RESUMEN
Background: The purpose of the study was to evaluate interand intra-observer reproducibility of Mason Johnston classification of radial head fractures in adults. Materials and Methods: Thirty radiographic images of radial head fractures (anteroposterior and lateral views) from adult patients were examined by five professionals in the field of Orthopaedics and Traumatology, including an expert member of the Brazilian Society of Orthopaedics, an experienced orthopaedic surgeon specialising in the elbow and shoulder, and three resident physicians (one each in the 1st, 2nd and 3rd years of residency at an Orthopaedics and Trauma unit). Inter- and intra-observer concordances were assessed using the kappa coefficient of agreement (κ). Results: The intra-observer reproducibility of the Mason Johnston classification system ranged from moderate to good whilst the inter-observer agreement varied from weak to good. Conclusion: The Mason Johnston´s classification system, although used throughout the world, possesses questionable reproducibility with respect to the assessment of radial head fractures. The level of professional expertise did not influence the outcome of the study.