Abstract: An apparatus for treating malformative and traumatic conditions affecting the knee area, having an external fixation means for fixing bone portions together and first and second bone screws to be engaged respectively in the epiphyseal and diaphyseal region of the femur/tibia and to which the fixation means is to be coupled. The apparatus includes a guiding means, which is separate from the fixation means, for guiding the surgeon in the operations for identifying a plurality of drilling points on these regions, for producing engagement holes in these regions at the drilling points, and for inserting the bone screws in the engagement holes. The separate provision of the guiding means allows to simplify the structure of the fixation means with respect to existing fixation means.