Pediatric Annals

Early Diagnosis and Pathology of Congenital Dislocation of the Hip

Ignacio V Ponseti, MD

Abstract

Screening tests for congenital dislocation of the hip have been described for over a century.1 Examination of the hips in newborn infants, however, has not been a routine procedure in many clinics until the last two or three decades. Early reports from some clinics indicated that the great majority of congenital hip dislocations could be diagnosed in the neonatal period.24 Recent publications, however, report problems encountered in the early recognition of this congenital deformity.5'6 There is overdiagnosis when all "loose" or "unstable" hips are considered abnormal and, on the other hand, dysplastic hips are missed in the neonatal period.

The degree of acetabular malformation at birth ranges from mild to severe, and similarly the femoral head and neck may be nearly normal or greatly misshapen. Because there are gradations of congenital dislocation of the hip from the mildest to the severest forms, "congenital hip dysplasia," as used by Ortolani," seems to be an appropriate, all-inclusive term to designate the many stages of this complex deformity.

The incidence of congenital dislocation of the hip is influenced by geographic and ethnic factors. In northern Europe and the United States the incidence was around 1.5 per 1000 live births before screening was started. Reports on screening results, however, have indicated that one in every 100 newborn infants may have unstable, "clicking" hips.5'6 These hips tend to become normal within the first weeks of life and should not be treated since even the mildest form of treatment for unstable hips in babies may be harmful and cause damage to the femoral head and proximal femoral growth plate.7 Babies with dysplasia of the hip have a typical diagnostic sign observed when the femoral head is caused to slide over an abnormal acetabular ridge with a jolt. This sign is found in 1.2 to 5 per 1000 babies, and the dysplasia may worsen unless treated in early infancy."

The incidence of failures of early diagnosis varies greatly. Thus, von Rosen in Malmo, Sweden reports a missed neonatal diagnosis in only 0.07 per 1000 live births.9 On the other hand, Bjerkreim in Oslo, Norway reports a missed early diagnosis in 2 per 1000 infants.10 Two recent publications from the United Kingdom report that a considerable number of congenital dysplasias are missed at neonatal examination and suggest that neonatal screening has not solved the problem of congenital dislocation of the hip and that early diagnosis may not always be easy and trouble free.5'6 It is obvious that in the screening for congenital hip dysplasia in infants we must try to avoid overdiagnosis and overtreatment and to reduce our failures in the detection of the truly dysplastic hips. For this we must understand clearly the pathology of the deformity and the anatomical basis for the diagnostic test used in the screening.

THE DIAGNOSTIC TEST

The diagnostic sign of congenital hip dysplasia was described by LeDamany in 1912 as "Signe de ressaut"" and by Ortolani in 1936 as "segno dello scatto."2 The words scatto used by Ortolani and ressaut used by LeDamany have been inadequately translated into English either as "click" or "clunk." These errors in translation have resulted in overdiagnosis of congenital hip dysplasia because clicks are so commonly elicited during the examination of the hips of newborn babies and have no diagnostic significance. Scatto and ressaut have been explained as "gliding over a ridge," and this sign that is rarely elicited has been termed "ridge phenomenon." '"

LeDamany's clear description of this sign in 19 1 2" is translated here:

The infant rests supine on a table. Thé examiner, facing him. gently, and without force, grasps the right…

Screening tests for congenital dislocation of the hip have been described for over a century.1 Examination of the hips in newborn infants, however, has not been a routine procedure in many clinics until the last two or three decades. Early reports from some clinics indicated that the great majority of congenital hip dislocations could be diagnosed in the neonatal period.24 Recent publications, however, report problems encountered in the early recognition of this congenital deformity.5'6 There is overdiagnosis when all "loose" or "unstable" hips are considered abnormal and, on the other hand, dysplastic hips are missed in the neonatal period.

The degree of acetabular malformation at birth ranges from mild to severe, and similarly the femoral head and neck may be nearly normal or greatly misshapen. Because there are gradations of congenital dislocation of the hip from the mildest to the severest forms, "congenital hip dysplasia," as used by Ortolani," seems to be an appropriate, all-inclusive term to designate the many stages of this complex deformity.

The incidence of congenital dislocation of the hip is influenced by geographic and ethnic factors. In northern Europe and the United States the incidence was around 1.5 per 1000 live births before screening was started. Reports on screening results, however, have indicated that one in every 100 newborn infants may have unstable, "clicking" hips.5'6 These hips tend to become normal within the first weeks of life and should not be treated since even the mildest form of treatment for unstable hips in babies may be harmful and cause damage to the femoral head and proximal femoral growth plate.7 Babies with dysplasia of the hip have a typical diagnostic sign observed when the femoral head is caused to slide over an abnormal acetabular ridge with a jolt. This sign is found in 1.2 to 5 per 1000 babies, and the dysplasia may worsen unless treated in early infancy."

The incidence of failures of early diagnosis varies greatly. Thus, von Rosen in Malmo, Sweden reports a missed neonatal diagnosis in only 0.07 per 1000 live births.9 On the other hand, Bjerkreim in Oslo, Norway reports a missed early diagnosis in 2 per 1000 infants.10 Two recent publications from the United Kingdom report that a considerable number of congenital dysplasias are missed at neonatal examination and suggest that neonatal screening has not solved the problem of congenital dislocation of the hip and that early diagnosis may not always be easy and trouble free.5'6 It is obvious that in the screening for congenital hip dysplasia in infants we must try to avoid overdiagnosis and overtreatment and to reduce our failures in the detection of the truly dysplastic hips. For this we must understand clearly the pathology of the deformity and the anatomical basis for the diagnostic test used in the screening.

THE DIAGNOSTIC TEST

The diagnostic sign of congenital hip dysplasia was described by LeDamany in 1912 as "Signe de ressaut"" and by Ortolani in 1936 as "segno dello scatto."2 The words scatto used by Ortolani and ressaut used by LeDamany have been inadequately translated into English either as "click" or "clunk." These errors in translation have resulted in overdiagnosis of congenital hip dysplasia because clicks are so commonly elicited during the examination of the hips of newborn babies and have no diagnostic significance. Scatto and ressaut have been explained as "gliding over a ridge," and this sign that is rarely elicited has been termed "ridge phenomenon." '"

LeDamany's clear description of this sign in 19 1 2" is translated here:

The infant rests supine on a table. Thé examiner, facing him. gently, and without force, grasps the right leg of the newborn with his left hand and the left leg with his right hand in a way that the web of histhumbembracestheknee of the infant. The pulp of the thumb is applied over the inner surface of the thigh, the index over the anterior surface, the middle finger extends along the lateral surface with its pulp resting over the trochanteric region. The ring and the little fingers cover the gluteal fold. The thigh is maintained at 90° flexion with the pelvis, the leg is equally bent at right angle with the thigh. The examiner uses one of the lower extremities to immobilize the pelvis while the other extremity is examined. In a first stage, the thigh held as indicated isadducted while the pulp of the thumb pushes the upper end of the thigh slightly laterally and the web of the thumb leans on the knee. If the hip is dislocatale, one may feel a jolt due to the subluxation of the femoral head. In a second stage, the examiner displaces the thigh in the opposite direction. The pulp of the middle finger pushes the trochanter anteriorly and medially while the thigh is abducted. With this maneuver, if the hip issubluxated. the head enters into the cotyloid cavity over its posterior border and with this reentry a jolt is always felt. The jolt ("ressaut") is sometimes slight, often it is quite clear, and it may happen that this jolt is strong enough to be heard.

What causes this sign was explained by Ortolani in 1948" but is commonly misunderstood. This lack of understanding may account in part for the problems encountered in the early recognition of congenital dysplasia of the hip.

The reduction test is not clearly elicited in infants born with an inveterate dislocation of the hip. The main clinical diagnostic test in these cases is restricted hip abduction. This restriction, however, may be slight if the child is loose jointed. In a complete, inveterate dislocation, the greater trochanter is palpated high underneath the glutei and the roentgenograms are diagnostic.

PATHOLOGICAL ANATOMY OF CONGENITAL DISLOCATION OF THE HIP

Anatomical, histological and histochemical studies of normal hips and of hips with congenital dysplasia of infants examined at autopsy, as well as arthrograms, will help in understanding the pathogenesis of the "ridge phenomenon" and the stages of severity of this congenital deformity.

The development of the hip joint is a complicated process. ' ' For normal acetabular development to occur as the pelvis enlarges, a most delicate balance must be maintained between the growth of the acetabular and triradiate cartilages enveloping a perfectly well centered femoral head. It is this balance, probably genetically controlled, that may be at fault in congenital dysplasia of the hip.14 There is also ample evidence that adverse intrauterine environmental features play a very important role in thé pathogenesis of hip dysplasia.15

Hip dysplasia often has been observed in premature infants and was well established in the right hip of a boy delivered after a 26-week gestation who weighed 800 grams and died shortly after delivery due to extreme prematurity and cardiopulmonary arrest secondary to pneumothorax. The right acetabulum was shallow and was spread out posteriorly where the atrophic labrum was flattened against the stretched joint capsule (Figure I). The acetabular joint surface was flattened in a small area posterosuperiorly and was divided into inner and outer parts by a smooth ridge of cartilage. This ridge was located between the outer and middle thirds of the superior, posterior, and inferior parts of the acetabular cartilage. The inner part of the articular surface had a smaller radius of curvature and in combination with the unaltered anterior acetabular cartilage surface formed the primary acetabulum. The articular surface peripheral to the cartilaginous ridge had a larger radius of curvature and was continuous laterally with the joint capsule with which it formed a cavity that accommodated the femoral head when it glided out over the ridge. The scatto or ressaut was produced when the femoral head glided over this ridge with a jolt.7

A more severe hip dysplasia was observed in the right hip of a girl with microcephaly and the Arnold-Chiari malformation. Her presentation was occipital and she was delivered after 42 weeks of gestation. She weighed 1,770 grams and died nine minutes after delivery. The right acetabular cavity was smaller than the left one (Figure 2). In the posterosuperior part of the acetabulum of the right dysplastic hip there was a shallow trough lying along the acetabular margin. At the anterior end of the trough, there was a bulge of cartilage, and extending posteriorly and down to the inferior margin of the acetabulum was a ridge. This ridge divided the acetabular articular surface into two parts as in the previous case; one, the inner two-thirds, central to the ridge, which in conjunction with the anterior wall formed the articular portion of the primary acetabulum; and the second, the posterosuperior outer third, which in conjunction with the joint capsule and labrum formed a rudimentary secondary acetabulum. The labrum at the periphery of the acetabular cartilage was atrophic and adherent to the joint capsule.

The acetabular cartilage was softer in the right hip than in the left. The ridge, or bulge, appeared to be produced by the pressure of the subluxated femoral head on the outer margin of the acetabular cartilage (Figure 3). On arthrograms this bulge appeared to be an inverted labrum. The ridge was not a fixed deformity, because it was observed to flatten out considerably when the femoral head was reduced.

Figure 1. Right acetabulum of a normal 26 week old male fetus. The acetabular cavity is shallow and has a ridge (arrow) which divides the joint surface into an inner and an outer part. The inner part forms the primary acetabulum. The outer part is continuous laterally with everted labrum and joint capsule.

Figure 1. Right acetabulum of a normal 26 week old male fetus. The acetabular cavity is shallow and has a ridge (arrow) which divides the joint surface into an inner and an outer part. The inner part forms the primary acetabulum. The outer part is continuous laterally with everted labrum and joint capsule.

This case and the previous one are typical of the usual degree of hip dysplasia seen in infants. The ridge appears to be formed exclusively by a bulge or thickening of soft acetabular hyaline cartilage. Within this cartilage the chondrocytes are irregular in size, shape and arrangement; in some areas they are clumped and in other areas they are large and show a tendency to undergo degeneration. The matrix stains irregularly with alcian blue, and cartilage canals are abundant.7 The labrum may be atrophic and pressed against the inner aspect of the joint capsule and does not participate in the formation of the acetabular ridge. In the dysplastic hips of these infants a jolt is felt when the femoral head is made to slide over the ridge.

Very severe degrees of hip joint dysplasia are occasionally seen in otherwise normal newborn children.16 These severe dislocations are more commonly found, however, among infants with other congenital anomalies and a high perinatal mortality.7 The femoral head is out of the primary acetabulum and cannot be fully reduced because the acetabular cavity is too small. The femoral head is misshapen and is found dislocated superoposteriorly in a false or secondary acetabulum. The femoral head is covered by a very thick and large joint capsule. The primary or true acetabulum is small and sharply demarcated from the secondary or false acetabulum by a large ridge. This ridge is formed by a bulge of acetabular cartilage covered by a hypertrophic, inverted labrum.7 The femoral neck may be anteverted.

Figure 2. Pelvis and upper femur of a full term female infant with dysplasia of the right hip. The acetabulum and femoral head are smaller on the right than on the left. There is a ridge (arrow) close to the posterior margin of the acetabular cartilage.

Figure 2. Pelvis and upper femur of a full term female infant with dysplasia of the right hip. The acetabulum and femoral head are smaller on the right than on the left. There is a ridge (arrow) close to the posterior margin of the acetabular cartilage.

Figure 3. Right acetabulum and femoral head of case seen in Fig. 2. The acetabular cartilage was soft and the ridge, or bulge, appeared to be produced by the pressure of the subluxated femoral head on the outer margin of the acetabular cartilage.

Figure 3. Right acetabulum and femoral head of case seen in Fig. 2. The acetabular cartilage was soft and the ridge, or bulge, appeared to be produced by the pressure of the subluxated femoral head on the outer margin of the acetabular cartilage.

In congenital dislocation of the hip, the cartilage of the femoral head appears histologically normal. The ossification of the femoral head, however, is greatly delayed, in contrast to the normal ossification observed in the upper femoral growth plate.

Figure 4. Roentgenogram of the pelvis of a female infant taken three days after birth (above) and at eleven months of age (below). The hips appear to be normal on the roentgenogram taken shortly after birth. The left hip was dislocated at eleven months of age.

Figure 4. Roentgenogram of the pelvis of a female infant taken three days after birth (above) and at eleven months of age (below). The hips appear to be normal on the roentgenogram taken shortly after birth. The left hip was dislocated at eleven months of age.

The hip joint capsule in congenital dislocation of the hip is thicker and longer than in the normal hip.'7 The bundles of collagen fibers are thicker than in the normals and there are areas of hyalinization in the older children.

In the normal hip joint capsule of infants, the elastic fibers are thin, evenly distributed and randomly oriented, although they are often parallel to the collagen fiber bundles. In the capsules of congenital hip dysplasia, the elastic fibers are of various sizes and unevenly distributed. Abundant and thick elastic fibers are present in some areas, whereas in other areas they are absent.17

ETIOLOGY OF CONGENITAL DISLOCATION OF THE HIP

The diagnostic test for congenital dislocation of the hip in early infancy described by LeDamany and by Ortolani is contingent on the presence of a ridge in a dysplastic acetabulum/ The acetabular cartilage is soft and histologically abnormal.7 Acetabular dysplasia, inherited in many families, appears to be the main etiological factor of congenital dislocation of the hip. Other factors, acting in utero or shortly after birth, also play an important role in the etiology of the deformity. Thus, oligohydramnios as seen (e.g., in anomalies of the urinary tract in breech presentation with hyperextended legs and in neuromuscular diseases) are well documented causal factors of congenital dislocation of the hip.15 Positioning the thighs in abduction after birth appears to favor improvement of the acetabular dysplasia whereas the deformity tends to worsen when the legs are wrapped together.

Laxity of the hip joint capsule has been implicated in the pathogenesis of Congenital dislocation of the hip.14 Hip joint laxity, often observed in infants, allows for some hip instability but a typical sign of dislocation cannot be elicited. On arthrograms a pool of contract medium may collect in the deeper part of the acetabulum. At postmortem examination of stillborn infants with unstable hips and a negative Ortolani sign, the capsule may appear stretched and the femoral head can be pulled slightly away from the acetabulum but there are no definite anatomical or histochemical anomalies in these hips.

The relaxation of the hip joint capsule has been blamed on hormonal imbalance produced by placental sex hormones and relaxin. 18 We have observed more collagen fibers and collagen fibrils of a smaller diameter in the capsule of infants with congenital dislocation of the hip than in the normals.17 The increase of collagen is in contrast with what is expected from the effects of increased estrogen.

Congenital dislocation of the hip is rare in patients with great looseness of joint capsules and ligaments, such as in Down's syndrome, and it has not been reported in patients with Ehlers-Danlos syndromes or in Marian's disease. Congenital dislocation of the hip is common in the Island Lake population in Manitoba, Canada. In the children of this population no correlation was shown between congenital dislocation of the hip and generalized joint laxity."

The mild changes observed in the hip joint capsule of patients with congenital dislocation of the hip appear to be secondary to the mechanical stresses caused by the dislocation and can hardly explain the major morphological and histochemical anomalies observed in the acetabulum of fetuses and infants with hip dysplasia. Since the great majority of the unstable hips in the neonatal period become normal in a few weeks without treatment, the laxity is believed to be a physiological stage of early infancy. I have not observed late subluxations of the hip in patients who have a negative Ortolani sign in infancy, such as has been reported by others.20

Complete inveterate congenital dislocation of the hip at birth is rare, and the diagnosis may be missed in the neonatal examination because the Ortolani's test in these cases is not clearly elicited. The greater trochanter, however, is palpated high above the acetabulum and hip abduction is greatly restricted. The roentgenogram in these cases is diagnostic. These dislocations occur often in children delivered by the breech with the legs extended or in cross-leg position.15 There may be olioghydramnios and the infant may have other congenital anomalies. It is important to obtain a prenatal history, since the mother may have felt fetal and hand movements but no kicking for one month or more before delivery. Under these circumstances, and particularly if there is a positive family history of congenital hip dislocation, the clinician should have a high degree of suspicion and obtain roentgenograms of the pelvis.

In the diagnosis of congenital hip dysplasia, the roentgenographic examination of the pelvis in an infant under three months of age is not fully reliable. The developmental anomalies in hip dysplasia occur in the cartilaginous acetabulum and femoral head and are not visible in the x-rays. The ossification of the ilium, ischium and pubis are usually normal for several months. Therefore, a negative roentgenogram at birth or in the first two or three months does not indicate that the hip is normal (Figure 4). A slanted acetabular roof, the proximal and lateral displacement of the femur and delayed ossification of the femoral head are reliable signs of hip dysplasia in roentgenograms taken after three to six months of age.

The screening for congenital hip dislocation must be repeated at three and six months of age since an occasional dysplastic hip may be missed in the neonatal screening. The Ortolani test may be negative at this age but the degree of hip abduction will be limited and the femur of the dislocated side may appear short. X-rays of the pelvis should then be obtained in all suspected cases.

Unilateral or bilateral tightness of the hip adductors is not uncommonly observed in normal children a few months old. The tightness may limit considerably the range of hip abduction. If the x-rays of the pelvis are negative, the hips can be considered normal and should not be treated to avoid damage to the femoral head. The adductor tightness may last several months but it eventually resolves.

CONCLUSION

Children with congenital dislocation of the hip have a faulty development of the acetabulum. At birth the acetabular joint surface is flattened and is divided into inner and outer parts by a smooth ridge of cartilage. When examining the infant with the thighs held at right angle with the pelvis, the femoral head can be felt to glide over the ridge with a jolt. This sign is negative in an inveterate dislocation when the head of the femur cannot be reduced into the primary acetabulum.

All infants should be screened for congenital hip dysplasia in the neonatal period and again at three and six months of age.

Roentgenograms may be misleading in the newborn since a dysplastic hip may appear normal. After three months of age roentgenograms are of value to establish the degree of dislocation.

REFERENCES

1. Howorth B: Development of present knowledge of congenital displacement of the hip. Clin Orthop 125:68. 1977.

2. Ortolani M: La lussazione congenita dell 'anca. Suovi criteri diagnostici profilattico correttivi. Bologna. Capelli. 1948.

3. von Rosen S: Early diagnosis and treatment of congenital dislocation of the hip joint. Acta Orthop Stand 26:136. 1956.

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

5. Walker G: Problems in the early recognition of congenital hip dislocation. Br Med J 1971, ? 147.

6. Noble TC. Pulían CR, Craft AW. et al: Difficulties in diagnosing and managing congenital dislocation of the hip. Br Med J 2:620, 1978.

7. Ponseti IV: Morphology of the acetabulum in congenital dislocation of the hip. J Bone Joint Surg 60-A:586, 1978.

8. Scapinelli R. Ortolani M: La displasia congenita delle anche nell'età pediatrica. Diagnosi e trattamento precoci e ultraprecoci. LVII Congresso della Società Italiana di ortopedia e Traumatologia. Bologna, 1972. Tipografìa editrice. La Grarangola, Padova.

9. von Rosen S; Diagnosis and treatment of congenital dislocation of the hip joint in the newborn. J Bone Joint Surg 44-B:284, 1962.

10. Bjerkreim I: Congenital dislocation of the hipjoint in Norway. Acta Orthop Stand (suppl) no 157, 1974.

1 1. LeDamany P: La Luxation Congénitale de Ia Hanche. Paris, Alean, 1912.

12. Fellander M, Galdnikoff H, Jacobsson E: Instability of the hip in the newborn. Acta Orthop Scand (suppl) no 130:36, 1970.

13. Ponseti IV: Growth and development of the acetabulum in the normal child. J Bone Joint Surg 60-A:575. 1978.

14. Wynne-Davies R: Acetabular dysplasia and familial joint laxity; two etiological factors in congenital dislocation of the hip. J Bone Joint Surg (Br) 52-B:704, 1970.

15. Dunn PM: Perinatal observations on the etiology of congenital dislocation of the hip. Clin Orthop 119:11. 1976.

16. Stanisavljevic S: Diagnosis and Treatment of Congenital Hip Pathology in the Newborn. Baltimore. Williams and Wilkins. 1964.

1 7. Ippolito E, Ishii Y, Ponseti IV: Histologic, histochemical, and ultrastructural studies of the hip joint capsule and ligamentum teres in congenital dislocation of the hip. Clin Orthop 146:246, 1980.

18. Andren L: Pelvic instability in newborns: with special reference to congenital dislocation of the hip and hormonal factors. Acta Radiologica (suppl) 212, 1962.

19. Walker JM; Generalized joint laxity in Igloolik Eskimos and in Island Lake Amerindians. Hum Biol 47:263, 1 975.

20. Ryder CT. Mellin GW, Caffey J: The infant's hip - normal or dysplastic. Clin Orthop 22:7. 1962.

10.3928/0090-4481-19820601-08

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