Abstract
An anisotropic mechanical behaviour of cortical bone and its intrinsic hierarchical microstructure act as protective mechanisms to prevent catastrophic failure due to natural loading conditions; however, they increase the extent of complexity of a penetration process in the case of orthopaedic surgery. Experimental results available in literature provide only limited information about processes in the vicinity of a tool–bone interaction zone. Also, available numerical models the bone-cutting process do not account for material anisotropy or the effect of damage mechanisms. In this study, both experimental and numerical studies were conducted to address these issues and to elucidate the effect of anisotropic mechanical behaviour of cortical bone tissue on penetration of a sharp cutting tool. First, a set of tool-penetration experiments was performed in directions parallel and perpendicular to bone axis. Also, these experiments included bone samples cut from four different cortices to evaluate the effect of spatial variability and material anisotropy on the penetration processes. Distinct deformation and damage mechanisms linked to different microstructure orientations were captured using a micro-lens high-speed camera. Then, a novel hybrid FE model employing a smoothed-particle-hydrodynamic domain embedded into a continuum FE one was developed based on the experimental configuration to characterise the anisotropic deformation and damage behaviour of cortical bone under a penetration process. The results of our study revealed a clear anisotropic material behaviour of the studied cortical bone tissue and the influence of the underlying microstructure. The proposed FE model reflected adequately the experimental results and demonstrated the need for the use of the anisotropic and damage material model to analyse cutting of the cortical-bone tissue.
Highlights
Penetration of a sharp tool into bone tissue is required in many clinical procedures, such as orthopaedic surgery, bone implant and repair operations
Cortical bone exhibited a higher peak force when the tool penetrated perpendicular to osteons (L–C and L–R), and a significantly lower peak force when the penetration direction was parallel to osteons (C–L and C–R)
In this study, statistical analysis using Tukey HSD tests (α1⁄4 0.05) revealed that there is no significant difference between cortices in this respect, except that between posterior and lateral cortices (p 1⁄40.03) for penetration parallel to the osteons. This result indicated that the penetration resistance is affected by, but not directly related to, the variation of microstructure constituents. It is rather a combined effect of various factors such as stiffness, toughness and localised damage mechanisms which diminish the extent of generality of the statistical analysis
Summary
Penetration of a sharp tool into bone tissue is required in many clinical procedures, such as orthopaedic surgery, bone implant and repair operations. The success of bone-cutting surgery depends largely on precision of the operation and the extent of damage it causes to the surrounding tissues. An excessive force, generated by a sharp surgical tool or an implant device, can lead to formation of micro-cracks and fracture (Ebacher et al, 2012; Launey et al, 2010), and, cause permanent damage to the adjacent area of cortical bone tissue that, in turn, can delay postoperative recovery of patients (Wazen et al, 2013). Information on deformation behaviour of cortical bone under penetration of a sharp tool is essential to understand the interaction process at tool–bone interface; this can improve the control of a surgical instrument to minimise damage caused to surrounding bone tissues. Sugita and co-authors (Sugita and Mitsuishi, 2009; Sugita et al, 2009) proposed a new cutting method based on the characteristics of crack propagation in cortical bone, indicating a fundamental difference between cutting of cortical bone tissue and metals
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