LAUSR

To evaluate the effect of joint line obliquity of the knee on intrasubstance degeneration of isolated medial meniscus horizontal cleavage tear (HCT) in young patients. Sixty knees of 50 patients aged < 40 years (mean age, 33.3 ± 5.5 years old), who underwent arthroscopic partial meniscectomy (APM) for HCT, were retrospectively reviewed. The radiologic parameters of alignment, including mechanical hip-knee-ankle (mHKA) angle, posterior tibial slope, and joint line obliquity, were measured on preoperative long-standing whole-leg radiographs. The patients were classified into two groups, simple horizontal type (type 1) and complicated type (type 2), according to the presence of diffuse intrasubstance degeneration of the meniscus on preoperative magnetic resonance imaging. The risk factors for intrasubstance degeneration of HCT were analyzed using multiple logistic regression analysis. Medial joint space width (JSW) on weight-bearing 45° flexion posteroanterior radiographs and the mHKA were measured to evaluate the radiographic outcomes. The clinical outcomes were evaluated using the modified Lysholm score. Among patients followed-up for > 5 years, the clinical and radiologic outcomes were compared between the two groups. The joint line obliquity was significantly greater in the type 2 group than in the type 1 group (2.9 ± 1.3 vs. 0.9 ± 1.4, P < 0.001), and a significant risk factor for diffuse intrasubstance degeneration (P < 0.001; odds ratio, 2.88; 95% confidence interval, 1.27–6.54). The relative changes in the JSW in the type 2 group were greater than those in the type 1 group during the mean follow-up period of 7.9 ± 2.5 years (26% vs 10%, P = 0.045). The modified Lysholm score was not significantly different between the two groups (n.s). The diffuse intrasubstance degeneration of medial meniscus HCTs in young patients is associated with increased joint line obliquity of the knee joints. The radiologic outcomes after APM were inferior in the patients with diffuse intrasubstance degeneration. However, the clinical outcomes were not different during the mid-term follow-up. Level III.