Variability of the posteromedial meniscocapsular junction of the knee on MRI: Pitfall to imaging diagnosis of ramp lesions.

Objective: A ramp lesion describes injury at the junction of the posterior horn medial meniscus and posteromedial joint capsule occurring with anterior cruciate ligament deficiency. We sought to apply the consensus of the literature's description of a ramp lesion on MRI (fluid signal interposed between the posterior medial meniscus and adjacent capsule) to a general population to determine how often this "abnormality" is present on routine MRI and help clarify its specificity. Material and methods: 100 consecutive MRI knee studies were retrospectively reviewed by 2 radiologists and in binary fashion characterized as either having features of a ramp lesion or normal appearance. If a ramp lesion was present, the lesion was subclassified according to the Thanaut et al. classification. Patient age, laterality, sex, clinical indication, and ancillary findings on MRI were recorded. Results: Thirty-five of 100 (35 %) knees had MRI findings suggesting a ramp lesion with 31/35 (88.6 %) most consistent with a Thanaut et al. type 1. Only 7 of the 35 (20 %) with ramp lesion had ACL insufficiency. Age (p = 0.00044), right laterality (p = 0.019), and female sex (p = 0.029) were statistically associated with this lesion. There was no association with clinical history indicating recent trauma (p = 0.2399). Conclusion: The appearance of the meniscocapsular junction of the posterior horn medial meniscus may be more varied than the literature discussing ramp lesions suggests. Most notably, fluid interposed between the posterior horn medial meniscus and adjacent posteromedial capsule is not uncommon in those undergoing knee MRI and appears to be nonspecific.