DISCUSSION
head movements, pain, TKA, depression, Morton et, EA reduced
CORTEX
The transmission of pain in the central nervous system is highly complicated and involves multiple brain regions (Kim et al., We found that patients had lower ALFF in right MFG, right SMA, bilateral precuneus, right CAL, and left IFGtriang following TKA (preintervention), compared with HCs without any pain symptoms. MFG and IFGtriang in the prefrontal cortex can modulate pain perception (Morton et al., This preliminary clinical trial has shown that EA reduced pain intensity and depression tendency after TKA. The analgesia effect of EA may be achieved through regulating the plasticity of brain functional activities, while SA cannot, exert such an effect. And this explains why the patients in EA group had higher ALFF in right cuneus, right angular gyrus, bilateral MOG, right MTG, and bilateral precuneus at POD 7 than at POD 3.The cuneus integrates somatosensory input with other sensory stimuli and cognitive processes, involving the emotion dimension of pain (Price, The EA‐stimulation (EA_POD 7 vs. POD 3) and group (HC vs. POD 3) difference as shown by ALFF overlapped in precuneus. The nucleus cuneiformist is an inhibitory region in the descending pathway, and the hypoactivity in this region indicates reduced inhibition of the pain response in patients, which produces a higher pain score (Schwedt et al., The pain intensity of patients in the SA group was also gradually eased over time after TKA. This may be attributed to the fact, the patients tended to limit their limb movement on the operative side to reduce the pain sensation due to the poor analgesic effect of SA. No changes (POD 7 vs. POD 3) in brain regions related to pain regulation were found on rs‐fMRI in SA group. The different changes of brain regions in the two groups indicated the central mechanisms of EA and SA were different. Part of the therapeutic effect of SA may be produced by the physiological effects on the skin during the stimulation. It should be noted that the AlphaSim correction was applied to explore the mechanism of EA analgesia in our study. Although the precuneus functional activities in EA group were closer to those HCs, the finding did not survive the more stringent FDR correction methods, and the AlphaSim correction method is relatively loose; therefore, further studies are needed.Taken together, we propose that EA relieves acute pain after TKA by increasing right cuneus, right angular gyrus, bilateral MOG, left MTG, and precuneus functional activity. The increased ALFF in pain‐related brain regions may exert beneficial impacts on pain‐regulating functions in patients after TKA. Besides, the EA‐stimulation and group difference overlapped in precuneus, suggesting that precuneus functional activities increase with the decreased pain intensity, which is pivotal to pain processing and regulation. Our research confirms the abnormal decrease of the precuneus functional activity can be reversed by EA, but the results need further validation.Our study has several limitations. (1) The small sample size of the study may increase the likelihood of a false positive error. Ours are preliminary findings, which lack prior power calculations, and thus should to be verified by studies with larger sample sizes. (2) This study only verifies the EA effect at the group level, and the specificity of EA analgesia is not fully explained. Future studies are needed to confirm the immediate effect of EA and validate our findings. (3) Due to excessive head movements, quite a few participants were excluded; but it should be emphasized that the exclusion of the images exerts no impact on treatment response. (4) Due to some practical difficulties and the limitations of experimental conditions, we failed to enroll an untreated group to investigate the effect of elapsed time on pain management after TKA. Hopefully, we will overcome the disadvantages in the subsequent work.