Pediatric discoid meniscus: can magnetic resonance imaging features coupled with clinical symptoms predict the need for surgery?

Background Magnetic resonance imaging (MRI) criteria for evaluating discoid meniscus is limited in the pediatric population. Objective To assess MRI features of intact discoid meniscus and correlate with clinical outcomes. Materials and methods In this institutional review board (IRB)-approved retrospective cohort study, knee MRIs at our institution from 2008 to 2019 were reviewed. The inclusion criterion was diagnosis of discoid meniscus on MRI. Exclusion criteria were torn discoid meniscus at presentation, previous meniscal surgery and confounding knee conditions. MRI features of discoid meniscus collected were craniocaudal dimension, transverse dimension, transverse dimension to tibial plateau (TV:TP) ratio and increased intrameniscal signal. The clinical course was reviewed for knee pain, mechanical symptoms and treatment type. Results Two hundred and nineteen of 3,277 (6.7%) patients had discoid meniscus. Of the 219 patients, 71 (32.4%) satisfied inclusion criteria. Seven patients had discoid meniscus of both knees resulting in 78 discoid menisci. The average patient age was 11.1 years (min: 2.0, max: 17.0). The average follow-up was 30.6 months. Of the 78 discoid menisci, 14 (17.9%) required surgery. Increased intrameniscal signal was found more in discoid meniscus requiring surgery (surgical: 10/14, nonsurgical: 19/64, P=0.009). Surgically treated discoid meniscus had a statistically significant increase in transverse dimension (surgical: 18.3 +/- 5.0 mm, nonsurgical: 15.7 +/- 4.3 mm, P=0.045) and TV:TP ratio (surgical: 0.55 +/- 0.15, nonsurgical: 0.47 +/- 0.12, P=0.036). Mechanical symptoms (surgical: 9/11, nonsurgical: 21/60, P=8.4x10(-6)) and pain >= 1 month (surgical: 11/11, nonsurgical: 17/60, P=0.006) were found more often in surgical patients. Clinical and imaging criteria of mechanical symptoms and knee pain >= 1 month and at least one of (1) increased intrameniscal signal or (2) TV:TP ratio greater than 0.47 identified discoid menisci that developed a tear and/or required surgery with a sensitivity of 0.86 and specificity of 0.88. Conclusion Mechanical symptoms and knee pain >= 1 month, and at least one of (1) increased intrameniscal signal or (2) TV:TP ratio greater than or equal to 0.47, identified discoid menisci that would go on to tear and/or require surgery with a sensitivity and specificity of 0.86 and 0.88, respectively.