Revisiting meniscal anatomical variants of the knee: a high-resolution 7-Tesla MRI study

OBJECTIVES: To examine anatomical variants of meniscal root insertions among asymptomatic individuals using high-resolution 7-T MRI. MATERIALS AND METHODS: This prospective study, approved by the local ethics committee, involved 57 knees from 48 participants (mean age 31.8 years; 19 females), being examined on a clinical 7-T MRI scanner with sagittal isotropic 0.24 mm 3D double echo steady state (DESS) sequence. Two radiologists identified the number and location of each meniscal root insertion. Two other radiologists repeated this evaluation, noting meniscofemoral ligaments. Inter-rater reliability was calculated. RESULTS: Majority of the posterior lateral meniscus roots featured double insertions (66.7%), followed by single (31.6%) and triple insertions (1.8%). Single roots mainly inserted into the intercondylar area (77.8%), the remaining into the posterior slope of the posteromedial eminence (22.2%). Double roots typically had a major insertion at the posteromedial aspect of the anterior cruciate ligament and a minor root at the posterior slope of the lateral eminence (78.9%). The remaining roots of both menisci featured only single insertions. Anterior medial roots inserted along the medial tibial edge (71.9%) and into the intercondylar area (28.1%). Inter-rater reliability for describing the posterior lateral meniscal root insertions was perfect (κ = 1), and strong for identifying all insertion sites (κ = 0.808). Meniscofemoral ligaments were prevalent (87.7%) with a broad heterogenous fan-shaped femoral attachment observed using the 3D DESS sequence. CONCLUSION: 7-T 3D-DESS imaging allows high-resolution visualization of the meniscal roots with excellent inter-rater reliability, highlighting anatomical variability mainly in the posterior root of the lateral meniscus. KEY POINTS: Question Anatomical variations of the number and insertion sites of meniscal roots are documented in anatomical and imaging studies. Findings High-resolution 3D dual-echo steady state on a 7-T MRI facilitates the visualization of the number of roots and their respective osseous insertions for both menisci. Clinical relevance The menisci demonstrate considerable variability in both root number and their insertion locations, particularly the posterior lateral meniscus exhibits up to three root insertions. Understanding anatomical variants is crucial for the accurate interpretation and reporting of knee imaging.