A semimembranosus-related band directed toward the posterior horn of the lateral meniscus: MRI prevalence and relationship to posterior knee stabilizing structures.

Abstract

To determine the MRI prevalence of the semimembranosus-lateral meniscus (SM-LM) attachment and the imaging plane on which it is most conspicuous, and to evaluate its relationships with the meniscofemoral ligaments and the oblique popliteal ligament (OPL). In this retrospective single-center study, 205 1.5-T knee MRI examinations in patients ≥ 18 years (134 women, 71 men; median age, 38 years) were evaluated by a musculoskeletal radiologist, with a random subset of 100 independently evaluated by a second reader; those with prior ipsilateral knee trauma or surgery or Kellgren-Lawrence grade 3-4 osteoarthritis were excluded. Interobserver agreement was evaluated with Cohen κ; logistic regression and chi-square analyses were performed. The SM-LM attachment was identified in 32 of 205 knees (15.6%), exclusively thin and most conspicuous on axial images. The ligament of Wrisberg was present in 139 knees (67.8%), the OPL in 129 (62.9%), and the ligament of Humphrey in 113 (55.1%); the meniscofemoral ligaments co-occurred inversely (χ2 = 46.2, p < 0.001). The OPL was inversely associated with the SM-LM attachment on univariable analysis, and this inverse association persisted on multivariable analysis (adjusted OR, 0.42; 95% CI, 0.19-0.91; p = 0.029). Interobserver agreement was substantial to almost perfect (κ range, 0.69-0.94). The SM-LM attachment is an identifiable, thin semimembranosus-related band on knee MRI whose definitive anatomical nature requires cadaveric or surgical correlation. Its inverse association with the OPL suggests that these semimembranosus-related structures may represent alternative patterns within the posterior stabilizing network.