No effect of dynamic loading on bone graft healing in femoral segmental defect reconstructions in the goat

We studied if a static or dynamic mode of nail fixation influenced the healing of segmental defect reconstructions in long bones. Defects in the femur of goats were reconstructed using a cage filled with firmly impacted morsellised allograft mixed with a hydroxyapatite paste (Ostim). All reconstructions were stabilised with an intramedullary nail. In one group (n=6) the intramedullary nail was statically locked, in the second group (n=6) a dynamic mode of nail fixation was applied. We hypothesised that dynamisation of the nail would load, and by that stimulate the healing of the bone graft. Mechanical torsion strength of the reconstructions of the femur with the static and dynamic mode of nail fixation appeared to be 74.8±17.5% and 73.0±13.4%, respectively as compared with the contralateral femurs after 6 months. In all reconstructions, the grafts united radiographically and histologically to the host bone, and remodelled into a new vital bone structure. No large differences were found between newly formed bone areas inside and outside the mesh of the two groups. The area of callus outside the mesh in the dynamic mode of fixation group was smaller (p=0.042), whilst the percentage of bone outside the mesh was larger (p=0.049), as compared to the static mode of fixation group. The data suggest that healing of these defects with impacted morsellised graft in a cage is not significantly influenced by the mode of fixation of the nail in this model.