Educational Objectives:
After evaluating this article, participants will be able to:
1. Develop strategies to clinically differentiate septic arthritis from transient synovitis
2. Incorporate into clinical practice ultrasound imaging of the pediatric hip

Sometimes you wish you were a pediatrician; other times you don’t. When you walk into the room and your patient immediately starts crying like you are a scary monster, you gain a new appreciation for your adult patients. But when everything you do elicits a smile or a giggle, you wish all your patients were three years old. Fortunately, today you are popular with the kids. When you gently shook the head of a febrile, vomiting 2-year-old to check for the “jolt sign” – all while smiling and making funny noises – she started giggling and laughing. No CNS infection likely there. When you played “poke the belly” with the constipated 3-year-old to make sure there was no appendicitis, he laughed and tried to poke your belly.

Your next pint-sized patient is a 5-year-old who “won’t walk”. His parents state that he was fine yesterday and last night, but wouldn’t get out of bed this morning because his right leg hurt. They tell you the pain seems to be in the hip. He is otherwise doing well with no trauma, fever, rash or other complaints. They say that he is normally very active and he has never demonstrated this kind of behavior in the past. He is otherwise a healthy 5-year-old with no prior surgeries or medical problems.

The child’s vital signs are all normal and his physical exam is as well, except for pain with any motion of the right hip. He will not stand or even do a straight leg-raise. The knee and ankle seem non-tender and show no warmth or swelling. Interestingly, your colleague mentioned she just admitted a similar patient for similar symptoms this past week.

You order a pelvic x-ray, and a knee x-ray in case this is referred pain; both are negative. A CBC shows a white count of 9.2 with 63% PMN’s and the sed rate is normal at 9 mm/hr. You think he probably has transient synovitis, but you definitely don’t want to miss a septic hip, so you decide to do a bedside pediatric hip ultrasound and a trial of non-opiate analgesia. His hip ultrasound is shown here. What does it show? Do you need to call someone to tap this hip or not? What should be the next step in your care? 

What do you see on the ultrasound image?
Conclusion here