Developmental Dysplasia of the Hip
Kier Maddox Blevins, MD, and Andrew K. Battenberg, MD
A 4-month-old girl is seen for her routine health maintenance visit. She is doing well and has no complaints. The results of the entire examination are within normal limits except for limited external rotation and abduction of the left hip, which is approximately 45°, in comparison to that of the right hip, which is almost 90°.
1. What factors are responsible for normal growth and development of the hip joint?
2. What specific physical maneuvers help in the evaluation of infants with decreased range of motion of the hip?
3. What are the clinical findings of hip dislocation during and after the neonatal period?
4. What are some conditions associated with hip dysplasia that may be noted on physical examination?
5. What is the appropriate diagnostic workup of infants with suspected hip dysplasia?
Developmental dysplasia of the hip (DDH) is a common pediatric orthopedic concern that requires a thorough understanding of normal development, pathoanatomy, natural history, and management. Although historically referred to as “congenital dislocation of the hip,” the term was changed because developmental dysplasia of the hip defines a spectrum of hip pathology, from congenital dysplasia of the hip, to partial dislocation of the femoral head (ie, hip subluxation), to acetabular dysplasia, to complete dislocation of the femoral head from the true acetabulum. Developmental dysplasia of the hip may exist at birth or manifest during infancy. In a newborn with true congenital dislocation of the hip, the femoral head dislocates into and out of the acetabulum. In an older child, the femoral head remains dislocated, resulting in secondary changes in the femoral head, the acetabulum, and the lateral pelvic wall where the displaced femoral head articulates with it. When DDH is recognized and managed appropriately, the affected child has the potential for normal development. If the diagnosis is missed or delayed, however, the child may suffer significant morbidity, including severe degenerative hip disease.
The prevalence of DDH is 1% to 7% of all live births. Ethnic variations exist; the incidence in Native American and black individuals is 76 and 0.06 per 1,000 live births, respectively. The literature indicates that pediatricians and orthopedic surgeons diagnose DDH in 8.6 per 1,000 live births and 1.5 in 1,000 live births, respectively. The use of ultrasonography in the evaluation of an infant with suspected DDH has resulted in the diagnosis of DDH in 25 in 1,000 live births. Hip instability in the neonate is estimated to range from 11.5 to 17 per 1,000 live births. Approximately 60% of these cases resolve by 1 week of age, and 90% resolve by 2 months of age. Approximately 60% of infants affected by DDH are firstborn.
Females are affected up to 7 times more frequently than males as result of estrogen-induced ligamentous laxity in utero. The prevalence of DHH is greater in infants with higher birth weights and those who are postmature. Approximately 20% of all DDH occurs in infants born in the breech position. A positive family history of DDH increases the risk by 10%. A female born in the breech position has a 1 in 35 chance of having DDH.
The left hip is involved in 60% of children with DDH and the right hip in 20%, and bilateral involvement occurs in 20% of such children. Developmental dysplasia of the hip has an increased association with lesions of mechanical molding, such as congenital torticollis (approximately 8% of affected children may have DDH), metatarsus adductus (approximately 2%–10% of these children may have DDH), and talipes calcaneovalgus.
The clinical presentation and signs of DDH in children vary with age. In neonates, diagnosis is made primarily by the physical examination (eg, Ortolani maneuver, Barlow maneuver). Classic signs of DDH in older infants are asymmetric skin folds, limitations demonstrated in hip abduction, and a positive Galeazzi sign, that is, unequal knee height when the patient is supine with both the hips and the knees flexed. Physical signs, which become more obvious after children are walking, include waddling gait, limping, and toe walking (Box 113.1).
Box 113.1. Diagnosis of Developmental Dysplasia of the Hip
•Positive family history or ethnicity
•Persistent hip asymmetry (eg, asymmetric skin folds, abduction of 1 hip and adduction of the other hip)
•Lower limb deformity (eg, limp, toe walking)
Developmental dysplasia of the hip encompasses a wide variety of conditions ranging from hip instability to dislocation. Normal growth and development of the hip joint is dependent on a genetically determined balance of growth of the acetabular and triradiate cartilages and a well-located and centered femoral head. In a normal hip at birth, a tight articulation exists between the femoral head and acetabulum; however, in DDH or dislocation, this tight articulation is absent. Dysplasia refers to either a hip that is dislocated but can be relocated, or a hip with a positive Ortolani sign (ie, it can be dislocated on provocation). The term dislocation refers to any hip with a negative Ortolani sign, that is, the hip is not reducible and is associated with secondary adaptive changes, such as shortening, decreased abduction, and asymmetric skin folds.
Dysplasia of the acetabulum is also associated with hip instability. The dysplastic acetabular cavity is more shallow, with a more vertical inclination angle (Figure 113.1). Although most dislocations occur at or near the time of delivery, this abnormal development of the acetabular cavity helps explain why dislocations can also occur later in infancy. Late hip dislocations are reported in 3% to 8% of affected infants.
The etiology of DDH is poorly defined but is thought to be multifactorial, involving genetic and intrauterine environmental factors. Newborns with a first-degree relative with a history of DDH have a 12-fold increased risk of DDH. The primary intrauterine environmental factors are tight maternal abdominal and uterine musculature; breech presentation, which causes abnormal hip flexion and resulting dislocation of the femoral head; and positioning of the fetal hip against the mother’s sacrum, causing increased femoral adduction and resulting in dislocation of the femoral head. In utero mechanical factors relate to molding and restriction of fetal movement. It is believed that the tight, unstretched maternal abdomen and uterine musculature of the primigravida may restrict fetal movement, thereby predisposing firstborn infants to DDH. The increased occurrence of other conditions thought to be secondary to molding (eg, congenital muscular torticollis) with DDH supports this theory of space restriction. Physiologic factors are related to ligamentous laxity and inherent instability of the hip at birth. In utero, a growth rate discrepancy exists between the femoral head and the acetabulum. The femoral head grows more rapidly, and at birth only 50% of the femoral head is covered by the acetabulum. Additionally, diffuse ligamentous laxity exists in the final 4 weeks of gestation in preparation for birth, including laxity of the hip capsule. Female infants may be even more sensitive to maternal hormones, such as estrogen and relaxin, which are thought to be responsible for this generalized physiologic laxity. Environmental factors that may predispose infants to DDH include swaddling with the legs in extension and adduction, which is still practiced in some societies (eg, use of cradleboards by Navajo individuals in North America). Such swaddling was also practiced in Japan until 1975, and after teaching proper swaddling methods, the incidence of DDH decreased fivefold. Other factors include muscle contractures resulting from neuromuscular disease, such as cerebral palsy.
Figure 113.1. Illustration shows the increased inclination angle characteristic of developmental dysplasia of the hip. The more vertical orientation of the acetabulum (compared with normal) results in a less stable hip articulation.
The differential diagnosis of hip dysplasia depends on the age of the child and the presenting complaint. An infant may have a “click” on abduction of the hip that represents the snapping of a ligament rather than the reduction of the dislocated hip into the joint. An infant with limited abduction may have a neuromuscular disorder, such as spastic diplegia, a form of cerebral palsy that affects the lower extremities. The older child who presents with a gait disturbance, such as limp, waddling gait, or toe walking, may have a neuromuscular condition, fracture, or infection (eg, osteomyelitis, septic arthritis).
Family history of DDH should be reviewed, and a careful neonatal history should be obtained, including presentation (eg, breech versus vertex), type of delivery, history of prenatal problems (eg, oligohydramnios), history of neuromuscular disorders (eg, cerebral palsy) and presence of congenital torticollis or metatarsus adductus (Box 113.2).
Box 113.2. What to Ask
Developmental Dysplasia of the Hip
•Was the infant in a breech presentation?
•Does the child have any muscular problems, such as torticollis?
•When did the gait disturbance begin?
•Does anything make the child’s gait better or worse?
•Is the child in any pain?
•Did any member of the family have hip dysplasia?