To identify the optimal temperature and infrared radiation wavelength parameters of moxibustion simulator intervention at “Neixiyan” (EX-LE4) and “Waixiyan” (ST35) acupoints for ameliorating knee osteoarthritis (KOA) in rats.

Male Sprague-Dawley (SD) rats were randomly assigned to a normal group, a model group, EX-LE4 or ST35 mild moxibustion groups, and EX-LE4 or ST35 moxibustion simulator groups with different wavelengths, with 6 rats in each group. The KOA model was established by intra-articular injection of a mixed solution of L-cysteine and papain into the left knee joint cavity. An infrared radiation measurement device was used to collect the characteristic infrared radiation wavelengths of EX-LE4 and ST35 acupoints. The mild moxibustion group received mild moxibustion intervention at EX-LE4 and ST35 acupoints separately with a moxa stick at 43 ℃, while the moxibustion simulator groups were treated with photothermal simulated stimulation with a fixed temperature of 43 ℃ combined with different wavelengths (1652, 3340, and 7500 nm). The spatial, temporal and dynamic parameters of rat gait were analyzed. ELISA was performed to quantitatively determine the serum content of interleukin-10 (IL-10), an anti-inflammatory cytokine. HE staining and Masson staining were conducted to evaluate the inflammatory response and collagenization degree of synovial tissue of the knee joints.

The characteristic infrared radiation wavelength of the acupoints was approximately 3340 nm in rats under the pathological state of KOA. Compared with the normal group, the model group showed significant alterations in gait spatial, temporal and dynamic parameters (P<0.001), a marked decrease in serum IL-10 level (P<0.05), as well as significant elevations in synovial Krenn score and collagen area percentage (P<0.0001). In comparison with the model group, the mild moxibustion group and moxibustion simulator groups at both EX-LE4 and ST35 acupoints exhibited varying degrees of improvement in gait spatial parameters (P<0.001, P<0.01, P<0.05) and dynamic parameters (P<0.001, P<0.01). The mild moxibustion group, 1652 nm moxibustion simulator group and 3340 nm moxibustion simulator group at both acupoints also achieved improvements in gait temporal parameters (P<0.01, P<0.05, P<0.001), with the mild moxibustion group and 3340 nm moxibustion simulator group showing superior ameliorative effects compared with the moxibustion simulator groups with other parameters (P<0.01, P<0.001, P<0.05). Compared with the model group, the EX-LE4 mild moxibustion group, EX-LE4 3340 nm moxibustion simulator group and ST35 3340 nm moxibustion simulator group presented a significant increase in serum IL-10 contents (P<0.05, P<0.0001, P<0.001). Moreover, the serum IL-10 contents in the EX-LE4 3340 nm moxibustion simulator group was significantly higher than those in the moxibustion simulator groups with other parameters (P<0.0001, P<0.01). In contrast to the model group, the mild moxibustion groups and 3340 nm moxibustion simulator groups at both acupoints displayed significant reductions in synovial Krenn score and collagen area percentage (P<0.01, P<0.0001, P<0.05, P<0.001), with the 3340 nm moxibustion simulator group yielding the best therapeutic outcome (P<0.05).

Moxibustion intervention with the parameter combination of 43 ℃ and 3340 nm at EX-LE4 and ST35 acupoints can significantly improve gait function and suppress inflammatory response in KOA rats, with consistent optimal parameter combinations for both acupoints. The synergistic effect may be attributed to the acupoint-moxibustion infrared radiation resonance effect formed between the specific wavelength infrared radiation generated by moxibustion and the spontaneous infrared radiation emitted by the acupoints of rats under KOA pathological conditions.