Factors associated with trial recruitment and retention of people with osteoarthritis: analysis of 215 randomised controlled trials from 2013-2021

Background
The prevalence of osteoarthritis (OA) increases with age, growing by approximately three percent annually. There are multiple treatment options available to reduce symptoms, including pharmacological, non-pharmacological, surgical and alternative interventions. Research is paramount to ensure this growing population has access to evidence-based interventions. High attrition (greater than 20%) and failure to recruit a predetermined sample size for statistical power result in inefficient trial designs, delaying or preventing answers to the original clinical questions with adequate power and precision.

Aims
To identify recruitment and retention rate in randomised controlled trials (RCTs) recruiting individuals with hip or knee osteoarthritis (OA) and to determine the factors that influence these rates.

Material and methods
PubMed search identified RCTs published between 2013 and 2021 that involved people with hip or knee OA. Regression analyses determined factors related to participants and the trial that may have affected recruitment or retention rates.

Results
215 RCTs were included in the study. Mean recruitment rate was 63.2%. Mean follow-up rate was 88.4%. Trials had higher recruitment rates if publicly-funded (Odd Ratio (OR): 1.47; 95% Confidence Intervals (CI: 1.12, 1.92), did not recruit individuals with medical comorbidities (OR: 0.55; 95% CI: 0.41, 0.73), offered a drug intervention as their experimental intervention (OR: 0.50; 95% CI: 0.29, 0.88), recruited from hospitals (OR: 1.42; 95% CI: 1.07, 1.80), and had shorter follow-up durations (OR: 0.95; 95% CI: 0.91, 0.99). Trials had higher retention rates if their experimental group had lower baseline pain scores (OR: 1.20; 95% CI: 1.02, 1.41), control group had higher pain scores (OR: 0.84; 95% CI: 0.72, 0.99), were recruited from fewer sites (OR: 0.98; 95% CI: 0.96, 0.99), with shorter follow-up durations (OR: 0.96; 95% CI: 0.92, 0.99).

Conclusions
Factors that impact patient recruitment and retention rates in OA RCTs include: funding source, baseline pain levels, comorbidity status, location and number of recruitment sites and follow-up duration. These factors should be considered when conducting future OA RCTs.