In 1973 Marmor first reported the use of unicondylar arthroplasty (UKA) for the treatment of severe osteoarthritis of the unicompartmental knee. In 1988, Marmor reported a success rate of 87% in 60 cases of UKA after 10-13 years of follow-up, and in 1990, Heck et al. reported an excellent rate of 91% in 294 cases of UKA after 10 years of follow-up, and Cartier and Sanoviller reported that 207 UKA cases had an excellent rate of 93% at 12 years of follow-up, and Goodfellow et al. reported that 160 UKA cases had an excellent rate of 96% at 10 years of follow-up. Berger et al. reported 62 unicondylar replacements with an excellent rate of 98% at 6 to 10 years of follow-up. The revision rate was close to that of the total knee (7-9%). Prosthetic systems with metallic pads better prevent deformation of the polyethylene liner, produce constant stress on the proximal tibia and protect the cancellous bone from loosening and subsidence, thus reducing the failure rate. Only the worn polyethylene liner is replaced during revision without disturbing the bone-prosthesis interface. Of course, the use of metal pads requires more bone to be removed to ensure the proper thickness of the tibial polyethylene liner. Since unicondylar replacement replaces only the diseased tissue, preserving the normal joint and normal cruciate ligament and proprioception of the contralateral compartment, the patient feels that the knee is close to a “normal joint” after unicondylar replacement. Because of its low surgical trauma, high bone volume preservation, short operation time, low blood loss, short hospital stay, fast recovery, low cost and less serious complications, unicondylar joint replacement is becoming more and more superior. Liu Yujie of the Department of Orthopedics, Beijing 301 Hospital, first performed arthroscopic exploration and found IV degree damage to the medial tibial or femoral cartilage of the knee with exposed subchondral bone for synovial debridement of the knee, arthroscopic lateral compartment meniscus damage, arthroscopic meniscus revision or partial resection, plasma knife patellar support band release and peripatellar ablation, and free body removal. A standard medial parapatellar skin incision is routinely used for unicondylar replacement, with a longitudinal skin incision parallel to the medial edge of the patella, an incision 8 to 12 cm long, and a longitudinal incision of the joint capsule. Intraoperative care is taken to avoid injury to the anterior cruciate ligament and the attachment point of the anterior foot of the lateral meniscus, pushing the patella outward and flexing the knee joint. Intraoperative wet gauze was used to cover the articular cartilage to avoid prolonged exposure of the cartilage surface. The medial meniscus and infrapatellar fat pad were removed, the femoral condyles and tibial plateau were excised, and the medial collateral ligament was released to correct the valgus deformity, and the knee was fully extended to give valgus tension. If the release of the medial collateral ligament is not complete, there will be excessive compressive stress on the prosthesis, which will lead to excessive wear of the polyethylene liner. The tibial osteotomy is performed using extramedullary positioning, first determining the lowest point of the articular surface of the medial tibial condyle, and osteotyping 2 mm below this point, with the angle of the osteotomy 90 degrees perpendicular to the long axis of the tibia and inclined 6 degrees posteriorly, and inserting the plate-like pulling hook between the medial and posterior soft tissues of the tibia and the posterior fork ligament during the osteotomy to avoid damage to the tissue. The tibial condylar osteotomy was performed to avoid damage to the intercondylar crest of the tibia and the ACL. the tibial plateau type was measured with a model for backup after completion of the osteotomy. The femoral end was positioned intramedullary and the distal femur and posterior condyle cartilage surfaces were osteotomized according to the osteotome. After the osteotomy, the osteotomy gap was measured in the knee in flexion and in extension so that the gap in both positions was equal in width. Care should be taken to avoid overcorrection of the valgus deformity when fitting the prosthetic trial, as overcorrection will result in increased stress on the lateral gap, which will accelerate the degeneration of the lateral cartilage. Therefore, after fitting the trial, a 2-3 mm gap gauge is inserted into the prosthetic gap in both extension and flexion. The prosthesis was fixed using a bone cement coating, which was too thick to affect the tension of the gap. Postoperative knee compression bandage, quadriceps isometric contraction exercises and straight leg raising exercises were performed early postoperatively, and postoperative radiographs were taken to observe the position. After the drainage tube was removed after surgery, the knee joint could be moved down with the help of crutches, and the knee flexion activity reached 900 within 1 week, and the weight-bearing activity was abandoned in 3 weeks. The failure rate after early unicondylar replacement is high, especially progressive joint degeneration on the non-replaced side, and the main reason for this high failure rate is the inappropriate selection of surgical indications in addition to the defective prosthesis design and inexperienced surgical technique. In particular, the degeneration of the lateral and patellofemoral compartments is closely related to the postoperative outcome. The use of means to identify the intra-articular cartilage, meniscus, ACL and other important structures in the knee joint is important to improve the postoperative outcome. Unicondylar replacement is used in severe osteoarthritis of the unicompartmental knee. In general, clinical selection of unicondylar replacement is mostly based on clinical symptoms, physical findings and imaging changes, and the indications for surgery. x-ray shows no involvement of the contralateral space and patello-femoral joint space, knee inversion deformity <10 degrees, knee valgus deformity <15 degrees, intact cruciate ligament, no knee subluxation, weight under 80 kg and age over 60 years. The absence of arthroscopic overall evaluation of important structures such as intra-articular cartilage, meniscus and cruciate ligaments inevitably carries certain limitations. In particular, 2nd-3rd degree damage to the articular cartilage, where the articular cartilage injury does not involve the subchondral bone, is difficult to detect abnormal changes on imaging such as X-ray plain film and MRI. We believe that for patients who are proposed to undergo unicondylar knee replacement before surgery, it is important to make an accurate assessment of the cartilage condition of the lateral compartment of the patellofemoral compartment, the degeneration of the meniscus and the cruciate ligament, and to correctly select the indication for surgery for long-term postoperative results. With the development of minimally invasive arthroscopic techniques, arthroscopy provides a good platform for the correct selection of surgical indications for unicondylar replacement. Arthroscopy allows visualization of important tissue structures such as cartilage, ligaments and menisci in the knee joint. It avoids the one-sidedness, limitations and blindness of relying solely on clinical physical examination and makes up for the clinical deficiencies. It makes the selection of surgical indications more reasonable. We have abandoned the surgical option of unicondylar replacement in patients who were proposed for unicondylar replacement, although preoperative examination did not reveal any obvious positive signs or imaging changes, but arthroscopic exploration revealed significant cartilage degeneration in the patellofemoral joint or lateral compartment. Osteoarthritis of the knee is difficult to detect intraoperatively for lateral interventricular meniscal degeneration damage in addition to cartilage changes. While performing intraoperative arthroscopy, the broken and degenerated meniscus tissue was partially excised or trimmed, and the synovial tissue was shaved and cleaned, which was conducive to relieving the symptoms of intra-articular strangulation and improving the symptoms of synovitis such as postoperative knee joint effusion. For patients with deviated patellofemoral joint motion trajectory, arthroscopic application of plasma knife for patellar support band release and peripatellar ablation is beneficial to improve patellofemoral joint pain symptoms and reduce cartilage wear. In conclusion, arthroscopic examination, accurate assessment of intra-articular conditions, strict screening of cases, and correct grasp of surgical indications to avoid blindness make unicondylar replacement more reasonable and help to further improve the efficacy of unicondylar replacement.