Hip disorders in children

Published on 10/03/2015 by admin

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Hip disorders in children

Every complaint of groin, thigh or knee pain in a child should be taken seriously and examined very carefully without delay. Furthermore, any child who limps or shows limitation of movement at the hip joint should undergo a thorough examination. Most hip lesions in children can be diagnosed adequately with the help of a radiograph. For almost all these lesions, there are good and effective treatments, provided the diagnosis is made early enough.

Congenital dislocation of the hip

The incidence of congenital dislocation is between 1 and 2 cases per 1000, but it is four times as frequent in girls as in boys.¹ There seems to be a hereditary factor, because there is about a 5% chance of a second child being affected. This rises to 36% if one of the parents also had congenital dislocation of the hip.²

Although there are still questions about its aetiology, the condition seems to occur in the presence of some weakness of the joint capsule and elongation of the ligamentum teres.³ A deficiency of the rim of the acetabulum may also contribute in the development of the disease.⁴ However, the most important aetiological factor seems to be an imbalance between the action of the psoas muscle and the hip extensors.⁵ A relative shortening of the psoas presses the head of the femur upwards and laterally when the hip is extended by the contraction of the stronger hip extensors. In the presence of a weakness of the capsule, dislocation then occurs.

It is vital to make the diagnosis of a congenital dislocation as soon after birth as possible. Conservative treatment with an abduction brace ⁶ before the child begins to walk is completely adequate, but after the age of 4 even surgical repositioning is difficult and after the age of 7 it is almost impossible. Without treatment the dislocation may lead to a shorter leg, the formation of a neoacetabulum at the blade of the ilium and the supervention of early arthrosis.

Radiographs are not reliable in making the diagnosis of congenital hip dislocation in newborn babies. Early diagnosis, therefore, relies entirely on clinical tests. Those most used are known as Ortolani’s and Barlow’s tests.7,8 It should be remembered, however, that positive tests only indicate a capsular laxity and therefore the possibility of dislocation. For instance, the incidence of positive Ortolani’s and Barlow’s signs in newborns is about 10–20 per 1000, which is 10 times more than at the age of 2 months, which suggests that there is a tendency towards resolution of the capsular laxity.⁹

Clinical tests

Ortolani’s test

During this test the luxated hip is replaced manually.

Technique

The baby lies on the back, hips flexed to 90° and the knees completely flexed (Fig. 1a). The examiner grasps the leg with the contralateral hand in such a way that the thumb presses on the inner side of the thigh. The ring and middle fingers are placed along the outer thigh, so that the fingertips touch the trochanter. The other hand fixes the opposite hip. Abduction of the hip is now performed (Fig. 1b). In a subluxated hip, resistance will be felt at 45–60°. The moment the resistance is overcome, the femoral head rides over the acetabular edge and reduces. This is felt by the examiner. This sensation has wrongly been called a click, whereas the feeling is rather that of moving two knuckles of the wrist over each other. Ortoloni described this as a ‘segno dello scatto’ (ridge sign). Under this definition, the sensation has to be felt rather than heard.

Fig 1 Ortolani’s test for congenital dislocation of the hip: (a) position of the baby, (b) reposition of the dislocated hip by abduction.

Barlow’s test

The purpose here is to dislocate the hip first and then replace it. The hips of the baby are grasped in the same way as Ortolani’s test.

Technique

In this test, the thumb is placed further proximally on the femur. If the capsule is elongated or weak, the examiner can easily push the femoral head over the posterior rim of the acetabulum. This is indicated by a click.

Pressure with the middle finger behind the trochanter then moves the head anteriorly, where it comes to lie in the acetabulum again (Fig. 2). This to-and-fro movement of the femoral head over the acetabular rim indicates that the joint is unstable.

Fig 2 Barlow’s test for congenital dislocation of the hip.

Technical investigations

The diagnosis can usually be made with plain radiographs. However, during recent decades sonographic screening examinations have been shown to be superior in the early detection of congenital dislocations of the hip.10,11 In a study of sonographic screening examinations on 4177 newborns, all cases of congenital dislocation of the hip joint were found and classified.¹² Consequently, ultrasound screening is currently offered to all newborns in Austria and Germany and to newborns with selected risk factors in the United Kingdom, Scandinavia, Italy and France.^12,13,14

Treatment

The majority of unstable hips at birth stabilize in a very short time,¹⁵ but since the outcome of an ‘unstable hip’ is impossible to predict, all cases of hip instability in newborns must be taken seriously and treated. Hence, as soon as a positive Ortolani’s or Barlow’s test is found, an abduction brace is given until these clinical signs disappear.^16–18

If the diagnosis is made when the child starts to walk, surgical repositioning is required. Surgical reduction is almost impossible after the age of 7 years. If a ‘false acetabulum’ develops at the iliac bone, the functional disability may be small, especially if the disorder is bilateral.¹⁹ Pain and serious disability then start only in the fourth or fifth decade, when pseudarthrosis has occurred. If pain is not too severe, treatment can be conservative;²⁰ often some relief is obtained by one or two infiltrations with 50 ml of procaine 0.5% at the posterior aspect of the capsule.²¹ If pain and disability are too severe, surgery is required.²²

Congenital limitation of extension

Some children have an excessive forward tilt of the pelvis, as the result of congenital limitation of extension at the hip joints. They walk with a hyperlordosis, extending at the back instead of at their hips. This limitation is probably the result of a shortening of the psoas muscles.

Treatment consists of stretching the psoas and capsule in the same way as for early osteoarthrosis (see p. 633).

Arthritis of the hip in children

Transient synovitis

This is the commonest cause of hip pain in children and usually occurs under the age of 10 years. The child complains of pain in the groin, thigh and knee after some previous exertion. Sometimes only knee pain is present. The child limps and clinical examination of the hip shows a capsular pattern.

Although the pathogenesis of the disorder remains obscure, the conventional view is that it results from ordinary overuse. However, a correlation between transient arthritis and the development of Perthes’ disease has been shown repeatedly.23,24

Sonographic examination, together with X-ray examination, represent the first choices in the evaluation of a capsular pattern in a child and in the follow-up of transient synovitis.²⁵ In transient synovitis there is effusion but the effusion persists for less than 2 weeks. In the early stage of Legg–Calvé–Perthes’ disease the capsular distension persists for more than 6 weeks. A differential diagnosis between transient synovitis and Legg–Calvé–Perthes’ disease is therefore only possible by observing the ultrasonographic course of the disease.²⁶

Treatment is bed rest and non-weight bearing. It is advisable, if excessive intra-articular effusion is demonstrated by ultrasonography, to aspirate the fluid.²⁷ Most cases recover completely and without sequelae after a few weeks of bed rest.²⁸

Septic arthritis

The differential diagnosis with a transient synovitis is difficult.²⁹ A septic arthritis of the hip may have similar early symptoms as a transient synovitis, with the spontaneous onset of progressive hip, groin, or thigh pain; limp or inability to bear weight, fever and irritability.³⁰ Clinical examination shows a capsular pattern. A variety of clinical, laboratory, and radiographic criteria are used to help differentiate septic arthritis from transient synovitis. The four clinical predictors to differentiate between septic arthritis and transient synovitis are: history of fever, pain at rest, erythrocyte sedimentation rate of at least 40 mm per hour, and serum white blood-cell count of more than 12 000 cells per mm³.³¹ In cases of doubt, hip aspiration should be performed.