A method for performing a high tibial, dome osteotomy to adjust the lateral and/or angular disposition of the tibial plateau relative to the lower portion of the tibia, the method comprising: forming an arcuate osteotomy cut in the tibia to subdivide it into upper and lower portions; manipulating the upper and lower portions to adjust their lateral and/or angular dispositions relative to one another; forming a pair of keyholes along the osteotomy cut; forming a keyhole slot to connect the two keyholes; forming a fixation hole in the tibia for each keyhole; providing an implant comprising a pair of keys connected by a bridge, each key comprising a bore for receiving a fixation screw therein; inserting the implant so that the keys are disposed in the keyholes, and so that the bores of the keys are aligned with the fixation holes; and inserting fixation screws through the bores of the keys and into the fixation holes of the keyholes so as to stabilize the upper and lower portions of the tibia.