<p num="28">FIELD: medicine.</p> <p num="29">SUBSTANCE: invention refers to medicine, namely to traumatology and orthopedics, and can be used for preoperative preparation of patient for surgical correction of deformation of middle foot. An X-ray image of the foot is made with a load in the forward projection. On the X-ray image of the foot, a point "a" corresponding to the transverse tarsal joint medial border is placed, and a point "b" corresponding to the lateral edge of the transverse tarsal joint. Line 1 is passed through points "a" and "b", in the middle of which point "c" is marked and line 2 is drawn from it at angle of 89° to line 1. Further, line 3 corresponding to mechanical axis of 2nd metatarsal bone is drawn. Cross point of lines 2 and 3 is the apex of deformation of middle foot. When performing virtual osteotomy, distal bone fragment is moved so that lines 2 and 3 are aligned.</p> <p num="30">EFFECT: method enables accurate determination of the apex of deformation of the middle foot and, acc