Robots and tools for remodeling bone

The field of robotic surgery has progressed from small teams of researchers repurposing industrial robots, to a competitive and highly innovative subsection of the medical device industry. Surgical robots allow surgeons to perform tasks with greater ease, accuracy, or safety, and fall under one of four levels of autonomy; active, semi-active, passive, and remote manipulator. The increased accuracy afforded by surgical robots has allowed for cementless hip arthroplasty, improved postoperative alignment following knee arthroplasty, and reduced duration of intraoperative fluoroscopy among other benefits. Cutting of bone has historically used tools such as hand saws and drills, with other elaborate cutting tools now used routinely to remodel bone. Improvements in cutting accuracy and additional options for safety and monitoring during surgery give robotic surgeries some advantages over conventional techniques. This article aims to provide an overview of current robots and tools with a common target tissue of bone, proposes a new process for defining the level of autonomy for a surgical robot, and examines future directions in robotic surgery

Analysis of Bone Cutting Mechanics in Orthopedic Surgery

Bone cutting has been widely used in orthopedic surgery for repairing bone fractures and attaching implantable prosthetics. Temperature rise in the cutting process can cause necrosis when it is beyond a threshold value, depending on the species and age of the bone. Excessive cutting force may induce bone micro-fractures which lead to breakdown at the repair site. This thesis investigates the effect of cutting parameters on temperature and force in cutting of bovine and equine cannon bones. Vibration assisted drilling which enables intermittent contact between the cutting tool and the bone is conducted, and the effect of vibration assistance on the cutting performance is evaluated. Damages caused at the drill site of the bone are characterized by Micro-CT. Bone milling is used to shave the end of the bone to fit the plane of the artificial joint precisely. In this study, Taguchi method is used to evaluate the influence of the parameters such as spindle speed, feed rate and depth of cut on the milling process. This thesis provides insights in the mechanics of bone cutting process used in orthopedic surgery. The results provide optimum cutting operations to minimize the process induced bone damage.Mechanical & Aerospace Engineerin

A novel cutting tool design to avoid surface damage in bone machining

With its anisotropic structure, bone machining occurs as shear/serrated cutting mechanisms at low values of uncut chip thickness while at high values it results in fracture cutting mechanisms which lead to significant tissues damages; hence, utilising conventional tools at high material removal rates comes with drawback on surface damages, situation that needs to be avoided. This paper reports on a novel design of a milling cutter which includes on the back of main cutting edge a succession of micro-cutting edges arranged on an Archimedes spiral that allows the limitation of surface damage. That is, by adjusting the feed rate, this tool design allows the change of the cutting mechanism as follows: (i) “shear/serrated” cutting mode: when the feed rate is smaller than a pre-established threshold, only the main cutting edges work which yields a shear/serrated cutting mechanism; (ii) combined “fracture & shear” cutting mode occurring at high feed rate caused by: the main cutting edges working in fracture cutting mechanism while the subsequent micro-cutting edges work under shear cutting mechanism, combination which leads to significant reduction of bone surface damages. This new tool concept was materialised on a solid diamond composite, characterised by excellent heat conduction and low wear rates. Cutting experiments with various values of feed rates showed that the proposed tool designed concept significantly reduced the fracture damage of bone cut surface as well as cutting temperature compared with the dimensionally equivalently conventional tool

Experimental Analysis of Parameters Influencing the Bone Burring Process

The experimental quantification of the bone removal characteristics associated with bone burring represents a desirable outcome mainly for the selection of optimal parameters. An experimental apparatus was developed that allowed for concurrent measurement of three outputs associated with the bone removal process (cutting force, vibration, and temperature) as a function of various burring-specific parameters. Initial process trends were established on a uniform sawbone analog through use of a fully balanced multivariate statistical analysis. A smaller set of optimal and suboptimal parameters were further validated using a porcine femur. From the parameters tested, an optimal tool configuration, to avoid high temperature and high vibration, was found to be a 6 mm sphere burr at a rotational speed of 15,000 rpm, feed rate of 2 mm/s and a path overlap of 50%. This set of parameters also provided flexibility in tool depth/orientation angle relative to the bone without sacrificing optimal process outcomes

A review on recent advances in numerical modelling of bone cutting

[EN] Common practice of surgical treatments in orthopaedics and traumatology involves cutting processes of bone. These operations introduce risk of thermo-mechanical damage, since the threshold of critical temperature producing thermal osteonecrosis is very low. Therefore, it is important to develop predictive tools capable of simulating accurately the increase of temperature during bone cutting, being the modelling of these processes still a challenge. In addition, the prediction of cutting forces and mechanical damage is also important during machining operations. As the accuracy of simulations depends greatly on the proper choice of the thermo-mechanical properties, an essential part of the numerical model is the constitutive behaviour of the bone tissue, which is considered in different ways in the literature. This paper focuses on the review of the main contributions in modelling of bone cutting with special attention to the bone mechanical behaviour. The aim is to give the reader a complete vision of the approaches commonly presented in the literature in order to help in the development of accurate models for bone cutting.The authors acknowledge to the Ministry of Economy and Competitiveness of Spain the financial support for this work received through the projects DPI2011-25999 and DPI2013-46641-R.Marco, M.; Rodríguez Millán, M.; Santiuste, C.; Giner Maravilla, E.; Henar Miguélez, M. (2015). A review on recent advances in numerical modelling of bone cutting. Journal of the Mechanical Behavior of Biomedical Materials. 44:179-201. https://doi.org/10.1016/j.jmbbm.2014.12.006S1792014

On modelling of cutting force and temperature in bone milling

© 2018 Elsevier B.V. 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

Experimental and numerical analysis of conventional and ultrasonically-assisted cutting of bone

Bone cutting is widely used in orthopaedic, dental and neuro surgeries and is a technically demanding surgical procedure. Novel surgical methods are continually introduced in orthopaedic, neuro and dental surgeries and are aimed at minimising the invasiveness of the operation and allowing more precise cuts. One such method that utilises cutting with superimposed ultrasonic vibration is known as ultrasonically- assisted cutting (UAC). The main concern in bone cutting is the mechanical and thermal damage to the bone tissue induced by high-speed power tools. Recent technological improvements are concerned with the efforts to decrease the force required by the surgeon when cutting the bone as well as increases in surgery speed. A programme of experiments was conducted to characterise properties of a bone and get a basic understanding of the mechanics of bone cutting. The experiments included: (a) nanonindentation and tension tests to obtain the properties for the finite element (FE) bone cutting model, (b) high-speed filming to observe the chip formation process, which influences thermomechanics of the cutting process in conventional drilling (CD) and ultrasonically-assisted drilling (UAD) and, (c) plane cutting and drilling experiments to measure the levels of force and temperature rise in the bone tissue. Novel two-dimensional finite element (FE) models of cortical bone cutting were developed for conventional and ultrasonically-assisted modes with the MSC.MARC general FE code that provided thorough numerical analysis of thermomechanics of the cutting process. Mechanical properties such as the elastic modulus and strain-rate sensitivity of the bone material were determined experimentally and incorporated into the FE models. The influence of cutting parameters on the levels of stress, penetration force and temperature in the bone material was studied using conventional cutting (CC) and ultrasonically-assisted cutting (UAC). The temperature rise in the bone material near the cutting edge was calculated and the effect of cutting parameters on the level of thermal necrosis was analysed. The necrosis depth in bone was calculated as a distance from the cut surface to the point where the thermal threshold level was attained. Comparative studies were performed for the developed FE models of CC and UAC of bone and the results validated by conducting experiments and using data from scientific publications. The main outcome of the thesis is an in-depth understanding of the bone cutting process, and of its possible application in orthopaedics. Recommendations on further research developments are also suggested

The design and control of an actively restrained passive mechatronic system for safety-critical applications

Development of manipulators that interact closely with humans has been a focus of research in fields such as robot-assisted surgery and haptic interfaces for many years. Recent introduction of powered surgical-assistant devices into the operating theatre has meant that robot manipulators have been required to interact with both patients and surgeons. Most of these manipulators are modified industrial robots. However, the use of high-powered mechanisms in the operating theatre could compromise safety of the patient, surgeon, and operating room staff. As a solution to the safety problem, the use of actively restrained passive arms has been proposed. Clutches or brakes at each joint are used to restrict the motion of the end-effector to restrain it to a pre-defined region or path. However, these devices have only had limited success in following pre-defined paths under human guidance. In this research, three major limitations of existing passive devices actively restrained are addressed. [Continues.

Study of Micro Rotary Ultrasonic Machining

Product miniaturization for applications in fields such as biotechnology, medical devices, aerospace, optics and communications has made the advancement of micromachining techniques essential. Machining of hard and brittle materials such as ceramics, glass and silicon is a formidable task. Rotary ultrasonic machining (RUM) is capable of machining these materials. RUM is a hybrid machining process which combines the mechanism of material removal of conventional grinding and ultrasonic machining. Downscaling of RUM for micro scale machining is essential to generate miniature features or parts from hard and brittle materials. The goal of this thesis is to conduct a feasibility study and to develop a knowledge base for micro rotary ultrasonic machining (MRUM). Positive outcome of the feasibility study led to a comprehensive investigation on the effect of process parameters. The effect of spindle speed, grit size, vibration amplitude, tool geometry, static load and coolant on the material removal rate (MRR) of MRUM was studied. In general, MRR was found to increase with increase in spindle speed, vibration amplitude and static load. MRR was also noted to depend upon the abrasive grit size and tool geometry. The behavior of the cutting forces was modeled using time series analysis. Being a vibration assisted machining process, heat generation in MRUM is low which is essential for bone machining. Capability of MRUM process for machining bone tissue was investigated. Finally, to estimate the MRR a predictive model was proposed. The experimental and the theoretical results exhibited a matching trend