The early diagnosis of developmental dysplasia of the hip

Transcription

1 Current Orthopaedics (2002) 16, 57^ 64 c 2002 Published by Elsevier Science Ltd. doi: /ycuor.235, available online at on CHILDREN The early diagnosis of developmental dysplasia of the hip M. Conybeare 74 London Road, Canterbury, Kent CT2 8LS, UK KEYWORDS hip dislocation, congenital diagnosis, ultrasonography Summary The meaning of the term developmental dysplasia of the hip is discussed and a brief description ofthe fetal developmentofthe hip isgiven.the potential methods for making the diagnosis of hip dysplasia are described with an emphasis on diagnostic indicators and upon clinical and ultrasonic methods.the application of these methods in the context of screening whole populations, it is suggested, is currently problematic and further researchis required before a solution is found which meets the ideals, which are described, of screening programmes in general. c 2002 Published by Elsevier Science Ltd. INTRODUCTION If, in any given community, no attempt whatsoever is made to make an early diagnosis of developmental dysplasia of the hip (DDH), no examination of the musculoskeletal system is made in the neonatal period and no screening e orts are made in the rst year of life, what do we believe that the consequences would be? Firstly, we know that they will vary considerably from place to place across the world. In the UK, for instance, approximately 1 in 1200 children will show a profound limp when they start walking and X-ray examination will demonstrate a displacement of the femoral head from within the acetabulum which may di er in degree but which will always, if left untreated, herald future pain and consequent disability. From Belgrade in 1975, Klisic reported a very much higher incidence of this condition whilst it is virtually unknown in the Bantu tribe of South Africa. Screening for hip dysplasia therefore constitutes apriorityinsomeplacesbutisoflittleconsequencein others. In addition, a certain number of individuals who have no limp during childhood go on to develop relatively early arthritis in adult life associated with the typical pathological ndings of hip dysplasia. Lloyd-Roberts, in his studies of the aetiology of osteo-arthritis, suggested that 30% was attributable to hip dysplasia whilst Wroblewski pointed out that the characteristic inturned labrum is frequently found on direct examination of the hip joint during replacement arthroplasty. If a simple means could be found to avoid both the limping child and late arthritis due to dysplasia, it would Correspondence to: MC.Tel.: ; Fax: clearly be extremely desirable that it should be applied in any at-risk community.on the face of it this seems a relatively simple proposition. In the light of the experience of the last 50 years, however, it has proved to be fraught with di culties of all sorts. What would be the requirements of a screening programme designed to prevent hip dysplasia and its consequent morbidity? They are in principle no di erent from the basicrequirements of screening programmes in general: 1. It should be able to make the diagnosis in all cases and yetitshouldnotleadto falsepositives (i.e.itshould be both sensitive and speci c). 2. It should be easy and inexpensive to apply. 3. It should not in itself produce any undesirable condition or complication. 4. The diagnosis, once made, should lead to straightforward, easily applied and totally successful treatment. This alone is the justi cation of all our attempts to make an early diagnosis in the rst place. To what extent have the methods of screening so far applied met up to these expectations? Before we attempt to answer this question, we need to understand what is meant by dysplasia and to explore what is known about the development of the hip joint. THE MEANING OF DYSPLASIA RELATED TOTHE HIP The classical derivation of the word dysplasia comes from the Greek and is translated as malformation. In practice, this means very simply that the joint fails to

2 58 CURRENT ORTHOPAEDICS develop normally and it would be reasonable to attribute abnormal development to either geneticor environmental in uences or to both these factors working together. We recognize dysplasia by di erent means at di erent ages. In the neonate (the group that primarily concerns us here), ultrasound examination is the most useful tool, identifying shallowness in the cartilaginous acetabulum and the displacement of the femoral head from the socket which we know may lead to dysplasia; this will be discussed in more detail later. As the infant develops through the early years of life, gradually exhibiting more bony development on both sides of the joint, X-ray examination takes over, primarily by identifying a delay in this process but also the failure of the joint to form appropriate matching surfaces. Secondarily the developmental failures give rise to abnormal clinical ndings such as instability of the joint or limitation of abduction movement but, whilst these ndings may lead to the suspicion of dysplasia, they are not diagnostic in themselves. For sake of simplicity, however, this whole spectrum of abnormality, however observed, has come to be known as DDH and it is for the clinician in charge to decide how serious the situation is from the information available and thereby to deduce what treatment he feels would be most e ective. THE DEVELOPMENTOF THE HIP JOINT The cavity of the hip joint appears in primitive cartilage at about 8 weeks of gestation when the fetus measures 30 mm in length. Manual dislocation of the femoral head from the acetabulum becomes theoretically possible at about 12 weeks of gestation when the femoral head is hardly bigger than a pin. The musculature surrounding the hip begins to initiate active movement of the joint at 16weeksandatthesametimeboneisforminginthe cartilaginous anlages of the pelvis and femoral shaft. Bone formation in the femoral head is very variable in its onset but on average does not take place until the child is 3 months old and may be deferred until 1 year or more. The relative positions of the pelvis and femur are important in our consideration of the factors causing abnormal development. Initially, the fetal hip joint posture is one of the exion, abduction and external rotation, more extreme on the left side (which is interesting as this is the hip which is more frequently involved with dysplasia). In normal pregnancy, movement increases as time goes on and it is believed that this movement aids the development of the matching femoral head and acetabulum. There is considerable variation from fetus to fetus but on average at12 weeks femoral neck anteversion is 5^101 and acetabular anteversion about 401. By the time of birth, femoral anteversion has reached 351 and thereafter, in the normal infant, it diminishes again. Apart from the inclinations of the acetabulum and femoral neck and their relative positions in utero, another anatomical feature of importance in stability, and therefore in development overall, is the depth of the acetabulum. Le Damanay showed that the cartilaginous depth of the acetabulum actually decreases towards term but Ralis and McKibbin later pointed out that the development of the labrum is the crucial factor at this stage, giving extra protection in the vital superior and posterior areas. PREDISPOSING FACTORS AND DIAGNOSTIC INDICATORS Anything that can be done to identify the infant at risk of having or developing DDH is to be welcomed in our attempts to make an early diagnosis of the condition since early diagnosis usually leads to more successful treatment. In this context, the environmental factor that has emerged most clearly is that of breech position in utero. The position of exion, abduction and external rotation, mentioned above, combined with the restriction of lower limb movement which occurs in the breech position or when there is oligohydramnios (lack of amniotic uid), can lead to displacement of the femoral head. This e ect is exaggerated if the fetal leg is also extended (the socalled extended breech position), presumably as a result of tension in the hamstrings. The other important predisposing factors are genetic though the exact nature of these have not been elucidated. Epidemiological studies have suggested that acetabular depth may be genetically determined and familial joint laxity has also been implicated but further research in this area is clearly required. For instance, other features of bony development such as the degree of femoral or acetabular anteversion may also be inherited. Other congenital anomalies may be present in conjunction with DDH. Torticollis and foot deformities are the most obvious on clinical examination and special screening attention should be given to all infants demonstrating these conditions. Whilst it is well known that DDH is at least four times more common in female babies and is also more common in rst-born children, these facts are not particularly helpful to us in our screening e orts. In our attempts to make an early diagnosis, the important thing ultimately is to recognize that a positive family history, breech position in utero and the presence of other congenital anomalies are the most useful indicators.they will, however, only be present in a proportion of cases. 1

3 THE EARLY DIAGNOSIS OF DEVELOPMENTAL DYSPLASIA OF THE HIP 59 CLINICAL EXAMINATION The cornerstone of the clinical examination for DDH in the neonate is the demonstration of instability although asymmetries of posture and movement such as limitation of abduction of the hip, shortening of the limb or attening of the buttock may also be observed.the main tests used over the last 40 years have been those described by Ortolani, popularized by Von Rosen, and by Barlow. They are dependent upon the examiner feeling the movement of the femoral head in and out of the acetabulum. Unfortunately, the sensation experienced by the examiner varies considerably from case to case; sometimes the femoral head can be felt to move in and out of the socket and sometimes the only sensation is the clunk of reduction. Further alteration in the exact ndings can be caused by variation of the position in which the infant s limb or pelvis is being held. Experience in the UK with a national screening programme 2 based on clinical methods is well summarized by Dezateux and Godward. 3 Numerous studies from round the world have demonstrated how di cult it is to organize e ective screening programmes using these methods. The reasons for failure may be summarized as follows: 1. In a condition such as DDH with a relatively small incidence, a recently trained observer may have never experienced the sensation of hip instability and may therefore have trouble in recognizing it. Most hospitals have found it di cult to arrange for experienced observers to be available at all times to make or supervise the examination. 2. Even experienced observers can fail to nd anything clinically abnormal on the neonatal examination of an infant which later demonstrated the features of DDH. This implies that the examination itself is unreliable and the suggested reasons are that (a) The infant is often tense and resists examination, (b) The hip was already dislocated at the time of the examination and was irreducible so that no movement could be demonstrated. This is particularly a problem in bilateral cases where there may be no asymmetry of any kind. (c) By the time of the examination the hip joint, although abnormally developed, has tightened up. It has clearly been demonstrated by Barlow that the incidence of hip joint instability reduces during the few days of life Screening programmes, to be e ective, demand constant monitoring and supervision which is rarely available. In addition, there remains the possibility that not all cases of DDH demonstrate abnormality at birth, clinically or otherwise. Further experience with ultrasound examination may well elucidate this (see below). X-RAY Although X-ray screening of neonates has in the past been advocated, the lack of ossi cation in the femoral head of the newborn child makes interpretation extremely di cult; this factor, together with anxieties about radiation safety, has led to the rejection of the method in favour of ultrasound examination. CTAND MR SCANNING On account of cost and di culties in practical application, both these techniques are inappropriate. ULTRASOUND The work of Graf, in particular, has focussed interest upon ultrasound as a screening method. Initially, there was an expectation that ultrasound screening of all infants in the neonatal period would prevent late presentation of hip dislocation in childhood and possibly detect hip dysplasia which would only manifest itself as osteoarthritis in the middle years of life. In reality, however, experience has shown up a number of problems which require further discussion. Method Graf initially described 5 a method of screening which is conducted with the infant in a lateral decubitus position and the hip placed in 351 of exion and101 of internal rotation. A coronal image is obtained with the head of the ultrasound transducer over the lateral aspect of the hip. No attempt is made to displace the femoral head, the identi cation of hip dysplasia depending upon the measurement of two angles, named the alpha and beta angles, which are de ned by the morphological characteristics of the cartilaginous and bony acetabulum (Fig. 1A and B). Hips may then be categorized into di erent types carrying di ering prognoses. For detailed discussion of the method, the reader is referred to Graf s monograph on this subject. 6 There was considerable criticism of this technique on the grounds of intra- and inter-observer error and, with thedevelopmentofmoresophisticatedhand-heldrealtime equipment, a dynamictechnique was developed and described by Harcke et al. 7 which emphasizes hip position and stability rather than the morphological characteristics of the acetabulum. This examination is performed with the infant in a supine position and the pelvis at. As a minimum two images are recorded. In the rst, the coronal/ exion view, the hip and knee are

4 60 CURRENT ORTHOPAEDICS Figure 1 (A) Diagram ofthe ultrasound appearance of aninfant s hip to illustrate the de nition of Graf s a and b angles: (1) the base line, (2) the cartilageroof line drawnfromthe bonyedge oftheiliumthroughthelabrumand (3) the bonyroof line drawnfromthe bony edge of the acetabulum through the lowest point of the ilium atthe centre of the joint. (B) Atypical coronal ultrasound image demonstrating (1) the jointcapsule, (2) the labrum, (3) the bony edge ofthe ilium and (4) the lowest point ofthe ilium. Figure 2 (A) The scanning position for coronal exion view; (B) The scanning position for the transverse neutral view. exed to 901 and the transducer is aligned at 901 to the femur. In the second, the transverse/neutral view, the hip and knee are extended and the transducer is rotated through 901 so that it then lies at 901 to the long axis of the body (Fig. 2A and B). Using this technique, a grading system can be obtained which guides the further management of the infant s hip (Fig. 3A^E). In the course of obtaining the coronal image, stress may be applied to the exed hip via the knee and thigh as described by Barlow for his provocation test in clinical examination. Harcke also describes using the Ortolani manoeuvre (again derived from the well-known clinical test) as part of a full dynamicultrasound examination. Up to 6 mm of displacement may be obtained normally in the rst few days of life and this, as will be seen, has an important bearing onthetimingandultimatelythemodeofemployment of the ultrasound examination as part of a screening programme. It should be noted at this stage that the exact method of examination is probably not criticalfthe most important factor being that, as in every other examination technique, the observer should be thoroughly trained in

5 THE EARLY DIAGNOSIS OF DEVELOPMENTAL DYSPLASIA OF THE HIP 61 Figure 3 (A) Grade1: the femoral head is well contained in the acetabulum. (B) Grade 2: the femoral head is in the acetabulum but not in contact with the oor. (C) Grade 3: the acetabulum appears shallow in the coronal view but there is only a small gap on the transverse view. (D) Grade 4: the acetabulum appears shallow.on the transverse view, the head is displaced posteriorly and a gap is present. (E) Grade 5:The femoralheadlies outside the acetabulum onthe coronalview; a transverse viewcannot be obtained because it is obscured by the greater trochanter.

6 62 CURRENT ORTHOPAEDICS Figure 3 Continued both the practical application and interpretation of the examination methods that are used. In fact,graf, Harcke and Clarke agreed at a concensus conference in1993 that a minimum examination should consist of 1. imaging of a coronal standard plane with measurements and quanti cation and 2. a dynamicstress test. 8 Sensitivity and speci city In considering these aspects of ultrasound examination, we must rst clearly de ne our objective.unfortunately, we cannot currently include the eradication of adult hip dysplasia as part of this objectivefthis is a bonus that may accrue in the course of time, but there will be no way of assessing success or failure of this aim until screening programmes have been in place for many more years.we will therefore adopt the abolition of hip dysplasia in children over 3 months of age as our end point.on this basis, it would appear that ultrasound examination at birth is highly sensitive but not very speci c. Many of the hips that have slight abnormalities at birth will on serial screening be shown to develop normally. In the series reported by Marks et al. 9 6% of babies had abnormal scans at birth and, whilst 20% of these were lost to follow-up (none with the more severe abnormalities) only 0.24% required active treatment. On the other hand, the same series reports a nil incidence of late-diagnosed cases. Timing of the examination If ultrasound screening is carried out at birth, the high sensitivity leads to the need to repeat the examination at intervals during the rst few weeks of life in the knowledge that a large proportion of hips showing a slight abnormality initially will be normal by the time that the infant is 6 weeks of age. In practice, this means that a lot of parental anxiety is created unnecessarily. In addition, uncertainty about interpretation can lead to the treatment of hips that were going to develop normally, with the concomitant risk that they might su er from a complication of treatment such as avascular necrosis of the femoral head. It is accepted, however, that this should not occur in units with highly trained and experienced sta conducting and interpreting the examination. In the ideal world, therefore, it might be recommended that every infant should have its hips examined by ultrasound at 6 weeks of age.

7 THE EARLY DIAGNOSIS OF DEVELOPMENTAL DYSPLASIA OF THE HIP 63 PRACTICALITIES In societies where childbirth usually takes place in hospital, it is theoretically possible to examine every neonate for hip abnormality by clinical examination and/or ultrasound, but recalling every baby for screening at 6 weeks of age is virtually impossible. Although this might lead us back to the examination being conducted at birth with all the subsequent follow-up of minor abnormality, as discussed above, there has been widespread anxiety about this on cost grounds alone. Clegg et al. 10 discuss this and conclude that the overall cost of the management of DDH increased marginally following the introduction of universal ultrasound screening at birth in their district but they pointed out that it is impossible to quantify in nancial terms the improvement in the quality of life which had been conferred on the children by early diagnosis resulting in simpler and more e ective treatment over a shorter period of time. On the other hand, the cost of training a large number of ultrasonographers and supervising clinicians is not mentioned and nor is the cost of running the supervising clinics. In Austria, universal screening at birth has been adopted nationwide but although Graf is reported in 1993 by Donaldson 11 as writing we no longer see late-diagnosis DDH in the Steirmarch region of Austria there are, as yet, no reports of the e cacy of this scheme on a nationwide basis and the cost is unknown. DISCUSSION Having reviewed the tools at our disposal and found that clinical diagnosis and ultrasound are realistically the only methods that can be applied to the problem, let us look back at the criteria which were outlined in the introduction to this paper and see to what extent the methods meet up to them. At the same time, it is appropriate to discuss how they might be used e ectively in combination. As far as sensitivity and speci city are concerned clinical diagnosis, although variable in its success, has been shown to be insu ciently sensitive to constitute by itself a successful screening method. 12 Ultrasound, on the other hand, is very sensitive and, when applied at birth, is su ciently speci c, probably being most accurate when applied at 6 weeks of age. On the other hand, as pointed out above, it is not realisticto attempt to recall whole populations for screening at that age, default rates would quite simply be too large. Ease of application and cost are inextricably bound together since both the proposed screening methods demand a high level of expertise in those individuals performing and interpreting the examinations. Training is a time-consuming and therefore costly activity which has to be taken into consideration as well as the time of the personnel and the cost of equipment in the examination itself. The cost of training can be reduced by having members of the permanent sta perform the examinations (rather than a paediatrictrainee, which is frequently the case for clinical examinations in the UK hospitals). Costs can be further reduced by using specially trained ultrasonographers rather than doctors to make recordings although a radiologist, orthopaedic surgeon or paediatrician will still be needed to interpret the scans.whatever the method used, close supervision and monitoring of performance is demanding but essential. Whilst it has been argued that repeated clinical examination of the newborn might in itself lead to persisting instability and dysplasia, there is no convincing evidence for this and it has to be said that neither clinical nor ultrasound examination is known to produce any undesirable condition or complication. Again, it would be possible to avoid repeated clinical examination of one infant by increasingly senior members of sta by using an experienced member of the team in the rst place or by making it a policy to order ultrasound examination in any case of doubt. Our nal criterion for successful screening was that the diagnosis once made should lead to straightforward, easily applied and totally successful treatment. Whilst it is not within the scope of this article to discuss treatment, the Pavlik harness, if properly supervised, will simply and successfully treat the vast majority of babies with persisting hip instability in the rst few weeks of life. The very small number of hips that are irreducible at birth provide a much more di cult problem and the most that can be said for early diagnosis by screening in these cases is that the result of earlier treatment, usually by surgery, should be better and more simply achieved than it would be otherwise. Clinical examination alone therefore does not, in the light of published experience, diagnose a su cient proportion of those infants a ected by the condition and ultrasound screening applied universally at birth, although e ective, leads to a large number of false positives, all of which have to be followed up, with associated expense and parental anxiety. Some centres have therefore employed selective screening in which clinical screening and careful assessment of risk factors are carried out at birth and ultrasound examination is carried out on the subgroup thus selected at 4 ^ 6 weeks. In this way, many of the hips which were unstable at birth can be con dently declared normal. The results of such a programme were reported by Boeree and Clarke. 13 They reduced the secondary (6 week) screening rate to 7% and the treatment rate to 0.44% of the original cohort of infants. Six (0.22 per 1000), however, presented with DDH after they were 12 weeks old. This contrasts with the results of Marks et al. 9 who screened all infants with ultrasound at birth and found 6% to be abnormal (including all those with clinical instability). The treatment rate was 0.24%. No hip in this cohort of infants was diagnosed later with DDH.

8 64 CURRENT ORTHOPAEDICS CONCLUSIONS 1. Energeticscreening for developmental hip dysplasia in the best centres has given su ciently good results overall for a recommendation to be made that screening e orts should continue on a widespread basis across those populations who have been shown to be at risk. 2. The planning of the screening process and the exact combination of methods used will depend to some extent upon the environment concerned but present evidence suggests that a combination of meticulous clinical screening at birth with ultrasound screening at around 6 weeks of age is organizationally and nancially realistic and should result in the early diagnosis of the vast majority of cases. 3. The success of this scheme is dependent upon a clear realization that awareness of risk factors at birth is critically important. 4. Successful screening leads to simpler, less expensive treatment and better outcomes, with all the attendant bene ts to patients and their families. RESEARCH DIRECTIONS K Develop an ultrasound method which is more speci c for the detection of DDH at birth so that the follow-up of hips that are going to develop normally is unnecessary K Establish more accurate monitoring of the performance of nationwide screening programmes K Follow a screened group of infants for 20 years or more in order to establish whether early treatment not only prevents dislocation but also prevents adult hip dysplasia. K Further elucidate the genetic factors predisposing an individual to the development of DDH ACKNOWLEDGEMENTS Figs. 2 and 3 are reproduced by kind permission of John Clegg and the Journal of Bone and Joint Surgery. REFERENCES 1. Clarke N M P, Clegg J, Al-Chalabi A N. Ultrasound screening of hips at risk for CDH. Failure to reduce the incidence of late cases. J Bone Joint Surg 1989; 71-B: Standing Medical Advisory Committee. Screening for the Detection of Congenital Dislocation of the Hip in Infants. London: Department of Health and Social Security, 1969 (revised 1986). 3. Dezateux C, Godward S. Evaluating the national screening programme for congenital dislocation of the hip. J Med Screening 1995; 2: Barlow T G. Early diagnosis and treatment of congenital dislocation of the hip. J Bone Joint Surg 1962; 44-b: Graf R. Classification of hip joint dysplasia by means of sonography. Arch Orthop Trauma Surg 1984; 102: Graf R, Wilson B. Sonography of the Infant Hip and its Therapeutic Implications. Weinheim. Chapman & Hall, Harcke H T, Clarke N M P, Lee M S, Borns P F, MacEwen G D. Examination of the infant hip with real-time ultrasonography. J Ultrasound Med 1984; 3: Harcke H T, Graf R, Clarke N M P. Concensus Meeting on Hip Sonography. Alfred I DuPont Institute, Wilmington, Delaware, September 23 24, Marks D S, Clegg J, Al-Chalabi A N. Routine ultrasound screening for neonatal hip instability. J Bone Joint Surg 1994; 76-B: Clegg J, Bache C E, Raut V V. Financial justification for routine ultrasound screening of the neonatal hip. J Bone Joint Surg 1999; 81-B: Donaldson J S, Feinstein K A. Imaging of developmental dysplasia of the hip. Pediatr Clin North Am 1997; 44: Leck I. An epidemiological assessment of neonatal screening for dislocation of the hip. J Roy Coll Physicians London 1986; 20: Boeree N R, Clarke N M P. Ultrasound imaging and secondary screening for congenital dislocation of the hip. J Bone Joint Surg 1994; 76-B: