Mucoid degeneration of the anterior cruciate ligament

PURPOSE: Mucoid degeneration of the anterior cruciate ligament (ACL) is not a well-known entity. Only 1 case of mucoid degeneration of the ACL has been reported in the English-language literature. This article describes 5 cases of mucoid degeneration of the ACL with clinical features, magnetic resonance imaging (MRI) findings, and a method of arthroscopic management of these cases. TYPE OF STUDY: Case series. METHODS: Over a period of 21 months from 1999 to 2001, 5 patients were diagnosed to be suffering from mucoid degeneration of the ACL using MRI, histopathologic, and arthroscopic criteria. All patients presented with progressive knee pain and restriction of flexion without history of a significant trauma or instability preceding the symptoms. MRI showed an increased signal in the substance of the ACL both in the T1- and T2-weighted images, with a mass-like configuration that was reported as a partial or complete tear of the ACL by most radiologists. At arthroscopy, the ACL was homogenous, bulbous, hypertrophied, and taut, occupying the entire intercondylar notch. The ligamentum mucosum was absent in all patients. A debulking of the ACL was performed by a judicious excision of the degenerate mucoid tissue, taking care to leave behind as much of the intact ACL as possible. Releasing it and performing a notchplasty treated impingement of the ACL to the roof and lateral wall. The ACL was not fully excised in any of the patients. RESULTS: All patients were pain free and had recovered full flexion except one who experienced painful flexion beyond 120 degrees. None of the patients showed symptoms of instability. Postoperative MRI performed after at least 12 months in 2 patients showed some intact ACL fibers in a now-thinned ACL mass. CONCLUSIONS: Mucoid degeneration of the ACL is a clinical condition afflicting active middle-aged people without a single significant traumatic episode with a specific MRI picture. They respond well to a judicious arthroscopic release of the ACL with notchplasty. LEVEL OF EVIDENCE: Level IV.