Patellar forces during knee extension.

A radiographical study of 20 loaded knees of healthy subjects and a knee dissection study of 20 specimens were performed in order to present a two-dimensional patello-femoral joint biomechanical model. A constant knee-extending moment gave 25-40% lower force magnitudes in the patellar tendon than in the quadriceps tendon if the knee was flexed to 60-120 deg. The magnitude of the patello-femoral joint compressive force reached its maximum at 90 deg knee angle and decreased slightly towards 120 deg. A compressive force between quadriceps tendon and femoral intercondylar groove was present above 60 deg knee angle and its magnitude was estimated. The patellar forces in women were about 20% higher than in men. The biomechanical model may be used in knee rehabilitation activities to optimize and individualize exercise programmes. The model may also be applied to daily activities in order to quantify patellar forces.