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U N I T 1 2
Musculoskeletal Function
The calcium and free fatty acids form lesions composed
of an insoluble “soap.” Because bone lacks mechanisms
for resolving the infarct, the lesions remain for life.
The symptoms associated with osteonecrosis are
varied and depend on the site and extent of infarction.
Typically, subchondral infarcts cause chronic pain that
is initially associated with activity but that gradually
becomes more progressive until it is experienced at rest.
Subchondral infarcts often collapse and predispose the
patient to severe secondary osteoarthritis.
Diagnosis of osteonecrosis is based on history, physical
findings, radiographic findings, and the results of special
imaging studies, including CT scans and technetium-99m
bone scans. Treatment depends on the underlying patho-
logic process. In some cases, only short-term immobili-
zation, nonsteroidal anti-inflammatory drugs, exercises,
and limitation in weight bearing are used. Osteonecrosis
of the hip is particularly difficult to treat. In persons with
early disease, limitation of weight bearing through the
use of a walker may allow the condition to stabilize.
Although several surgical approaches have been used,
the most definitive treatment of advanced osteonecrosis
of the knee or hip is total joint replacement.
SUMMARY CONCEPTS
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Osteomyelitis, or infection of the bone and
marrow, may be caused by a wide variety of
microorganisms introduced during injury,
operative procedures, or from the bloodstream.
Acute osteomyelitis is seen most often as a result
of direct contamination of bone by a foreign
object. Chronic osteomyelitis represents an
infection that continues beyond 6 to 8 weeks and
may persist for years. Tuberculosis osteomyelitis,
which is characterized by bone destruction
and abscess formation, is caused by spread of
infection from the lungs or lymph nodes.
■■
Bone infections are difficult to treat and eradicate.
Measures to prevent infection include careful
cleaning and debridement of skeletal injuries and
strict operating room procedures.
■■
Osteonecrosis, or death of a segment of bone,
is due to an interruption in blood flow rather
than an infection.The mechanisms are varied
and include mechanical interruption such as
occurs with a fracture, vessel injury, increased
intraosseous pressure with vascular compression,
and corticosteroid therapy. Sites with poor
collateral circulation, such as the femoral head,
are most commonly affected. Symptoms include
pain that varies in severity, depending on the
extent of infarction.Total joint replacement is the
most frequently used treatment for advanced
osteonecrosis.
Neoplasms
Neoplasms of the skeletal system, often referred to as
bone tumors
, may be benign or malignant, and in the
case of malignant neoplasms, may represent a primary
tumor or secondary metastatic lesion.
5,8,18,19,41
Benign
tumors greatly outnumber their malignant counterparts
and occur with the greatest frequency in the first three
decades of life, whereas in the elderly a bone tumor is
more likely to be malignant.
Both benign and malignant tumors can develop from
the cartilage (chondrogenic), bone (osteogenic), and sup-
porting (fibrogenic) elements of bone, and bone tumors
are generally classified according to their tissue coun-
terpart. As a group, these tumors affect all age groups
and arise in virtually every bone. Most develop during
the first several decades of life and have a propensity to
originate in the long bones of the extremities; however,
certain types of tumors target specific age groups and
anatomic sites. Thus, the location of the tumor provides
important diagnostic information.
There are three major manifestations of bone tumors:
pain, presence of a mass, and impairment of function.
5,8
Although benign tumors are frequently asymptomatic
and are detected as an incidental finding, malignant
tumors are associated with constant, deep aching pain
that does not go away with rest and is present at night.
However, certain benign tumors also cause night pain.
A mass or hard lump may be the first sign of a bone
tumor. A malignant tumor is suspected when a painful
mass exists that is enlarging or eroding the cortex of
the bone. The ease of discovery of a mass depends on
the location of the tumor; a small lump arising on the
surface of the tibia is easy to detect, whereas a tumor
that is deep in the medial portion of the femur may
grow to a considerable size before it is noticed. Benign
and malignant tumors may cause the bone to erode to
the point where it cannot withstand the strain of ordi-
nary use. A sudden increase in pain followed by trivial
trauma that is preceded by a history of mild, dull aching
pain is suggestive of a pathologic fracture. A tumor also
may produce pressure on a peripheral nerve, causing a
decreased sensation, numbness, a limp, or limitation in
movement.
The diagnosis of bone tumors relies on the history and
physical examination, as well radiography, computed
tomography, andMRI. Radiographs give themost general
diagnostic information, such as malignant versus benign
and primary versus metastatic status. The radiograph
demonstrates the region of bone involvement, extent of
destruction, and amount of reactive bone formed. CT
scans further aid diagnosis and anatomic localization
and can identify small pulmonary metastases not seen by
conventional radiographs. Magnetic resonance imaging
is the most accurate method of evaluating the intramed-
ullary extent of bone tumor and can demarcate the soft
structures in relation to neurovascular structures with-
out the use of contrast media. It is best used in conjunc-
tion with a CT scan. Radionuclide bone scans are used to
assess for metastasis. A biopsy may be done to determine
the histologic characteristics of the tumor.
