Septic hip in Kids, part 2: This time it's personal...

I wrote about the "textbook" approach to differentiating the septic hip from plain ol' synovitis in a previous post Septic hip in kids: 5 myths of ED evaluation. Today, I want to review a real case of mine, and highlight both the weakness of the older methods, and the advantages of the newer perspective.

The Case

A 4 year-old male complained of pain in his hip, bad enough that he couldn't put his weight on it. It had started 1 day ago, but had worsened despite acetaminophen. There was no significant recent trauma. He has seemed ill yesterday, though, and while the parents had not taken a temperature, he had "felt hot," and had some mild chills. His temperature in the ED was 100.2.

His right hip was held in slight flexion and external rotation, and he could not bear weight. Labs were obtained, and showed a WBC of 12.2, and (after hours of waiting) and ESR of 28. The CRP doesn't get run at night.

Were the Kocher criteria helpful? (Spoiler: No!)

Kocher-type criteria are applied to help decide on the need to perform an ultrasound, and then decide on the need for aspirating a hip effusion if it is found on US. How did our patient do?

• Non-weight-bearing - 1 point
• Temp < 38.5 - 0 points
• WBC > 12 - 1 point
• ESR < 40 - 0 point
• CRP - not available

So, 2 points, which means that he has a probability of having septic arthritis of...

Sultan 2010

... somewhere around 11 - 60%. But notice that if the WBC had been just trivially lower, say 11.8 instead of 12.2, we would have only had 1 point, and the risk would have dropped to 3- 36%.

Heck, say we also had given him a strong analgesic, and he was then able to walk a little. He would have then had 0 predictors, and so only had a risk of somewhere between < 0.2% and ... 17%???

Clearly, these criteria are not helpful at "ruling-out" the possibility of septic arthritis, so I decided to decide by looking at the hip.

Was Ultrasound helpful? (Spoiler: Yes!)

Quick guide to placing the probe :

From Tsung and Blaivas

First I checked the "good" hip, the left side:

I then checked the "bad" hip, the right:

Looked like there was a difference!

Generally, any effusion greater than 5 mm, or 2 mm greater than the contralateral side, is considered positive. This looks pretty unambiguous, and the radiologogist agreed, and told me that a formal ultrasound was not needed in this case.

Clinical course:

The hip was aspirated by IR in the ED (Those guys are total champs at this, but I'm doing this next time! Very straight-forward.), and the patient admitted. The cell count cam back quite high, around 100,000 white cells/ml, which would have placed this patient as a "true positive" case of septic arthritis in almost any study.

However, by the time this result came back, the patient was tearing around the pediatric floor, completely asymptomatic. The culture never grew out an organism, and he was discharged as a transient synovitis.

Bottom Line:

This was the first time I had a patient where I was truly concerned about septic arthritis of a pediatric hip. The use of US clarified the diagnosis early in the visit, and pointed to a greater role in future case. As I highlighted in my prior post, use of point-of-care US in the ED has the potential to "flip" the older diagnostic and therapeutic pathway - use it!