Developmental dysplasia of the hip (DDH), or congenital dislocation of the hip, is relatively uncommon. Failure to diagnose the condition during early infancy is associated with worse outcomes and the need for more complex surgical intervention to correct it. If untreated, DDH can lead to deterioration of the hip, arthritis, and disability. Primary care PAs are ideally situated to identify DDH early among infants and ensure that prompt intervention is made. In infants, diagnosis of DDH is usually made by physical examination. Neither radiography nor ultrasonography (US) is reliably diagnostic in newborns.1 In the first 6 to 8 weeks of life, DDH can be treated with a simple brace. If that golden period is missed, however, treatment is much more difficult. Examination of the infant's hip can be challenging. This article will review DDH and focus on practical tips for examination of the infant hip.
The term developmental dysplasia of the hip applies to a group of disorders that range from subtle growth disturbance to dislocation, which can be complete (luxation) or partial. Subluxation, or partial dislocation, refers to instability in which the femoral head moves in and out of the socket.1 The classic case is a newborn female delivered in a breech position with a dislocated hip, but not all cases occur at birth.2,3
The hip is fully formed by the 11th week of fetal life.3,4 Proper growth of the acetabulum requires the presence of a spherical femoral head.5,6 In dysplasia, this relationship is altered, leading to deformity and/or instability. In the typical case of DDH, the hip forms normally but dislocates around the time of birth. Once normal articulation between femur and acetabulum is disturbed, the acetabulum grows more saucerlike and the femoral head becomes flattened.
The extent of deformity varies widely. In 98% of DDH cases, pathologic changes are reversible. Normal positioning restores proper loading forces and stimulation, so normal growth resumes.3,5-7 Only about 2% of cases manifest with dysplasia that is severe and irreversible. Usually associated with neuromuscular abnormalities, arthrogryposis, or myelomeningocele, these “teratologic dislocations” are often fixed and high.3,8
CAUSES OF DDH
Hip dysplasia is multifactorial. Strong genetic and ethnic influences exist. Familial predisposition is clear.1,3,9 Hip dysplasia is rare among the African Bantu and southern Chinese9-11 but common among the Inuits and Navajos.12,13
Intrauterine mechanical factors are also important. Babies born in the breech position have a considerably higher incidence of DDH. Prolonged malpositioning can stretch the hip capsule, allowing dislocation. Capsular laxity decreases hip stability because the socket is quite shallow at birth.14 Females are more susceptible than males to the effects of the maternal hormone relaxin, which may increase capsular laxity, possibly accounting for the preponderance of DDH in girls.
Metatarsus adductus, clubfoot, and torticollis are often associated with DDH. All these conditions may result at least in part from intrauterine crowding.15-17
Extrauterine postnatal factors, such as swaddling, may also play a role. Populations that swaddle their babies (the Inuit, Navajo, and Turks) demonstrate a greater incidence of DDH than those that carry babies with their legs free (the Bantu and Chinese).5,10-13
DDH is more common in firstborn children and in those with oligohydramnios; persistent hip asymmetry; and some syndromes, eg, trisomy 21, or other congenital abnormalities.1,3
The incidence of DDH is unclear. As many as 1 in 100 hips may be lax or subluxed.1,3 Diagnosis in the newborn can be difficult, so while most cases are detectable at birth, some are not found until later.18 Because of these ambiguities, the true incidence of DDH remains controversial. Most authors agree on an incidence of one to two cases per 1,000 live births in the United States.1,3
NATURAL HISTORY, PROGNOSIS
The natural history of untreated DDH in adults is not good.3 The dysplastic hip fares poorly over time.3,19,20 Abnormal loading forces on the hip joint inevitably cause increased wear of articular cartilage and painful osteoarthritis.
The picture is less clear with infants. Diagnosis is challenging. Physical examination may miss cases,18 and US can be overly sensitive and misdiagnose normal neonatal ligamentous laxity as DDH.21 Many lax hips can resolve spontaneously, but predicting which ones will do so is impossible.22-24 Randomized prospective trials are needed but are not likely to be done because providers, parents, and review boards dislike trials involving infants.
▪ Treatment of developmental dysplasia of the hip (DDH) is most effective in the newborn period.
▪ Physical examination is the key to diagnosing DDH.
▪ Neither radiography nor ultrasonography (US) is reliable for diagnosing DDH in newborns.
▪ Risk factors for DDH include being a firstborn child, being female, being born breech, or having musculoskeletal abnormalities (eg, torticollis or metatarsus adductus), some syndromes (eg, trisomy 21), or a family history of DDH.
▪ Imaging studies are not reliable in newborns younger than 6 weeks. The hip is unossified and invisible on radiographs, and US detects too many false positives due to normal neonatal ligamentous laxity. From 6 weeks until about 4 months of age, US is the imaging modality of choice.
▪ DDH treatment with a Pavlik harness is safe and effective.
Conditions that can be confused with DDH include proximal femoral focal deficiency; coxa vara; septic hip; myelodysplasia; arthrogryposis; osteogenesis imperfecta with deformity; fractured femur; and leg length discrepancy from another cause, such as hemihypertrophy due to a vascular malformation. These conditions should be diagnosable with clinical examination, laboratory studies, and/ or imaging.
The best way to diagnose DDH in the newborn is by physical examination. Imaging studies are not reliable until weeks or months later. Treatment success depends on starting early, so the newborn examination is crucial. Because clinical findings may be subtle, repeated examinations are essential.
Physical examination of the infant hip Examination of the infant hip is one of the most difficult and misunderstood challenges in pediatric practice. Babies are often irritable and tense. Physical signs of DDH can be subtle and easily missed. Abnormalities cannot be seen; they must be felt.
Textbook descriptions of the infant hip examination can be confusing. While illustrations often appear to show the clinician examining both hips simultaneously,25-27 examining one hip at a time is the most reliable method for detecting infantile hip instability.1,25-27 Accomplishing such an examination can be trying. The secret is to stabilize the pelvis. Holding the infant's pelvis steady allows you to easily detect abnormal movements of one hip at a time.
In their book The Art and Practice of Children's Orthopaedics, Wenger and Rang present an elegant and detailed description of the hip examination and abnormal movement of the femoral head.25 While stabilization of the pelvis is mentioned only as a technique for difficult cases, I believe stabilization of the pelvis is helpful for every case. Here is the technique I recommend:
1. Make the parent and child comfortable. This may require a pacifier or bottle and a comfortable, firm surface on which to place the baby.
2. Loosen but do not fully remove the diaper. Keeping the infant's perineum and genitalia covered reassures parents and does not compromise the examination. With the diaper in place, you can concentrate on the changing relationship between the child's femoral head and the acetabulum.
3. Grasp the pubic symphysis and sacrum firmly with one hand to stabilize the pelvis (Figure 1).
4. Place your examining hand on the baby's bare thigh with your thumb along the medial thigh, your fingers along the lateral thigh, and your first web space or index finger anterior to the child's knee (Figure 2). Use your right hand to examine the child's left hip and vice versa.
5. With the baby's hip flexed to 90° and in slight adduction, use the first web space or index finger to create an axial load along the child's femur at the knee. Try to gently push the femoral head out of the acetabulum over the posterior rim (Figure 1). Known as the Barlow maneuver, this movement is best felt with the tip of your long or ring finger. Movement of the femoral head out of the acetabulum indicates instability (Figure 3).
6. Reverse your hand positioning, and repeat the maneuvers to examine the opposite hip.
7. If the baby's hip does not subluxate out of the socket on the Barlow maneuver, proceed to the Ortolani maneuver: With both hands in the same positions as for the Barlow maneuver, widely abduct the hip being examined. Palpate the trochanter as before with your long or ring finger while attempting to reduce the abducted hip into the socket (Figure 4). A palpable clunk of the femoral head as it reduces back into the acetabulum is a positive Ortolani sign.
8. Gently repeat both the Barlow and the Ortolani maneuvers several times to be sure of the hip's stability or luxation. These clinical signs may be difficult to reproduce—perhaps because of muscle spasm caused by the examination.
9. Reverse your hand position and examine the opposite hip in the reciprocal manner.
This method has proved reliable in my hands for many years. In some babies, removal of the diaper may be helpful but is not usually required. Keeping the diaper loosely in place makes parents more comfortable and protects you from soiling. Everyone involved—the baby, the parent, and the examiner—must be relaxed. The keys to accurate infant hip examination are patience, experience, gentleness, and stabilization of the infant's pelvis with one hand while you gently examine one hip at a time for signs of instability. For practice examinations, the commercially available model shown in Figure 2 (Baby Hippy; Medical Plastics Laboratory, Inc; Gainesville, Texas) can be helpful, but the model is much stiffer than a human infant.
When an infant's dislocated hip reduces, the feeling is unmistakable. It is as definite and satisfying as reducing a nursemaids' elbow. Baby's hips often produce minor clicks with movement. These are innocuous sensations or high-pitched sounds caused by popping tendons, like knuckles “cracking.” True instability feels completely different. Findings may be subtle and variable. When in doubt, repeat the examination at another visit or confer with a colleague. The practice guideline for DDH produced by the American Academy of Pediatrics (AAP) stresses the importance of repeated physical examination of infants to detect the condition early.24
Physical examination of the older child Children beyond the first few weeks of age no longer show hip instability. In those aged 3 to 12 months who are not yet walking, signs of DDH are subtle. Often, the only abnormal finding will be loss of abduction of the affected hip.1,3,25-27
An older child suspected of having hip dysplasia should be examined while supine, and hip abduction should be compared side to side. In this position, you may sometimes detect shortening of the thigh or abnormal skinfolds. Restricted abduction is the hallmark of DDH at any age and should raise suspicion of that diagnosis.
The child who walks and has bilateral dislocation will have hyperlordosis of the lumbar spine; in unilateral cases, there is usually a limp. The affected leg will be shorter than the other leg, but the difference can sometimes be difficult to determine. Any leg length discrepancy or suspicious limping deserves further study. The signs of DDH in older children and adults are short leg, motion loss, and limping.
Imaging As previously noted, imaging studies are not reliable in newborns younger than 6 weeks. The hip is unossified and invisible on radiographs, and US detects too many false positives due to normal neonatal ligamentous laxity. From 6 weeks until about 4 months of age, US is the imaging modality of choice. Femoral head and acetabular angles can be measured on static examinations, and stability can be documented with dynamic studies.28-30 I have more confidence in dynamic sonograms for documenting instability. After about 6 months of age, radiography is the imaging modality of choice. Classic radiographic findings of DDH are readily available in the literature.1,25-27
The window of opportunity for safe and simple treatment of DDH is narrow—from birth to about 6 weeks of age. If the condition is diagnosed during that period, treatment with a brace is highly successful. If the diagnosis is not made until later, treatment becomes much more difficult and risky. Diagnosing and treating DDH during the newborn period is critically important. That's when an astute clinician can literally save a child's hip.
The goal of treatment in DDH is a concentrically reduced femoral head. The sooner a dislocated or subluxed hip can be reduced and maintained in the acetabulum, the better the outcome. The Pavlik harness is the international gold standard of treatment for children younger than 6 months of age.31,32 It works best in neonates during the first 6 to 8 weeks of life but may also be effective for some older babies. The harness maintains hip flexion of 100° and prevents adduction, thereby encouraging gentle reduction and stabilization of the dislocation without excessive force. Pavlik treatment requires careful monitoring but is safe and effective in 80% to 90% of cases.32-34
Dislocated hips that are missed or do not reduce with Pavlik treatment require closed or open reduction and casting. Closed reduction is usually successful in younger patients, but those older than 2 years may require open reduction with or without femoral and/or pelvic osteotomy.1,3 Longer delays in treatment can make reduction more difficult and result in more frequent complications.35-37
Residual abnormalities of dysplasia can be treated with a number of innovative operations to reshape the joint.38-42 These operations are ingenious and successful, but they are major interventions entailing significant risks.
The treatment of DDH is one of the few areas of pediatric orthopedics on which there is general consensus. Early intervention is best.43 We know that untreated DDH can result in a lifetime of painful arthritis. We cannot predict which infantile cases may resolve, so we treat them all. Treatment success depends on diagnosing and treating every case during the first 6 to 8 weeks of life, when the Pavlik harness works so well. Careful, repeated physical examination of the infant's hip is the key to early diagnosis of DDH.1,3,5
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