C h a p t e r 4 3
Disorders of the Skeletal System: Trauma, Infections, Neoplasms, and Childhood Disorders
1091
Bone Infections and
Osteonecrosis
Bone like other body tissues is susceptible to infection
due to invasion by microorganisms. It also is susceptible
to osteonecrosis (bone death) when it loses its blood
supply.
Infections—Osteomyelitis
Osteomyelitis represents an acute or chronic infection
of the bone and marrow.
18,19
Despite the common use of
antibiotics, bone infections remain difficult to treat and
eradicate. All types of organisms, including parasites,
viruses, bacteria, and fungi, can cause osteomyelitis, but
certain pyogenic bacteria and mycobacteria are the most
common.
Pyogenic Osteomyelitis
Pyogenic osteomyelitis is almost always caused by
bacteria. Organisms may reach the bone by seed-
ing through the bloodstream (hematogenous spread),
direct penetration or contamination of an open fracture
or wound (exogenous origin), or extension from a
contiguous site.
The specific agents isolated in pyogenic bacterial
osteomyelitis are often associated with the age of the per-
son or the inciting condition (e.g., trauma or surgery).
Staphylococcus aureus
is the most common cause, but
organisms such as
Escherichia coli, Neisseria gonor-
rhoeae, Haemophilus influenzae,
and
Salmonella
species
are also seen.
19,20
Staphylococcus aureus
has two charac-
teristics that favor its ability to produce osteomyelitis: (1)
it has the ability to produce a collagen-binding adhesion
molecule that allows it to adhere to the connective tis-
sue elements of bone, and (2) it has the ability to evade
host defenses, attack host cells, and colonize bone per-
sistently.
31
Also, infection caused by methicillin-resistant
S. aureus
is becoming an increasingly common problem.
31
Hematogenous Osteomyelitis.
Hematogenous osteo-
myelitis originates with infectious organisms that reach
the bone through the bloodstream.
8,19,20,30–32
Acute
hematogenous osteomyelitis occurs predominantly in
children. In adults, it is seen most commonly in debili-
tated persons and in those with a history of chronic skin
infections, chronic urinary tract infections, and intrave-
nous drug use and in those who are immunologically
suppressed. Intravenous drug users are especially at risk
for infections with
Streptococcus
and
Pseudomonas.
The pathogenesis of hematogenous osteomyelitis dif-
fers in children and adults.
30
In children, the infection
usually affects the long bones of the appendicular skele-
ton. It starts in the metaphyseal region close to the growth
plate, where termination of nutrient blood vessels and
sluggish blood flow favor the attachment of blood-borne
bacteria (Fig. 43-8). With advancement of the infection,
purulent exudate collects in the rigidly enclosed bony tis-
sue. Because of the bone’s rigid structure, there is little
room for swelling and the purulent exudate finds its way
beneath the periosteum, shearing off the perforating
arteries that supply the cortex with blood, thereby lead-
ing to necrosis of cortical bone. The necrotic bone that is
formed may separate from the viable surrounding bone
■■
The complications of fractures include a loss
of skeletal continuity (malunion or nonunion),
pressure from swelling and hemorrhage (fracture
blisters and compartment syndrome), and
fat embolism syndrome (FES). Compartment
syndrome is a condition of increased pressure in
a muscle compartment that compromises blood
flow and potentially leads to death of nerve
and muscle tissue. Fat embolism syndrome is a
constellation of signs and symptoms including
a petechial skin rash, respiratory failure, and
cerebral dysfunction due to the presence of fat
droplets in small blood vessels after a fracture.
Sinuses
Trapped
necrotic bone
(sequestrum)
Periosteum
Reactive bone
(involucrum)
A
B
C
FIGURE 43-8.
Hematogenous osteomyelitis.
(A)
Infectious organisms reach the metaphysis through
a nutrient blood vessel.
(B)
Bacterial growth results in bone destruction and abscess formation. From
the abscess cavity, the infection spreads between the trabeculae into the medullary cavity of compact
bone and then through the cortex to the outside.
(C)
The purulent exudate finds its way beneath the
periosteum, shearing off the perforating arteries that supply the cortex with blood, thereby leading to
necrosis of cortical bone and formation of devascularized fragments, called sequestra.
