The Gluteal Muscles in End-stage Osteoarthritis of the Hip: Intra- and Interobserver Reliability and Agreement of MRI Assessments of Muscle Atrophy and Fatty Degeneration

Aim: To assess the intra- and interobserver reliability and agreement of muscular atrophy and fatty degeneration of the gluteal muscles on magnetic resonance imaging (MRI) in patients with end-stage osteoarthritis of the hip.

Materials And Methods: Thirty-nine patients with end-stage osteoarthritis of the hip, who scheduled for hip replacement surgery, were included in the study. The cross-sectional areas of the gluteus medius and minimus muscles were manually circumscribed and automatically calculated, while intramuscular fatty degeneration was assessed using the semi-quantitative classification system of Goutallier. Two independent observers performed all the evaluations.

Results: Good agreement and excellent reliability were found for the cross-sectional areas of the gluteus medius and gluteus minimus (intraclass correlation coefficient [ICC] for intra-observer 0.97 and 0.93, ICC for interobserver 0.98 and 0.95). Fair reliability was found for fatty degeneration of the gluteus muscles (mean kappa 0.23 and mean prevalence-adjusted kappa 0.53). The average proportion of agreement for the raters was 0.71.

Conclusion: The present study demonstrated substantial agreement and excellent intra- and interobserver reliability for the measurements of the cross-sectional areas of the gluteus medius and gluteus minimus. Assessment of fatty degeneration had fair intra- and interobserver reliability, but acceptable agreement.