Bone is living connective tissue that constantly changes. The bone marrow, where blood cells are produced, is surrounded by cancellous (spongy) bone that fills the medullary canal. Cortical bone, which is made up of the protein collagen infused with minerals, encircles the medullary canal and contains the cells that maintain bone tissue. The thin outer covering of
Joints bone is a membrane called the periosteum, which contains nerves and blood ves- 301
sels and is essential for the formation and growth of new bone. Bone tissue pro- Bones and duces its own cartilage to absorb shock and provide a tough, elastic surface between adjoining bones.
Osteoporosis is a disease in which the bones become thin, porous, weak, and more susceptible to fractures. Although osteoporosis is generally regarded as a women's health concern, the disease also can develop in men. Because men have larger, denser skeletons, they usually experience bone loss later in life than women. However, older men are at increased risk for hip fracture and other joint fractures as a result of osteoporosis. Men and women lose bone mass at an increased rate after age 65, and calcium absorption decreases with age in both sexes. About a third of men over age 75 have been diagnosed with osteoporosis, and one of every eight men over age 50 will experience a bone fracture as a result of osteoporosis. Therefore all men need to take steps to prevent osteoporosis (see following page).
Bone mass increases throughout childhood and young adulthood, reaching its peak at about age 20. After age 35, bone tissue breaks down faster than new bone is formed. Bone becomes more porous and structurally weaker. Dense, cortical bone tissue is replaced by spongy, cancellous bone. In many cases, osteoporosis is detected only after a fracture occurs. Men who are older, small-framed, or white or Asian are at increased risk for osteoporosis. The following factors can increase your risk of developing osteoporosis:
• long-term use of certain medications (including corticosteroids, heparin, anticonvulsants, aluminum-containing antacids, and some cancer drugs)
• low testosterone level
• excess thyroid hormone
• chronic or heavy alcohol consumption
• high intake of caffeine, protein, or sodium (salt)
• insufficient intake of calcium
• vitamin D deficiency
• sedentary lifestyle
• family history of osteoporosis
To detect bone loss, your doctor will perform urine and blood tests. He or she also will recommend that you undergo a bone density test, which is an imaging technique used to assess bone density and structure. In some cases a bone biopsy (removal of a small piece of bone tissue for microscopic examination) may be
Concerns required to rule out other possible bone disorders, such as osteomalacia (see page 318).
You can take steps to reduce your risk of developing osteoporosis. Lifestyle changes that focus on your risk factors will help prevent osteoporosis. If some bone loss has already occurred, lifestyle changes and treatment with medications such as calcitonin or alendronate can reduce the risk of fractures. Here are some steps you can take to help prevent osteoporosis:
• Take in plenty of calcium every day (see "How Much Calcium Do I Need?" on next page).
• Get an adequate supply of vitamin D. Fat-free milk fortified with vitamin D is an excellent source of this essential nutrient.
• Exercise regularly (especially weight-bearing exercise such as brisk walking, jogging, and stair climbing).
• Drink alcohol only in moderation.
• Limit your intake of sodium.
Primary bone cancer—that is, cancer that begins in the bone versus cancer that spreads to the bone from another part of the body—is rare but occurs most frequently in children and young men. Osteosarcoma is the most common form of primary bone cancer. Osteosarcoma and Ewing's sarcoma (another type of primary bone cancer) usually occur between ages 10 and 25. Other primary bone cancers include chondrosarcoma, fibrosarcoma, malignant giant cell tumor, and chordoma. These cancers occur mainly in adults over age 30.
Symptoms of bone cancer tend to develop slowly. Pain is the most frequent symptom, although in most cases, a firm lump or swelling on the bone can be felt through the skin. Bone cancer is often detected when a bone breaks without obvious cause or fails to repair itself after a fracture.
Tests for bone cancer include blood tests, bone scans, and X rays. If a tumor is detected, additional examinations will be performed to determine whether it is benign (noncancerous) or malignant (cancerous). These procedures include radionuclide scanning (a radioactive substance is injected into the bloodstream to produce images that show where the cancer is growing), computed tomography (CT) scanning (see page 90) or magnetic resonance imaging (MRI; see page 90), and angiography (X rays of the blood vessels taken after a special dye is injected into the bloodstream). A bone biopsy (removal of a small piece of bone tissue for microscopic examination) is performed to identify the type of tumor and to help plan a course of treatment.
Bone cancer is treated with surgery, chemotherapy (treatment with powerful
Joints anticancer drugs), and radiation therapy. Most bone tumors are removed surgi- 303
cally, even if they are benign. In many cases, primary bone cancer is success- Bones and fully treated with a bone graft (replacement of the diseased section of the bone with healthy human bone from a bone bank) and chemotherapy. In some cases, if a tumor is large or has begun to spread throughout the bone, amputation may be performed, followed by chemotherapy. Radiation therapy often is used if the cancer has spread to other tissues.
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