Extensor mechanism ruptures.

The extensor mechanism of the knee consists of the quadriceps muscle and tendon, the patella, the patellar tendon, and the tibial tubercle. Disruption of any of these can lead to an extensor mechanism rupture and render an otherwise perfectly good total knee replacement (TKR) useless. Quadriceps tears associated with TKR are difficult to treat and associated with a poorer prognosis than in the native knee. Transosseous sutures tied over the distal pole of the patella are recommended. Patella fractures may heal in continuity or may involve a disruption of the extensor mechanism. The blood supply may have been compromised during TKR, so healing may be delayed. The patella component may be loose and need to be removed or revised. Patellar tendon ruptures are the most common and serious form of extensor mechanism rupture. Prevention is more effective than treatment. Careful exposure during revision surgery includes anticipating the need for a quadriceps snip, pinning the tubercle to avoid avulsion, and preserving the fat pad during primary surgery. Treatment of patellar tendon ruptures is challenging. Primary repair may succeed in early intervention, but in established rupture, allograft reconstruction is often necessary. Achilles tendon allograft is preferred. The calcaneus fragment is embedded into the proximal tibia as a new tubercle, and the tendon is sutured into the remaining extensor mechanism. The repair is then protected using a cable loop from the superior pole of the patella to a drill hole in the upper tibia.