Step-Off Between the Lateral Femoral Condyle and the Lateral Tibial Plateau: Association with Degenerative Lateral Meniscal Tears and Lateral Osteoarthritis of the Knee

A naturally occurring step-off (SO) between the lateral femoral condyle and the lateral tibial plateau creates a zone where the middle part of the lateral meniscus (LM) is not covered by the femoral condyle. We assessed the effects of this SO on the development of meniscal damage and osteoarthritis (OA). A total of 82 patients who underwent meniscectomy of the LM were retrospectively reviewed. The patients were divided into two groups based on findings of OA on radiography. The control group consisted of patients without OA who were matched to those who had acute isolated anterior cruciate ligament injuries. The size of the SO and extrusion of the LM were obtained by preoperative magnetic resonance imaging. The mean size of the SO in the LM group was significantly larger than that in the control group (4.0 ± 0.92 mm vs. 1.6 ± 1.11 mm, <i>p</i> < 0.0001). Extrusion of LM was not significantly different between the two groups. Extrusion of the tibial side in patients with OA was significantly larger than that in the non-OA group (1.9 ± 1.2 vs. 0.50 ± 0.95, <i>p</i> < 0.001). However, the size of the SO was not significantly different (4.2 ± 1.28 vs. 4.0 ± 0.92, <i>p</i> = 0.53). A large SO was identified as an anatomical risk factor for degenerative LM tears, leading to extrusion of LM and development of lateral knee OA.