Mucoid Degeneration of the Anterior Cruciate Ligament Treated with Selective Arthroscopic Debridement: A Case Report with 54-Month Follow-Up

Background and Clinical Significance: Anterior cruciate ligament (ACL) mucoid degeneration is a rare, non-traumatic condition characterized by the deposition of mucoid material within the ligament, resulting in hypertrophy and potential impingement against surrounding intra-articular structures; Case Presentation: A 43-year-old man presented with knee pain, swelling, and restricted range of motion. Magnetic resonance imaging demonstrated mucoid degeneration of the ACL associated with mild articular degenerative changes, without evidence of a meniscal tear. Following the failure of conservative management, the patient underwent knee arthroscopy. Intraoperative findings revealed an enlarged ACL with impingement against the intercondylar notch and the lateral femoral condyle. The patient was treated with arthroscopic ACL debridement, which resulted in adequate decompression. At the 54-month follow-up, the patient remained pain-free, had regained full range of motion, and showed no clinical instability. The Lysholm score improved from 41 preoperatively to 95 postoperatively; Conclusions: Mucoid degeneration of the ACL is a rare but important cause of knee pain and restricted range of motion. When conservative treatment fails, arthroscopic management can provide symptom resolution and restore range of motion. However, careful preservation of healthy ACL fibers during debridement is a key technical consideration for achieving symptom relief while maintaining ligament function and knee stability. This case suggests that selective arthroscopic debridement may provide sustained symptom relief while preserving ACL stability in patients with isolated symptomatic mucoid degeneration, with favorable outcomes maintained at long-term follow-up.