The Relationship Between Static Posture and ACL Injury in Female Athletes

Transcription

1 The Relationship Between Static Posture and ACL Injury in Female Athletes )anice K. loudon, PhD, PT, ATC, SCS' Walter )enkins, MS, PT, ATC~ Karen I. loudon, MS, PT, ATC~ T he participation of women in athletics has steadily increased since the advent of Title IX (9). Due to the increase in athletic participation by women, the incidence of athletic injuries has increased (9,19). In this population, the knee is a common injury site, and injuries to the anterior cruciate ligament (ACL) are one of the most common knee injuries (29). From epidemiological studies, it appears that female athletes have a higher incidence of noncontact ACL injuries than males (2). This type of injury occurs due to deceleration of the lower limb, forced hyperextension of the knee, or forced tibial rotation (6,21,24,28). The injury may be an isolated tear of the ACL or a combined injury also involving secondary restraints. Athletes with lower extremity biomechanical deviations may be at greater risk of injury to the ACL than those without. Biomechanical abnormalities of the lower extremity are related to knee pathologies (eg., patellofemoral pain) (26), but the relationship between lower extremity biomechanical faults and injuries to the ACL has only briefly been investigated, especially with the female athlete. Beckett et al found that subjects with ACL injuries had greater amounts of subtalar joint pronation than noninjured subjects and concluded that hyperpronation of the foot and ankle may increase the risk Female participation in athletics has increased dramatically over the last decade. Accompanying the increase in participation in sports is the increase incidence of anterior cruciate ligament (ACL) injury. The purpose of this study was to examine the correlation between static postural faults in female athletes and the prevalence of noncontact ACL injury. Twenty ACL-injured females and 20 age-matched controls were evaluated. Seven variables were measured: standing pelvic position, hip position, standing sagittal knee position, standing frontal knee position, hamstring length, prone subtalar joint position, and navicular drop test. A conditional step-wise logistic regression analysis revealed the factors of knee recurvatum, an excessive navicular drop, and excessive subtalar joint pronation to be significant discriminators between the ACL-injured and noninjured groups. These findings may have implications regarding rehabilitation techniques in physical therapy. Key Words: anterior cruciate ligament, female athletes, postural faults ' Assistant Professor, Department of Physical Therapy Education, University of Kansas Medical Center, Kansas City, KS. Address for correspondence: 3056 Robinson, University of Kansas Medical Center, Kansas City, KS Associate Clinical Professor, Department of Physical Therapy, East Carolina University, Creenville, NC ' Staff Therapist, Watkins Memorial Hospital, University of Kansas, lawrence, KS of injury to the ACL (3). Woodford- Rogers et al measured navicular drop, calcaneal alignment, and anterior knee joint laxity in an ACL injured group and an age-matched control group (31). The investigators found that the ACLinjured group had greater amounts of navicular drop, suggesting increased subtalar joint pronation and greater anterior knee joint laxity in the uninvolved limb. Coplan reported that abnormal pronators were found to have increased passive knee rotation at 5" of knee flexion, and that there may be a very important relationship between pronation and rotational knee joint laxity (7). Vogelbach and Combs as well as Tiberio concluded that excessively or prolonged subtalar joint pronation results in increased internal tibial rotation, which leads to increased medial knee stress (26,27). Since noncontact ACL injuries may be produced by knee hyperextension or forced internal tibial rotation, abnormal postures that allow these positions to occur may also increase stress to the ACL and lead to injury. Repeated forces on the ACL may surpass the capacity and recovery limits of the ligament, resulting in disruption (21). A static posture, consisting of anterior pelvic tilt, anteverted hips, tight hamstrings, genu recurvatum, and subtalar joint pronation, may place an individual in knee hyperextension and increased internal tibial rotation during dynamic movement, putting greater stress on the anterior cruciate ligament and exposing this ligament to forceful JOSPT Volume 24 Number 2 August 1W6

2 RESEARCH STUDY stretch. The purpose of this study was to determine if static postural faults correlate with noncontact ACL injury in female athletes. MATERIALS AND METHODS Twenty females with one anterior cruciate ligament-injured knee and one normal knee were recruited for this casecontrol study (age range = years, X = years). Inclusion criteria included arthroscopic examination of the ACL rupture and injury occurrence within 2 years of test date. The involved limb was either reconstructed or the patient chose con- Since noncontact anterior crucia te ligament injuries may be produced by knee hyperextension or forced internal tibial rotation, abnormal postures that allow these positions to occur may also increase stress to the anterior cruciate ligament and lead to injury. semtive nonoperative management (eight surgical, 12 nonsurgical). "Athlete" was operationally defined as an individual who participated in a sport two to three times a week, which involved start-stop running/jumping, such as basketball, volleyball, tennis, or soccer. Twenty age-matched athletic - females (age range = years, X = 26.2? 7.8 years) with nonpathe Variables Anterior Cmciate,_,-, Ligamer Group - - X SD X SD Age (years) Height (cm) Weight (kg) Activity (hourshueek) TABLE 1. Characteristics of subjects. logical knees were recruited as a control group. Descriptive information for both groups is found in Table 1. After obtaining informed consent to take part in the study, seven measures were assessed on each subject, including the involved side for the ACLinjured group. The seven variables were pelvic position, femoral anteversion, hamstring length, standing sagittal knee extension, standing knee angle in the frontal plane, the navicular drop test, and subtalar joint neutral position. Each variable was classified into three categories. The categories were: normal range, low range, and high range. The categories were determined prior to the start of data collection and were decided upon by normative data found in the literature. One of the three authors UKL) was designated as the tester for all subjects. Intrarater reliability was assessed for each variable by the testretest method on 10 lower limbs. Tilt of the pelvis was assessed by the method described by Kendall et al (15). The alignment of the anterior superior iliac spine and pubic syrnphysis was assessed in standing using a straight edge. If these two landmarks fell within the same vertical plane, the subject's pelvis was classified as neutral; if the anterior superior iliac spine fell in front of the pubic symphysis, the subject's pelvis was classified as anteriorly tilted; and if the anterior superior iliac spine fell behind the pubic syrnphysis, the sub ject's pelvis was classified as posteriorly tilted. For classification purposes, neutral was classified as normal, ante- rior tilt was classified as high, and posterior tilt was classified as low. Testing for femoral anteversion was performed with a manual goniometer, according to the clinical method described by Ruwe et al (25). Subjects were placed in a prone position, with the knee flexed to 90". The greater trochanter was palpated, while the hip was passively moved from internal and external rotation by the tester. At the point where the greater trochanter was palpated in its most lateral position, the angle of the lower leg to the vertical plane was measured. If the measurement was greater than 15" of internal rotation, the hip was designated to be anteverted. A retroverted position was designated as less than 8" of internal rotation in the test position. Anteverted hips were documented as a positive number of degrees, with a negative number designating a retre verted hip. Anteverted hips were classified as high, retroverted hips were classified as low, and between 8 and 15" was considered normal. Hamstring length was assessed, with the subject in the supine position, by measuring the angle of maximal hip flexion with the knee placed in neutral rotation (15). An angle between 80 and 95" was classified as normal, an angle below 80" was classified as low, and an angle greater than 95" was high. Standing knee extension in the sagittal plane was measured with the subject standing in an erect posture, with the involved lower extremity placed in a position of hip extension and knee extension. The subject was asked to shift her weight onto the involved lower extremity and to bring the knee into a maximal position of knee extension. The knee extension angle was measured using a standard range of motion technique as described by Norkin and Levangie (22). An angle between 0 and 5" of hyperextension was classified as normal, an angle greater than 5" of hyperextension was classified as high and 92 Volume 24 Number 2 August 1996 JOSPT

3 RESEARCH STUDY termed genu recurvatum, and an angle less than 0" was classified as low. The relative position of the knee in the frontal plane was measured by the Qangle method as described by Magee (18). Subjects were measured in the standing position with the knee fully extended and the axis of a goniometer placed over the center of the patella. The lever arms were pointed toward the anterior superior iliac spine proximally and the tibia1 tubercle distally. Measures were recorded, with values between 18 and 22" designated as normal, values greater than 22" were designated as high, and values below 18" were designated as low. The navicular drop test was utilized as a clinical measure of pronation. Subjects were asked to begin this test by sitting with their subtalar joint palpated in the neutral position. The subtalar joint neutral position is defined as the position of maximum congruency between the talus and the calcaneus. Palpation of subtalar neutral was performed by palpation of the talar head on both the medial and lateral side of the joint (1 1). The height of the navicular was measured from the floor to the distal most point on the navicular bone. Subjects then stood with the foot in a relaxed position. The navicular distance was FIGURE 1. Ndvrcubr drop test: d vertical measurement from the navicular tubercle to the ground with the ioot in subtalar joint neutral. Variables Pelvic tilt Hip position Normal Value Neutral Neutral Sagittal knee position 0-5" Frontal knee position 18" Hamstring length 80-95" Navicular drop test Subtalar joint position TABLE 2. Variable components. 6-9 mm Neutral 0-2" varus remeasured (Figure 1). The difference between the two navicular distances was calculated. A difference value of 6 mm was considered normal, greater or equal to 9 mm was considered high, and values less than 6 mm were considered low. These values were determined from a consensus of the literature (5,20,31). Measurement of rearfoot position in subtalar joint neutral was accomplished by the palpation method described by Hunt and McPoil (13). Subjects were placed in the prone position with the hip in neutral rotation, the knee fully extended, and the foot and ankle off the plinth. The talus was then palpated on the medial side at the talonavicular joint when the foot was placed in a pronated position. The lateral aspect of the talus was then palpated in the sinus tarsus when the foot was supinated. When the talus was palpated equally on medial and lateral sides, the foot was gently dorsiflexed until there was slight tension; this position was identified as subtalar joint neutral. The rearfoot position was then observed by assessing the angle between the middle of the calcaneus and the middle of the lower leg. Measurement of this angle can be performed by aligning the axis of the goniometer posterior to the talus with the lever arms of the goniorneter parallel to the middle of the calcaneus and the middle of the lower leg. The subtalar joint measurement was then recorded in the number of degrees of varus 'from an ideal alignment in which the High Value Anterior Anteverted >15" internal rotation 6" or greater Greater than 18" Greater than 95" Greater than 9 mm Varus deformity >2" varus Posterior Retroverted <8" internal rotation Less than 0 Less than 18" Less than 80" Less than 6 mm Valgus deformity lower leg and calcaneus were parallel. A normal value was 0-2", a value of 3" or greater varus was considered high, and a value of 1" or greater valgus was considered low. Table 2 lists the seven variables measured and the classifications of each variable. Data Analysis Reliability of test measures is critical in any research project Intrarater reliability was assessed for each independent variable using a test-retest method on 10 limbs. Each variable for each limb was placed in a ca:egoiy (eg., pelvis was anteriorly tilted and classified as high). This was repeated on the same subject on the same day approximately 15 minutes apart. Cohen's kappa was used to assess intrarater reliability for all variables. To address the purpose of the study, univariate and multivariate statis tics were used. Each variable was assessed independently first. For statistical purposes, the low and high range groups were collapsed to an abnormal group. This was done because many of the variables were only represented in two of the three groups. The seven independent variables present as categorical data (normal or abnormal); therefore, the McNemar test of symmetry was used to assess univariate significance for each. Significance level was set at cr < Next, a multivariate analysis was undertaken to assess the combination of the seven variables in discriminating between ACLinjured and nonin- JOSPT Volume 24 Number 2 August 1W6 93

4 RESEARCH STUDY Variable Kappa Value Step Number Term Entered df Chi-square Value p value 1 Sagittal knee position Navicular drop Subtalar joint position Significant level set at p < TABLE 5. Conditional stepwise logistic regression. TABLE 3. Kappa values for intrarater reliability of seven variables. jured groups. A conditional stepwise logistic regression was used to assess for multivariate significance of all seven variables. From the logistic regression, the variables that were significant contributors to determining group membership were identified. Significance level was set at P < RESULTS lntrarater Reliability Results of the Cohen's kappa analysis are listed in Table 3. These values exceeded 0.61 for each variable, indicating substantial agreement (16,17). With these results, the study was then undertaken using the same tester for all subjects. Univariate Measures Table 4 lists the distribution of the two groups into one of three categories for each of the seven independent variables. In the ACLinjured group, only two categories were represented for the variables of pelvic tilt, hip position, sagittal knee position, frontal knee position, and hamstring length. In the normal group, all three categories were rep resented in two of the seven variable groups, including hip position, sagittal knee position, frontal knee position, hamstring length, and navicular drop test. Because so many variable groups only had representation in two categories, it was decided to divide the variables into a normal and abnormal class for statistical testing. The McNemar test of symmetry was used to determine the significance of individual variables as a discriminator between ACLinjured subjects and normals. Chi-square values are generated from this analysis, and these values are listed in Table 4. Significant values included the variables of anterior pelvic tilt, knee recurvatum, excessive navicular drop, and excessive subtalar joint pronation. Multivariate Measure The purpose of using a logistic regression model is to identify the variables which contribute significantly to group membership (ACL injured and noninjured). The results of the conditional stepwise logistic Anterior Cmciate Ligament-Injured Norm Normals regression are found in Table 5. Results indicate that excessive sagittal knee position, excessive navicular drop, and excessive subtalar joint pronation were predictors of group classification. All other variables did not significantly contribute to determination of group membership. DISCUSSION Abnormal Abnormal Norm High Low High Low Injuries to the female athlete have escalated with increasing participation in competitive sports. Malone et al found that female intercollegiate NCAA basketball players are significantly more likely than their male counterparts to have an ACL injury (19). Reasons for this increase in female injuries range from the theory of femoral notch size and shape to increased speed and aggressiveness of play (12). This present study was undertaken because the authors clinically found a specific postural pattern present in the female athletes with ACL injuries. An n postural model was developed, which included postural characteristics that may predispose the anterior cruciate ligament to abnormal stress. Figure 2 is an example in the sagittal view of this posture Chi- Square Pelvic position * Hip position Sagittal knee position ' Frontal knee position Hamstring length Navicular drop * Subtalar joint position * * Significant value (p < 0.05) included the variables of pelvis, knee position, navicular drop test, and subtalar joint position. TABLE 4. Classification of anterior cruciate ligament-injured and normals for seven variables (N = 20 for each group). p value 94 Volume 24 Number 2 August 1996 JOSPT

5 RESEARCH STUDY FIGURE 2. Faulty static posture: sagittal view of faulty posture, including anteriorly tilted pelvis and knee joint hyperextension. type. The posture includes an anterior pelvic tilt, internal rotation of the hip, increased valgus at the knee, recurvatum of the knee, and excessive subtalar joint pronation. The results of this study suggest there is a strong association between noncontact injuries to the anterior cruciate ligament in female athletes and females who display a standing posture of genu recurvatum with sub talar joint overpronation. Static posture is the starting point for dynamic movement. The proprioceptive system of the individual who presents with knee recurvatum and excessive subtalar joint pronation will recognize this position as normal. When this individual is placed in a dynamic situation in which the knee is stressed beyond normal, the ACL may be at greater risk. Pelvic Position According to Kendall et al, the pelvic position dictates lower ex- tremity alignment (15). An excessive anterior tilt of the pelvis causes tightening of the hip flexors, positioning the femur in relative flexion. A flexion moment at the hip is counteracted with an extensor moment at the knee, leading to hyperextension of the knee joint (15). In the present study, a significant relationship was found between pelvic position and incidence of ACL injury when pelvic position was analyzed as a univariate measure, but not when the multivariate test was used for analysis. Hip Position Hip anteversion is characterized by excessive internal rotation of the shaft of the femur in stance. According to Tiberio, internal rotation of the femur predisposes an individual to pronation of the foot (26). Feagin et a1 discussed the importance of femoral rotation in the transverse plane as a mechanism of injury to the ACL and found that, in tibia1 internal rotation, the ACL is stretched over the lateral femoral condyle (10). Arms et a1 found that internal rotation and varus movements increase ACL strain. In the present study, however, hip position did not discriminate between ACL injured and normal knees (1). Perhaps if the total range of internal rotation had been analyzed or if the measure had been taken in weight bearing, this factor may have been significant. Frontal Knee Position An excessive Qangle has frequently been associated with knee pathology, such as patellofemoral pain (14). An increased Qangle may be caused by increased femoral anteversion (8). Since our model included the anteversion measurement, we decided to include Qangle as a variable. Also, patellofemoral pain is a complaint of individuals with ACL injury (4). In the present study, the Hip position did not discriminate bet ween anterior cruciate ligament-injured and normal knees. Qangle variable did not significantly affect the predisposition to ACL injury. Surprisingly, most of the sub jects in both groups fell into the a b normal (low) category for frontal knee position. Woodall and Welsh report that the Qangle is a "less reliable physical finding than was previously believed" (30). If the patella sits laterally, this would introduce error into the measurement. Also, if the subject stands in a pronated position, this may affect the Qangle value. Sagittal Knee Position Norwood and Cross demonstrated in cadavers that the ACL impinges on the anterior intercondylar notch with the knee in full extension (23). Injury to the ACL usually results from the leg being in a position of internal rotation and hyperextension (4). The resting position of knee hyperextension may produce a preloading effect on the ACL since it increases the tension on the ligament (3). If an athlete starts or ends a jump or decelerates with the knees hyperextended, any additional extension force to the knee could lead to failure of the anterior cruciate ligament. A predisposition to noncontact injuries of the ACL may exist in female athletes with knee recurvatum as found in this study. Hamstring length Harner et a1 (12) found a significant difference in hamstring tightness in ACLinjured and normal females, in which the ACLinjured JOSPT Volume 24 Number 2 August 1996

6 RESEARCH STUDY possessed short hamstrings. It has been stated in the literature that tightness in the hamstrings will help prevent increased anterior translation of the tibia in the absence of the ACL (6). Our study found no significant difference between groups and hamstring length. The majority of the female athletes tested had tightness in the hamstrings. Subtalar Joint Pronation and Navicular Drop Test Subtalar joint pronation and tibial internal rotation occur together during the contact phase of the gait cycle. The anterior cruciate ligament becomes taut with tibial internal rotation. Pre longed pronation of the foot produces excessive internal tibial rotation and may produce a preloading effect on the ACL (7). Since abnormal pronation leads to increased strain on the ACL, athletes who abnormally pronate may be more prone to injury of this ligament, particularly with running, cutting, or twisting activities. Two independent studies have found a significant difference in the navicular drop test in individuals with ACL injury and matched controls (3,31). Beckett et al examined two groups of 50 athletes, a Previous inves tiga tions concluded that injury to the anterior crucia te ligament usually results from the femur being in a position of internal rotation and hyperextension in relationship to the fixed tibia. group with ACL injury and a group with normal knees (3). The ACL injured subjects had greater navicular drop test scores than noninjured sub jects. Woodford-Rogers et a1 examined 14 football players and eight gymnasts with ACL injuries and compared them with an agesex-sportsmatched control group (31). They also found an increase in navicular drop in the ACL injured group, suggesting increase in subtalar joint pronation. The results of both studies are consistent with the finding in the current study. A combination of genu recurvatum and subtalar joint pronation would cause greater strain to the anterior cruciate ligament than a single postural fault. Several previous investigations concluded that injury to the ACL usually results from the femur being in a position of internal rotation and hyperextension in relationship to the fixed tibia (3,4,25). Therefore, it is not surprising that athletes in this study with knee recurvatum and subtalar joint pronation had a greater prediction for ACL injury than those with only pronation or no postural faults. Clinical Implications Treatment for female athletes with postural faults should focus on optimal positioning of the joints to decrease stress on soft tissue, including ligaments. Appropriate footwear and orthotics would help with overpronation. Also, training the athlete to stand and move in optimal pos tural patterns should carry over to dynamic situations. SUMMARY The purpose of this study was to explore the relationship between selected static posture variables and prevalence of ACL injury in female athletes. The combination of knee hyperextension with excessive subtalar joint pronation proved to be a strong discriminator between injured and noninjured groups. As a result of the findings in this study, training to prevent hyperextension of the knee and correction of excessive pronation are worth addressing in this population. Future Study Further studies should investigate the cause and effect relationship between static posture and ACL injury in the female athlete, perhaps using a prospective design. Also, only static postures were examined in this present study and one cannot ignore the importance of motor control on movement. Continued studies need to focus on dynamic posture and its effect on ACL injury. JOSPT REFERENCES Arms S, Pope MH, lohnson R1, Fischer RA, Arvidsson I, Eriksson E: The biomechanics of anterior cruciate ligament rehabilitation and reconstruction. Am / Sports Med 1 2:8-18, Beck JL, Wildermuth BP: The female athlete's knee. Clin Sports Med 4: , 1985 Beckett ME, Massie DL, Bowers KD, Stoll DA: Incidence of hyperpronation in the ACL injured knee: A clinical perspective. / Athl Train 27:58-62, 1992 Bergfeld I, lohnson RL, Clancy WG, DeHaven KE: Injury to the anterior cruciate ligament (a round table). Phys Sportsmed 10:47-59, Brody DM: Techniques in the evaluation and treatment of the injured runner. Orthop Clin North Am 13: , 1982 Cabaud HE, Rodkey WG: Philosophy and rationale for the management of anterior cruciate injuries and the resultant deficiencies. Clin Sports Med 4 : , Coplan )A: Rotational motion of the knee: A comparison of normal and pronating subjects. I Orthop Sports Phys Ther 1 1 : , 1989 Cox IS: Patellofemoral problems in runners. Clin Sports Med 4: , 1985 Eisenberg I, Allen W: Injuries in a women's varsity athletic program. Phys Sportsmed 6: , Feagin /A, Cabaud HE, Curl WW: The anterior cruciate ligament: Radiographic and clinical signs of successful and unsuccessful repairs. Clin Orthop l64:54-58, Volume 24 Number 2 August 1996 JOSPT

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