Differences in patellofemoral alignment as a result of patellar shape in cruciate-retaining total knee arthroplasty without patellar resurfacing at a minimum three-year follow-up.

Abstract

Although the patellofemoral (PF) joint shape of the femoral implant in a particular prosthetic design is identical, the articular surface shape of the patella varies between individuals. The present study investigated the effects of patellar shape on the postoperative PF joint in a cruciate-retaining total knee arthroplasty (CR-TKA) without patellar resurfacing and with at least three years of follow-up. This study investigated 76 knees of 62 patients who underwent CR-TKA without patellar resurfacing for varus osteoarthritis. Shape of the patella was classified in terms of the patellar facet angle (angle formed by the medial and lateral articular surfaces) as measured on axial plain X-ray. Subjects were divided into Group A with patellar facet angle ≤126° (34 knees) and Group B with patellar facet angle >126° (42 knees). Anterior knee pain (AKP) was evident in four knees in Group A and one knee in Group B. Postoperative lateral patellar tilt angle was significantly larger in Group A than in Group B. Progression of osteosclerosis in the patella was present in 12 knees in Group A and three knees in Group B. This study found that for a patella with a small patellar facet angle, lateral tilt of the patella was significantly increased after TKA, and a high rate of osteosclerosis was evident at >3years after operation. Performing TKA without patellar resurfacing on a patella with a small patellar facet angle may entail a higher risk of postoperative AKP; pre-operative evaluation of the shape of the patella is therefore important.