Ankle ligament injury risk factors: a prospective study of college athletes

Transcription

1 ELSEVIER Journal of Orthopaedic Research 19 (2001) Journal of Orthopaedic Research Ankle ligament injury risk factors: a prospective study of college athletes Bruce D. Beynnon Per A. Renstrom a, Denise M. Alosa, Judith F. Baumhauer ', Pamela M. Vacek a Department qf Orthopaedics & Rehabilitation Mc Clure Musculoskeletul Resrurch Center Stufford Hull, Uniiwsity of I Prmont, Burlington, I'T USA Department of Orthopaedic Surgery, Unioersity of' Rochester Medical Center, 601 Elmwood Acenue. Rochester, NY USA Department of Medical Biostatistics, 25D Hills Agricultural Science Uniaersity of I'ermont, Burlington, VT 05405, USA Received 28 August 1998; accepted 24 May 2000 Abstract Over two million individuals suffer ankle ligament trauma each year in the United States, more than half of these injuries are severe ligament sprains; however, very little is known about the factors that predispose individuals to these injuries. The purpose of this study was to determine the risk factors associated with ankle injury. We performed a prospective study of 118 Division I collegiate athletes who participated in soccer, lacrosse, or field hockey. Prior to the start of the athletic season, potential ankle injury risk factors were measured, subjects were monitored during the athletic season, and injuries documented. The number of ankle injuries per 1000 person-days of exposure to sports was 1.6 for the men and 2.2 for the women. There were 13 injuries among the 68 women (19%) and seven injuries among the 50 men (1 3%), but these proportions were not significantly different. who played soccer had a higher incidence of ankle injury than those who played field hockey or lacrosse. Among men, there was no relationship between type of sport and incidence of injury. Factors associated with ankle ligament injury differ for men relative to women. with increased tibia1 varum and calcaneal eversion range of motion are at greater risk of suffering ankle ligament trauma, while men with increased talar tilt are at greater risk. Generalized joint laxity, strength, postural stability, and muscle reaction time were unrelated to injury Orthopaedic Research Society. Published by Elsevier Science Ltd. All rights reserved. Introduction The most common injury in recreational and athletic activity is ankle ligament injury [9]. The cost for treatment and rehabilitation of these injuries has been reported to be two billion dollars a year [33]. Reducing the incidence of ankle ligament injuries depends on identifying the conditions under which such injuries occur (e.g. extrinsic variables such as environmental conditions, equipment, etc.) and individual characteristics (e.g. intrinsic variables such as height, and ankle specific measures) that might predispose athletes to such injuries. In a recent review of the literature, we determined that there was little consensus with regard to what constitutes an ankle injury risk factor [l]. Sitler et al. [31] * Corresponding author. Tel.: fax: address: beynnon@salus.med.uvm.edu (B.D. Beynnon). have shown that the incidence of ankle sprains was lower in athletes that previously suffered an ankle sprain and wore a brace in comparison to those that did not. Even though height and weight have not been shown to be independent risk factors for ankle sprains [31], when expressed as a mass moment of inertia, or height squared multiplied by weight, it was predictive of ankle sprains [26]. Many other intrinsic and extrinsic ankle injury risk factors have been studied [I.23,27,28]; however, most of these investigations haw been limited by their retrospective design and have not gathered exposure data. The purpose of this investigation was to perform a comprehensive, prospective investigation of the risk factors for inversion ankle ligament sprain. Based on a review of the literature, we identified generalized and ankle joint laxities, anatomic alignment of the foot and ankle, strength, postural sway, and muscle reaction time as potential risk factors, and hypothesized that one or a combination could be used to identify athletes at risk for ankle ligament injury /01/$ - see front matter Orthopaedic Research Society. Published by Elsevier Science Ltd. All rights reserved. PII: S ( 0 0 )

2 214 B.D. Beynnon et ul. / Journal of Orthopaedic Research 19 (2001) Materials and methods One hundred 18 Division I National Collegiate Athletic Association varsity athletes (50 men and 68 women ranging between 18 and 23 years of age), who competed in either lacrosse, soccer or field hockey participated during the 1994 and 1995 seasons. Subjects were excluded if they had previously sustained an ankle ligament sprain. undergone surgery of the foot or ankle, sustained trauma to the lower extremity, or if they used ankle support. Prior to preseason training, the following potential ankle injury risk factors were evaluated. Demographic injormation was recorded by each participant on a health history survey, which included sport, gender, history of injury to the lower extremity, height, weight, and leg dominance. Generalized und ankle joint laxities. The modified Beighton method [6] was used by the same investigator (DMA) to quantify generalized joint laxity. This involved measuring the limits of motion for the fifth MCP joints, thumbs, elbows, knees, and trunk. A score of four or more, out of a maximum of nine, identified an athlete as having generalized joint laxity, while those who scored less were not. Laxity of both ankles was evaluated with the anterior drawer (a valid meastire of the anterior talofibular ligament [8,15,19,35]) and talar tilt exams (a sensitive measure of the anterior talofibular and calcaneofibular ligaments [18,25,19]) by the same investigator (DMA). The anterior drawer test was performed with the subject seated, knees flexed at 90" and the ankles at lo" of plantar flexion [30]. Anterior displacement of the talus relative to the fibula was evaluated: no or minimal displacement was assigned a grade of 0, moderate displacement (less than 4 mm) a grade 1+, and severe displacement (greater than 4 mm) a grade 2+. The talar tilt test was performed and graded as either positive (e.g. 20" or more of calcaneal inversion, or a 10" difference between right and left ankles [10,11]) or negative. Anatomic alignment oj'the,foot and ankle with the subject nonweighthearing was measured with a goniometer [17], by the same investigator (DMA) to provide consistent intra-rater reliability [5,14,32]. Both sides of the lower extremity were evaluated. The subtalar neutral position was used as a reference, or zero point, from which measures of foot and ankle position and range of motion were made. This was established with the subject prone, and the examiner palpating the medial and lateral portions of the talus with the thumb and forefinger from the anterior aspect of the ankle, while the other hand was used to maximally abduct and adduct the forefoot to determine the point during range of motion at which the head of the talus was felt equally between both fingers. Once congruency of the talus was established, slight dorsi-flexion was applied to the fourth and fifth metatarsal heads from the plantar aspect of the foot to maintain the subtalar joint in this neutral position. From the SUbtdlar neutral position, forefoot-torearfoot position was evaluated by measuring the angle between a line constructed through the fifth and first metatarsal heads (forefoot) and a line perpendicular to the mid-sagittal axis of the calcaneus (rearfoot). If the head of the first metatarsal was in a higher plane than the head of the fifth metatarsal. the foot was in a forefoot varus position. This was followed by evaluation of Rearfoot position. This was assessed with the calcaneus maintained in the subtalar neutral location with the thumb and finger of one hand while the other hand was used to measure the angle between the lines drawn such that they bisected the calcaneus and calf in the midsagittal planes. Next, calcaneal inversion range-of-motion was evaluated relative to the subtalar neutral position by applying an inversion moment to the calcaneus until the limit of rotation was met, and measuring the angle between the lines that bisected the calcaneus and calf in the midsagittal planes. Similarly, calcaneal eversion range-of-motion was measured relative to the subtalar neutral position by applying an eversion moment to the calcaneus until the end of rotation was observed and measuring the angle between the lines that bisected the calcaneus and calf in the midsagittal planes. Finally, ankle dorsi-flexion range of motion was measured with the knee in extension and then 90" of flexion. The talocrural joint was passively dorsi-flexed while the subtalar joint remained in neutral. The angle between a line constructed parallel to the base of the foot and a line parallel to the long axis of the fibula was measured. Anmtomic alignment of the foot and ankle with the subject weightheuring was evaluated while the subject was standing with knees extended and feet placed shoulder-width apart. Anatomic foot type was classified as either pronated, neutral, or supinated using the criterion reported by Dahle et al. [12]. The foot was pronated if the following conditions were met during relaxed stance: 3" or more of calcaneal valgus, medial bulge of the talonavicular joint, and navicular tuberosity below Feiss's line [24] (the line passing through the apex of the medial malleolus and the plantar portion of the first metatarsal head: Fig. 1). The foot was neutral if varus/valgus position of the calcaneous fell between 0" and 3", and the navicular tuberosity was aligned with Feiss's line. The foot was supinated if calcaneal varus was greater than 3", there was no medial bulge of the talonavicular joint, and the navicular tuberosity was aligned above Feiss's line. Next, tibia1 and calcaneal varushalgus position measurements were made with the subject standing with feet placed shoulder-width apart [32]. Tibia1 varuslvalgus position was evaluated by aligning one arm of the goniometer with an axis that bisected the lower leg in the midsagittal plane, aligning the other arm parallel with the floor, and measuring the included angle. Calcaneal varus/valgus position was evaluated by aligning one arm of the goniometer with the line that bisected the calcaneus in the midsagittal plane, aligning the other arm with the line that bisected the tibia in the midsagittal plane, and measuring the included angle. Irokinetic ankle, strength was evaluated using the Cybex 6000 dynamometer (Lumex, Ronkonkoma, NY [4,3,14,20]. Athletes were prone for the plantar dorsi-flexion test, and supine with the knee flexed at 90" for the inversion-eversion test. Plantar dorsi-flexion and inversion-eversion peak torque values, and corresponding strength ratios, were determined using both concentric and eccentric protocols for both ankles. Each test was performed at a speed of 30"/s using a comfortable range ofjoint motion. Five trials were performed for each test and all were used in the data analysis. Anterior-posterior center of' graoity (A-P COG) stcay angle was evaluated with the NeuroTest system (NeuroCom International, Clackamas OR, USA). This measure compensates for differences in subjects' heights because the angular limits of stability are similar for all adults, irrespective of height. The maximum A-P COG sway angle was measured while the subjects had their eyes closed (eliminating the contribution of the visual system to maintaining balance) and with the force platform in the fixed and sway referencing modes. In the fixed mode, subjects stood on the force plate and A-P COG sway angle was controlled by the subject's somatosensory (i.e. the mechanoreceptors about the ankle and the other joints of the lower extremity) and vestibular systems. In the sway reference mode, subjects stood on the same force plate with a servo-device engaged that matched the angular motion of the force plate to the estimated angular sway of the subjects center of gravity. This reduced angular displacement of the ankle joint, thereby delivering minimal proprioceptive information from the ankle so that the subject relied primarily on the vestibular system to maintain postural equilibrium. The maximum A P COG sway angle was measured for the following conditions: ( I) fixed platform with dominant C Fig. 1. The line passing through the apex of the medial malleolus (A) and the plantar portion of the first metatarsal head (C) was used to identify Feiss's line (24). The location of the navicular tuberosity (B), relative to this line, in combination with appearance of the talonavicular joint and calcaneal valgns measurements were used to establish anatomic foot type.

3 B.D. Beynnon et ul. I Journal of Orthopaedic Reseurch 19 (2001) leg stance: (2) fixed platform with nondominant leg stance; (3) swayreferenced platform with the subject using twolegged stance; (4) swayreferenced platform with dominant leg stance: and, (5) sway-referenced platform with nondominant leg stance. Three trials of each test condition were performed, each of which required 20 s to perfom. The maximum A-P COG sway angles were summed across the three trials and a mean value calculated for each of the five test conditions. hfusck reaction time, the time lag between joint perturbation and muscle activation, was measured with the Neuro Test system and electromyographic (EMG) signals from surface electrodes (Motion Control, Salt Lake City, Utah) placed over the muscles of interest for dorsi-flexion and inversion perturbation of the foot. For dorsi-flexion perturbation, electrodes were placed on the medial head of the gastrocnemius and on the tibialis anterior. This approach minimized crossover between electrodes by placing them as far apart as practical [21]. The subject was positioned so perturbation produced dorsi-flexion rotation of both feet. The stimulus followed as a 4' dorsiflexion rotation at a velocity of 5O"ls, eliciting the three characteristic EMG muscle reaction components: the short-loop gastrocnemius, medium-loop gastrocnemius, and long-loop tibialis anterior responses. EMG data were sampled with surface electrodes (one common and two active) that were fixed in a plastic housing and uniaxially aligned such that the common electrode (located in the center between the active electrodes) was spaced 0.5 cm from the active electrodes. Analog activity from the active electrode pairs was amplified by a differential amplifier and sampled at a frequency of 1000 Hz from 100 ms before the perturbation began until 400 ms after. Each subject underwent perturbations until 10 EMG trials were observed for each muscle on each leg. The EMG signal was rectified and then each trial was analyzed to identify the onset of the short-loop gastrocnemius, medium-loop gastrocnemius, and long-loop tibialis anterior responses using the validated technique described by Lawson et al. [Zl], and then combined to produce average values. Inversion perturbation of the ankle required that EMG electrodes be attached to the peroneal longus, peroneal brevis, and tibialis anterior. The subject was then positioned such that the perturbation produced a 4' inversion rotation of the foot at a velocity of 5O"/s, and the same data acqu on parameters described for dorsi-flexion perturbation were used. This stimulus produced the three characteristic EMG components termed the medium-loop peroneal longus, medium-loop peroneal brevis, and long-loop tibialis anterior reactions. Each subject underwent the inversion perturbations until ten EMG tracings were obtained for each muscle on each leg. These data were combined to produce average values. All athletes played outdoors on the same natural turf and were exposed to the same field at the same time. Thus, on any given day all study participants were exposed to the same conditions. Athletes were monitored throughout the athletic season, documenting their exposure to sports, and those whom sustained an ankle injury were evaluated immediately by an orthopaedic surgeon (PAR). If a sprain was diagnosed, then it was graded as either a I, 11, or I11 [7]. A grade I injury was defined as no loss of function, no loss of ligamentous stability (negative anterior drawer and talar tilt tests), little or no hemorrhage, and point tenderness. Grade 11 injuries demonstrated some loss of function, decreased motion, a positive anterior drawer and negative talar tilt test (the ankle mortise did not open with applied inversion stress), hemorrhage, swelling and point tenderness. Grade I11 injuries had nearly total loss of function, a positive anterior drawer and talar tilt test (the ankle mortise opened with applied inversion stress), diffuse swelling and hemorrhage, and extreme point tenderness. Pre-season potential risk factor measurements from men and women were compared using t-tests and Chi-square tests. Since there were gender differences for many of the outcomes, all other analyses were performed separately for men and women. Cox regression was used to test the effect of each variable on relative risk, taking into account differences in the lengths of time the athletes were at risk. This was accomplished by computing time at risk as the total number of games and practices in which each subject participated until injury or, if uninjured, the end of the sports season. Since the Cox model assumes that the effect of each variable is proportional to an underlying hazard function, subjects were stratified by sport to take into account differences in the hazard functions for different sports. For all analyses, data from only one leg was used ~ the injured leg for subjects with injuries and a randomly selected leg for those who were uninjured. Results The men had 4249 days of exposure to sports, while the women had 5813 days. The number of ankle injuries per 1000 person-days of exposure was 1.6 for men and 2.2 for women. There were 13 injuries among the 68 women (19.1%), and seven injuries among the 50 men ( 14%), but these proportions were not significantly different. Ten of the 13 injuries in women occurred in the right leg, which was significantly greater than would be expected if both legs were at equal risk (P = 0.046). This was not the case for men, where three of the seven injuries occurred in the right limb. The majority of injuries occurred during practice rather than games. The women sustained 11 injuries during practice and two during games, while for the men six injuries occurred during practice and one during a game. A majority of the injuries occurred during sunny weather when the turf was dry. The women suffered nine injuries when the weather was sunny and the playing field was dry, three injuries when the field was wet, and one injury when it was cold. The men sustained five injuries when the weather was sunny and the field was dry, one injury when the field was wet, and one injury when it was cold. and women differed substantially in terms of several pre-season risk factors; thus, data are presented separately for each gender (Tables 1-6). The mean height and weight of the men were 70.4 in. and 169 lbs, respectively, and for the women, 65.1 in. and 133 Ibs. As expected, the women were smaller and weighed less than the men (P < 0.05, Table 1). had larger dorsiflexion motion of the ankle, larger calcaneal inversion range of motion, and larger calcaneal eversion range of motion, compared to the men (P < 0.05, Table 3). The isokinetic strength measures were significantly lower for the women than the men (P < 0.05, Table 4). The A-P COG sway angle was significantly larger among the women for the single-leg stance nonsway referenced evaluation (P < 0.05, Table 5). had a faster short-loop reaction time of the gastrocnemius muscle in response to a dorsi-flexion perturbation of the foot, and a faster reaction time of the peroneal brevis in response to an inversion perturbation (P < 0.05, Table 6). There were no differences between men and women with regard to: limb dominance, generalized joint laxity, ankle joint laxity, anatomic foot type, the medium-ioop reaction time of the gastrocnemius muscle and the long-loop reaction time of anterior tibialis muscles in response to dorsi-flexion perturbation of the foot, and the peroneal longus and anterior tibialis reaction times in response to inversion perturbation of the foot. The P-values in Tables 1-6 correspond to the global chi-square statistic from the individual Cox regressions performed for each variable. This tests the significance of each variable on the hazard function, controlling for time at risk and sport. who played soccer had a

4 1 ~ ~ 216 B.D. Bejnnon et al. / Journal of Orthopaedic Research 19 (2001) Table 1 Demographic data for injured and uninjured subjects" Variable Uninjured Injured P-value (from Uninjured Injured P -value (from Cox regression) Cox regression) Subjects ~ Height (in.)b Weight, Ibs (S.D.)h 133 (14) 128 (14) (15.8) 172 (9.1) 0.38 Limb dominance Right N ("0) 52 (96) 10 (92) (91) 4 (57) Left N (";I) 2 (4) 3 (8) - 4 (9) 3 (43) ~ Sport Soccer N ("4) 12 (22) 7 (54) (54) 3 (43) 0.60 Field hockey N ('Iil) 28 (51) 3 (23) - - ~ Lacrosse N ("A,) 15 (27) 3 (23) 20 (46) 4(57) "The data are presented for women and men separately. The P-values are presented for the Cox-regression analysis. ' are significantly different in comparison to men for these specific factors P ~ Table 2 Joint laxity data for uninjured and injured subjectsd Uninjured N Injured N f-value (from Uninjured N Injured N P-value (from (UYI1) ('%I ) Cox regression) ('%I) (Yo) Cox regression) General joint laxity - 46 (85) 10 (77) (93) 7 (100) ~ + 8 (15) 3 (23) 3 (7) 0 (0) Anterior drawer 0 33 (61) 12 (92) (78) 5 (71) (39) 1 (8) 9 (22) 2 (29) ~ Talar tilt - 49 (91) I1 (85) (98) 5 (71) (9) 2 (15) ~ (2) 2 (29) - Generalized joint laxity was measured using the modified Beighton method, and subjects were classified as either having generalized joint laxity (+) or not (-). In addition ankle laxity was measured with the anterior drawer and talar tilt. Data are presented for men and woment seperately. The P-values are presented for the Cox-regression analysis. Table 3 Measurements of alignment of the foot and ankle for injured and uninjured subjects expressed in degrees" Uninjured Injured P-value (from Uninjured Injured P -value (from Cox regression) Cox regression) Anatomic foot type Pronated N ((%I) Neutral N ("A) Supinated N (Yn) Calcaneal inversion unweighted: mean (S.D.)b Calcaneal eversion unweighted: mean (S.D.)b Rearfool vadvalgus unweighted: mean (S.D.) FF/RF relationship unweighted: mean (S.D.) Dorsi-flexion KE: mean (S.D.)b Dorsi-flexion KF: mean (S.D.) Calc varus/valgus during 24 (44) 25 (46) 5 (9) 17.8 (4.6) 4 (31) 7 (54) 2 (15) 16.8 (5.4) (36) 20 (49) 6 (15) 15.3 (3.6) 2 (29) 2 (29) 3 (42) 18.0 (5.9) 5.2 (1.8) 6.1 (2.6) (2.4) 5.4 (2.3) (1.5) 4.2 (1.6) (1.8) 4.9 (0.9) (3.3) 2.7 (3.0) (3.6) 2.4 (3.2) (1.9) 12.3 (3.3) 7.2 (3.6) 5.3 (1.8) 12.8 (3.5) 6.1 (3.5) (2.7) 11.3 (3.7) 6.8 (4.2) 4.1 (0.9) 12.7 (3.9) 4.3 (5.3) weightbearing: mean (S.D.) Tibia1 varus/valgus during 5.4 (2.2) 6.6 (2.6) (2.5) 4.7 (2.0) 0.94 weightbearing: mean (S.D.) a These data are presented for women and men separately. The P-values are presented for the Cox-regression analysis ' are significantly different in comparison to men for these specific factors (P GO.05)

5 B. D. Bepnon et ul. I Journal of Orthopaedic Rcseurch I9 ( , Table 4 Isokinetic strength values for concentric (Con) and eccentric (Ecc) contractions of the leg muscles during plantar flexion (PF), dorsi-flexion (DF), inversion (INV), eversion (EV) modes for uninjured and injured subjects" Con strength PF' Con strength DF' Con strength INVb Con strength EV' Ecc strength PFh Ecc strength DF' Ecc strength lnvh Ecc strength EV' Con DFlCon PF Con EVlCon INV Ecc DFlEcc PFh Ecc EVlEcc INV Uninjured l' Injured S P-value (from Uninjured ~Y Injured A' P value (from (S.D.) (S.D.) Cox regression) (S.D.) (S.D.) Cox regression) 53.1 (11.3) 18.2 (2.6) 14.2 (4.2) 13.3 (2.7) (18.1) (4.1) (4.3) (3.8) 0.36 (0.09) 0.99 (0.30) 0.42 (0. I 1 ) 1.03 (0.24) 52.3 (12.3) (2.4) (5.9) (3.4) (16.3) I.OO (4.0) (3.7) (3.3) (0.08) (0.24) (0.09) (0.25) (13.7) 26.8 (3.8) 20.0 (5.3) 19.5 (5.3) (20.9) (6.1) (6.2) (5.8) 0.39 (0.09) 1.02 (0.30) 0.47 (0.15) 1.08 (0.30) 77.3 (13.0) 28.1 (4.2) 21.1 (5.1) 22.3 (5.6) (32.5) (6.1) (6.2) (5.4) 0.37 (0.09) 1.07 (0.26) 0.44 (0.17) 0.96 (0.19) "These data are presented for women and men separately. The P-values are presented for the Cox-regression analysis. ' are significantly different in comparison to men for these specific factors (P < 0.05) Table 5 Anterior-posterior center of gravity (A-P center of gravity) sway angle for uninjured and injured subjects expressed in degrees. A-P COG sway angle expressed in terms of degrees of sway is presented for women and men separately" Uninjured X Injured A' P-value (from Uninjured X Injured A' P-value (from (S.D.) (S.D.) Cox regression) (S.D.) (S.D.) Cox regression) Single leg stance nonsway 3.4 (0.33) 3.4 (0.32) (0.24) 3.6 (0.55) 0.21 referenced Single leg stance sway 4.8 (0.79) 5.0 (0.71) (0.77) 4.9 (1.1) 0.59 referenced Two leg stance sway referenced 3.9 (0.4) 4.0 (0.64) (0.39) 3.4 (0.36) 0.27 a The P-values are presented for the Cox-regression analysis. are significantly different in comparison to men for these specific factors (P ). Table 6 Muscle reaction times, expressed as ms, in response to dorsi-flexion and inversion perturbations of the foot for both uninjured and injured subjects> Uninjured.Y Injured X P-value (from Uninjured X Injured X P-value (from (S.D.) (S.D.) Cox regression) (S.D.) (S.D.) Cox regression) Short-loop GSTb 32.4 (2.5) 33.2 (3.1) (3.0) 34.3 (3.5) 0.68 Med-loop GST 82.4 (12.0) 77.8 (13.7) (11.6) 83.1 (15.1) 0.63 Long-loop AT 119 (15.4) 127 (17.7) (17.2) 135 (13.4) 0.41 Inversion PBb 83.5 (12.5) 80.5 (8.8) (11.6) 89.2 (4.8) 0.69 Inversion PL 83.0 (11.6) 83.4 (9.2) (12.5) 86.5 (4.6) 0.94 Inversion AT 117 (23.5) 125 (29.0) (27.5) 118 (26.4) 0.51 a Data are presented for dorsi-flexion perturbation (short-loop gastrocnemius, medium-loop gastrocnemius, and long-loop anterior tibialis responses) and for inversion perturbation (inversion PB (peroneal brevis), inversion PL (peroneal longus) and inversion AT (anterior tibialis)). The P -values are presented for the Cox-regression analysis. are significantly different in comparison to men for these specific factors ( P < 0.05). higher incidence of ankle injuries than those who played field hockey or lacrosse (P = 0.02, Table 1). Ankle injuries were more common among women with increased tibia1 varum and calcaneal eversion range of motion (P = 0.03 and 0.02, respectively). In spite of the fact that the reaction times of the muscles in response to inversion perturbation of the foot were not predictive of injury, we observed an interesting trend of the reaction times in response to dorsi-flexion perturbation of the foot. On average, the medium-loop reaction of the gastrocnemius muscle was 5 ms faster (P = 0.07) while the long-loop reaction of the anterior tibialis was 8 ms longer (P = 0.1) among female athletes who sustained injuries compared to those who did not (Figs. 2 and 3). Generalized and

6 118 B. D. Beynnon el al. I Journal of Orthopaedic Research 19 (2001), T" In T T'" In'Gm 2' Y I (4 I I I I I I i Fig. 2. Pre-season muscle reaction data from a female subject that was not injured. Shown is the reaction of the tibialis anterior muscles in response to a 4" rotation of the foot during approximately 125 ms (Fig. I(a)). The characteristic EMG reactions of the tibialis anterior for the left leg (L. Tibia, Fig. I(b)) and the right leg (R. Tibia, Fig. 1(c)) are presented. The long-loop response (LLI) occurred at 99 and 96 ms for the left and right muscles, respectively ankle joint laxities, anatomic foot type, strength, and A- P COG sway angle were similar among injured and noninjured women. Among the men, there was no effect of type of sport on incidence of ankle injury (Table 1). whose talar tilt exams demonstrated a rotation in excess of 20" sustained a greater proportion of ankle ligament injuries than those whose exams showed a rotation less than 20" (P = 0.003, Table 2). Strength, anatomic foot type, A-P COG sway angle, and the reaction time of the muscles in response to dorsi-flexion and inversion perturbations of the foot were no different among the injured than among the uninjured men. Discussion Our previous work concerned potential ankle injury risk factors in a similar group of intercollegiate athletes -who competed in the same sports [4] and showed that individuals with an increased calcaneal eversion rotation and muscle strength imbalances had a higher prevalence of inversion ankle sprains. The present study confirms our earlier findings, at least in part, since we found that, t (4 I I, I I I i Fig. 3. Pre-season muscle reaction data from a female subject that subsequently suffered an ankle sprain, presented for the purpose of comparison with the data from the uninjured subject (Fig. l(a)-(c)). Reaction of the anterior tibialis muscle in response to the 4" rotation of the foot (Fig.?(a)), the same perturbation used for the uninjured subject (Fig. l(a)), is presented along with the EMG reactions for the left leg (L. Tibia, Fig.?(b)) and right leg (R. Tibia, Fig. 2(c)). The longloop response (LLI) appeared to be delayed for this injured subject compared to uninjured subjects, occurring at 147 and 143 ms for the left and right muscles correspondingly. among women, ankle injuries were related to increased calcaneal eversion range of motion. The present investigation also showed that women with increased tibia1 varum and men with increased talar tilt were more likely to sustain ankle injuries. This finding was in contrast to our earlier study, as was the fact that, in the present study, we also found no relation between muscle strength or muscle strength imbalances and subsequent injury. The test-retest reliability of the ankle injury risk factor measurements we used has been shown to be highly repeatable [5,33], and therefore differences between injured and uninjured subjects for the anatomic alignment risk factors were not likely to have resulted from the examiner's learning effect or measurement artifact. Differences between the present and our previous study may derive from differences in methodology. Unlike the previous study, this time we evaluated women and men separately. If the effect of a risk factor is gender dependent, it will be obscured in analyses using combined data from men and women. Even risk factors

7 B.D. Beynnon et ul. I Journal of Orthopaedic Reseurch 19 (2001 I having similar effects in men and women may not be detected in analysis of combined data if high values for women correspond to low values for men. Conversely, variables whose values differ greatly between genders may falsely appear to have an effect on risk if women are inherently at higher risk. Also, in the current study we evaluated exposure data and performed data analysis using the Cox regression model to take into account both time at risk and differences in risk associated with different sports. Our earlier study did not document exposure data and used the Student s f test to analyze the data without adjustment for sport. Dahle et al. [12] and Barrett et al. 131 reported no correlation between anatomic foot type (pronated, neutral, or supinated) and the incidence of ankle sprains. Our investigation supports these findings; however, 70% of the ankle injuries in our study occurred in athletes with either a neutral or supinated foot type. Barrett et al. [2] reported that provocative testing of ankle ligament stability with the anterior drawer and talar tilt exams did not predict ankle injury. In our earlier work, on this same subject [4], we found that provocative testing with the anterior drawer test showed a trend toward prediction, while the talar tilt exam did not. In our present investigation, the same trend was observed among women (P = 0.1); however, we found an association between talar tilt and injury incidence among men. Jackson et al. [I61 and our group [4] reported that generalized joint laxity is not correlated with ankle ligament injury. The present investigation confirms these findings for men and women, considered separately. There is also conflicting evidence regarding the effect of limb dominance on the risk of ankle injury. Ekstrand and Gillquist [ 131 reported an increased risk of injury for the dominant ankle, but Surve et al. [34] found no difference in the incidence of ankle injury between nondominant and dominant ankles. The present study agrees with the findings of Surve et al. [34] for both men and women. Our earlier work also investigated the relationship between lower extremity strength and the incidence of ankle injury [4]. We found that ankle sprains were associated with higher ratios between ankle eversion and inversion peak torques, higher peak torque values during plantar-flexion, and a lower ratio between dorsiflexion and plantarflexion peak torque values [4]. In the current study, however, we found no difference in peak torque values among athletes who subsequently sustained injuries and those who did not for all test modes. Likewise, neither the ratio between ankle eversion and inversion peak torque values, nor the ratio between dorsi-flexion and plantar flexion peak torque values was related to subsequent injury. The muscle reaction times were not different for injured than for uninjured men. In contrast, we observed an interesting trend for the women: athletes who subsequently sustained an ankle injury had a gastrocnemius muscle that required less time to react while the anterior tibialis muscle required more time to react in response to a dorsi-flexion perturbation of the foot compared to the athletes that were not injured. This suggests that a neuromuscular deficit may have existed in these women athletes, and that the protective effect of the leg muscles on joint stability may have been compromised. The medium-loop gastrocnemius muscle reaction controls local muscle properties while the long-loop anterior tibialis reaction provides the first stabilization to the ankle joint in response to a perturbation. The delay in the anterior tibialis reaction may reflect some deficit of the musculoskeletal system that compromises the protective effect of the leg muscles on ankle joint stability, thereby predisposing these women athletes to ankle injury. Maintaining proper contact conditions between the foot and floor during stance or gait may require increased tibial varum rotation to be coupled with increased eversion rotation of the calcaneous. Therefore, our finding that amongst women, increased tibial varum and calcaneal eversion range of motion were both associated with increased risk of suffering ankle trauma introduced the prospect that these measurements were related. Post-hoc correlation analysis did not reveal a significant correlation between these two anatomic measurements; however, there was a moderate correlation between calcaneal eversion rotation (evaluated with the subject unweighted) and calaneal varushalgus orientation, evaluated with subject weightbearing (Y = 0.79; P = 0.032). This finding suggests, at least in part, that orientation of the hindfoot is an important anatomic parameter to consider when evaluating risk factors for inversion ankle trauma. In summary, this study has demonstrated that the risk factors that predispose an athlete to ankle ligament injury were different between men and women. with increased tibial varum rotation and a compensatory increase of calcaneal eversion range-of-motion sustained proportionately more ankle injuries. with an increased talar tilt sustained more injuries. For women, playing soccer (as opposed to field hockey or lacrosse) significantly increased their risk of ankle injury, whereas for men, type of sport (soccer versus lacrosse) had no effect on injury incidence. Strength and postural sway (as characterized by A-P COG sway angle) were not risk factors for both men and women. Currently, we are expanding on the efforts described in this investigation by including other sports. different playing conditions, and younger athletes to broaden the scope and applicability of our findings. Once we have established the risk factors associated with male and females athletes for different playing conditions, our next step will be to perform an intervention study that is

8 220 B.D. Beynnon rt a/. I Journal of Orthopaedic Research 19 (2001) designed to determine how we can reduce the high incidence of ankle trauma. Acknowledgements This work was funded in part by a grant from the National Collegiate Athletic Association (grant # ) and the National Institutes of Health (R01- AR45346). References Barker HB, Beynnon BD, Renstrom PA. Ankle injury risk factors in sports. Sports Med 1997:23: Barrett JR, Tanji JL, Drake C, et al. High versus lowtop shoes for the prevention of ankle sprains in basketball players: a prospective randomized study. Amer J Sports Med 1993;21: Baumhauer JF. A comparison study of ankle inversion and eversion strength in healthy and inversion ankle sprained individuals as assessed by Cybex I1+ dynamometer. Thesis, Middlebury College, Middlebury, Vermont, Baumhauer JF, Alosa DM, Renstrom PA, Trevino S, Beynnon BD. A prospective study of ankle injury risk Factors. Amer J Sports Med 1995;33: Baumhauer JF, Alosa DM, Renstrom PA, Trevino S, Beynnon BD. Test-retest reliability of ankle injury risk factors. Amer J Sports Med 1995;33:5714. Beighton P, Solomon L, Soskolne CL. Articular mobility in an African population. Ann Rheum Dis 1973:3(2): Bergfeld J, Halpern B. Sports Medicine: Functional Management of Ankle Injuries. Videotape Library of the American Academy of Family Physicians, 1991, V.T. No Black HM, Brand RL, Eichelberger MR. An improved technique for the evaluation of ligamentous injury in severe ankle sprains. Amer J Sports Med 1978;6: Brand RL, Black HM, Cox JS. The natural history of inadequately treated ankle sprains. Amer J Sports Med 1977;5: Chrisman OD, Snook GA. Reconstruction of lateral ligament tears of the ankle. J Bone Joint Surg 1969;51A Cox JS, Hewes TF. Normal talar tilt angle. Clin Orthop 1979; 140:3741. Dahle LK, Mueller M, Delitto A. et al. Visual assessment of foot type and relationship of foot type to lower extremity injury. J Orthop Sports Phys Ther 1991:14:70-4. [13] Ekstrand J, Gillquist J. Soccer injuries and their mechanisms: a prospective study. Med Sci Sports Exerc : [I41 Elveru RA, Rothstein JM, Lamb RL, et al. Methods for taking subtalar joint measurements: a clinical report. Phys Ther 1988:68: [I51 Jackson JP, Hutson MA. Castbrace treatment of ankle sprains. Injury 1986;17: [16] Jackson DW, Jarrett H, Bailey D, et al. Injury predictlon in the young athlete: a preliminary report. Amer J Sports Med 1978;6:6-11. [I71 James SL, Bates B, Osternig LR. Injuries to runners. Amer J Sports Med 1978;6: [I81 Johnson EE, Markolf KL. The contribution of the anterior talofibular ligament to ankle laxity. J Bone Joint Surg 1983: 65A:81-8. [I91 Karlsson J, Bergsten T, Lansinger 0, Peterson L. Reconstruction of the lateral ligaments of the ankle for chronic lateral instability. J Bone Joint Surg 1988;70A: Karnofel H, Wilkinson K, Lentell G. Reliability of isokinetic muscle testing at the ankle. J Orthop Sports Phys Ther : Lawson GD, Shepard NT, Oviatt DL, Wang Y. Electromyographic responses of lower leg muscles to upward toe tilts as a funciton of age. J Vistibular Res 1994;4: Lynch SA, Eklund U, Gottlieb DJ, Renstrom PA, Beynnon BD. Electromyographic latency changes in the ankle musculature during inversion moments. Amer J Sports Med 1996;24: Lysens R, Steverlynck A, van den Auweele Y, Lefevre J, Renson L. Claessens A, Ostyn M. The predictability of sports injuries. Sports Med 1984;l:fLlO. Magee DJ. Orthopaedic physical assessment. 2nd ed. Lower leg, ankle and foot. London: Saunders, 1987 (Chapter 12). Makhani JS. Lacerations of the lateral ligaments of the ankle. An experimental appraisal. J Int Coll Surg 1962;38:45&66. Milgrom C, Shlamkovitch N, Finestone A, Eldad A, Laor A, Danon YL, Lavie 0, Wosk J, Simkin A. Risk factors for the lateral ankle sprain: a prospective study among military recruits. Foot Ankle 1991; Moretz JA. Flexibility as a predictor of knee injuries in college football players. Phys Sportsmed 1982: 10:93-7. Nicholas JA. Injuries to knee ligaments; relationship to looseness and tightness in football players. J Amer Med Assoc 1970; Rasmussen 0. Stability of the ankle joint. Analysis of the function and traumatology of the ankle ligaments. Acta Orthop Scand (Suppl.) 1985;211:1-75. Renstrom P, Theis M. Biomechanics and function of ankle ligaments: experimental results and clinical application. J German Orthop Trauma 1993;7: Sitler M, Ryan J, Wheeler B, et al. The efficacy of a semirigid ankle stabilizer to reduce acute ankle injuries in basketball. Am J Sports Med 1994;22: Smith-Oricchio K, Harris A. Interrater reliability of subtalar neutral, calcaneal inversion and eversion. J Orthop Sports Phys Ther 1990;12:10-5. Soboroff SH, Pappius EM, Komaroff AL. Benefits, risks and costs of alternative approaches to the evaluation and treatment of severe ankle smains. Clin Orthor, 1984;183: [34] Surve I, Schwellnus MP, Noakes T, et al. A fivefold reduction in the incidence of recurrent ankle sprains in soccer players using the sportstirrup orthosis. Amer J Sports Med [35] Tohyama H, Beynnon BD. Renstrom PA, Theia MJ, Fleming BC, Pope MH. Bioniechanical analysis of the ankle anterior drawer test for anterior talofibular ligament injuries. J Orthop Res 1995:13: