Changes in patellofemoral compressive force after anterior or anteromedial displacement of tibial tuberosity for chondromalacia patellae.

Patellofemoral compressive force was measured before and after anterior displacement of the tibial tuberosity for patellofemoral disorders on 30 knees in 28 patients. All patients selected for this experiment were those who obtained relief of pain in the activities of daily living. Twenty-five women and three men, with an average age of 54 years (range, 21-79 years), were followed an average of 38 months (range, 24-84 months). The maximum strength of knee extension was measured by a myodynamometer with the knee at 45 degrees flexion. Patellofemoral compressive force was calculated using a vector of quadriceps muscle power. At the final follow-up evaluation, the quadriceps lever arm increased in all knees with an average rate of increase of 20% +/- 2%. The maximum strength of knee extension increased in all but three knees with an average rate of increase of 147% +/- 27%. Patellofemoral compressive force increased in 22 knees, was unchanged in five, and decreased in three, with an average rate of increase of 67% +/- 15% compared with the preoperative level.