THE INFLUENCE OF MEDIAL FEMORAL ROTATION ON LATERAL PATELLAR TILT DURING WEIGHTBEARING AND NON-WEIGHTBEARING MOVEMENTS

Abstract

Lateral tilting of the patella has been hypothesized as being contributory to excessive lateral pressure syndrome and patellofemoral pain (PFP). Previous work in our laboratory has suggested that the cause of patellar tilt (i.e. femoral versus patellar motion) may vary between weightbearing and non-weightbearing movements. PURPOSE: To quantify the contribution of patellar motion and femoral motion to patellar tilt angle during weight-bearing and non-weightbearing movements using kinematic MRI. METHODS: Six female subjects (8 knees) with documented patellar subluxation participated. Axial images of the patellofemoral joint were obtained using kinematic magnetic resonance imaging during active knee extension (non-weightbearing, 5% body weight resistance) and a unilateral squat (weightbearing) from 0° to 30° of knee flexion. Images were obtained dynamically in 3 increments. Measurements of patellar tilt angle (patella relative to the femur), medial/lateral patellar tilt (relative to the global reference frame), and medial/lateral femoral rotation (relative to the global reference frame) were obtained from mid-patellar images using a custom macro written for NIH image software (National Institute of Health, Bethesda, MD). A repeated measures ANOVA was used to compare patellar tilt angle, patellar tilt, and femoral rotation during the two movements. RESULTS: Maximum patellar tilt angle occurred at terminal knee extension during both movements, with greater values being observed in non-weightbearing compared to weightbearing (20.49 versus 14.89, p < 0.05). At terminal knee extension patellar tilt angle was more a function of medial femoral rotation during weightbearing than during non-weightbearing (14.19 versus 5.39, p < 0.05). Conversely, patellar tilt angle was more a function of lateral patellar tilt in non-weightbearing than weightbearing (15.09 versus 0.72, p < 0.05). CONCLUSION: These data suggest that the cause of patellar tilt relative to the femur is different during the weightbearing and non-weightbearing movements. Weightbearing movements are associated with medial femoral rotation underneath the femur, which causes relative lateral patellar tilt. In contrast non-weightbearing movements can be characterized by lateral patellar tilt over a relatively fixed femur. These findings suggest that clinical interventions aimed at controlling medial femoral rotation during weightbearing movements may be efficacious in improving patellar alignment in persons with PFP.