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Developmental Dysplasia of the Hip
Victoria L. Franklin, MD
Developmental dysplasia of the hip (DDH) is a disorder that may be detected in neonates. The hips at birth are rarely dislocated but rather "dislocatable." Dislocations tend to occur after delivery. The cause of DDH is multifactorial, having both physiologic and mechanical factors. The positive family history (20%) and the generalized ligamentous laxity are related etiologic factors. The majority of children with DDH have generalized ligamentous laxity, and this can predispose to hip instability. Maternal estrogens and other hormones associated with pelvic relaxation result in further, although temporary, relaxation of the newborn hip joint. There is also a 9:1 female predominance.
Approximately 60% of children with typical DDH are firstborn, and 30-50% developed in the breech position. The frank breech position with the hips flexed and the knees extended is the position of highest risk. The breech position results in extreme hip flexion and limitation of hip motion. Increased hip flexion results in stretching of the already lax capsule and ligament teres. It also produces posterior uncoverage of the femoral head. Decreased hip motion leads to a lack of normal development of the cartilaginous acetabulum.
There is also an association of congenital muscular torticollis (14-20%) and metatarsus adductus (1-10%) with DDH. The presence of either condition requires a careful examination of the hips.
Postnatal factors are also important determinants. Maintaining the hips in the position of adduction and extension may lead to dislocation. This puts the unstable hip under pressure because of the normal hip flexion and abduction contractures. An unstable femoral head, as a consequence, can be displaced from the acetabulum over several days or weeks.
Because hips are not dislocated at birth, the components of the hip joint, excluding the hip capsule and ligamentum teres, are relatively normal. There may be some variations in the shape of the cartilaginous acetabulum, especially if the child developed in a breech position. If a dislocation is allowed to occur, then acetabular dysplasia and maldirection, excessive femoral anteversion (torsion), and hip muscle contractures will develop.
The Barlow test is the most important maneuver in examining the newborn hip. This provocative test to dislocate an unstable hip is performed by stabilizing the pelvis with one hand and then flexing and adducting the opposite hip and applying a posterior force. If the hip is dislocatable, it is usually readily felt. After release of the posterior force, the hip will usually spontaneously relocate. It has been estimated that only 1 in 100 newborn infants have clinically unstable hips (subluxation or dislocation), whereas only one in 800 to 1,000 of these infants eventually experience a true dislocation. The Ortolani test is a maneuver to reduce a recently dislocated hip. It is most likely to be positive in infants who are 1-2 mo of age because adequate time must have passed for the true dislocation to have occurred. In performing this test, the thigh is flexed and abducted, and the femoral head is lifted anteriorly into the acetabulum. If reduction is possible, the relocation will be felt as a "clunk," not a "click." After 2 mo of age, manual reduction of a dislocated hip is usually not possible because of the development of soft tissue contractures.
Limitation of hip abduction is indicative of soft tissue contractures and may indicate DDH. Conversely, hip abduction contractures may indicate dysplasia of the contralateral hip. An asymmetric number of thigh skinfolds and apparent shortening of an extremity, uneven knee levels, when the supine infant's feet are placed together on the examining table with the hips and knees flexed (Galeazzi sign) indicate DDH with proximal displacement of the femoral head. Absent normal knee flexion contracture also occurs.
A common concern is the presence of hip clicks in infants. Hip clicks per se are usually not pathologic and are secondary to (1) breaking the surface tension across the hip joint, (2) snapping of gluteal tendons, (3) patellofemoral motion, or (4) femorotibial (knee) rotation.
In older or walking children, complaints of limping, waddling, increased lumbar lordosis, toe walking, and leg-length discrepancy may indicate an unrecognized DDH.
Hip stability as well as acetabular development may accurately be assessed by ultrasonography. Radiographic evaluation in older infants and children includes anteroposterior and Lauenstein (frog) lateral radiographs of the pelvis. The ossific nucleus of the femoral head does not appear until 3-7 mo of age, and it may be further delayed in DDH. Line measurements are usually made to determine the relationship of the femoral head to the acetabulum (acetabular index, quadrant assessment, Shenton line, and the center edge angle of Wiberg) . Arthrography, computed tomography, and magnetic resonance imaging (MRI) scans may be beneficial in difficult cases, especially in those involving older infants and children.
The treatment of DDH should be individualized and depends on the patient's age and whether the hip is subluxated or dislocated.
When an unstable hip is recognized at birth, maintenance of the hip in the position of flexion and abduction ("human" position) for 1-2 mo is usually sufficient. This position maintains reduction of the femoral head and allows for tightening of the ligamentous structures as well as for stimulation of normal growth and development. Methods that can be used to maintain the hip in this position include Pavlik harness, Frejka splint, and a variety of abduction orthoses. Double and triple diapers, although controversial, are commonly used in infants with dislocatable hips because the latter devices usually do not fit satisfactorily. Treatment is continued until there is clinical stability of the hip and ultrasonographic or radiographic measurements are normal.
During this age, a true dislocation may develop. As a consequence, treatment is directed toward reduction of the femoral head into the acetabulum. The Pavlik harness is the major mode of treatment in this age group. The harness attempts to place the hips in the human position by flexing them more than 90 degrees (preferably 100-110 degrees) and maintaining relatively full but gentle abduction (50-70 degrees). This redirects the femoral head toward the acetabulum. Usually, spontaneous relocation of the femoral head will occur within 3-4 wk. The Pavlik harness is approximately 95% successful in dysplastic or subluxated hips and 80% successful in true dislocations. If reduction is achieved, the harness is continued until radiographic parameters have returned to normal. If a spontaneous reduction does not occur, then a surgical closed reduction is indicated. This consists of (1) preliminary skin traction for 1-3 wk to bring the femoral head opposite the acetabulum, (2) percutaneous adductor tenotomy, (3) closed reduction, (4) arthrogram to assess the concentricity of the reduction, and (5) application of a hip spica cast in the "human" position. Treatment is continued until the radiographic parameters are within normal limits.
In the older infant, surgical closed reduction is the major method of treatment. If the reduced hip shows significant residual instability, an open reduction may be indicated. This can be through a medial or anterior approach.
After 18 mo of age, the progressive deformities are so severe that open reduction followed by pelvic (innominate) osteotomy, femoral osteotomy, or both are necessary to realign the hip. A femoral shortening derotation osteotomy is performed concomitantly if the reduction is tight, if there is excessive femoral anteversion, or if the child is 3 or 4 yr of age or older. Postoperatively, a hip spica cast is worn for 6-8 wk to allow for healing. Thereafter, the child may be permitted to return to full activities gradually. Implanted metal is removed shortly after healing to prevent incorporation into the growing bone. Eighteen months of age is not an arbitrary age for these procedures. It has been demonstrated that approximately 25% of children who have a closed reduction performed between 9 and 12 mo of age, 50% who have one between 12 and 18 mos, and 75% who have one between 18 and 36 mos will have residual acetabular dysplasia requiring a pelvic or femoral osteotomy at a later date.
The most important and severe complication of DDH is avascular necrosis of the CFE. This is an iatrogenic complication; reduction of the femoral head under pressure produces cartilaginous compression, and this can result in occlusion of the intra-articular, extraosseous epiphyseal vessels and produce CFE infarction, either partial or total. Revascularization follows, but abnormal growth and development may occur, especially if the physis is severely damaged. The hip is very vulnerable to this complication before the development of the ossific nucleus (4-6 mo). The management outlined previously is designed to minimize this complication; with appropriate use of these treatments, the incidence of avascular necrosis will be approximately 5-15%. Other potential complications in DDH include redislocation, residual subluxation or acetabular dysplasia, and postoperative complications such as wound infections.