The effects of tibial rotation on the patellofemoral joint: assessment of the changes in in situ strain in the peripatellar retinaculum and the patellofemoral contact pressures and areas.

The objective of this study was to determine the effects of tibial rotation on in situ strain in the peripatellar retinaculum and patellofemoral contact pressures and areas. Patellofemoral joint biomechanics demonstrate a strong correlation with the etiology of patellofemoral disorders, such as chondromalacia, and are significantly influenced by tibial rotation. Six human cadaveric knees were used along with a patellofemoral joint testing jig that permits physiological loading of the knee extensor muscles. Patellofemoral contact pressures and areas were measured with a Fuji pressure-sensitive film, and the changes in in situ strain in the peripatellar retinaculum were measured with four differential variable reluctance transducers. Tibial rotation had a significant effect on patellofemoral joint biomechanics. The data showed an inverse relationship between increasing knee flexion angles and the change in patellofemoral contact pressures and in situ strain with tibial rotation. At higher knee flexion angles, the patella is well-seated in the trochlear groove and the function of the peripatellar retinaculum is minimized and less affected by tibial rotations.