Introduction: The mechanical properties of bone can largely be explained by bone density and the anisotropic orientation of the trabecular bone. The type of trabecular structure plays an important role in determining the mechanical properties of cancellous bone. Gap-healing and implant fixation could be
affected by the various quality and quantity of bone in the local environment. Thus, implant fixation in one part might differ from the other part of the implant. This study aimed to investigate the influence of the sampling method on data evaluation.
Material and methods: Titanium alloy implants (Biomet Inc.) of 10 mm in length and 6 mm in diameter were inserted bilaterally into the proximal humerus of 8 skeletally mature sheep. Thus two implants with a concentric gap of 2 mm were implanted in each sheep. The gap was filled with allograft. Standardised surgical procedure was used. At sacrifice, 6 weeks after surgery, both proximal humeri were harvested. The specimens were randomized to superficial or profound groups. In the superficial group, mechanical testing or histological analysis was carried out on the superficial part of the implant. In the profound group, the mechanical testing or histological analysis was performed on the profound part of
the implant.
Result: The mechanical fixation, bone volume and bone ongrowth showed no statistically significant differences. Mechanical test demonstrated a slight tendency to increased strength and failure energy were observed in the superficial group. Histomorphomety revealed bone ongrowth was slightly increased and volume fraction was decreased in the profound group.
Conclusion: Histological analysis and mechanical testing can be applied to the superficial or profound part of the implant.