Bones are designed to withstand tremendous stress and use. The skeleton, which is made up of 206 individual bones, is designed not only to give the body its shape, but also to twist and bend in myriad ways to make movement possible. Individual bones are engineered to perform specific functions. For example, the thigh bone (femur) must bear the body's weight. Thus it is the body's longest and strongest bone, and its design as a hollow cylinder provides needed strength.
Although bone seems to be rock hard, it actually is one-third water with a rich blood supply. Bone is also metabolically active, with minerals and other substances constantly moving in and out of its honeycomb structure. Bones thrive on the stress of constant use. People confined to bed for long periods lose bone density at an alarming rate.
Most broken bones are due to accidents, such as a bad fall. But thinned, fragile bones break more easily; in fact, people with fragile bones may experience spontaneous fractures in which bones break for no reason.
Causes of bone fragility
Various cancers can cause bone fragility, including both cancers that arise in the bones as well as those that spread (metastasize) to the bones, or those that upset the body's metabolism in such a way as to deplete bones of minerals. Kidney cancers are an example of the latter. Breast and lung cancers often spread to the bones. Multiple myeloma is a cancer that depletes the bones of minerals, causing considerable bone pain and fragility. Primary bone cancers also cause pain and fragility.
Hereditary bone diseases
There are several relatively rare genetic bone diseases in which the body is unable to properly lay down bone tissue. The medical name for these diseases is osteochondrodysplasia. They become evident early in life.
Bone infections can cause destruction and weakening of bones. Sometimes the infection is spread from a nearby wound; in other instances, it may arise in the bone tissue itself. Initial symptoms include bone pain and local swelling; fevers also are common, especially in children. Sometimes the early symptoms are mistaken for rheumatoid arthritis, especially if the infection is near a joint. Tuberculosis of the bone is a particularly insidious infection that can cause tissue destruction unless it is treated promptly.
Patients on chronic kidney dialysis often experience gradual loss of bone tissue, resulting in weakening and fragility. In addition, the underlying kidney disease also may affect bone metabolism, thus compounding the problem of bone fragility.
This is the term for adult rickets. It is usually due to vitamin D deficiency, which may occur in a poor diet or among shutins who are not exposed to sunlight. Or the deficiency may be caused by a metabolic disorder that prevents the body from properly absorbing the vitamin.
This disease, which is most common among older women, is one of the most prevalent causes of bone fragility. For reasons that are not fully understood, the bones begin to lose calcium, becoming thin and brittle. The vertebrae become thin and compressed, resulting in stress fractures, humped back, and loss of height. Long bones, such as the thigh and arm bones, also become thin and brittle and will fracture more easily. Exercise and postmenopausal estrogen replacement can help slow or prevent bone loss. Since smoking increases the risk of osteoporosis, stopping smoking is also important in preventing osteoporosis.
Rickets is a childhood disease caused by vitamin D deficiency. It is uncommon in the United States but is still widespread in developing countries where the diet may lack vitamin D, as well as adequate amounts of calcium, to build and maintain bones. In rare instances, rickets is due to the body's inability to utilize vitamin D.
Advice about bone fragility
- Exercise is important in maintaining bone strength. Even if you have osteoporosis or some other disease that causes fragile bones, exercise is an important part of your therapy. Be sure, however, to follow your doctor's instructions; the wrong kind of exercise also can lead to fractures.
- Protective braces and lightweight casts may be needed to give bones extra support.
- A diet that provides adequate calcium and vitamin D is important in building and maintaining healthy bones. If you cannot tolerate milk — the best source of calcium — ask your doctor about alternative sources of calcium.
- Do not smoke. This is particularly true for anyone at high risk for developing osteoporosis. Smoking seems to interfere with bone metabolism and increases the risk of osteoporosis.
- If you are a woman who has gone through menopause, ask your doctor about estrogen replacement therapy. This is important if you are at high risk for developing osteoporosis (e.g., are small boned with a family history of the disease) since estrogen prevents bone loss.