Drilling Force and Temperature of Bone by Surgical Drill

Yixin Yang1,a, Chengyong Wang1,b, Zhe Qin1,c, Linlin Xu1,d,

Yuexian Song1,e and Hanyuan Chen2,f

1Guangdong University of Technology, Guangzhou, P.R. China

2Guangzhou Aquila Precise Tools LTD, Guangzhou, P.R. China

ayangyixin_1984@126.com, bcywang@gdut.edu.cn, cimt@gdut.edu.cn, dxulinlin1214@163.com, esongyx@gdut.edu.cn and faquilatools@vip.163.com

Keywords: Bone drilling, Drilling force, Drilling temperature, Surgical drill

Abstract: Drilling force and temperature of tibia at the high speed drilling for improving the design

of surgical drills are very important. In this paper we describe experiments using pig tibia bones,

measuring the drilling force and temperature of a new design of drill bit and compare the results

against a twist drill. The result shows that the drilling force and temperature are affected by the feed

rate and drilling speed, which vary with the drilling depth into the bone. The new surgical drill with

three top cutting edges can achieve lower temperature below 47oC and lower drilling force than with

the stainless steel twist drill and carbide twist drill.

Introduction

Bone is a composite material of many tissues. Because different types and different position of bones

existing diverse mechanical properties, as well as the demand of postoperative recovery and

rehabilitation cycle of bone tissue, orthopedic surgery has specificity of processing. In orthopedics

surgery, the doctor must force the drill into the bone smoothly by hand. The force acted on electric

drill device depends on different spot of bone to be drilled or the drilling depth. Considering the

improvement of the surgery quality and the reduction of health recovery time, surgical drill must be

easy to drill through the bone with smaller thrust force. It is very important to reduce the patient

hemorrhage, the generation of bone chipping and the doctor's physical labor intensity, avoiding the

winding of bone tissue and so on. By the way, the bone presents a curved surface shape, the surgery

drill needs to be able to locate accurately on the surface rapidly without slipping phenomenon.

Furthermore, the drilling temperature must be controlled below 47°C as much as possible in the

drilling process of surgery in order to avoid the thermal damage of bone tissue. This temperature is

the highest safe temperature which will prevent the generation of irreversible change of bone

structure and physical properties. These damages will not only affect the quality of the holes and the

installation of implants, but also greatly increase the patient's recovery time and cause the surgery

complication possibility.

The structure of drill and the drilling parameter (such as cutting force, feed rate, rotational speed,

cutting tool geometry angle and cutting temperature and so on) have the close relation to the bone

treatment. Larry measured the drilling temperature of corpse femur backbone using thermocouples.

They found that the force applied to the drill was found to be much more important than drilling speed

as a factor in both the magnitude and duration of cortical temperature elevations. The highest average

maximum temperature measured was 93.1°C at a drill speed of 2900 rpm and a force of two

Advanced Materials Research Vols. 126-128 (2010) pp 779-784Online available since 2010/Aug/11 at www.scientific.net© (2010) Trans Tech Publications, Switzerlanddoi:10.4028/www.scientific.net/AMR.126-128.779

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kilograms. When the load is twelve kilograms, the drills temperature is 51.2°C [2]. Allotta drilled the

swine femurs by changing the feed rate and drilling speed in the Instron testing machine. Comparing

with the datum of axial force and the theoretical model obtained by cortical bone drilling, the charters

of both of them was consistent [3]. Nam drilled the bovine rib bone with a constant drilling speed and

load by water cooling, and monitored the changes of temperature using Thermovision 900 system. It

was pointed out that the rise in temperature was significantly related to drilling speed and load. As the

load increased, the drilling temperature also increased. At the drilling speed of 1200 rpm and in the

load of 1000 g, the measured maximum temperature is 62.4°C [4]. Udiljak T. drilled the bone on the

ALG-100 tool-and-die milling machine, using the Kistler dynamometer to measure axial force at the

time of drilling. They found that the drilling speed, the drill feed rate and the drilling tool geometry

were the influencing factors of drilling process. At the drilling speed of 1132 rpm, the measured

maximum temperature is 62.4°C [1]. Only a few researches refer to the improvement of design and

the structure of drill. The generation mechanism and control of drilling force and temperature of bone

haven’t been mentioned.

In this paper, the axial drilling force and drilling temperature were measured and analyzed by

varied rotate speed, feed rate and drilling tool geometry for future quick evaluation of performance of

various bone drills.

Experiment

The stainless steel twist drill generally used in hospital and the new medical drill with "W" shape of

drill point are shown in Table 1, which are used to drill the fresh swine tibia without adding coolant.

At present, the rotational speed commonly used in surgical drill is from 1000 to 2000 rpm. In order to

study the drilling force and the temperature change of the drill comprehensively under each rotational

speed, we expand the research scope of rotational speed. For the measuring of drilling force and

drilling temperature, the experiment conditions are shown in Table 1, which is higher than the speed

used in surgery mentioned above now. The time of death of fresh pig tibia which is processed into a

100 mm long tubular shape beforehand, is not more than five hours.

Table 1 Experiment Conditions

Drill

Figure

stainless steel twist drill

new medical drill

Diameter (mm) 4 4

Point angle 108 95

Helix angle 25 26

Rotational Speed (rpm) 1000, 2000, 3000, 4000, 5000, 6000, 7000, 8000, 9000, 10000

Feed rate (mm/min) 50, 75, 100

Bone swine tibia (shear strength: 82±1.8 MPa)

High speed drilling experiment is carried out on high-speed machining center (DMU 60T) with the

highest spindle speed 24000 rpm. Drilling forces and cutting torque are measured by a piezoelectric

dynamometer, the signals are adopted by charge amplifier and A/D card, which is processed by

computer finally. The experimental device is shown in Fig. 1.

780 Advances in Abrasive Technology XIII

Spindle

Specimen

Drill

thermograph

Room temperature ( 26¡æ )

Clamping

element

Dynamometer

Osteon of

compact bone

Trabeculae of

spongy bone

Fig. 1 Schematic illustration of experimental system

Results and Discussions

Basic Characters of Drilling forces

The changes of the highest average maximum drilling force using stainless steel twist drill are shown

in Fig. 2(b). The change of drilling force is related to the structure of bone. As can be seen in Fig. 2(a),

the drill need to cross osteon of compact until trabeculae of spongy bone into the drilling process.

The drilling force increases slowly while the drill begins to drill in the osteon of compact. Because of

osteon of compact bone, the drilling force increases rapidly while the drill bit enter into the osteon,

and the drilling force achieves the maximum at the time when the whole the drill bit are all in the

osteon of compact. Finally, the drilling force declines quickly at the time of drilling trabeculae of

spongy.

50mm

3mm

Osteon of

compact bone

Trabeculae of

spongy bone

(a) (b)

0 0.5 1.0 1.5 2.0 2.5

50

100

150

200

250

Drilling time (s)

Drilling for ce (N)

3.0

Fig. 2 The drilling process and the drill force changes of Stainless steel twist drill

The Effect of Drilling Parameters

Drilling speed. As shown in Fig. 3(a), when the stainless steel twist drill is used, the highest average

drilling force would be reduced with the increase of drilling speed on a decreasing trend. When the

new medical drill is used for drilling, the drilling force would be changed with "U" shape in the whole

drilling process, and the drilling force would be reduced with the increase of drilling speed during

0-6000 rpm, increased with the increase of drilling speed during 6000-10000 rpm, and attain

minimum in the 5000 rpm of drill during as shown in Fig. 3(b).

Advanced Materials Research Vols. 126-128 781

(a)

0 2000 4000 6000 8000 10000

50

100

150

200

250

Drilling speed (rpm)

Drilling for ce (N)

F eed ra te5 0m m /m in 75m m /m in 1 00m m /m in

(b)

F e ed r a te50 mm /m in 75m m /m in 1 0 0m m /m in

0 2000 4000 6000 8000 10000

50

100

150

200

250

Drilling speed (rpm)

Drilling force (N)

Fig. 3 The changes of drilling force (a) stainless steel twist drill (b) new medical drill

Feed rate. With the increasing of the feed rate, the axial drilling force will increase as shown in

Fig. 3, but the processing time would be reduced. Compared with new medical drill, the drilling force

of stainless steel twist drill would be changed more obviously by the change of feed rate, which

means the new medical drill is more suitable for surgery.

Drilling tool geometry. The stainless steel twist drill hasn’t much distinction with general drills.

However, the structure of new medical drill bit has been designed with the "W" type, three cutting

edges on the top of drill to cut the bone. These cutting edges increase the rake angle of the top cutting

edges and reduce the drilling force, as shown in Fig. 3. So the drilling force of new medical drill is

significantly less than stainless steel twist drill. In addition, as the new medical drill drill the bone

with three point cutting edges will help the position of drill on the bone surface, the slipping of drill

would be prevented, and the suffering of patients would be reduced. Checking the drilling torques by

two drills as shown in Fig. 4, the drilling torque of stainless steel twist drill have few difference with

the structure change of drill bit, but the new medical drill show obvious change in drilling torque.

(a)

F e e d r a te5 0m m /m in 7 5m m /m in 1 0 0m m /m in

0 2000 4000 6000 8000 10000

1

2

3

6

7

Drilling speed (rpm)

Torque (N. m)

4

5

(b)

F e e d r a te5 0m m /m in 7 5m m /m in 1 0 0 m m /m in

0 2000 4000 6000 8000 10000

1

2

3

6

7

Drilling speed (rpm)

Torque (N. m)

4

5

Fig. 4 The changes of torque (a) stainless steel twist drill (b) new medical drill

Drilling Temperature

The measuring of temperature rising process is performed with a thermographic camera,

Research-N1 digital network thermovision and analysis system. The bone surface was cleaned from

tissue rests. What’s more, the camera was set at angle of 45 in relation to the hole axis (drilling

direction).

As it’s showed in Fig. 5, the temperature rising process between stainless steel twist drill and new

medical drill were recorded by the thermographic camera. From Fig. 5(a) to Fig. 5(b), the temperature

782 Advances in Abrasive Technology XIII

increased from 34.74°C to 48.42°C with a stainless steel twist drill. However, the temperature

increased from 33.8°C to 44.96°C with a new medical drill from Fig. 5(c) to Fig. 5(d).

(a)

Bone

Drill

Drill

Bone

(b)

(a) stainless steel twist drill

(c)

Bone

Drill

Drill

Bone

(d)

(b) new medical drill

(Condition: Drilling speed: n =2500 rpm, Feed rate: Vf =50mm/min)

Fig. 5 The temperature rising process of stainless steel twist drill and new medical drill

Table 2 The drilling temperature rise of stainless steel twist drill and new medical drill

Conditions

stainless steel twist drill

new medical drill Drilling speed

(rpm)

Feed rate

(mm/min)

1000

50

(a)

Bone

Drill

Drill

Bone

(b)

2500

Drill

Bone

(c)

Drill

Bone

(d)

5000

Drill

Bone

(e)

Drill

Bone

(f)

Advanced Materials Research Vols. 126-128 783

As shown in Table 2, the highest bone drilling temperature using the stainless steel twist drill is

41.1°C as the drill contacts with the bone in Table 2(a). Then its temperature does not increase

immediately because of the lower heat conduction of bone. For the new type of medical drill the

contact temperature are shown as 44.96 °C in Table 2(b) and as 41.48 °C in Table 2(d).

It can be seen that with the increase of the drilling speed, the highest drilling temperatures are also

increasing. For example, the highest temperature is 41.48°C at drilling speed 1000 rpm in Table 2(b)

and 44.96°C at drilling speed 2500 rpm in Table 2(d). When the drilling speed reaches 5000 rpm, the

highest temperature arrives at 67.02°C in Table 2(e) and 59.97°C in Table 2(f). Therefore, we should

try to reduce the drilling speed. The drilling temperature of new type of medical drill can be

controlled below safe temperature with higher drilling speed than that of stainless steel twist drill.

In the comparison of temperature rising process of the stainless steel twist drill and the new type of

drill, we can find that the stainless steel twist drill’s temperature is significantly higher than that of the

new type of medical drill with the same speed. This shows that the shape of the drill has a direct

relationship with the temperature rising. In addition, in the drilling process, most of the heat is

brought away by the drilling chip at a high temperature and the bone’s temperature will not increase

quickly, avoiding thermal damages of bones.

Conclusions

Drilling force decrease with the increase of drilling speed and feed rate. The change of drill’s shape

will cause a rapid reduction in drilling force and temperature. The drilling force of the new medical

drill is obviously smaller than the stainless steel twist drill. Therefore, shape designing of drills is also

an important factor for control of drilling force.

When the drilling speed increases, the drilling temperature is also increasing. The drilling

temperature of the new medical drill can be controlled below safe temperature with higher drilling

speed than that of stainless steel twist drill.

Acknowledgement

This project was granted by Panyu R & D research plan of China (No. 2009-Z-53-1).

Reference

[1] T. Udiljak, D. Ciglar, S. Skoric: Advances in Production Engineering & Management Vol.

2(2007), p. 103

[2] L. S. Matthews, C. Hirsch: J Bone Joint Surg Am Vol. 54 (1972), p. 297

[3] B. Allotta, F. Belmonte, L. Bosio, P. Dario: Mechatronics Vol. 6 (1996), p. 450

[4] O. Nam, W. Yu, M.Y. Choi, H.M. Kyung: Key Engineering Materials Vol. 321-323 (2006), p.

1044

[5] G. Augustin, S. Davila, K. Mihoci, T. Udiljak, D.S. Vedrina, A. Antabak: Arch Orthop Trauma

Surg Vol. 128 (2008), p. 71

784 Advances in Abrasive Technology XIII

Advances in Abrasive Technology XIII 10.4028/www.scientific.net/AMR.126-128 Drilling Force and Temperature of Bone by Surgical Drill 10.4028/www.scientific.net/AMR.126-128.779

DOI References

[1] T. Udiljak, D. Ciglar, S. Skoric: Advances in Production Engineering & Management Vol. (2007), p. 103

doi:10.1063/1.2710464 [3] B. Allotta, F. Belmonte, L. Bosio, P. Dario: Mechatronics Vol. 6 (1996), p. 450

doi:10.1109/3516.506150 [4] O. Nam, W. Yu, M.Y. Choi, H.M. Kyung: Key Engineering Materials Vol. 321-323 (2006), p. 044

doi:10.4028/www.scientific.net/KEM.321-323.1044 [4] O. Nam, W. Yu, M.Y. Choi, H.M. Kyung: Key Engineering Materials Vol. 321-323 (2006), p. 1044

doi:10.4028/www.scientific.net/KEM.321-323.1044