Effect of Bone Block Removal and Patellar Prosthesis on Stresses in the Human Patella

Thermoelastic stress analysis was used to examine stresses on the anterior surface of patellae after patellar bone block excision for autogenous graft anterior cru ciate 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 hypothesized that stresses in a bone block-compromised patella may be increased even further by insertion of a patellar prosthesis. All pa tellae were first tested intact and then were retested after a sequence of surgical modifications including pa tellar prosthesis implantation, tapered bone block ex cision, square bone block excision, and both shapes of excised bone blocks with a patellar prosthesis in place. Stresses in patellae with bone blocks excised were sig nificantly greater than stresses in intact patellae. The anterior surface stress pattern in the loaded patella was significantly altered by excision of a bone block. There were no significant differences between maximum stress in patellae with tapered and square bone blocks excised. A finite element analysis showed that excision of a larger trapezoid-shaped bone block greatly in creased maximum stress levels. Insertion of a patellar prosthesis did not significantly alter stress patterns or maximum stress levels in the patella.