Medial open wedge high tibial osteotomy (OWHTO) is usually performed with proximal tuberosity osteotomy or setting the osteotomy line proximal to the tuberosity. However, OWHTO can result in patellofemoral complications due to postoperative patella infera. A new OWHTO technique, biplanar osteotomy with a distal tuberosity osteotomy, was reported in 2004 to prevent postoperative patella infera. To ensure that the 2 osteotomy lines maintain perpendicular, we describe the OWHTO procedure with a distal tuberosity osteotomy technique using a TriS Medial HTO Plate System (Olympus Terumo Biomaterials Corp., Tokyo, Japan) and a right angle guide we developed. In this Technical Note, we describe the procedure and advantages, risks, and limitations, as well as the pearls and pitfalls based on our experience., Technique Video Video 1 A right angle guide for distal tuberosity osteotomy with medial open wedge high tibial osteotomy for varus knee osteoarthritis. Medial open wedge high tibial osteotomy (OWHTO) is recognized as a very useful treatment option for varus knee osteoarthritis. In this Technical Note, we describe the OWHTO procedure with the distal tuberosity osteotomy (DTO) technique using a TriS Medial HTO Plate System and a right angle guide we developed. The TriS Medial HTO Plate System is composed of a locking plate with 8 holes (A-D in the proximal part and I–IV in the distal part) and 8 cannulated locking screws. A right angle guide consists of two 1-mm thick stainless-steel plates (Plate I and Plate II) that are joined together at a right angle. The 2 ends of Plate I are referred to as the right and left wings. This video shows medial OWHTO with distal tuberosity osteotomy on the right tibia. The patient is placed in the supine position on the operating table. A skin incision starts 3 to 4 cm distal to the tibial tuberosity and near the tibial crest and continues proximally and posteriorly 1 to 2 cm distal to the knee joint line. After retraction of the skin and subcutaneous fatty tissue, the deep fascia, together with the semitendinosus and gracilis tendons, is then incised in an L-shaped fashion. The distal border of the incision is along the inferior border of the semitendinosus tendon. The incised fascia is reflected proximally to expose and completely release the superficial layer of the medial collateral ligament. After releasing the posterior periosteum of the tibia with a Cobb-type spinal elevator, a radiolucent retractor is then subperiosteally inserted just posterior to the tibia to protect the popliteal neurovascular structures. Next the first osteotomy, that is, medial OWHTO, is performed. Before the first osteotomy, 2 Kirschner wires are inserted in parallel to serve as guide pins. We usually fit the trial locking plate to the tibia and place the insertion point between holes D and I under fluoroscopic control. The 2 Kirschner wires are inserted using a parallel guide under fluoroscopic control. The direction of the wires is the proximal tibiofibular joint. The first osteotomy is also performed under fluoroscopic control using an oscillating saw with a 1.27-mm thick blade and osteotomes inserted along the distal surface of the 2 Kirschner wires. The end of the first osteotomy is about 5 mm medial to the lateral tibial cortex. Next, the right wing of Plate I is inserted into the first osteotomy line, and then the second osteotomy is performed along the upper surface of Plate II using an oscillating saw with a 1.27-mm thick blade, a reciprocating saw with a 0.8 mm thick blade, and osteotomes. After completion of both osteotomies, which is confirmed with the use of a metal ruler, the first osteotomy site is opened. At first, 5 osteotomes are inserted one by one in order to gradually open the osteotomy site. An HTO opener is then inserted to open the site to the desired distance as preoperatively calculated. When opening the first osteotomy site, it is necessary to check whether a gap had formed or not at the second osteotomy site. The accuracy of the acquired coronal alignment is determined under fluoroscopic control as to whether the mechanical axis (from the center of the femoral head to the center of ankle joint) passes through a point of 60% to 70% of the medial to lateral width of the tibia, which is examined using a metal alignment rod. Then, an artificial bone, β-tricalcium phosphate (β-TCP), is inserted into the first osteotomy site. At first, a 10-mm long β-TCP wedge with 60% porosity and an appropriate width (equal to the osteotomy gap) is inserted into the posterior and peripheral part of the osteotomy gap. Next, the second osteotomy site is fixed with a 4-mm diameter cannulated cancellous screw and a washer. β-TCP granules with 75% porosity are then stuffed into the osteotomy gap. Finally, a β-TCP wedge of an appropriate width and 10 mm in length is inserted at the anterior and peripheral part of the osteotomy gap. The released superficial layer of the medial collateral ligament is only repositioned onto the tibial surface. The reflected deep fascia is sutured to the surrounding soft tissue to cover the first osteotomy gap and to repair the semitendinosus and gracilis tendons. Finally, the first osteotomy site is fixed with a locking plate and 8 cannulated locking screws. Upon completion of the procedure, an aspiration device is set and the subcutaneous fatty tissue and skin are closed.