Purpose or Case Report: Clear MRI criteria for discoid meniscus in the pediatric population is limited in the literature. This has resulted in a range of meniscal sizes and shapes being called discoid. While the diagnosis may be correct, features that could predict patient symptoms or increase the likelihood of meniscal surgery are unknown. The purpose of this study was to assess MRI features of intact discoid menisci and correlate with clinical outcomes in order to improve the prognostic utility of MRI.
Methods & Materials: In this IRB-approved retrospective study, we reviewed all knee MRIs performed at our institution between 2008 – 2019. Our inclusion criteria were knee MRIs with a radiologic diagnosis of discoid meniscus. Our exclusion criteria were torn discoid meniscus, prior meniscal surgery (saucerization), and confounding diseases (eg: JIA, septic arthritis, etc.). Radiologic features of the discoid meniscus were recorded (largest cranio-caudal (CC) dimension, largest transverse dimension, transverse dimension to tibial plateau ratio, and presence of intrasubstance degenerative signal). Patient characteristics were collected.
Results: 72/3277 (2.2%) patients had a discoid meniscus. 33/72 (45.8%) patients were identified that satisfied the inclusion and exclusion criteria. Patient age ranged from 2 to 17 years with a mean of 10.4 years. Average follow up was 30.4 months with a range of 1.3 to 144.3 months. The average CC dimension was 7.6mm (±2.9) on coronal imaging. Average transverse dimension was 18.9mm (±4.3). 17/33 (51.5%) had intra-substance degenerative signal. 22/33 (66.7%) of patients had chronic pain, 22/33 (66.7%) of patients had mechanical symptoms, and 8/33 (24.2%) of patients required surgery for either symptom relief or subsequent progression to tear. Intrasubstance degenerative signal was found significantly more in the patients requiring surgery (p=0.019). Cranio-caudal dimension neared statistical significance for predicting chronic pain and mechanical symptoms (p=0.10, p=0.13 respectively).
Conclusions: Preliminary results of our ongoing study demonstrate that intrasubstance degenerative signal in discoid menisci was found more often in patients requiring surgery. Of the size characteristics, greater craniocaudal sizes neared statistical significance to correlate with mechanical symptoms and chronic pain.