9.5: Osteoporosis- A Bone Disease

Though normal bone matrix retains much of its strength throughout life, many individuals develop a disease called osteoporosis, which causes substantial reductions in the quantity and strength of bone matrix. Affected individuals develop bone fractures quite easily even when carrying out ordinary daily activities or simply walking or sitting.

Osteoporosis means "bones with pores." This name is appropriate since osteoporosis causes matrix production to be much slower than matrix removal, leaving bones full of holes. Affected bones become thin, hollow, and fragile.

Type I, or Postmenopausal, Osteoporosis

There are two types of osteoporosis. Type I osteoporosis is also called postmenopausal osteoporosis because it usually affects women after menopause. This occurs because the lowered estrogen levels after menopause seem to be the main factor in bone deterioration. Type I osteoporosis rarely occurs in men since the level of the hormone testosterone in men does not decline dramatically with aging.

Postmenopausal osteoporosis affects trabecular bone more than it affects cortical bone and thus leads to fractures in regions of the skeleton that consist largely of trabecular bone. These regions include the vertebrae, the neck of the femur near the hip, the radius near the wrist, and the humerus near the shoulder (Figure 9.1).

Type II, or Senile, Osteoporosis

Type II osteoporosis is also called senile osteoporosis because it usually affects people of advanced age, especially those over age 60. The late appearance occurs because senile osteoporosis affects cortical bone more that trabecular bone. Type II osteoporosis occurs twice as frequently in women as in men.

Though senile osteoporosis affects many areas of the body, most of the resulting fractures occur in the neck of the femur. Other fractures occur in the radius near the wrist, the humerus near the shoulder, the tibia (shin bone) near the knee, and the pelvis (Figure 9.1).

Incidence

Osteoporosis affects more than 24 million Americans, and this number is rising as the number of elderly people increases. Approximately 80 percent of those with osteoporosis are women, and as many as 60 percent of all women over age 60 have osteoporosis. In the three decades following age 50 and based on World Health Organization standards, the incidences of osteoporosis among women are 15 percent, 25 percent, and 40 percent respectively. A substantial percentage of women classified as not having osteoporosis have serious thinning of bone. The incidences among men are 33 percent less.

Effects

Each year osteoporosis causes more than 1.5 million fractures. Almost half are fractures of vertebrae, while about 20 percent are hip fractures.

Seven of eight vertebral fractures occur in women. The incidence of these fractures in women rises quickly and continuously, beginning soon after menopause. Vertebral fractures occur in about two-thirds of all women over age 65.

Vertebral fractures caused by osteoporosis are usually crush fractures, or fractures in which the supporting part of a vertebra, called the body, becomes so weak that it collapses (Figure 9.8b). When this happens, the upper part of the vertebral column settles down on the part below the fracture. These fractures often happen spontaneously or when a person is lifting a heavy object.

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

Crush fractures produce serious problems. Extreme pain often occurs because the nerves extending out from the spinal cord become pinched where they pass between the collapsed vertebrae. The misalignment of the vertebrae limits mobility, and the settling down of the vertebrae results in a decrease in height and a hunched-over or humpbacked posture. These people may have a drastically altered appearance, and their clothing often does not fit properly. The poor posture also produces complications in other systems, such as difficulty breathing and poor circulation. All these changes have an impact on the ability of affected individuals to care for themselves. Their social interactions change, they frequently have lower self-esteem and suffer from depression, and they may encounter problems in performing occupational tasks. These effects also affect the people in their families and communities.

Hip Fractures

The incidence of hip fractures is low until about age 60, after which the rate of occurrence increases gradually each year until about age 70. Then the rate of occurrence rises much more quickly each year. One-third of all women and one-sixth of all men who reach age 90 will have had a hip fracture due to osteoporosis.

Like vertebral crush fractures, many hip fractures occur spontaneously. Others often result from falling. It is sometimes difficult to tell whether a person fell because a hip fractured or fractured a hip because of a fall.

Fractures of the hip caused by osteoporosis lead to significant problems that are different from those resulting from vertebral fractures. Over half the individuals who suffer a hip fracture lose the ability to walk without assistance. Many people with hip fractures no longer can perform normal daily activities such as bathing and dressing without help. Between 15 and 25 percent of individuals with a hip fracture need to enter an institution for extended care. Most of these patients will never be able to return to living in the community. As with vertebral fractures, all-encompassing shifts in lifestyle are imposed on people who suffer hip fractures due to osteoporosis, and hip fractures have an impact on people associated with hip fracture patients. Finally, 20 percent to 30 percent of those who have osteoporosis-related hip fractures die within one year as a result of complications such as pneumonia and blood clots.

Causes

The cause of osteoporosis remains unknown, but the changes in bone matrix brought about by Type I osteoporosis in women result primarily from drastic reductions in estrogen. Low levels of estrogen result in profound changes because estrogen helps build and maintain bone matrix through numerous complex mechanisms. Type I osteoporosis occurs relatively infrequently in men, but when it does occur, it seems to follow abnormally large decreases in testosterone.

Type II osteoporosis is primarily due to an age-related decrease in vitamin D activation by the kidneys. In addition, the aging intestines seem to become less sensitive to vitamin D and less able to respond to bodily needs for calcium. The result is a declining supply of calcium to body cells, leading to breakdown of bone matrix. Since the intestines do not absorb enough calcium, the matrix that is destroyed is not replaced.

Diagnosis

Diagnosing osteoporosis is very difficult, and in almost all cases individuals do not find out that they have osteoporosis until they have suffered a fracture. The diagnosis is difficult because the appropriate tests are dangerous (e.g., radiation, surgery), time-consuming, expensive, and difficult to interpret. In addition, to truly determine that a person has osteoporosis, that person should be tested regularly every few years to track the rate of loss of bone matrix.

Modifiable Risk Factors

The best way to protect oneself from the effects of osteoporosis is to build as much bone matrix as possible before age 35 and keep the deterioration of matrix as slow as possible thereafter (Table 9.1). The first four items in the table seem to be the most important. Following these recommendations will minimize the modifiable risk factors for osteoporosis and diminish the incidence of fractures and the destructive immobility that usually follows.

Lifelong involvement in weight-bearing activities such as walking and running is one of the best ways to minimize the effects of normal bone demineralization and decrease the chances of developing osteoporosis. However, any increase in weight-bearing exercise by sedentary older individuals will be helpful. Any strenuous activity will slow the demineralization process.

Intrinsic Risk Factors

While all people should take the appropriate steps to protect themselves from osteoporosis, this is especially important for those who are intrinsically at high risk. These high-risk categories include being female; having early menopause; having the ovaries removed; being white or Asian; having fair skin; having relatives with osteoporosis; being very thin; having kidney disease; having thyroid or parathyroid gland disease; having an intestinal disease that inhibits calcium absorption; and having chronic bronchitis or emphysema. Of course, belonging to more than one category places a person at even greater risk. Individuals at very high risk may benefit from diagnostic testing by qualified professionals.

Treatments

Though prevention is the key to success in battling osteoporosis, individuals who have already lost much bone matrix because of this disease can be helped to some degree.

Strengthening Bone

Many treatments have been shown to slow the loss of bone matrix in at least some individuals. Often these treatments are based on the recommendations in Table 9.1.

For some individuals, such as very sedentary older women, vigorous exercise can reverse the process of demineralization and increase the amount of minerals in bones subjected to heavy loads. The length of time over which more minerals will be added to the bones depends on the nature of the exercise regimen. Regardless of the nature or duration of the activity, however, demineralization of the bones will eventually resume. If a high level of physical activity is continued, demineralization occurs at a slow rate. If the exercise is stopped, demineralization soon recurs at a rapid rate.

Many researchers believe that the exercise-induced addition of minerals to bones or the slowing of bone demineralization decreases the risk of fractures among the elderly. Exercise such as walking a mile three times a week has been shown to reduce the risk of fractures in many older individuals. Though exercise alone may be beneficial, the most successful treatment plans incorporate several recommendations. For example, an exercise program may be combined with dietary supplements of calcium and vitamin D.

Since changes in bone matrix occur slowly, treatment programs should be continued for many years. Because of the heterogeneity and the higher incidence of diseases among the elderly, a complete assessment of an older person should be performed before a treatment program is initiated.

The most successful treatment programs for postmenopausal women usually include estrogen replacement therapy, and most women can be helped by such therapy. However, there is a small risk from complications such as the formation of blood clots and the development of uterine or breast cancer. Women at high risk for these complications probably should avoid estrogen therapy. For other women, the risks are very small when estrogen is administered with certain types of progesterone like hormones. Women receiving such treatments have much higher life expectancies than do women who do not receive them. Not only are the effects of osteoporosis reduced, but, with the proper progesterone, the risk of other diseases such as atherosclerosis is reduced. To be most effective, estrogen therapy should begin at menopause and continue for up to 10 years afterward.

The use of other substances for treating osteoporosis is increasing. Biphosphonates (e.g., alendronate, etridonate) reduce the risk of vertebral fractures, and are most effective when combined with estrogen. Biphosphonates can cause inflammation of the esophagus and stomach. Fluoride has little effect on the femur and results in brittle matrix. Calcitonin is expensive and causes painful calcium deposits.

Avoiding Injury

A second aspect in treating osteoporosis patients involves minimizing traumatic injuries that may make weakened bones fracture. One way of doing this is to refrain from putting strain on the skeleton by, for example, lifting heavy objects. Perhaps an even more important factor is reducing the risk of falling, one of the most common causes of such injury among the elderly. Falling causes so many fractures that it has become an area of specialized research.

The risk of fractures and other injury from a fall increases with age. Reasons beyond the decreased strength of bones include weaker muscles and slower reflexes to break the fall, and reduced subcutaneous fat and muscle mass to absorb the shock.

Falls are more common as age increases, partly because of the increased occurrence of diseases such as atherosclerosis, stroke, and parkinsonism. Other contributing factors include poor vision, age changes in the ears, muscle weakness, joint stiffness, altered gait, slow reflexes, and certain medications.

Much can be done to reduce the incidence of falls, including providing adequate lighting and grab bars, avoiding slippery surfaces such as wet or highly waxed floors, removing obstacles such as throw rugs, and wearing well-fitted shoes.

After a Fracture

Various combinations of approaches are employed to help people who have sustained a fracture. Surgery may be performed to quickly mobilize the individual because surgical repair compensates for the slow healing of bones in older people. Rapid mobilization reduces further bone and muscle deterioration and the risk of blood clots, pneumonia, and psychological problems such as depression. Physical therapy and the use of support devices such as a back brace or cane can also help restore a person to activities. Medications are often prescribed to reduce pain.

In summary, four weapons are used to treat osteoporosis: reducing the loss of matrix; replacing matrix to strengthen bones; preventing injury; and assisting in the recovery from fractures. Currently, all except replacing bone matrix can be successfully employed.