How to increase the stability of external fixation units. Mechanical tests and theoretical studies.

From general physical laws simple formulae have been deduced from which the rigidity of an external fixation unit mounted in different ways becomes mathematically calculable. Furthermore, the stability of various mounting systems under bending forces was investigated experimentally. Particular attention was paid to details of operating technique which are of special importance to the stability of the whole construction. The calculated data are consistent with the mechanical test results. The best arrangement of the Steinmann pins and Schanz screws is discussed, and how to mount the frame optimally, depending on the specific type and location of the fracture. Special instructions concerning the mounting of the external fixation unit are given which, depending on the specific circumstances, guarantee optimum stability of the unit.