Patellar impingement against the tibial component after total knee arthroplasty.

Patella baja developed in seven knees in five patients after posterior stabilized total knee arthroplasties when the patella became impinged against the tibial component. Patellar replacement was performed in four knees, and all patients were able to achieve deep flexion postoperatively. The mean followup was 50 months (range, 24-73 months) for these patients. The mean Insall-Salvati ratio changed from 0.87 (range, 0.70-1) immediately postoperatively to 0.66 (range, 0.55-0.84) at followup. Patellar erosion occurred in three knees without patellar replacements, accompanied by pain and reduced range of flexion. The four knees with patellar replacements showed marked erosion of the patellar component or the patella, but all remained asymptomatic. Achieving deep flexion in addition to patella baja was thought to be a key element. Patellar replacement, joint line preservation, shaving the anterior portion of the tibial component, preventing surgically induced patella baja, and careful radiographic followup should be considered when deep flexion is achieved in a knee with patella baja after a total knee arthroplasty.