate larger knee valgus than male athletes during landing or many other athletic tasks [6 12]. Hewett et al.[13] measured kinematics and joint loads using kinetics during a jumplanding task prospectively: results showed that female athletes with increased dynamic valgus and high abduction loads are at increased risk of anterior cruciate ligament injury. Therefore, knee valgus has been recognized as a risk factor and one mechanism of ACL injury. Tibial rotation during athletic tasks has been examined recently: we examined gender differences of tibial rotation during single-limb drop landing and estimated that the risk factor and mechanism of ACL injury would be greater for tibial internal rotation combined with knee valgus [14]. Another approach to examination of the mechanism of ACL injury using motion capture systems is analysis of biomechanical characteristics during tasks that pose a high injury risk for ACL injury. In fact, ACL /$ see front matter 2008 Elsevier B.V. All rights reserved. doi: /j.knee Please cite this article as: Nagano Y, et al, Biomechanical characteristics of the knee joint in female athletes during tasks associated with anterior cruciate ligament injury, The Knee (2008), doi: /j.knee

197 ARTICLE IN PRESS 2 Y. Nagano et al. / The Knee xxx (2008) xxx xxx Fig. 1. Sequential photographs of experimental tasks: Single-limb landing (a), plant and cutting (b), and both-limb jump landing. injuries often occur in plant and cutting movements while leaning on one leg and forcing a knee valgus [4,5]. Sell et al.[15] examined the effects of direction during a two-legged stop-jump task and concluded that lateral jumps are the most risky manoeuvres for ACL injury. Pappas et al. [16] compared bilateral and unilateral landings and found that, in unilateral landings, subjects performed high-risk kinematics with increased knee valgus, decreased knee flexion, and decreased relative hip adduction. However, they only analyzed knee valgus at initial contact during landings and did not examine the plant and cutting manoeuvre, which is thought to pose greater risk for ACL injuries. The characteristics of plant and cutting and several athletic tasks have never been well established. This study was intended to compare biomechanical characteristics of the knee joint between plant and cutting tasks and normal singlelimb landing, and to compare characteristics between both-limb jump landing and single-limb tasks. Comparison of kinematics among tasks can elucidate the characteristics of these tasks, and enable examination of what tasks pose a risk for ACL injury. Understanding risky tasks and movements can help prevent ACL injury because team trainers and coaches might thereby be better able to instruct their athletes to avoid such movements. Our hypotheses were two. During a plant and cutting manoeuvre, subjects demonstrate riskier kinematics for ACL injury than during normal single-limb landing because of greater knee valgus and greater internal tibial rotation. In addition, during single- Please cite this article as: Nagano Y, et al, Biomechanical characteristics of the knee joint in female athletes during tasks associated with anterior cruciate ligament injury, The Knee (2008), doi: /j.knee

198 ARTICLE IN PRESS Y. Nagano et al. / The Knee xxx (2008) xxx xxx 3 Table 1 Mean (SD) for tasks observed power of joint angle at the time of foot contact *: pb0.05, pb0.01. Review Board of National Rehabilitation Center for Persons with Disabilities. The average age of subjects was 21.1 (1.3) yr (Mean (SD)); their average height was (8.3) cm and their average weight was 59.3 (8.2) kg. All subjects were right-leg dominant. The dominant leg was determined as the leg used to kick a ball Experimental task All subjects were measured in a static standing position and during performance of three athletic tasks: single-limb landing, plant and cutting, and both-limb jump landing. For the single-limb landing, subjects stood on a 30-cm-high platform with the left limb, and landed on a platform 30 cm away with the right limb (Fig. 1a). They were required to unyoke their left foot from a platform, and, when they start a landing motion, not to land the right limb along with their left limb on a platform. A trial was considered successful if they retained the landing position. For the plant and cutting, subjects stood on a platform, as in the single-limb landing. They were required to land with their right foot 45 abducted from the original direction and to push off their foot perpendicularly (to the left) with the right foot to make a cut (Fig. 1b). They also were required to make three steps after the cut. A trial was considered successful if they landed with their foot at the prescribed angle and made a cut to the prescribed direction. For both-limb jump landing, subjects performed vertical jumps five times using both legs with maximum effort [17] (Fig. 1c). They were instructed to stand with their feet shoulder-width apart and face the frontal plane during testing. The subjects were given verbal instruction to shorten their foot contact time as much as they were able and to jump as high as they were able. The landings from the second to fourth time of their dominant limb were measured for analysis. Throughout the experiment, the subjects were barefoot and kept their hands on their lower torso. The subjects were allowed to perform several preparation trials. Measurements were continued for three successful trials: each was conducted consecutively Data collection Fig 2. Comparisons of joint motion. Data are presented for knee abduction/adduction (a), external/internal tibial rotation (b), and knee flexion/extension (c). limb tasks, subjects demonstrate riskier kinematics than during bothlimb tasks. 2. Materials and methods 2.1. Subjects A power analysis conducted during a pilot study revealed that at least 24 subjects were necessary to achieve 80% statistical power with an α level of In all, 24 female athletes were recruited for the experiment. Half were basketball players; others were lacrosse players. Subjects were excluded from the study if they had a history of serious musculoskeletal injury, any musculoskeletal injury within the past 6 months, or any disorder that interfered with sensory input, musculoskeletal function, or motor function. Before participation, all subjects provided written informed consent in accordance with approval by the Institutional All experiments were performed at the National Rehabilitation Center for Persons with Disabilities in Saitama, Japan. A seven-camera high-speed motion analysis system (Hawk; Motion Analysis Corp., Santa Rosa, CA) was used to record the lower-limb movements threedimensionally. The motion and force data were recorded at 200 Hz. The laboratory was equipped with six force plates (9287A; Kistler Japan Co., Ltd., Tokyo, Japan). Vertical ground-reaction force was used to signal the initial contact to determine the data capture period. Table 2 Mean (SD) for tasks observed power of peak joint angle *: pb0.05, **: pb0.0l. Please cite this article as: Nagano Y, et al, Biomechanical characteristics of the knee joint in female athletes during tasks associated with anterior cruciate ligament injury, The Knee (2008), doi: /j.knee

199 ARTICLE IN PRESS 4 Y. Nagano et al. / The Knee xxx (2008) xxx xxx Table 3 Mean (SD) for angular excursion (deg) and rate of excursion (deg/ms) both-limb jump landing was significantly larger than that for either single-limb landing (pb0.01, respectively). The rates of excursion for knee abduction among three tasks were not significantly different. The excursion for internal tibial rotation in plant and cutting was significantly larger than for either single-limb landing or both-limb jump landing (pb0.01, respectively), whereas that in single-limb landing was significantly larger than that of both-limb jump landing (p b0.01). The rate of excursion for internal tibial rotation in plant and cutting was significantly faster than that for either singlelimb landing or both-limb jump landing (pb0.01, respectively). *: pb0.05, **: pb Discussion To each subject, 25 reflective markers of 9 mm diameter were secured to the lower limb using double-sided adhesive tape, as described in a previous study [14]. The markers were used to implement the Point Cluster Technique (PCT) [18]. We calculated knee kinematics using the joint coordinate system proposed by Grood and Suntay [19]. For PCT, the skin markers are classified into two groups: a cluster of points representing a segment and points representing bony landmarks. For a cluster of points, 10 and 6 markers were attached respectively to the thigh and shank segments. The bony landmarks were the great trochanter, the lateral and medial epicondyles of the femur, the lateral and medial edges of the tibia plateau, the lateral (fibula) and medial malleoli, and the fifth metatarsophalangeal joint Data analysis The coordinate data obtained from the markers were not smoothed because of the expected noise-cancelling property of the PCT. In each trial, we calculated the angular displacements of flexion/extension, abduction/adduction, and external/internal tibial rotation using the PCT. The reference position for these measurements was obtained during the static trial. We analyzed each variable at the time of foot contact and the peak value from the foot contact to 200 ms thereafter. Additionally, angular excursion for knee abduction and internal tibial rotation was calculated. A rate of excursion for knee abduction and internal tibial rotation was also calculated. All dependent variables were calculated for each trial, then averaged across the three trials. A repeated measures one-way ANOVA was used to test for task differences in joint angle at the foot contact and peak joint angle. The alpha level was set at pb0.05. A post hoc Bonferroni multiple comparison test was performed for each variable to determine differences among tasks. Intraclass correlation coefficients (ICC (1, 3)) were calculated to determine the measurement consistency. 3. Results Acceptable ICC (1, 3) values at the time of foot contact and a peak value were established for knee abduction/adduction (0.98, 0.97), external/internal tibial rotation (0.93, 0.98), and flexion/extension (0.96, 0.89). Fig. 2 portrays mean time course comparisons across tasks for the three angular displacements of the knee (abduction/ adduction, external/internal tibial rotation, and flexion/extension). Means, standard deviations and observed power for all variables at the time of foot contact are presented intable 1. The adduction angle inplant and cutting was significantly larger than that for either single-limb landing or both-limb jump landing (pb0.01, respectively); that in single-limb landing was significantly larger than that of both-limb jump landing (pb0.05). The external tibial rotation angle in plant and cutting was significantly larger than for either single-limb landing or both-limb jump landing (pb0.01); that in single-limb landing was significantly larger than that of both-limb jump landing (pb0.01). The flexion angle in both-limb jump landing was significantly larger than that of either single-limb landing or plant and cutting (pb0.01); that in plant and cutting was significantly larger than that of single-limb landing (pb0.01). Means and standard deviations of peak values for all variables are presented intable 2. The peak abduction angle in both-limb jump landing was significantly larger than that of either single-limb landing or plant and cutting (pb0.01 and pb0.05, respectively). During single-limb landing or plant and cutting, their knee was abducted from foot contact with time. However, even at their peak, it is adducted. The peak internal tibial rotation angles in plant and cutting and both-limb jump landing were significantly larger than that of singlelimb landing (pb0.05 andpb0.01, respectively). The peak flexion angle inplant and cutting was significantly smaller than both-limb jump landing (pb0.05). The angular excursion and velocity for knee abduction and internal tibial rotation are presented in Table 3. The excursion for knee abduction in plant and cutting and The primary purpose of this study was to analyze the biomechanical characteristics of the knee joint during several athletic tasks, and to examine what tasks present a risk for ACL injury. A plant and cutting manoeuvre is a movement that commonly causes ACL injury, of which most situations were single-foot push-offs [5]. However,biomechanical characteristics of plant and cutting and several athletic tasks are unknown. Therefore, to compare a plant and cutting and normal single-limb landing as well as both limb landing, we can understand these athletic tasks and examine what tasks are risky for ACL injury. The results of this study showed that greater excursion and more rapid knee abduction occur in plant and cutting than that which occurs in single-limb landing, in addition to greater internal tibial rotation. Furthermore, compared to similar single-limb tasks, both-limb jump landing knee flexion and knee abduction were greater; external tibial rotation at the foot contact was smaller Plant and cutting versus single-limb landing Some recent studies have compared biomechanical characteristics across different athletic tasks [8,15,20]. Nevertheless, these studies present some limitations. Although Chappell et al. [8] compared knee kinematics of forward, vertical, and backward stop-jump tasks, they did not examine lateral movement. Sell et al. [15] compared two-legged stop-jump tasks in three different directions. Although their results indicate that lateral jumps are the most dangerous of the stop-jumps, all tasks were two-legged tasks, not single-leg tasks. Besier et al. [20] compared the joint load during running, sidestep cutting, and crossover cutting. They inferred that external moments applied to the knee joint during the stance phase of the cutting tasks place the ACL and collateral ligaments at risk of injury, but they did not analyze joint kinematics and the frequency of the motion analysis system was too slow to support examination of high-speed athletic tasks. Therefore, the results of this study, along with those of the prior study, provide some implications of mechanisms causing ACL injury. The results of this study showed that, during plant and cutting, external tibial rotation at the foot contact and peak internal tibial rotation were greater than during single-limb landing. During plant and cutting, from foot contact, subjects rotated the tibia more rapidly and to a greater degree toward internal tibial rotation than during single-limb landing. Previous studies [8,15,16] that examined the mechanism of ACL injury have not analyzed tibial rotation during high-risk movement, probably because of technical issues. In this study, we analyzed tibial rotation using PCT. An anatomical study has demonstrated that internal tibial rotation increases the strain of ACL [21]. Therefore, biomechanically and anatomically, plant and cutting presents a high risk for ACL injury. During plant and cutting, subjects demonstrated more increased knee adduction at foot contact than during single-limb landing. After foot contact, during single-limb landing, subjects showed twin peaks of knee abduction. During plant and cutting, subjects moved toward knee abduction with time, although subjects did not exhibit a great magnitude of knee abduction. Consequently, during plant and cutting, excursion of knee abduction was greater than during single-limb landing. Therefore, during plant and cutting, greater excursion of knee abduction occurred than during single-limb landing combined with greater internal tibial rotation to push off their body to the other side and change direction. Please cite this article as: Nagano Y, et al, Biomechanical characteristics of the knee joint in female athletes during tasks associated with anterior cruciate ligament injury, The Knee (2008), doi: /j.knee

200 ARTICLE IN PRESS Y. Nagano et al. / The Knee xxx (2008) xxx xxx Both-limb jump landing versus single-limb tasks Some studies have analyzed kinematics or kinetics during bilateral landing to examine ACL injury mechanisms [11,12,22]; other studies have screened risks for ACL injury [13] or lower limb injury [23,24]. However, few studies have examined the characteristics of bilateral landing in comparison to single-limb landing. Only Pappas et al. [16] compared bilateral and unilateral landings. Their results indicated that, in unilateral landings, subjects performed high-risk kinematics with increased knee valgus, decreased knee flexion, and decreased relative hip adduction. However, they showed no peak knee valgus or tibial rotation during landing. The results of this study demonstrated that, during both-limb jump landing, knee flexion at foot contact was greater than for single-limb landing and plant and cutting, and that peak knee flexion was greater than plant and cutting. These results were consistent with those of a previous study [16]. Pappas et al.[16] speculated that subjects might attempt to prevent falls by limiting excessive knee flexion during unilateral landing compared to bilateral landing, while simultaneously increasing the forces in ACL. Additionally, in slight knee flexion, i.e. less than 30, contraction of the quadriceps strains the ACL [21,25,26]. For that reason, slight knee flexion is inferred as a risk factor of ACL injury. During a process of prevention training leading athletes to increased knee flexion can decrease the incidence of ACL injury. On the other hand, during bothlimb landing, external tibial rotation at the foot contact was less than that during single-limb landing and plant and cutting, while peak internal tibial rotation was not significantly different with plant and cutting. Unilateral landing has a greater excursion of tibial internal rotation than bilateral landing. As described above, an anatomical study has demonstrated that internal tibial rotation increases the ACL strain [21]. Consequently, characteristics of unilateral landing that have less knee flexion and greater internal tibial rotation present a higher risk for ACL injury than bilateral landings. During both-limb jump landing, peak knee abduction was greater than for either single-limb landing or plant and cutting, while knee adduction at foot contact was smaller. These results did not support our hypothesis. We speculate that knee abduction was limited compensatory for greater internal tibial rotation and smaller knee flexion to prevent ACL injury during single-limb tasks. The possibility of ACL injury arose when subjects allowed greater knee abduction during single-limb tasks. Another reason might be that, because ACL injury occurs not only in single-limb situations but also in both-limb jump landing, the latter also poses a risk for ACL injury. Krosshaug et al. [27] analyzed videos of ACL injury situations and reported that ACL injury occurred during two-legged landing in 9 of 22 cases of female player situations, although it occurred in only four cases of one-legged landing. Therefore, it is thought that both-limb landing with greater knee abduction might also pose a risk for ACL injury. Greater knee abductionwas apparent during a both-limb jump landing task. For screening of ACL injuries, we detected knee abduction well in this task. It is difficult to detect a risk demonstrating greater knee abduction during single-limb tasks because of these characteristics, which demonstrate limited knee abduction. Moreover, knee abduction during both-limb landing can be evaluated using a two-dimensional approach, which uses a video recorder and analyzes a frontal projected knee valgus angle [17]. Some studies have been conducted using comparable methods [23,28]. Consequently, considering convenience and efficiency, both-limb jump landing is thought to be valuable for screening the risk of ACL injury Limitations This study has important limitations. Influences of the hip and ankle have recently been suggested [9,29]. However, the present study analyzed the kinematics of the knee only. Additionally, although joint kinetics holds great importance for analyses of athletic tasks and for examination of the mechanisms of injuries, we only analyzed knee kinematics because we have not developed a joint-moment calculation system corresponding to PCT. Future studies should examine the relation between kinematic data and kinetics data to assess the ACL injury mechanism. 5. Conclusion We compare the biomechanical characteristics of the knee joint for several athletic tasks to elucidate the characteristics of single-limb landing, plant and cutting and both-limb landing, and to examine what tasks present a risk for ACL injury. 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