Toxic synovitis is a temporary condition that causes hip pain in children. It’s also known as transient synovitis.
Toxic synovitis mainly occurs in children between the ages of 3 and 8. It’s two to four times more common in boys than in girls.
Although it’s troubling for parents, this condition usually clears up on its own within a week or two and causes no lasting damage.
Toxic synovitis occurs when there’s inflammation in the hip joint. The cause is unknown, but it often occurs after a viral infection. It usually only affects one hip, but it’s possible for swelling and inflammation to spread to other joints.
The most common symptom of toxic synovitis is hip pain. This pain might occur on and off in one 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
- complaining of pain in the thigh or knee with no hip pain
- running a low-grade fever under 101°F
- refusing to walk if the pain is severe
- crying and irritability in younger children
Common signs of toxic synovitis in babies include crying, especially when moving their hip joints, and unusual crawling movements. Being unwilling or unable to crawl is another common sign.
Ruling out other conditions
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, your child’s doctor must first test for them before making a toxic synovitis diagnosis. These include the following:
- septic arthritis, a bacterial or fungal infection that results in joint inflammation and can lead to permanent joint damage if left untreated
- Legg-Calve-Perthes disease, a condition marked by insufficient blood flow to the hip joint, which leads to the collapse of the joint as the bone dies
- Lyme disease, a bacterial infection caused by tick bites that can result in long-term joint problems if left untreated
- slipped capital femoral epiphysis (SCFE), which occurs when the ball of the hip joint and the thighbone (femur) separate, leading to a joint disorder called osteoarthritis later in life
Diagnosing toxic synovitis
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.
Your doctor might order an ultrasound of your child’s hip to check for fluid in the joint, which is a sign of inflammation.
Blood tests can show how severe the swelling is. Your child’s doctor might also check for other causes of hip pain, such as Lyme disease. They might remove a fluid sample and send it 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 SCFE.
Treating toxic synovitis involves controlling or reducing its symptoms. The inflammation caused by the viral infection generally goes away on its own.
Over-the-counter (OTC) medications such as ibuprofen and naproxen can help reduce inflammation temporarily. This can provide short-term pain relief. Your child’s doctor might prescribe a stronger pain reliever if OTC medications don’t work.
Your child should rest the affected hip 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 hip.
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 after your child stops taking medication
- the anti-inflammatory medication doesn’t start working within a few days
In these cases, your child’s doctor might need to prescribe a different medication or perform additional tests to check for other causes of hip pain.
Toxic synovitis clears up in about one to two weeks in most cases, but it can last as long as five weeks. It can occur repeatedly in some children when they have viral infections like colds.