Design Of Fretting Corrosion Testing Set-Up For Hip-Joint Implants Literature Review Example

Abstract:

The total hip replacements are indispensable medical procedures that address the hip problems of people. The medical practice for some time has been an adequate solution for hip problems. However, problems has been discovered that the materials used for the implants that are composed of metals and alloys cause fretting corrosion which leads to various health complications and implant failure. This paper discusses the hip joint implants and the fretting corrosion that complicates the medical practice. It touches the adverse effects of the implant corrosion in the health of the patients. Furthermore, this paper divulges some of the design of fretting corrosion testing set-ups that has already been used and the set-ups that more or less considered as efficient set-up for testing design for hip joint implants. The various set-ups are used for testing the efficiency of the hip joint implants that is a great contributory factor to the consideration of success of the medical orthopaedics procedure.

Introduction:

Hip replacement is the surgical method that replaces the natural hip joints with artificial ones. Generally, the major reasons for these implants include (Drugwatch):

Fracture or any injury related to the hips

Wearing down of the joint
Arthritis
Increase mobility and reduce pain in the hips
Hip joint implant devices can be done with various materials such as polyethylene, ceramic, metal, composite plastics or any combination of materials. The use of metal has been prevalent in this surgical practice. Implants using metal can be done through Metal Ball and Polyethelene (Plastic) Cup or Liner (MOP) and Metal Ball and Metal Cup (MOM). MOP is an implant that offers less friction with the balls situated in the socket since it has smooth surface made up of plastic. However, the plastic debris may cause failure that would lead to osteolysis. MOM are implants are suitable especially to the younger patients since they are more durable. They wear less than other materials. Flaws of the design include metallosis, metal poisoning, which lead to serious health problems (Drugwatch). The metals that rub each other Corrosion is a challenge in the orthopaedics procedures where scientists continue to design implants that are resistance to corrosion. Metals rubbing each other such in the MOM implants create metal ions that may enter the bloodstream of the patient.

Review of Related Literature:

The total arthroplasty in the world is composed majorly of the hip replacements. In US alone, these medical procedures accounted for 95% of all the arthroplasty procedures in 1994. The long term success of the hip replacements is accounted in the long term dependability of the implanted prosthesis and their capacity to resist wear in the in vivo environments (Kennedy). The kinematics in the hip joint implants is categorized into three anatomic planes: the horizontal plane (coronal), the sagittal plane, and the horizontal plane (transverse). The three rotations of a hip joint include the abduction-adduction, the flexion-extension, and the internal-external rotations. The hip joint allows rotations via the ball-in socket joint giving way for three degrees of freedom. The hip replacements prosthesis, as much as possible, is designed to maintain the functionality of the natural hip joint achieving all the degrees of freedom it naturally does. The conformal ball-in-socket configuration of the hip joint generates contact interface to any of the femoral head’s rotation, requiring the flexion-extension motion of the hip to be primarily important. The combination of the hip’s rotational movements centers the contact between the acetabular cup’s surface and the femoral head of the hip joint prosthesis. The multi-directional motion directly affects the wear and tear of the prosthesis made up of polyethylene used in most of the acetabular cups (Kennedy). The total hip Arthroplasty (THA) are mostly designed with mixtures of metals. These initial models of made up of cobalt-chrome and titanium based alloys. Cobalt Chrome are excellent materials for femoral head due to its hardness. While the titanium alloys are good materials for femoral stem since it has closer modulus of elasticity o the bones. The use of these metals has a long rack of historical record for being the best used materials for implants. The crucial part of the implant is in the modular interface between the head and the neck. This modular junction is not impervious to fluid and becomes the vulnerable or weak part in the design of arthrosplasty. Fretting corrosion likely appears where the large metal-on-metal head increase forces with the bearing at the taper junction. The fretting corrosion debris increase significantly as it affects the health of the patient (Urish et al). The identified corrosion products at the modular junctions at various prosthesis procedures were similarly having issues that dawned upon the orthopaedics consciousness where consequential problems are already identified such as osteolysis, aseptic loosening due to polyethylene wear and implant failure (Kurtz). The effect of fretting corrosion contributes greatly to the initiation of other corrosions at the interface. There is also a correlation of the corrosion with the length of neck extensions. The implants with longer neck extensions are more susceptible to the fretting corrosion due to the instability of the interface. This problem is said to be addressed through reduction of the design that would cause instability of the interface (Brown et al).
The metals that are used in the orthopaedics are composed of biocompatible alloys with superior strengths primarily made for structural implants. They can be composed of metals such as stainless steel or Fe-based alloys, Titanium and its alloys, and CoCr alloys, which are almost used. Hip implants can undergo deterioration by wearing, fretting and corrosion. Wearing of the hip joint implants is evident in the surface damage due to progressive loss of material brought about by opposing surfaces motions. Fretting wear is when the materials in the contact surfaces is removed through movements such as oscillating and sliding motions between two mechanically joined parts subjected to loads. Corrosion is when the material are dissolved, consumed and undergo surface degradation brought about by electrochemical interactions where the metallic ions and salts are produced. Fretting corrosion is the mechanical action where the passive layer of the metal alloy is damaged permanently. This degradation further leads to the acceleration of corrosion of the other unporteced surfaces The contacting surfaces are then deteriorated as brought about y he interace of wo contacting surfaces. Fretting corrosion is the most observed forms of corrosion in the orthopaedic implants (CeraNews). The fretting corrosion in the orthopaedic implants causes adverse effects such as tissue reactions and structural failure of implants. The products of corrosion can be detected in the urine samples of patients. Studies show that metal ions are detrimental to health affecting osteoblast functioning and adverse responses to local tissues. The metal ions affect immunologic responses and the lymphocyte reactivity in the patients (Mroczkowski et al). Fretting corrosion is also present at other loading bearing taper-locking interfaces of prosthetic implants. The risk factors of the fretting corrosion that are already identified includes the material combination of the bearing couple, the head taper junction material combination, the diameter of the bearing, the length of neck of the ball head, and the other intra-operative assembly conditions (Preuss et al). The fretting corrosion promotes the exposure of fresh and non-oxidized metals to the aggressive surround body fluids where the metal ions and the particle debris promote a host-tissue response that further invokes immunological reactions and inflammations. Consequently, the implanted prosthesis loosens and metal debris migrates to other parts of the body. It then accelerates the wear of polyethylene found in the actebular cup and also leads to osteolysis which is the long-term adverse effect in the body. In other words, fretting corrosion is the start of a long chain of consequences that leads to negative impact in the outcome of the implant (Schaaf).

Discussion:

There have been many advances in the testing of hip joint implants. The rise of technology nowadays paved way for better materials used as implants that undergo various mechanical testing. The fretting corrosion mostly brought about by MOM is typically tested in in vitro. The components are disassembled and evaluated. Fluids are analyzed with presence of particulates and its morphology. The standard testing of ASTM F1875 is used to evaluate the fretting and corrosion of the implants. Several methodologies are used such as measurement of electrochemical potentials of the metals created during fretting corrosion, measurement of the dimensional changes brought about by fretting corrosion interactions, and the use of qualitative scale to rate the amount of fretting (Accutek). Other methodologies include evaluation of the area via light section microscopy, measurement of the area by profilometry, determination of the friction energy and its coefficient, the electrical contact resistance measurement, fatigue life determination, qualitative examination using transmission electron microscopy. Most of the fretting testing methods are combinations of several methods. The only quantitative methods remain to be the same though, which is the determination of the weight loss and volume. Small concentrations of fretting corrosion are measured through radioactive tracer atoms. Some experiments require liquid medium to test the aggressiveness of the implant in the surroundings. There are testing solutions used such as proteins that influence the fretting wear volume (Schaaf).
There are many basic science test method set-ups for fretting corrosion for orthopedic implants. The fretting corrosion happens in the junctions of implants corroded in vivo caused by multifactorial set of processes such as biomaterials surfaces, electrochemistry, surface mechanics and other biological interactions. Corrosions starts when fluid ingress influences the implants loaded with asperity-asperity contacts. There is abrasion of oxide films due to flexural rigidity and elastic displacements. The oxidation releases electrons in the metal causing voltage to incline to negativity. Oxygen is depleted while the pH lowers and the Cl increases. The voltage drops and the solution changes decreasing the stability of oxides. Fretting corrosion can be tested through pin-on desk testing where controlled parameters include friction load, load, coefficient of friction, displacement, contact area, voltage, solution and current. Also, there are instruments available to fretting corrosion where three regimes are captured which are the low-normal stress or slip regime, the intermediate stress or stick-slip regime and the high stress or stick and no sliding regime. The fretting areas and currents increase and decrease under normal stress. Current information tests the fretting corrosion in the various regimes of the implant.
The implant performance tests are combined fretting corrosion test methods where micro-motion measurements are used called MACC. These methods include analysis of the loadings, corrosions, and micro-motions. Testing set-ups include femoral stems mounted in acrylic bases, eddy current sensors, electrically isolated aluminum target plate. The micro-motions and fretting corrosion are measured every cyclic loading (Mihalko et al). The cyclic stresses causes the oxide film fractures thereby exposing the unprotected surfaces to the local aqueous environment further leading to a series of electrochemical reactions. Scratch test is also a ethod in investigating the chemical response of metal alloys implants such as the CoCrMo and the Ti-6AL4V subjected in a controlled oxide film fracture.
Mechanically assist corrosion or MACC is the combination of fretting and crevice corrosion where the surface composed of passivated layer is deteriorated by the constant micro-motions of cyclic loading. A study by Munir, et al showed that severity of corrosion in a year analyzing the different head materials, regions, bearing surfaces and the head size. The corrosion damage were quantified with scores. The results showed that the severity of the corrosion at the head-neck taper was greater for metals as compared with ceramic heads. The larger frictional force on the hard-on-hard earing surfaces were contributed by the moment arm that are significantly greater. In effect, there is higher exposure to fretting corrosion tearing the protective oxide layers and making the site inclined for more corrosion (Munir et al). The MACC mechanism allows investigation of the hip implants through the two electrodes used to monitor the open circuit potential and the fretting current. The decrease in the OCP and increase in the fretting current corresponds to the increasing load. Through the spectroscopic analysis of solutions also shows the presence of the metal ions coming from the fretting corrosion (Preuss, et al).
Tribocorrosion is one of the most significant multidisciplinary researches that contribute greatly to the testing set-up of fretting corrosion in hip joint implants. It utilizes tribometer that is integrated with electro-chemical set-up. A tribocorrosion system configured with a pin-on-ball is designed for hip joint implants. The set-up is composed of tribological contact comprised of the pin in the ball moving in rotating and oscillating motion. Components include tribocorrosion cell, vertical and horizontal load frames, and support bearings. A standard electrode is used. There are evolved electrochemical parameters that need to be followed for comparison with date collected (Matthew, et al).

References:

Accutek. “Hip Implant Testing”. Accutek Testing Laboratory. (2014). Web. 30 December 2014.
Brown SA., Flemming CA., Kawallec, JS., Vassaux, C., Merritt, K., Payer JH., Kraay, MJ. “Fretting
Corrosion Accelerates Crevice Corrosion of Modular Hip Tapers”. US national Libracry of medicine National Insititutes of Health. (1995). Web. 29 December 2014
CeraNews. “Ceramics in orthopaedics”. The Orthopaedic Landscape Information Journal.
(2013). Web. 29 December 2014
Drugwatch. “Hip Replacements”. Drugwatch. Peterson Firm LLP. (2014). Web 29 December
2014
Kennedy, FE. “Biomechanics of the hip and knee: implant wear”. Wear of Ortopaedic Implants
and ArtificialJoints. Woodhead Publishing Limited (2012). Web. 29 December 2014.
Kurtz, Steven. “Taper Corrosion Update: What is the role of Ceramic Femoral Ball Heads?”.
Resource Booklet. (2013). Web. 29 December 2014.
Matthew, MT, Uth, T., Hallab, NJ., Pourzal R., Fisher and Wimmer. “Construction of a Tribocorrosion test apparatus for the hip joint: Validation, Test Methodology and Analysis. Elsevier. (2011). Web. 30 December 2014
Mihalko, W., Goodman, St., Della Valle, C., Gilbert, J., Lemons, J., Jones, L. “Modularity in
Orthopaedic Devices: At What Cost?”. Web. 29 December 2014
Assembly on the Fretting Corrosion of Modular Hip Tapers”. Wiley InterScience. (2005). Web. 29 December 2014
Munir, S., Cross, M., Jenabzadeh, R., Sokolava, A., Esposito, C., Molloy, D., Walter, W., Zicat, B.
“The Efect of Bearing Surface On Corrosion At the Modular Junctions in Total Hip Arthroplasty”. Resource Booklet. (2013). Web. 29 Decembber 2014
Preuss, R., Heeussler, K.m Flohr, M., Streicher, R. “Fretting Corrosion and Trunnion Wear- Is it
also a Problem for Sleeved Ceramic Heads?” Resource Booklet. (2013). Web. 29
December 2014
Schaaf, P. “The Role of Fretting Damage in Total Hip Arthroplasty with modular design hip
joints- evaluation of retrieval studies and experimental simulation methods”. Journal of Applied Biomaterials & Biomechanics. (2004). 2:121-135.
Urish, K., Anderson, P., Mihalko, W., AAOS Biomedical Engineering Committee. “The Challenge
of Corrosion in Orthopaedic Implants”. American Academy of Orthopaedic Surgeons. (2014). Web. 29 December 2014