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Background: Randomized controlled trials (RCTs) are the most reliable way of evaluating the effect of new treatments by comparing them with previously accepted treatment regimens. The results obtained from an RCT are extrapolated from the study environment to the general health care system. The ability to do so is called external validity. We sought to evaluate the external validity of an RCT comparing the results of total hip arthroplasty with those of hemiarthroplasty for the treatment of displaced femoral neck fractures in patients ≥80 years of age.

Methods: This prospective, single-center cohort study included 183 patients ≥80 years of age who had a displaced femoral neck fracture. All patients were screened according to the inclusion and exclusion criteria for an RCT comparing total hip arthroplasty and hemiarthroplasty. The population for this study consisted of patients who gave their informed consent and were randomized into the RCT (consenting group, 120 patients) as well as those who declined to give their consent to participate (non-consenting group, 63 patients). The outcome measurements were mortality, complications, and patient-reported outcome measures. Follow-up was carried out postoperatively with use of a mailed survey that included patient-reported outcome questionnaires.

Results: We found a statistically significant and clinically relevant difference between the groups, with the non-consenting group having a higher risk of death compared with the consenting group. (hazard ratio, 4.6; 95% confidence interval, 1.9 to 11.1). No differences were found between the groups in terms of patient-reported outcome measures or surgical complications.

Conclusions: This cohort study indicates a higher mortality rate but comparable hip function and quality of life among eligible non-consenters as compared with eligible consenters when evaluating the external validity of an RCT in patients ≥80 years of age with femoral neck fracture.

Level of Evidence: Therapeutic Level II. See Instructions for Authors for a complete description of levels of evidence.