I. What is a unicondylar knee replacement? The knee joint contains the medial tibiofemoral interval, the lateral tibiofemoral interval, and the patellofemoral interval. Although knee disease can cause lesions in any of these compartments, clinical studies have shown that in about 1/3 of patients, the early lesions are limited to one compartment, primarily the medial tibiofemoral compartment, and do not involve the other two compartments. In these patients, total knee arthroplasty results in the loss of cartilage and ligaments of the normal intervertebral compartment, which is too traumatic and changes the mechanics of the joint. A unicondylar knee replacement is aimed at patients with unicompartmental osteoarthritis of the knee and is a minimally invasive procedure that replaces only the surface of the diseased side of the knee, replacing the diseased cartilage surface and preserving all of the ligamentous tissue and articular cartilage of the remaining compartment, resulting in a rapid postoperative recovery. II. What are the advantages of unicondylar knee replacement? The advantages of unicondylar knee arthroplasty are as follows: (1) Unicondylar replacement is more minimally invasive and has excellent postoperative results. In addition, because all ligaments in the knee are preserved, the patient has a greater range of motion in the knee and a gait that is closer to normal, making it easier to walk up and down stairs. (2) The unicondylar replacement has less intraoperative bone amputation, less surgical trauma, no blood transfusion, lower infection rate, shorter hospital stay, higher safety, and faster recovery. (3) Unicondylar replacement is more likely to be “forgotten” by the patient. With unicondylar replacement, the patient retains all the proprioceptive receptors in the ligamentous tissue. Patients can more easily perceive the change of force and position during the knee movement, and feel no significant difference between the postoperative knee and the normal joint, and after rehabilitation, they can more easily “forget” the surgery and move more freely. 3. What are the indications and contraindications for unicondylar knee arthroplasty? Indications for unicondylar arthroplasty: (1) osteoarthritis confined to the unilateral compartment of the knee with severe pain requiring arthroplasty; (2) X-ray signs requiring severe narrowing of the joint space of the affected compartment, while the contralateral compartment and patellofemoral compartment retain full cartilage; (2) knee deformity: internal and external rotation less than 15° and flexion contracture not exceeding 15°; (3) preoperative knee flexion of at least 100°; (4) Patients with functional integrity of the ligamentous structures around the knee joint. Contraindications: (1) inflammatory arthropathy; (2) obese patients weighing >100 kg with BMI >30; (3) patients with severe cartilage damage in the weight-bearing area of the contralateral inter-articular compartment, with anterior cruciate ligament injury and severe cartilage damage in the patellofemoral joint. In the face of patients with different stages and degrees of knee disease, a joint surgeon should fully evaluate the patient’s condition before surgery, make a correct diagnosis, and select an appropriate surgical approach. The use of unicondylar knee replacement for patients with unicompartmental osteoarthritis of the knee can not only reduce the cost of treatment, but also reduce the possibility of deep vein thrombosis and pulmonary embolism and infection after surgery; this can bring better clinical results for patients.