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Abstract Developmental dysplasia of the hip (DDH), formerly known as congenital dislocation of the hip, comprises a spectrum of abnormalities that include abnormal acetabular shape (dysplasia) and malposition of the femoral head, ranging from dislocatable hip and mild subluxation to fixed dislocation. (Dezateux C et al, 2007). The origin and pathogenesis of DDH are multifactorial. Abnormal laxity of the ligaments and hip capsule is seen in patients with DDH. The maternal hormone relaxin may also be a factor. Causes of oligohydramnios are thought to be reduced in utero space, movement restriction, and being a first-born child. Extreme hip flexion with knee extension, as in the breech position, tends to promote femoral head dislocation and leads to the shortening and contracture of the iliopsoas muscle. (Dezateux C et al, 2007). Delayed diagnosis of mild hip dysplasia is an important cause of secondary osteoarthritis despite routine screening of infants, accounting for approximately 25% of all patients requiring total hip arthroplasty. The radiographic diagnosis of hip dysplasia in the young adult may be subtle. (Beltran LS et al, 2013). Radiographs are readily available and relatively low in cost. The main limitations are radiation exposure and radiography’s inability to demonstrate the cartilaginous femoral head. Radiographs are of limited value during an infant’s first 3 months of life, when the femoral heads are composed entirely of cartilage, but they become more reliable for use in infants 4–6 months of age, with the appearance of femoral head ossification. (Dezateux C et al, 2007). Ultrasonography offers distinct advantages compared with other imaging techniques: First, unlike plain radiography, it can distinguish the cartilaginous components of the acetabulum and the femoral head from other soft tissue structures. Second, real-time Ultrasonography permits multiplanar examinations that can early determine the position of the femoral head in respect to the acetabulum; thus it provides the same type of information that can be obtained with arthrography, computerized tomography, or magnetic resonance imaging, but at lower cost. Third, although ultrasonography is more expensive than plain radiography, it doesn’t require sedation and doesn’t involve ionizing radiation. Fourth, unlike other techniques, it allows observation of changes in hip position with movement (Gerscovich, 2007). US during an infant’s first 4 weeks of life often reveals the presence of minor degrees of instability and acetabular immaturity in a normal hip; however, nearly all of these resolve on follow-up. To increase the reliability of this test, it is recommended that US studies be performed when infants are 4–6 weeks of age. (American Academy of Pediatrics. 2000). US evaluation of the hip is performed using a high-frequency linear array transducer with either one of the two methods have emerged: a static acetabular morphology method proposed by Graf and a dynamic stress technique proposed by Harcke. (Engesaeter LB et al, 1990). Dynamic maneuvers are performed similar to the Barlow clinical examination. The dislocated femoral head will migrate superiorly, posteriorly and laterally. The Ortolani manoeuver with abduction and flexion of the femur can also be performed to check for reducibility of the dislocated hip. (Ladino MF Torres et al, 2009). Additional features to assess by US include characterizing the acetabular margin. The normal acetabular margin should be mildly angulated and sharp. Dysplastic hip tend to have a rounded or blunt margin. The degree of hip dysplasia corresponds with the hypertrophy and pulvinar hypertrophy. (Shipman SA et al, 2006). MRI provides superior soft-tissue characterization compared with US. for precisely identifying soft-tissue obstacles that may interfere with concentric hip reduction. (Jaramillo D et al, 1998). The utility of MRI is not for diagnosis but for assessing outcome after treatment in children with DDH after SPICA placement for closed reduction. (Laor T et al, 2000). MRI can also be used to evaluate complex hip dislocations, for presurgical planning, and for evaluation of avascular necrosis. (Desai AA et al, 2011). After SPICA placement MRI is used to identify joint congruity in both the axial and coronal planes, acetabular morphology (dysplastic vs. nondysplastic), any growth disturbance or deficiencies of the capital femoral epiphysis, and intrinsic or extrinsic obstacles to concentric location. Intrinsic obstacles for reduction include the abnormal shape of the femoral epiphysis and acetabulum, inverted labrum hypertrophied pulvinar, ligamentum teres and transverse acetabular ligament. Summary Chapter 5 |