1.Frozen shoulder Freezing shoulder is a disease characterized by progressive shoulder joint pain and limitation of motion, which occurs in middle-aged and elderly people aged 50-60 years old. Calis et al. randomly divided 90 patients (95 shoulder patients) with frozen shoulder into Hyaluronic acid (HA) injection group, tretinoin injection group, physiotherapy group and control group. The physiotherapy group showed the most significant improvement. Nago et al. found that HA inhibited the proliferation of joint capsule fibroblasts and reduced the mRNA expression of adhesion-related procollagen and cytokines in an in vitro study, and the authors speculated that the inhibitory effect of HA on joint adhesions might be related to this. 2. Rotator cuff injury Chou et al. randomly divided 51 patients with partial rotator cuff injury into HA group (25 with subacromial injection of HA) and control group (26 with subacromial injection of saline). 6 weeks after the injection, it was found that Constant score and VAS score were significantly higher in the treatment group compared with the control group. 33.1 months of average follow-up was observed, and no significant adverse effects were found. In vitro studies found that HA down-regulated IL-1-induced mRNA expression of pro-inflammatory cytokines and COX-2/PGE-2 production in subacromial fibroblasts, which is presumed to be the reason for the effectiveness of HA in treating rotator cuff injury. 3. Rheumatoid arthritis Rheumatoid arthritis patients with osteoarthritis manifestations can be treated with HA. For example, Goto et al. performed intra-articular injection of HA in 25 patients with RA and found that the patients’ pain and inflammation improved significantly after the injection, and the synovial fluid PGE2 level decreased significantly. 4, joint sprains Joint sprains or fractures require prolonged joint braking patients can be intra-articular injection of HA to delay the degeneration of joint cartilage, reduce joint adhesions, and promote joint function recovery. For example, Jazrawi et al. found that intra-articular cavity injection of HA after acute knee injuries (such as meniscal tears and ACL tears) significantly improved patients’ pain symptoms and delayed the onset of post-traumatic osteoarthritis. Petrella et al. randomly divided 158 athletes with acute lateral ankle sprains into 2 groups, with HA and placebo injections around the joint, followed by the same standard treatment procedures. After 24 months of follow-up, it was found that the HA injection group had significant pain relief, earlier return to sports, lower ankle re-torsion rate and higher patient satisfaction than the control group. 5. after meniscectomy Recent studies have found that intra-articular injections of HA after arthroscopic meniscectomy can help to relieve pain and improve joint function. For example, Thein et al [9] randomly divided 56 patients with knee meniscus injury into HA and saline groups, and injected HA and saline into the joint cavity immediately after arthroscopic meniscoplasty, respectively. Mathies et al. For example, Ozgenel et al. injected HA and saline into the tendon suture immediately after the repair of flexor tendon injury and 1 and 2 weeks after the repair, and found that the active and passive mobility of the index finger was significantly better in the HA injection group than in the saline group after 3 months of follow-up, which may be related to the reduction of postoperative adhesions by HA. .