Nonsensus in the treatment of proximal humerus fractures: uncontrolled, blinded, comparative behavioural analysis between Homo chirurgicus accidentus and Macaca sylvanus

OBJECTIVE: To investigate the inter-rater reliability of Barbary macaques compared with an expert group of surgeons for the choice of treatment and predicted outcome of proximal humerus fractures. DESIGN: Uncontrolled, blinded, comparative behavioural analysis. SETTING: Germany and United States. PARTICIPANTS: 10 blinded experts in the field of orthopaedic trauma surgery (Homo chirurgicus accidentus), with special focus on upper extremity surgery from Germany and the US, and five Barbary macaques (Macaca sylvanus) from a semi-free range enclosure. MAIN OUTCOME MEASURES: The reliability of agreement between raters assessed with Fleiss’ ĸ. RESULTS: Barbary macaques seem to have inferior inter-rater reliability in comparison with experts for choice of treatment (non-surgical v surgical), but for the geriatric age group most frequently affected by proximal humeral fractures, they performed similarly to the experts in their choices of treatment and choice of surgical procedure. Agreement about predicted outcome was poor among the macaques and slight among the experts. All experts almost always predicted the outcome incorrectly and tended to underestimate it. While only 4 (4.4%) of 90 experts’ predictions were correct, 13 (28.9%) of 45 macaques’ predictions were correct. CONCLUSIONS: Consensus on treatment and expected outcomes of proximal humeral fractures is lacking even beyond the human species. Although Barbary macaques tend to predict the clinical outcome more accurately, their reliability to assist surgeons in making a consistent decision is limited. Future high quality research is needed to guide surgeons’ decision making on the optimal treatment of this common injury.