Patellar Fracture After Total Knee Arthroplasty

BACKGROUND: Patellar fracture can occur as a complication following total knee arthroplasty. The purpose of this study was to evaluate a large series of patellar fractures to determine the results of different forms of treatment of specific fracture types. METHODS: A retrospective review identified eighty-five fractures (in seventy-seven patients) following 12,464 consecutive total knee arthroplasties performed between 1985 and 1998. Seventy-eight fractures occurred after primary total knee arthroplasty and seven, after revision total knee arthroplasty. Five fractures were treated elsewhere, and two others were lost to follow-up. The results of treatment of the remaining seventy-eight fractures were reviewed. Fractures were classified according to three main criteria: integrity of the extensor mechanism, fixation status of the patellar implant, and quality of the remaining bone stock. The mean duration of follow-up was 3.6 years. RESULTS: The prevalence of patellar fracture after total knee arthroplasty was 0.68%; fractures were significantly more prevalent among men (1.01%) than among women (0.40%) (p = 0.0004). Thirty-eight fractured patellae had a stable implant and an intact extensor mechanism (Type I). All but one were treated nonoperatively, and there was only one late failure of nonoperative treatment, which required operative intervention. Twelve fractures were associated with disruption of the extensor mechanism (Type II). Eleven were treated operatively; six knees had complications and five had a reoperation. Twenty-eight fractures occurred in association with a loose patellar component (Type III). Twenty were treated operatively; nine knees had complications, and four had a reoperation. CONCLUSIONS: Patellar fractures after total knee arthroplasty are infrequent. Treatment can be guided by three main criteria: integrity of the extensor mechanism, fixation status of the patellar implant, and quality of the remaining bone. Fractures associated with a stable implant and an intact extensor mechanism were usually treated successfully with nonoperative means, with minimal complications. When operative treatment was required, it was associated with a high rate of complications and reoperations.