Inter-rater agreement of rotator cuff tendon and muscle MRI parameters evaluated preoperatively and during the first postoperative year following rotator cuff repair

Abstract Background MRI is standard-of-care for rotator cuff evaluation, with clinical interpretation usually limited to qualitative judgments. The reliability of MRI–based measurements and scoring systems have been evaluated only preoperatively or ≥6 months following rotator cuff repair (RCR) when repairs are in the later stages of healing. This study describes the MRI assessments and inter-rater agreement of various rotator cuff tendon and muscle parameters evaluated preoperatively and four times during the first postoperative year. Methods Two musculoskeletal radiologists independently assessed MRI scans of 42 patients preoperatively and 3, 12, 26 and 52 weeks after RCR. Using standardized reading rules, readers assessed tendon integrity (5-point Sugaya), tear dimensions, muscle fat (5-point Goutallier) and atrophy (4-point Warner), muscle cross-sectional areas and myotendinous junction (MTJ) distance. Raw exact agreement proportions, kappa statistics, and correlation coefficients were used to quantify inter-rater agreement. Results Readers showed moderate to substantial above-chance agreement in scoring RC tendon integrity and supraspinatus muscle atrophy, good to excellent agreement on tear dimensions and muscle cross-sectional areas, but only fair to moderate agreement for fatty infiltration and MTJ distance. Only fatty infiltration grades evidenced observer bias. Inter-rater agreement did not appear time dependent. Conclusion Using defined reading rules in a research setting, MRI evaluations of RC tendon integrity, tear dimensions, muscle atrophy and cross-sectional areas have reasonable reliability at all time points in the first postoperative year. However, the presence of clinically significant disagreements, even in such favorable circumstances, indicates need for improved imaging tools for precise rotator cuff evaluation.