Machining-induced thermal damage in cortical bone: Necrosis and micro-mechanical integrity

In bone cutting, the tissue is exposed to necrosis due to temperature elevation, which can significantly influence postoperative results in orthopaedic surgeries. This damage is usually revealed through histological analysis to show the necrotic extent; however, this technique does not capture mechanical damage, which is essential for a full material integrity assessment. Here, with micro-mechanics, it is demonstrated that machining-induced damage in bone extends beyond the necrotic region. Drilling with different conditions was performed on ex vivo bovine cortical bone, inducing different damage degrees. Micro-pillar compression tests were performed in the machined sub-surface to identify changes in properties and failure modes caused by drilling. It was revealed that at high cutting temperatures, the bone near the machined surface suffers from lower modulus (-42%), strength (-41%) and brittle behaviour, whereas the bulk bone remains undamaged with pristine properties and ductile behaviour. Histology was also performed to evaluate necrosis and, surprisingly, it was found that the brittle and weaker bone layer is more than three times larger when compared to the necrotic layer, clearly showing that the drilling thermo-mechanical effect could affect not only biologically, but also micromechanically. Consequently, these results reveal another kind of bone damage that has so far been neglected. (C) 2020 The Authors. Published by Elsevier Ltd.

Automated summary

The study reveals that damage induced by bone cutting extends beyond the necrotic region, with high cutting temperatures causing lower modulus, strength, and brittle behavior near the machined surface. In contrast, the bulk bone retains pristine properties and ductile behavior. This shows that drilling thermo-mechanical effects can impact bone both biologically and micromechanically, revealing previously neglected bone damage.