Discoid medial meniscus: report of four cases and literature review

Discoid medial meniscus is a rare abnormality, with incidence estimated at 0.12%. The present study describes this congenital abnormality anatomically and reports clinical results in four symptomatic cases managed by surgery.

A retrospective study included three patients (2 female, 1 male), one of whom had bilateral pathology. Mean age at consultation was 18.5 years (range, 13 to 28 yrs). Presenting symptoms were knee pain, associated with acute locking (1 case) or recurrent effusion (1 case). Plain X-rays were normal. MRI found discoid medial meniscus in all four cases, with intrameniscal hypersignal on T2-weighted sequences.

Arthroscopy confirmed the discoid abnormality of the medial menisci. Meniscal tear was systematically associated: horizontal in two cases and vertical in the other two. Three cases showed insertion defect of the anterior horn of the discoid medial meniscus. All two cases were managed by meniscoplasty, removing the central part of the meniscus and sparing its peripheral part. Meniscal repair was associated in one case. Subjective results were assessed by KOOS score. At a mean 23 months' follow-up (range, 7 to 54 months), mean KOOS score was 82.7 (range, 77.6 to 86.4): 88 ± 5 for pain, 89 ± 8 for other symptoms, 98 ± 1 for function, 69 ± 17 for sports activity, and 69 ± 16 for quality of life.

Symptomatic discoid medial meniscus is frequently associated with bone insertion abnormality of the anterior horn. Meniscal tear is consistently present and revelatory, indicating meniscal tissue fragility, as in the lateral meniscus. Meniscoplasty, possibly with associated meniscal repair if the remaining meniscal wall is unstable, provides satisfactory but imperfect results while avoiding total meniscectomy, which would be disabling in this age group.