COMMON ORTHOPEDIC PROBLEMS I

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DEVELOPMENTAL DYSPLASIA OF THE HIPTom F. Novacheck, MD

The purpose of this article is to emphasize the essential points regarding screening for and detection of developmental dysplasia of the hip (DDH). Background information is provided as necessary to understand why this entity presents in a variable fashion. This article is not intended to comprehensively cover treatment methodology for the orthopedist. Instead, the information provided is meant to aid the primary care practitioner in identification of the problem and in supporting the family during the treatment process when an abnormality is detected. The term developmental dysplasia of the hip is necessarily general and encompasses the many facets of the condition. DDH is variable at presentation but is defined as an abnormal formation of the hip joint occurring between organogenesis and maturity as a result of instability. It is intentionally nonspecific to include the entire spectrum of the disorder. The author finds it helpful to think of DDH as a spectrum in both time and severity. In other words, the individual findings depend extensively on the age of the child. They also depend heavily on the severity of that childs problem. This spectrum does not include hip abnormalities caused by other diseases, such as cerebral palsy or myelodysplasia. As in many other conditions, delays in detection lead to more severe consequences for treatment and prognosis; however, not all individuals at the same age of presentation have the same degree of

From the Motion Analysis Laboratory, Gillette Childrens Hospital; and the Department of Orthopaedic Surgery, University of Minnesota, St. Paul, Minnesota

PEDIATRIC CLINICS OF NORTH AMERICAVOLUME 43 NUMBER 4 * AUGUST 1996

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abnormality. Therefore, the concept of DDH as a spectrum in time and severity should be useful in organizing one's understanding of this rather enigmatic problem. DDH was formerly known as congenital dislocation of the hip. The disease did not change, but there are some very good reasons to adopt the new terminology.' The change from congenital to developmental is crucial because clear evidence has shown that not all cases are diagnosable at birth.8,3,13 Hips that are found to be normal at birth (and even in the first few months of life) can subsequently be found to be abnormal later. In addition, this terminology acknowledges that with the passage of time, changes occur. In other words, a subluxatable hip, if untreated, may progress to become dislocatable or ultimately dislocated. The choice of the term dysplasia rather than dislocated acknowledges a wider spectrum of cases rather than only the more uncommon, most severe cases. To persist with the label dislocation is misleading and under-emphasizes the milder forms of DDH. This change in terminology has some obvious important legal implications. In the spectrum of instability, some hips are subluxatable, or "loose," in which the femoral head slides in the acetabulum. At rest they lie in the normal position against the floor of the acetabulum. Subluxated hips lie in a position away from the floor of the acetabulum. They also slide within the acetabulum. Dislocafable hips lie within the acetabulum at rest but have even more laxity and can be manually displaced from the acetabulum (dislocated) with a palpable "clunk." Dislocated hips rest in the dislocated position, that is, the femoral head rests outside of the acetabulum. The ability to reduce the hip depends on the age of the patient and length of time that the hip has been dislocated. Another term that warrants definition is dysplasia. In addition to its use in the naming of DDH, it can refer to the abnormal formation of tissue, including the femur, acetabulum, or soft tissues. It is a general term, and because it is nonspecific, one must be wary of how it is used.

EPIDEMIOLOGY In general, the incidence in white neonates is 1.0% for dysplasia and 0.1% for dislocated hips.lo Incidence varies with race. There is an increased incidence in the Lapp and native American populations and a decreased incidence in the black, Korean, and Chinese populations. There is a fourfold increased likelihood in females, and the left side is involved in 60% of cases (right 20%, bilateral 20%). Associated birth factors include breech presentation, torticollis, talipes equinovarus, metatarsus adductus, and being first born. These fac-

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tors are believed to be packaging issues. Although 2% to 3% of all babies are breech presentations, 16% to 25% of DDH patients are born breech. Risk is relative to intrauterine position with cephalic 0.7%, footling breech 2.0%, and frank breech 20.0%. There is a familial predisposition that is believed to be multifactorial. DDH is present in 2% to 10% of siblings and in 1%to 2% of biologic parents. Idleberger7has documented a 34% risk for paternal twins and 3% for fraternal twins.

ETIOLOGY

Three theories have been postulated to account for the disease process of DDH: (1) mechanical, (2) primary acetabular dysplasia, and (3) ligamentous laxity. The mechanical theory helps to explain the increased incidence in firstborn and breech position as well as the association with the other packaging problems. It implies abnormal intrauterine positioning as a cause. The theory of primary acetabular dysplasia has two main proponents: (1) Faber5 and (2) Wynne-Davis.15 They believe that there is a primary acetabular dysplasia that predisposes to dislocation and an increased rate of acetabular dysplasia in biologic parents of patients with late DDH. The theory of ligamentous laxity is supported by Howorth and Massie.6 Wynne-Davis also has found an increased incidence of ligamentous laxity in neonatal DDH patients and their firstdegree relatives. The hormonal effects of relaxin on the collagenous structures of the infant are similar to those on the mother. This author believes that ligamentous laxity with or without associated mechanical factors is the basis for the pathologic changes and that the genetic aspects are related to familial laxity. A combination of this tendency with mechanical factors from malpositioning can cause the femoral head to move out of the confines of the acetabulum. The changes that occur in the acetabulum are secondary to these primary problems and are the result, rather than the cause, of the dysplasia.

PATHOLOGIC CHANGES IN PATIENTS WITH DDH

The pathologic changes in patients with DDH are the basis for understanding DDH as a spectrum in time and severity. Changes begin in the hip joint capsule. Laxity of this structure allows the femoral head to begin to migrate out of the acetabulum. Redundancy is present superolaterally. The labrum is a cartilaginous structure that normally enlarges the capacity of the bony acetabulum. With subluxation, the

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labrum everts. The ligamentum teres elongates. At this point, the femoral head is subluxated or subluxatable. With further laxity, the femoral head dislocates and the labrum inverts (Fig. 1A). At this point, intra-articular structures, including the ligamentum teres and the pulvinar (fibrofatty tissue in the floor of the acetabulum), may begin to hypertrophy. The labrum becomes pathologic in size and shape and is then referred to as the limbus. With these changes, the femoral head can no longer be relocated because of the obstruction to reduction caused by these soft tissues. The psoas tendon coursing across the front of the joint capsule causes a narrowing at the isthmus (Fig. 1B). The transverse acetabular ligament, capsule, limbus, pulvinar, and ligamentum teres all may have a role in preventing relocation of the femoral head, and at this point the dislocation is fixed. With the passage of time, contractures can develop in the iliopsoas and hip adductors, further prohibiting positioning of the leg and efforts to reduce the hip. Ultimately, because the growth forces have been abnormal, the cartilage models of the proximal femur and acetabulum deform with several possible consequences, including flattening of the femoral head, valgus neck-shaft angle, excessive femoral anteversion, and acetabular dysplasia.", l2

Figure 1. A, Inverted limbus. Infolding of the labrum prevents the femoral head from entering the acetabulum. A redundant and hypertrophied ligamentum teres and contracture of the transverse acetabular ligament also may hinder reduction. B, Hourglass configuration. The isthmus is caused by stretching and narrowing of the joint capsule and the iliopsoas tendon. (From Morrissy RT [ed]: Lovell and Winter's Pediatric Orthopaedics, ed. 3, vol. 2. Philadelphia, JB Lippincott, 1990, p 821; with permission.)

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NATURAL HISTORY

One should consider both the short-term and long-term outcomes for dysplastic hips. Barlow2 found that 1 in 60 infants at birth had evidence of instability, but that 58% became stable within 3.5 days. They had no residual abnormalities, and their hips went on to develop normally. The remaining children went on to develop hip dysplasia, either subluxation or dislocation. Hips that are abnormal after the immediate newborn period and remain untreated develop the long-term complications, including: osteoarthritis pain abnormal gait leg length discrepancy decreased agility Wedge and Wasylenko14 found that pain develops in subluxated hips earlier than in dislocated hips and therefore actually have a poorer long-term prognosis than hips with complete dislocation (Fig. 2). Osteoarthritis eventually develops in all, but pain develops in adolescents with

Figure 2. Anteroposterior radiograph of the left hip of a 35-year-old woman with pain in the left hip and marked early degenerative arthrosis caused by severe acetabular dysplasia.

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subluxation during the second decade, whereas persons with complete dislocation may not experience significant pain until their late third or early fourth decade. Regardless, both have a poor long-term outcome with pain and disability in early adulthood.

PRESENTATION

Because of the differences in severity of the dysplasia and the progressive changes that occur over time, presentation and the method of confirming the diagnosis are variable. Before walking age, the diagnosis is based on physical examination. Initially, the examination in the newborn nursery is the critical screening tool to detect loose, dislocatable, and dislocated hips. Detection up until approximately 4 to 6 months of age still depends primarily on the Barlow and Ortolani maneuvers as part of routine well-baby examinations. At approximately 6 months of age, the family may notice a difference in the range of motion with some difficulty with diapering. Occasionally the family may notice or the examination may indicate a leg length difference or an asymmetric appearance of the two legs (asymmetric skinfolds). The importance of frequent, routine screening hip examinations until walking age by an experienced examiner cannot be overemphasized. With the onset of walking, gait asymmetry (generally related to leg length discrepancy) is the hallmark for identifying an abnormal hip. Occasionally, asymmetric intoeing or outtoeing is the clue. If the hip abnormality remains undiagnosed, it will likely be the onset of pain or more noticeable gait asymmetry that draws attention to the hip as the child becomes older, larger, and more well developed. These various presentations are highlighted later in case presentations.

DIAGNOSIS

History

In recording the patient's medical history, one should have a higher index of suspicion if one or more of the many risk factors for DDH, including race, sex, family history, being first-born, and breech position, are present. None of these factors is sufficient alone to make the diagnosis, but their presence may cause sufficient concern to pursue further evaluation with ultrasonography, radiography, or pediatric orthopedic consultation. In the presence of one or more of these risk factors, further caution should be exercised and another level of screening considered.

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ExaminationPhysiologic hip flexion, abduction, and external rotation contractures are normal findings in neonatal hip examinations. Knee flexion contractures are also typical. These, of course, are related to normal intrauterine positioning. An asymmetric examination may be a subtle clue to the presence of hip dysplasia. As mentioned previously, the mainstay screening examination still consists of the Barlow provocative test and Ortolani reduction maneuver (Fig. 3). A helpful trick to remember is that the 0 Ortolani stands in for the hip is out. The examination is a reduction maneuver to place it back into a normal position. The Barlow provocative test, then, detects the subluxatable or dislocatable hip. The key to detection is not a click but rather a clunk. One tries to detect abnormal movement between the femoral head and the acetabulum. The author finds it helpful to minimize the movements of abduction and adduction and to emphasize the push of the Barlow test to try to move the femoral head posteriorly and the pull of the Ortolani reduction maneuver to draw the femoral

Flgure 3 A, The Ortolani (reduction) maneuver. In this technique, the hip is abducted . slightly. Then, with the index and long fingers over the greater trochanter, the thigh is raised (pulled forward) to gently reduce the hip. When performing the test, one hand should always be used to stabilize the pelvis; therefore, only one hip at a time can be examined. 3, The Barlow (provocative) test. The thumb is placed on the inner aspect of the thigh near the lesser trochanter. The hip is adducted. Longitudinal pressure is exerted on the thigh with the thumb, pushing it toward the table. The examiner again uses one hand to stabilize the pelvis, testing one hip at a time. (From Lovell WW, Winter RB [eds]: Pediatric Orthopaedics, ed. 2, vol. 2. Philadelphia, JB Lippincott, 1986, p 707; with permission.)

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head anteriorly back into place. One tries to detect translational movement between the femoral head and the pelvis. In the author's experience, if a lot of rotational movement occurs simultaneously (i.e., flexion/ extension or abduction/adduction), then detection of subtle translational movement is difficult. The child should be at rest and not struggling against the examiner. The author takes the approach to assume the hip is abnormal and to prove that it is not. If he is sure of the results of the examination, then no other evaluation is warranted. If not, then further assessment is indicated. The presence of asymmetric skinfolds is a sensitive but nonspecific indicator of abnormality. If the folds are symmetric, then it would be very unlikely that the hip is abnormal. Asymmetry is common and is present in approximately 30% of all infants. It can be used as an indicator to raise one's index of suspicion. This finding in the absence of any other abnormalities is insignificant. As time passes and secondary soft tissue contractures develop, the Barlow and Ortolani maneuvers become less dependable as the hip becomes fixed in its abnormal position. Limited abduction, skinfold asymmetry, and the Galeazzi sign (relative shortening of the femoral segment) become more important. Bilateral hip disease is especially difficult to identify because no asymmetry is present. At younger ages, the Barlow and Ortolani examinations are valid. After the development of secondary soft tissue contractures, findings on examination include widening of the perineum, symmetric limited abduction (less than 45"), and the appearance of abnormally short thigh segments for the child's overall size. After walking age, hyperlordosis and a waddling gait are the classic findings. Radiography Radiographs before 4 months of age can be fraught with problems and may provide a false sense of security if they seem normal. Because the secondary center of ossification of the femoral head has not yet developed, an abnormal relationship between the upper end of the femur and the acetabulum may not be apparent. In addition, unless the femoral head lies in an abnormal position at rest, the radiograph may provide false-negative information. Therefore, the only way that the radiograph can be useful is if it is abnormal. A normal radiograph before 4 months of age cannot rule out pathology. Figure 4 depicts several of the useful measurements that can be made to identify hip abnormalities. The reader should refer back to it for the case presentations later in the article. The better screening radiographic test prior to femoral head ossifi-

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BFigure 4. A, Hilgenreiners line is a horizontal drawn through the triradiate cartilage. Perkins line is drawn perpendicular to it at the lateral edge of the acetabulum. With these lines, the area about each hip is divided into four quadrants. The ossific nucleus of the femoral head (if present) or the medial beak of the metaphysis should be in the inner lower quadrant. The appearance of the ossific nucleus often is delayed in hip dislocation. H = distance from highest point of femoral neck to Hilgenreiners line (decreased in hip dislocation); D = distance from triradiate cartilage to intersection of H with Hilgenreiners line (increased A in hip dislocation). 6, normal acetabular index (angle) of the left hip (