Arthritis and Artificial Joints

Arthritis26 is a broad term for pain and inflammation of a joint and embraces more than a hundred different diseases of largely obscure or unknown causes. In all of its forms, it is the most common crippling disease in the United States; nearly everyone past middle age develops arthritis to some degree. Physicians who treat joint disorders are called rheumatologists.

The most common form of arthritis is osteoarthritis (OA), also called "wear-and-tear arthritis" because it is apparently a normal consequence of years of wear on the joints. As joints age, the articular cartilage softens and degenerates. As the cartilage becomes roughened by wear, joint movement may be accompanied by crunching or crackling sounds called crepitus. OA affects especially the fingers, intervertebral joints, hips, and knees. As the articular cartilage wears away, exposed bone tissue often develops spurs that grow into the joint cavity, restrict movement, and cause pain. OA rarely occurs before age 40, but it affects about 85% of people older than 70. It usually does not cripple, but in severe cases it can immobilize the hip.

Rheumatoid arthritis (RA), which is far more severe than osteoarthritis, results from an autoimmune attack against the joint tissues. It begins when the body produces antibodies to fight an infection. Failing to recognize the body's own tissues, a misguided antibody known as rheumatoid factor also attacks the synovial membranes. Inflammatory cells accumulate in the synovial fluid and produce enzymes that degrade the articular cartilage. The synovial membrane thickens and adheres to the articular cartilage, fluid accumulates in the joint capsule, and the capsule is invaded by fibrous connective tissue. As articular cartilage degenerates, the joint begins to ossify, and sometimes the bones become solidly fused and immobilized, a condition called ankylosis27 (fig. 9.27). The disease tends to develop symmetrically—if the right wrist or hip develops RA, so does the left.

Rheumatoid arthritis is named for the fact that symptoms tend to flare up and subside (go into remission) periodically.28 It affects women far more often than men, and because RA typically begins between the ages of 30 and 40, it can cause decades of pain and disability. There is no cure, but joint damage can be slowed with hydrocortisone or other steroids. Because long-term use of steroids weakens the bone, however, aspirin is the treatment of first choice to control the inflammation. Physical therapy is also used to preserve the joint's range of motion and the patient's functional ability.

Arthroplasty29 a treatment of last resort, is the replacement of a diseased joint with an artificial device called a prosthesis.30 Joint prostheses were first developed to treat injuries in World War II and the Korean War. Total hip replacement (THR), first performed in 1963 by English orthopedic surgeon Sir John Charnley, is now the most common orthopedic procedure for the elderly. The first knee replacements were performed in the 1970s. Joint prostheses are now available for finger, shoulder, and elbow joints, as well as for hip and knee joints. Arthroplasty is performed on over 250,000 patients per year in the United States, primarily to relieve pain and restore function in elderly people with OA or RA.

Arthroplasty presents ongoing challenges for biomedical engineering. An effective prosthesis must be strong, nontoxic, and corrosion-resistant. In addition, it must bond firmly to the patient's bones and enable a normal range of motion with a minimum of friction. The heads of long bones are usually replaced with prostheses made of a

Severe Case Rheumatoid Arthritis

Figure 9.27 Rheumatoid Arthritis (RA). (a) A severe case with ankylosis of the joints. (b) X ray of a hand with RA.

Figure 9.27 Rheumatoid Arthritis (RA). (a) A severe case with ankylosis of the joints. (b) X ray of a hand with RA.

metal alloy such as cobalt-chrome, titanium alloy, or stainless steel. Joint sockets are made of polyethylene (fig. 9.28). Prostheses are bonded to the patient's bone with screws or bone cement.

About 80% to 90% of hip replacements and at least 60% of ankle replacements are still functional 2 to 10 years later. The most common form of failure is detachment of the prosthesis from the bone. This problem has been reduced by using porous-coated prostheses, which become infiltrated by the patient's own bone and create a firmer bond. A prosthesis is not as strong as a natural joint, however, and is not an option for many young, active patients.

Arthroplasty has been greatly improved by computer-assisted design and manufacture (CAD/CAM). A computer scans X rays from the patient and presents several design possibilities for review. Once a design is selected, the computer generates a program to operate the machinery that produces the prosthesis. CAD/CAM has reduced the waiting period for a prosthesis from about 12 weeks to about 2 weeks and has lowered the cost dramatically.

26 arthr = joint + itis = inflammation

27ankyl = bent, crooked + osis = condition

28rheumat = tending to change

29arthro = joint + plasty = surgical repair

30prosthe = something added

Saladin: Anatomy & I 9. Joints I Text I I © The McGraw-Hill

Physiology: The Unity of Companies, 2003 Form and Function, Third Edition

Chapter 9 Joints 321

Pictures Artificial Femoral Head

Figure 9.28 Joint Prostheses. (a) An artificial femoral head inserted into the femur. (b) An artificial knee joint bonded to a natural femur and tibia. (c) A porous-coated hip prosthesis. The caplike portion replaces the acetabulum of the os coxae, and the ball and shaft shown below are bonded to the proximal end of the femur. (d) X ray of a patient with a total hip replacement.

Coxae Anatomy Mcgraw Hill

Figure 9.28 Joint Prostheses. (a) An artificial femoral head inserted into the femur. (b) An artificial knee joint bonded to a natural femur and tibia. (c) A porous-coated hip prosthesis. The caplike portion replaces the acetabulum of the os coxae, and the ball and shaft shown below are bonded to the proximal end of the femur. (d) X ray of a patient with a total hip replacement.

Saladin: Anatomy & I 9. Joints I Text I I © The McGraw-Hill

Physiology: The Unity of Companies, 2003 Form and Function, Third Edition

322 Part Two Support and Movement

Osteoarthritis

Osteoarthritis

Thank you for deciding to learn more about the disorder, Osteoarthritis. Inside these pages, you will learn what it is, who is most at risk for developing it, what causes it, and some treatment plans to help those that do have it feel better. While there is no definitive “cure” for Osteoarthritis, there are ways in which individuals can improve their quality of life and change the discomfort level to one that can be tolerated on a daily basis.

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Responses

  • Syed
    What is it called when a joint becomes solidly fused and immobilized?
    4 years ago
  • Kedija Sayid
    Can arthritis form on an artifical knee?
    4 months ago

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