Experimental analysis of internal rigid fixation osteosynthesis performed with titanium bone screw and plate systems

The authors report the results of an experimental analysis performed on titanium miniplates and screws in order to gain a better understanding of dynamic forces in internal rigid fixation. Ten segments of bovine scapula were prepared. Osteotomies were carried out along the minor axis, following which five were fixed with four hole straight miniplates and the other five with six hole double-Y miniplates. Each sample was fastened in a special clamp adapted to a tension test machine and shearing force was applied. Force versus time was recorded and the 50 bone fragments were examined by a pathologist. On the basis of the test results, two simple computer models were developed. No significant difference was evident between the mechanical and computed tests. The most critical sections were located near the hole proximal to the osteotomy and the microscopic findings confirmed this. On the basis of the experimental results, the authors propose a new plate design in which the area subject to most stress, proximal to the bone section, would be of miniplate thickness, the distal aspect being thinner as in a microplate. It is suggested that this design would provide sufficient stability and a high degree of anatomical adjustment of the system.