Mucoid degeneration of the anterior cruciate ligament: a scoping review

Background Mucoid degeneration of the anterior cruciate ligament (MD-ACL) is an uncommon but increasingly recognised cause of atraumatic knee pain and terminal motion loss. Three earlier systematic reviews separately addressed management outcomes, debridement technique, and morphometric associations, but none integrated these domains with recent histopathological, transcriptomic, and longitudinal imaging evidence, while newer conservative-management reports have added limited preliminary clinical data. This scoping review aimed to map and synthesise the available evidence on MD-ACL across terminology, epidemiology, pathophysiology, histopathology, clinical presentation, imaging, differential diagnosis, arthroscopic findings, treatment, and outcomes. Methods PubMed/MEDLINE and Embase were searched from database inception to 31 January 2026, following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses extension for Scoping Reviews (PRISMA-ScR) and the framework of Arksey and O’Malley as refined by Levac et al. Studies reporting clinical, radiological, histopathological, operative, or outcome data on MD-ACL in human subjects were eligible. Two reviewers screened titles, abstracts, and full texts independently and in duplicate; disagreements were resolved by consensus involving a third reviewer. Findings were synthesised narratively. Results Fifty-four publications were included, comprising case reports ( n = 7), case series ( n = 12), retrospective cohort or comparative studies ( n = 20), prospective cohort studies ( n = 3), one controlled clinical trial, three systematic reviews, five technical notes, and three narrative reviews. MRI typically demonstrated a thickened, hyperintense but continuous ligament, often with the celery stalk sign. Increased posterior tibial slope was the most consistently replicated morphometric association, whereas findings on notch width index were less uniform. Concomitant meniscal and chondral pathology was common. Arthroscopic partial debridement, with or without notchplasty, generally improved pain and range of motion, but postoperative laxity became more likely with more extensive resection. Conclusions MD-ACL is a recognised cause of atraumatic posterior knee pain in middle-aged adults with an otherwise stable knee. Current data support an association with meniscal and cartilage pathology, but do not establish a causal link with osteoarthritis progression. Prospective comparative studies with standardised diagnostic definitions and outcome reporting are needed to guide treatment more definitively.