Effects of Tai Chi combined with transcranial direct current stimulation on pain relief and pain matrix in people with knee osteoarthritis: a randomized controlled neuroimaging trial

Background Pain in knee osteoarthritis (KOA) may induce neuroplastic adaptations within the pain matrix network, potentially leading to maladaptive alterations in nociceptive processing and pain perception. Studies suggested that both Tai Chi and transcranial direct current stimulation (tDCS) each alleviated pain by modulating the neural activity of the dorsolateral prefrontal cortex (DLPFC), a key cortical hub within the pain matrix. Whether a combination of Tai Chi and tDCS enhance the analgesic effect and neuromodulatory effect are understudied. This study aimed to investigate the analgesic and neuromodulatory effects of the combined intervention of Tai Chi and tDCS, targeting DLPFC-mediated modulation of pain matrix circuitry in people with KOA. Methods A total of 152 participants were randomized in a 1:1:1:1 ratio to Tai Chi combined with tDCS group, Tai Chi group, tDCS group or health education control group for 12 weeks. Pain intensity was assessed using the pain subscale of the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), while resting-state functional connectivity (rsFC) between the DLPFC and the pain matrix was analyzed through fMRI. Both assessments were conducted at baseline and upon study completion. Results The results showed that Tai Chi combined with tDCS group reduced WOMAC pain subscores compared with health education control group ( P  < 0.001), tDCS group ( P  = 0.003) and Tai Chi group ( P  = 0.048). fMRI showed that all intervention groups decreased rsFC between right DLPFC (DLPFC_R) and left posterior cingulate cortex (PCC_L), bilateral thalamus, left precuneus (precuneus_L), left superior frontal gyrus (SFG_L); Tai Chi combined with tDCS group decreased rsFC of DLPFC_R - PCC_R compared to health education control group and Tai Chi group. There were significant positive correlation between the reduction of WOMAC pain subscores and the attenuation of rsFC on DLPFC_R - PCC_L, DLPFC_R - Precunues_L. Conclusion Tai Chi combined with tDCS might relieve KOA pain by modulating DLPFC_R rsFC with pain matrix, provide a promising regimen with superiority on pain alleviation for people with KOA. Trial registration This study was registered with the Chinese Clinical Trial Registry (ChiCTR2100047287).