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Diseases of the Musculoskeletal System

C H A P T E R

Learning Objectives

After studying this chapter, you should be able to

■ Understand the normal structure and function of bones, joints, and muscle

■ Describe the etiology, signs and symptoms, diagnostic tests, and treatment of infectious diseases of bone

■ Explain how vitamin and mineral deficiencies lead to bone disease

■ Describe the etiology, signs and symptoms, diagnostic tests, and treatment of bone cancer

■ Describe the etiology, signs and symptoms, diagnostic tests, and treatment of the common types of arthritis, gout, and bursitis

■ Identify the etiology, signs and symptoms, diagnostic tests, and treatment of dislocations, sprains, strains, and carpal tunnel syndrome

■ Describe the etiology, signs and symptoms, diagnostic tests, and treatment of muscular dystrophy and myasthenia gravis

■ Understand age-related changes and diseases of the musculoskeletal system

15 Rest is best for rheumatoid arthritis.

Fiction:Unless pain is too se- vere, daily low-impact exercise maintains mobility and range of motion.

Fact or Fiction?

Duchenne’s muscular dystro- phy. Cross section of gastroc- nemius muscle shows exten- sive replacement of muscle fibers by adipose cells. (Courtesy of the CDC/Dr. Edwin P. Ewing, Jr., 1972)

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Human Diseases: A Systemic Approach, Seventh Edition, by Mark Zelman, Ph.D., Elaine Tompary, PharmD, Jill Raymond, Ph.D., Paul Holdaway, MA, and Mary Lou Mulvihill, Ph.D. Published by Prentice Hall. Copyright © 2010 by Pearson Education, Inc.

415

Arthritis

Arthritis in its various forms has long plagued humans. Lackof understanding of medical science, coupled with a desper-ate search for relief, produced unusual prescriptions inAmerican traditional and folk medicine. One folk healer sug- gested that relief from gout could be obtained by cutting a hole in a tree, holding the affected body part to it, and sealing the hole with sand, trapping the disease. Another nineteenth-century prescription required the sufferer to carry a potato in the hip pocket. Treating “like with like” was the basis for treating gout with an earthworm, whose curled shapes resemble gnarled gout-afflicted appendages. How the earthworm was administered is not clear. A home remedy from Texas called for ingestion of wintergreen oil. These ineffective treatments were benign compared to some prescriptions. Citing bad blood as the culprit, some people were subjected to regular bleed- ings. Cashing in on the public’s misunderstanding of uranium’s pow- ers in the 1950s, predatory entrepreneurs recommended baths in ura- nium pools or ingestion of uranium-laced water. Our understanding and treatment of arthritis has progressed significantly. Still, un- scrupulous individuals and companies espouse ineffective and expen- sive treatments that prey upon vulnerable people.

Disease Chronicle

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Interaction of Bones, Joints, and Muscles

Bones, joints, and muscles work together. The bones of the skeleton provide the body with a sturdy framework. Bones are held together by a variety of joints, some of which permit move- ment at portions of the skeletal framework. Be- cause skeletal muscle is attached via tendons to bones, when muscle contracts, or shortens, it moves the skeleton. Thus, the muscles that span a joint bring about action at that joint. Groups of muscles may have opposite or antag- onistic actions on a joint. For example, one group of muscles extends (straightens) the knee, while another group flexes (bends) the knee. Still other muscles stabilize joints, pre- venting undesired movements. In this chapter, the principal diseases and disorders of bone, joints, and muscles—the musculoskeletal sys- tem—are explained.

Structure and Function of Bone, Joints, and Muscle

Bone may appear inert, but changes constantly occur within it. Bone development, growth, and homeostasis rely on interplay among its con- stituent minerals, proteins, and living cells. Calcium and phosphate, bone’s primary minerals, are embedded in collagen, bone’s main protein. The minerals confer hardness and rigidity to bone, while the collagen imparts flexibility. Ma- ture bone cells, osteocytes, along with bone- forming cells, osteoblasts, and bone-resorbing cells, osteoclasts, reside within this bony matrix. The cells receive nutrients by an organized sys- tem of blood vessels that course throughout the bone.

Bones are long, flat, or irregularly shaped, but most are covered with a layer of a type of bone tissue called compact bone. The cells, min- erals, proteins, and blood vessels of compact bone are arranged in a regular, organized fash- ion. Another type of bone tissue, spongy bone, contains many bone-marrow-filled spaces. This

▼ ▼ red-colored marrow is found at the ends of long

bones and is the site of blood cell formation. The long bones found in the arms and legs

contain a hollow cavity, the medullary cavity, filled with yellow bone marrow primarily con- sisting of fat. The growth of long bones occurs at the growth plate, an area of cartilage near each expanded end of the bone (Figure 15–1 �). At this site, new bone is formed, pushing the ends apart from each other until full growth is achieved, at which time the cartilage turns into bone, a process called ossification. Damage to the growth plate before maturity tends to pre- vent the bone from reaching its mature length.

Diaphysis

Proximal epiphysis

Spongy bone

Compact bone

Medullary cavity

Endosteum

Nutrient foramen

Nutrient vessel

Epiphyseal plate (growth plate)

Distal epiphysis

Periosteum

Figure 15–1 � Cut view of long bone.

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Chapter Fifteen Diseases of the Musculoskeletal System ■ 417

The periosteum is a highly vascular layer of fi- brous connective tissue that covers the surface of bones. It contains cells that are capable of forming new bone tissue and serves as a site of attachment for tendons or muscles.

Joints are the articulating sites between bones. Various degrees of movement, called range of motion, are possible in different kinds of joints. The amount and type of movement at a joint is defined by the shapes of bones and the type of connective tissue holding the bones together at the joint. The shoulder (joint be- tween humerus and scapula) is the most freely movable joint, but it is also the one most easily dislocated.

Articulating bones are held together by ligaments. Dense strands of collagen impart great strength to ligaments. A joint capsule con- sisting of ligaments and connective tissue sur- rounds the bone ends. The inner surface of the capsule is lined with a synovial membrane that secretes synovial fluid, which lubricates the joints. Sacs of this fluid, the bursae, are situated near some joints, such as the shoulder and knee, where they reduce friction during move- ment. The articulating surfaces of the bone ends are covered with a layer of cartilage, which

also reduces friction. A typical joint is illus- trated in Figure 15–2 �.

Skeletal or voluntary muscle tissue is found in muscles that are firmly attached to bones by tendons. Some voluntary muscles (the muscles of facial expression, for example) are attached to soft tissue. Muscles consist of bundles of mus- cle fibers held together by connective tissue. When stimulated by nerves at the myoneural junction, muscle fibers contract, and because muscles are attached to bones, the shortening of the muscles moves the bones.

The diseases of muscle described in this chapter are diseases of voluntary muscle. Be- cause muscle action requires nerve stimulation, some nervous system diseases are manifested in muscles. Those diseases are discussed with the nervous system in Chapter 13. This chapter discusses a few muscle diseases that are not di- rectly caused by nervous system disease. Smooth muscle, or involuntary muscle, is a dif- ferent type of muscle found in the walls of the internal organs and the walls of blood vessels. Cardiac muscle is an involuntary striated mus- cle and is present only in the heart (Chapter 6). This chapter does not address cardiac or smooth muscle disease.

Ligament

Synovial membrane

Synovial fluid

Cartilage

Articulating bone

Spongy bone

Joint capsule

Articulating bone

Figure 15–2 � Typical joint.

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Diagnostic Tests for Musculoskeletal Diseases

X-rays can reveal fractures, joint dislocations, bone deformities, and calcification; measure bone density; and detect signs of other bone damage. MRI (magnetic resonance imaging) uses strong magnetic fields to visualize details of joint anatomy and can show trauma and arthritis damage. CT (computed tomography) scans show details of soft tissues like tendons and ligaments as well as muscle. Arthroscopy is used to visualize the inside of a joint cavity such as the knee. Joint fluid can be aspirated for mi- croscopic and chemical analysis. Myelography detects abnormalities of the spinal cord by visu- alizing the distribution of a radio opaque dye in- jected into the subarachnoid space. Myelogra- phy can detect tumors and herniated discs. Electromyography measure electrical activity of muscles and reveals some abnormalities of muscle function. Biopsy can show muscle tis- sue abnormalities.

Diseases of Bone

Bone can be affected by disease in various ways. Infectious agents can enter bone through a compound fracture, transmission in the blood, or extension from an adjacent infection. Mineral and vitamin deficiencies prevent proper forma- tion or maintenance of bone structure. Bones atrophy with disuse and fracture, or sponta- neously in certain diseases. Tumors can also develop in bone.

Infectious Diseases of Bone Osteomyelitis is an inflammation of the bone, particularly of the bone marrow in the medullary cavity and the spaces of spongy bone. Osteomyelitis affects 2 in 10,000 people, princi- pally children and adolescents, mostly boys, whose bones are still growing. In children, the long bones—the femur, the tibia, and the humerus—are most frequently affected near their ends at the growth plate. In adults, os-

▼ ▼ teomyelitis usually affects the pelvis and verte-

brae following trauma and surgery. The main risk factor for developing osteomyelitis is a re- cent bacterial infection that may have escaped treatment, permitting the bacteria to become blood-borne.

Osteomyelitis is caused by bacteria, usually Staphylococcus aureus and occasionally Strep- tococcus pyogenes, Pneumococcus, or Escher- ichia coli. The bacteria are carried by blood to the bone from some other site in the body, such as infection adjacent to the bone. Hence, the chief risk factor for osteomyelitis includes infec- tions, including open wounds of a compound fracture.

In osteomyelitis, the infection develops into an abscess in the bone, which compresses small blood vessels, reduces circulation, and causes bone necrosis. Infections may spread under the periosteum, lifting sections of it from bone sur- face, further reducing circulation to bone. In an attempt to heal, bone may be deposited around this area of necrosis.

Local symptoms of bone infection include pain, redness, and heat. Systemic symptoms of chills, fever, and leukocytosis, tachycardia, nausea, and anorexia also occur. Diagnosis be- gins with history and physical exam and can be confirmed with white blood cell count, an ele- vated erythrocyte sedimentation rate, blood cul- ture of causative microorganism, and magnetic resonance imaging or bone scans. An x-ray will not reveal early infections.

Early antibiotic therapy is an effective treat- ment and has reduced the incidence of ad- vanced serious cases. Surgery may be required to remove necrotic bone tissue (Figure 15–3 �).

Tuberculosis of bone is rare and is associated with untreated pulmonary tuberculosis. This infection occurs when bacteria spread to the bones from the lungs. Commonly affected areas are the ends of long bones and knees. Usually seen in children, Pott’s disease is tuberculosis of the vertebrae, leading to deformity and paral- ysis. As in the lungs, tuberculosis of bone leads to cavitation and tissue destruction (Chapter 8). The infection can be treated with antibiotics, al- though strains of Mycobacterium tuberculosis have developed multiple-drug resistance. Surgery may be able to correct bone deformities.

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Initial infection

Periosteum

Initial infectionA Acute phase

Blood supply blocked

Pus-filled abscess

B Chronic phase

Necrotic bone

Pus escape

New bone formation

Figure 15–3 � Three phases of bone infection.

Bone Disease and Vitamin and Mineral Deficiencies Vitamins and minerals are key to bone health. Calcium and phosphorus are required in ap- propriate quantities for proper bone formation and maintenance. However, dietary calcium cannot be absorbed from the digestive tract without vitamin D. Thus, mineral or vitamin D deficiencies may result in soft, malformed, or fragile bones.

Rickets is a disease of infancy or early child- hood in which the bones do not properly ossify, or harden. Rickets is rare in the United States but occurs occasionally in infants fed unforti- fied formula. A child with rickets develops bones that are soft and tend to bend. Over time the weight-bearing bones of the body become de- formed: The legs become bent (“bow-legged” or “knock-kneed”) and the vertebral column be- comes misaligned. The sternum projects for- ward, and bony nodules form on the ends of ribs and at wrists, ankles, and knees. The skull is large and square. The pelvic opening in a girl may narrow, leading to problems with childbirth later. Other signs and symptoms of rickets in- clude flaccid muscles, delayed teething, and a characteristic potbelly. Each of these symptoms can be explained by calcium deficiency.

Rickets can be prevented with vitamin D–for- tified milk and exposure to sunlight. Sunlight converts a substance (dehydrocholesterol) in the skin to vitamin D in the body. This need for

sunlight explains the higher incidence of rickets in large, smoky cities where buildings are close together and shut out the sun. Children with rickets respond well to sunlight exposure and treatment with vitamin D concentrate.

Osteomalacia is the softening or decalcification of bones in adults. Osteomalacia is rare in the United States. It is most prevalent in Asia among women who have had multiple births, eat a ce- real-based diet, and have little exposure to sun- light. Symptoms include muscle weakness, weight loss, and bone pain. Bones of the verte- bral column, legs, and pelvis become susceptible to bending and fracturing with mild stress.

Osteomalacia is caused by inadequate dietary vitamin D and dietary deficiency of calcium or phosphorus; it is treated with vitamin D supple- ments and adding adequate calcium and phos- phorous to the diet.

Both rickets and osteomalacia may be sec- ondary to malabsorption syndrome because vit- amin D is not absorbed from the intestine.

Osteoporosis is a disease characterized by porous bone that is abnormally fragile and sus- ceptible to fracture. Eighty percent of those af- fected by osteoporosis are women. While some bone loss is expected with aging, the cause of the accelerated bone loss observed in osteoporo- sis is unknown. However, risk factors for osteo- porosis have been identified, and these include being female, advanced age, and having a small frame (Box 15–1 �).

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Box 15–1 � Risk Factors for Osteoporosis

Low bone mass Low calcium intake Female Vitamin D deficiency Small frame Sedentary lifestyle Family history Cigarette smoking Postmenopausal Excessive alcohol use Hysterectomy Caucasian or Asian Amenorrhea

Unfortunately, osteoporosis can quietly be- come advanced because no symptoms accom- pany bone loss until bones weaken enough to fracture. Weight-bearing bones of the vertebrae and pelvis are especially susceptible, and accu- mulated compression fractures in these bones cause a decrease in height and bending of the spine (Figure 15–4 �). Compressed vertebrae press on spinal nerves, causing great pain. Fractures are common in the hip and wrists.

Osteoporosis is diagnosed using patient his- tory and bone density tests. No cure exists, so prevention is strongly recommended. A lifelong diet rich in calcium and vitamin D along with weight-bearing exercise stimulates the develop- ment of dense and strong bone and slows pro- gression of the disease. Smoking should be avoided, and alcohol and caffeine consumption

5'6"

5'3"

4'9"

4'6"

4'3"

Height

Age 40 60 70

Figure 15–4 � Spinal changes caused by osteoporosis.

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should be minimized. Treatment requires med- ication. Various medications facilitate calcium uptake in bone and include estrogens, calci- tonin, parathyroid hormone, as well as estro- gen-receptor modulators and bisphosphonates.

Other Bone Deformities Paget’s disease, or osteitis deformans, results in overproduction of bone, particularly in the skull, vertebrae, and pelvis. Paget’s disease is rare worldwide, but in the United States it af- fects approximately 2.5 million people, mostly men over 40. The cause of Paget’s disease is un- known, but approximately 20% to 30% of cases are genetically based.

The disease begins with bone softening, which is followed by bone overgrowth. The new bone tissue is abnormal and tends to fracture easily. The excessive bony growth causes the skull to enlarge, which often affects cranial nerves; thus, vision and hearing are affected. Abnormal bone development causes curvatures in the spinal column and deformities in legs.

Another complication of this disease is osteo- genic sarcoma; see discussion following.

Paget’s disease is diagnosed by examination, x-rays, bone scan, and bone biopsy. Treatment requires calcitonin and etidronate, which re- duce bone resorption, and mithramycin, which decreases calcium.

Scoliosis is an abnormal lateral curvature of the spine that occurs to varying degrees of severity and is usually first identified during childhood. Scoliosis may be caused by abnor- mal development that results in fusion of the vertebrae. Scoliosis may also have a neuro- muscular origin. Weak or asymmetric muscle development can pull the spine laterally. This can result from diseases such as polio, muscu- lar dystrophy, spina bifida, or cerebral palsy. Finally, scoliosis may be idiopathic. Symptoms may include lower back pain and fatigue. Diag- nosis is based on history, physical exam, and x-rays. Mild curvatures of less than 20 degrees are common in adolescents and may require no treatment. More severe curvatures of 30 de- grees in growing adolescents must be treated

▼ ▼

▲ X-ray of pelvis in 18-year-old female showing normal bone density. (©B. Bates/Custom Medical Stock Photo)

SIDE by SIDE ■ Osteoporosis

▲ X-ray of female pelvis with osteoporosis. Note greatly decreased bone density especially visible in hip bones. (© Custom Medical Stock Photo)

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Normal vertebral column

Scoliosis Normal vertebral column

Kyphosis

Figure 15–5 � The two most common deformities of the spinal column are scoliosis and kyphosis.

with braces to prevent further curving of the vertebrae. Curves of 40 degrees require surgery to correct the misalignment. The outcomes are promising following treatment. However, neu- romuscular scoliosis may be more difficult to treat because it is usually accompanied and caused by another disease, such as polio, muscular dystrophy, spina bifida, or cerebral palsy.

Kyphosis, an exaggerated posterior curve of the thoracic spine, sometimes called hunch- back, occurs most commonly in adults and be- comes more noticeable in the elderly (Figure 15–5 �). It is most often caused by collapse of vertebrae affected by osteoporosis and by de- generative changes associated with arthritis of the vertebrae. Symptoms include mild back pain, back fatigue, perhaps tenderness, and, in severe cases, difficulty breathing because of compression of the thoracic cage. It can be diag- nosed with physical exam and x-rays. Treat- ment options are few and provide no cures.

Treatment of the underlying osteoporosis can slow progression of kyphosis. Treatment of un- derlying arthritis can relieve pain and immobil- ity but only to a limited degree.

Lordosis, “swayback,” is an inward curvature of the lumbar vertebrae. Some degree of curva- ture is normal and most cases of lordosis are benign. Any unusual pain or curvature should be evaluated.

Bone Cancer Malignant Bone Tumors Bone cancer is rare, comprising 1% of malignancies. Most bone can- cer is secondary and results from metastasis from a tumor located elsewhere in the body. Pri- mary malignancy of bone occurs most often in males, especially children and adolescents. One type of bone cancer, osteogenic sarcoma, arises in the bony tissue itself and frequently affects the ends of long bones, frequently at the knee, where enlargement of the bone is observed. The cause

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of osteogenic sarcoma is unknown. Signs and symptoms include dull localized bone pain that intensifies at night. Masses may be noted and fractures accompany sarcomas. Bone cancer is diagnosed with biopsy. X-rays and CT scans are used to locate and measure tumors. Treatment may involve chemotherapy to reduce tumor size followed by surgical removal. See Chapter 4 for a discussion of cancer.

Bone Trauma: Fractures Several diseases and disorders discussed in this chapter may result in bone loss or other damage that can result in fracture. Trauma, however, is also a common cause of bone fractures. Exces- sive force, twisting, or compression can lead to

bone fractures. The chief signs and symptoms of a fracture include

• Visibly out-of-place or misshapen limb or joint

• Swelling, bruising, or bleeding • Intense pain • Numbness and tingling • Broken skin with bone protruding • Limited mobility or inability to move a limb

These signs and symptoms require diagnosis and medical attention in order to promote heal- ing and to prevent infections. A variety of frac- tures can occur (Figure 15–6 �). Most fractures require immobilization with a splint or cast, while others, like compound fractures, require surgery, pins, and plates to promote healing.

FRACTURE TYPE DESCRIPTION COMMENTS FRACTURE TYPE DESCRIPTION COMMENTS

Closed Bone breaks Also called a Depressed Broken bone is Common in skull cleanly but does simple fracture. pressed inward. fractures. not penetrate skin.

Open Broken ends of Serious; may result bone protrude in osteomyelitis. through soft tissues Also called a com- and skin. pound fracture. Spiral Jagged break due Common fracture

to twisting force due to sports applied to bone. injuries.

Comminuted Bone fragments Common in those into many pieces. with conditions causing

brittle bones, such as osteogenesis imperfecta

Bone breaks in- Common in Compression Bone is crushed. Common in clients completely, much children, whose

with osteoporosis.

Greenstick

in the way a green bones have pro- twig breaks. portionally more

Impacted Broken ends of Commonly results organic matrix bone are forced from falls; also and are more flex- into each other. common in hip ible than those of

fracture. adults.

Figure 15–6 � Fractures. Adapted from Marieb, E.N. (1998). Human anatomy and physiology (4th ed., (p. 180). Menlo Park, CA: Benjamin Cummings.)

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Figure 15–7 � Contractures of rheumatoid arthritis.

Diseases of the Joints

Joints permit movement of the skeleton; thus diseases of the joints cause pain and limit mo- bility. Joints that bear weight—the lower verte- brae, hips, and knees—receive a great deal of stress and are especially susceptible to the dis- eases and disorders discussed in this chapter. Even the muscles, nerves, and bones may be af- fected by joint disease.

Arthritis Arthritis means “inflammation of a joint.” Symptoms of arthritis include persistent joint pain and stiffness. Joints may be swollen and may lose mobility and become deformed to the point of losing function. Commonly affected joints include the lower vertebrae, hips, fin- gers, and knees.

Rheumatoid Arthritis A chronic and debilitating autoimmune disease, rheumatoid arthritis is a systemic inflammatory disease that affects sev- eral joints and the surrounding muscles, ten- dons, and ligaments. Rheumatoid arthritis af- fects 1.3 million Americans and affects nearly three times more females than males, usually be- ginning between ages 30 and 60. No risk factors have been linked to rheumatoid arthritis and the cause of rheumatoid arthritis remains unknown, but it appears to be an autoimmune disease. Rheumatoid factors, such as antiglobulin antibod- ies, combine with immunoglobulin in the syn- ovial fluid to form antibody complexes. Neu- trophils are attracted to the joint space and cause destruction. The condition is aggravated by stress, and there is a genetic predisposition toward development of the disease.

Symptoms include joint pain and stiffness, particularly on waking. The joints are swollen, red, and warm. The same joints are often af- fected on both sides of the body. As the disease is systemic, the patient experiences fatigue, weakness, and weight loss. Rheumatoid arthri- tis begins with an inflammation of the synovial membrane that lines the joints, particularly the small joints of the hands and feet. The mem- brane thickens and extends into the joint cavity,

▼ sometimes filling the space with a thickened granulation tissue, called a pannus, which eventually erodes and scars the articular carti- lage of the bone ends. When this scar tissue turns to bone, the ends of the bones fuse, a con- dition called ankylosis. The fusion immobilizes and deforms the joint. Figures 15–7 � and 15–8 � illustrate the crippling swan neck defor- mity and ulnar deviation characteristic of ad- vanced rheumatoid arthritis in the hands. Rheumatoid nodules may form under the skin, usually near the joints, but they sometimes de- velop on the white of the eye, too.

Diagnosis is based on physical exam, x-rays showing joint changes, a rheumatoid factor test, and synovial fluid analysis. Early diagno- sis and a comprehensive treatment program that includes medicine and exercise can reduce pain and the amount of damage done to the joints. Anti-inflammatory medications are effec- tive when prescribed by a physician, with as- pirin (salicylates) and similar drugs being the most commonly used. Other nonsteroidal anti- inflammatory medications commonly used in- clude indomethacin, fenoprofen, and ibuprofen. Immunosuppressants such as corticosteroids and methotrexate are now administered in early stages of the disease. COX-2 inhibitors like Celebrex have also been used. A balance between exercise and rest should be achieved.

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Bouchard’s node Heberden’s node

Figure 15–8 � Typical joint changes associated with osteo- arthritis. (Courtesy of the American College of Rheumatology)

In an acute phase, the joint should be rested to prevent further inflammation. Physical thera- pists can teach patients how to perform range- of-motion exercises that help preserve joint mo- bility. Exercises for good posture are directed toward removing stress on weight-bearing joints.

Osteoarthritis Osteoarthritis is the most com- mon form of arthritis. Osteoarthritis affects 27 million Americans, including 14% of those over age 25 and 34% of those over age 65. Men and women are affected equally, usually after age 40. Osteoarthritis may be described as primary or secondary. They are the same disease, but with slightly different origins. Primary osteoarthritis occurs with normal aging. Secondary osteoarthri- tis is associated with joint injury, trauma, or obe- sity. Other than injury, risk factors and causes are not well understood.

Unlike rheumatoid arthritis, osteoarthritis may affect only one joint. Signs and symptoms include pain and stiffness in the joint. Muscle tension and fatigue contribute to the aches and pain of osteoarthritis. Arthritis in the lower

back may pinch a spinal nerve, such as the sci- atic nerve, in which case pain radiates down the back and leg. Affected joints lose their range of motion, and associated muscles be- come weak.

Degeneration occurs at the articular cartilage of the joint. This cartilage caps the bone surface where bone meets another bone in a joint. This cartilage erodes, exposing the underlying bone, which degenerates and leads to new bone de- posits in and around the joint. The bone ends thicken and develop sharp irregular bony sur- face structures called spicules and spurs. Small joints such as the knuckles enlarge and become knobby (Figure 15–9 �).

Diagnosis of osteoarthritis is made princi- pally by x-rays that show the joint damage and a history of the symptoms. There is no cure for osteoarthritis, but treatment can greatly relieve the pain. A combination of rest and mild exer- cise to maintain range of motions, medication, and heat applications is generally prescribed. Nonsteroidal anti-inflammatory medications commonly used include aspirin, indomethacin, fenoprofen, and ibuprofen. Steroids such as cortisone are sometimes injected into the joint capsule to relieve pain. Surgical replacement of

Figure 15–9 � Acute gouty arthritis of the finger joints. (Courtesy of the American College of Rheumatology)

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a damaged joint like the hip and knee has be- come very effective, although factors such as age are important considerations.

Gout Also called gouty arthritis, gout affects the joints of the feet, particularly those of the big toe, and sometimes of the hand, fingers, wrist, or knee. Gout affects an estimated 3 million Amer- icans, is most prevalent among men over age 40, but also affects postmenopausal women. The cause of gout is unknown. It sometimes follows a minor injury or excessive eating or drinking, and there may be no explanation for its occur- rence, but heredity seems to play a role. The pathogenesis of gout is better understood than its cause. Gout attacks are related to excess uric acid in blood, which results either from a defect in metabolism of purines (a component of nucleic acids), or from abnormal retention of uric acid, or both. The high uric acid level leads to deposits of uric acid crystals in the joints. Uric acid crystals also deposit in the kidneys, stimulating kidney stone formation and irritating the kidney.

The onset of an acute attack of gout is gener- ally sudden. The affected joints exhibit typical signs of inflammation: pain, heat, swelling, and redness (see Figure 15–9). Signs and symptoms may last from days to many weeks. Resolution of an acute attack may be followed by symp- tom-free periods of 6 months to more than 2 years before recurrence. A chronic form of gout also occurs in which a person experiences per- sistent arthritis.

Gout can be diagnosed by microscopic exam- ination of aspirated joint fluid, which reveals needle-like urate crystals. High serum level of uric acid is consistent with gout. X-rays of af-

fected joints may initially appear normal until repeated attacks of chronic gout damage the bone and cartilage at joints.

Acute gout attacks can be treated with rest, application of hot or cold compresses, anal- gesics, colchicine, and corticosteroids. Chronic gout may be treated with colchicine, which pre- vents acute attacks, and uricosuric agents such as probenecid that promote excretion of uric acid. If diagnosed early and treated properly, the development of chronic gout can be prevented.

Septic Arthritis Septic arthritis is considered a medical emergency. It develops as a result of bacterial infection of a joint. Cartilage and bone destruction may lead to ankylosis and life-threat- ening septicemia (blood-borne bacterial infec- tion). Streptococci and staphylococci cause sep- tic arthritis by invading a joint following trauma or surgery. Neisseria gonorrhea, the cause of gon- orrhea, may spread to joints via blood from a pri- mary infection site. Antibiotics are required to control the joint infection and to prevent sep- ticemia.

Bursitis Bursae are small, fluid-filled sacs located near the joints that cushion and reduce friction on movement. Bursitis is an inflammation of these bursae, and it is a very painful condition. The bursae of the shoulder joint are the most fre- quently affected, although bursitis can develop at any joint. Repeated irritation or injury of a bursa can cause bursitis. Limitation of move- ment results from the pain of the inflammation. Treatment includes rest, anti-inflammatories,

Prevention PLUS! Bones, Joints, and Muscles Benefit from Exercise In a healthy aging body, muscles lose strength and coordination, bones become thin and brittle, and joints stiffen and lose flexibility. The consequences include greater risk of falls and fractures. These can result in immobility, disability, di- minished quality of life, and susceptibility to depression and disease. A vigorous exercise program benefits the bones, joints, and muscles as well as the cardiovascular and respiratory system. However, such a program should not be under- taken without physician guidance. A systematic vigorous program of exercise may not be feasible due to health or may not be appealing to the individuals. Nonetheless, significant physical and psychological benefits can be reaped from daily activities that engage the musculoskeletal system: walking, gardening, doing laundry, and climbing stairs.

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and moist heat applications. Steroids are some- times injected into the joint to reduce the in- flammatory response.

Dislocations, Sprains, and Strains A dislocation is a displacement of bones from their normal position in a joint. Dislocations are most common in the shoulder and finger joints, but they can occur anywhere. The dislocation causes pain and reduced mobility at the in- volved joint. The bone must be reset and immo- bilized to allow healing of torn ligaments and tendons. Congenital dislocations of the hip re- sult from an improperly formed joint, and they are treated in infancy with a cast or surgery.

Sprains result from the wrenching or twisting of a joint such as an ankle that injures the liga- ments. Blood vessels and surrounding tissues, muscles, tendons, and nerves may also be dam- aged. Swelling and discoloration due to hemor- rhaging from the ruptured blood vessels occur. A sprain is very painful, and the joint should not be used while it is severely inflamed. Immo- bilization with a splint or cast might be neces- sary for more severe sprains. Cold compresses reduce the swelling immediately after the injury, whereas later, heat applications relieve discom- fort and speed healing. A “whiplash” is a sprain in which the cervical (neck) ligaments and tis- sues are injured. Whiplash injuries are often the result of rear-end motor vehicle accidents.

Strains, also called pulled muscles, result from a tearing of a muscle and/or its tendon from excessive use or stretching. Conditioning and warm-up before exercise prevent strains. Strains should be treated with rest, initially with ice to reduce inflammation, and later with warm compresses to encourage blood flow and healing. Severe strains may require many months to heal before safely resuming activity.

Carpal Tunnel Syndrome A painful condition of the hand known as carpal tunnel syndrome (CTS) affects up to 10% of the working population in the United States, caus- ing disability and lost work time. It is actually one of a larger class of problems known as repetitive strain injuries (RSIs). Women are three

times more likely to develop CTS than in men. Many women report the symptoms during preg- nancy, which is attributed to accumulation of fluid within the tissues. Risk factors for CTS in- clude the performance of repetitive manual tasks such as knitting, driving, typing, comput- ing, and piano playing (Figure 15–10 �). It usu- ally begins as numbness or tingling in the hand but progresses to pain that can radiate up the arm to the shoulder; the pain is most severe at night. Simple tasks requiring finger movements become difficult.

A physician may diagnose carpal tunnel syn- drome by requiring certain hand maneuvers. The diagnosis is confirmed by an electromyogram. The test measures the velocity of sensory and motor nerve conduction. If electrical impulses are slowed as they travel through the carpal tunnel, compression of the nerve is indicated.

Conservative treatments begin with avoiding the repetitive action where possible, at least temporarily. Immobilizing the hand and wrist with a lightweight, molded plastic splint is often

Ulnar nerve

Ligament Bones

Tendons

Median nerveCarpal tunnel

Figure 15–10 � Crosssection of the wrist showing tendons and nerves involved in carpal tunnel syndrome.

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adequate for the inflammation to subside. Injec- tion of a steroidal anti-inflammatory drug into the carpal tunnel is sometimes effective. For some individuals, nonsteroidal anti-inflamma- tory drugs such as aspirin and ibuprofen can reduce symptoms. Surgery may be required to divide the transverse ligament, which is com- pressing the median nerve. The procedure gen- erally provides permanent relief without affect- ing hand movement or strength.

Diseases of the Muscles

Skeletal muscle moves the body and provides much of the body’s heat. Skeletal muscle func- tion is intimately associated with nervous sys- tem function. Muscles cannot function unless they are stimulated by nerves. In Chapter 13, diseases in which the nerves fail to innervate muscles were discussed. Muscles themselves can also be diseased and lose their ability to con- tract. Another cause of muscle failure is the im- proper transmission of the impulse for contrac- tion at the myoneural junction, the site at which a nerve ending sends its signal to a muscle cell.

Muscular Dystrophy (MD) The term muscular dystrophy (MD) includes sev- eral forms of the disease, all of which are hered- itary. The various forms are transmitted differ- ently and affect different muscles, but all forms result in muscle degeneration, which totally dis- ables the individual.

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The most common and serious type is Duchenne, which is caused by a sex-linked gene and affects approximately 2 per 10,000 people. Muscular dystrophy can appear at any age, but generally signs appear in the third to fifth year. In Duchenne’s muscular dystrophy, a cytoskeletal protein called dystrophin is missing. As a result of this defect, muscle fibers die and are replaced by fat and connective tissue. Because neither of these tissues has the ability to contract, skeletal muscles weaken. A severe form can progress rapidly and affect the muscle of the heart, caus- ing death; other forms progress slowly. In the most severe form of muscular dystrophy, the calf muscles enlarge as a result of fat deposition. The shoulder muscles are weak, which causes the arms to hang limply. A child with this form of muscular dystrophy is very weak and thin and does not usually live to adulthood.

The diagnosis is based on electromyography, which shows weak muscle contractions. Biospy of muscle shows abnormal muscle fibers: varia- tion in sizes, fat deposits, and absence of dys- trophin. Immunologic and molecular biology techniques can diagnose the disease prenatally as well as at birth.

No cure exists. Treatment includes physical and occupational therapy, exercise, and use of orthopedic appliances.

Myasthenia Gravis (MG) Myasthenia gravis (MG) is a disorder of the my- oneural junction in which the nerves fail to transmit an impulse for contraction to the mus- cles. Lack of stimulation and use leads to mus-

Prevention PLUS! Carpal Tunnel Syndrome: An Occupational Hazard Carpal tunnel syndrome, caused by damage to the median nerve, is a common problem of data processors, computer users, typists, beauticians, and dentists, who often maintain a flexed wrist position. Frequent rest and splinting may help prevent the complications of carpal tunnel syndrome. If surgery is required to relieve pressure on the nerve, a new technique is greatly reducing recovery time and lost work. A tiny video camera enables the surgeon to make two tiny in- cisions in the wrist and palm, each requiring only one stitch. Recovery is therefore much faster than with the traditional longer incision.

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cle atrophy and muscle weakness. The cause is unknown, but myasthenia gravis may be classi- fied as an autoimmune disease. Antibodies at- tach near the myoneural junction and destroy acetylcholine or its receptors. Myasthenia gravis is rare, affecting about 3 per 10,000 and occurring more frequently among women than men. No risk factors are known. An autoim- mune disease, myasthenia gravis is probably genetic in origin.

The principal symptoms of this disease are fatigue and the inability to use the muscles. The voluntary muscles of the body are affected, in- cluding the muscles of facial expression, ren- dering the person’s face expressionless. Eyelid control is lost, and simple actions such as chewing and talking become difficult. The great- est danger in this disease is respiratory failure because the muscles required for respiratory ventilation are unable to contract.

Treatment includes drugs that increase acetylcholine levels at the myoneural junction. The thymus gland, which is involved in the im- mune response, is often enlarged in myasthenia gravis patients. Removal of this gland some- times brings about a remission but not a cure.

Tumors of Muscle Muscle tumors are rare, but when they occur, they are usually highly malignant. A malignant tumor of skeletal muscle is a rhabdomyosarcoma. The tumor requires surgical removal, and the prognosis is poor. The rhabdomyosarcoma metastasizes early and is usually an advanced malignancy when it is diagnosed. Muscle malig- nancy is rare because muscle cells do not con- tinually divide like blood or skin cells.

Age-Related Diseases

Bones Osteoblast activity declines with age. Because these cells build bone tissue in response to stress, for remodeling or repair, this results in age-related thinning of bones. In addition, aging bone has more minerals and less protein, mak- ing the tissue more brittle. Overall, the total

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amount of bone declines steadily with age. At menopause, bone loss accelerates, making women more susceptible to osteoporosis and its effects. More than 80% of those with osteoporo- sis are women, and a majority of women over age 60 have osteoporosis.

Joints Joint mobility decreases with age because carti- lage in movable joints becomes stiffer, ligaments lose flexibility and elasticity, and synovial mem- branes become fibrous and stiff and produce less synovial fluid. These changes begin at age 20 and become significant by age 30, especially if the joints and muscles are not regularly exer- cised and stretched. The incidence of arthritis increases with age: While fewer than 20% of young adults have arthritis, 60% of adults over age 60 have some form of arthritis. Most of these cases are osteoarthritis.

Muscles Muscles become less sensitive to stimulation with age, meaning that they take longer to con- tract when stimulated. Recovery following con- traction becomes slow, diminishing the ability to sustain repeated contractions and reducing endurance. With age, the number of muscle fibers decreases, and they become shorter and thinner, reducing muscle strength and range of motion. Exercise reduces the rate of these changes and helps maintain muscle mass, strength, and flexibility.

R E S O U R C E S

American Academy of Orthopedic Surgeons: www.aaos.org

American College of Sports Medicine: www.acsm.org

American Physical Therapy Association: www.apta.org

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DISEASES AT A GLANCE Musculoskeletal System

DISEASE ETIOLOGY SIGNS AND SYMPTOMS

Osteomyelitis Infection by staphylococci Pain, redness, heat, chills, fever, tachycardia, nausea, weight loss

Rickets Vitamin D deficiency in childhood Deformation of bones, knock-knee, bow-leg, curved spine, nodular swellings at rib ends and joints, enlarged and square head, flaccid muscles

Osteomalacia Vitamin D deficiency in adults Muscular weakness, weight loss, pain in bones, deformation of bones, easily fractured bones

Osteoporosis Calcium deficiency, decreased bone density

Decreased height from vertebral compression fractures, curvature of spine, easily fractured bones

Paget’s disease Idiopathic, genetic Enlarged skull, nerve compression curvatures in spine, and deformed legs

Bone tumors Idiopathic; commonly metastatic Painless lump in bone tissue, fracture without trauma

Rheumatoid arthritis

Autoimmunity Pain and stiffness in joints, swollen, red, warm joints, bilateral involvement, exacerbation and remission, rheumatoid nodules, crippling deformities

Osteoarthritis Idiopathic; may follow joint injury or chronic irritation

Aches, pain, stiffness in joints, limited range of motion, muscle weakness around affected joint, enlarged joints, bone spurs; may involve only one joint

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DIAGNOSIS TREATMENT PREVENTION LIFESPAN

Bone scan, CT scan, MRI, WBC count

Antibiotics, surgery Antibiotics for compound fractures or other infected wounds

Any age

Physical exam, x-ray Vitamin D–fortified milk, sunlight, cod liver oil

Vitamin D–fortified milk, sunlight, cod liver oil

Children

Physical exam, x-ray Vitamin D–fortified milk, sunshine, cod liver oil, calcium and phosphorous supplements

Vitamin D–fortified milk, sunshine, cod liver oil, calcium and phosphorous supplements

Adults

X-ray and bone scan Pain relief, fracture treatment, some medical treatment (estrogens, calcitonin, bisphosphonates)

Calcium supplements, weight- bearing exercises

Postmenopausal women

Physical exam Surgical, limited None Older men

X-ray, biopsy Surgery None Children and adolescents

Physical exam, presence of rheumatoid factor in blood

Mild exercise, anti-inflammatories, steroids

None Adults

X-ray, history Pain relief, mild exercise and rest, heat applications, steroids, surgery

None Adults

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DISEASES AT A GLANCE Musculoskeletal System (continued)

DISEASE ETIOLOGY SIGNS AND SYMPTOMS

Gout Inherited defect in uric acid metabolism leads to high levels of urate and uric acid deposition in joints

Severe pain, heat, swelling, redness in affected joint; acute onset

Septic arthritis Bacterial infection of joint Pain, redness, swelling, bone and joint destruction

Bursitis Overuse of joint Pain at joint, especially during use

Carpal tunnel syndrome

Repetitive use of wrist Numbness and tingling of hand, pain radiating to shoulder, limited finger movement, severe at night

Muscular dystrophy

Defect in X-linked gene for muscle protein dystrophin

Weakened muscles, muscles may enlarge as fat is deposited; muscles degenerate

Myasthenia gravis Autoimmunity interferes with nerve transmission to muscles

Fatigue, muscle paralysis

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DIAGNOSIS TREATMENT PREVENTION LIFESPAN

Uric acid level in blood, x-ray Analgesics, hot and cold compresses, colchicine, probenecid

Avoid triggers, which may be dietary

Men over age 40

History, blood and synovial cultures

Antibiotics Treat infected wounds or other infections with antibiotics to prevent sepsis

Any age

Physical exam and history Moist heat, analgesics, steroids, rest Reduce or avoid triggering activities

Adults

Physical exam, electromyography

Splinting hand and wrist, surgery Reduce or avoid triggering activities

Adults and adolescents

Physical exam, serum enzymes, muscle biopsy

Physical therapy, orthopedic procedures

None; screening helps detect early onset

Onset in young adults

Antibody level, response to anticholinesterase drugs, electromyography

Thymectomy, anticholinesterase drugs, steroids, immune suppression

None Onset in young adult women

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1. Bones are soft in rickets due to a ____________________ deficiency.

a. vitamin A b. vitamin C c. vitamin D d. vitamin K

2. Osteomalacia affects which of the following?

a. the joints of young children b. the joints of adults c. the bones of children d. the bones of adults

3. Carpal tunnel syndrome is caused by damage to the ____________________.

a. wrist b. fingers c. median nerve d. forearm muscles

4. Biopsy in addition to electromyography is a diagnostic test for ____________________.

a. gout b. sprain c. carpal tunnel syndrome d. Duchenne’s MD

5. ____________________ is the most common form of arthritis.

a. Rheumatoid arthritis b. Osteoarthritis c. Septic arthritis d. Gout

6. Ankylosis and immobility results in severe ____________________.

a. rheumatoid arthritis b. osteoarthritis c. septic arthritis d. gout

7. Colchicine and corticosteroids are used to treat acute cases of ____________________.

a. rheumatoid arthritis b. osteoarthritis c. septic arthritis d. gout

8. Which of these is NOT due to calcium deficiency?

a. osteoporosis b. osteomalacia c. osteogenic sarcoma d. rickets

9. Which of these is a type of autoimmune disorder?

a. rhabdomyosarcoma b. Duchenne’s MD c. myasthenia gravis d. osteitis fibrosa cystica

10. Streptococci and staphylococci are associated with ____________________.

a. Pott’s disease b. tuberculosis c. osteomyelitis d. osteoporosis

3. A 20-year-old woman has worsening pain in her leg below the knee. She says she feels “a little weak and out of sorts” and has stopped her jogging routine. How can you deter- mine whether she has a type of arthritis, a bone infection, a fracture, or a joint sprain?

1. A 68-year-old woman visits her physician and reports that her back hurts. Physical exam finds kyphosis and that she has lost height since her last visit a few years ago. What is a likely diagnosis for this case? Name two treatment possibili- ties that the physician might suggest. Name something that might have helped prevent this condition, especially if it had been initiated and applied at an earlier age.

2. A 55-year-old carpenter reports persistent swelling and pain in the knuckles of his right hand. What information do you need to determine the type of joint disease he has?

Interactive Exercises

Cases for Critical Thinking

Multiple Choice

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True or False

_______ 1. Osteomyelitis affects principally children and adolescents.

_______ 2. Women with large bone mass are most prone to osteoporosis.

_______ 3. An osteoma is a malignant bone tumor.

_______ 4. Rheumatoid arthritis is the most crippling form of arthritis.

_______ 5. Osteomyelitis is a local and systemic infection.

_______ 6. Osteoarthritis is the most common form of arthritis.

_______ 7. Muscular dystrophy is a hereditary disease.

_______ 8. Myasthenia gravis is an infectious disease of the muscles.

_______ 9. Rhabdomyosarcoma is a malignant bone tumor.

_______ 10. There is no cure for osteoarthritis.

Fill-Ins

1. A special form of tuberculosis that affects the vertebral column of children is called ____________________.

2. A disease of infancy and early childhood in which the bones do not properly ossify, or harden, is called ____________________.

3. The word ____________________ means increased porosity of the bone, which makes the bone abnormally fragile.

4. A very painful condition caused by deposits of uric acid crystals in the joints is called ____________________.

5. The principle minerals in bone are ____________________ and ____________________.

6. Bone is deposited by cells called ____________________.

7. The ____________________ membrane becomes inflamed in rheumatoid arthritis.

8. Antibodies against acetylcholine receptors are the cause of ____________________ ____________________.

9. Colchicine is an effective treatment for ____________________.

10. Vitamin D is required for dietary absorption of ____________________.

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Labeling Exercise

Use the lines below to label the following images.

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Multimedia Preview

Additional interactive resources and activities for this chapter can be found on the Companion Web- site. For videos, audio glossary, and review, access the accompanying DVD-ROM in this book.

DVD-ROM Highlights▼

Word Search Terms are hidden throughout the grid and we provide you with clues to find them. Your task is to discover which terms to find and then seek them out. Grab a magnifying glass and your thinking cap—you’ll need both!

Cognition Use your memory to make a match. This variation on the game Concentration will challenge you to study the eight terms and then remember their location to complete a quiz. Click on each tile to reveal the correct answers.

Web Links Take advantage of the free-access online study guide that accompanies your textbook. This online activity challenges you to visit selected web links where you can explore important issues to reinforce your under- standing. By clicking on this URL you’ll also access links to current news articles and an audio glossary.

Website Highlights—www.pearsonhighered.com/zelman▼

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