Double-Layered Lateral Meniscus Including a Ring-Shaped Accessory Meniscus: A Case Report.

CASE:We report the rare case of a double-layered lateral meniscus that was comprised of a normal meniscus and a ring-shaped accessory meniscus. An 11-year-old boy presented with left knee pain, and magnetic resonance imaging initially was interpreted as showing a horizontal meniscal tear. However, arthroscopic exploration revealed a double-layered meniscus. A superior accessory meniscus was fused with the inferior normal meniscus at the posterior horn and had more mobility compared with the normal meniscus. The symptoms improved substantially after resection of the superior accessory meniscus. The patient returned to sports at 4 months postoperatively; at 15 months postoperatively, radiographs demonstrated no evidence of degenerative changes. CONCLUSION:A double-layered lateral meniscus that includes a ring-shaped accessory meniscus is a rare abnormality that can be corrected arthroscopically by resection of the accessory meniscus.