Mucoid degeneration of the anterior cruciate ligament (ACL) is a little-known entity. The clinical presentation is one of posterior pain with limited flexion. Its interstitial nature within the ACL structure contrasts with synovial cyst of the ACL. Arthroscopic treatment may include ACL resection, which raises the questions about the harmlessness of this procedure and the risk of anterior instability.

Arthroscopic resection of ACL mucoid degeneration is effective for treating pain and flexion limitation, but at the expense of anterior laxity.

This bicentric, retrospective cohort study with an average follow-up of 6years involved 27 patients (29 knees) presenting with symptomatic ACL mucoid degeneration validated by magnetic resonance imaging (MRI). Noninfiltrating synovial cysts of the ACL were excluded. Average patient age was 49 (22 to 68) years. Preoperative assessment included a questionnaire, clinical examination (Lachman and pivot shift tests), MRI and standard radiography. Arthroscopic examination analyzed the ACL aspect and its associated lesions (meniscus, cartilage). Anatomopathology samples were collected in 18 cases. Postoperative follow-up included standard radiography and dynamic examination, measuring laxity with a Telos™ device.

Pain was posterior in 23 knees (80%). Fourteen knees (48%) had limited flexion, on average 97°. Twelve partial and 17 total resections were performed. Twenty knees (69%) had associated cartilaginous lesions and 19 (66%) had meniscal lesions. Meniscectomy was undertaken in 11 cases (41%). Posterior pain disappeared in 27 cases (93%), on average 3.7weeks after the procedure. Average improvement in flexion was 21.5° (0 to 60°). Twenty-eight knees (97%) showed soft and/or delayed stops on postoperative Lachman testing. Average postoperative differential laxity on the Telos™ device was 8.3mm (5 to 13mm). Average postoperative International Knee Documentation Committee (IKDC) and Knee Injury and Osteoarthritis Outcome Scores (KOOS) were 71.2 (42.5 to 92.0) and 78.2 (26.4 to 99). Two patients uderwent secondary ligamentoplasty.

Treatment of ACL mucoid degeneration by arthroscopic resection is effective for posterior pain and flexion limitation. It results in postoperative laxity, but rarely in frank instability. Therefore, indications for ACL resection must be carefully selected. Young and active patients should be warned about the risk of requiring secondary ligamentoplasty.

IV (retrospective cohort study).