Although arthroscopic surgery is a minimally invasive and highly effective procedure, it is not always possible to see immediate results. Arthroscopic surgery is also not a one-and-done procedure. Different patients respond differently to arthroscopic surgery, with some patients experiencing immediate relief and others experiencing worsening symptoms. Many factors are involved, and only with a thorough understanding of these factors is it possible to predict the outcome of arthroscopic surgery and successfully guide patients through their recovery. The evolution of the disease after arthroscopic surgery is generally divided into three phases: the reactive synovitis phase, the periarticular aseptic inflammation phase, and the functional rehabilitation phase. There are different rehabilitation methods for different stages. 1. Reactive synovitis: Although arthroscopic surgery is minimally invasive, the synovial membrane of the knee may still respond to the procedure more severely. The normal knee joint cavity is always under negative pressure, and in order to expand the joint capsule during arthroscopic surgery it must be perfused with 100-150 mm of water column, or even higher, of perfusion pressure. The large change in intra-articular pressure causes a disruption in the sympathetic response of the synovial membrane, which often results in reactive synovial congestion and edema when the positive pressure state is over, also known as reactive synovitis. Clinically, this is characterized by unrelieved or increased knee pain, fluid accumulation in the knee joint, and limited extension and flexion. The severity of reactive synovitis is independent of the severity of the surgical trauma, and a minimally invasive arthroscopic irrigation can cause a severe reaction. Reactive synovitis is associated with gender and age. In male patients, the duration of reactive synovitis is short, usually disappearing two weeks after the procedure, and in some patients there is even no synovial reaction; in female patients, the reaction is longer. In younger women (<35 years) and older women (>55 years), the reaction period is generally six weeks; in women aged 45-55 years, the reaction period is the longest, often taking three months for the synovial reaction to completely resolve, and in some patients it may take up to six months; in patients suffering from menopausal syndrome, the synovial reaction may not even subside until after menopause. To avoid or reduce the occurrence of reactive synovitis, the first step is to focus on case selection. For women in the 45-55 age group, the true cause of the patient’s knee pain symptoms should be clarified through clinical and various ancillary tests. In patients with significant psychiatric factors, arthroscopy and surgery should be postponed unless the patient expresses a full understanding of the reactions produced by the procedure. Second, the patient should be made fully aware of the reaction before the procedure, and the physician should avoid overstating the effects of arthroscopic surgery so that the duration of reactive synovitis is instead significantly reduced as the patient’s expectations are lowered and the psychiatric factors are relieved. During the period of reactive synovitis, treatment consists of two main areas of functional exercises and medication. First, gradual functional exercises for the knee joint. In the first week after surgery, straight back elevation training is performed: supine position, knee straightened, lower limb elevated to 30-45°, maintained for 10 seconds and then lowered, repeatedly. The straight back elevation training should be performed once in the morning and once in the evening for 30-60 minutes each time, starting with empty leg training, and after the muscle strength of the thigh has recovered, it can be performed with weights tied to the ankle until 5 kg weights can be tied to the ankle. In the first week after surgery, weight-bearing activities can be performed as long as pain permits, but knee extension and flexion activities should be minimized during weight-bearing. In the second and third weeks after surgery, knee extension and flexion mobility training should be performed on the basis of straight back elevation and weight-bearing exercises. Do not forcefully extend and flex the knee joint with pain, as this may cause the synovial membrane to squeeze inside the joint, aggravating synovial congestion and edema, and even causing synovial damage. Exercises for extension and flexion activities should be performed twice daily for 30 minutes each time. Starting four weeks after surgery, the duration of straight back elevation, extension and flexion activities and weight-bearing exercises can be gradually extended according to the recovery of the disease, but the total training time should not exceed 4 hours. Second, drug application. ① Non-steroidal anti-inflammatory and analgesic drugs are effective in relieving synovial inflammatory reaction, and it is advisable to use fenbendazole-type long-acting slow-release drugs. The general dosage is fenbuterol 0.3, bid. anti-inflammatory pain, aspirin effect can also be. ② Reactive synovitis is also sensitive to the response of intra-articular hormone injections in the knee. One injection is usually given at 6 weeks postoperatively and another at 12 weeks postoperatively. Subsequent injections are given at 3-month intervals. The average patient needs only one injection. Methylprednisolone and dexamethasone can be used, but a suspension such as definitive inflammasone A is recommended because the suspension is slowly absorbed, has a long local duration of action, and has minimal systemic side effects. The method of use is 10 ml of 2% lidocaine with 1 ml of Zolpidem A, injected intra-articularly. The intra-articular hormone injection should firstly be aseptic to prevent knee infection, secondly to ensure that it is injected into the joint cavity, otherwise the effect is greatly reduced, and thirdly it should not be used too early after surgery, otherwise it is likely to cause intra-articular infection. ③ Intra-articular sodium hyaluronate injection also helps to relieve painful symptoms. 2. Periarticular aseptic inflammatory period: There are proprioceptive nerve fibers on the meniscus, but no nociceptive nerve fibers. Pain after meniscal injury arises from the aseptic inflammatory response of the synovial membrane, joint capsule and pericapsular tissue around the damaged meniscus, which is caused by the damaged meniscus embedded in the joint or by abnormal activities. When the damaged meniscus is removed or repaired by arthroscopic surgery, the factors causing the aseptic inflammatory response are removed, but because the aseptic response does not disappear, the patient’s pain does not disappear immediately and the patient will not experience the effects of arthroscopic surgery until most of this aseptic inflammation has subsided. The time required for this inflammation to subside is more related to the length of preoperative onset and less related to the degree of intra-articular damage. The longer the preoperative onset, the longer the postoperative time to resolution of symptoms. Similarly, there are no nociceptive nerve fibers in the articular cartilage, and the symptoms of articular cartilage degeneration are due to other secondary reactions, which also take time to resolve after joint debridement. As with reactive synovitis, the resolution of periarticular aseptic inflammation is significantly related to gender and age. In men, the inflammation resolves most rapidly, typically in 2-4 weeks, while in menopausal women it is slowest and the time required is often difficult to determine. There are several reasons why arthroscopic surgery is ineffective or aseptic inflammation does not completely resolve in individual patients. (1) Prolonged preoperative course of disease. Patients with an excessively long preoperative course should be psychologically prepared for the postoperative recovery time. (ii) Incomplete arthroscopic surgery. In arthroscopic surgery, thorough examination and treatment can ensure the efficacy of the surgery. (iii) Combined injuries and lesions cannot be treated. For example, if a medial meniscus injury is combined with an inversion of the knee, after the meniscus injury is treated, the pain is often not relieved due to the lack of treatment of osteoarthritis in the medial space of the knee, and the symptoms can often be significantly relieved if an osteotomy is performed with an exostosis. ④ Sympathetic reactive bone atrophy (Sudeck’s bone atrophy). The onset of this disease is beyond the surgeon’s control. However, the likelihood of an attack can often be predicted by examining the patient before surgery. The chance of an attack is about 1-2%, making a mockery of the arthroscopic surgeon’s delicate and brilliant surgery. Any knee surgery, including arthroscopic surgery, should be done with caution in those patients who are stressed, extremely sensitive to pain, and suffering from menopausal syndrome. Treatment at this stage still consists of both functional exercises and medication. First, functional exercises. At this stage, the mobility of the affected knee has been restored, but there is still slight pain at the end of knee extension and flexion, and the pain is still similar to the preoperative pain when walking with weight, but to a lesser extent. The functional exercises in this stage are mainly functional exercises for the quadriceps muscle, and the time and method are the same as in the reactive synovitis stage. Second, physical therapy. Hot compresses and microwave therapy at the site of pressure and pain, and local massage all help to reduce inflammation and relieve symptoms. Third, drug treatment. ① Oral non-steroidal anti-inflammatory and analgesic drugs are also effective in relieving peri-articular aseptic inflammation, and the use of topical drugs such as Fotarine emulsion after applying heat to the painful area is also effective. Periarticular aseptic inflammation is less sensitive to intra-articular hormone injections in the knee, and injections at pressure points outside the joint capsule are more effective. Generally, injections are given once a week, and four times a course of treatment. Generally speaking, hormone injections are no longer effective after more than two courses of treatment. (3) If the pain is more severe when bearing weight, it is usually caused by cartilage degeneration, etc. Intra-articular sodium hyaluronate injection can help relieve the symptoms. 3. Functional recovery period: After the first two stages, although the mobility of the knee joint has been basically restored and the pain symptoms of the knee joint have been relieved, it does not mean that the function of the knee joint has been restored. This is because the relevant muscle strength of the knee joint, the proprioceptive function of the knee joint, the responsiveness of the knee joint and the mobility of the knee joint are necessary for the knee joint to perform its full function. At this stage, we should focus on knee proprioceptive function and knee responsiveness. Knee proprioceptive training: Half squat exercises, jogging activities, and stationary bike riding can enhance proprioceptive function. Knee joint responsiveness training: lateral movement training and balance board can enhance knee joint responsiveness.