Knee osteoarthritis (KOA) is a common degenerative osteoarthritis, characterized by chronic pain and disability, and relatively severe KOA will lead to irreversible structural damage to the joint1. The high global prevalence of KOA has become a major global public health challenge2,3, which seriously impairs the quality of life of patients4,5. Studies have shown that KOA affects more than 260 million people worldwide6. With the aging of the population, the total prevalence rate of KOA in China is as high as 17.0% over the age of 40, which puts a heavy burden on the families of those affected7,8.
According to Chinese medicine, KOA belongs to the category of "paralysis"9, and the Yellow Emperor's Classic of Internal Medicine associates tendons, bones, and flesh with paralysis. Hence, we need to pay attention to the connection between the cartilage, muscle, synovium, as well as other tissues around the knee joint in KOA. In modern medicine, both muscle and bone inflammation, which are major components of the immune homeostasis of arthritis, drive the progression of KOA pain. However, most studies focus on cartilage inflammation and synovial inflammation in bone joints, and there is a paucity of articles examining inflammatory phenomena in skeletal muscles. Therefore, more research on the role of skeletal muscle in inflammation is needed to gain a more comprehensive understanding of KOA and provide ideas for more effective treatment modalities. In a review of the literature, we found that inhibition of the immune-related factor programmed death ligand 1 (PD-L1) exacerbated the progression of KOA10,11 and that there was differential expression of IL-15 and FOXO1 in the skeletal muscle of patients with KOA12, as well as significant skeletal muscle inflammation in patients with end-stage KOA, which was also associated with changes in gait. It has been shown that the skeletal muscle can also secrete factors closely related to inflammatory immunity such as IL-6, and that TNF-α is also closely related to the PD-L1 pathway and KOA13,14,15.
Currently, available treatments for KOA include weight control, exercise, medication, and surgery, which usually include intra-articular injections, analgesic medication, arthroscopic surgery, and periprosthetic osteotomy of the knee16. Currently, KOA disease progression cannot be completely stopped or reversed, and without a clear understanding of the complex mechanisms underlying KOA pain, KOA patients are at risk for overuse of analgesic medications and a high incidence of side effects8. Most treatment strategies are effective only for short periods and focus only on the temporary relief of symptoms rather than on the pathogenesis of the disease. Therefore, KOA pain remains a priority and a challenge for treatment, posing a serious clinical challenge. However, Tuina can directly stimulate the skeletal muscles around the affected joint in KOA treatment and can provide some benefits. Combined with the previous description, it is the ideal therapy to study the role of skeletal muscle tissue in KOA, and clarifying the role of skeletal muscle tissue in inflammation can also provide better theoretical support for Tuina of KOA.
Studies have shown that massage therapy, osteopathic manipulative therapy, and spinal manipulation can help relieve pain and restore body function17,18. These manipulations can act on local inflammation and relieve spasms and analgesia through external mechanical action. They can relieve pain after total knee arthroplasty, reduce the use of analgesic drugs, promote postoperative recovery, and improve biomechanical balance19. Swedish massage is feasible in the treatment of osteoarthritis and can reduce stress and improve quality of life20. The therapeutic effect of Tuina on KOA has been preceded by certain studies.
In this experiment, our team will explore whether the expression of PD-L1 and related inflammatory factors in skeletal muscle can induce KOA and promote its development based on the MIA-induced KOA model in rats. Tuina will also be implemented to see whether it can alleviate KOA symptoms caused by increased inflammatory factor expression. Tuina will be combined with PD-L1 inhibition to demonstrate the association between Tuina-mediated PD-1 pathway in skeletal muscle inflammation affecting KOA development and pain, laying the foundation for further multi-level studies on the therapeutic mechanisms of Tuina intervention in KOA.
In summary, this paper describes the investigation and elaboration of the mechanisms of skeletal muscle inflammation in the development of KOA and its pain, as well as the therapeutic effects of Tuina on KOA, from the perspective of immune-inflammatory factor expression, combined with behavioral related indicators, to provide modern research evidence for the "imbalance of tendon and bone" theory in traditional Chinese medicine.