1102
U N I T 1 2
Musculoskeletal Function
The clinical manifestations of osteogenesis imperfecta
include a spectrum of disorders marked by extreme skel-
etal fragility. Four major subtypes of the disorder have
been identified
18
(Table 43-2). The disorder is character-
ized by thin and poorly developed bones that are prone
to multiple fractures. These children have short limbs
and a soft, thin cranium with bifrontal prominences that
give a triangular appearance to the face. Other prob-
lems associated with defective connective tissue synthe-
sis include thin skin, blue or gray sclera, abnormal tooth
development, hypotonic muscles, loose-jointedness, sco-
liosis, and a tendency toward hernia formation. Hearing
loss due to otosclerosis of the tiny bones in the middle
ear is common in affected adults.
The most serious defects occur when the disorder is
inherited as a recessive trait (type II). Severely affected
fetuses have multiple intrauterine fractures and bowing
and shortening of the extremities. Many of these infants
are stillborn or die during infancy. Less severe forms
occur when the disorder is inherited as a dominant trait.
The skeletal system is not as weakened, and fractures
often do not appear until the child becomes active and
starts to walk, or even later in childhood. These frac-
tures heal rapidly, although with a poor-quality callus.
In some cases, parents may be suspected of child abuse
when the child is admitted to the health care facility
with multiple fractures. There also is an increased inci-
dence of complications such as hernias and congenital
heart abnormalities.
There is no definitive treatment for correction of
the defective collagen synthesis that is characteristic
of osteogenesis imperfecta. However, a short course of
treatment with bisphosphonates has been shown to pro-
duce an increase in cortical bone width and cancellous
bone volume, as well as increased bone strength and
mineral content. In children treated with intravenous
pamidronate, this has led to a decrease in fractures,
improvements in mobility, and less pain.
62
Prevention
and treatment of fractures is important. Precise align-
ment is necessary to prevent deformities. Nonunion is
common, especially with repeated fractures. Surgical
intervention often is needed to stabilize fractures and
correct deformities (e.g., internal fixation of long bones
may be done with an intramedullary rod that “grows”
with the child).
Developmental Dysplasia of the Hip
Developmental dysplasia of the hip (DDH), formerly
known as
congenital dislocation of the hip,
is an abnor-
mality in hip development that leads to awide spectrumof
hip problems in infants and children, including hips that
are unstable, malformed, subluxated, or dislocated.
63–65
In less-severe cases, the hip joint may be unstable, with
excessive laxity of the joint capsule, or subluxated, so
that the joint surfaces are separated and there is a partial
dislocation (Fig. 43-19). With dislocated hips, the head
of the femur is located outside of the acetabulum.
The results of newborn screening programs have
shown that 1 of 250 infants have some evidence of hip
instability, whereas actual dislocation of the hip is less
common, being found in 1 to 1.5 of every 1000 live
births.
55
The left hip is involved more frequently than
the right hip because of the left occipital intrauterine
positioning of most infants. The disorder occurs most
frequently in first-born children and is six times more
common in female than in male infants. The cause of
DDH is multifactorial, with heredity, environmental, and
mechanical factors playing a role. A positive family his-
tory and generalized laxity of the ligaments are related.
The increased frequency in girls is thought to result from
their susceptibility to maternal estrogens and other hor-
mones associated with pelvic relaxation. Dislocation
also may result from environmental factors such as fetal
position, a tight uterus that prevents fetal movement,
and breech delivery. The presence of other congenital
abnormalities is associated with an increased incidence
TABLE 43-2
Types of Osteogenesis Imperfecta
Type Subtype
Inheritance
Major Features
I
Postnatal fractures, blue sclera
Autosomal dominant
Normal stature, skeletal fragility, hearing
impairment, joint laxity, blue sclera
II
Perinatal, lethal
Autosomal recessive
Death in utero, or during infancy
Skeletal deformity with excessive
fragility, multiple fractures, blue sclera
III
Progressive deformity
Autosomal dominant (75%)
Autosomal recessive (25%)
Growth retardation, multiple fractures,
progressive kyphoscoliosis, hearing
impairment, blue sclera at birth
IV
Postnatal fractures, normal sclera
Autosomal dominant
Moderate skeletal fragility, short stature
Developed from Kumar V, Abbas AK, Fausto N, et al. Robbins & Cotran Pathologic Basis of Disease. 8th ed.
Philadelphia, PA: Elsevier Saunders; 2010:1212.
Capsule
Normal
Subluxated
“dislocatable”
Dislocated
FIGURE 43-19.
Normal (left) and abnormal relationships of hip
joint structure in subluxation (middle) and dislocation (right).
