TL;DR
What it is: Transient synovitis in children is inflammation of the hip joint synovium triggered by a recent viral illness. Most common cause of acute hip pain and limping in kids ages 3 to 10. Resolves on its own within one to two weeks.
First question to ask: Has this child been sick in the last two to four weeks?
Don’t miss: Septic arthritis. Fever, hot joint, or significant tenderness on exam means send to the ED for the full workup.
Management: Rest, ibuprofen, next-day labs if no red flags are present. Most kids are better within a week.
Early in my career as an ortho PA, I had a mom bring in her 4-year-old because he had been limping since he woke up that morning. She said nothing obvious happened and he was still walking, but he was fussy and she felt like something was off.
I remember standing at my desk trying to figure out where to start. Is it their hip or knee or are they just being dramatic for attention?
What I didn’t know to ask at the time, and what I ask every single time now, was whether he had been sick recently.
Turns out, he had. A week before, he’d had a mild cold that went away on its own, and interestingly enough, these two symptoms were connected.
What Transient Synovitis Actually Is
Transient synovitis is inflammation of the synovial lining of the hip joint. It’s the most common cause of acute hip pain and limping in kids between ages 3 and 10, and it almost always has a viral trigger somewhere in the recent history (like a cold, ear infection, stomach bug, etc.). The immune response from that illness causes inflammation in the hip joint, sometimes days later, sometimes a couple of weeks later. The child doesn’t have to still be sick when they come in, and actually, most of the time they are completely fine.
Boys get it more than girls and the hip is the most commonly affected joint. The word “transient” is key — it resolves on its own, usually within a couple of weeks, without any lasting damage.
What makes it easy to miss is that these kids often seem fine. I’ve had parents almost apologize for bringing them in because their child was running around the waiting room. They just have a limp nobody can explain.
The First Question I Ask
Before I look at imaging, before I order anything, I ask whether they’ve been sick in the last two to four weeks.
A cold, a fever that came and went, an ear infection, a GI bug — any of it counts. Parents often don’t connect a resolved illness to a limp that showed up a week later, so just ask directly.
Beyond that, I want to know:
- Which leg, and when did the limp start?
- Did it come on gradually or suddenly?
- Any trauma, even something minor?
- Is the child still willing to walk, or refusing entirely?
- Any fever now, or in the last day or two?
On exam, I’m looking at the hip specifically. A child with transient synovitis will usually still bear weight, even if they’re favoring the leg. They tend to hold the hip in a flexed, abducted, externally rotated position (think like a cowboy) because that’s what takes pressure off the joint. When I try to internally rotate the hip, it’s restricted and uncomfortable. That finding plus the recent illness history usually moves transient synovitis to the top of my list.
The Differential You Can’t Miss
One of the major differentials you can’t miss with these kids is septic arthritis. Septic arthritis is a bacterial infection inside the joint that, when untreated, can destroy cartilage — particularly in a child whose hip is still developing. It’s less common than transient synovitis, but missing it can lead to permanent joint damage, so I’m always thinking about it.
What’s hard is that early on, the two can look similar. What I’m looking for is fever, how the joint feels on exam, and whether the child is willing to bear weight at all.
If they have a fever, a hot joint, or the hip is significantly tender on exam, I’m sending them to the ED for the full workup. They usually need STAT labs and imaging that I just don’t have access to in my clinic.
If none of those things are present and they overall seem healthy, I’ll get labs and follow up the next day. In the outpatient setting, a lot of us won’t have access to same day labs, and that’s okay. The clinical picture — fever, warmth, tenderness, weight-bearing status — is what drives my decision in the moment.
How I Manage the Child Who Stays
If the history fits, the exam is consistent, and nothing has me worried, most of these kids can be managed outpatient.
I get X-rays of the hip, not because it will show me synovitis, but because they help rule out fracture, Legg-Calvé-Perthes disease, and other bony pathology. Normal imaging moves transient synovitis higher on my differential.
Ultrasound is more sensitive for picking up joint effusion and is my preferred next step when I’m seriously considering the diagnosis, but most of you won’t have access to that. If ultrasound isn’t available, a normal X-ray in a child who seems well and is still bearing weight is usually enough for me to feel comfortable managing outpatient.
Management is supportive: rest, activity restriction, ibuprofen for pain and inflammation, and clear return precautions. I tell parents that most kids are noticeably better within three to five days and fully resolved within two weeks. If they’re not improving on that timeline, I want to see them back.
Who I Send to the ED
I send the following patients to the ED:
- They have a fever, a hot joint, or significantly tender hip on exam
- They’re completely refusing to bear weight
- Something about them just looks unwell, even if I can’t fully explain it
- They’re not improving after 48 to 72 hours of appropriate management
One More Thing
If I want to quickly run through my approach or double-check something before I go back in the room, I’ll use Blox IQ for exactly this. Ask it something like “transient synovitis vs septic arthritis in a child” and you’ll have a clean breakdown in front of you while the parent is still waiting. It doesn’t make the call for me, but having the framework organized in the moment is genuinely useful.