EFFECT OF BONE BLOCK REMOVAL AND PATELLAR PROSTHESIS ON STRESSES IN THE HUMAN PATELLA

Thermoelastic stress analysis was used to examine stresses on the ante rior surface of patellae after patellar bone block excision for autoge nous graft anterior cruciate ligament reconstruction. Complications of anterior cruciate ligament injury often lead to degenerative changes in the knee that can require total knee joint replacement. It was hypo thesized that stresses in a bone block-compromised patella may be incr eased even further by insertion of a patellar prosthesis. All patellae were first tested intact and then were retested after a sequence of s urgical modifications including patellar prosthesis implantation, tape red bone block excision, square bone block excision, and both shapes o f excised bone blocks with a patellar prosthesis in place. Stresses in patellae with bone blocks excised were significantly greater than str esses in intact patellae. The anterior surface stress pattern in the l oaded patella was significantly altered by excision of a bone block. T here were no significant differences between maximum stress in patella e with tapered and square bone blocks excised. A finite element analys is showed that excision of a larger trapezoid-shaped bone block greatl y increased maximum stress levels. Insertion of a patellar prosthesis did not significantly alter stress patterns or maximum stress levels i n the patella.