International Conference on Global Trends in Engineering, Technology and Management (ICGTETM-2016)
An Investigation of Relation between Necrosis and Drilling
Parameters
Rajesh V. Dahibhate#1 Ashish B. Deoghare#2
Research Scholar, Dept. of Mechanical Engineering, G.H.R.C.E Nagpur, Maharashtra (India).
Assistant professor, Dept. of Mechanical Engineering, N.I.T. Silchar, Assam. (India).
Abstract-Drilling is a cutting process that uses a drill
bit to cut a hole of circular cross section in solid
materials. The drill bit is a rotary cutting tool often
multipoint. The bit is pressed against the work piece
and rotated at rates from hundred to thousand of
revolutions per minute. This forces the cutting edge
against the work piece, cutting off chips from the hole
as it is drilled. This cutting and frictional force
increases the temperature above 47 degree Celsius
during routine orthopedic bone cuts causing
osteonecrosis with potentially negative impacts on
bone healing and implant failure.
The current literature on bone drilling and
thermal necrosis is reviewed. The methodologies
involved in the experimental and clinical studies are
described and compared. Areas which require further
investigation are highlighted and the potential use of
more precise experimental setup and future
technologies are addressed. Important drill and
drilling parameters that could cause increase in bone
temperature and hence thermal osteonecrosis are
reviewed and discussed: drilling speed, drill feed rate,
Experimental methods of temperature measurement
during bone drilling are defined and thermal
osteonecrosis is discussed with its path physiology,
significance in bone surgery and methods for its
minimization.
Keywords-thermal necrosis, histopathology, Abaqus
software.
1. INTRODUCTION
During bone drilling heat generation may
result in thermal injury due to temperature rise of
bone, with potentially devastating the effects on the
outcome of orthopedic surgery. During bone drilling
shear deformation and friction between the rake face
of drill bit causes heat generation. Hyperthermia and
carbonization resulting in cell death and bone property
changes may be the results of heat generation. A
thermal effect damages the vascular system
immediately which adds to bone death due to
insufficient blood supply. Secondary effects of
heating are driven by friction between the chips, drill
bit body and the bone. The drill bits are manufactured
of a standard such as DIN 1.4112 or AISI 440B and
have chemical composition of approximately 0.85%
C, 18% Cr, 1% Mo, 1% Mn 1% Si, and trace
elements, with the remainder made up of iron. The
drill bit material requires to withstand repeated
sterilization cycles at temperatures up to13580c.
ISSN: 2231-5381
2. LITERATURE REVIEW
Heat generation results in necrosis and in extreme
conditions even carbonization is possible [1-3].To
prevent thermal necrosis favorable drilling conditions
and drill bit geometries are studied by experimental
investigation in literature [4-7], they concluded that
the level of temperature elevation and the duration of
thermal exposure should be minimized.
The drill bit geometry determines the heat
generation [8, 9] the design of drill bit point and
cutting edges controls the cutting forces. Rake face is
an important place which transforms the energy of
shear deformation and friction into heat. Although
smaller point angle could reduce shear stress, making
cutting edge longer, but in overall literature the effect
of point angle is negligible. Since the chisel edge
contributes to thrust force its effect is secondary to
cutting edges.
Furthermore the geometry of the drill bit
flutes contributes to the speed of chips expelled from
the cutting region [12].and as the chips absorb a large
part of heat generated, they can also contributes to
heat removal. The other parameter is helix angle that
affects the cutting edge geometry and fluted region
geometry. It also has effect on generated temperature.
If other parameters are kept constant, heat
generation increases linearly with the cutting speed.
Similarly if drill bit diameter is increased heat
generation increases [5].also to be pointed,
increasing feed rate and independently the spindle
speed also increases temperature. The initial
thermal damage and post surgery bone healing is
observed to be affected most by spindle speed
[14].although it can be said that lower feed rate and
slower spindle speed are always a favorable in
reducing thermal effects. Other effects like low
conductivity material drilling, the chip stream
material itself convects the heat from the cutting
edge, along the flute, creating a cooling mechanism,
where a higher a feed rate leads to a faster chip
stream. Davidson and James [15] suggested a
thermal model to predict temperature elevation in
the bone during drilling. A homogeneous
differential equation of heat conduction was derived
in the radial direction only and one dimensional
conduction equation was solved analytically,
kalindini [16].most recently an elastic plastic model
was presented by Tu et al.[17] to simulate
temperature rise with ABAQUS software to
estimate the temperature rise. In general, the
literature shows that if the temperature rises above
550C for a period of longer than one-half a minute,
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3.2 Drill bit specifications- 1. Drill diameter- 3,
6,9mm, 2. Drill tip angle- 1180, 3. Rake angle- 350,
4.Helix angle-280.
ISSN: 2231-5381
TABLE I DRILLING PARAMETERS
SR.NO
SPEED(RPM)
TEMPERATURE (0C)
1
600
FEED
RATE
(mm/sec)
0.3
41.2
46.5
54.2
2
1200
0.6
43.5
47.8
56.5
3
1800
0.9
44.6
49.9
58.4
4
2400
1.2
45.2
51.3
60.2
3mm
6mm
9mm
80
60
40
3mm
20
6mm
0
9mm
600 1200 1800 2400
spindle speed (rpm)
Fig. 2 The variation of temperature with spindle speed and drill
diameter. All the values are calculated for the initial temperature of
250c and 370c for the drill bit and bone respectively.
Temp.(Degree celcius)
serious damage
.Will be done to the bone, which may take several
weeks to
fully recover.
3. Aim of the research
The objective of this work is to measure the thermal
necrosis in bone during orthopedic drilling and to see
the effect of various parameters of drilling process on
temperature rise.
Methods and materials-Sheep bone was selected
because it is readily available. Furthermore sheep
bone has been used in previous studied on the effect of
drilling and cutting.
Sheep rib bone was obtained from a local
butcher. The soft tissues attached to bone were
cleaned with a sharp cutter and saline water and then
the bone specimen was dipped in buffer solution. The
average specimen thickness was 2mm and average
area of the surface across which heat distribution to be
studied is 10mmX5mm.
3.1
Experimental
apparatus
and
procedure-To avoid the vibrations and to achieve
accuracy CNC milling machine is used for the drilling
purpose. the specimen during the drilling process was
kept in Phosphate Buffer Solution (sodium salt) with
ph 7.4.for this Stock solution A-(Na2HPO4.2H2O), 0.2
molar
solution
containing
35.61g/L
or
(Na2HPO4.12H2O), 0.2 molar solution containing
71.64g/L .and Stock solution B-(NaH2PO4.2H2O), 0.2
molar solution contains27.67g/L or (NaH2PO4.2H2O),
0.2 molar solution containing 31.21g/L .on addition of
A and B, (X ml of A+Y ml of B), diluted to a total of
200 ml. that is X=19.0,Y=81.0,PH=7.4.For 100 ml-A
solution 3.561 g/100 ml, B solution 3.121 g/100
ml.The solution was maintained at 37.80C to simulate
live body temperature. The temperature at the drilling
site is measured with the help of a infrared
thermometer. Four speed range 600, 1200, 1800 and
2400rpm were preferred. These were chosen in order
to go below and above the speeds recommended in the
literature for the drilling of bone. The drill bit
diameter was 3,6 and 9mm and feed rates used were
0.3,0.6,0.9 and1.2 mm/sec.These feeds were chosen
arbitrarily, since in orthopedic practice the feed rate
varies from surgeon to surgeon and in the case of a
particular surgeon there will also be a variation, since
the drill is hand-held.After each drilling the specimens
were dipped in different bottles containing 10%
formalin. After a gap of 45 days and an interval of 4
days the chemical solution was replaced with a new
one.
80
60
40
3mm
20
6mm
0
9mm
0.3
0.6
0.9
1.2
Feed rate (mm/sec)
Fig. 2 The variation of temperature with spindle feed rate and drill
diameter.
4. Histology- An Introduction to Decalcification
Bone consists of cells (osteocytes) surrounded by a
calcified matrix. In the matrix calcium is in the form
of hydroxyapatite crystals [Ca10(PO4)6(OH)2] which
are deposited between the fibrous elements. These
crystals are dissolved out during the process of
decalcification which leaves cohesive tissue with the
physical characteristics of dense fibrous connective
tissue. There are a number of options available when
the histologist is required to produce sections from
bone or other calcified specimens. In choosing a
technique and processing method consideration must
be given to the type of investigation being carried out.
In order to protect the cellular and fibrous elements of
bone from damage caused by the acids used as
decalcifying agents, it is particularly important to
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thoroughly
fix these
specimens
prior
to
decalcification. After completion of the following
steps of fixation, dehydration, clearing and
embedding, section cutting, staining with the help on
microtome machines the section were made and
observed under microscope The ratio of fixed and
empty lacunae indicates the spread of heat over bone
along length.
6. CONCLUSIONS
Fig 3 Histological appearance of bone sections depicting the
vascular response.Empty lacunaes indicating traumatized bone.
5. ABAQUS SOFTWARE- A model was made in
CATIA software with dimensions of length-50mm,
width-10mm and thichness-3mm.the model was then
imported in Abaqus. Following properties were
applied to it.
During the experimentation work it is observed that
the effect of spindle speed as well as feed rate should
be considered the effect of drill bit diameter like 3, 6,
and 9mm that are the general diameters also affect the
temperature generation linearly. The selected bone
was a rib bone of a three months old lamb which is
having almost the same characteristics as that of a
human bone. Again from histopathological point of
view thinner bones had to be selected. To provide the
best cutting conditions and maintaining temperatures
at a manageable level it recommended drill bit of
3mm diameter, feed rate of 0.6 mm/sec and speed of
1200 rpm.
TABLE II
PROPERTY VALUES USED DURING ABAQUS SOFTWARE.
PROPERTY
1.Thermal
conductivity.
2. Specific heat.
3. Thermal diffusivity.
4. Density.
5. Porosity.
6. Elastic modulus.
UNIT
w/m0c
VALUE
0.15-0.35
Jkg/0c
M2/sec
Kg/m3
N/m2
KJ/m2
1300
0.3*10-6
1800
5-10%
1.Tension-11-19*109
2.compression-15-20*109
1.Tension-107-146*109
2.compression-156-212*109
3.shear-72-82*109
1. Longitudinal-11-21.
2. Transverse-5-13.
1. Tensile strength-60-70.
2. Compressive strength-70280.
1. Tensile strength-50.
2. Compressive strength-50.
0.5-3%.
KJ/m2
1.5
2
7.Ultimate stress
N/m
8.Youngs modulus
Gpa
9.
Longitudinal
strength.
Mpa
10.
Transverse
strength.
11. Maximum total
elongation.
12. Fracture energy.
Mpa
Fig. 4 Temperature distribution in drilled bone using Abaqus.
ISSN: 2231-5381
ACKNOWLEDGMENT
The author wishes to acknowledge the contributors for
developing the histopathological sections and
conducting drilling processes. The authors also wish
to thank the graduation students for their assistance in
managing Abaqus software.
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