The patellar clunk syndrome. A complication of posterior stabilized total knee arthroplasty.

Patellofemoral pain due to an unusual suprapatellar fibrous nodule developed in three patients after posterior stabilized total knee arthroplasty. Each patient had a "catch" or "clunk" associated with pain on extension of the knee. At revision, a prominent fibrous nodule was found at the junction of the proximal patellar pole and the quadriceps tendon. The pathogenesis of this proximal fibrous nodule may involve impingement of the anterosuperior edge of the intercondylar notch area of the femoral component into the proximal quadriceps tendon or may involve impingement of the patellar prosthesis itself on the quadriceps tendon. Roentgenographic examination revealed an abnormally proximal placement of the patellar prosthesis on the patella. Surgical removal of the fibrous nodule resolved the symptoms. Revision of the patellar prosthesis may be necessary.