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.
Journal of Biomechanics, 2013, Vol 46, p. 1415-1419