Hip dysplasia encompasses a spectrum of abnormalities in which one or all of the components of the hip, including the capsule, the proximal femur, and the acetabulum, are defective; the condition presents itself from subtle clicks to frank dislocation.

Actual dislocation of the hip occurs most often at delivery or in the perinatal period. The aetiology is believed to be related to the laxity induced by the maternal hormones that traverse the placenta. The same hormones that permit the cervix to dilate presumably affect the ligaments of the joint capsule. The key to successful treatment is early treatment. During the first few days, or possibly longer, the hip can pop in and out of the socket. If the hip is held in place early, the ligaments tighten in that position, whereas if the hip is left dislocated, the ligaments tighten in that position, and treatment of the dislocation becomes more difficult.

There are other factors involved. Position is considered important, particularly so with breech deliveries when the femoral head may be levered out. Hyperextension of the hip has also been implicated, and the old custom of slapping the baby on the buttocks to induce crying has been abandoned since it may cause the hip to pop out. Our studies showed that even if all the muscles were removed from the hip of a still-born fetus, the hip is stable. If air is introduced into the capsule with a needle, the hip is easily dislocated. Salter has demonstrated that hyperextension of a joint leads to breaking of the joint seal, causing air to enter. It is possible that the same thing happens at birth.

Most orthopaedic surgeons believe that the bony acetabulum is normal. If the hip has been reduced, radiographs are normal in dislocations occurring around the time of birth. Later, if the dislocation is permitted to proceed, they will become abnormal.

Diagnosis, in the newborn, is made by invoking the Ortolani or the Barlow manoeuvre. The Ortolani manoeuvre is a reduction of the dislocated hip, by abducting the hip and feeling a ‘clunk’ (Fig. 1) 2560. The Barlow manoeuvre is a dislocating manoeuvre, followed by reduction. The patient lays supine; both hips are flexed and adducted. With the finger over the greater trochanter, the hip is lifted up into the socket, and slightly abducted. While performing this manoeuvre, it is useful to press the hip against the acetabulum. Sometimes if the posterior lip is shallow, the click of dislocation-location will not be felt and pressing the hip against the pelvis accentuates it.

Often, in children, there is what has been described as a ‘soft click’. Traditionally this was thought to represent a tendon, perhaps the tensor fascia lata, snapping over the trochanter. Historically, few orthopaedic surgeons treated this phenomenon, and most patients never had problems. These soft clicks often could be felt in children aged 1 or 2 years. With the advent of ultrasonic diagnostic techniques, there is a suggestion that the soft clicks may represent partial subluxation over the cartilaginous limbus. The exact significance of this phenomenon is not yet appreciated, but more of these patients are now being treated as if they had a dislocatable hip.

In older children the Ortolani and Barlow signs are negative. The main diagnostic sign is lack of abduction of the hip. Abducting both hips at the same time can be misleading. The pelvis is rocked, and abduction appears symmetrical. To avoid falling into this trap, one should stabilize the pelvis by pushing down one hip or holding on to the pelvis and abducting only one hip at a time (Fig. 2(a) - (c)) 2561,2562,2563.

The other positive physical findings are the Allis or Galleazi signs (Fig. 3) 2564, asymmetry of the gluteal creases (Fig. 4) 2565, and shortening. Galleazi's sign is elicited by examining the patient on a firm surface, flexing the hips, and pressing the buttocks against the table. One hip will appear shorter than the other.

One of the more difficult diagnoses to make is that of a bilateral dislocation. The problem is that abduction is usually equally limited. One positive physical finding that may assist is widening of the perineum. Normally, when the legs are adducted, the perineum is masked by the legs coming together. If both hips are dislocated, or if there is congenital bowing or coxa vara, the perineum is more exposed.

The radiographic features that are used to define early or late dislocation are the position of the femoral head in relationship to the acetabulum. Because the femoral head is not ossified until about 3 months in girls, or 6 months in boys, lines are drawn to determine the position of the head. Hilgenreiner's line is a line drawn through the tri-irradiate cartilage of both acetabulae. Perkins' line is a vertical drawn through the outer edge of the acetabulum. The femoral metaphysis should be equidistant below Hilgenreiner's line and inside Perkin's line (Fig. 5) 2566. Another line should be a smooth hemicircle drawn along the inner border of the femoral shaft and the superior border of the obturator foramen, known as Shenton's line. Interruption of Shenton's line usually means that the ball of the femoral head is not concentrically seated in the acetabulum. Today, many orthopaedic surgeons use ultrasound, arthroscopy, and, in some cases, CT or magnetic resonance imaging to give themselves more exact location of the hip.

On the frog-leg lateral view, the hips should be pointed to the tri-irradiate cartilage. In cases where the hip has been dislocated for a time, the roof of the acetabulum becomes more shallow. A line drawn from Hilgenreiner's line to the outer edge of the acetabulum describes the acetabular index. This is normally about 30⁰, but in the newborn, since so much of the acetabulum is cartilage, slight tilting of the pelvis can give widely different angles (Fig. 6) 2567. Because the acetabulum really represents a growth plate, if the head is not making contact, there is no suppression of growth, and the roof flattens out. Flattening increases the index above 30⁰. When the hip has been dislocated for a time, and the femoral head is resting against the acetabulum, an indentation of the iliac wall, or a ‘false acetabulum’ appears.

The description given so far is that of the ‘dislocatable hip’. If the hip is out of the socket for several weeks or longer, it becomes a dislocated hip, with a negative Ortolani sign, and all the findings described above. There are hips which are dislocated at the time of birth. These ‘dislocated hips’ are often teratological in origin, for example, arthrogryposis or muscle imbalance, as is seen in myelodysplasia. If the hip has been out of the socket in utero, a false acetabulum is often present at birth. Closed methods of treatment usually fail to reduce the hip. Another category of hip dysplasia or abnormality is the subluxed hip. Unfortunately, this term is used by different physicians for widely disparate conditions. Some use it to mean a dislocatable hip. In the context of this chapter, it refers to a hip that is in the socket, but not perfectly seated. In most cases, this condition is related to an adducted position in utero, which persists after birth. As a result of limited abduction, the hip socket does not develop well.

The standard treatment for the dislocatable hip noted at the time of birth is the Pavlik harness (Fig. 10) 2571. This is a device that holds the hip in flexion and moderate abduction. Generally, we try to hold the hip in greater than 90⁰ flexion, and attempt to abduct the hip enough to hold it reduced. The harness prevents adduction, but it should not be held in maximum forced abduction. Forced abduction tends to lead to avascular necrosis. For the ‘subluxed’ hip, the abduction improves quickly; usually within a month the harness can be switched to night use only. Almost any abduction splint (for example the von Rosen or the Ilfield) will work.

When treating with the Pavlik harness, the patient is seen weekly. It is not necessary to repeat radiographs each time, and often the hips can be followed up with ultrasound examination. If that technique is not available, the examiner tries to hold the hip in a reduced position, and tightens the straps accordingly. It is possible to use the Pavlik harness for later dislocated hips, probably up to 6 months. In these cases, the hip is held in an even more flexed position initially, and it is hoped that the child will kick into position by not letting the hip adduct. In these later dislocations care should be taken when using the Pavlik harness and the treating physician, if successful, should reduce the severe amount of flexion soon. If the hip is left in that position too long it will dislocate posteriorly.

If the harness is successful, it is usually kept on, or switched to an abduction splint after about 6 weeks, although some physicians keep the harness on throughout the treatment period. It may usually be stopped at about 3 months if the socket is developing well, and if the hip can no longer be dislocated. Treatment can be considered to have failed if the hip is not reduced by about 3 to 4 weeks, or if it is still dislocating after about 4 to 6 weeks, although some surgeons will continue to try.

Our preference for late dislocations, from about 6 months to 1 year, and even earlier if reduction is not readily obtained with the harness, is to use traction, adductor tenotomy, and closed reduction with spica application. The aim is to obtain gentle closed reduction. Forced closed reduction usually leads to avascular necrosis. There are various forms of traction available. All require that the hip should be pulled down with the hip in a flexed position, because the iliopsoas tendon tends to lie across the acetabulum and blocks reduction; flexion relaxes the tendon. There is also some experimental evidence suggesting that blood flow to the hip is better in the flexed position. One approach is to use Bryant's traction, where both hips are pulled straight up. We prefer to use Buck's skin traction, but with a bolster under the thighs, permitting the hip to be flexed and the hamstrings to be relaxed. About 3 or more weeks are required for the traction to be effective; radiographs show the hip is being pulled down to the acetabulum. Once the hip is opposite the acetabulum, or if it easily reduces in the bed, a subcutaneous adductor tenotomy is performed. This should take some of the pressure off of the hip, although some workers have abandoned this technique. An arthrogram is then performed to indicate that the hip, in a reduced position, is well seated, and that there is no soft tissue blocking reduction.

The best seating of the hip is usually in 90⁰ or more of flexion, and the surgeon will determine at what amount of abduction it reduces. It is usually abducted 10 or 20⁰ more. The aim is not to abduct the hip overly, since forced abduction stretches the medial circumflex femoral vessels, and increases the risk of avascular necrosis. The surgeon, however, should be forewarned that the hip can dislocate out at the back as the fat and muscles atrophy in the cast. In our experience, the surgeon should have his fingers over the trochanter as the hip is abducted, so that there can be an anterior push on the trochanter. There should be pressure on the cast over the trochanter to keep the hip up in the socket.

In children in whom a closed reduction is unobtainable, open reduction is necessary. This advice applies to most children over 1 year of age, to teratological dislocations, and to unreducible earlier dislocations. We prefer the anterior Smith-Peterson approach, between the sartorius and the tensor, taking down both heads of the rectus femoris, and always cutting the psoas tendon to permit reduction. The hip capsule is opened with a ‘T’ incision, and the ligamentum teres is followed into the true acetabulum. Then with the head reduced in the socket, the capsule can be imbricated to hold the reduction secure.

In recent years, there has been a tendency to bypass the traction technique by doing femoral shortening: this is also supposed to reduce the pressure on the head. For this technique an osteotomy is made just below the greater trochanter, and the hip is then reduced. The osteotomy is held with a small dynamic compression plate. The hip is held in a spica cast for 3 months. Usually further bracing is not necessary, but some physicians continue it until a good socket is developing.

In the United States, in the treatment of hips that have been dislocated for about 18 months or more, it is felt that the socket may not have enough development left to become normal. In that case, an innominate osteotomy is usually also performed by placing a Gigli saw in the sciatic notch, and cutting through to just above the anterior inferior iliac spine. The inferior fragment is then pulled forward to cover the head, and a wedge of bone taken from the anterior superior iliac spine is placed between the two fragments, and held with two Kirschner wires or threaded pins.

The hips can usually be reduced up to about 5 years of age. After that age, results are poor, and a bilateral dislocation is usually left alone. The hips are quite symmetric in such cases, and treatment may increase the risk of one hip becoming reduced and the other left dislocated. It is more likely, however, that we will treat a solitary dislocation later than 5 years of age.

Allan DB, Gray RH, Scott TD, Tonkin M, Hughes JR, Evans GA. The relationship of ligamentous clicks arising from the newborn hip and congenital dislocation. J Bone Joint Surg 1985; 67: 491.

Andren L. Aetiology and diagnosis of congenital dislocation of the hip in newborns. Radiology, 1961; 1: 89.

Arzimanoglu A. Treatment of congenital hip dislocation by muscle release, skeletal traction and closed reduction in older children. Clin Orthop 1976; 119: 70.

Astley R. Arthrography in congenital dislocation of the hip. Clin Radiol 1967; 18: 253.

Barlow TB. Early diagnosis and treatment of congenital dislocation of the hip. J Bone Joint Surg, 1962; 44B: 292.

Browning WH, Rosenkrantz H, Tarquinio R. Computed tomography in congenital hip dislocation. The role of acetabular anteversion. J Bone Joint Surg, 1982; 64A: 7.

Chapchal GJ. The intertrochanteric osteotomy in the treatment of congenital dysplasia of the hip. Clin Orthop, 1976; 119: 54.

Chiarai K. Pelvic osteotomy for hip subluxation. J Bone Joint Surg, 1970; 52B: 174.

Chuinard EG. Femoral osteotomy in the treatment of congenital dysplasia and dislocation of the hip. In: Tachdjian MO, ed. Congenital Dislocation of the Hip. New York: Churchill-Livingstone, 1982: 437 - 78.

Clarke NMP, Clegg J, Al-Chalabi A. Ultrasound screening of hips at risk for CDH. Failure to reduce the incidence of late cases. J Bone Joint Surg, 1989; 71B: 9.

Cooperman DR, Wallensten R, Stulbrey SD. Post reduction avascular necrosis in congenital dislocation of the hip. J Bone Joint Surg, 1980; 62A: 247.

Fredensborg J, Nilsson BE. The effect of early diagnosis of congenital dislocation of the hip. Acta Paediatr Scand 1976; 65: 241.

Gallien R, Bertin D, Lirette R. Salter procedure in congenital dislocation of the hip. J Pediatr Orthop 1984; 4: 427.

Graf R. New possibilities for the diagnosis of congenital hip joint dislocation by ultra-sonography. J Pediatr Orthop 1983; 3: 354.

Harris NH, Lloyd-Roberts GC, Gallien R. Acetabular development in congenital dislocation of the hip. J Bone Joint Surg 1975; 57B: 46.

Ishii Y, Ponseti IV. Long-term results of closed reduction of complete congenital dislocation of the hip in children under one year of age. Clin Orthop 1978; 137: 167.

Iwasaki K. Treatment of congenital dislocation of the hip by the Pavlik harness: mechanism of reduction and usage. J Bone Joint Surg 1983; 65A: 760.

Lindstrom JR, Ponseti IV, Wenger DR. Acetabular development after reduction in congenital dislocation of the hip. J Bone Joint Surg 1979; 61A: 112.

MacEwen GD, et al. In: Lovell WW, Winter RB, eds. Pediatric Orthopaedics. 2nd edn. Philadelphia: JB Lippincott, 1986: 706 - 11.

Ortolani M. The classic: congenital hip dysplasia in the light of early and very early diagnosis. Clin Orthop 1976; 119: 6.

Rosen S von. Instability of the hip in the newborn. Fifteen years' experience in Malmo. Acta Orthop Scand 1970; 130: 13.

Schoenecker PL, Strecker WB. Congenital dislocation of the hip in children. Comparison of effects of femoral shortening and of skeletal traction in treatment. J Bone Joint Surg 1984; 66A: 21.

Tachdjian MO, ed. Pediatric Orthopaedics. 2nd edn. Philadelphia: WB Saunders, 1990: 298 - 526.

Wynne-Davies R. Acetabular dysplasia and familial joint laxity: two aetiological factors in congenital dislocation of the hip. A review of 589 patients and their families. J Bone Joint Surg 1970; 52B: 704.