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To determine the extent to which select lower extremity alignment characteristics of the pelvis, hip, knee, and foot are related to the Q angle.
Descriptive cohort study design.
Applied Neuromechanics Research Laboratory.
Two hundred eighteen participants (102 males, 116 females).
Eight clinical measures of static alignment of the left lower extremity were measured by a single examiner to determine the impact of lower extremity alignment on the magnitude of Q angle.
Q angle, pelvic angle, hip anteversion, tibiofemoral angle, genu recurvatum, tibial torsion, navicular drop, and femur and tibia length.
Once all alignment variables were accounted for, greater tibiofemoral angle and femoral anteversion were significant predictors of greater Q angle in both males and females. Pelvic angle, genu recurvatum, tibial torsion, navicular drop, and femur to tibia length ratio were not significant independent predictors of Q angle in males or females.
Greater femoral anteversion and tibiofemoral angle result in greater Q angle, with changes in tibiofemoral angle having a substantially greater impact on the magnitude of the Q angle compared with femoral anteversion. As such, the Q angle seems to largely represent a frontal plane alignment measure. As many knee injuries seem to result from a combination of both frontal and transverse plane motions and forces, this may in part explain why Q angle has been found to be a poor independent predictor of lower extremity injury risk.
Anatomical alignment of the lower extremity has been proposed as a risk factor for lower extremity injuries, in particular, knee injuries.1–7 Among these lower extremity alignment variables, the quadriceps angle (Q angle) has been frequently studied, which is defined as the angle formed by a line from the anterior superior iliac spine to the patella center and a line from the patella center to the tibial tuberosity.8 As Q angle represents the direction of the quadriceps muscle force vector in the frontal plane,9 excessive angulation is thought to predispose individuals to injuries caused by abnormal quadriceps forces acting at the knee and patellofemoral joints. However, the extent to which excessive Q angle increases the risk of knee injury remains unclear. Although the Q angle has been suggested as a risk factor for anterior cruciate ligament injury (ACL),10–13 retrospective risk factor studies4,5,14 have failed to confirm this relationship. Q angle has also been associated with patellofemoral pain syndrome,15–17 but others18–21 have observed no difference in Q angle when comparing patients with patellofemoral pain with healthy individuals. Moreover, the degree of angulation that is thought to be excessive and predispose one to knee pathology remains unclear.15–17
A reason for these inconsistent findings may be in part due to the multiple anatomical factors that may influence the magnitude of the Q angle, which may differentially impact how the Q angle relates to dynamic knee function. It has been suggested that the Q angle is a composite measure of pelvic position, hip rotation, tibial rotation, patella position, and foot position.22–24 Specifically, Q angle may increase with excessive anterior pelvic tilt (changing the orientation of the acetabulum and internally rotating the femur), femoral anteversion and knee valgus (displacing the patella medially relative to the anterior superior iliac spine and tibial tuberosity), and external tibial rotation (displacing the tibial tuberosity laterally).24 Although a change in any one of these alignment characteristics could theoretically change the position of 1 or more landmarks used to measure the Q angle, and thus its magnitude, research has yet to examine the collective anatomical contributions to the Q angle. Determining the anatomical factors that have the potential to impact the magnitude of the Q angle may allow clinicians and researchers to better determine its role in dynamic motion and risk of knee injury. Hence, the purpose of this study was to determine the extent to which lower extremity alignment characteristics of the pelvis, hip, knee, and foot are related to the Q angle. Based on their potential to change the orientation of anatomical landmarks used in the measurement of Q angle, our expectation was that greater anterior pelvic tilt, femoral anteversion, knee valgus, and pronation would be predictive of greater Q angle in both males and females.
Two hundred eighteen subjects (102 males: 23.1 ± 3.2 years, 177.3 ± 8.4 cm, 80.8 ± 13.0 kg; 116 females: 21.8 ± 2.7 years, 163.5 ± 7.4 cm, 63.4 ± 12.4 kg) participated in this investigation. Participants were predominantly college-aged students and had no current injury to the lower extremity or any previous history that would affect the alignment of the lower extremity joints (ie, fractures or surgery). The population of this study was part of an ongoing database of which sex differences, bilateral asymmetries, and postural relationships among lower extremity alignment characteristics have been previously reported.25–27 All participants read and signed an informed consent form approved by the University’s Institutional Review Board for protection of human subjects before participation.
Before assessment of alignment characteristics, demographics of age, height, and weight were recorded for each subject. Eight alignment characteristics were measured on the left pelvis and lower extremity. These alignment characteristics were based on commonly identified variables suggested to influence dynamic motion and risk of lower extremity injuries. All measurement procedures were performed by a single examiner who had previously established good to excellent test–retest reliability on all measures (ICC2,3 ≥ 0.87).28,29 All standing measures were taken in a standardized stance with the left and right feet spaced equal to the width of the left and right acromion processes and toes facing forward. The stance was achieved by instructing subjects to march in place and then take a step forward. Subjects were instructed to look straight ahead during all standing measures with equal weight over both feet. Each measure was repeated 3 times.
All alignment characteristics were measured using identical techniques that have been previously described in detail.25,28–30 Q angle was measured in the standardized stance using a goniometer and represented the angle formed by a line from the anterior superior iliac spine to the patella center and a line from the patella center to the tibial tuberosity. Pelvic angle was measured in the standardized stance using an inclinometer and represented the angle formed by a line from the anterior superior iliac spine to the posterior superior iliac spine relative to the horizontal plane.31Femoral anteversion was measured with a goniometer with subjects in a prone position and the knee flexed to 90 degrees.32 The angle between the true vertical and the shaft of the tibia was measured, whereas the greater trochanter was palpated to be in its most lateral position. Tibiofemoral angle was measured in the standardized stance with a goniometer and represented the angle formed by the anatomical axis of the femur and tibia in the frontal plane.28 Genu recurvatum was measured with a goniometer in a supine position with a bolster positioned under the distal tibia and represented the sagittal plane alignment of the femur and tibia.28 Tibial torsion was measured in a supine position with a goniometer and represented the angle between the true vertical and a line bisecting the bimalleolar axis with the femur positioned parallel to the horizontal plane.33 Navicular drop was measured in the standardized stance with a ruler and represented the difference between the height of navicular in subtalar joint neutral and a relaxed stance.28 Femur length and tibia length were measured in the standardized stance using a sliding anthropometric caliper. Femur length represented the distance from the superior aspect of the greater trochanter to the lateral joint line of the knee, whereas tibia length was the distance from the medial joint line of the knee to the inferior medial malleolus.28
The average of 3 measurements for each alignment characteristic and the femur to tibia length ratio (femur/tibia) were computed and used for data analysis. Multiple linear regression, with all variables entered simultaneously into the model, was used to examine the extent to which the lower extremity alignment variables predicted Q angle for males and females. We chose to run separate regression models for males and females because both the quadriceps angle5,15,25,34–37 and many of the other alignment characteristics we examined25 are known to significantly differ by sex, and it is possible that the relationships may not be the same for males and females. Power calculations determined that with alpha level set at P = 0.05, and a maximum of 8 predictor variables, 100 subjects were required to have 95% power to detect a multiple R2 of 0.20, which is considered a moderate to large effect.38 These criteria were considered acceptable because a relatively large effect would be required to establish lower extremity alignment variables as meaningful and accurate predictors of Q angle.
Means, standard deviations, and ranges (minimum to maximum) for each alignment characteristic by sex are presented in Table 1. Multiple linear regression summary results for males and females are presented in Table 2. The amount of variance in Q angle explained by the 7 alignment characteristics was 19.1% (P < 0.005) and 17.9% (P = 0.003) for males and females, respectively. Once all alignment variables were accounted for, greater tibiofemoral angle and femoral anteversion were statistically significant predictors of greater Q angle in both males (tibiofemoral angle P = 0.001, femoral anteversion P = 0.040) and females (tibiofemoral angle P = 0.002, femoral anteversion P = 0.025). Considering only these significant predictors, the largest predicted change in Q angle (in terms of magnitude of change) in males was due to tibiofemoral angle, with a predicted 0.60-degree change in Q angle for a 1-degree change in tibiofemoral angle. Similarly, tibiofemoral angle was also the predictor of the largest change in the value of the Q angle in females, with a predicted 0.62-degree change in Q angle for each 1-degree change in tibiofemoral angle. In both males and females, a 1-degree change in femoral anteversion predicted a 0.18-degree change in Q angle. Measures of pelvic angle, genu recurvatum, tibial torsion, navicular drop, and femur to tibia length ratio were not found to be significant independent predictors of Q angle in males or females when all alignment variables were accounted for.
Our primary finding was that alignment of the knee and hip is associated with the magnitude of the Q angle in both males and females. Specifically, tibiofemoral angle and femoral anteversion had the strongest association with greater Q angle, and their impact on the magnitude of Q angle was similar in both males and females.
These findings in part support our hypothesis that lower extremity alignment characteristics may change the position of the anatomical landmarks used to measure the Q angle, thus impacting its magnitude. Specifically, increased tibiofemoral angle, which represents the valgus angle formed by the anatomical axes of the femur and tibia, would move the patella medially relative to the anterior superior iliac spine (as the femur is in an adducted position) and the tibial tuberosity laterally (as the tibia is in an abducted position),24,37,39 thus increasing the Q angle. Femoral anteversion on the other hand represents a medial torsion of the femur as the femoral neck is projected forward relative to the femoral condyles.32,40 Excessive femoral anteversion would essentially place the femur into a more medially rotated position, potentially resulting in a medial displacement of the patella. In addition, excessive femoral anteversion is associated with an intoeing gait41 that is compensated by an external rotation of the tibia on the femur,42 which would displace the tibial tuberosity in a more lateral position.
Although both measures seem to have the potential to alter the position of the landmarks used to measure the Q angle and were statistically significant predictors of the magnitude of the Q angle, changes in tibiofemoral angle seem to have a substantially greater impact on the magnitude of the Q angle than femoral anteversion. This is based on interpretation of the regression coefficients (B), which revealed that every 1-degree change in tibiofemoral angle predicted approximately a 0.60-degree change in Q angle in both males and females, whereas every 1-degree change in femoral anteversion predicted only a 0.18-degree change in Q angle. This suggests that a greater change in the magnitude of femoral anteversion is required before an appreciable change in the frontal plane positions of the landmarks is reflected in the measure of Q angle. This may be explained by previous findings43 that in weight-bearing, rotation of the femur may occur underneath the patella and potentially not change its position, resulting in a minimal medial displacement of the patella. Collectively, these findings suggest that although various malalignments of the hip and knee are related to changes in Q angle, those that involved frontal plane deviations seem to have a greater impact on the magnitude of change compared with deviations in other planes.
Further supporting this premise is the lack of relationships between pelvic angle and navicular drop with the Q angle. Based on clinical expertise and observation,3,22–24,44–46 we hypothesized that greater anterior pelvic tilt and pronation (as measured by navicular drop) would also predict Q angle magnitude. Specifically, we expected that greater anterior tilt of the pelvis would change the spatial orientation of the anatomical landmarks similar to hip anteversion where the patella would displace medially and the tibial tuberosity would displace laterally. This was based on a previous report47 that an anterior pelvic tilt results in the acetabulum shifting backward, causing the femur to internally rotate on the pelvis. Our hypothesis that a greater navicular drop would also be a predictor of greater Q angle was based on previous studies that reported that an excessive pronation is associated with internal rotation of the lower extremity and increased knee valgus3,44 and is therefore suggested to result in greater Q angle.45,46 As previously discussed, both increased anterior pelvic tilt and navicular drop would result in rotational changes in the femur and tibia,3,22–24,44–46 displacing the patella medially and the tibial tuberosity laterally, which do not seem to be sufficient to alter the frontal plane landmarks used in the measurement of Q angle.
The literature consistently demonstrates that females have greater Q angles compared with their male counter-parts15,25,34–37,48; however, reasons for this sex difference are still unknown. Previously, it was thought that the greater Q angle in females was a result of females having a wider pelvis compared with males; however, this has been well disputed.34,35,49 To our knowledge, a study by Pantano et al50 is the only study that has empirically shown that sex differences in anatomical characteristics contribute to greater Q angle in females. They report that subjects with a high Q angle (≥17 degrees) had a greater pelvic width to femur length ratio compared with subjects with a low Q angle (≤8 degrees). The limitation with this study was that these results are based on a relatively small sample size (n = 10 per group). Although not the primary purpose of this study, our results suggest that greater Q angle in females may be a result of females having greater structural femoral anteversion and tibiofemoral angle compared with males. This is based on previous work noting that each of these values is greater in females compared with males25 and our current observations that greater femoral anteversion and tibiofemoral angle were associated with greater Q angle, regardless of sex.
As previous studies examining Q angle as a risk factor for knee injuries have reported inconsistent findings,4,5,14–21 identifying the anatomical factors that may influence the anatomical landmarks from which the Q angle is derived may help clarify its role in dynamic knee function. Given that more than 1 anatomical variable has the potential to alter the Q angle and that their independent effects differ in magnitude, it may be that the measurement of Q angle alone is not sufficient to identify individuals at risk for knee injury. Rather, it may be the unique combination of alignment characteristics that collectively contribute to the increased risk of knee injury.
For example, a dynamic alignment characterized by a combination of hip adduction and internal rotation and knee valgus has been observed to be a mechanism and predictor of ACL injuries.12,51,52 Based on our finding that the impact of rotational alignment on Q angle was low compared with alignments in the frontal plane, it is not surprising that the measurement of Q angle alone was not predictive of the likelihood of suffering an ACL injury in retrospective risk factor studies.4,5,14 Rather, it may be that a combination of static alignment characteristics increases the valgus and rotational positions common to ACL injuries. In fact, previous studies have reported an interactive effect of frontal and transverse plane alignment variables on dynamic knee function53 and when identifying risk factors for ACL injuries.4–6 Whether a unique combination of excessive magnitudes of both frontal and transverse plane alignment measures may predispose individuals to land and cut with greater dynamic knee valgus angles and moments is unknown and warrants further investigation.
In regard to pathologies of the patellofemoral joint, greater Q angle has been shown to be highly correlated (r = 0.919) to a larger laterally directed muscle force vector on the patella.9 This larger laterally directed muscle force may in turn lead to lateral patellar tracking9 and an increase in patello-femoral contact pressures,54 which are thought to predispose an individual to patellofemoral pain.24 However, a relationship between excessive Q angle and the development of patellofe-moral pain has not been clearly established.15–21 The lack of consistent findings in these investigations may again be explained by the influence of other lower extremity alignment factors (ie, rotational deformities), along with Q angle, that have been suggested to result in abnormal patellofemoral mechanics.24,55 Because rotational lower extremity malalign-ments are largely not accounted for in the measurement of Q angle, investigating the effects of other lower extremity alignment variables along with Q angle may provide a clearer picture as to the role that lower extremity static alignment plays in the development of patellofemoral pain.
The relationships identified among the lower extremity alignment characteristics in the current study are limited to the alignment characteristics measured by a single examiner with known measurement reliability. We also acknowledge that other anatomical and postural measures could potentially influence Q angle (eg, coxa vara, joint laxity, patella mobility, muscular properties, and knee version) and impact dynamic motion and knee injury risk. In fact, approximately 80% of the variance in the Q angle was unexplained by the alignment measures studied in the current investigation. Although we are continuing work in this area, we hope that the findings of this study lead to a more comprehensive approach in the examination of a lower extremity alignment when considering anatomical contributions to dynamic lower extremity motion and knee injury risk.
Excessive Q angle has been identified as a potential risk factor for knee injuries, but evidence to support this relationship is unclear. A reason for these inconsistent findings may be in part due to limited understanding of how other anatomical characteristics influence the magnitude of the Q angle. This is the first study to our knowledge that has examined the collective alignment of the lower extremity and its relationship to Q angle. Our findings that the Q angle largely represents a frontal plane measure suggest that independently examining the Q angle for its effects on lower extremity injuries may not be sufficient. The rotational alignments not accounted for in the Q angle may be important factors toward understanding knee injuries, which are thought to result from a combination of transverse and frontal plane motions. Until all relevant postural characteristics are accounted for in future study designs, the relationships between static alignment, dynamic knee function, and injury risk will remain largely theoretical. Continuing to understand the relationship among alignment characteristics may help clinicians effectively identify those that may be at greater risk for injury and therefore help us develop intervention strategies to subsequently reduce the risk of a lower extremity injury.
Funded in part by NIH-NIAMS # R01 AR053172.
The authors state that they have no financial interest in the products mentioned within this article.