Interim Findings from a Systematic Review on Patient Attrition over the past Two Decades of Spinal Surgical Trials

Introduction: Patient attrition refers to the loss of patients during follow-up, which lowers study power and can introduce bias, impairing the quality of the conclusions drawn. It is particularly important in spinal surgery trials investigating the long-term effects of interventions. In this systematic review, we investigated differences in attrition rates based on study design in all spinal surgery trials published over the last two decades.

Methods: MEDLINE and Embase databases were searched via Ovid to find articles relating to “prospective spinal surgery trials” between 2000 and 2023. Interventional spinal surgery studies reporting outcomes in adults published in English and in a peer-reviewed journal were included. Articles were excluded if they didn’t include attrition data, were not prospective spinal surgery trials, or involved patients with trauma, infection, or inflammatory disease. Data were extracted from each published article in relation to (i) study design characteristics, and (ii) patient numbers at each stage, which formed the basis of attrition calculations.

Results: A total of 2199 articles were discovered, after screening abstracts 1379 remained. So far 470 have been included for analysis. On average, patients were followed up an average of 4.2 times over a duration of 22 months. The overall attrition rate across these studies was 8.0%. LMIC-led studies (3.7%) had lower rates of attrition than HIC-led studies (9.56%). Studies funded by governmental grants and multi-centre trials had higher attrition rates (12.4% and 16.6%, respectively) than single-centre studies (5.6%). Increased follow-up duration correlated with increased attrition rates (r=0.25). However, attrition rates were not correlated with increased number of follow-ups (r=0.10), increased study size (r=0.10) or increased age (r=-0.07). Studies registered in a trial registry (8.8%) had similar attrition rates to those not registered (7.7%).

Conclusion : Spinal surgical trials had an attrition rate of 8.0%. Attrition rates were higher in studies across multiple sites, those funded by governmental grants and those with longer follow-up durations. LMIC-led studies had much lower attrition rates than HIC-led studies.