1 Congenital and Developmental Disorders

Congenital and Developmental Disorders 1 1 Congenital and Developmental Disorders David Wilson and Ruth Cheung CONTENTS The dysplasias that predominantly involve the skeleton may be classified in a variety of ways, but 1.1 Introduction 1 the commonest is to define the part of bone most 1.2 Developmental Dysplasia of the Hip 1 1.2.1 Clinical Background 1 affected, epiphysis, metaphysis or diaphysis. Sub- 1.2.2 Role of Imaging in Detection 2 groups include the region of the skeleton most 1.2.2.1 US Methods 3 affected or other nonskeletal disorders. For exam- 1.2.3 Role of Imaging in Treatment 4 ple, spondyloepiphyseal dysplasia is a condition that 1.2.4 Potential Developments 5 affects the epiphyses and the spine. 1.3 Focal Defects 7 1.3.1 Clinical Background 7 There are a good number of texts that compre- 1.3.2 Role of Imaging 8 hensively describe syndromes that affect the muscu- 1.3.3 Potential Developments 9 loskeletal system and the reader is referred to them 1.4 Talipes Equinovarus 9 for the analysis of a particular case. In this chapter, 1.4.1 Clinical Background 9 we deal with those disorders where the imaging has 1.4.2 Role of Imaging 9 1.4.3 Potential Developments 10 a particular pivotal role in management and where 1.5 Neural Tube Defects 10 ultrasound (US) has a special value. 1.5.1 Clinical Background 10 1.5.2 Role of Imaging 11 1.5.3 Potential Developments 16 References and Further Reading 16 1.2 Developmental Dysplasia of the Hip 1.2.1 1.1 Clinical Background Introduction Developmental dysplasia of the hip (DDH) is a There are a large number of congenital birth defects diagnosis made when the infant’s hip is either that affect the spine and appendicular skeleton. They abnormally shallow or even dislocated at birth range from isolated defects affecting one part of the but also when a shallow hip fails to mature to one body to complex syndromes with several body sys- that is mechanically stable. Its cause is not fully tems involved. In practice most patients are atypical understood. Although there is a genetic predispo- and some may cynically suggest that each case is a sition, there is also evidence that abnormal stress new syndrome. However, there are real reasons for on the hip in the later stages of pregnancy may giving as accurate a description as possible. Prog- lead to modelling deformity [1]. If untreated, a full nosis and outcome may be predictable and there is dislocation will lead to the child failing to walk likely to be concern about the type of inheritance. normally at around one year of age. A shallow and Geneticists will look for as precise a diagnosis as potentially unstable hip may not cause any symp- possible and radiology, especially plain films, is part toms until much later in life when the abnormal of that process (Fig. 1.1). stresses lead to an acetabular labral tear or premature osteoarthritis. DDH diagnosed in infancy, D. Wilson, FRCP, FRCR by clinical examination and plain film analysis, R. Cheung, FRCR is reported to occur between one and three times Department of Radiology, Nuffi eld Orthopaedic Centre, NHS per thousand live births; the incidence of shallow Trust, Windmill Road, Headington, Oxford, OX3 7LD, UK or dysplastic acetabulae is much more frequent 2 D. Wilson and R. Cheung The goals of diagnosis and treatment are to permit affected children to walk normally and to prevent premature degeneration. We consider detection and treatment separately. 1.2.2 Role of Imaging in Detection Most developed countries have established clinical screening methods to detect children with dislocated or dislocatable hips and there are advocates of this as the sole screening test [4]. The manoeuvres of Ortolani and Barlow are effective in detecting around 74% of cases of dislocation or subluxation that may be demonstrated on imaging. The level of training and experience required to accurately perform these tests is substantial, and sadly the task is often placed in the hands of the more junior members of the team. There are undoubtedly occa- sions when a child with DDH is overlooked when a clinical abnormality might have been detected by a more experienced clinician. Training and audit of practice are crucial, but even in the best hands there will be errors, as clinical manoeuvres alone are not capable of detecting every case. Indeed it is also likely that some stable hips become unstable, and if the timing of the clinical examination does not coincide with this developing problem then a child may miss the chance of early treatment that could potentially limit or reverse the process. The need for early diagnosis is based on the window of opportunity that exists in the first few months of life when relatively simple treatment may be very effective. Methods range from wearing double nappies to splint therapy and corrective sur- Fig. 1.1 Plain fi lm of the forearm of a child with metaphyseal gery. In general the later the diagnosis is made the chondrodysplasia. This examination is part of a full skeletal harder the treatment will be, leading to greater risk survey. of complications and a higher chance of failure [5]. There is a real need for a method of diagnosis that is simple, cheap, safe and effective, and US arguably provides such a technique. Unfortunately, the practice of US screening for DDH has developed with no [2]. It is difficult to identify statistics to support randomized control trials to judge its efficacy, and this comment, but experience suggests that per- the only evidence is from observational studies, sisting shallow acetabulae are at least ten times albeit with very large numbers of cases [6]. more common. Whilst many of these children will In early infancy plain films will not show the fem- remodel and spontaneously recover stability, some oral head or much of the acetabulum as these struc- will fail to mature properly and require a variety of tures are not ossified until later in the first year of complex surgical procedures [3]. It has been argued life. Whenever reasonable, plain film examination that around one-tenth of hip replacements are per- should be deferred until 3 to 6 months of age when formed for premature osteoarthritis secondary to more structures are ossified. Radiographs will dem- mild or subclinical hip dysplasia. onstrate malalignment of the hips and show anoma- Congenital and Developmental Disorders 3 lies of the pelvis and sacrum. The initial plain film Table 1.1 Risk factors for DDH examination should be performed without any gonad shielding as this normally overlaps parts of Female (not a criterion commonly used in high-risk screening protocols) the pelvic ring and sacrum. Defects in these areas such as sacral agenesis may otherwise be masked. First degree relative with hip dysplasia Subsequent examination should use the shields to Premature birth minimize radiation dose. Despite these comments, Breech presentation subtle or even moderate degrees of acetabular dys- Other congenital limb defects plasia will not be seen on plain films, especially in early infancy when treatment is more effective. Spinal defects CT and MRI would be effective ways of exam- ining the cartilaginous parts of the hips and they would allow assessment of the three-dimensional 1.2.2.1 shape of the acetabulum. However, the high radia- US Methods tion burden from CT and the need for anaesthesia or sedation for most infants undergoing MRI preclude 1.2.2.1.1 these as practical screening methods. US is safe, rel- Morphology atively cheap and repeatable with no need to sedate the infant. Its disadvantages are that it is labour- The method pioneered and developed by Reinhart intensive and it requires skill and specific training Graf in Austria has gained the widest acceptance [7]. both to perform and interpret the images. Studies The infant is examined shortly after birth or at least have shown great sensitivity for US and a number in the first 6 weeks. The infant is laid in a foam-lined of national bodies now require routine US screen- trough in the lateral decubitus position. The knee ing of infants for hip dysplasia. Others, including and hip of the uppermost side are flexed. The US those of the United Kingdom, recommend that US is probe is placed in a true coronal plane over the hip used only in infants at high risk of developing DDH and the angle adjusted to give an image that shows (Table 1.1). the maximum depth of the acetabulum (Fig. 1.2). Fig. 1.2 US examination of the hip images the cartilaginous structures that are invisible on plain fi lms in a coronal plane. 4 D. Wilson and R. Cheung Care must be taken not to place the probe at an argue that subluxation is a dynamic process and oblique angle to the coronal plane as the hip may using the real-time capabilities of US it is possible be made to look erroneously deep or shallow. The to detect abnormal movement predicting dysplasia need for a precise plane of imaging is a critical issue with perhaps greater sensitivity. The methods used that demands training and audit of the technique. vary but in general they are modifications of the Measurements are made from the US image to assess stress tests of Ortolani and Barlow combined with the amount of the bony and cartilaginous cover of US examination [10]. Gentle but firm pressure is the femoral head by the acetabulum either using placed on the upper part of the leg as if to subluxate angles or the Morin (Terjesen) method in which the the hip in a posterior and/or lateral direction.

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