Therapeutic Effects of Fire Needling Acupuncture on Pain Relief and Cartilage Protection in MIA-Induced Knee Osteoarthritis Rats: The Role of Macrophage Polarization in Synovium and Angiogenesis in Subchondral Bone.

PURPOSE: Knee osteoarthritis (KOA) is a prevalent degenerative disease impacting bone and joint health. Clinical studies indicate that fire needling acupuncture can alleviate joint stiffness, pain, and dysfunction in KOA. Previous research demonstrated its efficacy in reducing pain, mitigating cartilage damage, and regulating macrophage polarization, but its effects on subchondral bone remain unclear. This study aimed to evaluate the therapeutic effects of fire needling acupuncture on subchondral bone in KOA. METHODS: Sprague-Dawley rats were divided into three groups: control (CON), monosodium iodoacetate (MIA), and fire needling acupuncture (FNA) (n=6 per group). A KOA model was established using 0.3 mg/50 µL MIA, followed by acupuncture at acupoints SP10, ST34, ST35, EX-LE5, and ST36 twice weekly. Evaluations included body weight, joint diameter, weight distribution, and mechanical withdrawal threshold. Micro-CT imaging assessed tibial plateau bone mass changes. Histological evaluations used HE, Safranin O/Fast Green, and toluidine blue staining. Immunohistochemistry examined COL2, MMP9, and MMP13 expression, while macrophage polarization was analyzed using immunofluorescence for F4/80, iNOS, and Arg-1. TRAP staining assessed osteoclast activity, and immunofluorescence for CD31/Emcn and VEGF evaluated angiogenesis in subchondral bone. RESULTS: Fire needling acupuncture significantly improved weight distribution and mechanical withdrawal thresholds, reduced synovial inflammation and abnormal changes in subchondral bone, and preserved cartilage integrity in MIA-induced KOA rats. Notably, F4/80 and iNOS expression levels decreased, while Arg-1 expression increased after treatment. Additionally, TRAP, CD31/Emcn, and VEGF expression in subchondral bone decreased following fire needling acupuncture. CONCLUSION: Fire needling acupuncture mitigates pain behavior, synovial inflammation, cartilage degradation, and abnormal changes in subchondral bone in MIA-induced KOA rats. The therapeutic mechanism may involve modulation of synovial macrophage polarization and subchondral bone angiogenesis. Further research is warranted to elucidate the precise molecular pathways and the interaction between macrophage polarization and angiogenesis.