Examination of the mechanical properties of impacted morsellised bone grafts

Background. In order to successfully apply the technique of impacting morsellised bone grafts in order to fill out bone defects, it is essential to determine the mechanical properties of the grafts. The aim of our study was to determine the type of forces enabling optimal graft impacting (static or dynamic forces), the force values needed for bone graft impacting, the number of impacting cycles needed to obtain a homogenous medium of a definite biomechanical strength, and the properties of the osseous bed after impacting, when exposed to forces similar to those to which the joints are subjected after surgery. Material and methods. The tests were carried out on a strength-testing stand based on the INSTRON 8501 Plus universal strength-testing machine. The tests were performed with both static and dynamic cyclic loads applied to grafts 2 cm thick. Results. In tests of static loads, the greatest displacement of the rammer was observed during the first attempt to knead the grafts with a force of 2 kN. The dynamics of the graft impacting process decreased rapidly in successive cycles and stabilized after ten cycles. A slight increase of rammer displacement was observed. Conclusions. The results from the static and dynamic tests demonstrate that both the value and the character of the force applied influence the mechanical properties of the bed made of frozen bone grafts. Significantly better quality of impacting was obtained with dynamic compacting of the grafts than with application of the same force in a static character. With cyclic impacting of the bed, only the first dozen or so cycles were effective, and further action was of an elastic strain character and failed to improve the quality of impacting.