Rohit Kumar 801785010
Research Assignment –cum-Short Term Report
On
Recent Progress on the Friction and Wear in Artificial joints
Submitted to - Submitted by -
Dr. H.L Bhowmick Rohit Kumar
801785010
1
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Rohit Kumar 801785010
Research Assignment –cum-Short Term Report
On
Recent Progress on the Friction and Wear in Artificial joints
Submitted to - Submitted by -
Dr. H.L Bhowmick Rohit Kumar
1
Rohit Kumar 801785010
ABSTRACT
A tribological presence in artificial joints is discuss throughout in this report. Nowadays a
friction and wear of artificial joints is a significant problems in a huge number of patients. In
order to acquire or gathered a knowledge about friction and wear in artificial joint. Like in
total hip prosthesis are discussed in this report. A several researchers done work on different
material used in surgery of total hip replacement. A metal on metal, metal on plastics,
combinations of ceramics and metals and a evolution of total hip surgery of synovial joint is
discussed in this report. The aim of report is to review the current status of friction and wear of
artificial joint and how to minimize and eliminate this by selected suitable material.
2
Rohit Kumar 801785010 MoC- Metal on ceramic OA- Osteo Arthratis EHL- Elastrohydrodynamics Lubrication LHMoM- Large head metal on metal SF- Synovial fluid Ra- Surface roughness CrCoMo- cobalt chromium molibidnum alloy CoP- Ceramic on plastic CoC- Ceramic on Ceramic THR- Total hip replacement 4
Introduction:
A long decades before when animals and humans suffering from tribological failure of their joints. The inflammation of the joints called Arthritis or in layman language the pain formed in soft tissues. Osteoarthritis is the one type of arthritis which is common in older people where the articular cartilage begins to break down. This is a very severe problem where the patient had go through it. A human population by the age of 70 years are 90% affected by the osteoarthritis[1].A healthy joint consist of two bones each of bone with its own layer of articular which is a type of connective tissues that allows the bones to range of motion or glide against each other without friction. With osteoarthritis we are really talking about one particular kind of joint which is a synovial joint. It forms a inner lining of joint space consist of synovial fluid which acts as a natural lubricant , a synovial membrane which acts as a seal of synovial fluid and a articular capsule which keeps the bones together and gives a strength to them. The main cause of Osteoarthritis is the loss of articular cartilage which means not more separating the two bones anymore, which cause friction in between them which further then generated inflammation and start a severe pain in joint space. This decrease your range of motion and fell discomfort also. The pain can affect ability to walk, to climb stairs, to get out of a chair and to undertake normal everyday household activities. This loss of articular cartilage damaged it has not capacity to heal by itself. A specialized cell called chondrocytes is job to maintain a articular cartilage make healthy [2]. The only treatment of this osteoarthritis is remove the damaged joint surgically and replace it with a artificial joint. The replacement is also done to treatment to broken bones or injury but it depends where the bone has broken.
- Fig. Anatomy of Synovial joint
1.1 Tribology in Artificial joints :
Due to an ageing population joint replacement is rapid growing sector National joint Registry (2012) figures shows total 88,984 total hip and 93,080 knee replaces recorded in year 2012 in England. After a years of artificial joints installed there is also need to second surgery of existing prosthesis. The failure of joints is due to wear of the articulating surfaces. By abrasion or corrosion mechanisms damage may occur in joints and loss the material.so this need a replace again the worn out joint with new one. In a past in 19th^ when ivory was used as a material to treat the joint replacement but due to complexity other material is used as to cover the joint is Glass, Bakelite or cobalt-chromium alloy. The records show that the glass broke soon, the debris of Bakelite caused
effect on human body by reaction between tissues. This make also a reason of revise the surgery again where a failure prosthesis replaced by a new artificial joint. This process is still very expensive and dangerous and complexity for a surgeon. 1.2.2 Coefficient of friction and frictional Torque in Joint : The coefficient of friction is measure of resistance against the moving one body on other. It is denoted by μ , and its depend upon the material of the body , temp, and surface properties of the body.
- Coefficient of friction for normal joint in between 0.008 to 0.02.
- Coefficient of friction for MoM is 0.8.
- Coefficient of friction for plastic is 0.02. [ source of information by Wikipedia] A frictional torque force is produced when the loaded hip moves through an arc of motion. It is product of the frictional force times the length of the lever arm i.e., the distance of given point on the surface of the head moves during arc of motion. 2 Evolution of selecting material for THR (Literature review) A number of material are used as a femoral head and for acetabulum like cobalt-chromium-molybdenum alloy (CoCrMo), UHMWPE, Aluminum, polyurethane, titanium and stainless steel so forth. In a arthroplasty where replacing articulating surfaces McKee-Farrar first using same metal on both ball and socket (MoM) but this will not give a good results because friction was high and damage surface due to adhesive wear in tribo- pair.[4]. Despite of this a material used to hold the joint i.e. cement is also wear the material comes into contact in between joints. This wear make a joint loose.in 1950s professor Sir john charnley introduced metal on plastic joint which gives a very good result when it run on a hip simulator. A metal on plastic minimizing the friction as well as produce torque by frictional torque. Figure [3] shows the metal on metal and metal on (MoP) joint. To reduce the frictional torque charnley use
smaller size ball compared to natural ball (femoral head) this cause an low frictional torque hence the joint become known as the charnley low friction arthroplasty[1]. For those patients who have allergic with metals, a ceramics are used with combination of various metal or plastic. Like Ceramic on metal (COM), ceramic on polyethylene (COP), Ceramic on Ceramic (COC) are often used. However where McKee-Farrar joint had some positive result from some patients which states MoM had good survivorship more than 20 years with no major problems. In the 1980s revolution changed change MoP to MoM hips because MoP found inappropriate for long run. The second generation of metal on metal is comes with larger head diameters (LHMoM) and better surface than previous MoM. An LHMoM gives a better fitment of joint and reduced the dislocation and also easy implantation [4]. Even a hip simulator indicates minimize wear by using large head MoM. The design study has shown that head diameters should be as large as possible by Dowson et al., 2004; Isaac et al 2006 [5]. This implant failure due to several reasons which includes body reaction with wear debris, breakage in bones, loosening of components so forth. Due to this patient feels a sudden pain and high volume of metal ions in their blood. So the main reasons behind failure prosthesis is friction and wear in between components. The solution of this problem is select a suitable wear-resistant material and provide a thin layer of lubrication in between them which separates the tribo-surfaces. Figure-3. Metal on plastic and metal on metal joint. ( *Image from OrthoInfo AAOS )
3 Lubrication mechanism in artificial joints:
The approach of improving wear performance by provide lubrication to joints for better range of motion we need to understand the film formation mechanism occurring during articulation. The requirements for lubrication in bone joints are : The lubricant should contain proteins that stick to cartilage layer resulting in smooth sliding. Coefficient of friction should be ~ 0.01.[3] The lubricant should contains mineral that provide the nourish to cell and nerves Lubricant should have a capability to increase viscosity when a pressure is applied It should have proper specific film thickness.
and low fluid viscosity. The asperities of both surfaces are in contact and deformation of
asperities occurs.
4.2 Fluid film lubrication
The alternate of lubrication mechanism used in total hip replacement is
fluid film formation between two rubbing surfaces. In fluid film lubrication surfaces are
separated by EHL film. This mechanism is different from boundary lubrication where
friction is low due to fluid forces so the eliminate the wear which is comes by the intraction
of two surfaces. The wear comes in this case is by chemical corrosion or 3
rd
body abrasion.
4. 3 Protein Aggregation Lubrication:
The EHL film thickness is are time dependent because it gives
much thicker film thickness during low load. A new lubrication models used where protein
particles added in lubrication which helps the constant flow by generating drag forces [4].
5. Conclusion –
Since Artificial implant are most difficult problem in tribology research
and progress in wear resistant material is continue till the objective of minimize the effect of
friction and wear in artificial joint. With the different operating condition we discuss the
progress in THR w.r.t to material and select best suitable lubrication mechanism.
6. Reference and bibliography :
[1] A.Unsworth.,’recent development in in the tribology of artificial joints’ Centre for Biomedical Engineering, School of Engineering and Computer Science, University of Durham, Durham DH1 3LE, UK. [2] Martin JA , Backwalter JA., The role of chondrocyte matrix interactions in maintaining and repairing articular cartilage. 2000;37(1-2):129-40. [3] Fundamentals of engineering tribology with applications © Harish Hirani 2016 ISBN 978-1-107-06387-
[4] Connor Myant, Philippa Cann On the matter of synovial fluid lubrication: Implications for Metal-on- Metal hip tribology 2013 Tribology Group, Imperial College London, UK [5] Dowson, D.,et al., 2004. A hip joint simulator study the performance of metal on metal joint. Part ll : design. J. Arthroplasty 19, 124-130.