FINITE ELEMENT SIMULATION OF THREE SURGICAL TREATMENTS OF
DISTAL RADIUS INTRA-ARTICULAR FRACTURE
ARASH NASROLLAHI SHIRAZI
A report submitted in partial fulfillment of the
requirements for the award of the degree of
Master of Engineering (Mechanical)
Faculty of Mechanical Engineering
Universiti Teknologi Malaysia
NOVEMBER 2010
iii
To my beloved mother and father, Fakhrosadat Banaroei and Mohsen Nasrollahi
Shirazi and my brother and sister, Pooyan and Sanaz for their never ending support.
Thank you for everything.
iv
ACKNOWLEDGEMENT
To complete this Master Degree Project report, I learned many useful
softwares and I had received a lot of information and valuable guidance from my
supervisor, Assoc Prof. Eng. Dr. Rafiq Abdul Kadir. His knowledge and proficiency
in Biomechanics supported and encouraged me to complete this project.
I respect and thank my beloved family Mrs. Fakhrosadat Banaroei and Mr.
Mohsen Nasrollahi Shirazi, my sibeling, Mr. Amir and Mrs Fateme for their
constantly love and support.
I would like to thank my precious friends Mr. Jamal Kashani, Mr. Nazri
Bajuri, Mr. Amir Hossein Goharian, Mr.Ali Falahi and his wife Mrs. Mina Alizade,
Mr. Ahmadreza Abassi, Mrs. Eliza yusup, Mr. Raja and all who concerned with my
project or not and for their moment that they shared with me in joys and difficulties.
v
ABSTRACT
Distal radius fractures are the most common injuries, with an estimate overall
crude incidence of 36.6/10,000 person-year in women and 8.9/10,000 person years in
men. Assuming a continuous rise in the incidence of distal radius fractures with age,
and based on the fact that older population continues to grow, incidence of distal
radius fractures can be expected to increase. Different surgical methods can be used
to fix the complicated, unstable and displaced distal radius fractures. The
conventional surgical method with volar plating has been described the good results
in young patient. However, the elderly patients especially who has the osteoporotic
bone may have higher risk of loss of reduction in conventional types of fixation. The
aim of this study is to compare the latest treatment angle-stable constructs with
conventional model for unstable three fragmental intar-articular distal radius fracture
(AO 23-C2.1) under various load conditions using finite element analysis in order to
find the stiffer surgical methods to facilitate the anatomic reduction and maintenance
of the reduction. The fixation methods consist of 1 I-shape styloid plate and 1
intermediate dorsal plate (Group 1), single T-shape volar plate (Group 2) and 1 Ishape styloid plate and single T-shape volar plate (Group 3). This study analysed the
rigidity base on linear load-displacement graph. To compare the rigidity, the fixation
methods analysed under the applied loads (axial-loads, bending and torsion). The
displacement and von Mises stress values showed the superior stability and rigidity
for angle-stable double plates constructs.
vi
ABSTRAKT
Tulang yang patah pada bahagian distal radius adalah kecederaan yang paling
umum, dengan anggaran kasar secara keseluruhan sebanyak 36.6 bagi setiap 10, 000
orang (perempuan) dan 8.9 bagi setiap 10 000 orang (lelaki) setiap tahun.
Pertambahan kes dijangka akan terus berlaku lantaran wujudnya pertambahan warga
tua (berikutan peningkatan taraf kesihatan) yang pastinya lebih terdedah kepada
kecederaan tulang, Terdapat banyak kaedah yang boleh digunakan bagi merawat
masalah kepatahan tulang radius distal Kaedah pembedahan konvensional dengan
menggunakan plat pada bahagian volar telah memberi impak yang baik pada pesakit
muda tetapi tidak kepada pesakit tua, terutama yang menghidap penyakit
osteoporosis. Tujuan kajian ini adalah untuk membuat perbandingan antara kaedah
terbaru iaitu sudut-stabil baru konstruk dengan model konvensional bagi merawat
kes kepatahan tulang bercirikan ‘unstable three fragmental intar-articular distal
radius fracture’ (AO 23-C 2.1). Analisis ini menggunakan kaedah simulasi komputer
dengan menggunakan ‘Finite element ’ bertujuan mencari kaedah terbaik dalam
mennghasilkan kaedah fiksasi yang lebih kukuh. Terdapat tiga kumpulan utama bagi
kaedah fiksasi, iaitu penggunaan satu plat styloid berbentuk I dan satu plat pada
bahagian pertengahan dorsal (Kumpulan 1), penggunaan satu plat di bahagian volar
berbentuk T (Kumpulan 2) dan penggunaan satu plat berbentuk I pada bahagian
styloid dan satu plat berbentuk T pada bahagian volar (Kumpulan 3). Analisa ke atas
kekukuhan struktur dibuat berdasarkan graf beban-perpindahan linier. Bagi tujuan
itu, kaedah fiksasi dikaji dengan menggunakan keadaan beban yang pelbagai (paksibeban, lentur dan torsi). Hasil daripada kajian ini (berdasarkan nilai tekanan von
Mises dan juga perubahan bentuk) menunjukkan bahawa plat ganda sudut-stabil
pembinaan yang menggunakan dua plat adalah lebih baik dari segi kekukuhan
struktur berbanding penggunaan hanya satu plat sahaja.
vii
TABLE OF CONTENT
CHAPTER
1
TITLE
PAGE
TITLE
i
DECLARATION
ii
DEDICATION
iii
ACKNOWLEDGEMENTS
iv
ABSTRACT
v
ABSTRAK
vi
TABLE OF CONTENTS
vii
LIST OF TABLES
xi
LIST OF FIGURES
xii
LIST OF ABBREVIATIONS
xiv
INTRODUCTION
1
1.1
Introduction
1
1.1.1 Wrist anatomy
1
1.1.1.1 Bones and joints
1.2
2
Wrist fracture
3
1.2.1 Distal radius fracture
3
1.3
Problem Statement
4
1.4
Objective of Study
5
1.5
Scope of study
5
viii
2
LITERATURE REVIEW
6
2.1
Introduction
6
2.1.1 Classification of intra-articular fracture
6
(1) Intra-articular fracture with displaced
dorsal fragment
(2) Dorsal split with dorsal dislocation
7
(3) palmar split with palmar dislocaton
8
(4) Complex distal radius fractures with
metaphyseal separation
(5) Destruction of the articular surface
2.2
9
9
Different studies on fixation methods
10
2.2.1 Clinical Method
10
2.2.1.1 Non-invasive Techniques
11
2.2.1.1.1 Conservative treatment
11
2.2.1.1.2 External Fixation
12
2.2.1.1.3 Pining
13
2.2.1.2 Open surgery
14
(a) Plates
14
(b) Fragment-specific Fixation
15
(c) Volar locking plates
16
2.2.2 Protocol for surgical treatment
17
2.3 Experimental Method
2.3.1 A novel non-bridging external fixator versus
volar angular stable plating
2.3.2
Comparing volar with dorsal fixation plates on
unstable extra-articular fractures
2.4
7
Computer Simulation Method
18
19
20
22
2.4.1 Biomechanical evaluation of three types of
implants
3
METHODOLOGY
22
27
ix
3.1
Introduction
27
3.2 Mimics Software
27
Step 1: Imported the medical data
28
Step 2: Thresholding
29
Step 3: Segmentation density masks
29
Step 4: Region growing
30
Step 5: 3D Reconstruction
31
3.2.1
32
Constructed of fractured bone
3.3 Implant Design
3.3.1 Introduction of Solidworks Software
35
3.3.2 Designing the implants
36
Simulation of surgical fixation
37
3.5 Introduction to MSC.Marc Software
39
3.4
4
35
3.5.1
Analysing the three fixation methods
40
3.5.2
Applying the loads
41
RESULTS AND DISCUSSION
43
4.1
Introduction
43
4.2 Axial-loads results
44
4.2.1
Displacement
44
4.2.2
Von-Mises Stress
46
4.3 Bending results
4.4
49
4.3.1
Displacement
49
4.3.2
Von-Mises Stress
51
Torsional results
53
4.4.1
Displacement
54
4.4.2
Von-Mises Stress
55
4.5
Overviewing of three three fixation methods
58
4.6
Validation of study
60
4.6.1
Surgical validation
60
4.6.2
Experimental validation
60
x
5
DISCUSSION AND RECOMMENDATION
62
5.1 Discussion
62
5.2
63
Recommendations
REFERENCES
64
xi
LIST OF TABLES
TABLE NO.
TITLE
PAGE
4.1
Maximum displacement (mm) and maximum von
Mises stress (MPa) values of the bone around the
screws of all three groups under the applied loads
47
4.2
Maximum displacement (mm) and maximum von
Mises stress (MPa) values of the bone around the
screws of all three groups under the bending loads
52
4.3
Maximum displacement (mm) and maximum von
Mises stress (MPa) values of the bone around the
screws of all three groups under the torsional
loads
57
xii
TABLE OF FIGURES
FIGURE NO.
TITLE
1.1
Distal and proximal rows of carpal bones
2
2.1
CT-based classification of comminuted intra-articular
7
PAGE
fractures of the distal radius. Type I: intra-articular
fracture with displaced dorso-ulnar fragment
2.2
Type II: dorsal split with dorsal dislocation
8
2.3
Type III: palmar split with palmar dislocation
8
2.4
Type IV: complex distal radius fractures with
9
metaphyseal separation
2.5
Type V: destruction of the articular surface
10
2.6
Schematic drawing of a monolateral external fixator
13
with double ball joints after application to the radial
aspect of the second metacarpal and diaphysis of
the radius: the distal ball joint is centred between
the capitate (C) and lunate bone (L) (intraoperatively
by identification with a bone elevator under image
intensification, lower part of the image) to allow for
mobilisation of the fixator.
xiii
2.7
Typical placement of two T-pins for fixation a distal
14
radius fracture is shown in this posterior-anterior
radiograph. The surgeon has inserted two T-pins from
the radio styloid to stable fracture fixation. The
surgeon has inserted two T-pins from the radio styloid
to stable fracture fixation
2.8
A fragment-specific wrist fixation system
15
2.9
A 31-year-old woman with reverse Barton fracture
16
fixed by volar locking plate
2.1O
The southern Sweden treatment protocol for DRF
18
when selecting different treatments the patient’s age
and demands
2.11
Experimental test with isolated radius placed of
19
custom-made compensator to applied ratio (60-40%)
of the forces transferred to scaphoid and lunata
fragments. (A) Non-bridging external fixation method.
(B) Volar locking fixation method
2.12
(A)The LDRS 2.4-mm intermediate and styloid plates.
21
(B)The LDRS 2.4-mm volar plate.
(C)The LDRS 2.4-mm volar and styloid plates.
(D) The 3.5-mm stainless steel T plate.
2.13
Finite element of different surgical methods. (A) T
shape single volar plate meshing model. (B) Meshing
model of double-palates fixation method. (C) The
modified double-plating (MDP) meshing model
23
xiv
2.14
Loading conditions for model. Axial loading bending
24
and torsion are indicated with arrows. The axial
loading was applied in the middle of the upper radius
surface. The bending force was applied on the volar
side of radius. Torsion is applied on both sides of the
radius representing the external rotating force
2.15
(A) Average total displacement of the fracture site
25
under 50 N axial compression, 2 N-m bending and 2
N-m torsion loads. (B) Maximum displacement of the
fracture site under 50 N axial compression, 2 N-m
bending and 2 N-m torsion loads
2.16
(A) Maximum von Mises stress value for bone in
26
single, DP, and MDP models under 50 N axial
compression, 2 N-m bending and 2 N-m torsional
loads. (B) Maximum von Mises stress value of T plate
in single, DP, and MDP models under 50 N axial
compression, 2 N-m bending and 2 N-m torsional loads
3.1
CT scan image for using in mimic
28
3.2
The top and side views for radius bone that
29
Thresholding by the white color triangular to separate
the radius bone
3.3
The side view of region growing that shown in pink
30
color
3.4
The process of smoothing (A, B and C) to achieve
31
radius bone
3.5
The measured guide lines for cutting (A)
Approximately 10 mm(10.44 mm) from the from
articular surface. (B) About 15° (14.81°) volar wedge
33
xv
3.6
The simulated three segments unstable intra-articular
33
fracture (AO 23-C2.1 fracture). The circle shows the
cut with the curve tool
3.7
(A) The scaphoid segment cleaned meshes.
34
(B) The lunate segment cleaned meshes. (C) The distal
part of the radius cleaned meshes (all segment related
to the cortical parts only)
3.8
(A) Intermediate dorsal LDRS 2.4 mm plate. (B) Volar
37
T-shape LDRS 2.4 mm plate. (C) I-shape Styloid
LDRS 2.4 mm plate
3.9
Fixed all the meshes around the screws on both cortical
38
and cancellous parts of bone
3.1O
Fixed all the interfaced meshing part between all
39
cancellous and cortical and screws. (The red parts
show the interfaced parts)
3.11
Defined the young’s modulus, Poisson’s ratio and
40
contact parts for each part (that showed in collared
parts)
3.12
Axial loading that applied on scaphoid and lunate
42
regions base on each percentage and tilt angle, bending
load that exerted on simulated bone on volar side of the
radius and the torsion applied of the radius part of the
bone
4.1
Model rigidity under axial compressive load
45
4.2
Maximum displacement of the bone around the screws
45
under the 10 N, 25 N, 50N, and 100 N loads
xvi
4.3
Maximum von-Mises stress under the 10 N, 25 N, 50N
46
and 100 N loads
4.4
Maximum von-Mises stress of the bone around the
47
screws under the 10 N, 25 N, 50N, and 100 N loads
4.5
The contour plots of displacement for three groups of
48
fixations under applied 100 N axial load
4.6
The mean maximum displacement under bending loads
50
(1 N-m, 1.5 N-m, 2 N-m)
4.7
The maximum displacement around the screws under
50
applied bending loads (1 N-m, 1.5 N-m, 2 N-m)
4.8
The maximum von-Mises stress under applied bending
51
loads (1 N-m, 1.5 N-m, 2 N-m)
4.9
The maximum von-Mises stress around the screws
51
under applied bending loads (1 N-m, 1.5 N-m and
2 N-m)
4.1O
The contour plots of displacement for three groups of
53
fixations under applied 2 N bending load
4.11
The mean maximum displacement under torsion loads
54
(1.5 N-m, 2 N-m, 2.5 N-m)
4.12
The maximum displacement around the screws under
55
applied torsion loads (1.5 N-m, 2 N-m, 2.5 N-m)
4.13
The maximum von-Mises stress under applied bending
56
loads (1.5 N-m, 2 N-m and 2.5 N-m)
4.14
The maximum von Mises stress around the screws
under applied torsion loads (1.5 N-m, 2 N-m and
2.5 N-m)
56
xvii
4.15
The contour plots of displacement for three groups of
58
fixations under applied 2 N torsional load
4.16
(A) Average total displacement of the fracture site
under the 100 N axial compression, 2 N-m bending
and 2.5 N-m torsional loads. The total displacement
was averaged from the displacement of the nodes on
the fracture site. (B) Maximum von Mises stress value
for bone in three groups of fixations under 100 N
compression load, 2 N-m bending and 2.5 N-m
torsional loads
59
xviii
LIST OF ABBREVIATIONS
2D
-
Two Dimensional
3D
-
Three Dimensional
CAD
-
Computer-Aided design
CT
-
Computerized Tomography
DRFs
-
Distal Radius Fractures
DP
-
Double Plating
FEA
-
Finite Element Analysis
HU
-
Hounsfield Scale
LCPS
-
Locking Compression Plate System
LCPS
-
Locking Compression Plate System
LDRS
-
Locking Distal Radius System
MDP
-
Modified Double Plating
MRI
-
Magnetic Resonance Imager
CHAPTER 1
INTRODUCTION
1.1 Wrist joint
Wrist joint is the most complex of all joints in the body. The wrist must be
extremely mobile to give our hands a full range of motion. At the same time, the wrist
must provide the strength for heavy gripping. The kinematics and kinetics of the wrist
hasn’t been completely understood yet. The wrist joint plays a significant role in
maintaining a normal daily life. Normal wrist motions involve with the ligaments as well
as the carpal, radius and ulna bones [1].
1.1.1
Wrist anatomy
Wrist structure can be divided in to several categories:
2 •
bones and joints
•
ligaments and tendons
•
muscles
•
nerves
•
blood vessels
1.1.1.1 Bones and joints
The connections from the end of the forearm to the hand there are 15 bones. The
wrist itself contains 8 bones, called carpal bones, the ulna and the radius. The carpal
bones are separated into two rows, namely the proximal and distal that shown in Fig1.1.
Fig 1.1: Distal and proximal rows of carpal bones.
3 The wrist joint comprises into three different parts, the radiocarpal joint,
intercarpal joint and the distal radioulnar joint. Most of the movements of the wrist
occurs at the radiocarpal joint, which is a synovial articulation composed by distal end of
the radius and the scaphoid, lunate and triquetrum bones [2].
1.2 Wrist fracture
Wrist fractures are kind of fractures that happen any of carpal bones and two
forearm bones (radius and ulna). The most commonly wrist fractures are distal radius
and scaphoid fractures.
1.2.1 Distal radius fracture
Comminuted fractures of distal end of the radius are caused by high-energy
trauma and present as shear and impacted fractures of the articular surface of the distal
radius with displacement of the fragments. The position of the hand and the carpal bone
and also the impact of the forces cause the articular fragmentation and the displacement.
Distal radius fractures are very common. In fact, the radius is the most commonly
broken bone in the arm. The break usually happens when a fall causes someone to land
on their outstretched hands. It can also happen in a car accident, a bike accident, a skiing
accident, and similar situations [3].
4 1.3 Problem Statement
Distal radius fractures are among the most common injuries, with an estimate
overall crude incidence of 36.6/10,000 person-years in women and 8.9/10,000 personyears in men. Assuming a continuous rise in the incidence of distal radial fractures with
age, and based on the fact that older population continues to grow, incidence of distal
radius fractures can be expected to increase. To allow for good functional outcome
following unstable distal radius fractures, restoration of both the radiocarpal and the
radioulnar relationship is essential, therefore surgical treatment should facilitate for
anatomic reduction and maintenance of the reduction. It means different surgical
methods can be used to fix the complicated, unstable and displaced distal radius
fractures.
The conventional volar plating for treated the dorsal displaced distal radius
fractures has been described with good results in young patients and with a mix of
fracture complexity. However, elderly patients with osteoporotic bone may have higher
risk of loss of reduction in conventional types of fixation because of screw loosening
and because of the toggle effect of the screws within the distal part of the plate.
Therefore the necessity of an optimum technique for restore not only the anatomical
alignment of the wrist but also its proper biomechanics such as preventing redisplacement of the fragments and re-establishing the normal wrist load transmission
pattern has been provided new studies.
5 1.4 Objective of study
The objective summery of this study included:
1) Simulation of the distal part of the wrist and also simulation the intraarticular distal radius fracture (AO 23-C2.1).
2) To develop 3D model of the fractured bone for all types of fixation
methods.
3) To simulate various surgical treatments for this type of intra-articular
fracture.
4) To compare between all different types of surgical treatments for fracture
fixation of the distal radius.
1.5 Scope of study
The scope the study, to simulate the 3D model of radius bone and also simulated
the unstable intra-articular fracture on bone. The next step to find the surgical methods
for this kind of distal radius fracture and simulated these surgical method as same as the
real plates of fixations. Then according to surgical open reduction and internal fixation
should find the optimum positioning for all types of fixations on fractured bone. To
provide the valid analysis should find the best positions for boundary condition and
exerting the loads. Should mention that the loads values should be choose base on the
daily motions that fractured wrist faces. Finally, should compare the results of all types
of fixation under the loads and find the most stabile and rigidness of fixation method.
CHAPTER 2
LITERATURE REVIEW
2.1
Introduction
In this chapter discussed about the different types of intra-articular fractures
and also the previous studies on fixation methods for distal radius fractures.
2.1.1 Classification of intra-articular distal radius fracture
CT scan can classify the intra-articular fractures in five distinctive fracture
types.
7
(1) Intra-articular fracture with displaced dorsal fragment (Fig.2.1)
This kind of intra-articular fracture the dorso-ulnar fragment is displaced and
rotated. This fracture should be treated with a single screw or small dorsal straight
plate to reduce the fragment parts via a limited dorsal approach [54].
Fig.2.1: CT-based classification of comminuted intra-articular fractures of the distal
radius. Type I: intra-articular fracture with displaced dorso-ulnar fragment.
(2) Dorsal split with dorsal dislocation (Fig.2.2)
This fracture type is defined by a transverse dorsal split with dorsal
dislocation of the fragment(s) and the carpus. These fractures are actually fractures of
the dorsal articular margin with dorsal radiocarpal subluxation and are therefore
unstable [4]. Most of the bony ridges are very small and therefore difficult to refix
with implants such as screws or plates and indirect techniques of reduction of the
fragment and the carpus (by ligamentotaxis with an external fixator) will reduce the
fracture. After reduction those fragments will be fixed indirectly with the means of
screws through palmar plates [54].
8
Fig.2.2: Type II: dorsal split with dorsal dislocation.
(3) Palmar split with palmar dislocation (Fig.2.3)
These fractures are caused by an opposite (palmar) displacement of the
carpus disrupting a small palmar margin of the articular surface and are equally
unstable. Here reduction of the palmar is achieved via a palmar approach and small
buttress plating. Again the deforming forces and palmar (sub)luxation of the carpus
are counteracted by a neutralising external fixator [54].
Fig.2.3: Type III: palmar split with palmar dislocation.
9
(4) Complex distal radius fractures with metaphyseal separation (Fig.2.4)
These fractures are defined by complete additional dorsal or palmar
disruption of the metaphysis with severe comminution. They often show a total
disruption of the DRUJ and gross displacement [54].
Fig. 2.4: Type IV: complex distal radius fractures with metaphyseal separation.
(5) Destruction of the articular surface (Fig.2.5)
On this CT evaluation there is destruction of the very distal aspect of the
distal radius, with involvement of the greater part of the articular surface. These
fractures are the most difficult ones to treat, because major parts of the articular
surface are destroyed and displaced. A combination of reconstruction of the articular
surface and minimal distraction of the carpus is necessary to unload the articular
cartilage during bone healing [54].
10
Fig.2.5: Type V: destruction of the articular surface.
2.2
Different studies on fixation methods
To provide the best stability for distal radius fractures the best way of fixation
method should find to apply as surgical treatment. To achieving this goal analysing
the fixation methods should be provided by applying the clinical method,
experimental method and computer simulation.
2.2.1 Clinical Method
Recently development in distal radius fractures (DRFs) influenced by rapid
developments of many osteosynthesis and fixation devices. The reported by Colles
and many authors expected the good results from a relative conservative policy of
treatment; however, we are facing now another method of open reduction and
internal fixation. We have to be careful not to treat all patients with the latest
implants that exist in the market. We should consider the types of fractures, the
characteristic of the injury, the age of patients and the expected activity level. The
prospective surgical methods that were applied to the severity comminuted distal
11
radius fractures were treated base on the prospective protocol. Distal radius fractures
(DRFs) are unique in that emergence of technology has generated renewable interest
in the treatment of these fractures and an increase in production of a variety of
specific fixation devices [5].
2.2.1.1 Non-invasive Techniques
Non-invasive techniques are kind of fixation methods that don’t need to do
the surgery to put the implant on fractured bone. These methods consist of
conservative treatment, external fixation and pinning.
2.2.1.1.1
Conservative treatment
Close reduction and also suggested a tin splint for facture stability described
by Colles in 1847. Closed reduction and splitting is still today the most commonlyused method of treatment in the DRF. In conservative treatment the position of
immobilization and type of splinting has same importance [6]. Although many
methods of closed reduction have been developed during the years, there is no
evidence-based on randomized studies to support the choice of closed reduction
method. Handoll and Madok had many systematically evaluation non-randomized
reports of methods of closed reduction [5]. However, in many cases conservative
treatment appropriate especially for primarily or secondary unstable fractures,
surgical are needed.
12
2.2.1.1.2
External Fixation
During the three decades external fixation has been used for distal radius
fractures [7]. In some countries such as Sweden external fixation uses as a standard
method and it used as reference to compare with new methods. External fixation uses
ligamentotaxis to both reduce as well as to hold the fracture in position during
healing [8]. Although in comparison with the below-elbow cast external fixation has
been reported better results, the external fixation was noted as having more
complications [9]. External fixation can be applied for complex and intra-articular
factures [10] (Fig. 18). The traction of the wrist ligaments may cause stiffness and
therefore dynamic fixation with an articulated device [11, 12] or nonbridging fixation
has been proposed with better results reported than for traditional bridging technique
[13]. A recent randomized study was unable to find any difference between the
bridging and the non-bridging external fixator in regard to clinical results in elderly
patients [14].
13
Fig 2.6: Schematic drawing of a monolateral external fixator with double ball joints
after application to the radial aspect of the second metacarpal and diaphysis of the
radius: the distal ball joint is centred between the capitate (C) and lunate bone (L)
(intraoperatively by identification with a bone elevator under image intensification,
lower part of the image) to allow for mobilisation of the fixator.
2.2.1.1.3
Pinning
Pinning is other types of close reduction techniques to fix the fracture.
Pinning consist of various techniques such as intra-focal pinning [15], intra-focal
intra-medullary pinning [16] or pinning in combination with external fixation [17].
According to one studies, compared intra-focal pinning with volar-locking plate
shown the privilege in using volar-locking plate [18].
In patients over 60, the
pinning was found to provide only a marginal improvement in the radiological
parameters compare with immobilisation in a cast alone [19].
14
Fig.2.7: Typical placement of two T-pins for fixation a distal radius fracture is
shown in this posterior-anterior radiograph. The surgeon has inserted two T-pins
from the radio styloid to stable fracture fixation. The surgeon has inserted two T-pins
from the radio styloid to stable fracture fixation.
2.2.1.2
Open surgery
Recently open surgery has had more popularity in comparison with other
types of treatments. Open surgery several types of fixation such as plates, fragmentspecific fixation and volar-locking plates.
(a) Plates
A volar plate is a kind of plates that applied for volarly-dislocated fractures
especially Baron or Smith type of fractures [20]. The other techniques that used
standard AO-plates and screws have been considered for other types of fractures
15
have had good results. To provide more stability, usually two or more columns of the
radial cortex have to be fixed to achieve good results [21, 22]. Open techniques has
become increasingly popular especially for distal radius fractures.
(b) Fragment-Specific Fixation
A fragment-specific fixation is a kind of fixations that used the combination
of plates, pins and screws. This fixation uses for radial and unlar columns separately
or single fracture fragments on both dorsal side and volar side fracture fragments. In
fragment-specific fixation basically used pinning but to provide more stability and to
prevent from bending or the fragments from sliding on the pin, a stabilizing plate was
used to secure the pins. Moreover, wire forms to support the subchondral bone or
small fragment can be used. This profile is low profile and offer good stability [2325] (Fig. 20).
Fig. 2.8: A fragment-specific wrist fixation system.
16
(c) Volar locking plates
The volar locking plate provided the newest concepts in open surgery method
of fixation. In this method the volar locking plates has been used with angle screws
or pegs has provided more stability and a safe approach to the fracture. The fracture
is approached from the volar side using the Henry approach just radially to the flexor
carpi radius, ulnarly to the radial artery. This provided easy access to the volar part of
the radius. Latest biomechanical studies on volar locking plates showed the most
stability in comparison with other fixation especially external fixation for dorsallycomminuted fractures [26-28]. The best combination of fixation is provided by the
volar locking plates and the fragment-specific system [29, 30]. Good clinical results
have reported in a few series [31, 32]. However, in clinical studies reported the
irritation of the tendon because of the screws [33, 34].
Fig.2.9: A 31-year-old woman with reverse Barton fracture fixed by volar locking
plate.
17
For many it seems that the volar locking plates have provided the best and
final solution to the treatment of both intra-articular and extra-articular fractures.
However, this treatment and also other types of treatments show follow the standard
protocol for applying to the fracture that this standard mentions the age of patients,
types of fracture.
2.2.2 Protocol for surgical treatment
A standardized treatment programme, base on the radiographic appearance
but taking into account the age and the demands of the patients when selecting the
proper treatment use the way of treatment. The group for distal radius fracture in
southern Sweden in 2004 consisting of dedicated surgeons from Orthopaedic and
Hand Surgery department of distal radius fracture analysed the literature at the time
and define according to it the following protocol [5] (Fig.22)
18
Fig .2.10: The southern Sweden treatment protocol for DRF when selecting different
treatments the patient’s age and demands.
2.3
Experimental Method
In this type of biomechanical study the survey focused on fresh frozen human
cadaver to find the real situation for this study. The first step of procedure is to
simulate the real fracture on bone. After that the fixation method was applied to the
fractured bone base on the clinical studies. Finally we should applied the loads base
on the daily loads that were affected the fracture bone. Experimental studies because
of providing the real situations the results are so important for validation in other
19
methods. Most of the times the experimental methods comparison the two or more
types of fixation to assess which one provided more stability.
2.3.1
A novel non-bridging external fixator versus volar angular stable
plating
Recently the two ways of fixation such as non-bridging external fixation and
the volar angular plating introduced as an effective ways for fixation the intraarticular distal radius fracture. In this study five pairs of frozen human cadaveric
darii were used. The pairs were randomly assigned to two study group: (1) volar
plate (two right and three left bones) and (2) External fixation group (three right and
two left bones) (Fig.23).
A
B
Fig.2.11: Experimental test with isolated radius placed of custom-made compensator
to applied ratio (60-40%) of the forces transferred to scaphoid and lunata fragments.
(A) Non-bridging external fixation method. (B) Volar locking fixation method.
20
The fractured bone were placed in a servo-hydraulic testing machine (MTS
858 Minibionex II, 1 kN load cell, MTS, Eden prairie,USA) the proximal part of the
radius was fixed to the machine actuator. The distal part of the radius positioned on a
custom-made compensator to generated a true load ratio (60-40%) that transferred to
the scaphoid and lunate fragments respectively [36]. The comparison in this study
showed the more stability for the volar locking plate fixation than the external
fixation for unstable intra-articular fractured model. Also the volar locking plate
demonstrated the superior properties under cycling loading [35].
2.3.2 Comparing volar with dorsal fixation plates on unstable extra-articular
fractures
Volar plating with conventional plates has been demonstrated the good
clinical results for dorsally displaced fractures and also for the mix fracture
complexity in younger patients [37, 38]. However, elderly patients which have
osteoporotic bone may have higher risk of the loss of reduction because of screw
loosening and also the toggle effect of the screws within the distal part of the plate.
Recently the comparison between the volar and dorsal fixed-angle distal
radius constructs is controversial. In this study compare the stability and stiffness of
4 groups of plates that used combination of a dorsal and styloid plate (group 1)
(Fig.24A), a single volar plate (group 2) (Fig.24B), and combination of a volar and
styloid plate (group 3) (Fig.24C) and also single volar 3.5-mm steel locking plate
was used in group 4 (Fig. 24D). Each construct was tested on 6 fresh-frozen radii
with simulated unstable dorsally commuted extra-articular distal radius fractures
[39]. The plates that used in this study were new low profile 2.4-mm titanium
Locking Distal Radius System (LDRS) (Synthes Ltd., Paoli, PA). The precontoured
plate system offers volar, dorsal, and styloid fixation options with locking head
screws forming an angle-stable constructs.
21
A
B
C
D
Fig.2.12: (A) The LDRS 2.4-mm intermediate and styloid plates. (B) The LDRS 2.4mm volar plate. (C) The LDRS 2.4-mm volar and styloid plates. (D) The 3.5-mm
stainless steel T plate.
For calculating the stiffness of the plate used the linear part of the
load/displacement curve. Load to failure was defined as a sudden change in the
load/displacement curve, construct breakage, or closure of the osteotomy.
22
The final results showed the dorsal plating had the strongest and stiffest.
During this test no construct failed under cyclic fatigue loading of 250 N it means
that all types of fixations were stable enough for early postoperative unloaded
mobilization in osteoporotic patients with extra-articular fractures. Group 1 with
dorsal and styloid plate showed the significantly higher stiffness values than other
group this one cause by the buttress effect for a dorsally positioned plate but not
volar plate. The styloid plates are useful when styloid fragment was difficult or
supplementary fixation was required [40].
2.4
Computer Simulation Method
Clinical study is the most authentic method to investigate the effect of
different surgical methods on patients, however, sometimes it is difficult to identify
and isolate important parameters because of confounding variables. Also
experimental studies often faced with problems because of limited cadaver
availability and also by the problems originated from performing several
comparative experiments. To solved these kinds of problems finite element (FE)
method provides mechanical responses and alters parameters in more controllable
manner, driving its common use as an analytical tool in biomechanical studies [41].
2.4.1 Biomechanical evaluation of three types of implants
In this study, first simulated the distal radius fracture by finite element
method then applied the three different fixation methods that designed before and
consist of double-plating and, modified double-plating and single. Various surgical
techniques should use to fix the complicated, unstable and displaced distal radius
23
fractures. The effective technique is the one which can restore not only the
anatomical alignment of the wrist but also the proper biomechanics such as
preventing re-displacement of the fragments and re-establishing the normal wrist
load transmission pattern [42]. Three models were built for comparison including a
Modified Double Plating (MDP) model (Fig.25A), a Double Plating (DP) model
(Fig.25B) and a single T plate model (Fig.25C). In the modified model a 2.0-mm
titanium single T shape volar plate with I shape styloid plate (Synthes, Solothurn,
Switzerland) were selected as the two buttressed plates to stabilize the placement on
the dorsoulnar side and dorsoradial side, respectively [43].
A
B
C
Fig. 2.13: Finite element of different surgical methods. (A) T shape single volar plate
meshing model. (B) Meshing model of double-palates fixation method. (C) The
modified double-plating (MDP) meshing model.
To assess the biomechanical properties of three different methods should
apply various load conditions, four sets of axial loads (10 N, 25 N, 50 N and 100 N),
bending (1.0 N-m, 1.5 N-m, 2.0 N-m and 2.5 N-m) and torsion moments loads (1.0
24
N-m, 1.5 N-m, 2.0 N-m and 2.5 N-m) were applied at the end of the distal radius
under the same boundary conditions onto the three models [42,44-46] (Fig.26).
Fig. 2.14: Loading conditions for model. Axial loading bending and torsion are
indicated with arrows. The axial loading was applied in the middle of the upper
radius surface. The bending force was applied on the volar side of radius. Torsion is
applied on both sides of the radius representing the external rotating force.
The magnitude and directions of the loads applied were to simulate the
physiological load experienced with active wrist joint movement during daily
activities [44, 46-48]. This study was monitored the von-Mises stress values of bone
and fixation plates/screws and the average rigidity (that defined as the slope of the
straight line of the load/displacement curves) to find out the potential loosening of
the fracture fragments.
25
In final results, the model rigidity revealed similar stiffness under axial loads.
In bending, MDP demonstrated the highest stiffness compare to the other two, while
the DP and single plate model showed the similar stiffness. For the case that applied
the torsion loads the DP and the single plate showed the higher stiffness than the
MDP (Fig.27).
A
B
Fig.2.15: (A) Average total displacement of the fracture site under 50 N axial
compression, 2 N-m bending and 2 N-m torsion loads. (B) Maximum displacement
of the fracture site under 50 N axial compression, 2 N-m bending and 2 N-m torsion
loads.
26
In von-Mises stress, the MDP had less stress in a case of bending and axial
load in comparison with other two groups. However, the double plating technique
showed less stress in comparison with two other groups. The maximum bone stresses
occurred around the plates at the fracture site. As for the maximum von Mises stress
of T plate (Fig.28) [44].
A
B
Fig.2.16: (A) maximum von Mises stress value for bone in single, DP, and MDP
models under 50 N axial compression, 2 N-m bending and 2 N-m torsional loads. (B)
Maximum von Mises stress value of T plate in single, DP, and MDP models under
50 N axial compression, 2 N-m bending and 2 N-m torsional loads.
The results from finite element simulation were base on an objective to
provide a way to eliminate the problems encounter with the usual fixation methods
and find superior fixation methods as a clinical treatments substitution.
CHAPTER 3
METHODOLOGY
3.1
Introduction
This chapter mentions the process of working which consist of simulating the
solid bone, making the fractured bone, designing the proper implants, setting the
implants on fractured bone and finally analyzing the fixed model.
3.2 Mimics Software
Mimics software (Mimics, 6.1-Materialise software, Leuven, Belgium, UK)
is a kind of image-processing with three dimensional (3D) visualization functions
that interfaces with common scanner formats. This software extracts the 3D solid
bone from the images such as computer tomography (CT), µCT or magnetic
resonance imager (MRI). The software gives the ability to control and correct the
segmentation of CT-scans and MRI-scans.
28
This software can process any number of two dimensional (2D) image slices
(rectangular images are allowed). The interface created to process the image provides
several segmentation and visualization. In this research for provided the meshed 3D
solid bone model should followed five steps in mimics:
Step 1: Imported the medical data
The Mimic software allowed automatic importation of 507 slice images of the
upper limb of a 34 years old man generated in the CT scanner (Siemens, Sensation
16, SOMATOM Scanner, MI, USA) (Fig.3.1). A pixel size of 0.977 mm was
automatically calculated accounting the present image resolution (512×512 pixels).
The slice increment correctly determined corresponding to 1.5 mm and the number
of slices is 507. The pixel size and the slice distance guarantees the coherent
dimensional reproducibility of the models generated during the segmentation
process.
Fig 3.1: CT scan image for using in mimic.
29
Step 2: Thresholding
CT images are a pixel map of the linear X-ray coefficient of tissue. The pixel
values are scaled so that the linear X-ray attenuation coefficient of air equals -1024
and that of water equals 0. This scale is called the Hounsfield (HU) scale (Mimic,
2007) Thresholding base on Hounsfield scale was used to separate the radius part of
the forearm that positioned in the lateral side of the ulna bone (Fig.3.2). In order to
include all the cortical and trabecular parts of the bone at the radius bone structure.
Fig 3.2: The top and side views for radius bone that Thresholding by the white color
triangular to separate the radius bone.
Step 3: Segmentation density masks
For special length of the radius bone, individual and separated masks were
created. This process allows the posterior generation of independent geometrical files
30
and 3D models. Some manual operations to eliminate residual pixels were
conducted. Cavity fill operations to rule out some voids at the density masks were
also realized in order to obtain independent and smoother primary 3D models. For a
better visualization of the internal boundaries in the masks, polylines were generated
what allows the use of the cavity fill from polylines tool, in order to eliminate in an
easier way, mask’s internal voids.
Step 4: Region growing
The region growing process allows splitting the segmentation in different and
separated parts, correspond each part to one mask that can be distinguished by the
different applied mask’s colours. For the complete definition of the radius structure
and different regions (radius, ulna, and soft tissue) were defined. The side view of a
region growing process on the bone (Fig 3.3).
Fig 3.3: The side view of region growing that shown in pink color.
31
Step 5: 3D Reconstruction
The generated region masks were used to develop 3D models for each the
both the cortical and cancellous part of the radius bone. The 3D reconstruction is
based on 3D interpolation techniques that transform the 2D images (slices) in a 3D
model. For this reconstruction case, gray values interpolation was used associated
with the accuracy algorithm for achieving a more accurate dimensional
representation of the radius structure. Shell and triangle reduction, respectively were
used for elimination small inclusions and reducing the number of mesh elements.
Each region was then reconstructed to obtain both cortical and cancellous volume
that geometrically defines the radius structure. The relative positions of the different
parts constituting the primary model assembly of the radius intact model shown in
Fig 3.4.
A
B
C
Fig 3.4: The process of smoothing (A, B and C) to achieve radius bone.
32
3.2.1 Constructed of fractured bone
After simulation of the radius bone, should make the unstable distal radius
fracture in intra-articular part of the radius bone. The cut with curve tool in Mimics
Software provided the instrument to simulate the fracture on intact radius bone.
Before that by using measurements tool, measured nearly 10 mm proximal to the
articular and approximately 15° volar wedge (Fig 3.5) to provide the guide lines for
removed the bones with cut with the curve tool to simulate a comminuted zone and
showed the three fragmental AO 23-C2.1 fracture. This process followed for both
cortical and cancellous part of the radius (Fig 3.6). After cut the intact bone and
made the bones in six parts (3 cortical and 3 cancellous parts) should modify the ugly
meshing and corrected the meshing parts (Fig 3.7). The meshed cortical and
cancellous parts of the radius had interfaced together and that was shown the errors
in MSC.Marc software for finite element simulation. To solve this problem, all
cancellous bones were filliped in Marc software and brought back to Mimic software
and removed the interfacing in Magic.
33
A
B
Fig 3.5: The measured guide lines for cutting (A) Approximately 10 mm(10.44 mm)
from the from articular surface. (B) About 15° (14.81°) volar wedge.
Fig 3.6: The simulated three segments unstable intra-articular fracture (AO 23-C2.1
fracture). The circle shows the cut with the curve tool.
34
A
B
C
Fig 3.7: (A) The scaphoid segment cleaned meshes. (B) The lunate segment cleaned
meshes. (C) The distal part of the radius cleaned meshes (all segment related to the
cortical parts only).
35
3.3 Implant Design
For designing the implant, the previous studies didn’t follow the standard
protocol for their designs; however, in this study tried to design the new low profile
2.4-mm titanium Locking Distal Radius System (LDRS) (Synthes Ltd., Paoli, Pa).
The plates system offers volar, dorsal, and styloid fixation option with locking head
screws. But before designing, in Mimics software the effective length for implants
measured on the fractured radius bone. The measurements should mention all the
length that was used the length of the implants and also the curve of the styloid part
of the bone for designed the I-shape styloid plate. All the implants designed in
Solidworks Software.
3.3.1 Introduction of Solidworks Software
Solidworks is a 3D mechanical CAD (computer-aided design) program that
was introduced in 1995 as a competitor to CAD programs such as Pro/Engineer,
AutoCAD, and Unigraphics solutions. Jon Hirschtick was founded the Solidworks in
1993. He recruited a team of engineers to build a company that developed 3D CAD
software that was easy-to-use, affordable and available on the desktop, with its
headquarters at Concord, Massachusetts, and released its first product, Solidworks
95, in 1995. Sketching the model in Solidworks should start on 2D plane. To sketch,
should use different parameters such as points, lines, arcs, conics (except hyperbola),
and splines. Dimensions are added to defined size and locations of the geometry.
36
3.3.2 Designing the implants
To fix the fractured distal radius bone and base on the surgical methods three
different implant that consist of 1 dorsal intermediate plate (Fig 3.8A), 1 styloid Ishape plate (Fig 3.8B), and 1 T-shape volar plate (Fig 3.8C). All implants designed
base on standard 2.4mm locking screw and also the low profile designed of these
implants made them near to reality. Moreover, the dimensions that measured in
Mimic software applied in designed implants. The most difficult part of the
designing was the curve of the styloid implants that solved with created the various
plane on the implant. After finished the implants designed they meshed on ABAQUS
software (is a suite software application for finite element analysis and computer
aided engineering) and saved as "stl" files to transfer them to the Mimic software
again. The size of mesh for implants and also screws were 1mm.
37
A
B
C
Fig 3.8: (A) Intermediate dorsal LDRS 2.4 mm plate. (B) Volar T-shape LDRS 2.4
mm plate. (C) I-shape Styloid LDRS 2.4 mm plate.
3.4 Simulation of surgical fixation
In this part the implants exported to the Mimic software to fix them on a right
place base on surgical method. After fixed the implants, it’s time to meshing the
screws not only for fractured bone (both cortical and cancellous) but also the
implants. To achieve this goal, first flipped the screws for all implants then fixed the
38
meshes on bone and implants (Fig 3.9). When the meshing around the bone and also
implants finished and there were no interfacing between them there were found new
interfacing between the new meshing cortical and cancellous in this case the
cancellous again brought to the MSC.Mrac Software (Computer Aided Engineering,
Marc software, Santa Ana, California, USA) to flipped the cancellous part of the
bone and then fixed the meshes in cortical bone. After finished the all meshes that
there were no interfacing in all parts of bone, screws, and implants, saved all the
parts with "stl" files. And then bring it to the MSC.Marc to get the results (Fig 3.10).
Screw position
on cortical
Screw position
on cancellous
Fig 3.9: Fixed all the meshes around the screws on both cortical and cancellous parts
of bone.
39
Fig 3.10: Fixed all the interfaced meshing part between all cancellous and cortical
and screws. (The red parts show the interfaced parts)
3.5 Introduction to MSC.Marc Software
MSC.Marc is a powerful, general-purpose, implicit nonlinear finite elemnt
analysis (FEA) software program that quickly and accurately simulates static and
dynamic and coupled physics problems for a wide range of design and
manufacturing applications. The linear FEA methods that rely upon making
simplifying assumptions and approximations, MSC.Marc enables you to follow the
complex nature of real-world structural behaviour and mechanical process to ensure
highest design confidence and product performance under realistic environments and
operating conditions. Since 1971 MSC.Marc has recognized as the first commercial
nonlinear FEA software because of delivering innovation, easy to use, and powerful
for analyzing the structural integrity and performance of parts experiencing
geometric, material, and/or boundary nonlinearities.
40
3.5.1 Analysing the three fixation methods
The stl files that saved from Mimic software brought to the Marc software
and save it and checked the meshes and saved to the "mfd" files. After the mfd files
categorised to the three groups, group 1 consist of 1 styloid plate, 1 dorsal
intermediate plate, group 2 consist of single T-shape volar plate, and the group 3
comprise 1 styloid plate and 1 single T-shape volar plate in all groups included a
three fragmental fractured bone. Each group of fixations merged in the one separate
file. In Marc software should define some parameters such as material properties,
friction coefficient for all contact bones, and Poisson’s ratio. For all contact surfaces
the value for friction coefficient was o.3 [43]. The cortical and cancellous bones were
assumed linear, elastic and isotropic material with the young’s modulus of 18 GPa
for cortical and 100 MPa for cancellous. The Poisson’s ratio for simulated cortical
and cancellous were 0.2 and 0.25 respectively [51] (Fig 3.11).
Fig 3.11: Defined the young’s modulus, Poisson’s ratio and contact parts for each
part (that showed in collared parts).
41
3.5.2 Applying the loads
Before running the program to get the results, defining the load points and the
boundary condition are indispensable. In this study base on the previous studies that
mentioned in literature review the end of the distal part of the radius bone was fixed
in all directions [43] and the loads that consist of axial load, bending, and torsion
exerted to the distal radius intra-articular fractured bone in same condition for all
three groups.
For the four axial loads (10 N, 25 N, 50 N, and 100 N) applied to the defined
ratio (60-40%) load transferred to the scaphoid and lunate fragments [36]. At first the
load directions was set as perpendicular to the articular surface; however, the results
showed wrong in comparison with previous experimental method. The problem was
the direction of the load, so the true direction of the load found by exerted the load
base on the tilt angle that was mentioned 13.4° for this bone [52]. The tilt angle
should minus the declination of the bone in MSC,Marc software (20° with the
vertical axis) that finally found the 6.6° with the vertical axis (cranial-caudal) for
exerted the axial loads.
For bending loads, loads (1 N-m, 1.5 N-m, and 2 N-m) applied to the volar
side of the fractured bone. To provide the bending moment on fractured bone, the
calculated load points exerted to the proximal point that had 50.47 mm (0.05047 m)
distance from the bounded distal end of the radius that found from the two nodes in
Marc.
In case of torsion loading, loads (1 N-m, 2 N-m, and 2.5 N-m) applied to the
proximal part of the radius. The distance that measured between two nodes was
24.887 mm (0.024887 m). The two nodes were the places of inserting the coupleforce (Fig.3.12).
42
After finished all these procedures the model is ready to save and run the
program to get the results. Each case categorised in one folder to analyse the data and
plotted the chart base on results.
Bending
Torsion
%60
%40
Axial loading
Fig 3.12: Axial loading that applied on scaphoid and lunate regions base on each
percentage and tilt angle (6.6° to the cranial-caudal direction), bending load that
exerted on simulated bone on volar side of the radius and the torsion applied of the
radius part of the bone.
These all steps that mentioned here followed the procedure for only group 3
of fixation methods the other two groups also followed all the steps one by one to
provided the excellent situations to get the results.
CHAPTER 4
RESULT AND DISCUSSION
4.1 Introduction
In this chapter, the fixation methods categorised in 3 groups:
(1) Group 1 consist of 1 I-shape styloid plate and 1 dorsal intermediate,
(2) Group 2 consist of single T-shape volar locking plate, and
(3) Group 3 comprised 1 T-shape volar locking plate and 1 I-shape styloid
plate.
These three groups of fixation methods which created in the previous chapter
used to analyse the displacements and the von-Mises stress. Also the graphs of
rigidity and the maximum stress and displacement measured on fractured bone.
44
4.2 Axial-loads results
This part demonstrated the two most important parameters such as maximum
displacement and von-Mises stress to assess the stability and the rigidity of the three
groups of fixations. The applied loads that mentioned previously consisted of four
axial-loads (10 N, 25 N, 50 N, and 100 N) that exerted base on tilt angle.
4.2.1 Displacement
In axial loading, the displacement in all groups showed the reasonable
displacements on applied 100N axial load. However, the purpose of this study was to
find the superior stability. The final results showed the angle-stable double plates
constructs which was considered in group1 and group 3 had less displacement in
comparison with group 2. But the difference between group 1 and group 2 was not
too much.
The averaged rigidities, defined as the slope of the straight-line region of the
averaged load-displacement curves under axial, bending and torsion loads, were also
computed to understand the differences of the biomechanical strength for these three
surgical methods. The Fig 4.1 that shown the load-displacement graph under applied
axial loads demonstrated the highest rigidity for group 3 and the lowest rigidity
related to the group 1.
45
Displacement
120
Load (N)
100
80
60
Group 1
40
Group 2
Group 3
20
0
0
0.2
0.4
0.6
0.8
1
1.2
Displacement (mm)
Fig. 4.1: Model rigidity under axial compressive load.
This study also considered the maximum displacement around the screw on
fractured bone by monitored the nodes around the maximum displaced part. The
linear Fig 4.2 also had shown the most rigidity for group 3.
Displacement (Bone)
120
Load(N)
100
80
60
Group 1
40
Group 2
20
Group 3
0
0
0.2
0.4
0.6
Displacement(mm)
Fig 4.2: Maximum displacement of the bone around the screws under the 10 N, 25
N, 50N, and 100 N loads.
46
4.2.2 Von-Mises Stress
The average maximum von Mises stress value was lower in group 3 that the
other two groups during axial loads. The stress for group 1 and group 2 showed
approximately the same (Fig.4.3).
Von Mises Stress
120
Load (N)
100
80
60
Group 1
40
Group 2
20
Group 3
0
0
100
200
300
400
500
600
Von Mises Stress (MPa)
Fig. 4.3: Maximum von-Mises stress under the 10 N, 25 N, 50N and 100 N loads.
The maximum von Mises stress value on fractured bone around the screw
was lower in group 3 (1 I-shape styloid plate and 1 T-shape volar plate) that 2 other
groups during the axial loads (Fig.4.3).
47
Von Mises Stress(Bone)
120
Load(N)
100
80
60
Group 1
40
Group 2
20
Group 3
0
0
10
20
30
40
Stress(MPa)
Fig 4.4 Maximum von Mises stress of the bone around the screws under the 10 N, 25
N, 50N, and 100 N loads.
The maximum stress and the displacement values around the screw that
caused by the axial loads demonstrated the superior results for all three groups
(Table.4.1).
Table 4.1 Maximum displacement (mm) and maximum von Mises stress (MPa)
values of the bone around the screws of all three groups under the applied loads.
Axial-load
Group 1
Group 2
Group 3
10 N
25 N
50 N
100 N
Displacement
(mm)
0.02684
0.085
0.1693
0.3385
von-Mises
stress (Mpa)
3.074
7.89
15.69
31.47
Displacement
(mm)
0.02959
0.1264
0.2746
0.5306
von-Mises
stress (Mpa)
2.233
6.985
13.87
27.72
Displacement
(mm)
0.005863
0.03667
0.06833
0.1476
von-Mises
stress (Mpa)
0.9895
5.21
10.37
20.07
48
The finite element plot graphs for displacements of the three groups of
fixation methods showed in contour plots (Fig 4.4).
Group 1
Group 2
Group 3
Fig 4.5: The contour plots of displacement for three groups of fixations under
applied 100 N axial load.
49
4.3 Bending results
Bending is one of the important factors for distal radius fractures, this study
wanted to find the superior bending resistance method of fixation for unstable intraarticular fractures. In this case the displacements and the von Mises stress monitored
during applied the three bending loads (1 N-m, 1.5 N-m, and 2 N-m).
4.3.1 Displacement
In bending, group 1 and group 3 showed considerably less average
displacement in comparison with group 2 (Fig.4.6). The interesting point that
achieved in this study the approximate same results for group 1 and group 3 and this
one could show the validation of this study [53] which showed the better effect of
bending resistance in dorsal fixation methods rather than conventional T-shape single
volar plate. The reason is the intermediate dorsal plate acts as buttress to provide the
resist load for bending loads that exerted on volar side of the fractured bone.
However, group 3 approximately showed the same results with group 1.
50
Displacement
2.5
Bending (N.m)
2
1.5
Group 1
1
Group 2
0.5
Group 3
0
0
0.2
0.4
0.6
0.8
Displacement (mm)
Fig 4.6: The mean maximum displacement under bending loads (1 N-m, 1.5 N-m, 2
N-m).
To survey displacement on fractured bones by monitored the nodes around
the screws showed the same results as average displacement. It demonstrated the less
displacement on fractured bone in group 1 and group 3 (Fig 4.7).
Displacement (Bone)
2.5
Bending (N.m)
2
1.5
Group 1
1
Group 2
0.5
Group 3
0
0
0.1
0.2
0.3
0.4
Displacement (mm)
Fig 4.7: The maximum displacement around the screws under applied bending loads
(1 N-m, 1.5 N-m, 2 N-m).
51
4.3.2 Von-Mises Stress
In bending, the average total maximum von-Mises stress showed the same
results for group 1 and group 2. Group 3 showed the less stress mean maximum vonmises stress than two other groups (Fig.4.8). However, the values for the stress
around the screws showed the same results in all three groups of fixations. This may
should be the good point for the volar T-shape volar plate, but the displacement
showed the maximum displaced fracture bone for group 2 (Fig 4.9).
Bending (N.m)
Von Mises Stress
2.5
2
1.5
1
0.5
0
Group 1
Group 2
0
100
200
300
400
Group 3
Stress (MPa)
Fig 4.8: The maximum von-Mises stress under applied bending loads (1 N-m, 1.5 Nm, 2 N-m).
Von Mises Stress(Bone)
Bending (N.m)
2.5
2
1.5
1
Group 1
0.5
Group 2
0
Group 3
0
5
10
15
20
Stress (MPa)
Fig 4.9: The maximum von-Mises stress around the screws under applied bending
loads (1 N-m, 1.5 N-m, and 2 N-m).
52
The maximum von-Mises stress and the maximum displacement values that
caused by the applied bending loads monitored by the nodes around the screws on
bone (Table 4.2).
Table 4.2: Maximum displacement (mm) and maximum von Mises stress (MPa)
values of the bone around the screws of all three groups under the bending loads.
Bending loads
Group 1
Group 2
Group 3
1 N-m
1.5 N-m
2 N-m
Displacement
(mm)
0.0816
0.1225
0.1624
von-Mises
stress (Mpa)
8.342
12.47
16.61
Displacement
(mm)
0.181
0.2772
0.367
von-Mises
stress (Mpa)
7.223
10.84
14.46
Displacement
(mm)
0.09338
0.1399
0.1876
von-Mises
stress (Mpa)
8.073
12.09
16.1
The finite element contour plot for displacements of the three groups of
fixation methods under the 2 N-m bending loads (Fig 4.10).
53
Group 1
Group 2
Group 3
Fig 4.10: The contour plots of displacement for three groups of fixations under
applied 2 N bending load.
4.4 Torsion results
Applied the torsion by exerted the two loads around the proximal side of the
radius bone provided the simulating other daily loads that may applied to the radius
54
bone. In this study to provide this circumstance for the fractured bone applied 1.5 Nm, 2 N-m, and 2.5 N-m torsion loads.
4.4.1 Displacement
In torsional force, the styloid plate with T-shape volar locking plate in group
3 had the same displacement values as the styloid plate with intermediate dorsal plate
in group 1. The fixation method in group 2 that consist of 1 single T-shape volar pate
had highest displacement (Fig 4.11). The highest rigidity in both group 1 and group 3
that they consisted the angle-stable constructs showed the superior results for these
kinds of fixations in comparison with conventional fixation with single T-shape volar
locking plate in case of torsional loading.
Displacement
3
Torsion (N.m)
2.5
2
1.5
Group 1
1
Group 2
0.5
Group 3
0
0
0.2
0.4
0.6
0.8
1
1.2
Displacement (mm)
Fig 4.11: The mean maximum displacement under torsion loads (1.5 N-m, 2 N-m,
2.5 N-m).
55
For assessed the maximum displacement around the screws on fractured bone
should traced the nodes around that place. The values from that survey demonstrated
slightly the same result as the mean maximum displacement which showed the
highest displacement in group 2 (Fig 4.12).
Displacement (Bone)
3
Torsion (N.m)
2.5
2
1.5
Group 1
1
Group 2
0.5
Group 3
0
0
0.1
0.2
0.3
0.4
0.5
Displacement (mm)
Fig 4.12: The maximum displacement around the screws under applied torsion loads
(1.5 N-m, 2 N-m and 2.5 N-m).
4.4.2 Von-Mises Stress
The other parameters of comparison was average total von mises stress in
torsional loads which shows the lowest stress value related to group 3 after that
group 1 and group 2 has low stress respectively (Fig 4.13). It was indicated that
group 2 has the highest stress on the bone.
56
Von Mises Stress
3
Torsion (N.m)
2.5
2
1.5
Group 1
1
Group 2
0.5
Group 3
0
0
100
200
300
400
500
Stress (MPa)
Fig 4.13: The maximum von-Mises stress under applied bending loads (1.5 N-m, 2
N-m and 2.5 N-m).
The nodes around the screws showed the same stress values for both group 1
and group 3. Group 2 has the highest stress around the screws in comparison with
group 1 and group 3 (Fig 4.14).
Von Mises Stress (Bone)
3
Torsion (N.m)
2.5
2
1.5
Group 1
1
Group 2
0.5
Group 3
0
0
10
20
30
40
50
Stress (MPa)
Fig 4.14: The maximum von Mises stress around the screws under applied torsion
loads (1.5 N-m, 2 N-m and 2.5 N-m).
57
The node around the screws showed the maximum von Mises stress and
displacement to survey the stability between these three groups of fixation (Table
4.3).
Table 4.3: Maximum displacement (mm) and maximum von Mises stress (MPa)
values of the bone around the screws of all three groups under the torsional loads.
Torsional loads
Group 1
Group 2
Group 3
1.5 N-m
2 N-m
2.5 N-m
Displacement
(mm)
0.08853
0.118
0.1475
von-Mises
stress (Mpa)
14.24
19
23.77
Displacement
(mm)
0.2794
0.3836
0.4733
von-Mises
stress (Mpa)
27.61
35.57
45.99
Displacement
(mm)
0.06741
0.09398
0.1173
von-Mises
stress (Mpa)
13.01
17.34
21.66
The finite element plot graphs for displacements and the von Mises stress of
the three groups of fixation methods demonstrated the mean maximum stress and
displacement on implants under the torsional loads (Fig 4.15).
58
Group 2
Group 1
Group 3
Fig 4.15: The contour plots of displacement for three groups of fixations under
applied 2 N torsional load.
4.5 Overviewing of three fixation methods
This study showed the stability and the rigidity of three fixation methods and
the comparison between these three groups. The important point is this study focus
on the unstable intra-articular fracture and should not expand these results for other
59
types of distal radius fractures. The overall view for displacement and the von-mises
stress in all cases of applied loads (axial loads, bending, torsion) shown in Fig 4.16.
A
B
Fig 4.16: (A) Average total displacement of the fracture site under the 100 N axial
compression, 2 N-m bending and 2.5 N-m torsional loads. The total displacement
was averaged from the displacement of the nodes on the fracture site. (B) Maximum
von Mises stress value for bone in three groups of fixations under 100 N
compression load, 2 N-m bending and 2.5 N-m torsional loads.
60
4.6 Validation of study
For verified the methods of fixation first should mentioned about the surgical
method it means we should become sure that this kind of fixations were usual for
treating the patients or not. After that the value of the results should be verification
with other experimental results or finite elements results that assessed these kinds of
fixations before.
4.6.1 Surgical validation
According to the recently studies on used double plating methods showed the
efficacy of these methods of fixation by assessing their ability to maintain
radiographic reduction and evaluating their functional outcome using validation
measures over time. This study mentioned that these groups of fixations provided the
stability which radial inclination and volar tilt did not show any significant change
from surgery to final follow up. Moreover, this study showed the advantage of the
locking plate system provides a more secure and reliable fixation for osteoprotic
bones [53].
4.6.2 Experimental validation
After found the confidence about the validation surgical methods now it’s
time to validate our results with either experimental methods or finite elements
methods. The unique point of this study is this one is the first computer simulation
for analysing and comparison these ways of fixation for unstable intra-articular
61
fracture. However, there were other experimental studies that dedicated to the
conventional intra-articular fracture with T-shape volar locking plat. In this study
provided the same simulation to make unstable intra-articular fracture. In case of
fixation, the validate fixation method for this study was group 2 under applied the
100 N axial load. With simulated the same situation for this model the values for
group 2 fixations was showed as same results as previous studies [35]. In previous
study showed the acceptable displacement for fixation methods should be less than
0.6 mm that this study showed all the models valid for our results.
CHAPTER 5
DISCUSSION AND RECOMMENDATION
5.1 Discussion
The clinical method know as a technique to compare different fixation plated
on patients and achieve the results base on follow up evaluation, however, the
clinical results shown the general result and they cannot specify the results for all
patients. Also experimental methods are other authentic methods for comparison the
different fixation methods, however, due to the limitation cadaver availability these
studies are often limited by problems originated from performing several
comparative experiments on the same specimen. On the other hand, finite element
analysis is a facilitated tool to analyse the feasibility, efficacy and overall
biomechanical factors on different fixation plates. The importance of this study is the
first finite elements studies on unstable intra-articular fracture.
Internal fixation has priority with external fixation because of more
preservative and restorative in case of radial length and volar tilt. The 2.4 mm
locking compression plates system (LCPS) provided more security reliability
because of more stiffer and stronger buttress effect of plates.
63
This study used all locking compression plate system that consist of 1 styloid
plate and 1 intermediate dorsal plate (Group1), single T-shape volar plate (Group 2)
and the 1- styloid plate and 1 single T-shape volar plate (Group 3). All three groups
of fixations showed the good results for young patient; however, the elderly patients
with osteoporotic bone may have a higher risk of loss of reduction because of screw
loosening and because of the toggle effect of the screws within the distal part of the
plate. This study showed the most stability in double-plate constructs in group 1 and
3. The negative points of using the dorsal fixation in group 1 might be associated
with complications of the extensor tendon irritation and rupture in patients.
The results demonstrated that the superior stability of the double-plate
constructs in groups1 and 3 in comparison with the conventional methods in group 2.
The applied compression axial loads, bending and torsional loads provide the daily
situation loads for fractured bone. The results values in all applied loads
demonstrated the highest rigidity for group 3 than the other two groups.
5.2 Recommendation
To further study on the wrist joint, some recommendations are listed below:
1. The problem of the screws that should insert to the bone for fixation has
provided the tendon irritation is undeniable, however, this irritation can
deduct with eliminate the redundant screws. In future studies should first
focus on the removed the necessity screws and compare the results with
this study which may provide the same stability with fewer screws.
2. Use other types of implants with different length or shape. In this study
the finite element results showed the less stress on the distal part of the
radius. It means the future studies can consider other length of the plates
to deduct the price of fixation if the stability of the results will show the
same result as this study or better results.
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