Anomalies of the discoid medial meniscus

Anomalies associated with a discoid medial meniscus have been described. However, the clinical relevance of these anomalies has not been previously reported. Therefore, we report the clinical relevance of some of these anomalies based on our experience with a 21-year-old soldier with a 3-month history of medial right knee pain. Magnetic resonance imaging (MRI) revealed bilateral discoid medial menisci, cupping of the medial tibial plateau, and an abnormal anteroinferior transposition of the anterior horn of the meniscus. Partial meniscectomy was performed in the usual manner and the meniscus reshaped, including its anteromedial corner. Six weeks postoperatively, the patient reported knee pain. Follow-up MRI showed that the anteromedial edge of the cup shaped tibial plateau directly contacted the femoral condyle and subchondral signal changes at the contact point. Several reports have addressed subluxation or dislocation of the anterior horn of the medial meniscus. However, the clinical significance of these lesions has not been clearly defined. In our case, however, subluxation of the anterior horn was combined with a discoid medial meniscus and cupping of the tibial plateau, which may have increased contact stress between the tibia and femur. Our experience suggests that in cases with combined anomalies, anteroinferior transposition of the anterior horn of the discoid medial meniscus, and cupping of the tibial plateau, trimming of the anteromedial corner should be performed conservatively, because even minimal trimming or reshaping of anteromedial corner of the meniscus can cause direct bone-to-bone contact due to insufficient anterior coverage.