To investigate the pathogenesis of patellofemoral degenerative arthrosis caused by tibial malrotation. Seven human knee joints from 7 fresh cadavers were used in vitro to test the contact pressure and the peak Pressure with Fuji Pressure sensitive film in the conditions of normal status, 10°, 20°, 30° both external tibial rotation and internal tibial rotation under the isometric tension of 196 N attached to the quadriceps tendon for 30°, 60° and 90° knee flexion. Results showed that the increase of the degree of external tibial rotation resulted in a nonlinear incline up in patellofemoral contact pressure on the lateral facet of patellar, while a nonlinear decline on the medial facet. However, the internal tibial rotation resulted in gradual decreasing of contact pressure on lateral facet and marked increasing on medial facet. These changes were regular during the range of 20° external rotation to 20° internal rotation. All of these prompted that tibial malrotation might bring out the patellofemoral degenerative althrosis by serious disorder of contact pressure distribution.