Fractures of the forearm are one of the most common injuries in adults. Healing of non-anatomic position, so-called malunions, are the most common complication of these fractures. The presenting symptoms include acute pain and swelling, and local tenderness and visible deformity at the site of trauma. In utmost cases, the forearm can be out of function. The aim of treatment is the restoration of initial anatomical shape and bone position. The surgical treatment of such post-traumatic deformities consists in cut the bones (osteotomy) and reposition of bones into initial anatomical position. The computer tomography images of the remaining healthy forearm bones serve as a reference model. During the surgery, the osteotomy is done under sciagraphy inspection and afterwards a bone reposition is realized. The realign bones are in the best position fixed by osteosynthesis material. This classical approach brings into the bone reposition inaccuracy risks on several levels. By using 3D technologies, a precise information about malunions can be inspected. After that a virtual surgical protocol can be realised so that a precise bone cut position and implants can be planned. Moreover, a cutting guide can be printed by 3D printing technology. The talk will present this technique in detail with clinical cases demonstration.