Bones and Joints
Your skeleton consists of about 206 sepa- rate bones, which range in size from the femur (the long bone in your leg) to the malleus, incus, and stapes (the three tiny bones in your inner ear). The skeleton matures and stops growing at about age 20, although the bone tissue itself remains alive and active, producing blood cells in the bone marrow and storing minerals such as calcium and phosphorus. Tendons attach your muscles to your bones to per- mit movement of the skeleton. Ligaments connect bone to bone and provide stability to joints. Any point where bone meets bone is a joint. Most, but not all, joints are capable of motion. Your skeleton also sup- ports your body and protects your internal organs.
Disorders of the Bones
Bone is living connective tissue that con- stantly 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
bone is a membrane called the periosteum, which contains nerves and blood ves- sels and is essential for the formation and growth of new bone. Bone tissue pro- 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 osteo- porosis (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, anti- convulsants, 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
• disorders that affect absorption of calcium, such as lactose intolerance, peptic ulcers, or celiac disease
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
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).
• Stop smoking (see page 107).
• Drink alcohol only in moderation.
• Cut back on caffeine.
• 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 fre- quently in children and young men. Osteosarcoma is the most common form of primary bone cancer. Osteosarcoma and Ewing’s sarcoma (another type of pri- mary 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 tomogra- phy (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 anticancer drugs), and radiation therapy. Most bone tumors are removed surgi- cally, even if they are benign. In many cases, primary bone cancer is success- 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.
How Much Calcium Do I Need?
According to nutritional guidelines from the National Institutes of Health, adolescents and young adults should take in 1,200 to 1,500 milligrams of calcium per day; men ages 25 through 65 should take in 1,000 milligrams of calcium per day; and men over age 65 should take in 1,500 milligrams of calcium per day. Good sources of calcium include low-fat and nonfat dairy products; green, leafy vegetables; dried peas and beans; and cal- cium-fortiﬁed foods. The following table lists some good sources of calcium and the approximate amount of calcium they contain:
A fracture—a break in bone or cartilage—usually results from injury or an underlying bone disease, such as osteoporosis (see page 301). Fractures are cat- egorized as either simple (closed), in which the broken bone does not
break the skin, or compound (open), in which the broken bone punc- tures the skin. When the two ends of a fractured bone have not sepa- rated, it is called a nondisplaced fracture. When the two ends have separated, it is a displaced fracture. Within the categories of simple and compound are other types of fractures (see box), including transverse fracture, spiral fracture, comminuted fracture, and greenstick fracture. The type of fracture determines the choice of treatment.
In general, fractured bones are painful and limit use of the injured limb or body part. Often the injured area appears misshapen. Bruising may occur, and the limb below the fracture may tingle or become numb, cold, or pale. However, sometimes it is possible to walk on a fractured leg or continue to use a fractured arm without realizing it is broken.
Bones can break or crack in various patterns, depending on the direction and force of impact. Here are some of the most common types
of fractures and how they are treated:
Transverse fracture. Transverse fractures are breaks straight across a bone that usually arise from a direct blow or an angled force. Doctors treat this type of fracture by immobilizing the bone in a cast.
Spiral fracture. Spiral fractures, which usually affect arm bones or leg bones, often occur when someone violently twists a limb. The bone can break through the skin and damage surrounding nerves and blood vessels. Doctors treat this type of fracture with immobilization in a cast or, sometimes, with traction (the application of tension to a bone to align and immobilize it) or surgery.
Comminuted fracture. Comminuted fractures, in which a bone splinters into three or more pieces, are usually caused by a high-impact injury or a direct blow. This type of fracture is sometimes difﬁcult to treat because the pieces of bone need to be carefully repositioned.
Greenstick fracture. In greenstick fractures, a long arm bone or leg bone snaps or buckles on only one side, usually from a severe blow or a jar- ring force. Greenstick fractures are more common in children than in adults. Doctors treat this type of fracture by immobilizing the bone in a cast.
After any serious injury, you should seek medical attention to rule out frac- tures or detect them before they become worse. If you think you may have a frac- ture, take immediate steps to immobilize the injured bone to prevent further damage to the bone and surrounding blood vessels and nerves, and elevate the affected body part to reduce swelling. With an open fracture, be sure to place a clean cloth or a bandage gently over the wound to reduce the risk of infection.
Fractured bones must ﬁrst be restored to their normal position and alignment. This process is referred to as “reduction.” A cast or a splint may be sufﬁcient to hold a broken bone in place for healing. If you fracture a large bone or experi- ence a complicated break, you may need surgery. Sometimes bones must be screwed together or rejoined using metal plates or rods. Pins or screws also may be inserted to hold an external frame in place that immobilizes the bone while it heals. You will need to rest the affected limb and avoid overuse until the bone heals.
A stress fracture refers to a condition in which a tiny crack (or cracks) occurs in a bone that has been exposed to repeated injury or overuse. Your lower leg and foot are especially prone to stress fractures. Early symptoms include sharp pain and swelling in the affected area. If the cracks are too small to see on an X ray, the doctor may perform a computed tomography (CT) scan (see page 90) to determine the location and extent of the fracture. Treatment consists of resting the affected area long enough to allow healing to take place.