Paper 110: Patellar Cut Obliquity in the Sagittal Plane May Be Predictive of Peri-prosthetic Patella Fracture in Cemented Total Knee Arthroplasty

Abstract

Patellar cut geometry has been proposed to influence patellar fracture after total knee arthroplasty (TKA). To our knowledge, there are no large studies in current literature directly examining the association of patella fractures to the integrity of the patellar cut. This paper examines the thickness and obliquity of the bony patellar resection in 74 patella fractures occurring in cemented all-polyethylene patellar components. We retrospectively reviewed 5,073 TKAs performed between 10/4/88 to 8/31/2004 by a single surgeon. Within this period, 74 peri-prosthetic patella fractures in 68 patients were identified and compared to a matched control group. Post-operative radiographic assessments of all patellae included merchant and lateral views of the patellae. Thickness of the remaining patellar bone was measured using both merchant and lateral radiographs. Patellar cut tilt was evaluated on lateral and merchant views using 10mm thickness measurements from the midpoint on each view. Geometric and statistical analysis was conducted. With greater sagittal obliquity angles, patellae were 1.196 times more likely to experience a fracture than our controls. Patella fracture after TKA may be due to trauma or a stress fracture around the construct. Bone removal for the fixation lugs can weaken the patella, causing fracture through the stress risers. This effect may be magnified with a more generous or oblique cut. Improvement in surgical technique to retain a more level cut could theoretically help prevent the problem.