A, Calculation of size of bone wedge to be removed to accomplish desired degrees of correction with high tibial osteotomy. Apex angle (a) is number of degrees of correction desired for wedge osteotomy. Line ab corresponds to width of tibia and is marked off in 4-, 5-, 6-, and 7-cm distances from point a. Height of base of wedge can be measured (line bc for tibia, 7 cm wide). When tibia is 4 cm wide, height of base measured from diagram is 8 mm. B, Transferring calculations of size to wedge of osteotomy of tibia. Line ab represents transverse saw cut 2 cm below joint line with metal ruler inserted into cut. Angle at a represents correction desired and distance down second ruler. Line bc represents height of base of wedge to achieve this angular correction when ab represents width of tibia being osteotomized.