Objectived Using electric stress analysis and pressure measuring film techniques, to determine muscular stress changes, contact and pressure distribution over the patellofemoral joint. Materials and Methods f & human knee specimens with reserved capsule and quadriceps tendon. The pressure measuring films were put into the retropatellar space and the stress transducers were fixed on the tendons. Results f (1)the unbalanced quadriceps forces may influence the patellar stability, the normal contact and pressure distribution of the patellofemoral joint. (2)On the specimens of the experimentally produced malalignment, we found that the pressure in the lateral facet increased significantly and were limited in scope, resulting in a stress concentration.(3) After releasing of the lateral retinaculum the high contact pressure in the lateral facet decreased significantly, but the influence of quadriceps forces still remained. Conclusions attention should be paied to the rehabilitation of the quadriceps forces, especially vastus medialis.