Alex is doing fairly well today - we was able to walk around a bit this evening. We just talked to the orthopedist again about the blood work they've done today and how he's responding and the issue is that there are two possible diagnoses: septic arthritis (bacterial) or toxic synovitis (viral). His white cell count is elevated, but not as high as they'd expect with septic arthritis. Other counts are elevated, but only nominally, and with septic arthritis he should be in a lot more pain, unable to move his hip. But his pain level yesterday seemed greater than would be expected with toxic synovitis. Finally, the ultrasound, which showed some fluid but not much, doesn't do anything to clear up the other inconclusive observations or results.
So that leaves us with two ways to be rule out septic arthritis: one is to continue the aggressive approach with antibiotics, put him under general anesthesia and aspirate his hip to test the fluid. This would give us a clear-cut answer, but it would also be more traumatic for Alex, and perhaps for no good reason other than giving us an easier diagnosis.
The other option is be less aggressive, take him off the antibiotic and closely observe him. IF his fever spikes and his pain and range of movement worsens, then it's more likely to be septic arthritis and the aggressive approach of aspirating his hip (and putting him under) is called for. But if he continues to get better (which would be exactly what would happen with toxic synovitis), he'll go home on Monday afternoon and we'll just watch him for fever over the next few days.
I've already done a good bit of reading on both these conditions and what the doctor said was exactly what I expected. We agree that it's in Alex's best interest to go with the less aggressive and less invasive approach. So we'll hang out here tomorrow with lots of observation and they'll give him ibuprofen for pain (he hasn't wanted/need any pain medication since last night, though). If he continues to improve, they'll do another run of blood work on Monday morning to confirm his counts are still moving in the right direction and we'll go home with instructions to take his temp every few hours and call the doc and return to the ER if his fever returns.
Not fun and not comfortable but we think it's the best option.