LAS VEGAS — If a limping child presents to your office and imaging is being considered, make sure to consult a radiologist who has experience imaging the pediatric hip and spine, Dr. Melvin O. Senac Jr. advised at a meeting sponsored by the American Academy of Pediatrics' California Chapters 1, 2, 3, and 4 and the AAP.
“Have a radiologist you can trust,” said Dr. Senac, medical director and chief of radiology at Children's Hospital San Diego. “The imaging modalities are changing so fast, whether it's the new 64- channel CT scanners or new sequences in MRI, it's hard to really keep up. If you have a problem with one of your kids and you just don't know how to approach it from an imaging standpoint, pick up the phone and call or go by and talk to your radiologist. We're really trying to do the fewest [number of imaging] tests possible.”
He discussed these causes of limping in children:
▸ Diskitis. This condition is marked by back pain, limping, failure to bear weight, and low-grade fever. It can affect infants less than 1 year old as well as teenagers.
In toddlers, nerve root irritation often causes hip pain that is worse than back pain, said Dr. Senac, who is also a professor of radiology at the University of California, San Diego. The white blood cell count is usually normal but the erythrocyte sedimentation rate is usually elevated.
Bacterial infection, usually Staphylococcus aureus, is the most common etiology of diskitis. The primary nidus is the vertebral end plate. Long-term sequelae include normal to severe kyphosis.
“One of the hallmarks of plain film findings in diskitis is narrowing of the disk space with end-plate irregularity,” Dr. Senac said.
“It's usually going to be at L 3–4 or L 4–5. We see it throughout childhood, [but] it takes about 2 weeks for us to start seeing plain film findings of these irregularities. The earliest manifestation we see of diskitis is on MRI.”
▸ Developmental dysplasia of the hip (DDH). The four radiographic hallmarks of this condition include a small or nonossified femoral head on the affected side, increased acetabular angle, a laterally displaced femoral head, and interruption of Shenton's line.
“The earlier you pick it up, the better that child is going to do,” he said.
If the DDH diagnosis is made at under 6 months of age, treatment involves use of a Pavlik restraint harness to position the hip in flexion and abduction. These children “do well and they'll go on to have a normal hip,” he said.
If the diagnosis is made between ages 6 and 24 months, “those kids generally have to be hospitalized, put in traction, then taken to OR,” he said. “Then, under general anesthesia, there's an attempt at reduction. Then they're put in a cast for 6–9 months.”
If the diagnosis is made after the age of 24 months, treatment involves an open reduction. “Those kids will always have gait problems down the line,” Dr. Senac said.
But even if a diagnosis is made early, several months of treatment is required. “If you pick it up in the first 6 weeks, then the average stay in a harness is about 3.5 months,” he said. “If you don't make the call until 6 weeks to 3 months of age, the average stay in the harness is about 7 months. It goes up to 9 months if you diagnose it between 3 and 6 months.”
To confirm DDH, Dr. Senac recommends ultrasound in children younger than 4 months of age and radiographs in children aged 4 months and older. He pointed out that there is a steep learning curve to performing hip ultrasound on young infants, “so if you don't have a pediatric radiologist who does this, I suggest that the family drive somewhere to a facility that's doing a lot of these.”
▸ Transient synovitis. This is the most common nontraumatic cause of acute limp in children aged 5–10 years. The etiology is unknown but is thought to be a nonspecific anti-inflammatory response of synovium to an antecedent viral or bacterial infection.
Clinical exam may reveal limp, or hip or knee pain. Affected children have low-grade fever in about 25% of cases and a mildly elevated erythrocyte sedimentation rate in 50% of cases.
“It is a diagnosis of exclusion,” Dr. Senac said. “If we do sophisticated MRI or [ultrasound], we'll find a little fluid in the joint. That's all we see.”
Radiographs are usually normal but may show a small hip effusion. Scintigraphy is more sensitive but nonspecific.