Predictors of Discoid Morphology in Lateral Meniscal Tears: Introducing a Novel Meniscal Height Ratio

Identifying underlying discoid morphology in the setting of a lateral meniscal tear (LMT) can be challenging with no clear consensus on its definition. We aim to determine the magnetic resonance imaging (MRI) characteristics of discoid morphology, including a novel meniscal height ratio.

A retrospective study of patients undergoing arthroscopic repair of isolated LMT between 2018 and 2023. MRIs were reviewed for the presence of discoid morphology, meniscocapsular ligaments and bone contusion, tear patterns, and lateral/medial meniscal height comparison to generate a ratio. Logistic regression was employed to assess predictive factors for discoid. Descriptive statistics were used to determine MRI diagnostic performance and receiver operating characteristic (ROC) curve to identify an optimal threshold for the meniscal height ratio.

We included 283 knees (mean age 14.9 years; 76% male); 112 with discoid morphology (group 1, G1), and 171 non-discoid (group 2, G2). Lateral bone contusions were less common in G1 than G2 (P<0.001). Meniscocapsular ligaments were identified in 68% of G1 versus 88% in G2 (P=0.001). G1 patients had a significantly greater meniscal height ratio compared with G2 (P<0.001). Female sex, younger age and horizontal tears were statistically significantly associated with G1. ROC analysis identified an optimal threshold of 1.21. Similar diagnostic accuracy for binomially determining underlying discoid morphology comparing a height ratio of 1.21 and lateral tibiofemoral meniscal coverage >50%. Selectively combining both parameters gives 100% specificity.

The meniscal height ratio plays a complementary role with other imaging and demographic findings to identify underlying discoid morphology.