The effect of drilling parameters on bone

For orthopaedic biomaterial implantation testing, specimens are often implanted into cortical bone defects. The implantation site is assumed to be one of the factors that influence the bone response to biomaterials. The aim of this study was to investigate the bone-healing process in drilled cortical defects at different sites with respect to time. Sheep metatarsus was implemented, since it is a long straight bone with four flat faces. Thus, the different drilling sites were obtained by changing the longitudinal level (proximal, middle and distal) and bone aspect (anterior, lateral and posterior). Metatarsi were obtained at 1, 2, 3 and 4 months post-operatively and with non-decalcified sections the newly formed bone area was measured using a microscope connected to an image analyser. The rate of bone formation was higher in the anterior aspect (P<0.05). The new bone did not form concentrically from the hole edge towards the centre, and the principal direction of bone growth was different between the anterior and the posterior aspects (P<0.05). However, there was no difference with respect to the longitudinal axis. These results indicate that the implantation site must be considered when analysing the bone response to biomaterials implanted in cortical defects.