Stress fracture of the patella following duopatellar total knee arthroplasty with patellar resurfacing.

Stress fracture of the patella can occur with significant frequency following patellar replacement with the duopatellar knee prosthesis. In the first 372 knees with patellar resurfacing, the incidence was 0.7% in rheumatoid arthritis (2 fractures in 286 knees) and 3.5% in osteoarthritis (3 fractures in 86 knees). The incidence may be greater in osteoarthritic patients because they have more function and are generating greater force across the patellofemoral joint. There was an association with osteonecrosis of the patella in at least three cases in which a lateral retinacular release had been performed and the lateral superior genicular artery sacrificed. This vessel should be preserved during a lateral release to save its contribution to the blood supply of both the patella and the lateral skin flap. Initial treatment of the stress fractures can be nonoperative, with surgery necessary only if the patellar prosthesis has become dislodged, or if pain or inadequate active extension persists. If the fracture can not be repaired, patellectomy can yield a good result. To avoid stress fracture, a minimal amount of patellar articular surface should be resected and the peripheral cortex of both the medial and lateral facets preserved. Fewer stress fractures may occur if a smaller fixation lug is used, thereby preserving more patellar bone stock.