Imaging appearance and prevalence of the anteromedial meniscofemoral ligament: A potential pitfall to anterior cruciate ligament analysis on MRI.

PURPOSE: To describe the aspect of the anteromedial meniscofemoral ligament on MRI and to assess its prevalence. METHOD: One thousand five hundred sixty knee MRI studies were retrospectively evaluated for the presence of an anteromedial meniscofemoral ligament. In addition to these studies, nine full MRI studies from our department's image archive were also analysed. The anteromedial meniscofemoral ligament length, thickness, and angle with respect to the tibial plateau were evaluated independently by two radiologists. For comparison purposes, the anterior cruciate ligament was assessed in the same manner. RESULTS: There was a 0.77% prevalence of the anteromedial meniscofemoral ligament in the study population. Compared to the anterior cruciate ligament, the anteromedial meniscofemoral ligament was 80.6%-83.8% thinner according to both observers (P =  0.0002), with a mean thickness of 1.53 ±â€¯0.47 mm and 1.80 ±â€¯0.66 mm determined by observers 1 and 2, respectively. The anteromedial meniscofemoral ligament angles were 15%-17.7% lower than the anterior cruciate ligament angles (P <  0.003). Interobserver reproducibility was considered excellent for the length and angle measurements (ICCs varying from 0.85-0.97) and good for the thickness measurements (ICCs 0.66-0.77). CONCLUSIONS: The anteromedial meniscofemoral ligament is a rare structure that can be differentiated from the anterior cruciate ligament based on morphologic criteria.