Correlation between varus knee malalignment and patellofemoral osteoarthritis

Purpose To evaluate the relationship between patellofemoral osteoarthritis (OA) and varus OA of the knee with a focus on the location of joint space narrowing. Methods Eighty-five patients scheduled to undergo total knee arthroplasty caused by varus OA were enrolled in this study. The relationship between patellofemoral OA and varus knee malalignment was elucidated. To determine the alignment of the patellofemoral joint in varus knees, patellar tilt, and the tibial tuberosity–trochlear groove (TT–TG) distance were measured, and patellofemoral OA was classified using computed tomography. Results The femorotibial angles in patients with stage II–IV patellofemoral OA were significantly larger than those in patients with stage I patellofemoral OA, and the patellar tilt in patients with stage II–IV patellofemoral OA and the TT–TG distance in patients with stage IV patellofemoral OA were significantly larger than those in patients with stage I patellofemoral OA. The TT–TG distance was strongly correlated with patellar tilt (R 2 = 0.41, P < 0.001). Patellofemoral joint space narrowing was mainly noted at the lateral facet, and it was found on both sides as patellofemoral OA worsened. Conclusion Varus knee malalignment was induced by patellofemoral OA, especially at the lateral facet. Patellar tilt and the TT–TG distance are considered critical factors for the severity of patellofemoral OA. Understanding the critical factors for patellofemoral OA in varus knees such as the TT–TG distance and patellar will facilitate the