Knee pain is a symptom, and the prerequisite for its treatment is to identify the cause of the pain and thus the nature and extent of the lesion. The choice of surgical treatment is usually based on a combination of factors such as etiology, extent of the lesion, duration of symptoms, imaging, patient condition, and sometimes pathological diagnosis. (A) Knee meniscus, collateral ligament and cruciate ligament injury lesions: 1. Arthroscopic treatment of meniscal injury: If the diagnosis of meniscal injury is clear, symptoms are frequent, such as frequent “interlocking” or recurrent joint effusion, and conservative treatment is ineffective, arthroscopic surgery can be considered, The surgical methods mainly include total meniscectomy, partial meniscectomy and meniscus repair, according to the severity of meniscus injury and the type of treatment. 2.Meniscal cysts: Most meniscal cysts usually require surgery. 3.Discoid meniscus: If there are obvious symptoms, arthroscopic meniscoplasty should be performed. 4, cruciate ligament injury: ligament injury can occur in the ligament itself and in the ligament-bone union causing avulsion fractures, complete rupture or most ruptures usually require ligament reconstruction. 5. Lateral collateral ligament injury: Depending on the severity of the injury and the combination of other structural injuries, ligament repair, or reconstruction may be an option. (B) Knee deformity: 1. Knee valgus deformity: early conservative treatment methods such as, splints, braces, casts, etc. The aim of treatment is to prevent the deformity from worsening and to correct the deformity with non-surgical treatment as much as possible. Patients with more severe deformities, where conservative treatment is not effective, may be considered for surgical treatment. According to the patient’s age and the degree of deformity, the corresponding surgical methods are selected, including epiphyseal block, epiphyseal stimulation, and osteotomy, in order to obtain normal lower limb force lines. (2) Knee inversion deformity: surgical treatment can be considered for severe deformity, and surgical methods such as closed fracture method, epiphyseal block, epiphyseal stimulation and osteotomy can be selected according to the age and degree of deformity to obtain normal lower limb force line. (iii) Patellar lesion: 1. Patellar dislocation: Patellar dislocation can cause knee joint pain and weakness. The cause of patellar dislocation should be searched for and should generally be treated surgically. The purpose of surgery is to reconstruct the line of pulling force of the patella. According to the patient’s pathological basis and the degree of lesion, adjustment of the force line of the proximal patella, adjustment of the distal patella pulling force line, quadriceps plication and femoral condyle osteotomy can be chosen, mainly including lateral knee release, medial knee tightening and medial femoral muscle stop transposition. 2. Patellar chondromalacia: if conservative treatment is ineffective for 3-6 months and the symptoms are severe, arthroscopy is feasible. Surgery is performed after determining the presence of patellar chondromalacia. Intra-articular surgery includes patellofemoral joint surface grinding, patellofemoral joint cleanup, patelloplasty, patellar replacement, patellar resection and lesion excision and decompression. If there is severe osteoarthritis of the severe total knee joint, total knee replacement should be considered. (iv) Intra-articular free body and synovial osteochondroma stalk: Arthroscopic removal of the free body is usually required. (e) Synovial and fat pad lesions of the knee: 1. Synovitis: Synovitis of the knee has different etiologies, including rheumatoid, tuberculosis, septic infection, nonspecific, etc. The treatment should be based on different etiologies, scope and severity, and the appropriate conservative and surgical treatment modalities should be selected. 2. Infrapatellar fat pad hypertrophy or infrapatellar fat pad inflammation: for patients with a clear diagnosis, heavy symptoms and long duration, arthroscopic surgery is feasible to remove part of the hyperplastic synovial tissue. 3, knee synovial crease syndrome: conservative treatment is ineffective can be examined under arthroscopy, the crease is released, total or partial excision. 4, pigmented villous nodular synovitis: according to the location, extent and severity of the lesion, choose arthroscopic lesion removal, incisional lesion removal, joint replacement can be considered for severe joint destruction. (vi) Septic arthritis of the knee: Surgical treatment, as one of the components of comprehensive treatment of septic arthritis, should be implemented on the basis of strict conservative treatment. Commonly used surgical treatment methods include: joint aspiration and injection of antibiotics, arthroscopic lavage, closed continuous irrigation, negative pressure suction and arthrocentesis drainage, and the corresponding methods should be selected according to the patient’s age and degree of lesion. For early septic arthritis, arthrocentesis and injection of antibiotics may be chosen, and arthroscopic lavage therapy combined with closed continuous irrigation and suction therapy is feasible for poor results. (vii) Knee tuberculosis: The prevalence of knee tuberculosis is very high, ranking first among the six major joints of the extremities. Surgical treatment of joint tuberculosis should be performed on the basis of strict anti-tuberculosis treatment and enhanced supportive therapy, and regular anti-tuberculosis treatment should be continued after surgery. 1.Treatment of simple synovial tuberculosis: Synovectomy of the knee joint is suitable for those whose non-surgical treatment is ineffective or the effect is not obvious. 2. Treatment of simple bone tuberculosis: Focal debridement can be chosen if conservative treatment is ineffective or the lesion develops gradually. 3.Treatment of early total joint tuberculosis: lesion removal should be used to save joint function. 4.Treatment of advanced total joint tuberculosis: lesion removal and joint fusion surgery can be chosen according to the condition, severity of lesion and patient’s physical condition, and deformity correction should be performed at the same time if there is joint deformity. (H) Rheumatoid arthritis of the knee: 1. For patients who have not been treated with strict conservative medical therapy for more than six months, synovectomy may be chosen for severe joint lesions with synovial inflammation and hyperplasia as the main cause. The risk of perioperative complications and postoperative complications of joint replacement surgery is higher in patients with rheumatoid arthritis. Therefore, the risk of perioperative complications and postoperative complications of joint replacement surgery are high, and the surgery is complicated and difficult. Therefore, we should strictly grasp the indications for surgery, make good perioperative evaluation and preparation with the cooperation of rheumatology and other disciplines, and improve the technical level of joint replacement in order to effectively reduce complications and achieve the expected results. (ix) Knee osteoarthritis: 1. Arthroscopic joint cleanup: especially for cases with free bodies, joint interlocking manifestations, significant inflammatory exudation, and early to mid-stage lesions. 2, periprosthetic osteotomy: the indications for surgery are a certain degree of internal and external knee deformity, middle age, no serious osteoarthritis manifestations, normal muscle strength, and good lower limb mechanical force line and good joint function can be obtained through osteotomy orthopedics. Conditions that are not suitable for osteotomy include: old age such as greater than 60 years, internal and external derangement greater than 15°, bilateral interval lesions, flexion contracture greater than 15°, significant limitation of knee motion, severe osteoarthritic manifestations, and significant joint instability. 3. Artificial knee replacement: The main purpose of knee replacement is to relieve pain, correct deformity, and obtain a stable joint with good motion. When a patient is clearly diagnosed with severe osteoarthritis based on medical history, clinical manifestations and imaging evidence, is 55 years of age or older, has failed with other treatments, and has severe impact on daily life, artificial knee replacement can be considered. The contraindications are local or systemic infection, and relative contraindications include neuroarthropathy, such as Charcot arthritis; severe osteoporosis; and poor systemic condition that does not tolerate surgery. Since most of these patients are elderly patients and often have local and systemic lesion bases, good outcomes can be achieved by strict preoperative evaluation and various perioperative management, including control and reduction of various complications, infection prevention, VTE prevention, blood management, pain management, and reasonable functional rehabilitation. Depending on the location, extent and severity of the lesion, patellofemoral prosthesis replacement, unicondylar replacement, and total knee surface replacement can be selected. 4, osteochondral (cell) transplantation: for young and middle-aged patients with isolated lesions of articular cartilage, requires surgical qualification, strict standardization of procedures, and should be carried out scientifically and gradually. (X) Gout: Gout can also occur in the knee joint, causing pain. Treatment is based on dietary control and medication. For those with large gout stones that affect function and cannot be relieved by acid-reducing drugs, the gout stones can be surgically removed, and those with severe effects on joint function can undergo artificial joint replacement, the effect of which depends on the extent and severity of the lesion. (xi) Knee joint and peri-knee tumors: Knee pain can come from peri-knee tumor lesions, early manifestation of knee pain or adjacent knee pain, such as osteosarcoma, giant cell tumor of bone, aneurysmal bone cyst, chondrosarcoma, osteochondroma, etc., most commonly seen in adolescents, young and middle-aged people, imaging manifestations including X-ray plain film, CT, MRI, etc. have their own characteristics, when necessary The treatment is mainly based on the nature and stage of the tumor, and surgery is often one of the main treatment modalities. (xii) Intra- or periprosthetic fractures: usually with a clear history of trauma, they can be manifested as avulsion fractures of the cruciate ligament, avulsion fractures of the collateral ligament, tibial plateau fractures, femoral condyle fractures, proximal fibula fractures, etc. Imaging examinations can make a clear diagnosis, and conservative treatment or corresponding surgical treatment can be chosen according to the location, displacement and type of fracture. (XIII) Knee pain from lesions outside the knee: Knee pain can come from lesions in the hip joint or from lesions in the spine and lumbar spine. If the concern for knee pain is only limited to the knee localization, it may lead to a missed diagnosis or misdiagnosis, and it may also lead to misdiagnosis and mistreatment due to misdiagnosis. It is important to be alert to pain caused by extra-knee pathology in the diagnosis and treatment of knee pain.