Biomechanical factors in designing screws for the Orthofix system.

In a monolateral external fixation system, bone grip is achieved optimally using half pins. This article reports the mathematical modeling used to design the screws and the drills of the Orthofix system. The diameter of the shank must be such that there is no risk of fracture at the screw entry point. It must also provide high strength under weight-bearing deformation stresses. The shape of the threaded part must allow the highest possible bone-gripping strength while minimizing slackening in relation to external and internal loads. The thermal effects of drilling and screw insertion must be considered to minimize necrotic damage that may stimulate reabsorption phenomena around the screw. The design of the different components of the pins must vary according to all the above factors to ensure optimal interaction between the fixator, screw, and bone.