Methods

The study follows the guidelines of the COMET-Initiative (Core Outcome Measures in Effectiveness Trials). A systematic review of the literature was performed to identify a list of outcomes reported in previous studies, which was supplemented by a qualitative study exploring the experiences of families affected by Perthes’ disease. Collectively, these outcomes formed the basis of a Delphi survey (two rounds), where 18 patients with Perthes’ disease, 46 parents, and 36 orthopaedic surgeons rated each outcome for importance. The International Perthes Study Group (IPSG) (Dallas, Texas, USA (October 2018)) discussed outcomes that failed to reach any consensus (either ‘in’ or ‘out’) before a final consensus meeting with representatives of surgeons, patients, and parents.