eMedicine Specialties > Radiology > Pediatrics

Developmental Dysplasia of the Hip

Author: Karen I Norton, MD, Professorial Lecturer, Mount Sinai School of Medicine; Director, Pediatric Radiology, Children's Hospital of New Jersey, Newark Beth Israel Medical Center
Coauthor(s): Sandra A Mitre Polin, MD, Assistant Professor of Radiology, Department of Radiology, Abdominal Imaging and Mammography, Georgetown University Hospital
Contributor Information and Disclosures

Updated: May 20, 2008

Introduction

Background

Developmental dysplasia of the hip (DDH) is a spectrum of disorders affecting the proximal femur and acetabulum that leads to hip subluxation and dislocation. Early diagnosis and treatment is important because failure to diagnose DDH in neonates and young infants can result in significant morbidity.¹

Related eMedicine topics:
Developmental Dysplasia of the Hip (Orthopedic Surgery)
Dislocation, Hip

Related Medscape topics:
Case Q&A: Developmental Dysplasia of the Hip, Part I-Diagnosis
Case Q&A: Developmental Dysplasia of the Hip, Part II-Treatment
Resource Center  Neonatal Medicine
Resource Center  Joint Disorders

Pathophysiology

DDH is the result of a disruption in the normal relationship between the acetabulum and femoral head. Without adequate contact between them, neither develops normally. At birth, the acetabulum has small bony and large cartilaginous contents, and the percentage of the femoral head covered by the acetabulum is smaller than it is at any other time in development; therefore, the first 6 weeks of an infant's life are critical to healthy hip joint formation.^2,3

Frequency

United States

DDH occurs in approximately 1.5% of neonates.

International

Because of genetic susceptibility and differences in medical care and diagnosis, the reported incidence of DDH varies throughout the world. Worldwide, DDH occurs in approximately 1% of all neonates. The incidence increases in colder climates; this is believed to be the result of tight swaddling of the infant with the legs in hyperextension.

The risk factors for DDH include female sex; a familial history (children of a parent who had DDH have a 12% risk, and subsequent siblings of a child with DDH have a 6% risk); breech presentation; multiple gestation; first pregnancy; high birth weight; oligohydramnios; and postural and nonpostural abnormalities, including clubfoot deformity and congenital torticollis. It should be noted, however, that most cases of DDH occur in infants without identified risk factors.^4,5,6,7

The left hip is affected 3 times more often than the right hip. This difference is possibly related to the left occiput anterior position of most neonates, which may limit abduction of the left hip as it lies against the mother's spine.

Mortality/Morbidity

The failure to diagnose and treat DDH in the immediate neonatal period can result in significant morbidity, including closed treatment failure, the need for open reduction, and the eventual development of osteoarthritis.

Possible complications of treatment include persistent dysplasia, recurrent dislocation, and, most significantly, avascular necrosis of the femoral head.

Race

DDH is more common in white neonates than in African American, Korean, or Chinese neonates. The incidence of DDH in Lapp infants, as well as in indigenous North American groups, is high. This observation may be related to the traditional methods that these groups use to carry their young (for example, some cultures use papooses, which keep the infants' legs in adduction).

Sex

DDH is 4-8 times more common in female infants than in male infants. This difference is believed to be the result of the increased levels of circulating estrogens and relaxin at the time of birth and an increased susceptibility to them. These hormones cause a generalized ligamentous laxity.⁴

Age

Two types of dislocations occur: teratologic and typical.

Most cases of DDH involve typical dislocations. They occur in neurologically intact infants in the perinatal period and, therefore, are developmental.

Teratologic dislocations occur in infants with underlying neuromuscular disorders, such as myelodysplasia and arthrogryposis. Teratologic dislocations occur in utero and, therefore, are truly congenital.

Anatomy

The normal hip develops from a single block of cartilage that separates into femoral and acetabular components at 7-8 weeks of gestation. The characteristic shape of the hip is a result of reciprocal contact between the acetabulum and the femur during growth. At birth, the acetabulum has a small bony component and a larger cartilaginous component. During the first 6 postnatal weeks, the acetabulum is particularly susceptible to modeling. If the femoral head is in the normal position in the acetabulum, a normal hip results. If the femoral head is in an abnormal position that is not corrected, the result may be a dysplastic hip.

Presentation

Physical examination is an important method for diagnosing DDH, and it is part of the routine clinical evaluation of the neonate. The Barlow maneuver is used to determine if a hip is dislocatable. The femur is flexed and adducted while posteriorly-directed pressure is applied. This maneuver displaces an unstable hip from the acetabulum.

The Ortolani maneuver is used to reduce a dislocated hip. This is performed by abducting and flexing the femur; a palpable low-frequency "clunk" is noted as the femoral head slides back and reduces into the acetabulum. Hip "clicks" are benign findings that are palpable and have higher-frequency noises; they result from stretching and snapping of the joint capsule and tendons.

As infants mature, capsule laxity decreases and muscle tightness increases, diminishing the sensitivity of the Ortolani and Barlow maneuvers. The Allis, or Galeazzi, sign is an asymmetry of the skin folds caused by an apparent shortening of the thigh. This is best noted by comparing the lengths of the 2 flexed thighs when they are held together.

The goal of treatment is to restore contact between the femoral head and the acetabulum. Treatment varies with the patient's age and the degree of instability. In neonates, most unstable hips normalize spontaneously within the first 2-4 weeks after birth; therefore, observation and reexamination when the neonate is aged 3-4 weeks is most commonly recommended for subluxatable hips in the immediate neonatal period.

The initial treatment for DDH involves the use of a brace that maintains the hip in flexion and abduction. The brace is worn until the clinical and radiologic examination findings are normal. Children older than 6 months usually are too large to tolerate a brace. Closed reduction under general anesthesia is usually attempted first. The reduction can be evaluated with magnetic resonance imaging (MRI) or an arthrogram and a postreduction computed tomography (CT) scan. If reduction is successful, the hip is held in a spica cast for several months. If it is unsuccessful, open reduction can be performed. If the diagnosis is made after deformity of the bones has occurred (usually in children older than 2 years), femoral or pelvic osteotomy and open reduction may be performed.

Preferred Examination

Ultrasonography (US) is the preferred modality for evaluating the hip in infants who are 6 months or younger. US enables direct imaging of the cartilaginous portions of the hip that cannot be seen on plain radiographs.⁸ Furthermore, US enables dynamic study of the hip with stress maneuvering. Practically speaking, the examination can often be successfully performed after 6 months of age (even up to 10-12 months) depending upon the degree of ossification of the capital femoral epiphysis. An attempt at US examination is suggested, to limit the neonates exposure to ionizing radiation. If unsuccessful, plain films can follow.

An Austrian orthopedist, Professor Reinhard Graf, first introduced US examination of the hip in 1980.² His technique included the calculation of numerous angles, a complicated classification system of hip subtypes, and the orientation of the B-mode images so that all hips were displayed on right coronal projections. Proponents of static scanning cite that it is fast, easy to perform, and reproducible. Widespread usage in Western Europe has reduced the incidence of undetected DDH requiring open reduction to the lowest in the world.^9,10

With the advent of real-time US in 1984, Dr. H. Theodore Harcke and associates at the DuPont Institute in Wilmington, Delaware, introduced a dynamic approach to studying the hips. Dr. Harcke is the principal drafter of the American College of Radiology (ACR) standard, and his dynamic approach is predominantly used in US examination.^8,11

The capital femoral epiphyses begin to ossify when an infant is aged 2-8 months. As the size of the ossification centers enlarge, shadowing may obscure the deeper acetabulum and limit US examination. Plain radiography then becomes the preferred modality for evaluating the hip. Plain radiographs are typically obtained in the frontal pelvis, with the legs in the neutral position. If the hips are displaced or dysplastic, a second view may be obtained, with the hips in flexion and external rotation (ie, the frog-leg position) to look for reduction. The gonads of male patients should be shielded whenever possible.^{12,13,14,15,16}

Limitations of Techniques

Dynamic US examination is operator-dependent, and it requires training and experience for confident evaluation of the infant hip. Also, because US is highly sensitive in hip imaging, minor abnormalities or normal early laxities may be revealed. This is especially true of static imaging alone. Some abnormalities detected by US may not be clinically significant, but they may be mistakenly overdiagnosed and overtreated.

Differential Diagnoses

Septic Arthritis

Other Problems to Be Considered

Traumatic hemarthrosis
Congenital coxa vara
Cerebral palsy - Incomplete femoral head coverage as a result of developmentally smaller but normally shaped acetabulum
Abnormal joint laxity - Down syndrome, Ehlers-Danlos syndrome, familial joint laxity
Tight hip adductors

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