EFFECTS OF SIMULATED FIXED FEMORAL ROTATION ON THE PATELLOFEMORAL JOINT: IN VITRO AND IN VIVO BIOMECHANICAL ASSESSMENT IN CANINES

Abstract

The quantitative effects of fixed femoral rotation on the patellofemoral joint were assessed in canines in vitro and in vivo. For the in vitro study, ten canine knees were examined in neutral and 30 degrees of internal and external fixed femoral rotations. Fuji film was inserted into the patellofemoral joint and quadriceps loading was simulated at 60 and 90 degrees of knee flexion. There was significant increase in patellofemoral contact pressures on the contralateral facets of the patella with 30 degrees of fixed femoral rotation at both knee flexion angles (p < 0.05). For the in vivo study, 12 skeletally mature mongrel dogs were subjected to either internal or external bilateral femoral rotational deformity of 30 degrees. Three animals served as controls. Biomechanical evaluation of the articular cartilage showed a statistically significant decrease for both the unrelaxed and relaxed apparent shear modulus at six months for both internal and external femoral rotations (p < 0.05) in comparison to the control. In vivo results from fixed femoral rotation on the patellofemoral joint correlate with that expected from in vitro biomechanical results. The results from this study suggest that rotational deformity of the femur should be corrected within six months to prevent patellofemoral joint arthrosis.