Early diagnosis of developmental dysplasia of the hip (DDH) in childhood presents challenges for the primary care provider. Many of the difficulties in diagnosis arise from an overly simplistic view of this complex problem. In contrast to the rare patient with a completely dislocated hip, most patients will have more subtle variations of this condition. A delayed diagnosis of DDH results in a patient requiring complex reconstructive surgical procedures, which rarely produce normal hips.1-3
The advent of neonatal ultrasound imaging has made the diagnosis of hip instability much easier. However, ultrasound is extremely sensitive and can detect mild levels of hip instability, which requires the ordering provider to arrange specialty consultations for patients in whom these minor levels of instability are self-correcting.4
What is needed, therefore, is a more rational approach to the use of ultrasound for imaging newborn hips to bring more balance to the problem of overdiagnosis. An understanding of this broad spectrum of physiologic instability and application of an algorithm for management can lessen the chances of missed cases of hip instability while minimizing unnecessary referrals and treatment.
Risk Factors and False Clinical Findings in Hip Dysplasia
Although the exact etiology of developmental dysplasia of the hip has not been identified through quality studies, specialists are aware of certain risk factors that increase the incidence of this diagnosis. The incidence of hip instability is increased in patients who were in the breech position during pregnancy.5-7 A positive family history of hip dysplasia in the mother or older sibling is also a significant risk factor for hip instability.6,7 In these cases, ultrasound testing is justified.
The American Academy of Pediatrics recommends that infants can be considered for ultrasound testing between 6 weeks to 6 months of age if they are determined to be at high risk for hip dysplasia despite having normal findings on physical examination.7 Additional factors that have been shown to increase the incidence of DDH include female gender with girls being 7 to 9 times more frequently diagnosed with DDH at birth than boys, post-terminal gravidity, vaginal compared to cesarean delivery, tight swaddling of the lower extremities, and limited fetal mobility related to oligohydramnios, high birth weight, or primiparity.7,8
In an 1936 article, Prof Marino Ortolani described the clinical finding of “segno della scatto” to detect hip instability in infancy. This roughly translated to “click sign”, this misnomer has often led to confusion during the physical examination as the click is felt rather than heard during the Ortolani manuever.9 To perform the maneuver, the examiner holds the suspected limb with pressure placed behind the greater trochanter and the limb is lifted anteriorly as it is abducted. The previously dislocated, but reducible hip, is felt to reduce into the acetabulum. This sign would be best described as the feeling of the femoral head sliding into the acetabulum with a clunk and not a click.
When performing the maneuver on a baby without DDH, a mild catching sensation often can be felt within the acetabulum as the femoral head is rolled within the acetabulum. This is likely produced by the thick ligamentum teres that runs from the center of the acetabulum to the fovea of the femoral head, which contains blood vessels that provide nourishment to the femoral epiphysis. With certain motions, the ligamentum teres may be temporarily pinched between the cartilage surfaces of the femoral head and the acetabulum and is likely responsible for many of the clicks that are noted on physical examination. Additionally, a clicking sensation from the patella may be felt when the examining hand is placed over the flexed knee of the limb being examined while performing the Ortolani maneuver. This sensation can also be misinterpreted as arising from the hip.
The inexperienced examiner may not have had many opportunities to examine a truly dislocated hip in a newborn. Thus, these clicking sensations may lead to the false conclusion that the hip is dislocated. Ultimately, many of ultrasound tests ordered for clinically normal hips are the result of these misinterpreted physical findings.10-12 Neonatal laxity may be described by the ultrasound examiner in these clinically normal hips.
The Spectrum of Hip Dysplasia
Developmental dysplasia of the hip is not one condition but rather a broad continuum of instability. Considering each stage of this continuum will help guide the evaluation and treatment of this condition. At one end of the continuum is neonatal laxity and at the other is teratologic dislocation (Table).13 Each of these stages is somewhat artificial and arbitrary, but dividing the condition along these lines can assist with treatment decisions.
Table: Physical Examination and Imaging Findings Along the Spectrum of Developmental Dysplasia of the Hip
|Neonatal Laxity||Subluxation||Dislocatable||Dislocated||Dislocated||Teratologic Dislocation|
|Physical Examination||Normal||Often normal||• +Barlow |
• Skin creases normal
|• +Ortolani |
• Abnormal skin creases
|• -Ortolani |
• Abnormal skin creases
• May have decreased abduction
|• +Galeazzi (unless bilateral) |
• Decreased abduction
• Other major signs of syndromes
|Radiographic*||Normal||Normal until at least 3 months of age||Visible signs by 3 months of age||Visible signs by 3 months of age||Visible signs by 3 months of age||Visible at birth|
|Ultrasonographic||+ laxity||Displacement of the femoral head with stress||Dislocation of the femoral head with stress||Femoral head reduces but not stable in the acetabulum||Femoral head does not seat into the acetabulum||Femoral head does not seat into the acetabulum|
*Delay in appearance of ossific nucleus of the femoral epiphysis or increased acetabular angle