Mucoid degeneration of the anterior cruciate ligament: MRI, clinical, intraoperative, and histological findings.

PURPOSE: To describe the clinical, MRI, intraoperative, and histological features of mucoid degeneration of the anterior cruciate ligament (ACL). METHODS: This study included 10 patients (average age 47 years, range 19-69 years) who underwent surgery due to clinical diagnoses of mucoid degeneration of the ACL. All patients underwent preoperative magnetic resonance imaging (MRI) and were arthroscopically treated. RESULTS: All 10 patients reported preoperative posterior knee pain. MRI indicated a thickened ACL with increased signal on all sequences. Postoperatively, only six of 10 patients were confirmed by biopsy to have a mucoid degeneration of the ACL. An associated intraosseous tibial cyst or ganglion was observed only in patients with a definitive diagnosis of mucoid degeneration. CONCLUSIONS: Mucoid degeneration of the ACL can be suspected in patients with posterior knee pain associated with a thickened ACL. Associated findings such as an intraosseous tibial or ganglion cyst help to rule out differential diagnosis.