|
|
In the elderly,
fractures are a major cause of morbidity and mortality. Most result from low-energy
injuries and involve bone weakened by osteoporosis or other pathologic processes. Compared
with fractures in younger people, fractures in the elderly occur more often, in different
locations within the bone, and in different patterns. The prognosis for uncomplicated
healing also differs in the elderly, who have a greater tendency to develop joint
stiffness from immobilization and medical complications from enforced bed rest.
Consequently, treatment goals in the elderly emphasize a rapid return to the activities
necessary for independent living rather than a restoration of perfect limb alignment or
length using prolonged casting or traction.
Most elderly people do not need to perform
strenuous work, and high-strength functional capabilities are not a priority. Because they
place less stress on the musculoskeletal system, many older people do well with a fracture
alignment or a prosthetic replacement that would be unsuitable in younger patients.
Descriptive and Anatomic Terms
A typical long bone is divided into three
anatomic regions: the diaphysis, or shaft, consists of a tube of cortical
bone surrounding a medullary cavity of hematopoietic or fatty marrow; the epiphysis
lies at the end of the bone between the growth plate, or physis, and the articular
surface; the metaphysis is the intermediate, flared region joining the
other two. The skeleton consists of two forms of bone: trabecular and cortical.
Most of the metaphysis and epiphysis is composed of trabecular, or porous, bone, which
varies widely in density and strength, depending on age, skeletal location, and associated
pathologic conditions (eg, osteoporosis). The diaphysis is composed of cortical, or
lamellar, bone. Its dense histologic architecture of parallel haversian systems gives it
great strength.
Standard terminology facilitates the description
of fracture patterns. Proximal, midshaft, and distal describe the location. The
orientation of a fracture line may be transverse, oblique, or spiral. Comminution refers
to fragmentation. Open or closed indicates whether or not the fracture communicates to the
outside through a soft tissue wound. (The archaic terms "simple" and
"compound" should be avoided.) Alignment refers to the relative position of the
main fracture fragments. Their apex may point anteriorly, posteriorly, laterally (varus
angulation), or medially (valgus angulation). The bone ends may be overriding, distracted,
or impacted.
Incidence and Epidemiology
In 1990, about 281,000 hip fractures occurred in
the USA. As the population ages, the problem continues to grow. Census projections
indicate that by 2000, about 340,000 hip fractures will occur annually, about half of them
in those age 85 and older. One in three women and one in six men who live to age 90 will
sustain a hip fracture. In the year following the fracture, the mortality rate increases
by 15%. Of functionally independent patients who live at home before the fracture, 20%
require institutional care for more than a year, and another 30% become dependent on
mechanical aids or assistive personnel.
With advancing age, the incidence of certain
kinds of fractures increases. Long bone shaft fractures, which involve predominantly
cortical bone, do not correlate with age. In contrast, the incidence of vertebral body and
hip fractures is low until the fifth and sixth decades of life, when it increases
dramatically. Fractures of the proximal humerus and tibia, wrist, and pubic rami follow a
similar pattern. These fractures that occur increasingly with age involve predominantly
trabecular bone.
Etiology and Pathophysiology
The most common cause of fractures, falls
account for about 90% of geriatric hip, forearm, and pelvic fractures. The frequency of
falls among the elderly results in part from a high incidence of underlying medical
conditions: failing vision, neurologic diseases and their sequelae, arthritis that impairs
leg function, orthostatic hypotension, and the use of sedatives and other medications.
Also, slowed reflexes, decreased muscle strength, and impaired coordination may reduce
older people's ability to protect themselves from the impact of falls, increasing the
likelihood of fractures. Most fractures in the elderly result from the relatively
low-energy trauma incurred by a fall on level ground.
Pathologic fracture refers to any
fracture involving abnormal (weakened) bone, eg, from underlying malignancy, benign
bone tumor, metabolic disorder, infection, or osteoporosis. Thus, a pathologic fracture
should be suspected in any patient who sustains a fracture after minimal trauma. Usually,
the patient will have a history of progressively increasing pain in the affected region,
especially noticeable at night and on weight bearing. Diagnosing pathologic fracture is
important because the choice of treatment and prognosis may depend on the underlying
pathologic condition.
Occasionally, patients present with an impending
pathologic fracture, in which the bone has not yet broken entirely. Such patients feel
pain in the affected area when using the limb. For instance, a patient with a lesion of
the femur may feel thigh pain when rising out of a chair. Prophylactic internal fixation
of such fractures with metal plates, rods, or prostheses is often indicated to prevent
displacement, provide pain relief, and preserve function. If the impending fracture breaks
through completely and becomes displaced, treatment can be considerably more difficult,
with decreased function and increased morbidity.
Most skeletal malignancies are metastatic
lesions, with the breast, lung, prostate, gastrointestinal tract, kidney, and
thyroid being the most common primary sites. The typical x-ray shows multiple lytic
lesions. All these tumors can produce lucencies on x-ray; prostatic and breast metastases
may also produce sclerosis. Primary bone malignancies occur much less
frequently. Multiple myeloma and lymphoma are the most common; osteosarcoma, fibrosarcoma,
and chondrosarcoma are rare. Osteosarcoma occurs more commonly in people with Paget's
disease, however.
Osteopenia, or abnormally
decreased bone density, results from four conditions that are indistinguishable on x-ray
but involve different pathologic processes: osteoporosis, due to too
little bone; osteomalacia, due to decreased mineralization; hyperparathyroidism,
which causes increased resorption; and myeloma, which destroys bone.
Thus, patients with osteopenia require laboratory evaluation to identify the underlying
condition.
Biomechanics
The force required to break a bone depends on
both its material properties and its geometry. Material properties determine the force per
unit area required to cause material failure. These properties are referred to as ultimate
tensile or ultimate compressive strength (expressed in megapascals [MPa], with 1 MPa equal
to 145 lb/sq in).
The ultimate tensile strength of cortical bone
decreases only slightly with aging from about 140 MPa in the second decade to about 120
MPa in the eighth decade. With age, the diameter of the diaphysis increases as bone is
resorbed from the inner, or endosteal, surface and is added to the outer, or periosteal,
surface. This change increases the resistance of the diaphysis to bending forces and
compensates for the decreased strength of the cortical bone. Thus, fractures of the
diaphysis do not occur more frequently with advancing age.
The ultimate compressive strength of trabecular
bone is proportional to its density and ranges between 1 and 10 MPa. Since normal
cancellous bone has a density > 1.4 gm/cm3, a density of
1 gm/cm3 represents a halving of strength. An increased rate of
fracture of the vertebrae and ends of the femur does not occur until bone density falls
below 1 gm/cm3. This loss of bone density is usually caused by
osteoporosis. Most fractures in the elderly occur in the metaphyseal region, which does
not remodel with age and thus does not compensate for the decreased density of the
trabecular bone.
Normal Healing
Clinical management of fractures is based on an
understanding of the physiology of bone repair. Fracture healing can be divided into three
overlapping phases: inflammation, repair, and remodeling.
The inflammatory phase includes
the initial response to injury and lasts several days. The trauma that fractures the bone
also injures the surrounding blood vessels, muscles, and other soft tissues. Hemorrhage at
the fracture site results in a hematoma. Traumatic devascularization of the fractured ends
and bony fragments may result in nonviable or necrotic bone. This necrotic material
elicits an immediate and intense acute inflammatory reaction. The fracture site is swollen
and tender.
The reparative phase begins
within 24 h after the injury and reaches peak activity after 1 to 2 wk. Diaphyseal
fractures that are not rigidly stabilized heal by formation of rapidly created new bone
around the fracture site called the external callus. External callus is
not visible radiographically until about 3 to 6 wk after the injury. Until sufficient
external callus forms and provides stability--a process that can take several months in
long-bone fractures--collapse and displacement of the fracture can occur. Metaphyseal
fractures heal by direct union of the trabecular bone, a faster process that begins within
2 to 3 wk.
During the remodeling phase,
the rapidly formed callus is slowly resorbed and replaced by mechanically stronger bone
distributed to best resist load-bearing stresses. These events proceed slowly in the
elderly and may result in many months of discomfort after a fracture. |