Based on our clinical experience, we postulate that the unilateral "posttraumatic genu valgum" develops on the grounds of an unreduced primary valgus deformity. This induces a disturbance of the consolidation on the medial aspect of the fracture. Subsequently, a partial medial stimulation of the epiphyseal plate develops resulting in a secondary valgus deformity. We succeeded in proving experimentally this postulate using the Mini Pig as an experimental model. We investigated 33 tibiae of 17 Mini Pigs. With radiological follow-up studies we were able to show that the operatively created primary valgus deformity induces an increased valgus deformity of functional significance. This is a model of the unreduced fracture in men. However, the transection of the pes anserinus and the periost per se did not provoke a significant valgus formation. Based on these experimental results and our clinical findings we postulate the following treatment for the metaphyseal bending fractures of the proximal tibia in men: 1. Accurate, usually conservative, reduction of any primary valgus malposition of the fracture. 2. Retention of the corrected position of the tibia in a plaster cast. 3. Compression of the medial aspect of the fracture to prevent disturbance of consolidation and subsequent development of valgus deformity.