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
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).
Viral infection Bone mass Ectopic bone formation
Paget's disease increases
osteoclast Increased Inherited conditions
Unknown cause activity osteoblast Marfan's syndrome
Osteopetrosis Total bone mass
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)
osteoblast Inherited conditions
osteoclast activating Bone mass
(Osteopenia) Hormonal disorders
Osteoporosis in post-
Inactivity menopausal women
Bed rest, paralysis, and elderly men
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.
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
Acromegaly Neuromuscular problems
Nutritional problems Osteoporosis (some forms) Muscular dystrophies
Osteomalacia Amyotrophic lateral
Spinal cord injuries
Aging process Fractures
Osteopenia Heterotopic bone
Anatomical problems Physiological problems
Cleft palate Marfan’s syndrome
Spina bifida Osteogenesis imperfecta
Abnormal spinal Achondroplasia
Aging process Rheumatoid
Osteoarthritis Systemic lupus
(some forms) erythematosus
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-
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
(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)
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
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
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)
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.
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
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
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.
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
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
intervertebral Spinal cord
• Slipped disc
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-
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
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?
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
bones of the lower limbs were of normal size, and
the markings indicated that only minimal muscle