Published: 19-08-2010, 10:23

Developmental displacement of the hip

The termdevelopmental displacement of the hip has replaced the previous more confining and incriminatory terminology congenital dislocation of the hip. Although the vast majority of idiopathic hip dislocations are recognizable at birth, a number of hips will not have sufficient clinical findings of displacement until later in the first year of life (at three to nine months). The implications of this terminology are obvious and the broader spectrum should help clarify our understanding of the evolution of hip displacement, particularly in those in which spontaneous relocation does not occur.
This condition has its origins of recognition with the ancients; Hippocrates aptly described its existence and its treatment. Current concepts of etiology focus primarily on intrauterine and extrauterine factors. Females, first-born children (pressure from strong maternal abdominal muscles), breech malposition and delivery, large body size, oligohydramnios, and genetics have all been strongly implicated as risk factors. This condition is associated with congenital muscular torticollis approximately 20 percent of the time. In those regions of the world where hip extension “strapping” and “cradleboards” are utilized on newborns, the incidence of developmental displacement of the hip occurs approximately 40–50 percent of the time. The highest risk is posed by a first-born, 4.5kg (approx. ten pound) female infant delivered by breech extraction to a primiparous mother with a family history of developmental displacement of the hip. Established dislocation at birth is nearly always associated with other disorders such as cerebral palsy, myelodysplasia, arthrogryposis and other syndromes. It is generally believed that undue pressure on the hip, combined with a lax hip joint capsule (i.e., breech) coupled with strong uterine and abdominal musculature, and large baby size, will sufficiently stretch the hip joint supports and make the hip “dislocatable.” This “dislocatability” or instability is commonly evident at birth, and determined by a series of hip examination maneuvers requiring only one to two minutes to perform.
The hip is initially examined with the baby supine and the hips flexed to 90 degrees, and with gentle but firmdownward pressure on the femurs to fix the potentially moveable pelvis to the examination table. The fingers are positioned to provide for downward pressure on the femurs and to allow for direct vision of the thighs when abduction and adduction movements are attempted. Asymmetry of the thigh creases is readily appreciated in this position, as are differences in the height of the knees (Figure 3.1).
Developmental displacement of the hip

Figure 3.1. The unequal knee heights and asymmetric skin folds in the thigh, seen in developmental displacement of the hip.

The thighs are then gently and slowly parted (abducted with the middle or ring fingers palpating the greater trochanters). In unstable but “reducible” hips a discernible “clunk” will often be discerned in the neonate but commonly may recede to a “click” over the ensuing few months and then eventually disappear. This easily recognizable “clunk” is termed Ortolani’s sign (Figure 3.2).
Developmental displacement of the hip

Figure 3.2. The technique of eliciting Ortolani’s sign.

The later discernible “click” obtained in near full abduction is usually a sign that the acetabular labrum has not firmly attached and stabilized, but is a sign of improved stability. If a true dislocation is evident, abduction will be clearly limited, as the head will not enter into the acetabular confines with attempts at reduction. A positive Barlow sign is actually a provocative dislocation or subluxation test, and is elicited using the thumb and fingers to laterally move the femoral head out of the acetabular confines by lateral pressure of the inner aspect of the thigh (Figure 3.3).
Developmental displacement of the hip

Figure 3.3. The technique of performing the Barlow maneuver.

A discernible “clunk” or “click” will be readily appreciated. Perhaps the most valuable sign of hip instability (subluxation or dislocation) is the “pistoning” or “telescoping” sign. It is generally elicited by stabilizing the pelvis with one hand firmly against the anterior iliac spine, grasping the femur in the other hand, then “pumping” downward and upward in a vertical direction with the hip flexed to 90 degrees (Figure 3.4).
Developmental displacement of the hip

Figure 3.4. The technique of producing “telescoping” or “pistoning.”

The femur will glide up and down within the soft tissue envelope of the thigh and independent of the stable pelvis. As the femur glides within the soft tissue envelope, the pelvis remains fixed with each up and down thrust. A positive “telescoping” sign always reflects hip joint instability. It is imperative that the novice clinically examines as many hips as possible during residency training, as there can never be too many opportunities. The skills achieved in examination are the product of many clinical examinations of both normal and abnormal hips. As the child approaches six months of age, dislocation may lead to an adduction contracture, and reduction of the hip becomes much more difficult with the disappearance of the Ortolani sign. Diagnosis in the ambulatory child should be much easier with shortening, limp, and telescoping more obvious.

The natural history or evolution of a displaced hip in infancy has been the topic of considerable investigation and commentary. Most people agree that there is a tremendous tendency for the hip to stabilize spontaneously, with a likelihood of 85–90 percent of all hips achieving stabilization by 9–10 months of age. Unfortunately, we are presently unable to predict which hips will stabilize, and we are left with 10–15 percent who will remain with varying degrees of hip malpositioning, including even frank dislocation. The future of hip joint function appears directly related to the early recognition of this problem. Careful hip examination should take place from birth to one year of age at regular intervals.
The role of radiographic examination or the use of ultrasound is less clearly defined. The femoral head does not normally ossify its secondary ossification center until roughly three to six months of age, and that ossification of the center is commonly delayed even further in developmental displacement of the hip. While there is nothing wrong with performing an imaging examination at three to six months of age, particularly in high risk infants, it should never replace a careful hip examination. Bilaterally involved hips pose the greater hazard, and make the individual hip examination even more important, as “widening” of the perineum seen in bilaterality is very difficult to discern in infants and young children. Radiographic examination of the hips in very young children is fraught with potential misinterpretation errors. To be at all meaningful, anteroposterior examination must be done with the hips and knees maximally extended, and with the patella directed vertically (Figure 3.5).
Developmental displacement of the hip

Figure 3.5. The positioning of the child for standard anteroposterior radiographs of the hip.

Abduction views of the hips tend to induce femoral head relocation, and external rotation positioning promotes lateralization of an already anteverted femoral head and neck. At birth nearly 40 percent of the acetabulum is formed in cartilage. If one couples that information with the fact that the femoral head is for all parts a chondroepiphysis, with an occasional degree of secondary ossification, it is possible to visualize only a small portion of the hip joint on plain radiography in the very young child (Figures 3.6a, b and 3.7a, b).
Developmental displacement of the hip

Figure 3.6a. Anteroposterior radiographs of neonate highlighting the absence of the ossification center and the large amount of femoral head/ acetabulum that is not visible on standard radiographs at this age.

Developmental displacement of the hip

Figure 3.6b. Lateral radiographs of neonate highlighting the absence of the ossification center and the large amount of
femoral head/ acetabulum that is not visible on standard radiographs at this age.

Developmental displacement of the hip

Figure 3.7a. Anteroposterior radiographs demonstrating hip subluxation in a young child prior to ossification of the secondary center of the femoral head.

Developmental displacement of the hip

Figure 3.7b. Lateral radiographs demonstrating hip subluxation in a young child prior to ossification of the secondary center of the femoral head.

Currently the use of ultrasound has gained an increasingly important role in the diagnosis and even the management of developmental dislocation of the hip. Ultrasound in the hands of a competent examiner can provide useful information regarding the femoral head and acetabular relationship particularly prior to the appearance of the secondary center of ossification of the femoral head. It is to be emphasized that the individual performing the ultrasound test be very experienced as the provocative testing is extremely critical and the learning curve can be steep.
In the first month of life, many children who in fact do not have developmental dislocation of the hip, will have sufficient normal “laxity” of the soft tissue that provide hip joint stability to produce false-positive instability on ultrasound that will spontaneously disappear on later testing. Given this normal sequence of events, ultrasound is probably best utilized between one month of age and prior to the appearance of the ossified femoral head. It is merely an additional imaging technique to assist the primary care physician’s arsenal of evaluation techniques. Ultrasound is safe, noninvasive and does not involve the use of ionizing radiation although it is currently much more expensive than conventional radiography. In the presence of risk factors for developmental dislocation of the hip, it would seem appropriate to screen patients with ultrasound when they are four to six weeks of age. The number of risk factors that need to be present to initiate the ultrasound testing is still very controversial. None of the currently available “imaging” techniques should replace a careful clinical examination. Once a displaced hip is recognized at birth or shortly after birth, the hip should be allowed to lie in the fetal human position of flexion and unforced abduction. Nearly 50 percent of all “displaced” femoral heads will relocate in the first 30–45 days of life, and a simple soft device that provides flexion above 90 degrees and abduction of roughly 45–60 degrees is usually adequate (double/triple diapers, pillow splints, abduction brace or harness). If signs of clinical hip instability persist beyond this point, a more concerted effort to contain the hip is generally indicated (rigid splint, Ilfeld type brace, Pavlik harness, hip abduction cast). Treatment is generally employed for six weeks to three months for unstable, but not dislocated hips. Frank hip dislocation in children three months to one year of age are generally best treated by manual relocation under anesthesia often combined with adductor tenotomy if necessary, a hip spica cast, or by brace or harness reduction. The length of treatment time is usually three to six months. Failures of this treatment regime will likely require surgical repositioning, and often femoral and pelvic realignment procedures to maintain hip stability.
Clearly the overall role of the primary care physician rests with the diagnosis, where early or late recognition likely will determine the ultimate prognosis for future hip stability. However, some few cases will escape detection, even in the hands of competent examiners, and be recognized only later (at nine to ten months of age) when the clinical signs can be more readily perceived (Figure 3.8).
Developmental displacement of the hip

Figure 3.8. Anteroposterior radiograph of an 8-month-old child with a “late appearing” developmental displacement of the hip.
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