Abstract

Cutting force and temperature are the key factors to be controlled during the orthopaedic surgery which could result in mechanical damage and necrosis of the bone tissue. Mechanistic modelling of the bone cutting process is expected to be an efficient method to understand and control these process challenges. However, due to the special structure and properties of the bone tissue (consist of osteon fibres and interstitial lamellae matrix), the conventional metal cutting models are not applicable in bone cutting process. This paper presents a novel cutting force and temperature mechanistic models for milling of bone. A cutting stress model of bone material was developed which takes into account its anisotropic characteristics based on the orthogonal cutting data. The cutting force coefficients are predicted incorporating the osteon orientation, tool geometry and edge effect with unified mechanics of cutting approach. Furthermore, a model of the induced cutting temperature based on heat flux developed during the process was proposed to predict the temperature distribution on bone cut surface. The experimental results showed a better consistency with the proposed model compared with the conventional Johnson-Cook model under different cutting conditions. A necrosis (potential cell injury from thermal effect) penetration depth was also proposed to evaluate the extent of thermal damage of bone tissue by the developed models. The proposed model can be used to assist the robotic surgery, to optimize the cutting parameters as well as to guide the orthopaedic tool design.

Highlights

  • Bone cutting is an important procedure in orthopaedic surgery that can span from amputations to finely controlled tissue removal to match the implant surfaces

  • In order to obtain real bone cutting stress for calibrating the proposed cutting stress model (Eq 4) with different osteon cutting angles, orthogonal cutting trials have been performed using an in-house developed 4-axis miniature machine tool to collect the cutting force data with varied osteon cutting angle from 0 to 180 degree under different uncut chip thickness while the cutting speed was fixed as 100mm/min to reduce the thermal effect during the modelling of bone strength

  • 4.1 Milling force validation To calibrate the proposed bone cutting stress and friction model (Eq (4) and (5)) the orthogonal cutting tests were employed, where the real cutting stress and friction coefficient can be obtained from Eq (6) and (7)

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Summary

Introduction

Bone cutting is an important procedure in orthopaedic surgery that can span from amputations to finely controlled tissue removal to match the implant surfaces. This is a challenging process due to bone unique structure, which is consisted of osteons (fibres) and interstitial lamellae (matrix) where the osteons showing a higher strength than interstitial lamellae and inherently results in an anisotropic property. Hillery and Shuaib (1999) reported that when the cutting temperature exceeds 55°C and for more than 30 seconds the bone tissue is damaged irreparably with necrosis These two thresholds have been accepted by researchers as the critical temperatures during the orthopaedic surgery. To minimize the mechanical and thermal damage of the bone tissue during the cutting process, the cutting force and temperature have to be critically controlled

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