Porth's Essentials of Pathophysiology, 4e

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Musculoskeletal Function

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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 Death in utero, or during infancy Skeletal deformity with excessive fragility, multiple fractures, blue sclera Growth retardation, multiple fractures, progressive kyphoscoliosis, hearing impairment, blue sclera at birth Moderate skeletal fragility, short stature

II

Perinatal, lethal

Autosomal recessive

III

Progressive deformity

Autosomal dominant (75%) Autosomal recessive (25%)

IV

Postnatal fractures, normal sclera

Autosomal dominant

Developed from Kumar V, Abbas AK, Fausto N, et al. Robbins & Cotran Pathologic Basis of Disease. 8th ed. Philadelphia, PA: Elsevier Saunders; 2010:1212.

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

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).

Capsule

Normal

Subluxated “dislocatable”

Dislocated

FIGURE 43-19. Normal (left) and abnormal relationships of hip joint structure in subluxation (middle) and dislocation (right).