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

Abstract

Thermoelastic stress analysis was used to examine stresses on the anterior surface of patellae after patellar bone block excision for autogenous 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 hypothesized that stresses in a bone block-compromised patella may be increased even further by insertion of a patellar prosthesis. All patellae were first tested intact and then were retested after a sequence of surgical modifications including patellar prosthesis implantation, tapered bone block excision, 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 significantly 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 increased maximum stress levels. Insertion of a patellar prosthesis did not significantly alter stress patterns or maximum stress levels in the patella.

Indirect patella fractures following ACL reconstruction: A review

“…A change in orientation of principal surface strain was observed by Steen et al (1999), from a longitudinal to a more transverse axis at the medial patella. Friis et al (1994) reported a generalized increase in stress magnitude, especially superior to the graft site. An increase in mean axial strain at all degrees of flexion has also been recorded (Sharkey et al 1997).…”

Contemporary Graft Options in Anterior Cruciate Ligament Reconstruction

“…30 As a result, many authors believe the patellar defect should be packed with cancellous bone graft. 26,32,33 Ferrari and Bach 26 followed 693 cases of ACL reconstruction with BPTB autografts in which the patellar defect was grafted and found no patellar fractures and less donor-site pain.…”

Graft Selection in Reconstruction of the Anterior Cruciate Ligament

“…Neither harvesting the central 10 mm of the patellar tendon nor closing the gap significantly altered the area of patellofemoral contact or the pressure. However, Friis et al 16 using thermoelastic analysis showed that stresses on the anterior surface of the patella were significantly greater when the bone block had been excised than in the intact patella. Following hamstring grafting patients may experience symptoms at the donor site 9 which may be of concern in football and in sprinting sports.…”