Comparing genuine and sham surgery for sacroiliac joint pain using self-assessments, pain testing, and neuroimaging

Contrasting active treatment against a placebo has long been the gold standard in clinical medicine. The possible impact of placebo responses in surgery has recently been investigated using sham surgery. Despite indications that both genuine and placebo surgeries may lead to positive outcomes, no investigation into the differential routes to improvement has been performed.

To assess the mechanisms involved in improvements seen in patients with sacroiliac joint pain who undergo genuine or placebo surgery.

This randomized controlled trial incorporated both subjective and objective assessments, including functional magnetic resonance imaging and experimental pain testing, at baseline and 6-month follow-up in a surgical trial including patients with chronic pain. Twenty-three patients were randomized to receive genuine surgery (sacroiliac joint fusion) or placebo (sham). An additional 7 patients were included as observational controls.

There was a significant reduction in weekly pain intensity for both the genuine and placebo groups at follow-up, with greater reductions in the genuine group compared with placebo (P = 0.04). The difference was driven by a few "super-responders" in the genuine group. Clinical improvements correlated with experimental pain outcomes at the operated sacroiliac joint. Functional brain connectivity between the somatosensory cortex and the default mode network decreased more in the genuine group compared with the placebo group.

Preliminary findings indicate decreased connectivity between somatosensory and default mode networks for patients in the genuine vs sham group, demonstrating the first findings of differential neural processing in pain-relevant brain networks after genuine vs placebo surgery using objective measures. Understanding the active mechanisms of surgery may lead to personalized treatments, more effective pain reduction, and less side effects for patients with pain.