Tests of stability on the fixateur externe under bending strain. Vertical and excentric strain under compression of the fracture

How to increase the stability of external fixation units

“…In our tests we measured the deflection under load of various Steinmann pins mounted on AO and Hoffmann frames with a Fraunhofer micrometer, varying the length of the pin between the clamps and the diameter of the pin It became evident that the bearing factor c is only insignificantly dependent on L and d. The values ranged from 2 to 3, no matter which of the two mounting methods was tested These results correspond to investigations carried out by other authors (Hild et al , 1978) Consequently, a mediumbearing factor of 2 5 can be substituted when u is calculated by the formula ( 1). In our tests we measured the deflection under load of various Steinmann pins mounted on AO and Hoffmann frames with a Fraunhofer micrometer, varying the length of the pin between the clamps and the diameter of the pin It became evident that the bearing factor c is only insignificantly dependent on L and d. The values ranged from 2 to 3, no matter which of the two mounting methods was tested These results correspond to investigations carried out by other authors (Hild et al , 1978) Consequently, a mediumbearing factor of 2 5 can be substituted when u is calculated by the formula ( 1).…”

“…Following to several other authors (Hild, 1978 ;Kleining, 1976 ;Hierholzer, 1977Hierholzer, , 1978, the proximal part was firmly clamped, the distal part loaded with weights The inclination a and the displacement x were measured with dial gauges We think these two parameters were more suitable for the determination of relevant movements within the fracture gap than the displacement measured on certain test-points as indicated by other authors Interfragmentary compression was recorded by an load cell developed for these particular measurements (Fig 6) By means of this load cell the load acting within the fracture could be measured at two areas of cross-section of the bone, so that the geometry of the inclination could be better realized than by point measuring By measuring a and x for various geometrical arrangements of the Steinmann pins and Schanz screws, the fracture movements calculated could be verified by mechanical testing. Following to several other authors (Hild, 1978 ;Kleining, 1976 ;Hierholzer, 1977Hierholzer, , 1978, the proximal part was firmly clamped, the distal part loaded with weights The inclination a and the displacement x were measured with dial gauges We think these two parameters were more suitable for the determination of relevant movements within the fracture gap than the displacement measured on certain test-points as indicated by other authors Interfragmentary compression was recorded by an load cell developed for these particular measurements (Fig 6) By means of this load cell the load acting within the fracture could be measured at two areas of cross-section of the bone, so that the geometry of the inclination could be better realized than by point measuring By measuring a and x for various geometrical arrangements of the Steinmann pins and Schanz screws, the fracture movements calculated could be verified by mechanical testing.…”