Hip Dysplasia

• Identify the normal anatomy of infant hips.

• List the risk factors associated with infant hip dysplasia.

• Describe the clinical maneuvers used in evaluation for hip dysplasia.

• Describe the sonographic protocol for imaging of infant hips.

• Differentiate hip laxity, subluxation, and dislocation.

CLINICAL SCENARIO

An 8-week-old boy with a grossly abnormal physical examination is seen for a hip sonogram to rule out hip dysplasia. The parents report that their older daughter was also treated for hip dysplasia as an infant. The images of the right hip demonstrated the finding in Figure 31-1, A-C, and did not change much with the Ortolani maneuver. Computed tomography (CT) (Fig. 31-1, D) is consistent with the sonographic findings. The left hip appeared similar. What is the diagnosis, and what is the possible treatment for this infant?

FIGURE 31-1 **(A),** Coronal view of hip shows relationship of femoral head to acetabulum. **(B),** The alpha angle was 44 degrees. Transverse/flexion view **(C)** and CT scan **(D)** shows posterior displacement of the femoral head in relation to the acetabulum. (Courtesy Judith Williams, BS, RDMS.)

Every newborn examination includes an evaluation of the infant’s hips for assessment for developmental dysplasia of the hip (DDH). This chapter presents the risk factors for DDH and the clinical examination that may be used to identify DDH. The various modes of testing, including ultrasonography, are examined, in addition to the types of treatment available on the basis of the severity of the disease. The sonographic evaluation of infant hips includes a review of normal hip anatomy and imaging protocol for evaluation of DDH.

Anatomy of the Hip

The hip comprises the femoral head and the acetabulum. The femoral head is cartilaginous at birth and begins to ossify between 2 and 8 months, with ossification occurring earlier in girls. The acetabulum comprises cartilage and bone. The bony acetabulum (Fig. 31-2) consists of the ilium, the ischium, and the pubis, which is joined by a growth plate known as the triradiate cartilage. The cartilaginous labrum is located at the acetabular rim and extends over the superolateral aspect of the femoral head.

At birth, the hip has a large cartilaginous component, and the femoral head is more shallow in its relationship to the acetabulum. The hip is subject to molding, especially in the first 6 weeks of life. The normal development of the hip is contingent on the femur having adequate contact with the acetabulum without an abnormal amount of stress. When the femoral head is subluxed or dislocated for a significant amount of time, the acetabulum becomes increasingly dysplastic, the femoral head becomes deformed, and the supporting ligaments deform.

The purpose of early treatment of abnormal hips is to position the hip so that the femoral head and acetabulum can develop normally, avoiding possible surgery and disability. Clinical evaluation and identification of risk factors can be used to identify infants at risk for development of hip dysplasia. Sonographic evaluation can be used to define further infants who would benefit from treatment and to follow their progress. Screening for hip dysplasia is usually reserved for infants with an abnormal clinical examination or for infants with identified risk factors to avoid overtreatment of infants with physiologic laxity.

Developmental Dysplasia of the Hip

DDH describes a spectrum of abnormalities that involve an abnormal relationship of the femoral head to the acetabulum, which includes mild instability, subluxation, and frank dislocation. DDH also has been referred to as congenital hip dysplasia, although this is a misnomer because hip dysplasia may develop after birth. The incidence varies depending on whether or not the neonatal population is routinely screened, with a higher incidence in the screened population. In the United States, the incidence is 1.5:1000 to 15:1000 live births.¹ There is also geographic and ethnic variability that may be secondary to environmental or genetic factors or both. An example of this variability is the lower incidence in native Africans versus African Americans; however, the incidence is lower in African Americans compared with the overall prevalence of DDH in the United States.¹

Hip instability is associated with joint laxity and may be identified in newborns affected by maternal hormones. This laxity often resolves within the first few weeks of birth and necessitates no treatment. Unless there is a significant instability or dislocation, sonographic evaluation of the infant hip is not recommended before 3 to 4 weeks of age to avoid overtreatment in populations in whom the instability would spontaneously resolve.² Subluxation of the hip refers to a femoral head that is shallow in location, allowing it to glide within the confines of the acetabulum. Hip dislocation is defined as a femoral head that is located outside of the acetabulum and may be reducible or irreducible. Hip dislocation can also be associated with congenital neurologic or musculoskeletal anomalies, including spina bifida, scoliosis, arthrogryposis, talipes, and numerous syndromes, and is referred to as teratologic hips.^1,2

Risk Factors

Many risk factors associated with DDH are related to the inability of the fetus or newborn to move freely. These conditions include pregnancies affected by oligohydramnios (including serious renal anomalies), breech presentation, first pregnancy (primigravida), high birth weight, and postmaturity. Other infants at risk include infants born in the cold seasons of the year, female infants, and infants with torticollis. There is an increase in infants born where swaddling is prevalent, including in Saudi Arabia, Turkey, and Japan as well as Navajo Indians.¹ The left hip is affected more commonly than the right, and DDH is bilateral in 20% of cases.¹ Family history is also an important factor in identification of infants at risk for development of DDH, especially when parents or siblings are affected.

Clinical Evaluation

Evaluation for hip dysplasia is part of every newborn examination. The accuracy of the evaluation is affected by the experience of the physician. Infants in whom hip dysplasia does not develop until after birth may initially have a normal examination. Clinical findings associated with DDH include asymmetric skin folds of the thighs and one knee appearing lower than the other when the hips and knees are flexed. The subluxed or dislocated hip appears shorter (known as the Galeazzi or Allis sign). Also, limited abduction of the hip may be observed.³

Clinical maneuvers also can be used to detect hip instability and dislocation, but performance of these maneuvers may be difficult if the infant is not relaxed and are best performed in a warm room after feeding. The two maneuvers are performed with the infant’s hips and knees flexed, and one hip should be examined at a time. The Ortolani maneuver (Fig. 31-3) involves abduction of the thigh while the hip is gently pulled anteriorly. If the hip is dislocated, the hip may relocate into the acetabulum with a palpable (and possibly audible) “click.” The Barlow maneuver (Fig. 31-4) is performed with adduction of the hip with a gentle posterior push in an effort to solicit subluxation or dislocation in an abnormal hip.³ These maneuvers are similar to maneuvers performed in a dynamic sonographic evaluation.

Sonographic Evaluation of Infant Hips

The technique for imaging the infant hip was initially described by Graf, who used a static approach. Harcke developed a dynamic approach to sonographic imaging. The two approaches were combined to develop a minimum standard examination.⁴ The imaging protocol should incorporate two orthogonal views with one view that includes stress views; this typically includes the coronal/neutral or coronal/flexion view and the transverse/flexion view. Additional views, including anterior views, and measurements are considered optional, although they may be dictated by institutional protocol.⁴ Particular care should be taken to image each view in the correct plane and with the appropriate anatomy identified because a minimal shift in the image may lead to an inaccurate diagnosis. This chapter defines the images for the minimum standard examination and describes normal and abnormal findings.

Infant hips may be examined sonographically during the first year of life or until the ossification of the femoral head prevents adequate visualization. A linear transducer is preferred to avoid distortion and to cover a broader field of view. The highest frequency transducer should be used to penetrate the soft tissues of the hip, and this depends on the age of the infant.

A successful examination requires that the infant be relaxed for accurate stress maneuvers. Infants should be imaged in a warm environment with distracters such as toys, pacifiers, or bottles. A parent should be available and visible to the infant to assist in maintaining a relaxed environment. The infant should be placed in a supine or lateral decubitus position to accommodate the lateral and posterolateral position of the transducer. Bolsters should be used as needed to stabilize the infant’s position. For easier access, the left hip may be scanned with the right hand while maneuvering the hip with the left hand, and the right hip may be scanned with the left hand while performing stress maneuvers with the right hand. Because two hands are needed to image and maneuver the hip adequately, sonographic evaluation is often a joint effort between the sonographer and radiologist. The second person may assist in maneuvering the hip or producing the images, depending on institutional protocol.