| Print Date: | May 24, 2013, 6:24 am |
| Title | Developmental Dysplasia of the Hip |
| Text | Developmental Dysplasia of the Hip (DDH) is a spectrum of disorders sharing an abnormal relationship of the femoral head and acetabulum. The disorder ranges from stable, mildly dysplastic and non-displaced hips to those that are severely dysplastic and dislocated. In developed countries, the incidence of DDH is 1.5 to 20:1000 births, varying with the screening method used. Although many of those affected will undergo spontaneous resolution within the first months of life, DDH can result in chronic pain, gait abnormalities and degenerative arthritis, ultimately being the cause of 9% of all primary hip replacements.
There are three main risk factors in the development of DDH. These are mechanical constraint, either intrauterine or postnatal, abnormal intrauterine positioning, and genetic predisposition. Intrauterine factors include large birth weight for gestational age, breech position at delivery and oligohydraminos. Of these, vaginal delivery of breech-positioned babies has a 17-fold increased risk of DDH, with a 7-fold increase if caesarean section is used. It has been proposed that some swaddling practices in which the hips are kept in abduction is a postnatal risk factor for DDH. Genetic risk factors include familial disposition and female gender. Females have a six-fold increase in the incidence of DDH over males. It is important to note that the majority of those found to have DDH have no identifiable risk factors, however. Along with identifying risk factors, the first step in the workup of DDH is the clinical exam. Symptoms of DDH vary with age with newborns presenting with hip instability, infants with limited hip abduction on exam, and older children showing limp, joint pain and osteoarthritis. In the United States, the Barlow and Ortolani maneuvers are used as provocative tests for DDH in the newborn up to the third month of life. After 8 to 12 weeks of age these maneuvers are no longer valid due to increased muscle tightness and decreased capsule laxity. The Barlow maneuver, developed in 1962, identifies a dislocatable hip by forced adduction of the hip while flexed at 90 degrees. The Ortolani maneuver, developed in 1932, attempts to relocate an already dislocated hip by forced abduction of the hip, again while flexed at 90 degrees. Both of these exams are highly operator dependant, and distinguishing a pathologic “clunk” from a normal “click” may be difficult. Other possible clinical findings include leg length difference, skin fold asymmetry, flattening of the buttock, and limited abduction, but these are variable and have low sensitivity. There are several indications for radiologic exam in suspected DDH of the newborn, with neither the American Association of Pediatrics (AAP) nor the U.S. Preventative Services Task Force recommending universal screening. The AAP guidelines for imaging include a questionable physical exam or specific risk factors. These risk factors include female infants with a family history of DDH, or female infants born in the breech position. Other uses for imaging include confirmation of hip reduction when using treatment devices, preoperative and postoperative assessment and following disease course. Until 4 to 6 months of age, sonography is the imaging modality of choice in the assessment of DDH. Prior to this time incomplete ossification of the femoral head makes conventional radiography insensitive. Ultrasound also has the additional advantages of eliminating radiation exposure and providing superior anatomical imaging of the mostly cartilaginous infant hip joint. The Graf method of DDH assessment examines joint morphology by creating three lines and two angles while viewing the hip in the coronal plane. • Baseline: through the ilium, connecting to the osseous acetabular convexity. • Inclination line: lateral end of the acetabulum to the labrum. • Acetabular roof line: along the plane of the osseous acetabular convexity. • Alpha angle: between roofline and baseline. • Beta angle: between baseline and inclination line. The alpha angle, a measurement of acetabular concavity, is considered normal at 60 degrees or greater. The angles between 50 and 60 degrees may be physiologic, but require follow up. An alpha angle less than 50 degrees is considered abnormal and requires treatment. The beta angle measures acetabular cartilaginous roof coverage. An angle less than 55 degrees is considered normal, with lesser degrees indicating less cartilaginous coverage and better bony acetabular coverage of the femoral head. Another method of measuring bony coverage of the femoral head is by calculating the ratio of the distance between the medial aspect of the femoral head and the baseline (d), compared to the maximum diameter of the femoral head (D). This d/D ratio, expressed as a percentage, is considered normal if it is 50% or greater. Finally, maneuvers such as Barlow’s can be used to assess for joint stability while imaging. After 4 to 6 months of age, plain radiography of the hips in the anterioposterior neutral position becomes useful as ossification of the capital femoral epiphyses occurs. As cartilage is replaced by bone, sonography becomes more difficult and less sensitive. Three lines and one angle are drawn to help identify abnormal positioning of the femoral head in the acetabulum using the anterioposterior hip view. • Hilgenreiner line: horizontal line between triradiate cartilages. • Perkins line: outer acetabular margin perpendicular to Hilgenreiner line. • Shenton line: arc connecting medial femoral metaphysis and superior edge of the pubic ramus. • Acetabular angle: angle between the Hilgenreiner line and a line connecting the superolateral and inferomedial margins of the acetabular roof. A normal acetabular angle is 28 degrees at birth and decreases with age. This angle is often increased in DDH. The Perkins line divides the hip into quadrants to estimate where the unossified femoral head is located, normally the inferomedial quadrant. The Shenton line should be a smooth, unbroken arc. Disruption of this line suggests DDH. The treatment of choice for newborns diagnosed with DDH is the Pavlik harness. Sonography is used to assess for hip reduction after placement and to follow disease course. There is no defined duration that the Pavlik harness should be used, although the resolution of clinical and radiologic findings of DDH is usually used to determine when the harness should be removed. In those diagnosed with DDH after 6 months of age, closed reduction is the treatment of choice. This closed reduction is usually performed with arthrography in order to determine the success in reduction. In those diagnosed after the age of two, or in those in which non-surgical correction has failed, surgical closed reduction is the preferred treatment. The most feared complication in all treatment modalities is avascular necrosis of the femoral head. The frequency of avascular necrosis varies, from between 0 and 14% with non-surgical treatment and 5 to 60% with surgical treatment. If diagnosed within the first 6 to 8 weeks of life, 96% of those with DDH have regression of dysplastic changes. Those who are not treated until three years of age or older have much poorer results, with only 28% having good or better outcomes following treatment. In this population, 41 to 43% develop degenerative hip disease, 60% have disturbed proximal femur growth, and 11 to 14% require total hip replacement or hip arthrodesis. |
| References: | 1: Keller MS, Nijs EL. The role of radiographs and US in developmental dysplasia of the hip: how good are they? Pediatr Radiol. 2009 Apr;39 Suppl 2:S211-5. Review. PubMed PMID: 19308388.
2: Dezateux C, Rosendahl K. Developmental dysplasia of the hip. Lancet. 2007 May 5;369(9572):1541-52. Review. PubMed PMID: 17482986. 3: Gelfer P, Kennedy KA. Developmental dysplasia of the hip. J Pediatr Health Care. 2008 Sep-Oct;22(5):318-22. Review. PubMed PMID: 18761234. 4: Norton, Karen, and Sandra A. Mitre Polin. "Imaging in Developmental Dysplasia of the Hip: EMedicine Radiology." EMedicine.com. EMedicine, 23 Sept. 2009. Web. 26 Oct. 2010. 5: McCarthy, James J. "Developmental Dysplasia of the Hip: EMedicine Orthopedic Surgery."EMedicine.com. EMedicine, 23 Sept. 2009. Web. 26 Oct. 2010. |
| Contributor | Nicholas D Romano (Childrens Hospital of Dayton, OH) |
| Peer Reviewer | Dawn E Light (Childrens Hospital of Dayton, OH) |
| Record Number | : 9678 |
| Created | 2010-10-26 15:37:15-04 |
| Modified | 2010-10-28 06:35:21.915581-04 |
| Category: | Congenital, malformation |
| Location: | MSK - Musculoskeletal |
| Sublocation: | Hip (Femur and Acetabulum) |
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