[Biomechanical studies of the spine. Their significance for the development of rational treatment techniques].

A treatment is rational when the goal of restoring form and function can be achieved safely and with the least possible technical input and iatrogenic damage. In the field of spinal surgery a number of techniques have recently been developed than can be termed rational. Biomechanical investigations have made a decisive contribution to the progress achieved. Forces acting on the spine and their cyclic frequency are determined from (1) calculations based on models of the human body, (2) measurement of physical parameters, e.g. intradiscal pressure, and (3) loads acting on implants. Selection of the size and form of implants and investigation of their mechanical properties are based on the values recorded for forces and cycles. In vitro examinations on deformation of bone-implant complexes exposed to predetermined loads lead to improvements in form and dimensions of implants. Finally, comparative in vitro studies with different techniques can help in answering the question as to what technique is best suited to solve a given clinical problem.