Commonly Requested but Misunderstood Imaging Studies: Imaging Infant Hips and the Limping Child

Julianne Dean BA1, Brent Cully MD2, Lisa H Lowe MD FAAP 2,3, and Cindy Taylor MD2
1Midwestern University, Glendale, AZ, 2Children’s Mercy Hospitals and Clinics, Kansas City, MO, and 3The University of Missouri-Kansas City

In continued support of the Image Gently Campaign, the Radiology Department at Children’s Mercy continues this newsletter series entitled “Commonly Requested but Misunderstood Studies” with a discussion on imaging infant hips and the limping child.

The most common reason for hip imaging in the newborn is hip dysplasia. Risk factors include being female, breech presentation, firstborn and family history of hip dysplasia (1).

Due to patient size and lack of epiphyseal ossification, ultrasound is the initial study of choice for possible hip dysplasia in children less than 6 months of age. After 6 months, radiographs of the pelvis are indicated.

In children with a limp or hip pain, the appropriate study (plain radiographs vs. ultrasound vs. MRI vs. bone scan) is strongly determined by the clinical history and physical exam. Specifically, one must know: (1) The child’s age (2) If a fever is present, how high (3) If there is hip pain with manipulation (4) Does the child refused to bear weight and (5) If there are positive lab inflammatory markers (ESR, CRP) and if so, how positive? Using this information, it may be possible to distinguish viral versus bacterial joint infection versus osteomyelitis and determine the appropriate imaging.

History and Physical	Probable Diagnosis	Imaging Modality of Choice
No signs of infection (fever, WBC, sed rate, etc.	Transient (viral) synovitis or AVN	NO ACUTE IMAGING NEEDED Request radiographs if persistent
Minimal signs of infection	Transient synovitis	NO ACUTE IMAGING NEEDED Hip tap rarely for pain control
Many signs of infection and severe limp or refusal to bear weight and severe pain on passive exam	Septic hip Osteomyelitis	Refer to Emergency Department and/or Orthopaedic Sugery Consider ultrasound to search for hip effusion
Many signs of infection and no or mild limp and mild-moderate pain on passive exam	Osteomyelitis	MRI Forego hip ultrasound as an effusion may be present, but may not need to be tapped

Children with transient (toxic) synovitis, are generally 3 to 8 years of age, present with a limp and less often refusal to bear weight. Symptoms usually resolve spontaneously within a few days. A low grade fever may be present or the child may be afebrile. Moderate pain is associated with passive motion of the hip on physical exam. NO IMAGING or HIP ASPIRATION is needed in children with toxic synovitis although many will have hip effusions. If symptoms persist, pelvic radiographs may be useful to evaluate for avascular necrosis.

If there are concerns regarding imaging approach or modality to be used, the ACR appropriateness criteria may be found on line at http://www.acr.org/SecondaryMainMenuCategories/quality_safety/app_criteria/pdf.aspxor you may contact the Department of Radiology at Children’s Mercy Hospitals and Clinics.

To learn more about the Image Gently Campaign and take the pledge to reduce radiation in children, please visit http://www.pedrad.org/associations/5364/ig/.

References
1. Beaty, James H. “Congenital and Developmental Anomalies of the Hip/Pelvis”. Canale and Beaty: Campbell’s Operative Orthopaedics, 11th Ed. 2007. Accessed www.mdconsult.com
2. Frick, Steven L. Evaluation of the Child who has Hip Pain. Orthopedic Clinics of North America. 2006; 37:133-140.

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