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The Skeletal System
 

The Skeletal System

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    The Skeletal System The Skeletal System Document Transcript

    • 50 The Body Systems: Clinical and Applied Topics The Skeletal System 2. The applied physical stresses: Heavily stressed bones become thicker and stronger, and lightly The skeletal framework of the body is composed of stressed bones become thinner and weaker. at least 206 bones and the associated tendons, lig- Skeletal weakness can therefore result from aments, and cartilages. The skeletal system has a muscular disorders, such as myasthenia gravis variety of important functions, including the sup- (p. 66) or the muscular dystrophies (p. 65), and port of soft tissues, blood cell production, mineral conditions that affect CNS motor neurons, such and lipid storage, and, through its relationships as spinal cord injuries (p. 75), demyelination dis- with the muscular system, the support and move- orders (p. 72), or multiple sclerosis (pp. 72, 82). ment of the body as a whole. Skeletal system disor- 3. Circulating hormone levels: Changing levels of ders can thus affect many other systems. The 6 skeletal system is in turn influenced by the activi- growth hormone, androgens and estrogens, thyroid hormones, parathyroid hormone, and ties of other systems. For example, weakness or calcitonin increase or decrease the rate of min- paralysis of skeletal muscles will lead to a weaken- eral deposition in bone. As a result, many dis- ing of the associated bones. orders of the endocrine system will have an Although the bones you study in the lab may impact on the skeletal system. For example: seem rigid and permanent structures, the living skeleton is dynamic and undergoing continual • Conditions affecting the skin, liver, or kid- remodeling. The remodeling process involves bone neys can interfere with calcitriol production. deposition by osteoblasts and bone resorption by osteoclasts. As indicated in Figure A-16, the net • Thyroid or parathyroid disorders can alter result of the remodeling varies depending on: thyroid hormone, parathyroid hormone, or calcitonin levels. 1. The age of the individual: During development, bone deposition occurs faster than bone • Pituitary gland disorders or liver disorders resorption, and the skeleton grows larger. At can affect GH or somatomedin production. maturity, bone deposition and resorption are in • Reproductive system disorders can alter balance; as the aging process continues, the circulating levels of androgens or estrogens. rate of bone deposition declines and the bones become less dense. This gradual weakening, Many of these conditions will be detailed in the called osteopenia, begins at age 30–40 and may section dealing with the endocrine system (pp. ultimately progress to osteoporosis (p. 54). 87–94). Mechanical stresses Viral infection Bone mass Ectopic bone formation Paget's disease increases Decreased (Hyperostosis) osteoclast Increased Inherited conditions Unknown cause activity osteoblast Marfan's syndrome activity Osteopetrosis Total bone mass in skeleton Osteoblasts Hormonal disorders Normal range maintained by adding to bone mass Gigantism Osteoclasts Regular exercise Acromegaly removing Vitamins A, D, C bone mass Dietary calcium Normal levels of growth hormones, thyroid hormones, Vitamin deficiencies sex hormones, parathyroid Osteomalacia hormone, calcitonin, and Rickets (vitamin D) calcitriol Scurvy (vitamin C) Decreased osteoblast Inherited conditions Cancer activity Osteogenesis Increased imperfecta Stimulation by osteoclast Achondroplasia osteoclast activating Bone mass activity factor decreases (Osteopenia) Hormonal disorders Pituitary dwarfism Osteoporosis in post- Inactivity menopausal women Bed rest, paralysis, and elderly men immobility, weightlessness Figure A-16 Factors Affecting Bone Mass
    • The Skeletal System 51 4. Rates of calcium and phosphate absorption and disorder. Chronic, aching bone or joint pain may excretion: For bone mass to remain constant, be tolerated, and a person often will not seek med- the rate of calcium and phosphate excretion, ical assistance until more definitive symptoms primarily at the kidneys, must be balanced by appear. This may not occur until the condition is the rate of calcium and phosphate absorption relatively advanced. For example, a symptom that at the digestive tract. Kidney failure or dietary may require immediate attention is a pathologic calcium deficiencies or problems at the diges- fracture. Pathologic fractures are the result of tive tract affecting calcium and phosphate weakening of the skeleton by disease processes, absorption will have a direct effect on the skele- such as osteosarcoma (a bone cancer). These frac- tal system. tures may be caused by physical stresses easily 5. Genetic and environmental factors: Genetic or tolerated by normal bones. 6 environmental factors may affect the structure of bone or the remodeling process. There are a EXAMINATION OF THE number of inherited abnormalities of skeletal development, such as Marfan’s syndrome and SKELETAL SYSTEM achondroplasia (p. 53). When bone fails to form The bones of the skeleton cannot be seen without embryonically in certain areas, underlying tis- relatively sophisticated equipment. However, there sues can be exposed and associated function are a number of physical signs that can assist in can be altered. This occurs in a cleft palate (a the diagnosis of a bone or joint disorder. Important condition in which the palatine processes of the factors noted in the physical examination include: maxillary bones do not fuse) and in spina bifida (p. 58). Environmental stresses can alter the 1. Limitation of movement or stiffness: Many joint shape and contours of developing bones. For disorders, such as the various forms of arthri- example, some cultures use lashed boards to tis, will restrict movement or produce stiffness shape an infant’s skull to a form considered at one or more joints. fashionable. Environmental forces can also 2. The distribution of joint involvement and inflam- result in the formation of bone in unusual loca- mation: In a monoarthritic condition, only one tions. These heterotopic bones may develop in a joint is affected. In a polyarthritic condition, variety of connective tissues exposed to chronic several joints are affected simultaneously. friction, pressure, or mechanical stress. For example, cowboys in the nineteenth century 3. Sounds associated with joint movement: Bony sometimes developed heterotopic bones in the crepitus (KREP-i-tus) is a crackling or grating dermis of the thigh from friction with the saddle. sound generated during movement of an abnormal joint. The sound may result from the Figure A-17 diagrams the relationships between movement and collision of bone fragments fol- the major classes of skeletal disorders affecting lowing an articular fracture or from friction and bones and joints. Some of these conditions are the abrasion at an arthritic joint. result of conditions that primarily affect the skeletal system (osteosarcoma, osteomyelitis) and others 4. The presence of abnormal bone deposits: result from problems originating in other systems Thickened, raised areas of bone develop around (acromegaly, rickets). These conditions affect the fracture sites during the repair process. structure and function of the bones of the skeleton. Abnormal bone deposits may also develop Traumatic injuries, such as fractures or dislo- around the joints in the fingers. These deposits cations, and infections also affect the cartilages, are called nodules or nodes. When palpated, tendons, and ligaments associated with the bones nodules are solid and painless. Nodules, which involved. A somewhat different array of conditions can restrict movement, often form at the inter- affect the soft tissues of the bone marrow. Areas of phalangeal joints of the fingers in osteoarthritis. red bone marrow contain the stem cells for red 5. Abnormal posture: Bone disorders that affect blood cells, white blood cells, and platelets. The the spinal column can result in abnormal pos- bone marrow becomes abnormal in diseases of the ture. This is most apparent when the condition blood that are characterized by blood cell overpro- alters the normal spinal curvature. Examples duction (polycythemia, leukemia, pp. 98, 103) or include kyphosis, lordosis, and scoliosis (p. 56). underproduction (several anemias, pp. 99, 101). A condition involving an intervertebral joint, such as a herniated disc, will also produce THE SYMPTOMS OF BONE AND abnormal posture and movement. JOINT DISORDERS A common symptom of a skeletal system disorder Abnormalities in Skeletal is pain. Bone pain and joint pain are common Development EAP p. 131 symptoms associated with many bone disorders. Several inherited conditions result in abnormal bone As a result, the presence of pain does not provide formation. Three examples are osteogenesis imper- much help in identifying a specific bone or joint fecta, Marfan’s syndrome, and achondroplasia.
    • 52 The Body Systems: Clinical and Applied Topics Endocrine problems Acromegaly Neuromuscular problems Hyper-/hypoparathyroidism Nutritional problems Osteoporosis (some forms) Muscular dystrophies Myasthenia gravis Osteomalacia Amyotrophic lateral Rickets sclerosis Spinal cord injuries Cerebrovascular accidents Cancer BONE Osteosarcoma DISORDERS 6 Trauma Aging process Fractures Osteopenia Heterotopic bone Osteoporosis formation Infection Genetic Osteomyelitis Abnormalities Paget’s disease Anatomical problems Physiological problems Cleft palate Marfan’s syndrome Spina bifida Osteogenesis imperfecta Abnormal spinal Achondroplasia curvature (some) Clubfoot, clawfoot (a) Autoimmune diseases Aging process Rheumatoid arthritis Osteoarthritis Systemic lupus (some forms) erythematosus JOINT Infection DISORDERS Rheumatic Trauma fever Gonococcal Dislocations arthritis Fractures Septic arthritis Genetic abnormalities Degenerative joint disease (some forms) Gout (b) Figure A-17 An Overview of Disorders of the Skeletal System (a) Bone disorders. (b) Joint disorders.
    • The Skeletal System 53 Osteogenesis imperfecta (im-per-FEK-ta) is sexual and mental development remain unaffected. an inherited condition, appearing in 1 individual in An adult with achondroplasia is an achondroplastic about 20,000, that affects the organization of colla- dwarf (Figure A-18b). gen fibers. Osteoblast function is impaired, growth In osteomalacia (os-tƒ-|-ma-L£-shƒ-uh; is abnormal, and the bones are very fragile, leading malakia, softness), the size of the skeletal elements to progressive skeletal deformation and repeated remains the same, but their mineral content fractures. Fibroblast activity is also affected, and decreases, softening the bones. In this condition the ligaments and tendons are very “loose,” permit- the osteoblasts are working hard, but the matrix ting excessive movement at the joints. isn’t accumulating enough calcium salts. This can Marfan’s syndrome is also linked to defective occur in adults or children whose diet contains connective tissue structure. Extremely long and inadequate levels of calcium or vitamin D3. 6 slender limbs, the most obvious physical indica- tion of this disorder, result from excessive carti- Hyperostosis and lage formation at the epiphyseal plates (Figure A-18a). (Marfan’s syndrome is discussed further Acromegaly EAP p. 133 on p. 110.) The excessive formation of bone is termed Achondroplasia (¥-kon-dr|-PL£-sƒ-uh) is hyperostosis (hª-per-os-T«-sis). In osteopetrosis another condition resulting from abnormal epiphy- (os-tƒ-|-pe-TR«-sis; petros, stone) the total mass seal activity. In this case the epiphyseal plates of the skeleton gradually increases because of a grow unusually slowly, and the individual develops decrease in osteoclast activity. Remodeling stops, short, stocky limbs. Although there are other skele- and the shapes of the bones gradually change. tal abnormalities, the trunk is normal in size, and Osteopetrosis in children produces a variety of Figure A-18 Disorders of Bone Formation (a) Marfan’s syndrome. (b) Achondroplasia. (c) Acromegaly. (a) (b) (c)
    • 54 The Body Systems: Clinical and Applied Topics skeletal deformities. The primary cause of this porosis (os-tƒ-|-por-|-sis; porosus, porous) there is relatively rare condition is unknown. a reduction in bone mass sufficient to compromise In acromegaly (akron, extremity + megale, normal function. The distinction between the “nor- great), an excessive amount of growth hormone is mal” osteopenia of aging and the clinical condition released after puberty, when most of the epiphyseal of osteoporosis is therefore a matter of degree. plates have already closed. Cartilages and small Current estimates indicate that 29 percent of bones respond to the hormone, however, resulting women between the ages of 45 and 79 can be con- in abnormal growth at the hands, feet, lower jaw, sidered osteoporotic. The increase in incidence skull, and clavicle. Figure A-18c shows a person after menopause has been linked to decreases in with acromegaly. the production of estrogens (female sex hormones). 6 The incidence of osteoporosis in men of the same Stimulation of Bone age is estimated at 18 percent. Growth and Repair EAP p. 133 The excessive fragility of the bones frequently leads to breakage, and subsequent healing is Despite the considerable capacity for bone repair, impaired. Vertebrae may collapse, distorting the every fracture does not heal as expected. A delayed vertebral articulations and putting pressure on union is one that proceeds more slowly than antici- spinal nerves. Therapies that boost estrogen levels, pated. Nonunion may occur as a result of compli- dietary changes to elevate calcium levels in the cating infection, continued movement, or other blood, and exercise that stresses bones and stimu- factors preventing complete callus formation. lates osteoblast activity appear to slow but not com- There are several techniques for inducing bone pletely prevent the development of osteoporosis. repair. Surgical bone grafting is the most common Osteoporosis can also develop as a secondary treatment for nonunion. This method immobilizes effect of some cancers. Cancers of the bone mar- the bone fragments and provides a bony model for row, breast, or other tissues release a chemical the repair process. Dead bone or bone fragments known as osteoclast-activating factor. This com- can be used; alternatively, living bone from another pound increases both the number and activity of site, such as the iliac crest or part of a rib, can be osteoclasts and produces a severe osteoporosis. inserted. As an alternative to bone grafting, sur- Infectious diseases that affect the skeletal sys- geons can insert a shaped patch, made by mixing tem become more common in older individuals. In crushed bone and water. Bone transplants using part this reflects the higher incidence of fractures, bones from cadavers are performed, but in this case combined with slower healing and reduction in thorough sterilization is required to prevent the immune defenses. transmission of blood-borne diseases, such as AIDS. ¯ Osteomyelitis (os-tƒ-|-mª-e-LI -tis; myelos, The calcium carbonate skeleton of tropical corals marrow) is a painful infection of a bone most often has been sterilized and used as another alternative. caused by bacteria. This condition, most common Another approach involves the stimulation of in people over 50 years of age, can lead to danger- osteoblast activity by strong electrical fields at the ous systemic infections. A virus appears to be injury site. This procedure has been used to pro- responsible for Paget’s disease, also known as mote bone growth after fractures have refused to ¯ osteitis deformans (ost-ƒ-I-tis de-FOR-manz). This heal normally. Wires may be inserted into the skin, condition may affect up to 10 percent of the popu- implanted in the adjacent bone, or wrapped around lation over 70. Osteoclast activity accelerates, pro- a cast. The overall success rate of about 80 percent ducing areas of acute osteoporosis, and osteoblasts is truly impressive. produce abnormal matrix proteins. The result is a One experimental method of inducing bone gradual deformation of the skeleton. repair involves mixing bone marrow cells into a soft matrix of bone collagen and ceramic. This combina- tion is used like a putty at the fracture site. Individual Variation in the Mesenchymal cells in the marrow divide, producing Skeletal System EAP p. 137 chondrocytes that create a cartilaginous patch that is later converted to bone by periosteal cells. A second A comprehensive study of a human skeleton can experimental procedure uses a genetically engineered reveal important information about the individual. protein to stimulate the conversion of osteoprogenitor For example, there are characteristic racial differ- cells into active osteoblasts. Although results in ani- ences in portions of the skeleton, especially the skull mal experimentation have been promising, neither and pelvis, and the development of various ridges technique has yet been approved for human trials. and general bone mass can permit an estimation of muscular development and body weight. Details Osteoporosis and Age-Related such as the condition of the teeth or the presence of Skeletal Abnormalities EAP p. 136 healed fractures can provide information about the individual’s medical history. Two important details, Our maximal bone density is reached in our early sex and age, can be determined or closely estimated twenties and decreases as we age. Inadequate cal- on the basis of measurements indicated in Tables A- cium in the diet of teenagers reduces peak density 15 and A-16. Table A-15 identifies characteristic dif- and increases the risk of osteoporosis. In osteo- ferences between the skeletons of males and
    • The Skeletal System 55 TABLE A-15 Sexual Differences in the Human Skeleton Region/Feature Male (as compared to female) Female (as compared to male) SKULL General appearance Heavier, rougher Lighter, smoother Forehead Sloping More vertical Sinuses Larger Smaller Cranium About 10% larger (average) About 10% smaller Mandible Larger, robust Lighter, smaller Teeth Larger Smaller 6 PELVIS General appearance Narrow, robust, heavy, rough Broader, lighter, smoother Pelvic inlet Heart-shaped Oval to round Iliac fossa Relatively deep Relatively shallow Ilium Extends farther above sacral articulation More vertical; less extension above sacroiliac joint Angle inferior to Under 90° 100° or more pubic symphysis Acetabulum Directed laterally Faces slightly anteriorly as well as laterally Obturator foramen Oval Triangular Ischial spine Points medially Points posteriorly Sacrum Long, narrow triangle with Broad, short triangle with less curvature pronounced sacral curvature Coccyx Points anteriorly Points inferiorly OTHER SKELETAL ELEMENTS Bone weight Heavier Lighter Bone markings More prominent Less prominent TABLE A-16 Age-Related Changes in the Skeleton Region/Feature Event(s) Age (Years) GENERAL SKELETON Bony matrix Reduction in mineral content Values differ for males versus females between ages 45 and 65; similar reductions occur in both sexes after age 65. Markings Reduction in size, roughness Gradual reduction with increasing age and decreasing muscular strength and mass. SKULL Fontanels Closure Completed by age 2. Metopic suture Fusion 2–8 Occipital bone Fusion of ossification centers 1–4 Styloid process Fusion with temporal bone 12–16 Hyoid bone Complete ossification and fusion 25–30 Teeth Loss of “baby teeth”; appearance Detailed in Chapter 17 (digestive system). of secondary dentition; eruption of posterior molars Mandible Loss of teeth; reduction in bone Accelerates in later years (60+). mass; change in angle at mandibular notch VERTEBRAE Curvature Appearance of major curves Shown in Figure A-20 and EAP Figure 6-16 (p. 000). Intervertebral discs Reduction in size, percentage Accelerates in later years (60+). contribution to height LONG BONES Epiphyseal plates Fusion Ranges vary, but general analysis permits determination of approximate age. PECTORAL AND PELVIC GIRDLES Epiphyses Fusion Overlapping ranges somewhat narrower than the above, including 14–16, 16–18, 22–25 years.
    • 56 The Body Systems: Clinical and Applied Topics females, but not every skeleton shows every feature slightly out of alignment, usually by spasms in in classic detail. Many differences, including mark- one of the jaw muscles. The individual experi- ings on the skull, cranial capacity, and general ences (1) facial pain that radiates around the ear skeletal features, reflect differences in average body on the affected side and (2) an inability to open size, muscle mass, and muscular strength. The gen- the mouth fully. eral changes in the skeletal system that take place TMJ syndrome is a repeating cycle of: muscle with age are summarized in Table A-16. Note how spasm → misalignment → pain → muscle spasm. It these changes begin at age 1 and continue through- has been linked to unconscious behaviors, such as out life. For example, fusion of the epiphyseal plates grinding of the teeth during sleep, and emotional begins about age 3, and degenerative changes in the stress. Treatment focuses on breaking the cycle of 6 normal skeletal system, such as a reduction in min- pain and muscle spasm and, when necessary, pro- eral content in the bony matrix, typically do not viding emotional support. The application of heat begin until age 30–45. to the affected joint, coupled with the use of anti- An understanding of individual variation and of inflammatory drugs or local anesthetics or both, the normal timing of skeletal development is impor- may be helpful. If teeth grinding is suspected, spe- tant in clinical diagnosis and treatment. Several cial mouth guards may be worn at night. professions focus on specific aspects of skeletal form and function. Kyphosis, Lordosis, Scoliosis EAP p. 146 Septal Defects and Sinus Problems EAP p. 143 In kyphosis (kª–F«-sis), the normal thoracic curva- Flushing the nasal epithelium with mucus pro- ture becomes exaggerated posteriorly, producing a duced in the paranasal sinuses often succeeds in “roundback” appearance (Figure A-19a). This can removing a mild irritant. But a viral or bacterial be caused by (1) osteoporosis or a compression frac- infection produces an inflammation of the mucous ture affecting the anterior portions of vertebral bod- membrane of the nasal cavity. As swelling occurs, ies, (2) chronic contractions in muscles that insert the communicating passageways narrow. Drainage on the vertebrae, or (3) abnormal vertebral growth. of mucus slows, congestion increases, and the vic- In lordosis (lor-D«-sis), or “swayback,” tboth tim experiences headaches and a feeling of pres- the abdomen and buttocks protrude abnormally. sure within the facial bones. This condition of The cause is an anterior exaggeration of the lum- sinus inflammation and congestion is called bar curvature (Figure A-19b). sinusitis. The maxillary sinuses are often involved. Scoliosis (sk|-lƒ-«-sis) is an abnormal lateral Because gravity does little to assist mucus curvature of the spine (Figure A-19c). This lateral drainage from these sinuses, the effectiveness of deviation may occur in one or more of the mov- the flushing action is reduced, and pressure on the able vertebrae. Scoliosis is the most common dis- sinus walls typically increases. tortion of the spinal curvature. Scoliosis may Temporary sinus problems may accompany result from developmental problems, such as allergies or the exposure of the mucous epithelium incomplete vertebral formation, or from muscular to chemical irritants or invading microorganisms. paralysis affecting one side of the back. In four Chronic sinusitis may occur as the result of a devi- out of five cases it is impossible to determine the ated (nasal) septum. In this condition the nasal structural or functional cause of the abnormal septum has a bend in it, most often at the junction spinal curvature. Scoliosis usually appears in between the bony and cartilaginous regions. Septal girls during adolescence, when periods of growth deviation often blocks drainage of one or more are most rapid. Treatment consists of a combina- sinuses, producing chronic cycles of infection and tion of exercises, braces, and sometimes surgical inflammation. A deviated septum can result from modifications of the affected vertebrae. Early developmental abnormalities or injuries to the detection greatly improves the chances for suc- nose, and the condition can usually be corrected or cessful treatment. improved by surgery. Problems with the Intervertebral TMJ Syndrome EAP p. 144 Discs EAP p. 146 An intervertebral disc compressed beyond its nor- The temporomandibular joint permits a consider- mal limits may become temporarily or permanently able degree of mandibular movement. The con- damaged. If the posterior ligaments are weakened, nective tissue sheath, or capsule, that surrounds as often occurs with advancing age, the com- the joint is relatively loose, and the opposing pressed inner, gelatinous core (the nucleus pulpo- bone surfaces are separated by a fibrocartilage sus) may distort the outer, fibrocartilage layer (the pad. In TMJ sydrome, the mandible is pulled annulus fibrosus), forcing it partway into the verte-
    • The Skeletal System 57 6 (b) (c) Figure A-19 Spinal Deformities (a) (a) Kyphosis. (b) Lordosis. (c) Scoliosis. bral canal. This condition is often called a slipped If the nucleus pulposus breaks through the disc (Figure A-20a), although the disc does not annulus fibrosis, it often protrudes into the verte- actually slip. The most common sites for disc prob- bral canal. This condition is called a herniated lems are at C5–C6, L4–L5, and between L5 and S1. disc (Figure A-20b). When a disc herniates, sen- A disc problem can occur at any age as the result sory nerves are distorted, and the protruding of an accidental injury, such as a hard fall or a mass can also compress the nerve roots passing “whiplash” injury to the neck. through the adjacent intervertebral foramen. The T12 Normal intervertebral Spinal cord disc • L1 • • • Slipped disc • Spinal nerve L2 Nucleus • pulposus (soft, Anulus gelatinous fibrosus core) (fibrocartilage layer) (a) (b) FIGURE A-20 Damage to the Intervertebral Discs (a) Lateral view of the lumbar region of the spinal column, showing a distorted intervertebral disc (a “slipped” disc). (b) Sectional view through a herniated disc, showing release of the nucleus pulposus and its effect on the spinal cord and adjacent nerves.
    • 58 The Body Systems: Clinical and Applied Topics result is severe back pain, an abnormal posture (abnormal vertebral flexion), abnormal sensory Problems with the Ankle function, often a burning or tingling sensation and Foot EAP p. 156 from the lower back and lower limbs, and in some The ankle and foot are subjected to a variety of cases a partial loss of control over skeletal and stresses during normal daily activities. In a sprain, pelvic muscles innervated by the compressed a ligament is stretched to the point where some of nerve fibers. Loss of bowel or bladder control is the collagen fibers are torn. The ligament remains very rare (but a medical emergency if it occurs). functional, and the structure of the joint is not The location of the injured disc can usually be affected. The most common cause of a sprained determined by noting the distribution of abnormal ankle is a forceful inversion of the foot that 6 sensations. For example, someone with a herniat- stretches the lateral ligament. An ice pack is usual- ed disc at L4–L5 will experience pain in the hip, ly required to reduce swelling, and with rest and groin, the posterior and lateral surfaces of the support the ankle should heal in about three thigh, the lateral surface of the calf, and the top weeks. of the foot; a herniation at L5–S1 produces pain In more serious incidents, the entire ligament in the buttocks, the posterior thigh, the posterior may be torn apart, or the connection between the calf, and the sole of the foot. ligament and the malleolus may be so strong that Most lumbar disc problems can be successful- the bone breaks before the ligament. In general, a ly treated with some combination of rest, back broken bone heals more quickly and effectively braces, analgesic (painkilling) drugs, and physical than does a ruptured ligament. A dislocation may therapy. Surgery to relieve the symptoms is accompany such injuries. required in only about 10 percent of cases involv- In a dancer’s fracture, the proximal portion of ing lumbar disc herniation. The primary method of the fifth metatarsal is broken. This usually occurs treatment involves removing the offending disc while the body weight is being supported by the and, if necessary, fusing the vertebral bodies longitudinal arch. A sudden shift in weight from together to prevent relative movement. Accessing the medial portion of the arch to the lateral, less the disc requires that the laminae of the nearest elastic border breaks the fifth metatarsal close to vertebral arch be removed. For this reason the its distal articulation. procedure is known as a laminectomy (la-mi-NEK- Individuals with abnormal arch development to-mƒ). are more likely to suffer metatarsal injuries. In rare cases in which the herniated portion of Someone with flat feet loses or never develops the the disc does not extend far into the vertebral fora- longitudinal arch. “Fallen arches” may develop as men, portions of the disc may be removed with a tendons and ligaments stretch and become less small tool that is guided to the site by radiological elastic. Obese individuals or those who must con- imaging. This procedure is faster and easier than is stantly stand or walk on the job are likely candi- a laminectomy. dates. Children have very mobile articulations and elastic ligaments, so they often have flexible flat feet. Their feet look flat only while children are Spina Bifida EAP p. 147 standing flat-footed, and the arch appears when they stand on their toes or sit down. This condition ¯ Spina bifida (SPI-nuh BI-fi-duh) results when the usually disappears as growth continues. vertebral laminae fail to unite during fetal develop- Clawfeet are also produced by muscular abnor- ment. The neural arch is incomplete, and the mem- malities. In this case the median longitudinal arch branes that line the dorsal body cavity bulge becomes exaggerated because the plantar flexors outward. In mild cases, most often involving the are overpowering the dorsiflexors. Muscle cramps sacral and lumbar regions, the condition may pass or nerve paralysis may be responsible; the condi- unnoticed. This condition, called spina bifida occul- tion tends to develop in adults, and it gets progres- ta, can be detected only through X-ray or other sively worse with age. scanning procedures. Spina bifida occulta is very Congenital talipes equinovarus (“clubfoot”) results common, and it may affect 10 percent of the U.S. from an inherited developmental abnormality population. In some cases, the protective layers, or that affects 2 in 1000 births. Boys are affected meninges, that surround the spinal cord may bulge roughly twice as often as girls. One or both feet through the open vertebral laminae. The result is a may be involved, and the condition may be mild, prominent fluid-filled sac, or meningocele, beneath moderate, or severe. The underlying problem is the skin of the back. abnormal muscle development that distorts grow- The vertebral abnormalities in more severe ing bones and joints. Usually the tibia, ankle, forms of spina bifida are often associated with and foot are affected, and the feet are turned abnormal development of the spinal cord and asso- medially and inverted. The longitudinal arch is ciated nerves and muscles. Symptoms may range exaggerated, and if both feet are involved, the from mild problems with balance and movement to soles face one another. Prompt treatment with a general sensory and motor paralysis of the lower casts or other supports in infancy helps alleviate body. the problem, and fewer than half of the cases
    • The Skeletal System 59 require surgery. Kristi Yamaguchi, Olympic Gold factors have all been proposed. The synovial Medalist in figure skating, was born with this membrane becomes swollen and inflamed, a con- condition. ¯ dition known as synovitis (sª-n|–VI-tis). The car- tilaginous matrix begins to break down, and the process accelerates as dying cartilage cells release Rheumatism, Arthritis, lysosomal enzymes. and Synovial Function EAP p. 159 Advanced stages of inflammatory and degener- Rheumatism (ROO-muh-tizm) is a general term ative forms of arthritis produce an inflammation that indicates pain and stiffness affecting the that spreads into the surrounding area. Ankylosis, skeletal system, the muscular system, or both. common in the past when complete rest was rou- There are several major forms of rheumatism. tinely prescribed for arthritis patients, is rarely 6 ¯ Arthritis (ar-THRI-tis) includes all the rheumatic seen today. Regular exercise, physical therapy, and diseases that affect synovial joints. Arthritis drugs that reduce inflammation, such as aspirin or always involves damage to the articular cartilages, ibuprofen, can slow the progress of the disease. but the specific cause may vary. For example, Surgical procedures can realign or redesign the arthritis can result from bacterial or viral infec- affected joint, and in extreme cases involving the tion, injury to the joint, metabolic problems, or hip, knee, elbow, or shoulder, the defective joint autoimmune disorders. can be replaced by an artificial one. Joint replace- Proper synovial function depends on healthy ment has the advantage of eliminating the pain articular cartilages. When an articular cartilage and restoring full range of motion. Prosthetic (arti- has been damaged, the matrix begins to break ficial) joints, such as those shown in Figure A-21, down, and the exposed cartilage changes from a are weaker than natural ones and deteriorate in 10 slick, smooth gliding surface to a rough feltwork of or 15 years, but elderly people seldom stress them bristly collagen fibers. This feltwork drastically to their limits. increases friction, damaging the cartilage further. Eventually the central area of the articular carti- lage may completely disappear, exposing the Hip Fractures, Aging, underlying bone. and Professional Athletes EAP p. 165 Fibroblasts are attracted to areas of friction, and they begin tying the opposing bones together Today there are two very different groups of people with a network of collagen fibers. This network may suffering hip fractures: (1) individuals over age 60, later be converted to bone, locking the articulating whose bones have been weakened by osteoporosis, elements into position. Such a bony fusion, called and (2) young, healthy professional athletes, who ankylosis (an-ke-L«-sis), eliminates the friction subject their hips to extreme forces. When the and pain, but as a result movement becomes injury is severe, the vascular supply to the joint is impossible. damaged. As a result, two problems gradually The diseases of arthritis are usually considered develop: as either degenerative or inflammatory in nature. 1. Avascular necrosis: The mineral deposits in Degenerative diseases begin at the articular carti- the femur bones are turned over very rapidly, lages, and modification of the underlying bone and and osteocytes have high energy demands. A inflammation of the joint occur secondarily. reduction in blood flow, to the femoral heads Inflammatory diseases start with the inflammation especially, first injures and then kills the of synovial tissues, and damage later spreads to osteocytes. When bone maintenance stops in the articular surfaces. We will consider a single the affected region, the matrix begins to example of each type. break down. This process is called avascular ¯ Osteoarthritis (os-tƒ-|-ar-THRI -tis), also necrosis. known as degenerative arthritis or degenerative 2. Degeneration of articular cartilages: The chon- joint disease (DJD), usually affects older individu- drocytes in the articular cartilages absorb als. In the U.S. population, 25 percent of women nutrients from the synovial fluid, which circu- and 15 percent of men over 60 years of age show lates around the joint cavity as the bones signs of this disease. The condition seems to result change position. A fracture of the femoral neck from cumulative wear and tear on the joint sur- is usually followed by joint immobility and poor faces. Some individuals, however, may have a circulation to the synovial membrane. The genetic predisposition to develop osteoarthritis, for combination results in a gradual deterioration researchers have recently isolated a gene linked to of the articular cartilages of the femur and the disease. This gene codes for an abnormal form acetabulum. of collagen that differs from the normal protein in only 1 of its 1000 amino acids. In recent years, the frequency of hip fractures has Rheumatoid arthritis is an inflammatory increased dramatically among young, healthy pro- condition that affects roughly 2.5 percent of the fessional athletes, the best-known example being Bo adult population. The cause is uncertain, Jackson. At age 28 he was playing professional foot- although allergies, bacteria, viruses, and genetic ball with the LA Raiders and professional baseball
    • 60 The Body Systems: Clinical and Applied Topics (a) Shoulder (b) Hip (c) Knee Figure A-21 Artificial Joints for the Kansas City Royals—and starring in both After more than a year of rehabilitation, Bo sports. He was also the centerpiece for successful Jackson had surgery to replace the damaged joint advertising campaigns for sporting goods, using the with an artificial hip. In this “total hip” procedure, “Bo knows” slogan. But on January 13, 1991, the damaged portion of the femur was removed, things changed dramatically when Bo was tackled and an artificial femoral head and neck is attached near the sidelines in an NFL playoff game. The com- by a spike that extends into the marrow cavity of bination of pressure and twisting applied by the the shaft. Special cement may be used to anchor it tackler and the tremendous power of Bo’s thigh in place and to attach a new articular surface to muscles produced a fracture-dislocation of the hip. the acetabulum. After this procedure, Bo reentered Roughly 15 percent of the inferior acetabular fossa professional baseball for a short time as a desig- was broken away. The femur was not broken, but it nated hitter and occasional first baseman, but his was dislocated. Although he experienced severe speed was diminished. pain, the immediate damage to the femur and hip Joint replacement eliminates the pain and was sufficiently limited. restores full range of motion. However, prosthetic The initial optimism began to fade when it (artificial) joints, such as those shown in Figure became apparent that the complications of the A-21, are weaker than natural ones. They are injury were more damaging than the injury itself. usually implanted in older people who seldom The dislocation tore blood vessels in the capsule and stress them to their limits. Current models deteri- along the femoral neck, where the capsular fibers orate in 10 to 15 years, so young patients may attach. The result was avascular necrosis and the need multiple replacements. degeneration of the articular cartilages at the hip. CRITICAL-THINKING QUESTIONS physician diagnoses the fracture as a vertebral fracture most likely due to: 2-1. Diane, a 65-year-old woman, is brought a. osteomalacia into the emergency room by her daughter, Mary. b. osteomyelitis Diane has had severe back pain since she fell acci- c. osteoporosis dentally yesterday. Her daughter insists it was a d. Paget’s disease minor fall and is confused about the severity of the pain and tenderness over the thoracic spine. X-ray 2-2. Beth, a dentist, has a patient complaining studies of the thoracic vertebrae reveal fractures of of a toothache on the lower right side of his mouth. T 10 , T 11 , and T 12 . The X-rays also reveal a Examination shows severe tooth decay in the first decreased bone density in all the vertebrae. mandibular molar, with facial swelling along the Laboratory tests are within normal limits. The mandibular angle. Beth suspects an infection and
    • The Skeletal System 61 takes an X-ray that shows a reduction in bone den- stress had been applied during life. How old do you sity around the root of the decayed tooth. What is think these individuals were when they died, and the likely diagnosis? what does the skeletal information tell you about a. osteomalacia the lifestyle of the males? b. osteomyelitis 2-4. Lori suffers from a severe case of temporo- c. fracture of the mandible mandibular joint syndrome. What symptoms would d. tumor of the mandible you expect to observe as a result of this condition? 2-3. While studying a 2000-year-old campsite, 2-5. Two patients sustain hip fractures. In one an archeologist discovers several adult male and case, a pin is inserted into the joint and the injury female skeletons. Chemical analysis of the bones of heals well. In another, the fracture fails to heal. both sexes indicates that osteopenia had been Identify the types of fractures that are probably occurring for several years before their deaths. The involved. Why did the second patient’s fracture not male skeletons all showed heavy thickenings and heal, and what steps could be taken to restore nor- prominences in the bones of the upper limbs. The mal function? bones of the lower limbs were of normal size, and the markings indicated that only minimal muscle