Mucoid degeneration of the anterior cruciate ligament: a case report.

Mucoid degeneration of the ACL is an unusual entity that has only been recently described. The imaging features of this entity have been described to a sufficient degree to provide diagnostic criteria, and its appearance can be characteristic. It is important to recognize this entity as a chronic process as its presentation and appearance can mimic a tear of the ACL. The etiology of mucoid degeneration of the ACL is unclear, but it may represent part of a continuum between early degeneration of the collagen fibrils of the ACL and frank formation of a ganglion cyst. The mucoid degeneration usually produces symptoms similar to those of an intra-articular mass, but pain may also be associated with this process. Treatment may require partial or complete resection of the ACL, but percutaneous aspiration of the fluid components of the affected ACL may also be effective at alleviating the associated symptoms.