The assembly of an external fixation apparatus must fully accord with the most recent developments in transosseous osteosynthesis. The experimental/theoretical and clinical knowledge base is currently such that the rigidity of bone fragment fixation in relation to the diameter of the transosseous elements used, their type and crossing angle, the geometry of the external supports, the distance between external supports, etc., can be predicted. As discussed in Chap. 2, the biomechanics of external fixation consist of three interconnected parts: (1) the relationship between the transosseous elements (wires, half-pins) and the surrounding tissue; (2) the control of bone fragment position; (3) the control of bone fragment rigidity.