In a review of 250 total knee arthroplasties, five patients with rheumatoid arthritis incurred supracondylar fractures of the femur. These fractures may be associated with a surgical encroachment of the anterior femoral cortex during resection of the patellar trochlea. Forty-two percent of patients with excessively deep resections of the patellar trochlea suffered fractures. No fractures occurred in patients without encroachment of the anterior femoral cortex. All patients with fractures also had significant osteoporosis, which may have predisposed them to fracture. A resection of the patellar trochlea that is made too deeply would interrupt the transmission of stresses through the cancellous bony trabeculae of the anterior femoral cortex and could predispose to fracture.