Toxic synovitis is a temporary condition that causes hip pain in children. It’s also known as transient synovitis. According to the Nemours Foundation, this condition is the leading cause of hip discomfort in kids (Brescia, 2011). It mainly occurs in children under 8 years of age. It generally clears up on its own within 10 days.
A viral infection that affects one of your child’s hip joints causes toxic synovitis. It leads to swelling and inflammation in the affected joint and can spread to the other joint over time. According to the National Institutes of Health, it occurs roughly four times more often in boys than in girls (NIH).
The most common symptom of toxic synovitis is hip pain. This pain might occur on and off in one hip or both hips. It might flare up when your child gets up after sitting or lying down for a long time.
Other symptoms include:
- limping or walking on tiptoe due to discomfort
- pain in the thigh or knee and no hip pain
- low-grade fever that is under 101 F
- refusing to walk if the pain is severe
- crying in younger children
Common signs of toxic synovitis in babies include crying, especially when their hip joints are moved, and unusual crawling movements or being unwilling or unable to crawl.
Toxic synovitis can be difficult to diagnose. Other conditions that are much more serious can also cause hip pain. Since these conditions require prompt medical treatment, doctors must first test for them before making a toxic synovitis diagnosis. These include:
This condition is caused by a bacterial or fungal infection that results in joint inflammation. It can lead to permanent joint damage when left untreated.
This disease occurs when there is not enough blood flow to the hip joint. This causes the joint to collapse as the bone dies.
This bacterial infection is caused by bites from deer ticks (also known as blacklegged ticks). It can result in long-term joint problems if left untreated.
Slipped Capital Femoral Epiphysis
This condition occurs when the ball of the hip joint and the thighbone, or femur, become separated. It can lead to a joint disorder called osteoarthritis later in life.
Your child’s doctor will perform a physical exam to find out which movements are causing pain. This involves moving your child’s hips, knees, and other joints.
An ultrasound of your child’s hip might be done to check for fluid in the joint, which is a sign of inflammation.
Blood tests can be done to show how severe the swelling is. They might also be done to check for other causes of hip pain, such as Lyme disease.
Your child’s doctor might remove a fluid sample and have it sent to a lab for testing. This is usually done when the swelling or fever is serious and septic arthritis hasn’t been ruled out.
Your child’s doctor might take X-rays to rule out Legg-Calve-Perthes disease or slipped capital femoral epiphysis.
Treating toxic synovitis involves controlling or reducing the symptoms it causes. The inflammation caused by the viral infection generally goes away on its own.
Over-the-counter medications such as ibuprofen and naproxen can help reduce inflammation temporarily. This can provide short-term pain relief. Your child’s doctor might have your child take a prescription pain reliever if over-the-counter medications don’t work.
Your child should rest the affected hip in order to help it heal. Walking is usually safe, but your child should avoid strenuous activities, such as contact sports. Your child should also try not to put too much weight on the affected hip.
Toxic synovitis clears up in about one to two weeks in most cases, although it can last as long as five weeks. It can occur repeatedly in some children when they have viral infections such as colds. According to Pediatric Orthopedics in Practice, this happens in up to one-third of toxic synovitis cases. (Hefti, et al., 2007).
Although this condition is rarely serious, you should call your child’s doctor if:
- the fever or pain becomes worse even after taking anti-inflammatory medication
- the joint pain lasts longer than three weeks or comes back once your child stops taking medication
- the anti-inflammatory medication doesn’t start working within a few days
Your child’s doctor might need to prescribe a different medication or perform additional tests to check for other causes of hip pain.