Introduction: Many orthopaedic procedures require drilling of bone, especially fracture repair cases. Bone drilling results in heat generation due to the friction between the bone and the drill bit. A high-level of heat generation kills bone cells. Bone cell death results in resorption of bone around bone screws.Methods: We searched in the literature for data on parameters that influence drilling bone and could lead to thermal necrosis. The points of view of many orthopaedists and neurosurgeons based upon on previous practices and clinical experience are presented.Results: Several potential complications that lead to thermal necrosis are discussed and highlighted.Discussion: Even in the face of growing evidence as to the negative effects of heat induction during drilling, simple and effective methods for monitoring and cooling in real-time are not in widespread usage today. For that purpose, we propose some suggestions for the future of bone drilling, taking note of recent advances in autonomous robotics, intelligent systems and computer simulation techniques.Conclusions: These advances in prevention of thermal necrosis during bone drilling surgery are expected to reduce the risk of patient injury and costs for the health service.

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An overview of thermal necrosis: present and future

Drilling is one of the most common procedures in orthopaedic surgery. However, drilling-induced trauma occurs frequently and affects the processing damage and position accuracy of the holes, which strongly influence the postoperative recovery. Therefore, there is an urgent need to design a dedicated drill bit that can satisfy low-trauma requirements such as low cutting force, low temperature, self-centring, and low surface damage during orthopaedic surgery. In this work, a novel three-step drill structure is proposed to modify the cutting conditions at the entrance and exit of drilling, to effectively reduce the mechanical and thermal damages and improve the position accuracy in bone drilling. As the first step drill, a unique tip with thinned web was adopted by considering the drill skidding mechanisms under a non-perpendicular drilling condition. The second step was achieved by using an optimal point angle for balancing the effects of the cutting force and temperature. Moreover, a transition arc design was proposed as the third step to adjust the point angle during the finishing stage for switching the cutting mechanism from ‘fracture & shear crack’ cutting to ‘shear’ cutting in association with a certain range of feeding rates. This could reduce the mechanical and thermal damages to the finished hole surface. Drilling experiments under various process conditions demonstrated that the proposed drill design significantly reduced the drilling force, temperature, and damage and also improved the position accuracy of the holes compared to the conventional drill design. The proposed design provides an effective tool to achieve low-trauma bone drilling in orthopaedic surgery.

A novel self-centring drill bit design for low-trauma bone drilling

Excessive drilling forces can result in drill breakage, bone breakthrough, and thermal necrosis during bone drilling process. However, the effect of drilling process parameters, drill geometry parameters, and bone material type on drilling forces have not been fully investigated. Three designs of experiments are introduced separately to study single factor's effect on drilling forces, identify significant geometry parameters and possible interactions for drilling forces, and formulate direct relationship between drilling forces and process parameters. The results show that thrust force and torque are increased with feed rate, drill diameter or web thickness. The effect of spindle speed, point angle, helix angle, and chisel edge angle on drilling forces is complex. The results also show that the drilling forces are affected by bone type significantly, which are highest for bovine cortical bone, and lowest for Sawbones 3401. The levels of significance of geometry parameters are identified and different for thrust force and torque, which can assist new surgical drill development. Quadratic regression equations obtained by response surface methodology can predict thrust force and torque accurately in a wide range of process parameters, which can be used to control drilling conditions for robot assisted surgeries to realize safe drilling.

Experimental Study of Thrust Force and Torque for Drilling Cortical Bone.

This study investigates neurosurgical bone grinding with varying parameters on skull bone using a miniature grinding burr. Three process parameters, namely, rotational speed, feed rate, and depth o...

In vivo evaluation of machining forces, torque, and bone quality during skull bone grinding.

As drilling generates substantial bone thermomechanical damage due to inappropriate cutting tool selection, researchers have proposed various approaches to mitigate this problem. Among these, improving the drill bit design is one of the most feasible and economical solutions. The theory and applications in drill design have been progressing, and research has been published in various fields. However, pieces of information on drill design are dispersed, and no comprehensive review paper focusing on this topic. Systemizing this information is crucial and, therefore, the impetus of this review. Here, we review not only the state-of-the-art in drill bit designs-advances in surgical drill bit design-but also the influences of each drill bit geometries on bone damage. Also, this work provides future directions for this topic and guidelines for designing an improved surgical drill bit. The information in this paper would be useful as a one-stop document for clinicians, engineers, and researchers who require information related to the tool design in bone drilling surgery.

Surgical Drill Bit Design and Thermomechanical Damage in Bone Drilling: A Review

Parameters affecting mechanical and thermal responses in bone drilling: A review

This paper presents an experimental measurement of the thermal conductivity of bovine cortical bone by an improved parallel plate method to increase the accuracy of the measurement. An experimental apparatus was designed to measure the thermal conductivity of the cortical bone using a reference material with a known thermal conductivity by the heat transfer through the samples. To improve the measurement accuracy, a reference material was selected as quartz, which is of the same order of magnitude of the thermal conductivity of bovine cortical bone reported in the existing literature. Additionally, the temperatures at the heat source and heat sink were set to ±5°C from the ambient temperature to reduce the inevitable heat loss in the measurement. The temperature offset was determined numerically. The current experimental measurement was validated by an in-house finite-difference numerical program. The heat loss in the measurement was predicted from the numerical program. The thermal conductivity of the bovine cortical bone was then determined to be 0.55 ± 0.02 W/mK with compensating heat loss.

Experimental Determination of Thermal Conductivity of Cortical Bone by Compensating Heat Loss in Parallel Plate Method

The heat generated during bone drilling can cause significant thermal damage to the tissue. Hence, prediction of the developing temperature field as a function of the drilling parameters is of high clinical value. However, no experimentally validated model has been reported yet. Furthermore, prior theoretical studies are limited to the drilling process, while extending the analysis beyond drill-bit retraction may be of equal interest. Therefore, the current study aims at experimental validation of a recently published thermal model for temperature distributions both during bone drilling, which is now expanded beyond drill-bit retraction. For validation of the model, a set of experiments was conducted on bovine cortical bone, following the new procedures suggested in the previous study in order to ensure a high degree of accuracy and repeatability. This study is based on thermal data collected at a distance range of 0.15 mm to 0.5 mm from the drilled hole, using thermocouples. Measuring temperatures closer to the drilled hole enabled better understanding of temperature distributions in the tissue in bone drilling. Comparison of experimental data and theoretical simulation results validate the model used. Additionally, about 57°C of difference of the maximum temperatures measured at the radii locations between 0.15 mm and 0.5 mm was observed.Copyright © 2016 by ASME

Modeling and Measurement of Temperature Distributions in Bone Drilling


 Deep-hole bone drilling is critical in many surgical implantation procedures. Unlike most common bone-drilling processes, deep-hole bone drilling is performed using a high drilling depth to drill-bit diameter ratio, which can lead to undesirable mechanical and thermal damage during surgical procedures. The objective of this study was to investigate the thrust force and torque generated in deep-hole bone drilling. Drilling tests were performed on bovine cortical bones at a drilling hole depth of 36 mm using a 2.5 mm diameter twist drill bit with a spindle speed of 3000 rpm and feed rates of 0.05, 0.075, and 0.1 mm/rev. Bone chips were collected at different depths and examined using a fiber-optic microscope. Not only are drilling forces a good indicator to assess drilling performances but also chip formation and morphology are important aspects for understanding bone-drilling behaviors. The force signals revealed two distinct states, which were referred to as normal and abnormal states in this study. In the normal state, the force signals remained constant once the drill tip became fully engaged in bone cutting, whereas after a certain drilling depth, the forces considerably increased in the abnormal state. The results of this study indicate that the rapid increase in the force in the abnormal state is mainly attributed to chip clogging inside the flutes as the drilling depth increases. This study also demonstrated that the chip morphology varies with respect to drilling depth, where fragmented chips are produced at shallow drilling depths and powdery chips are produced at deeper drilling depths.

JuEun Lee

Papers

Parameters affecting mechanical and thermal responses in bone drilling: A review

Experimental Determination of Thermal Conductivity of Cortical Bone by Compensating Heat Loss in Parallel Plate Method

Modeling and Measurement of Temperature Distributions in Bone Drilling

An Experimental Investigation of Forces on Cortical Bone in Deep-Hole Bone Drilling