[Biomechanical studies of the role of the interfragmentary traction screw in plate osteosynthesis exemplified by a short oblique tibial shaft fracture].

In oblique fractures of the shaft of the tibia, plate osteosynthesis is combined with an interfragmentary traction screw to enhance the stability. Depending on the position of the fracture, the screw is introduced separately or via a plate hole near to the fracture. The maximum resistance to bending and the plastic deformation of plate osteosyntheses were studied in the tibiae of human corpses, with or without traction screw; in some cases, pure traction screw osteosyntheses were used in this study. It was found that the additional traction screw enhanced the stability by 52%, whereas plastic deformation was markedly reduced. Furthermore, the traction screw more than doubled the rigidity of the osteosynthesis, facilitating early healing of the fracture. Theoretical considerations show that a traction screw will greatly reduce the harmful shear stress of the fracture and increase interfragmentary compression, depending on the direction of the screw. If the screw is introduced, as recommended by Danis, in the bisector of the angle between the perpendicular on the fracture fissure and the perpendicular on the bone axis, one obtains high interfragmentar compression and reduction of shear stress by one-half. If the traction screw progresses perpendicularly to the bone axis, however, interfragmentary compression will be less, whereas the shear forces are fully compensated. Hence, the procedure according to Danis is meaningful in low-tension plate osteosyntheses (e.g. neutralisation plates), whereas transverse positioning of the screw appears to yield more favourable results in osteosyntheses applied under high tension.