[The significance of postoperative stability for osseous repair of a multiple fragment fracture. Animal experiment studies].

The significance of postoperative mechanical stability for bony repair of a comminuted fracture was investigated in an animal experimental study comparing four commonly applied operative methods of stabilizing fractures: (1) flate osteosynthesis combined with lag screw fixation after reduction of the fragments; (2) bridging plate osteosynthesis; (3) external fixation; (4) static interlocking intramedullary nailing. As the fracture model, a triple-wedge osteotomy of the right sheep tibia was used. The results of in vitro testing of stiffness (N/mm) of each of the four osteosyntheses was as follows: anatomical plate: 746 N/mm; bridging plate 434 N/mm; external fixation 625 N/mm; nailing 416 N/mm. Eight weeks after the operation, the tibiae were explanted and the contralateral tibiae of six sheep were taken as a control group. The three-point bending test revealed no significant difference in bending deviation: anatomical plate 47.58 +/- 22.57 microns; bridging plate 33.93 +/- 7.67 microns; external fixation 33.83 +/- 8.02 microns; nailing 33.0 +/- 17.23 microns. However, it was noted that there was a slightly higher tendency towards stiffness of the bones after bridging plate osteosynthesis, external fixation and interlocking intramedullary nailing and that the amount of stiffness resembled that in non-operated control animals (25.56 +/- 6.66 microns). On the other hand, anatomical plate osteosynthesis showed less stiffness. To assess the tensile strength at the osteotomy area, bone samples were prepared and tested for failure on a material testing machine. The tensile strength of the bone samples showed a distinct difference in all experimental groups according to their anatomical location.(ABSTRACT TRUNCATED AT 250 WORDS)