Indications A valgus angle >10°-15° in the lower extremity, between the normal anatomic and mechanical axes, with pain in the lateral interval, may be relieved by DFO. Although medial closed-wedge HTO is feasible for correction of valgus deformity, it may result in joint line tilt and instability.Contraindications to DFO include: knee ligament instability, osteonecrosis of the femoral epicondyle, severe tricompartmental arthritis, rheumatoid arthritis, and severe valgus deformity (>20°) with tibial subluxation. Preoperative planning Preoperative planning is critical and should avoid overcorrection to valgus. The patellofemoral trajectory and patellofemoral pain will improve somewhat in patients with mild degenerative changes in the patellofemoral joint due to appropriate internal displacement of the tibial tuberosity as a result of DFO. The lateral open-wedge osteotomy is more representative; however, the medial closed-wedge osteotomy may reduce the rate of bone nonunion in patients with comorbid risk factors, such as: smoking and obesity. Plan for correction of angulation The osteotomy was planned according to the method of Dugdale et al. On an orthopantomograph of the full-length lower extremity in the hip-ankle standing position, the gravity line should fall on 48%-50% of the outward width of the medial tibial plateau cortex and a marker point should be made there. Subsequently, a line is drawn from the center of the femur to the selected marker point of the tibial plateau and another line is drawn from the center of the ankle to the marker point of the tibial plateau. The angle of intersection of the two lines is the number of degrees of angle to be corrected. The size of the osteotomy wedge depends on the width of the femoral osteotomy plane. Surgical technique Lateral opening – wedge osteotomy The surgical incision is made from the distal lateral femoral condyle two transverse points straight upwards towards the proximal femur to 15 cm. the iliotibial bundle is incised and the lateral femoral muscle is pulled forward from the lateral interval. To protect the neurovascularity, a Hohmann pulling hook is placed to the posterior side and the knee is flexed at 30°. With the aid of navigation, two guide wires were passed unassisted from lateral to medial over the distal femur. The first guidewire was passed parallel to the joint line through the epiphysis. The second guidewire is inserted at the lateral condyle and three transverse fingers above the femoral talar sulcus, reaching the medial epicondyle in a 20° (relative to the angle of the first guidewire/joint line) angled direction from proximal to distal. The osteotomy plate is placed perpendicular to the long axis of the femoral stem. The osteotomy swing saw enters 1 cm from the lateral cortex and completes the rest of the osteotomy with a bone cutter, leaving 1 cm medially. after removal of the osteotomy block, the osteotomy is fixed using a locking plate (with or without an intermediate wedge) or external fixation. Medial closed-cuneiform osteotomy Medial closed-cuneiform DFO reduces the pressure in the lateral compartment. Its main effects are to reduce the risk of bone nonunion and to allow for conversion of the surgical approach to TKA. The drawbacks of the medial closed-wedge DFO include greater surgical complexity and the need for two separate osteotomies to complete the procedure. A straight 15-cm incision is made medial to the distal femur. The medial femoral muscle is retracted anteriorly to expose the medial femoral cortex and medial femoral condyle. A small arthrotomy is made adjacent to the medial tuberosity to expose the intercondylar fossa. The knee is flexed at 90° and a parallel guide wire is inserted medially to laterally, 1 cm from and parallel to the articular surface of the distal femur. A blade is inserted medial to the femoral condyle and parallel to both guide wires, 2 cm from the joint line. a 1 cm closed-wedge osteotomy is made at the proximal end of the blade. The osteotomy surface was then fixed using a 90°-eccentric distance power compression plate. Clinical outcomes Most studies have shown that DFO can prolong the need for TKA for more than a decade. Kosashvili et al. reported that 6.1% of patients will convert to TKA at 10 years and that the overall failure rate was 48.5% at a mean of 15.6 years after osteotomy. The same study found that the modified KSS score improved from 36.8 to 77.5 1 year after osteotomy, and Jacobi et al. found that the KOOS score was 31 before osteotomy and 69 after osteotomy, a significant improvement in the score. The major complications of DFO include intraoperative intra-articular fractures, dislocation of the osteotomy area, non-union, venous thrombosis and infection. In conclusion Knee osteotomy is a viable option for joint preservation with reduced degenerative interbody pressure in young, active patients with unilateral interbody osteoarthritis with inversion or valgus. Studies have shown that knee osteotomies are beneficial for cartilage repair (decompression of the medial interventricular or lateral interventricular cartilage zone). In severe patellofemoral degeneration or tricompartmental lesions, the clinical results of knee osteotomy (HTO or DFO) are not promising and alternative treatments need to be sought.