A new magnetic resonance imaging grading system for anterior cruciate ligament myxoid degeneration in osteoarthritis of the knee

Abstract

BackgroundThis study aimed to investigate association between magnetic resonance imaging (MRI) and histological findings of degenerated anterior cruciate ligament (ACL) in knee osteoarthritis (OA), and based on this result, to develop a new ACL degeneration grading system by MRI that corresponds to histological findings of degenerated ACL. HypothesisMRI signal intensity of the ACL could correspond to histological findings of collagen degeneration. Patients and methodsA collection of 106 ACL specimens from 85 patients who underwent primary total knee arthroplasty was investigated for signal intensity of the ACL and muscle on axial Fat-saturated proton density-weighted MRI and MRI signal intensity ratio (ACL/muscle) was calculated. The correlation between ACL histological degeneration and MRI ACL/muscle signal intensity ratio was analyzed. The ACL was stratified into 3 grades based on signal intensity relative to muscle intensity (grade 1, low; grade 2, iso; and grade 3, high), and the extent to ACL degeneration in each MRI ACL degeneration grade was evaluated. ResultsCollagen degeneration (53.5±24.0%) and myxoid change (25.2±18.8%) in degenerated ACL significantly correlated with MRI signal intensity ratio of the ACL/muscle (r=0.62, p<0.0001; r=0.67, p<0.0001). ACL were assigned to grade 1 (n=22 [20.8%]), grade 2 (n=56 [52.8%]), and grade 3 (n=28 [26.4%]). ACL collagen degeneration was 34.8±18.4% in grade 1, 49.3±21.7% in grade 2, and 76.6±12.0% in grade 3. ACL myxoid change was 10.0±11.3% in grade 1, 21.3±14.1% in grade 2, and 45.0±15.3% in grade 3. DiscussionThe ACL/muscle signal intensity ratio on MRI correlated with the extent to ACL myxoid degeneration. The new MRI ACL degeneration grade is helpful to estimate the extent to ACL myxoid degeneration in knee OA. Level of evidenceIII; retrospective cohort study.