Lowering of the patella secondary to anterior advancement of the tibial tubercle for the patellofemoral pain syndrome.

From a series of 72 patients treated with anterior advancement of the tibial tubercle for patellofemoral pain syndrome, secondary lowering of the patella was noted in eight. In all eight patients the results were poor following surgery, with severe disabling retro- and peripatellar pain and atrophy of the quadriceps muscle. We describe this complication and illustrate and discuss the biomechanical consequences. The shortening of the patellar ligament and lever arm of the ligament were determined from radiographs of the knee joints before and after surgery. A theoretical analysis was made of the compressive force in the patellofemoral joint in one of these patients. The Insall-Salvati index decreased from 0.88-1.25 (mean 1.07) preoperatively to 0.54-0.78 (mean 0.70) at follow-up, 1.0-2.5 years post-operatively. The lowering of the patella was correlated to a reduction of the lever arm of the patellar ligament in seven patients. The mechanism behind the lowering of the patella is obscure, but the reduced lever arm of the patellar ligament will increase the compressive force in the patellofemoral joint, and this might be one explanation of the poor results. Impaired congruity of the patellofemoral joint, increased tension in the patellar ligament, and increased pressure against the quadriceps tendon are other possible explanations.