Clinical presentation, MRI and clinical outcome scores do not accurately predict an important meniscal tear in a symptomatic discoid meniscus.

PURPOSE: Discoid menisci can be symptomatic from instability or a tear. A torn discoid meniscus is likely to require repair to preserve meniscal function and should not be missed. This is the first study to evaluate a range of pre-operative methods to predict the likelihood of a torn discoid meniscus. METHODS: A retrospective analysis of prospectively collected data was performed. Clinical, radiographic and operative data were reviewed. Patients were grouped based on the presence of a tear or not during surgery. All patients underwent MRI scans pre-operatively which were validated with arthroscopy findings to calculate sensitivity. All patients completed Pedi-KOOS and Pedi-IKDC pre-operative scores. RESULTS: There were 32 discoid menisci in 27 patients. Mean age at surgery was 10.4 years (6-16). Nineteen patients were female. Seventeen menisci were identified as torn at time of arthroscopy (53%), 15 were unstable but not torn. Clinical findings did not differentiate between the torn or unstable menisci. MRI was only 75% sensitive and 50% specific at identifying a torn discoid meniscus. There was no statistical difference between KOOS-child (n.s.) and Pedi-IKDC (n.s.) scores between the groups. CONCLUSION: MRI is neither sensitive nor specific at identifying tears in discoid menisci. There is no difference in pre-operative outcome scores for patients with a torn or unstable discoid meniscus; pre-operative PROMs are a poor predictor of a meniscal tear. This study emphasises that pre-operative tests and clinical findings are not conclusive for identifying a meniscal tear and the operating surgeon should be vigilant in identifying and repairing tears at the time of surgery. Pre-operative findings poorly correlate to arthroscopic findings and potential surgical interventions required. Patients and parents/carers should, therefore, be appropriately counselled prior to surgery that post-operative measures are dependent on intra-operative findings and not pre-operative findings in patients. LEVEL OF EVIDENCE: III.