We present four technical modifications of high tibial osteotomy which improve its safety and reproducibility. (a) Open wedge correction: opening wedge osteotomy from the medial side avoids lateral muscle detachment, dissection of the peroneal nerve, proximal fibula osteotomy, and leg shortening; only one osteotomy needs to be performed and the correction can be adapted intraoperatively. (b) Biplanar osteotomy: in addition to the transverse osteotomy of the posterior tibia a second ascending osteotomy in the coronary plane underneath the tibial tuberosity is performed. This provides improved rotational stability of the osteotomy and creates an anterior buttress against sagittal tilting of the osteotomy planes. (c) Incomplete osteotomy with plastic deformation of the tibia: 10 mm of lateral bone stock is left intact. The osteotomy is opened gradually over several minutes by sequential impaction of flat chisels or by use of a special spreading tool. Manifest fractures of the lateral cortex with resulting instability are avoided. Rapid bone healing is promoted. (d) Rigid fixation: stable osteosynthesis allows for early mobilization and avoids losses-of-correction. We use a medial plate-fixator which can be applied percutanously. In 112 patients operated on using this modified technique no pseudarthosis or loss-of-correction was observed.