The Anteroposterior Diameter of Complete Discoid Lateral Meniscus Versus the Diameter of Normal Lateral Meniscus: An MRI Study in Adults.

Background: The abnormal morphology of complete discoid lateral meniscus (CDLM) is associated with a greater propensity for tears. The magnetic resonance imaging (MRI) morphology of CDLM is most often described in the coronal plane, with few morphological studies in the sagittal position.

Hypothesis: The sagittal anteroposterior diameter of CDLM is smaller than that of normal meniscus and is increased after tear in adults.

Study design: Cross-sectional study; Level of evidence, 3.

Methods: The authors searched the radiology records at our institution from June 2018 to December 2023 for patients aged from 18 to 55 years with knee pain. According to inclusion and exclusion criteria, 70 knees (66 patients) with torn CDLM were enrolled as group A, 36 knees (31 patients) with intact CDLM were enrolled as group B, and 48 knees (32 patients) with normal lateral meniscus (LM) were enrolled as group C. The coronal view passing through the middle point of the lateral tibial plateau (LTP) were identified the referrence coronal view, then the sagittal view passing through the middle point of the LTP on the referrence coronal view were selected for the measurements, the anterior distance, posterior distance, and anteroposterior diameter of the LM, sagittal tibial diameter (TD) were measured. The 4 measurements and the ratios were compared among the groups by independent sample t test.

Results: The reliability of all measurements was excellent, except that posterior distance was classified as good in group B. The anteroposterior diameter and TD were smaller in group A than in group C (both P < .001) and smaller in group B than in group C (P < .001 and P = .007). anteroposterior diameter and anteroposterior diameter/TD in group A were larger than in group B (P = .003 and P < .001), while anteroposterior diameter/TD in group A and group C were similar (P > .05). The anterior distance and anterior distance/TD were smaller in group A than in group B (P = .02 and P = .03) and smaller in group A than in group C (P < .001 and P = .008). Posterior distance, posterior distance/anteroposterior diameter, and posterior distance/TD were larger in group A than in group C (P < .001, P < .001, and P < .001) and larger in group B than in group C (P < .001, P < .001, and P < .001).

Conclusion: Our study demonstrates that in adults, the meniscal anteroposterior diameter and the TD are smaller in CDLM than in normal LM, and the anteroposterior diameter of torn CDLM is larger than intact CDLM.