Impact of surrogate outcomes in randomized controlled trials for shoulder rotator cuff tears

Surrogate outcomes are clinical endpoints that are used as substitutes for direct measures of how a patient feels, functions, or survives. The present study aims to analyze the impact of surrogate outcomes on the results of randomized controlled trials on shoulder rotator cuff tears disorders.

Randomized controlled trials (RCTs) related to rotator cuff tear conditions published up until 2021 were retrieved from the PubMed and ACCESSSS databases. The primary outcome of the article was considered a surrogate outcome when the authors used radiological, physiologic, or functional variables. The result of the article was considered positive when results supported the intervention based on the trial's primary outcome. We recorded the sample size, the mean follow-up, and the type of funding. Statistical significance was set at p < 0.05.

A total of 112 papers were included in the analysis. The mean sample size was 87.6 patients; mean follow-up period was 25.97 months. Thirty-six out of 112 RCTs used a surrogate outcome as a primary endpoint. More than half of papers using surrogate outcomes reported a positive finding (20 out of 36), while 10 out of 71 RCTs using patient-centered outcomes favored the intervention (14.08%, p < 0.001) [RR = 3.94 (95% CI 2.07-7.51)]. The mean sample size was smaller in trials using surrogate endpoints (75.11 vs 92.35 patients, respectively, p = 0.049), while the follow-up was shorter (14.12 m vs. 31.9 m, p < 0.001). Approximately 25% of the papers that reported surrogate endpoints (22.58%) were industry-funded projects.

The substitution of surrogate endpoints for patient-important outcomes in shoulder rotator cuff trials quadruplicates the chances of obtaining a favorable result that favors the analyzed intervention.