Medial Meniscus Posterior Horn Horizontal Tears are Associated with Knee Posteromedial Impinging Structures Inducing Shearing Forces in Patients with Meniscus Degeneration

Purpose This study aimed to identify potential impinging and shear stress-inducing factors in knees with medial meniscus posterior horn horizontal tears (MMPHHT) using magnetic resonance imaging (MRI) in middle-aged patients with meniscal degeneration. Materials and Methods We retrospectively analyzed and compared consecutive patients with MMPH signal changes or MMPHHT on MRI from January 2015 to January 2022. After 1:1 propensity score matching, 80 patients in each group were analyzed. Bony impinging factors, including the femoral condylar offset ratio, the ratio of posterior condylar offset (PCO) to tibial width, posterior medial tibial plateau concavity, and the medial tibial slope, were assessed. Soft tissue impinging factors, such as the MMPH coverage ratio, presence of medial femoral condyle focal cartilage defects or posterior tibial osteophytes, were also analyzed. Results Demographic data did not differ between MMPHHT and MMPH signal change groups. MMPHHT group showed increased medial tibial slope (5.33 ± 2.05° vs 4.21 ± 2.58°, P = .003), higher incidence of posterior medial tibial plateau concavity ( P = .040), greater MMPH coverage ratio (0.43% ± 0.05% vs 0.41% ± 0.04%, P = .022), and more posterior tibial osteophytes ( P = .012). Multivariate logistic regression identified higher medial tibial slope (OR = 1.288, P = .016), MMPH coverage ratio (OR = 1.369 × 10 4 , P = .020), and posterior tibial osteophytes (OR = 4.525, P = .009) as independent factors associated with MMPHHT. Conclusion In conclusion, we have determined several anatomical contributing factors related to MMPHHT. Such factors may be useful in understanding the progression of meniscus degeneration in early OA knees. Furthermore, addressing correctable factors during surgery such as tibia slope correction or osteophytectomy may improve repair results of MMPHHT in the future.