Clinical Features and Operative Treatments of Discoid Medial Meniscus in Children

BACKGROUND: The discoid medial meniscus is a rare congenital anomaly of the knee. The literature on discoid medial menisci is limited, with few reported cases in children. PURPOSE: To report the clinical manifestations and operative treatments of discoid medial menisci in children from multiple centers in North America. METHODS: A retrospective review of medical records including operative reports was performed to identify patients diagnosed with a discoid medial meniscus confirmed via direct surgical observation across eight children’s hospitals between January 2000 and March 2020. RESULTS: Twenty-one patients (9 female, 12 male) with 22 discoid medial menisci were identified, one with bilateral discoid medial menisci. The mean age at time of diagnosis was 12.7 years (range, 3-18 years). One patient had discoid medial and discoid lateral menisci in the same knee. The most common symptoms and signs of patients with a discoid medial meniscus were locking and/or clunking, present in over 50% of patients. Twelve discoid medial menisci were complete (55%), 8 were incomplete (36%), and two were indeterminate (9%). Tears were present in 13 knees. Of those with tears, 7 were horizontal tears (4 posterior, 1 anterior, and 2 mid-body), 5 were complex (3 posterior, 1 anterior, and 1 mid-body), and 1 was a posterior vertical tear. Five of these discoid medial menisci were unstable (23%). The average time between initial diagnosis and treatment was 13 months (range, 0-121 months). All knees underwent arthroscopic saucerization, and of the 13 torn discoid medial menisci, 7 were repaired (54%). The mean length of clinical follow-up postoperatively was 24 months (range, 1-82 months). Four of these discoid medial menisci underwent re-operation, most commonly for persistent symptoms. All knees which required re-treatment initially presented with a tear, all of which had been repaired. There was a significant association between initial presence of a tear and need for re-operation, [χ(2) = 4.1, p = 0.044]. CONCLUSIONS: In this multicenter study of patients treated for a discoid medial meniscus, symptoms and signs at presentation and findings at arthroscopy were similar with those commonly seen in patients with a discoid lateral meniscus. Tears were present in more than half of knees, and reoperation was more common in knees identified with tears of their discoid medial menisci than those without tears. Future studies should seek to determine the long-term functional and patient-reported outcomes following treatment of discoid medial menisci.