Discoid medial meniscus completely coalesced with the anterior cruciate ligament

Discoid meniscus is an abnormality of the knee in which the meniscus is discoid rather than semilunar in shape. Medial discoid menisci are rare, and no specific associated symptoms suggest this condition. Several medial meniscus anomalies, including discoid variants, have been reported in the literature. This article describes a rare case of medial discoid meniscus completely coalesced with the anterior cruciate ligament (ACL). A 22-year-old man presented with intermittent right knee pain of 6 months' duration. Physical examination revealed mild wasting of the quadriceps with medial joint line tenderness but no effusion. Radiographically, hypoplasia of the lateral tibial spine, increased medial joint space, and increased concavity of the medial tibial condyle were noted in both knees. Arthroscopic examination revealed a complete discoid medial meniscus that was contiguous with the ACL. On probing, a horizontal tear in the medial meniscus was noted. A meniscectomy was performed, and deep longitudinal furrows with exposed subchondral bone were noted underlying the posteromedial tibial condyle. At the patient's 6-month follow-up visit, he had no knee symptoms and had returned to his daily activities, which included jogging. Discoid medial meniscus is a rare anomaly, and this case represents only the second reported in the literature of discoid medial meniscus completely coalesced with ACL. This case supports the theory that the ACL and menisci can be differentiated from 1 mesenchyme.