SPRINGER BRIEFS IN APPLIED SCIENCES AND TECHNOLOGY  COMPUTATIONAL MECHANICS Mohammed Rafiq Abdul Kadir Computational Biomechanics of the Hip Joint SpringerBriefs in Applied Sciences and Technology Computational Mechanics Series Editors Andreas Öchsner Holm Altenbach Lucas F. M. da Silva For further volumes: http://www.springer.com/series/8886 Mohammed Rafiq Abdul Kadir Computational Biomechanics of the Hip Joint 1 3 Mohammed Rafiq Abdul Kadir Faculty of Health Science and Biomedical Engineering Department of Biomechanics and Biomedical Materials Universiti Teknologi Malaysia Johor Malaysia ISSN 2191-5342 ISSN 2191-5350 (electronic) ISBN 978-3-642-38776-0 ISBN 978-3-642-38777-7 (eBook) DOI 10.1007/978-3-642-38777-7 Springer Heidelberg New York Dordrecht London Library of Congress Control Number: 2013941344 © The Author(s) 2014 This work is subject to copyright. 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Violations are liable to prosecution under the respective Copyright Law. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. While the advice and information in this book are believed to be true and accurate at the date of publication, neither the authors nor the editors nor the publisher can accept any legal responsibility for any errors or omissions that may be made. The publisher makes no warranty, express or implied, with respect to the material contained herein. Printed on acid-free paper Springer is part of Springer Science+Business Media (www.springer.com) Preface The number of people undergoing hip joint replacement surgery has increased over the past decades. In the UK alone, more than 60,000 total hip arthroplast- ies (THA) are performed annually, 15 % of which are performed in the younger age group (less than 57 years old) (Tennent and Goddard 2000). Most hip replace- ments are performed on patients suffering from osteoarthritis, a joint disease associated with the wearing away of the cartilage covering the bone ends. Other degenerative hip disorders that could require THA include rheumatoid arthritis and avascular necrosis. The primary aim of the replacement surgery is to relieve pain and regain mobility. Pioneered in 1962 by the renowned English surgeon, Sir John Charnley, the development of orthopaedic implants used in hip arthroplasty has improved steadily, making it one of the most successful surgical procedures. However, with the increase in the number of hip replacements performed, the scope and frequency of complications appear to be increasing. Complications such as stress-shielding, osteolysis and aseptic loosening remain some of the major problems in hip arthroplasty [1]. There are mainly two types of hip arthroplasty in use today—cemented and cementless. Hip prostheses with the use of cement are the most commonly used but the cementless techniques are gaining popularity. Fixation of these femoral components is a major concern because bone growth could only be achieved on stable implants (Pilliar 1991; Simmons et al. 1999). Failure to achieve a strong fix- ation will result in the formation of fibrous tissue layer at the bone-implant inter - face and the eventual loosening of the implant [2]. PMMA is used in the cemented type prostheses to provide strong primary fixation. However, cement debris can cause complications such as inflammation and bone lysis. One of the solutions to this problem is to abolish the use of cement, thus the cementless femoral compo- nent. However, without the cement these implants could not achieve initial fixa- tion, unless the design is modified so that proper and adequate stability could be achieved. The design of femoral prostheses, together with the surgical techniques of implantation, continues to receive much attention in the hip biomechanics community. This monograph will concentrate on the cementless hip replacement because instability is a cause of concern for this type of implant, more so than the cemented one. In this monograph, Finite Element Analyses (FEA) is used to v vi Preface investigate the issues of stability by calculating, through the use of a specially written computer code, the relative motion at the bone-implant interface. The qual- ity of results for hip joint replacement depends on various factors, several of which such as the design, the surgical error and bone quality will be analysed in this monograph. Malaysia, 2012 Mohammed Rafiq Abdul Kadir References 1. Macdonald DA (1998) Mini symposium: Total hip replacement—(i) Risks versus rewards of total hip replacement. Curr Orthopaed 12 (4):229–231 2. Pilliar RM, Lee JM, Maniatopoulos C (1986) Observations on the effect of movement on bone ingrowth into porous-surfaced implants. Clin Orthop Relat Res (208):108–113 Contents 1 Introduction ................................................ 1 1.1 The Anatomy and Physiology of the Hip Joint ................. 1 1.1.1 Femoral Morphology Classification .................... 2 1.1.2 Muscles of the Femur ............................... 3 1.2 Hip Joint Diseases and Skeletal Disorders ..................... 4 1.3 Hip Arthroplasty ......................................... 5 1.3.1 Type of Hip Implant ................................ 7 1.4 Primary Stability in Cementless Stems ....................... 9 1.4.1 The Use of Finite Element Analysis in Orthopaedic Biomechanics ..................................... 12 References .................................................. 13 2 Finite Element Model Construction ............................ 19 2.1 Pre-processing .......................................... 19 2.1.1 Three-Dimensional Model Construction of the Femur ..... 19 2.1.2 Three-Dimensional Model Construction of the Hip Stems ... 21 2.1.3 Alignment of the Hip Stems .......................... 24 2.1.4 Construction of Bone-Implant Contact ................. 25 2.2 Contact Modelling ....................................... 27 2.3 Material Properties Assignment ............................. 28 2.4 Boundary Conditions ..................................... 28 2.5 Implant Stability Subroutine ............................... 29 2.6 Convergence Study ....................................... 31 2.6.1 Mesh Convergence ................................. 31 2.6.2 Load Increment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 2.7 Verification of Micromotion Algorithm ....................... 36 2.7.1 Rohlmann’s Model ................................. 36 2.7.2 Comparative Analysis ............................... 37 2.7.3 The Effect of Location for Micromotion Measurement ..... 39 References .................................................. 41 vii viii Contents 3 The Effect of Implant Design on Stability. . . . . . . . . . . . . . . . . . . . . . . . 43 3.1 The Global Geometry ..................................... 43 3.1.1 Finite Element Modelling ............................ 48 3.1.2 Biomechanical Assessment of Different Hip Stem Designs ..................................... 49 3.2 The Material Stiffness .................................... 55 3.2.1 Finite Element Modelling ............................ 56 3.2.2 Biomechanical Effect of Different Mechanical Properties. . . 56 3.3 The Effect of Stem Length ................................. 61 3.3.1 Finite Element Modelling ............................ 62 3.3.2 Biomechanical Assessment of Different Stem Lengths ..... 62 3.4 Proximal Versus Distal Fixation ............................. 65 3.4.1 Finite Element Modelling ............................ 66 3.4.2 Biomechanical Effect of Different Stem Fixations ........ 66 References .................................................. 71 4 Surgical and Pathological Parameters Affecting Micromotion ...... 75 4.1 Surgical Gaps ........................................... 75 4.1.1 Finite Element Modelling: First Method ................ 76 4.1.2 Micromotion of the Stems ........................... 79 4.1.3 Finite Element Modelling: Second Method .............. 80 4.1.4 Micromotion of the Stems ........................... 83 4.1.5 Biomechanical Evaluation of the Influence of Interfacial Gaps ................................... 85 4.2 Undersizing and Malalignment ............................. 89 4.2.1 Finite Element Modelling ............................ 90 4.2.2 Biomechanical Assessment of Different Undersizing and Malalignment of the Stems ....................... 92 4.3 Pathological Condition of Bone ............................. 96 4.3.1 Finite Element Modelling ............................ 97 4.3.2 Biomechanical Effect of Different Pathological Conditions of Bone ................................. 98 References .................................................. 103 Summary ..................................................... 107 Index ......................................................... 111 Notations ABG Anatomique benoist giraud AML Anatomic medullary locking AVN Avascular necrosis BMD Bone mineral density CAD Computer aided design CT Computed tomography CoCr Cobalt chromium E Young’s modulus FE Finite element GPa Giga pascal HA Hydroxyapatite inc Inch kN Kilo newton mm Milimeter MPa Mega pascal N Newton Nm Newton meter OA Osteoarthritis OP Osteoporosis SEM Scanning electron microscopy stl Stereolithographic TCP Tricalcium phosphate THA Total hip arthroplasty TiAl Titanium alloy VHP Visible human project WHO World health organisation x, y, z Cartesian coordinates 2D Two-dimensional 3D Three-dimensional µm Micrometer % Percentage º Degree ix Chapter 1 Introduction Abstract This chapter introduces the hip joint and hip disorders that may lead to total replacement of the joint. The internal morphology of the proximal femur, which can be categorised into one of three types, is of primary importance as it will affect the type of implant most suitable for the treatment. Osteoarthritis is one of the most common reasons for hip replacement where in certain cases can severely limit patient mobility and reduce quality of life. Implants for total hip arthroplasty (THA) can be categorised into one of two types, cemented and cementless. Whilst cemented has been regarded as the gold standard, the cementless coutnerpart is gaining popu- larity. However, the issue of primary stability has to be addressed and tackled if the cementless approach was to be widely accepted. Finite element method will be used to analyse the stability of the cementless implants for hip arthroplasty. Keywords Hip joint • Hip disorders • Arthroplasty • Primary stability • Finite  element method 1.1 The Anatomy and Physiology of the Hip Joint The hip bone consists of three fused bone parts, the ilium, ischium and pubis. There is a large cup-shaped articular cavity, called the acetabulum, acted as the socket for articulation with the head of the femur. The ilium is the superior broad and the ischium is the lowest and strongest portion of the bone. The pubis which extends medialward and downward from the acetabulum forms the front part of the pelvis. The femur is the longest human bone and can be divided into three parts; proxi- mal, middle and distal. The proximal part consists of a head, a neck, a greater tro- chanter and a lesser trochanter. The hemispherical head forms a ball-and-socket joint with the acetabulum via the femoral head ligament and by strong surrounding ligaments. The neck of the femur connects the shaft and head at an average normal angle of 125°. The Greater Trochanter provides leverage to the muscles that rotate M. R. Abdul Kadir, Computational Biomechanics of the Hip Joint, SpringerBriefs in 1 Computational Mechanics, DOI: 10.1007/978-3-642-38777-7_1, © The Author(s) 2014