[Spontaneous ruptures of the extensor system of the knee following joint replacement in patients with rheumatoid arthritis].

Spontaneous ruptures of the quadriceps tendon and the patellar ligament following total knee arthroplasty in two patients with rheumatoid arthritis are reported. Degenerative and steroid-induced changes of tendinous tissue, circulation problems as well as mechanical changes to the patellofemoral joint by resurfacing the patella are discussed being possible causes of these complications of the extensor mechanism of the knee.