Stable valley-like concavity at the midbody of the medial meniscus mimicking meniscocapsular separation: a case report

A 39-year-old woman presented with catching, pain during deep knee flexion, and intermittent locking. Magnetic resonance imaging showed no definite meniscal tear, and diagnostic arthroscopy was performed. Arthroscopy revealed hypermobility of the posterior horn of the lateral meniscus with no tear identified. This hypermobility was considered the source of the patient's mechanical symptoms and was stabilized with three all-inside sutures. In addition, systematic inspection of the medial compartment incidentally identified a smooth, well-demarcated valley-like concavity at the meniscocapsular junction, predominantly involving the midbody of the medial meniscus and extending to the anterior segment. The peripheral rim appeared cliff-like, and the capsule was continuous beyond the concavity, which created a separation-like appearance. However, probing and dynamic assessment did not reproduce gapping, abnormal translation, or impingement, and there were no corresponding medial symptoms. Therefore, the concavity was left untreated. At 24 months postoperatively, symptoms had not recurred, and the Knee injury and Osteoarthritis Outcome Score was 100 in all subscales, with no complications or reoperation. A stable valley-like concavity at the medial meniscocapsular junction can mimic meniscocapsular separation but may remain asymptomatic and dynamically stable. Repair decisions should be guided by symptom correlation and arthroscopic dynamic stability rather than morphology alone.