How many sites should an orthopedic trauma prospective multicenter trial have? A marginal analysis of the Major Extremity Trauma Research Consortium completed trials.

"Declarations Ethics approval and consent to participateAll the underlying trials analyzed were approved by an IRB at the corresponding author’s home institution: Johns Hopkins Bloomberg School of Public Health (IRB: FWA 00000287). Consent for publicationNot applicable. Competing interestsThe authors declare that they have no competing interests. Competing interests The authors declare that they have no competing interests."

"Funding This work was supported by the Department of Defense Peer Reviewed Orthopaedic Research Program [grant numbers W81XWH-09-2-0108, W81XWH-10-2-0090, W81XWH-12-1-0588, W81XWH-10-2-0134, W81XWH-15-2-0074, W81XWH-10-2-0133] and the National Institutes of Health, National Institute of Arthritis and Musculoskeletal and Skin Diseases [grant number R01AR064066]. The funding bodies had no role in writing the manuscript or in the design of the study and collection, analysis, and interpretation of the data."

"Trial registration Please see Table 1 for individual trial registration numbers and dates of registration."