HUMAN BIOLOGY

98 Chapter 5

disorders of the skeleton

slight hollow between a wrist ligament and the underside of

the wrist’s eight carpal bones (see Figure 5.7). Squeezed into

this tunnel are several tendons and a nerve that services

parts of the hand. Chronic overuse, such as long hours typ-

ing at a computer keyboard, can inflame the tendons. When

the swollen tendons press on the nerve, the result can be

pain, numbness, and tingling in fingers. Simply avoiding

the offending motion can help relieve carpal tunnel

syndrome. In more serious cases injections of an anti-

inflammatory drug are helpful. Sometimes, however, the

wrist ligament must be surgically cut to relieve the pressure.

Joints are susceptible to strains, sprains,

and dislocations

Synovial joints such as our knees, hips, and shoulders get

a lot of use, so it’s not surprising that they are vulnerable

to mechanical stresses. Stretch or twist a joint suddenly

and too far, and you strain it. Do something that makes a

small tear in its ligaments or tendons and you will have

a sprain. In fact, a sprained ankle is the most common

joint injury. Sprains hurt mainly because of swelling and

bleeding from broken small blood vessels. Applying cold

(such as an ice pack, 30 minutes on, then 30 minutes off)

for the first 24 hours will minimize these effects; after

that, doctors usually advise applying heat, such as a

tissue in bones or joints may break down

As we age, bone tissue may break down faster than it is

renewed. This steady deterioration is called osteoporosis

(Figure 5.11). When it occurs, the backbone, pelvis (hip

bones), and other bones lose mass. Osteoporosis is most

common in women past menopause, although men can be

affected, too. Deficiencies of calcium and sex hormones,

smoking, and a sedentary lifestyle all may contribute to

osteoporosis. Exercise (to stimulate bone deposits) and

taking in plenty of calcium can help minimize bone loss.

Medications can slow or even help reverse the bone loss.

Sports injuries, obesity, and simply getting older are

among the causes of osteoarthritis. In this disorder, years

of mechanical stress or disease wear away the cartilage

covering the bone ends of freely movable joints. Often, the

arthritic joint is painfully inflamed, and surgeons now rou-

tinely replace seriously arthritic hips, knees, and shoulders.

Figure 5.12 shows just one of many types of artificial joints

that are available.

The degenerative joint condition called rheumatoid arthri­

tis results when the immune system malfunctions and

mounts an attack against tissues in the affected joint. You

will read more about it in Chapter 9.

inflammation is the culprit in repetitive

motion injuries

Repetitive movements can cause inflammation when they

damage the soft tissue associated with joints. Tendinitis,

the underlying cause of conditions such as “tennis elbow,”

develops when tendons and synovial membranes around

joints such as the elbow and shoulders become inflamed.

Today one of the most common repetitive motion inju-

ries is carpal tunnel syndrome. The “carpal tunnel” is a

Figure 5.11 in osteoporosis, bone tissue breaks down faster

than it is rebuilt. A Normal bone tissue. B Bone affected by

osteoporosis. In osteoporosis, the replace ment of mineral ions

lags behind their withdrawal during remodeling. In time the tissue

erodes, and the bone becomes hollow and brittle. (Both: Prof. P. Motta,

Dept. of Anatomy, Univ. of La Sapienza, Rome/SPL/Science Source)

Figure 5.12 Knees, hips, and some other joints may be

replaced. Each year in the United States hundreds of thousands

of patients have one or more joints replaced. In this replacement

knee a projection of the joint has been fitted into the end of the

patient’s femur (center) and another projection has been fitted

into the tibia below. The hatlike disk at the upper left attaches to

the patella—the kneecap. After surgery, walking and standing put

stress on the new joint, so the patient’s osteoblasts make new

bone that grows into pits on the prosthesis.

Mike Devlin/SPL/Science Source

A B

5.6

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