Abstract
A key component to the success of total knee replacement is the health and integrity of the extensor mechanism. While there are issues related to the patella, such as fracture, dislocation, subluxation, clunk due to peripatellar fibrosis and anterior knee pain, the overall integrity of the extensor mechanism is of tantamount importance in providing an excellent functional outcome. During total knee replacement it is of utmost importance to preserve the anatomic insertion of the patellar tendon on the tibial tubercle. However, after total knee replacement, a fall or extreme osteoporosis of the patella may cause a rupture of the patellar tendon, distally or proximally, and possibly the quadriceps tendon off of the proximal pole of the patella.
Simple repairs of the patellar tendon avulsion may involve use of the semitendonosis and gracilis tendons along with primary repair of the tendon. Usually, patella infera develops after such a repair affecting overall strength and function. For severe disruptions of the extensor mechanism that are accompanied by a significant extensor lag, autologous tissue repair may not be possible. Thus, there are three techniques for reconstruction of this difficult problem: Extensor mechanism allograft with bone-patellar tendon-patella-quadriceps tendon, extensor mechanism allograft with os calcis-Achilles tendon construct and Marlex-mesh reconstruction for patellar tendon avulsion.
The key to success of extensor mechanism allograft is proper tensioning of the allograft at full extensor and immobilisation for 6 weeks. Rosenberg's early experience showed that the allograft works best placed at maximum tension in extension. Rubash has described the use of the os calcis-Achilles tendon which does not utilise a patellar substitute. Hansen has recently described excellent results with the use of Marlex mesh to act as a structural reinforcement to the patellar tendon when it is avulsed.
