Mucoid degeneration of the anterior cruciate ligament: A step toward standardized classification

Objectives: This study aimed to develop and validate a novel MRI-based classification system of SHRINK (S-Sonal ; Shirodkar; R- Rajesh; I-Intakhab, Iyengar; N- Nathan, Neha; K- Kapil, Karthikeyan) for mACL to improve diagnostic consistency and facilitate communication between radiologists and orthopedic surgeons. Mucoid degeneration of the anterior cruciate ligament (mACL) is a non-traumatic condition characterized by myxoid changes within the ligament, leading to thickening without disruption. mACL often presents diagnostic challenges due to atypical symptoms and subtle imaging findings. Magnetic resonance imaging (MRI) plays a pivotal role in identifying hallmark features such as the “celery stalk” sign. However, no standardized classification system currently exists for this condition. Materials and Methods: In this retrospective study, 100 knee MRI scans were analyzed, encompassing normal anterior cruciate ligament and varying degrees of mACL. A 5-category classification system was proposed, differentiating based on the extent of femoral/tibial involvement, thickness increase, associated ganglion cysts, and bony abnormalities. Two independent musculoskeletal radiologists classified the scans, and inter-observer agreement was assessed using the intraclass correlation coefficient (ICC). Results: The proposed classification demonstrated good inter-observer reliability (ICC 0.679). Category 4 (mACL with ganglion cysts) was the most frequent, while tibial involvement (Categories 3a/3b) was rare. Minimal disagreement was observed between readers, validating the system’s reproducibility. Conclusion: The proposed system enhances diagnostic precision for mACL, bridging imaging findings with clinical management, and sets a foundation for future research. Limitations include the retrospective design and the need for validation in diverse cohorts.