The outcomes of Perthes' disease of the hip: a study protocol for the development of a core outcome set

Perthes' disease is an idiopathic osteonecrosis of a developmental hip that is most frequent in Northern Europe. Currently, the absence of a common set of standardised outcomes makes comparisons between studies of different interventions challenging. This study aims to summarise the outcomes used in clinical research of interventions for Perthes' disease and define a set of core outcomes (COS) to ensure that the variables of primary importance are measured and reported in future research studies investigating Perthes' disease.

A systematic review of the current literature will be used to identify a list of outcomes reported in previous studies. Additional important outcomes will be sought by interviewing a group of children with Perthes' disease, adults who were treated with the disease in infancy and parents of children with the disease. This list will then be evaluated by experts in Perthes' disease using a Delphi survey divided into two rounds to ascertain the importance of each outcome. The final outcomes list obtained from the Delphi survey will be then discussed during a consensus meeting of representative key stakeholders in order to define the COS to be reported in future clinical trials related to Perthes' disease.

The absence of high-quality research and clear guidelines concerning the management of Perthes' disease is, at least in part, due to the difficulties in the comparing the results from previous studies. The development of a COS seeks to standardise outcomes collected in future research studies to enable comparisons between studies to be made and to facilitate meta-analyses of results.

Core Outcome Measures in Effectiveness Trials Initiative (COMET), 1003 . Registered on 20 July 2017. Prospero International Prospective Register of Systematic Reviews, CRD 42017069742 . Registered on 10 July 2017.