9.7: Diseases of Joints

The problems caused by age changes in the joints are often compounded by a disease called arthritis, which means "joint inflammation." The name was chosen because arthritis results in injury and pain in the joints.

The incidence of arthritis increases with age. More than half the cases occur in people over age 65. In fact, arthritis is the most common disease among the elderly and is second only to heart disease in causing older people to visit a physician.

Different cases of arthritis vary greatly in severity. In some individuals the symptoms are so mild as to be barely noticed. At the other extreme, arthritis can cause excruciating and unremitting pain as well as deformity and crippling incapacitation. This disease results in more limitation in activity and more disability than does any other chronic illness. Only heart disease causes people to spend more days in bed.

There are more than 100 types of arthritis, and different forms are prevalent at different stages of life. A person may have two or more forms at the same time. The two types discussed below are the forms most frequently encountered in the elderly.

Osteoarthritis

Osteoarthritis (OA) is by far the most common type of arthritis in adults. It causes more than half of all cases of arthritis. Approximately 75 percent of people reaching age 75 will have OA in at least one joint. Most cases of osteoarthritis occur in women.

The cause of osteoarthritis is still unknown, there is no method of prevention, and there is no cure. It usually progresses continuously, though the rate of progress differs among individuals. Main risk factors for OA include injury to joints, inadequate treatment of injured joints, and extreme overuse of joints.

Osteoarthritis often affects weight-bearing joints, including the knees, the hips, and the intervertebral joints in the lower (lumbar) region of the vertebral column. The joints in the cervical vertebrae and those in the fingers are also frequent sites of this disease.

Effects

When osteoarthritis attacks freely movable joints, it causes breakdown of the cartilage between bones, and the cartilage becomes rougher and softer and cracks. The cartilage becomes weaker and thinner because its cells are removing cartilage faster than they are replacing it. Because of these changes, the cartilage loses the ability to cushion and lubricate the ends of the bones, diminishing the operation of the joints (Figure 9.10).

Figure 9.10 Osteoarthritis. (Copyright 2020: Augustine G. DiGiovanna, Ph.D., Salisbury University, Maryland. Used with permission.)

So much cartilage may be removed that the hard ends of the bones bump and rub against each other. This contact can sometimes be heard and felt when a person moves. The bones respond to the resulting abuse by producing extra bone matrix at the joint. When this buildup occurs in arthritic finger joints, it may be observed as enlargements of the joints.

The new bone matrix produced is rough and sometimes jagged, and it abrades the softer tissues in the area, causing pain. As the bone matrix grows, it protrudes farther, making movement of the joint more difficult and reducing its range of motion because the edges of the bones bump against each other.

Other changes from osteoarthritis often reduce the action of the joint even further. The injured synovial membrane becomes more irregular, thick, and stiff. It may bind the bones abnormally by adhering more tightly to them. Pieces of cartilage and bony spurs sometimes break off from the bones and become lodged within the joint.

Osteoarthritis of the symphysis joints in the vertebral column causes the same type of extra bone formation that occurs in freely movable joints (Figure 9.8d). This extra bone may cause pain by irritating surrounding tissues or pressing on nerves attached to the spinal cord, reduce ease of movement, and reduce the range of motion permitted by the joints.

Figure 9.8d Vertebrae and slightly movable joints: (d) Intervertebral joints with osteoarthritis. (Copyright 2020: Augustine G. DiGiovanna, Ph.D., Salisbury University, Maryland. Used with permission.)

Treatments

Treatment of osteoarthritis is aimed at slowing its progress and reducing the pain and disability it causes. Affected individuals can be taught how to perform activities in ways that minimize abuse of diseased joints. The use of canes and other devices that support some body weight helps in this regards. Mild exercise reduces stiffness and loss of range of motion, and a variety of medications relieve pain.

Severely diseased joints may be repaired surgically. Often the diseased joint is removed and replaced with an artificial one. Total hip replacement is a common example. Since replacement of intervertebral joints is impossible, surgeons may eliminate the joint by fusing the vertebrae above and below the joint. Though this procedure prevents further motion at the joint site, it relieves the pain and deformity that usually accompany osteoarthritis of the spine.

Rheumatoid Arthritis

Rheumatoid arthritis (RA) has a much lower frequency of occurrence than does osteoarthritis. Only about 1 percent of all adults have RA. Two of every three RA patients are women. Most cases begin between the ages of 30 and 40, and the number of cases increases with age.

Effects

Rheumatoid arthritis usually attacks the freely movable joints of the wrists and hands as well as those in the ankles and feet; the joints closest to the ends of the fingers are spared. It sometimes affects other joints, including the shoulders, elbows, and knees. Like osteoarthritis, RA causes pain and loss of joint mobility. Unlike osteoarthritis, it often produces many other effects, including weakness, fatigue, and damage to organs such as the heart, blood vessels, lungs, nerves, skin, and eyes. This widespread damage occurs because RA can attack fibrous materials everywhere in the body. Another peculiarity of RA is that it goes into temporary remission in some individuals.

Though the cause of RA is unknown, the method by which it destroys joints is understood. The root of the problem lies in the immune system, which mistakenly identifies normal connective tissues as being foreign to the body. The immune system then reacts in its usual manner by trying to eliminate the "foreign" substances. In so doing, it kills and removes these normal connective tissue materials. This reaction is called autoimmunity since the body is attacking itself.

In joints, the immune system kills and removes cartilage, which is replaced with a unique type of scar tissue, called a pannus (Figure 9.11). The pannus releases enzymes that destroy more of the cartilage. The immune system also removes bone material and the synovial membrane. As more normal tissues are eliminated, the pannus enlarges and spreads into the joint, substituting for normal components. All these activities cause considerable pain and joint swelling, and proper functioning of the joint becomes impossible.

Figure 9.11 Effects of Rheumatoid arthritis on joint structure. Effects of rheumatoid arthritis on joint structure: (a) Normal joint. (b) Cartilage replaced with pannus. (c) Pannus and immune reaction remove cartilage and bone. (d) Bones fused by calcification of pannus. (Copyright 2020: Augustine G. DiGiovanna, Ph.D., Salisbury University, Maryland. Used with permission.)

As the joint weakens, the bones shift out of position. Sometimes, the pannus becomes calcified and stiff. Progressive calcification sometimes results in fusion of the bones. In addition, the ordinary scar tissue produced at the joint shrinks as time passes, pulling the bones farther out of alignment and locking them into abnormal positions. Thus, the joint becomes distorted and immovable. The result is crippling deformity, a condition most easily seen in the hands and feet.

Treatments

There is no way to prevent or cure RA. The goals of treatment are the same as those for osteoarthritis: slowing the progress of the disease and minimizing pain and disability. Various medications may be prescribed to inhibit the immune system and relieve pain. Mild exercise helps maintain joint mobility. A variety of other treatment modalities may be initiated. Unfortunately, not all individuals respond well to these treatments.