Developmental dysplasia of the hip (DDH) denotes aberrant development of the hip joint and results from an abnormal relationship of the femoral head to the acetabulum. There is a clear female predominance, and it usually occurs from ligamentous laxity and abnormal position in utero. Therefore, it is more common with oligohydramniotic pregnancies. This article describes the commonly used radiographic measurements and lines involved in DDH.
The reported incidence varies between 1.5 and 20 per 1000 births 1, with the majority (60-80%) of abnormal hips resolving spontaneously within 2-8 weeks 1 (so-called immature hip).
Risk factors include 1,4:
- female gender (M:F ratio ~1:8)
- family history
- breech presentation
- metatarsus adductus
DDH is usually suspected in the early neonatal period due to the widespread adoption of clinical examination (including Ortolani test, Barlow manoeuvres, Galeazzi sign). The diagnosis is then usually confirmed with ultrasound, although the role of ultrasound in screening is controversial 1,3.
Ultrasound is the modality of choice prior to ossification of the proximal femoral epiphysis. Once there is a significant ossification then x-ray examination is required.
For some reason, the left hip is said to be more frequently affected 4. One-third of cases is affected bilaterally 5.
Ultrasound is the test of choice in the infant (<6 months) as the proximal femoral epiphysis has not yet significantly ossified. Additionally, it has the advantage of being a real-time dynamic examination allowing the stability of the hip to be assessed with stress views.
Some values are used to 'objectively' assess morphology.
The alpha angle is formed by the acetabular roof to the vertical cortex of the ilium. This is a similar measurement as that of the acetabular angle (see below). The normal value is greater than or equal to 60º.
The beta angle is formed by the vertical cortex of the ilium and the triangular labral fibrocartilage (echogenic triangle). The normal value is less than 77º 6 but is only useful in assessing immature hips when combined with the alpha angle.
The percentage of the femoral epiphysis covered by the acetabular roof. A value of >50% is considered normal 7.
The key to plain film assessment is looking for symmetry and defining the relationship of the proximal femur to the developing pelvis. The ossification of the superior femoral epiphyses should be symmetric. Delay of ossification is a sign of DDH.
Hilgenreiner line is drawn horizontally through the superior aspect of both triradiate cartilages. It should be horizontal but is mainly used as a reference for Perkin line and measurement of the acetabular angle.
Perkin line is drawn perpendicular to Hilgenreiner line, intersecting the lateral most aspect of the acetabular roof. The upper femoral epiphysis should be seen in the inferomedial quadrant (i.e. below Hilgenreiner line, and medial to Perkin line)
The acetabular angle is formed by the intersection between a line drawn tangential to the acetabular roof and Hilgenreiner line, forming an acute angle. It should be approximately 30 degrees at birth and progressively reduce with the maturation of the joint.
Shenton line is drawn along the inferior border of the superior pubic ramus and should continue laterally along the inferomedial aspect of the proximal femur as a smooth line. If there is a superolateral migration of the proximal femur due to DDH then this line will be discontinuous.
Treatment and prognosis
Management options include:
- 1. US Preventive Services Task Force. “Screening for Developmental Dysplasia of the Hip: Recommendation Statement.” PEDIATRICS 117, no. 3 (3, 2006): 898-902. doi:10.1542/peds.2005-1995.
- 2. Graf R. The diagnosis of congenital hip-joint dislocation by the ultrasonic Combound treatment. Arch Orthop Trauma Surg. 1981;97 (2): 117-33. Pubmed citation
- 3. Roposch Andreas, Nicole M. Moreau, Elizabeth Uleryk and Andrea S. Doria. “Developmental Dysplasia of the Hip: Quality of Reporting of Diagnostic Accuracy for US1.” Radiology 241, no. 3 (December 2006): 854-860. doi:10.1148/radiol.2413051358.
- 4. Taeusch H. William, Roberta A. Ballard, Christine A. Gleason and Mary Ellen Avery. Avery's diseases of the newborn. Elsevier Health Sciences, 2005. ISBN: 0721693474, 9780721693477.
- 5. Donnelly LF. Pediatric Imaging. Saunders. (2009) ISBN:1416059075. Read it at Google Books - Find it at Amazon
- 6. Omeroğlu H. Use of ultrasonography in developmental dysplasia of the hip. J Child Orthop. 2014;8 (2): 105-13. doi:10.1007/s11832-014-0561-8 - Free text at pubmed - Pubmed citation
- 7. Coley BD. Caffey's Pediatric Diagnostic Imaging, 2-Volume Set: Expert Consult - Online and Print, 12e. Saunders. ISBN:0323081762. Read it at Google Books - Find it at Amazon
- 8. Sewell MD, Eastwood DM. Screening and treatment in developmental dysplasia of the hip-where do we go from here?. International orthopaedics. 35 (9): 1359-67. doi:10.1007/s00264-011-1257-z - Pubmed