Reliability of Magnetic Resonance Imaging Interpretation of Lateral Discoid Meniscus: A Multicenter Study
Authors: Niu Emily , Milewski Matthew D. , Finlayson Craig J. , Stinson Zachary S. , Joughin Elaine , Nepple Jeffrey J. , Schmale Gregory A. ,   PRISM Meniscus Research Interest Group, Beck Jennifer J. 
Published: May 2022

Background: Lateral discoid meniscus (LDM) often present with complex morphology that can be challenging to assess and treat arthroscopically. Preoperative magnetic resonance imaging (MRI) is frequently used for diagnosis and surgical planning, however it is not known whether surgeons are reliable and consistent in their interpretation of MRI findings. Hypothesis/Purpose: We hypothesize that surgeons experienced in treating LDM are able to reliably interpret discoid pathology using MRI, with the exception of evaluating dynamic factors (i.e. instability). Methods: Forty five discoid meniscus MRI selected from a pool of surgical discoid meniscus cases were included in this review. Five reviewers (experienced pediatric sports medicine surgeons) who were not involved in the MRI selection process performed independent review of each MRI to determine discoid meniscus classification. More than 4 weeks later, a second reading was performed by 3 of the 5 reviewers. Interobserver and intraobserver reliability of the primary (width, presence of instability or tear) and secondary (location of instability or tear, tear type) rating factors was assessed using the Fleiss κ coefficient, designed for multiple readers with nominal variables (reliability: fair, 0.21–0.40; moderate, 0.41–0.60; substantial, 0.61–0.80; excellent, 0.81–1.00). Reliability is reported as κ (95% CI). Results: Interobserver reliability of assessment of meniscal width was substantial 0.67 (0.58-0.76), and intraobserver was moderate 0.52 (0.35-0.69). Assessment of presence of peripheral instability had moderate interobserver reliability 0.54 (0.45-0.63) and substantial intraobserver 0.61 (0.44-0.78). Presence of tear had fair interobserver reliability 0.39 (0.29–0.48) and substantial intraobserver 0.68 (0.51-0.85). When identifying location of instability or tear, interobserver reliability was moderate while intraobserver agreement was substantial for assessment of anterior instability (0.47 (0.37-0.56) and 0.68 (0.51-0.85), respectively); posterior instability (0.56 (0.47-0.65) and 0.62 (0.45-0.79), respectively); and posterior tear (0.41 (0.32-0.50) and 0.69 (0.52-0.86), respectively). The exception was identifying anterior tear, with fair interobserver reliability 0.33 (0.23-0.42) and moderate intraobserver 0.56 (0.39-0.73); Interobserver reliability was fair for tear type 0.34 (0.28-0.41) and intraobserver reliability moderate 0.55 (0.43-0.67). Conclusion: Orthopaedic surgeons experienced in the treatment of LDM vary from each other in their classification using MRI, especially with regard to assessment of meniscus tears. MRI evaluation may be helpful to diagnose discoid by width and identify presence of instability, two major factors in the decision to proceed with surgery. However, definitive treatment should be guided by a comprehensive arthroscopic evaluation.