Validation of the height-width measurement in Perthes disease among interpreters of different experience levels

The epiphyseal height and metaphyseal width ratio estimated lateral pillar involvement with limited generalizability among various interpreters. The aim of the study was to evaluate the reliability and the validity of height-width ratio measurement in Perthes disease among interpreters of different experience levels. A cross-sectional study was conducted between 2019 and 2020. We included four groups of interpreters: orthopaedic residents, orthopaedic fellows, radiology residents and radiology fellows who were unaware of radiographic study materials. Each interpreter blindedly evaluated Perthes hip radiographs twice at 1-month intervals using the height-width ratio method. Patients' and interpreters' characteristics, height-width ratio and height-width ratio converted to lateral pillar classification (A, B and C) were collected. Intra- and interobserver reliability validated with the paediatric orthopaedist were estimated. Twenty-four interpreters assessed 18 Perthes radiographs. Intraobserver level of agreement (95% confidence interval) for height-width ratio was 0.022 (-0.017 to 0.062), -0.027 (-0.074 to 0.019), -0.010 (-0.095 to 0.074) and 0.019 (-0.109 to 0.146); and interobserver reliability compared with the paediatric orthopaedist was -0.007 (-0.091 to 0.077), 0.003 (-0.056 to 0.061), -0.021 (-0.077 to 0.035) and -0.002 (-0.090 to 0.086) for orthopaedic residents and fellows, radiology residents and fellows, respectively. Kappa statistics of height-width ratio converting to lateral pillar classification indicated intraobserver agreement of orthopaedic residents and fellows, radiology residents and fellows was 0.83, 0.75, 0.54 and 0.91; and interobserver agreement compared with the paediatric orthopaedist was 0.92, 0.83, 0.42 and 0.83, orderly. Height-width ratio and lateral pillar estimation by orthopaedic and radiology trainees have moderate to excellent reliability. Level of evidence: Level II - diagnostic study.