Hip rotation as a risk factor of anterior cruciate ligament injury in female athletes

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1 J Phys Fitness Sports Med, 5 (1): (2016) DOI: /jpfsm JPFSM: Regular Article Hip rotation as a risk factor of anterior cruciate ligament injury in female athletes Tadashi Yasuda 1,2*, Yuki Yokoi 2, Keiichi Oyanagi 2 and Kazutaka Hamamoto 2 1 Department of Orthopaedic Surgery, Kobe City Medical Center General Hospital, Minatojima-minamimachi, Chuo-ku, Kobe , Japan 2 Department of Rehabilitation, Kobe City Medical Center General Hospital, Minatojima-minamimachi, Chuo-ku, Kobe , Japan Received: July 17, 2015 / Accepted: January 7, 2016 Abstract No specific hip joint anatomy has been identified as a risk factor for anterior cruciate ligament (ACL) injury in females. This study was conducted to elucidate the correlation of hip rotation with ACL injury incidence in female handball players, and to clarify the association of hip rotation with knee valgus motion, during ACL injury screening tasks, that is a strong predictor of ACL injury. Of 17 female university handball players, the 8 ACL-injured players displayed greater internal and smaller external rotation of the hip than the 9 uninjured players. Logistic regression analyses demonstrated significant association between hip rotation and ACL injury. Hip internal rotation dominance (internal rotation range is greater than external one) was found in 7 out of the 8 ACL-injured females in contrast to 3 out of the 9 uninjured. Knee valgus was induced in 24 and 22 of the 31 healthy female volunteers by vertical jump and single-leg squat tests, respectively. The knee valgus-positive females showed a smaller range of hip external rotation than the negative ones, which was significantly associated with knee valgus during the screening tests. Hip internal rotation dominance was significantly related to knee valgus induced by each screening test. In contrast to the females, male subjects showed lower rates of knee valgus induction by the screening tests, whereas there was no clear association between hip internal rotation dominance and the knee valgus induction. The present findings may indicate the important role of hip rotation measurement in identification of females at risk for ACL injury. Keywords : anterior cruciate ligament injury, hip rotation, risk factor, knee valgus, injury screening test, handball Introduction Anterior cruciate ligament (ACL) injury occurs at a higher incidence in female athletes compared to males 1,2). Most ACL injuries in female athletes are via a noncontact mechanism while the individual is landing from a jump, rapidly stopping, cutting, or suddenly decelerating with a change in direction 3). Before the onset of puberty, ACL injuries are relatively rare with no apparent gender-related differences in the injury rate 4). During the pubertal process, anatomical, hormonal, and neuromuscular factors differ between males and females, which may play a role in the gender discrepancy in ACL injury rates after puberty 5). The gender-related difference stems from maladaptive neuromuscular recruitment patterns and poor jumping/ landing biomechanics that lead to greater risk for ACL injuries in females. Among multiple gender differences in *Correspondence: tadyasu@kcho.jp lower-extremity neuromuscular control and biomechanics, the knee valgus moment during landing has recently been shown to predict ACL injury in young female athletes with high specificity and sensitivity 6). Knee valgus loading can provide increased ACL strain that may result in ligamentous failure. The majority of these studies have focused specifically on the knee joint. However, the lumbopelvic-hip region may have a significant effect on knee joint biomechanics 7,8) because the center of gravity is located in the lumbopelvic-hip region that plays an important role in athletic function for maintenance of the stability of the whole system and optimal production, transfer and control of force and motion to the terminal segment (proximal to distal) to achieve maximal efficiency 9). Indeed, increasing evidence indicates the contribution of the lumbopelvic-hip region to neuromuscular control of the knee. Identified gender differences in the hip biomechanics include altered hip flexion angles and increased hip adduction and internal rotation during sports maneuvers in females, compared to males 10).

2 106 JPFSM: Yasuda T, et al. In contrast to the neuromuscular factors, the implications of anatomical factors for ACL injuries remain obscure. From video analyses of non-contact ACL injuries, Ireland proposed the position of no return concept, indicating that the hip with an adducted and internally rotated femur and in little hip flexion creates knee valgus, tibial external rotation and forefoot pronation 11). Therefore, the knee injury could be the result of a more proximal hip position. Understanding of proximal anatomical factors may be necessary to identify female athletes at high risk of ACL injury. Among healthy college-age individuals, females have greater femoral anteversion, quadriceps angle, tibiofemoral angle, and genu recurvatum than males 12). Greater femoral anteversion is associated with hip internal rotation and contributes to a compensatory increase in knee external rotation 13). Static lower extremity alignment with a more internally rotated hip and valgus knee alignment may be related to commonly observed components of functional valgus collapse during the single-leg squat 14). However, no previous study has demonstrated the relationship of specific hip anatomy with ACL injuries or the risky landing pattern of ACL injuries in females. In addition, a direct comparison between female athletes with or without a history of ACL injury at the same sport would be helpful to identify the predisposing factors of ACL injuries in females. Currently, no such data are available on anatomical factors such as hip rotation. The purposes of this study were 1) to elucidate the correlations of hip rotations with ACL injury incidence in female handball players, and 2) to clarify the association of hip rotations with knee valgus motion during ACL injury screening tasks that is the strong predictor of ACL injury in females 6). We hypothesized that the hip range of rotation would be associated with the occurrence of ACL injury in female handball players. The secondary hypothesis was that the hip range of rotation would predict knee valgus induced by ACL injury screening tests in females. Materials and Methods Subjects. Seventeen female players on the varsity handball team that belonged to Kansai Collegiate Handball Association division 1 were recruited for this study during the period of data collection. Healthy recreational athletes (31 females and 15 males) were also recruited from the university. Volunteers were excluded if they had a musculoskeletal injury to the lower extremity or a history of hip or knee joint injury, or were otherwise unable to perform the study tasks at the time of data collection. When generalized joint laxity, that is associated with an increased risk of noncontact ACL injury 15), was evaluated by the Beighton (score) test 16), each handball player and volunteer exhibited a Beighton score of 3/9 that indicated no generalized joint hypermobility 17). This study was designed and conducted in accordance with the Helsinki Declaration and approved by the Institutional Review Board of Tenri University. Prior to participation, each subject read and signed a consent form approved by the university s Institutional Review Board. Lower extremity data collection. Six measurements of hip joint motion (flexion, extension, abduction, adduction, external rotation, and internal rotation) and two measurements of knee joint motion (flexion and extension) were taken by standard procedure using a goniometer 18). Spinal and pelvic substitutions were restricted during each measurement. External and internal hip rotations were measured with the subject prone and knee flexed to 90. Knee extension was measured with the subject in supine and a bolster positioned under the distal tibia. A single investigator (orthopedic surgeon) with excellent measurement reliability collected the variables from all the subjects. The passive motion was measured carefully without exerting undue force to increase the range 19). The 3 measurements taken for each measurement variable and side were averaged for analysis. No appreciable mean difference between right and left sides was found in any of the measurement variables (data not shown). Knee valgus evaluation. According to the previous study 20), medial knee displacement in the frontal plane induced during the following screening tests for ACL injury was employed as representative of knee valgus motion. Each subject was instrumented with 12 reflective markers placed on the medial femoral condyle, the fibular head, the tibial tubercle, the medial and lateral malleoli of ankle, and the dorsal surface of the second metatarsal base, as already demonstrated in the previous study 21). 1. The drop vertical jump test 22) The participants were positioned at the top of a box (30 cm high) with their feet 30 cm apart. They were instructed to drop directly down off the box onto the landing spot marked 30 cm apart from the box and immediately perform a maximum vertical jump. The subjects were also instructed to stand still on the landing spot for a reference of each subject s neutral position 21). 2. The single-leg squat test 23) The dominant foot was established by interviewing the subjects to determine which side was used to kick a ball 24). The participants were instructed to perform five single-leg squats on their dominant leg on the step, lowering themselves as far as possible with the non-dominant leg below the level of the step and then returning to a standing position without losing balance. The subjects were also instructed to stand still for a reference of each subject s neutral position 21). We employed the two dimensional video analysis method that has been shown to provide reliable evaluation of frontal plane knee valgus motion 25,26). The trials as described above were recorded using two standard digital

3 JPFSM: Hip rotation as a risk factor for ACL injury in females 107 video cameras (30 Hz) positioned 3.8 m apart from the subject in the frontal and sagittal planes. After the origin of the coordinate axes was set on the basis of the position of one of the markers on the medial and lateral malleoli of the ankle and dorsal surface of the second metatarsal base on the frontal video frame of the reference position, the segment on the horizontal axis between the origin and one of the markers on the medial femoral condyle, the fibular head and tibial tubercle were determined on the same video frame using Dartfish Software (Dartfish Japan, Co. Ltd., Tokyo, Japan). Medial knee displacement was evaluated by the difference in length of the horizontal segments between the video frames at the reference position and at the peak knee valgus during the trial, according to the previous study 20) (Fig. 1). Statistical analysis. Data were presented as mean ± SD. After the Shapiro-Wilk normality test, each measurement of hip and knee range of motion and demographic data were compared between the female handball players with and without a history of ACL injury and between the female volunteers with and without knee abduction induced by each ACL injury screening test by t test and Mann- Whitney test for parametric and nonparametric tests, respectively. Fisher s exact test was used to compare the frequency of ACL injury between the female handball players with different hip rotation measurements. Fisher s exact test was also used to compare the distribution of knee valgus incidence by each ACL injury screening test among the female or male volunteers with different hip rotation measurements. Logistic regression models were applied for the assessment of the relationship between predictor variables (hip motions) and the occurrence of ACL injury or knee abduction by ACL screening tests. Odds ratios (ORs) and respective 95% confidence intervals (95% CIs) were presented. Differences were considered to be statistically significant for P < Statistical analyses were conducted using SPSS for Windows, Version 22.0 (SPSS Inc., Chicago, Illinois, USA). Results Hip and knee motion measurements in female handball players. There were 17 females on the active list of the varsity handball team during the period of data collection. Whereas 8 females had a history of non-contact ACL injury followed by reconstruction surgery, there were 9 females with no history of ACL injury. Each measurement of hip motion was compared between the ACL-injured and uninjured players (Table 1). The range of external and internal rotation in the ACL-injured players was significantly smaller for external (P = 0.006) and greater for internal rotation (P = 0.012), respectively, compared to uninjured players. There was no difference in total range of hip rotation (external plus internal rotation) between females with and without a history of ACL injury. The ACL-injured female players showed greater range of hip extension than the uninjured (P = 0.013). The ACL-injured females also displayed a smaller range of abduction (P = 0.026). Logistic regression analyses of hip motion revealed that external (P = 0.023) and internal (P = 0.035) rotation and extension (P = 0.043) of the hip were associated with ACL injury (Table 2). When ACL injury incidence was evaluated on the basis of hip rotation measurements, 7 of the 8 ACL-injured females showed that the internal rotation range was greater than the external range (internal rotation dominance), while one ACL-injured female exhibited that the external rotation range was greater than the internal range (external rotation dominance). Of the 9 uninjured females, 3 displayed internal rotation dominance and 6 exhibited external rotation dominance. Thus, hip internal rotation dominance was significantly Fig. 1 Two dimensional video analysis method for knee valgus motion. On the frontal video frame of the reference position and the peak knee valgus during the vertical jump test, the origin of the coordinate axes is set on the basis of the position of the markers on the dorsal surface of the second metatarsal base. The arrow on the video frame at the peak knee valgus indicates medial displacement of right knee.

4 108 JPFSM: Yasuda T, et al. Table 1. Comparison of demographic data and hip and knee motion measurements among female handball players with or without a history of anterior cruciate ligament (ACL) injury ACL-injured (n=8) uninjured (n=9) P age (years) 20.8 ± ± height (cm) ± ± body weight (kg) 50.6 ± ± body mass index (kg/m 2 ) 20.7 ± ± hip motion ( ) normal range flexion ± ± ± 7 extension 23.8 ± ± ± 4.8 flexion + extension ± ± abduction 51.3 ± ± ± 3.8 adduction 20.6 ± ± ± 3.2 abduction + adduction 71.9 ± ± external rotation 36.3 ± ± ± 7.7 internal rotation 55.6 ± ± ± 9.2 external + internal rotations 91.9 ± ± ± 9.7 knee motion ( ) flexion ± ± extension 6.3 ± ± Values are expressed as mean ± SD. Normal range of each hip motion in healthy females with an average age of 23 is shown for reference 19). Table 2. Logistic regression analyses of explanatory factors for the occurrence of ACL injury variables OR 95% CI P flexion extension abduction adduction external rotation internal rotation OR = odds ratio; CI = confidence interval.

5 JPFSM: Hip rotation as a risk factor for ACL injury in females 109 correlated with ACL injury incidence in the female handball players (P = 0.036) (Table 3). Knee valgus during ACL injury screening tests. Association of hip range of motion with knee valgus during ACL injury screening tests was evaluated because knee valgus induction during designated tasks can predict ACL injury in female athletes with high specificity and sensitivity 6). Of the 31 healthy volunteer females, knee valgus was induced by the vertical jump and single-leg squat tests in 24 and 22 females, respectively. When each measurement of hip motion was compared between females with and without knee valgus using the vertical jump test (Table 4), the range of external rotation in the knee valgus-positive females was significantly smaller than in the females that were knee valgus-negative (P = 0.004). However, Table 3. Comparison of ACL injury incidence on the basis of hip rotation measurement among female handball players with and without a history of ACL injury ACL-injured (n=8) uninjured (n=9) OR 95%CI ER<IR 7 3 ER>IR ER = hip external rotation; IR = hip internal rotation; OR = odds ratio; CI = confidence interval. *Comparison by Fisher s exact test. Table 4. Comparison of demographic data and hip and knee motion measurements among females with or without knee valgus induced by vertical jump test knee valgus positive (n=24) negative (n=7) P height (cm) ± ± body weight (kg) 50.8 ± ± knee motion ( ) flexion ± ± extension 5.2 ± ± logistic regression analyses hip motion ( ) OR 95%CI P flexion ± ± extension 19.6 ± ± abduction 30.8 ± ± adduction 16.9 ± ± external rotation 43.3 ± ± internal rotation 60.2 ± ± Values are expressed as mean ± SD. Logistic regression analyses were performed for induction of knee valgus using hip motions as explanatory variables. Knee valgus was evaluated by medial knee displacement in the frontal plane during the test using a two dimensional video analysis method as described in Materials and Methods. OR = odds ratio; CI = confidence interval.

6 110 JPFSM: Yasuda T, et al. there was no significant difference in hip internal rotation between the two groups. Logistic regression analyses of hip motion revealed that external rotation of the hip was associated with knee valgus induced by the vertical jump test (P = 0.017) (Table 4). The single-leg squat test (Table 5) also demonstrated that the range of external rotation in the knee valgus-positive females was significantly smaller than in the knee valgus-negative females (P = 0.024). External rotation of the hip was associated with knee valgus induced by the single-leg squat test (P = 0.031). When knee valgus incidence by vertical jump test was evaluated on the basis of hip rotation measurements, 19 of the 24 knee valgus-positive females and 2 of the 7 knee valgusnegative females exhibited internal rotation dominance (Table 6). Concerning knee valgus induced by the singleleg squat test, 18 of the 22 knee valgus-positive females and 3 of the 6 knee valgus-negative females exhibited internal rotation dominance (Table 6). Thus, a higher incidence of knee valgus induced by each screening test was found in the females with hip internal rotation dominance compared to those with external rotation dominance. In contrast to the females, 15 male subjects showed lower rates of knee valgus induction by the screening tests. In addition, there was no clear difference in knee valgus induction between males with hip internal rotation dominance and those with external rotation dominance (Table 6). Discussion The most common mechanism of ACL injury in female handball players is a non-contact cutting maneuver with a forceful knee valgus motion in combination with lowerextremity rotation 27). The videographic sequence analyses of sports knee injuries have provided speculation about a possible relationship between the lumbopelvic-hip region and ACL injuries 11,28). However, the link between proximal control mechanisms and abnormal knee-joint loading and motions specifically related to gender differences remains unclear. Previous studies have shown that functional valgus collapse during the single-leg squat is related to a more internally rotated hip 14). This study has extended the previous findings and has indicated for the first time that a smaller range of hip external rotation may correlate with knee valgus induced by the ACL injury Table 5. Comparison of demographic data and hip and knee motion measurements among females with or without knee valgus induced by single-leg squat test knee valgus positive (n=22) negative (n=9) P height (cm) ± ± body weight (kg) 49.9 ± ± knee motion ( ) flexion ± ± extension 5.5 ± ± logistic regression analyses hip motion ( ) OR 95%CI P flexion ± ± extension 20.2 ± ± abduction 31.1 ± ± adduction 16.8 ± ± external rotation 43.4 ± ± internal rotation 61.4 ± ± Values are expressed as mean ± SD. Logistic regression analyses were performed for induction of knee valgus using hip motions as explanatory variables. Knee valgus was evaluated by medial knee displacement in the frontal plane during the test using a two dimensional video analysis method as described in Materials and Methods. OR = odds ratio; CI = confidence interval.

7 JPFSM: Hip rotation as a risk factor for ACL injury in females 111 Table 6. Comparison of knee valgus-positive incidence by ACL injury screening tests on the basis of hip rotation measurement female (n=31) knee valgus ER<IR ER>IR OR 95%CI vertical jump test single-leg squat test male (n=15) knee valgus ER<IR ER>IR OR 95%CI vertical jump test single-leg squat test Knee valgus was evaluated by medial knee displacement in the frontal plane during the tests using a two dimensional video analysis method as described in Materials and Methods. ER = external rotation; IR = internal rotation; OR = odds ratio; CI = confidence interval. *Comparison by Fisher s exact test. screening tests in females. This could be supported by our logistic regression analyses in female handball players that a smaller range of hip external rotation may be associated with the occurrence of ACL injury. Furthermore, the logistic regression analyses in the female handball players also demonstrated that a greater range of hip internal rotation could be associated with the occurrence of ACL injury. Femoral anteversion shows a substantially higher value in females than in males after the onset of puberty, which results in a more inwardly rotated femur at full maturity in females 29). Because there is a significant correlation between femoral anteversion and the range of hip rotation 13), smaller external rotation with or without greater internal rotation of the hip is likely to result from greater femoral anteversion. Hip position and stiffness may influence lower extremity biomechanical factors 30). Thus, female athletes with smaller external rotation of the hip due to greater femoral anteversion may maintain the femoral head within the acetabular cavity through internal rotation of the hip. Such compensatory changes in femoral internal rotation could lead to the knee valgus observed during the ACL injury screening tests. Higher ACL injury rates in female athletes make its prevention a priority. Effective preventive measures require identification of athletes with risk factors that contribute to susceptibility to non-contact ACL injury. Gender differ- ences in ACL injury rates may be explained by anatomical, hormonal, and/or neuromuscular factors. Through an attempt to identify gender-related neuromuscular factors, knee valgus has been found to be one of the strongest predictors of ACL injury in female athletes 6). However, knee valgus measurements require expensive biomechanical laboratories that use costly measurement tools and laborintensive data collection. Therefore, it is important to develop simple measurement methods of predisposing factors, for determining female athletes at increased risk of ACL injury, that are readily available to coaches, athletic trainers, physical therapists, and athletes. Based on present findings, a smaller range of hip external rotation and internal rotation dominance of the hip, which means that the internal rotation range is greater than the external rotation range, may be such predisposing factors for determining the occurrence of ACL injury and knee valgus motion during ACL injury screening tests in females. In contrast to knee valgus as a neuromuscular factor, hip internal rotation dominance as an anatomical factor can be appreciated by athletes themselves. Gender differences in laxity and neuromuscular control with a divergence in ACL injury rates between genders emerge after the onset of puberty 5). This indicates that preadolescence or early puberty seems to be a critical phase related to the increased risk factors for ACL injury.

8 112 JPFSM: Yasuda T, et al. Before the onset of puberty, no significant difference in femoral anteversion is found between genders 31,32). For both genders, femoral anteversion increases from 11 to 14 years of age. Thereafter, from 14 to 18 years of age, femoral anteversion decreases particularly in males. Consequently, femoral anteversion becomes greater in females than in males after the onset of puberty 29). Greater femoral anteversion is associated with increased internal rotation of the hip 13). Because this study has suggested that hip rotation may be related to ACL injury, hip rotation assessment around 14 years of age could be helpful to identify female athletes at greater risk of ACL injury before the surge in ACL injury occurring after 15 years of age 33). However, this study had some limitations. First, a relatively small number of subjects was recruited only from a handball team. Other sports at high risk for ACL injury should be included in a future study. A second limitation of this study was retrospective analyses of the handball players with a history of ACL injury, although a high incidence of ACL injury in female handball players was significantly associated with hip rotation. In addition, precedent ACL injury may influence the resultant range of hip motion. Prospective validation on a large scale is necessary to establish hip internal rotation dominance as a potential prescreening indicator in assessment of ACL injury risk in female athletes. Thirdly, this study conducted no investigation on the effect of hip rotation on neuromuscular and biomechanical factors that cause ACL injury. In addition to hip rotation, logistic regression analysis has revealed the association between hip extension and ACL injury in female handball players. Gender differences in proximal control of the knee joint indicate that ACL injury risk may result from a combination of the biomechanics of the hip in sagittal, coronal and transverse planes 10). Biomechanical contributions of all three plane motions of the hip to female ACL injuries should be investigated in a future study. In conclusion, smaller external and greater internal rotation ranges of the hip and hip internal rotation dominance were associated with the occurrence of ACL injury in female handball players. There was significant association of smaller external rotation range of the hip and hip internal rotation dominance with knee valgus induced by ACL injury screening tests, which can predict ACL injury with high specificity and sensitivity 6). These findings strongly suggest the importance of hip rotation measurement for identification of female athletes at risk for ACL injury. However, evidence from prospective research is needed to confirm the predisposing role of hip rotation in ACL injuries in female athletes. Conflict of Interests The authors declare that there is no conflict of interests regarding the publication of this article. 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