Background: Randomized clinical trials (RCT) are the most reliable way to evaluate theeffect of treatments by comparing them to previously accepted treatment regimes. The resultsobtained from a RCT are extrapolated from the study environment to the general health caresystem. This parameter is called external validity. The present study we sought to evaluatethe external validity of an RCT comparing the results of total hip arthroplasty tohemiarthroplasty in displaced femoral neck fracture in patients 80 years of age and above.
Methods: In a prospective cohort study, 267 patients (76% females, mean age 87 [SD] 4.7years) were included in the cohort study. All were screened according to the inclusion andexclusion criteria to be included in a RCT comparing total hip arthroplasty andhemiarthoplasty. Those who gave their informed consent and were randomized (RCT group,92 patients), those that were asked to participate in the RCT but would not give theirinformed consent (Non-consenters group, 54 patients) and all patients missed in the screeningprocess (Missed screening group, 121 patients). The primary end point was hip functionevaluated with Harris hip score at 1 year. Secondary end points included quality-of-lifeevaluated with EQ-5D mortality and hip re-operations. Follow up was performed at 1 yearpostoperatively by a mailed survey including patient reported outcome.
Results: We did not find any difference between the groups regarding HHS and EQ-5D, alsowhen adjusting for confounders. There was a statistically significant difference between thethree groups (p=0.047) as the Non-consenter group had a higher risk of death than thoseincluded (HR 2.06, 95% Cl 1.13 to 3.75). The rate of reoperation was lower in the MS groupcompared to the RCT and NC groups (4.1% vs 7.6% vs 9.3%). This difference did not reachstatistical significance when adjusting for confounders
Interpretation: This cohort study indicates a higher mortality rate but comparable hip functionand quality-of-life among eligible non-consenters compared to eligible consenters whenevaluating the external validity of a RCT patients with femoral neck fracture age 80 andabove.