LAS VEGAS — A radiologist experienced with imaging the pediatric hip and spine is key to evaluation of a limping child, 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.

“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,” said Dr. Senac, medical director and chief of radiology at Children's Hospital San Diego.

He discussed these causes of limping in children:

▸ Diskitis. This condition is marked by back pain, limping, inability 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” at L 3–4 or L 4–5. It takes 2 weeks for these findings to show on plain film. MRI shows diskitis sooner.

▸ 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,” Dr. Senac 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.” Delayed diagnosis and treatment result in gait problems, Dr. Senac said.

“If you pick it up in the first 6 weeks, 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, he 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 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.

Children can expect complete recovery within a few weeks.

▸ Septic arthritis. He called this condition “the scariest thing that we have to face in this age group [aged 1–4 years] in regard to the limping child.” Affected kids experience severe pain in the involved joint, most often the hip. They usually have a fever and an elevated white blood count. On radiographs, “we're looking for widening of the joint space to see if there's evidence of a hip effusion,” Dr. Senac said.

The condition is hematogenous, “so you commonly have underlying osteomyelitis coupled with the septic joint.”

If conventional radiographs are nondiagnostic and the physical exam is equivocal, then an MRI or a radionuclide bone scan should be obtained on an urgent basis. “Time is of the essence, as the proteolytic enzymes from the hip infection can rapidly destroy cartilage and subsequently the hip joint,” he noted.

Treatment consists of draining the hip surgically and placing the child on intravenous antibiotics. If there is adjacent osteomyelitis, then this bone needs to be drained, generally by drilling.

Radiologist Integral to Work-Up of Limping Child