What Causes Toxic Synovitis?

Toxic Synovitis: Causes, Symptoms, and Diagnosis

Children who develop or complain of limping must be examined to make sure that their condition is not an orthopedic emergency like in the case of septic arthritis. After being examined, children's parents may hear about a toxic synovitis diagnosis. Such diagnosis might sound scary, but it is actually not. 

What is toxic synovitis?

Toxic synovitis is a form of arthritis in children that usually affects the hips. The condition tends to suddenly occur and suddenly disappears without long-term effects. For this reason, this condition is often called transient synovitis. 

Toxic synovitis usually occurs in children after having viral infections. Experts believe that the condition may be due to the children's immune response to the virus, which is why the condition is also called postinfectious arthritis. The following viruses can cause some type of toxic synovitis in children:

  • Adenovirus
  • Varicella-zoster virus (VZV) or chickenpox 
  • Cytomegalovirus (CMV)
  • Coxsackievirus
  • Epstein-Barr virus (EBV) or human herpesvirus 4
  • Hepatitis B 
  • Herpes simplex virus
  • Mumps
  • Rubella or German measles
  • Parvovirus B19

This condition is most commonly observed in boys aged between 3 to 10 years old, especially after an infection of the upper respiratory tract. In acute toxic synovitis, inflammation of the synovial membrane, which surrounds the hip occurs. Although the exact cause of the condition is still unclear, other possible causes may include:

  • A fall, an injury, or any history of trauma (a predisposing factor or a cause)
  • Poor blood flow (may lead to Perthes disease)
  • Inflammation of the hip joint
  • Increased viral antibody titers
  • Postvaccination or drug-mediated reaction
  • Allergic disposition 


The following symptoms of toxic synovitis have been reported:

  • Limping
  • Walking on tiptoes
  • Hip pain mostly on one side 
  • Pain in front and toward the middle of the thigh 
  • Pain in the knees
  • Low-grade fever
  • Crying in younger children
  • Refusal to walk (in some cases)

The most common symptom reported is unilateral hip or groin pain. Thigh or knee pain is also reported by some patients with toxic synovitis. Others may only limp. In nearly half of the patients with toxic synovitis, a recent history of an upper respiratory tract infection, otitis media, pharyngitis, or bronchitis is elicited. Usually, the children are afebrile or have a mild fever. It is very rare for children to have a high fever in toxic synovitis.

When it comes to babies, the most common signs of toxic synovitis are persistent crying and abnormal crawling. Babies with toxic synovitis often cry when their hips are being moved, especially during diaper changes.


Diagnosing toxic synovitis can be somewhat difficult. There are other serious causes of hip pain, which is why doctors first rule out other conditions through tests before making a diagnosis. The following conditions have similar symptoms to toxic synovitis:

  • Septic Arthritis - This is a type of bacterial or fungal infection that results in joint inflammation. This infection can also lead to permanent joint damage if left untreated. 
  • Lyme Disease - This is another bacterial infection caused by tick bites. The infection can also result in long-term joint problems if left untreated. 
  • Slipped Capital Femoral Epiphysis (SCFE) - This hip disorder occurs when the ball of the hip joint and the thigh bone (femur) separate, leading to a joint disorder called osteoarthritis later in life. 
  • Legg-Calve-Perthes Disease - This childhood condition is due to an insufficient blood flow to the hip joint, which leads to the collapse of the joint as the bone dies. 

A physical examination will involve finding out which of your child's movements are causing pain. The doctor usually checks your child's joints, knees, and hips. To check for any inflammation in the child's joints, an ultrasound may be ordered by the doctor. An X-ray may also be taken to rule out Legg-Calve-Perthes disease. 

Blood tests can help identify the severity of an infection. When it comes to diagnosing Lyme disease, a fluid sample may be collected for further laboratory analysis. Such test is usually performed when your child has a high fever and septic arthritis is still not ruled out. 

Call your doctor if you notice any of the following:

  • Your child complains of worsening pain even after taking NSAIDs 
  • Your child's joint pain persists for more than three weeks
  • Your child's pain comes back after not taking pain medications
  • Pain medications do not work at all

In such cases, the doctor might prescribe an alternative medication or order additional tests to determine other causes of your child's hip pain. 


Children need some rest when they have toxic synovitis. Until the pain is completely gone, children should not take part in activities that can strain their knees or hips. The condition usually starts to resolve within three days of rest

The problem will start to resolve within three days of rest, and within two weeks, the pain should be gone. Normally, there is no need for hospitalization. Instead, nonsteroidal anti-inflammatory drugs can be prescribed by the doctor for pain relief. The usual medications for toxic synovitis are acetaminophen, ibuprofen, and naproxen

Parents should seek immediate medical attention if the condition does not resolve, if the symptoms persist, or if the pain worsens to rule out other underlying health problems. If the child has toxic synovitis, it does not necessarily mean that the child is prone to developing joints disorders such as arthritis later in life. 


Toxic synovitis is usually not preventable. However, your child can avoid it if he or she does not contract any type of viral infection, which can trigger the condition. 


Children can comfortably walk again within a day or two, especially after taking NSAIDs. However, sports activities or gym class will have to wait until they have fully recovered from the condition. Toxic synovitis usually resolves on its own within 1-2 weeks. In some cases, children have to endure the condition for as long as five weeks. Toxic synovitis may also repeatedly occur in children, particularly after having viral infections, such as colds or flu. 

Most children have no long-lasting effects from toxic synovitis. Some children may even experience the condition multiple times during their childhood years. When your child has another type of illness, let the doctor know about your child's history of toxic synovitis.