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Arthritis The Disease Affects Joints Health And Social Care Essay

The term "arthritis" encompasses more than 100 diseases and conditions that affect joints, the surrounding tissues and other connective tissues[1]. The word arthritis comes from arthron, meaning joint, and itis, inflammation. Arthritis can, therefore, be defined as being the inflammation of a joint. This condition is marked by local tenderness and pain, local redness and swelling and local elevation of temperature[2]. Approximately 46 million Americans have some type of arthritis or related condition, it causes damage to cartilage and bones, causing joint pain, swelling, stiffness and loss of function.[1]

The various forms of arthritis and related conditions can affect anyone, no matter their race, gender or age. However, it is especially important for women to be educated about these diseases since they affect women at a much higher rate than men. Sixty percent of all people who have arthritis are female, and several of the more common forms are more prevalent in women. The most common form of arthritis is Osteoarthritis (OA), also known as degenerative joint disease. Of the nearly 27 million Americans who have osteoarthritis approximately 16 million are women. Women usually develop OA after age 40.[1]

1.2 Treatments

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There is no cure for arthritis, an early diagnoses and appropriate treatment are the best way to control it.[1] In the last few years, a shift in strategy toward the earlier institution of disease modifying drugs and the availability of new classes of medications have greatly improved the outcomes that can be expected by most patients. The goal of treatment is to achieve the lowest possible level of arthritis disease activity and remission when possible, the minimization of joint damage, and enhancing physical function and quality of life. Inflammation must be suppressed and mechanical and structural abnormalities corrected or compensated by assistive devices. Treatment options include medications, reduction of joint stress, physical and occupational therapy, and ultimately, surgical intervention.[3]

1.3 Total hip arthroplasty (THA)

Artificial-joint replacement is an effective treatment for serious forms of osteoarthritis and for disabling effects of rheumatoid arthritis, congenital deformities, and particular kinds of post traumatic conditions. Osteoarthritis (OA) is the most frequent indication for joint replacement, it is responsible for the majority of cases involving musculoskeletal discomfort and, second only to cardiovascular conditions, is an important cause for partial or complete disabilities.[4]

The development and application of artificial-joint replacement, particularly total hip arthroplasty (THA) and total knee arthroplasty (TKA), has achieved a tremendous reduction in disabilities, particularly in the older segment of the population. The majority of the estimated 400,000 patients receiving THA annually can hardly walk at all and suffer serious continuous pain, day and night. A few weeks after the operation they will, with few exceptions, be pain free, able to function normally, resume jobs and sometimes even active sports.[4]

The hip joint is of the ball-and-socket type, formed by the head of the femur fitting into the acetabulum of the coxal (hip) bone.[2] Because of the rigid ball-and-socket configuration, the hip joint is one of the most stable joints in the body.[5] A illustration of a normal hip versus one with arthritis can be viewed below (Figure 1.1).



Figure 1.1: Illustration of a normal hip (a) and one with arthritis (b).[6]

Total hip replacement prosthesis intervention consists of replacing both the ball (femoral head and neck) and the socket (acetabulum) bone with the implant materials (Figure 1.2); a femoral component and an acetabular component. Femoral stem is composed of three sections; head, neck and shaft.

Figure 1.2: Hip before and after a total hip arthroplasty (THA) with the components in place.[7]

The stem is made using a metal alloy, usually it is made of Ti or CoCr alloy (that came to replace 316L stainless steel which was used earlier), it is fixed to the intramedullary canal using cement or by press fitting. Different materials can be used to make the femoral head like CoCr, alumina or zirconia (Figure 1.3 a). Ti alloy heads work very well under good articulating conditions however, the use of this alloy has been decreasing due to their low resistance to third-body wear.[5] The acetabular component is usually made of ultra-high-molecular-weight polyethylene (UHMWPE). It consists of a metallic shell and an UHMWPE insert (Figure 1.3 b). The metallic shell is used to decrease UHMWPE microdeformation and provide a porous surface fixation for the cup.[5]



Figure 1.3: Implant materials, femoral (a) and acetabular component (b) for THA.[8]

1.4 Cemented fixation

Polymethylmethacrylate (PMMA) bone cement is a material widely used for artificial joint fixation. This technique largely contributes to the success of modern joint replacement, it is a highly successful way to restore pain free function to patients suffering from arthritis and it remains the most common method of fixing a total joint prosthesis (Figure 1.4).[9]

Figure 1.4: Fixation of the implant to the bone using bone cement as a grouting agent.[10]

For about 40 years, bone cement has been used extensively in orthopedic surgery; however, it's application goes back roughly 60 years where it's usage has been the primary constituent of the vast majority of artificial dentures in the United States.[11] Ever since the introduction of bone cement for fixation of artificial hip joints by Dr. John Charnley[12] the procedure has been adopted throughout the world.

Acrylic bone cements have undergo very little change since Dr. Charnley introduce them to orthopedics in the early 1960's.[12] It has been shown in previous work that the failure mechanisms in PMMA bone cement are directly related to its microstructure.[13]

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Fracture of the bone cement leads to loosening at the implant site, and correction via revision surgery is required.[14-15] Load transfer to the implant site due to everyday human gate leads to localized bone cement fatigue which, will eventually result in micro-crack propagation. As the number of micro-cracks grow, the mechanical response of the bone cement changes, changing the way stress is transferred causing the bone to remodel enough to cause prosthesis loosening resulting in total implant failure.[14-17]

1.5 Market

The combined orthopedic large joint replacement and bone cement market had a value of $7 billion in 2009. There has been a consistent double digit growth for hip and knee arthroplasty since the early 2000s. Growth slowed during 2008 when the recession began, however it nearly resumed its previous growth rate by the end of 2009. Large joint arthroplasty, even no being the fastest growing orthopedic market, has proven to be incredibly resilient to economic shifts due to the high demand for hip and knee implants.[18]

The future outlook for the arthroplasty market is healthy. Large joint reconstruction will continue to be fueled by the baby boomer generation, but at the same time, interest is growing in all areas of small joint reconstruction: the small bone and extremity devices market was valued at $673.8 million in 2008.[19-20] The most dominant products within the orthopedic sector are devices that are implanted for reconstruction in hip, knee, and spine. These are the areas that continue to experience the most growth, at a rate over 20%.[21-22]

1.6 Success rate and long-term outcome

In 2000, 309,000 total hip arthroplasty (THA) procedures were performed in the United States. The 20 year success rate of a hip replacement is approximately 80% for elderly patients, although men, younger patients and patients who weigh more than 165lbs, have higher rates of failure [23]. At 10 years postoperatively success exceeds 90%.[24]

The successful, long-term performance of orthopedic implants depends on implant material, prosthesis design, biocompatibility of the components, wear of the articular surfaces, quality of the bone, and stability of fixation.[9] Problems with wear and particle debris exist and eventually may necessitate additional surgery, including replacing the prosthesis.[23] An estimated 32,000 revision THAs were also performed in 2000, of which approximately 45% required cement removal.[23] Total knee arthroplasty (TKA) implant failure rates are even higher mostly in younger patients. There is also a record of early failures, but these are considered to be due to implantation or surgical technique.[14, 16, 25-27]

The most frequent fixation problems are related to infection, wear and wear particles, mechanical failure of implants and consequent loosening.[5] Many factors, such as deterioration of physical properties of implant materials, problems with surgical techniques, design of the implant, selection of patients and post surgical care are related to the (late) loosening and consequent failure of the implant.[5]

The initial success of the procedure in the total hip arthroplasty (THA) was extended to the total knee arthroplasty (TKA)[5] and also used by neurosurgeons to form replacements for skull defects.[11] A major problem of orthopedic joint prosthesis, after fixation, is maintaining the integrity between the implant and the host tissue at the cellular and organ levels.[5]

1.7 Specific aims

Artificial joint replacement is one of the most successful treatments for arthritis. The long term success of the implant is intrinsically related to the bonding material between bone and implant. There is evidence that suggest that stable cracks can exist in well cemented prostheses; thus a mechanism that increases the amount of energy absorption in a fracture damage zone would be of great clinical benefit. This would increase the longevity of the bone cement by reducing the possibility that the crack reaches a critical length.

PMMA bone cement consists of 4 material phases: 1) the "bead" phase - the polymerized, spherical PMMA beads in the original commercial package powder remain as spherical beads, 2) the "interbead" matrix PMMA (polymerized monomer), 3) the radiopacifier (usually BaSO4 or ZrO2) and 4) porosity. The phases are illustrated in Figure 1.5.

Figure 1.5: The four phases of bone cement shown together in a cross section (X160). Pores (p) are approximately 100µm, beads (b) range from 10 to 50 µm, BaSO4 particles visible as white specks embedded in the matrix (im) are approximately 1µm in diameter.[28]

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By improving the mechanical properties of the bone cement we hope to eliminate (or reduce) failure at the implant site. We hypothesize that increased fracture and fatigue resistance will both be achieved by changing the microstructure of existing polymethylmethacrylate (PMMA), incorporating novel particles into the matrix. The mechanical properties will change, which will lead to increased longevity of cemented artificial joints.

The purpose of this research was to investigate the effect of two novel particle types in the bone cement's microstructure. To that end, the Specific Aims were:

-Specific Aim 1: Create new bone cement by designing fracture resistant microstructures, and perform fracture toughness testing on the new cements as an initial indicator of fracture performance by:

-Specific Aim 1A: replacing part of the powder phase with cross-linked beads.

-Specific Aim 1B: modifying the interbead matrix by adding soluble rubber modifiers to the monomer.

-Specific Aim 2: To understand fracture mechanisms, SEM observation of the new fracture surfaces resultant from the fracture toughness tests will be performed.

-Specific Aim 3: To determine fracture properties, tensile and fatigue tests on the new cements will be conducted.

-Specific Aim 4: Use of a Hysitron Tribometer nano-indentor to quantify the changes of the mechanical properties at the microstructural level resultant from the addition of the new materials.

In collaboration with Rohm and Haas, two methods were chosen to modify the microstructure. Based on Rohm and Haas previous experience with commercial PMMA (not bone cement) or laboratory experiments with bone cement. Two modifiers (as reflected in Specific Aim 1A and 1B) were chosen; 1) irregular and/or cross-linked PMMA particles on the same size scale as the current PMMA beads (Figure 1.5) and 2) liquid rubbers that will modify the interbead matrix.

It is know that cross-linking polymer molecules leads to a significant increase in mechanical strength. To our knowledge, no bone cement has ever incorporated a cross-linked phase. These particles derive from commercial available PMMA and are monolithic, without microstructure. By mixing rubber modifiers within the cement, we get a new phase that absorbs and dissipates the energy for fracture. In contrast to the cross-linked particles, where the particle size is fixed, the liquid rubber first dissolves and disperses into the liquid monomer, and then precipitates (or phase separates) during polymerization of the monomer to form microscopic rubber domains in the interbead matrix. The liquid rubber polymers are low glass transition temperature (Tg), low molecular weight, acrylic based polymers derived from acrylic monomers. We propose that the resulting new microstructures (Figure 1.6) will create toughening mechanisms to increase the fracture and fatigue resistance in PMMA bone cement.



Figure 1.6: (a) Fracture path through PMMA with radiopacifier and (b) an example of the fracture path through one of the proposed new microstructures showing crack arrest by the novel particles.

Mechanic failure of the cement mantle is linked to failure of the total joint prosthesis. Ideally, the implant should outlive the patient. Revision THA surgery brings complications due to damaged bone, loss of bone stock, infection and cement removal, these are reasons why surgeons recognize that a revision THA has higher chances of complications than a primary THA. Also, a revision THA can cost almost twice than the previous intervention.

Eliminating or reducing bone cement failure is imperative, longer life of the implant results in increased patient physical condition and prevents costly revision surgeries.

1.8 Thesis overview

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