FINITE ELEMENT SIMULATION OF THREE SURGICAL TREATMENTS OFDISTAL RADIUS INTRA-ARTICULAR FRACTURE

ARASH NASROLLAHI SHIRAZI

A report submitted in partial fulfillment of therequirements for the award of the degree of

Master of Engineering (Mechanical)

Faculty of Mechanical EngineeringUniversiti 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 I-

shape 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.

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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 (paksi-

beban, 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.

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TABLE OF CONTENT

CHAPTER 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

1 INTRODUCTION 1

1.1 Introduction 1

1.1.1 Wrist anatomy 1

1.1.1.1 Bones and joints 2

1.2 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

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2 LITERATURE REVIEW 6

2.1 Introduction 6

2.1.1 Classification of intra-articular fracture 6

(1) Intra-articular fracture with displaced

dorsal fragment7

(2) Dorsal split with dorsal dislocation 7

(3) palmar split with palmar dislocaton 8

(4) Complex distal radius fractures with

metaphyseal separation9

(5) Destruction of the articular surface 9

2.2 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 18

2.3.1 A novel non-bridging external fixator versus

volar angular stable plating19

2.3.2 Comparing volar with dorsal fixation plates on

unstable extra-articular fractures20

2.4 Computer Simulation Method 22

2.4.1 Biomechanical evaluation of three types of

implants 22

3 METHODOLOGY 27

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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 Constructed of fractured bone 32

3.3 Implant Design 35

3.3.1 Introduction of Solidworks Software 35

3.3.2 Designing the implants 36

3.4 Simulation of surgical fixation 37

3.5 Introduction to MSC.Marc Software 39

3.5.1 Analysing the three fixation methods 40

3.5.2 Applying the loads 41

4 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 49

4.3.1 Displacement 49

4.3.2 Von-Mises Stress 51

4.4 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

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5 DISCUSSION AND RECOMMENDATION 62

5.1 Discussion 62

5.2 Recommendations 63

REFERENCES 64

xi

LIST OF TABLES

TABLE NO. TITLE PAGE

4.1 Maximum displacement (mm) and maximum vonMises stress (MPa) values of the bone around thescrews of all three groups under the applied loads

47

4.2 Maximum displacement (mm) and maximum vonMises stress (MPa) values of the bone around thescrews of all three groups under the bending loads

52

4.3 Maximum displacement (mm) and maximum vonMises stress (MPa) values of the bone around thescrews of all three groups under the torsionalloads

57

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TABLE OF FIGURES

FIGURE NO. TITLE PAGE

1.1 Distal and proximal rows of carpal bones 2

2.1 CT-based classification of comminuted intra-articular

fractures of the distal radius. Type I: intra-articular

fracture with displaced dorso-ulnar fragment

7

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

metaphyseal separation

9

2.5 Type V: destruction of the articular surface 10

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.

13

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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

14

2.8 A fragment-specific wrist fixation system 15

2.9 A 31-year-old woman with reverse Barton fracture

fixed by volar locking plate

16

2.1O The southern Sweden treatment protocol for DRF

when selecting different treatments the patient’s age

and demands

18

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

19

2.12 (A)The LDRS 2.4-mm intermediate and styloid plates.

(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.

21

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

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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

24

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

25

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

26

3.1 CT scan image for using in mimic 28

3.2 The top and side views for radius bone that

Thresholding by the white color triangular to separate

the radius bone

29

3.3 The side view of region growing that shown in pink

color

30

3.4 The process of smoothing (A, B and C) to achieve

radius bone

31

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

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3.6 The simulated three segments unstable intra-articular

fracture (AO 23-C2.1 fracture). The circle shows the

cut with the curve tool

33

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)

34

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

37

3.9 Fixed all the meshes around the screws on both cortical

and cancellous parts of bone

38

3.1O Fixed all the interfaced meshing part between all

cancellous and cortical and screws. (The red parts

show the interfaced parts)

39

3.11 Defined the young’s modulus, Poisson’s ratio and

contact parts for each part (that showed in collared

parts)

40

3.12 Axial loading that applied on scaphoid and lunate

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

42

4.1 Model rigidity under axial compressive load 45

4.2 Maximum displacement of the bone around the screws

under the 10 N, 25 N, 50N, and 100 N loads

45

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4.3 Maximum von-Mises stress under the 10 N, 25 N, 50N

and 100 N loads

46

4.4 Maximum von-Mises stress of the bone around the

screws under the 10 N, 25 N, 50N, and 100 N loads

47

4.5 The contour plots of displacement for three groups of

fixations under applied 100 N axial load

48

4.6 The mean maximum displacement under bending loads

(1 N-m, 1.5 N-m, 2 N-m)

50

4.7 The maximum displacement around the screws under

applied bending loads (1 N-m, 1.5 N-m, 2 N-m)

50

4.8 The maximum von-Mises stress under applied bending

loads (1 N-m, 1.5 N-m, 2 N-m)

51

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)

51

4.1O The contour plots of displacement for three groups of

fixations under applied 2 N bending load

53

4.11 The mean maximum displacement under torsion loads

(1.5 N-m, 2 N-m, 2.5 N-m)

54

4.12 The maximum displacement around the screws under

applied torsion loads (1.5 N-m, 2 N-m, 2.5 N-m)

55

4.13 The maximum von-Mises stress under applied bending

loads (1.5 N-m, 2 N-m and 2.5 N-m)

56

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

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4.15 The contour plots of displacement for three groups of

fixations under applied 2 N torsional load

58

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

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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 person-

years 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 re-

displacement 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 intra-

articular 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.