Anatomically the knee is divided into three compartments, the medial compartment, the lateral compartment, and the patellofemoral compartment. A knee lesion can affect any of these compartments. Unicondylar arthroplasty (unicompartmental kneearthroplasty UKA) is a surface replacement of only the diseased compartment, but currently it is primarily a medial condyle replacement. Unicompartmental knee arthroplasty started almost simultaneously with total knee arthroplasty in the early 1970s, but unicompartmental knee arthroplasty is narrowly indicated for patients with early osteoarthritis (OA) and limited cartilage damage within a single compartment without patellofemoral joint involvement. In unicompartmental knee osteoarthritis, total knee replacement inevitably disrupts the normal compartment, which can lead to an extended treatment of limited lesions, significant surgical damage, and difficulty in subsequent revision. High tibial osteotomies are more appropriate in the treatment of unicompartmental osteoarthritis, especially in young patients with heavy deformities and high mobility needs. However, early weight-bearing of the affected limb is not possible after surgery, and the long-term outcome is uncertain, especially since changes in force lines after failure may affect it. The goal of unicondylar arthroplasty is to preserve as much normal joint structure as possible in order to achieve better functional recovery and to allow for future total arthroplasty. Compared to total knee replacement, the advantages of unicondylar joint replacement are: (1) the surgery only removes the diseased joint surface, so much less bone is removed than total knee replacement; (2) fewer foreign objects (including metal, polyethylene, and bone cement) are implanted in the body; and (3) the surgery time is shorter, with fewer surgical trauma and complications and faster postoperative recovery. Compared with high tibial osteotomy, unicondylar arthroplasty has a higher success rate in obtaining early and long-term results, fewer early complications, no external fixation, and the knee can reach functional range of motion when walking early after surgery. Early unicondylar arthroplasty has a high failure rate. In recent years, with improvements in prosthesis design and surgical techniques, as well as strict restrictions on case selection indications, the surgical results of this procedure have improved considerably. The ten-year excellent rate of unicondylar arthroplasty has been reported to be around 95%. In our experience, the results are better than those reported abroad. Indications: 1) Unilateral intercompartmental space narrowing in the knee (weight-bearing phase) without contralateral compartment and chondromalacia of the patellofemoral joint 2) Knee inversion less than 15° 3) Structural integrity of all ligaments of the knee 4) Non-inflammatory arthritis, such as osteoarthritis and traumatic arthritis 5) Patients aged 55 years or older, often in a sitting position or engaged in light physical activity, with low postoperative functional requirements Contraindications: 1) Not suitable For inflammatory arthritis, such as rheumatoid arthritis, systemic lupus erythematosus arthritis, ankylosing spondylitis, psoriatic arthritis, etc. 2) Those who have had infectious arthritis within a short period of time before surgery 3) Two or three inter-articular compartments are involved at the same time, and X-ray examination reveals joint space alteration, joint medial and lateral subluxation, greater than 3 mm, unicondylar arthroplasty should not be used.