BACKGROUND: Radial meniscal tears (RMTs) interrupt circumferential collagen fibers, disrupt hoop stress transmission, and accelerate compartmental cartilage wear. Despite their clinical and biomechanical importance, reporting remains inconsistent because widely used taxonomies are heterogeneous and often assessed with nominal agreement statistics that overlook the ordered nature of tear morphology.
PURPOSE: To (1) quantify the interobserver and intraobserver reliability of a 5-type morphology-based classification system for RMTs using ordinal agreement metrics and (2) evaluate criterion validity against arthroscopy and construct validity against a prespecified morphology→treatment matrix.
METHODS: A harmonized case bank of 400 unique RMTs (80 per type I-V; 55.0% medial and 45.0% lateral) was assembled across 5 centers. There were 7 expert knee surgeons (>10 years' experience) who performed test-retest classifications at T1 and T2 (mean washout time, 24.7 ± 3.6 days); a broader panel of 40 knee surgeons (>10 years' experience) conducted classifications at T1 only. Raters were blinded; used a 1-page atlas with explicit criteria (depth/extent, gap thresholds of ≤3/>3 mm, vascular zone); and recorded type (I-V), confidence (Likert), and recommended treatment. The primary endpoint was the Light kappa (κ) (mean of pairwise Cohen κ; quadratic weighting) with bootstrap 95% confidence intervals (CIs) (5000 resamples, stratified by type). The coprimary endpoint was the Gwet AC2 (ordinal). Criterion validity was determined using an arthroscopy-referenced subcohort (n = 260). Construct validity examined concordance between assigned type and the prespecified treatment matrix. Secondary endpoints included exact agreement and ±1-category agreement, the Fleiss κ (nominal), and subgroup analyses (compartment, gap magnitude).
RESULTS: Interobserver ordinal agreement was high (Light κ = 0.902 [95% CI, 0.889-0.914]) (AC2 = 0.918 [95% CI, 0.906-0.929]). Agreement was stable by compartment (medial: κ = 0.897; lateral: κ = 0.909) and gap magnitude (no/≤3 mm: κ = 0.907; >3 mm: κ = 0.893). Exact agreement was 83.5%, and ±1-category agreement was 96.8%; nonadjacent misclassifications were 3.2%, with a predictable boundary at type III↔IV. Intraobserver reliability among experts was excellent (mean weighted Cohen κ = 0.913 [range, 0.882-0.942]). Criterion validity versus an arthroscopic reference was strong (weighted κ = 0.887 [95% CI, 0.871-0.902]). Construct validity showed 86.2% exact agreement (κ = 0.842; AC1 = 0.861). Sensitivity analyses (category collapsing, alternative weights, leave-one-rater-out) confirmed robustness.
CONCLUSION: This 5-type classification system demonstrated high reproducibility (ordinal κ≈ 0.90) and clinical validity, providing a practical framework for standardized reporting and treatment selection and a defensible stratification scheme for future trials and meta-analyses.
STUDY DESIGN: Cross-sectional study; Level of evidence, 3.
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