Effect of electroacupuncture on chronic pain in patients with knee osteoarthritis and its influence on central sensitization

To observe the clinical therapeutic effect of electroacupuncture (EA) on chronic pain in patients with knee osteoarthritis (KOA) and to investigate its influence on serum biomarkers related to central sensitization.

Ninety patients with chronic pain caused by KOA were randomly assigned to an EA group (45 cases, 3 cases dropped out) and a sham-EA group (45 cases, 5 cases dropped out and 1 case was eliminated). The patients in both groups received health education. Additionally, in the EA group, EA was performed at the acupoints such as Neixiyan (EX-LE4), Dubi (ST35), Heding (EX-LE2) and Xuehai (SP10) on the affected side, with dense-disperse wave, at the frequency of 2 Hz/100 Hz and the electric current of 1 m A to 2 mA, it was operated for 30 min in each session, once daily, 6 sessions a week, and for 4 consecutive weeks. In the sham-EA group, sham-EA was operated at the same acupoints as the EA group, with the same duration of interventions, but without electric stimulation exerted. In the baseline (week 0), and week 2, 4, 8 and 16, the score on numerical rating scale (NRS) for pain at rest and during activity, as well as pressure pain thresholds (PPTs) at the local and distal of knee joint were observed in the two groups separately. In week 0, 4, and 16, the Western Ontario and McMaster universities osteoarthritis index (WOMAC) and the 12-item short form health survey (SF-12) were scored. In week 0 and 4, the score on central sensitization inventory (CSI) and the levels of serum biomarkers related to central sensitization, such as glutamate (Glu), glutamine (Gln), substance P (SP), and calcitonin gene-related peptide (CGRP) were observed in the two groups.

Compared with the baseline, the EA group showed the decrease in NRS scores at rest and during activity in week 2, 4, 8, and 16, in the scores on subscales and the total score of WOMAC in week 4 and 16, as well as in CSI score and serum levels of Glu, Gln, SP, and CGRP in week 4 (P<0.05); and presented higher PPTs at the local and distal knee joint in week 2, 4, 8 and 16 and the scores on physical and mental health of SF-12 in weeks 4 and 16 (P<0.05). The sham-EA group presented the reduced resting-related NRS scores in week 2, 4, and 8, the activity-related NRS score in week 4, the scores on pain and function subscales and the total score of WOMAC in week 4 and 16, and serum CGRP level in week 4 when compared with the baseline, separately (P<0.05); and PPTs at the center of knee point in week 2 and 4 and the lateral side in week 4 increased (P<0.05). After treatment and at each time point of follow-up visit, NRS scores at rest and during activity, the scores on each subscale and the total score of WOMAC, the score of CSI and serum levels of Glu, Gln, SP, and CGRP in the EA group were lower than those in the sham-EA group (P<0.05); PPTs at each site (except at the lateral side of knee point in week 2 and the deltoid point in week 16) and the scores of SF-12 (except mental health score of SF-12 in week 16) were higher in the EA group when compared with the sham-EA group (P<0.05). Change scores of NRS at rest and during activity were positively correlated with those of CSI in the EA group (P<0.05).

Electroacupuncture effectively alleviates chronic pain of KOA, improves joint function and quality of life, which may be achieved through the inhibition of central sensitization.