[Contact surfaces, compressive forces and pressure distribution in osteosynthesis. Model studies using...

Previous pressure gauges have been unable to measure exactly the stress over the cross-section of fractures or osteotomies. This first became possible with the pressure sensitive foil. Known operative procedures were examined with this foil using a self-compressing plate and a synthetic tube model. Contact area, compressive force, pressure and pressure distribution were measured simultaneously and analogously. A straight plate produces extremely little force and pressure on the gap. Both are limited to about a quarter of the cross-section just below the plate. The consequence is no sufficient stability. Also, using a prebent plate results in inhomogeneous pressure distribution with high values, but a distinct decrease of the stress on the opposite side of the plate, especially by compression applied at the end of the plate. But compression from near the fracture side gives the highest values and a most homogeneous force distribution. In this case the force recorded 1700 N, the mean pressure 5,2 MPa and the contact 90% of the cross-section. The length thrust of the plate ends approximately at a torque of screw tightening at 1,0 Nm. Using torques up to 2,5 Nm, force and pressure increase isometrically. Higher torques have no influence. Converging screws result in smaller contact, force and pressure, because they produce a vector force away from the gap and a smaller length thrust.