What is Transient Synovitis?
Transient synovitis is a sudden inflammation affecting the lining of the joint, especially common among children, where it often results in hip pain. Although this condition naturally resolves itself and isn’t serious, medical professionals should be able to tell the difference between transient synovitis and a serious infection.
What Causes Transient Synovitis?
The exact cause of transient synovitis, a temporary inflammation of the joints, is unknown. While research has offered several theories, none have been definitively proven. These speculated risk factors include having a recent upper respiratory infection (like the common cold), bacterial infection, particularly after a Streptococcal infection, or injury. However, none of these are certain causes.
Many children who have transient synovitis tend to have a history of recent symptoms of an upper respiratory infection, or have experienced a recent injury. According to a study by Kastrissianakis and Beattie, those diagnosed with transient synovitis are more likely to have had recent symptoms of a viral infection, such as vomiting, diarrhea, or common cold symptoms.
Another interesting finding is that patients with transient synovitis tend to have higher levels of a protein called interferon in their blood. Also, whether the occurrence of transient synovitis changes with the seasons has been a topic of debate. One study found more cases in October and fewer in February, but such findings are not always consistent.
Research to find links between transient synovitis and certain viral infections, like parvovirus B-19 and human herpes simplex virus-6, have not shown conclusive evidence. Other proposed risk factors include hypersensitivity reactions after vaccination or drug use, or particular allergies.
There is also a possible link, though controversial, between transient synovitis and a disease called Legg-Calvé-Perthes disease (LCPD). Some studies found a slightly higher risk of LCPD occurrence (up to 3%) among patients who had transient synovitis compared to the general population, where the incidence is approximately 0.9 per 100,000 patients.
Risk Factors and Frequency for Transient Synovitis
Transient synovitis of the hip often happens in children between 3 to 10 years old. It has an average incidence rate of 0.2% per year and a total lifetime risk of 3%. A 2010 study in the Netherlands found that the average age of children when they first had this condition was around 4.7 years old. While it’s most common in children between 3 and 10, there are also rare cases in babies and adults. Boys are twice as likely to get this condition as girls. Also, 1% to 4% of patients might have this condition in both hips.
- Transient synovitis of the hip is common in children aged 3 to 10.
- On average, 0.2% of children have this condition each year, and there’s a 3% chance of getting it in a lifetime.
- The average age of children when they first have this condition is 4.7 years old.
- This condition is rare in babies and adults but it can happen.
- Boys are twice as likely to get this condition as girls.
- 1% to 4% of patients might have this condition in both hips.
Signs and Symptoms of Transient Synovitis
Transient synovitis is a condition that commonly shows up as sudden difficulty using a limb, usually with symptoms ranging from general pain in the hip or a slight limp to refusing to put weight on the affected limb. Kids or infants with this condition might appear to be more upset or cry more than they usually do. To identify this condition, doctors should look for signs of discomfort or pain that either originates from or extends to the lower back. An important part of the diagnosis often includes getting information from the child’s parents or guardians, observing the child in a medical setting, and considering any recent illnesses the child may have had, such as respiratory infections, sore throat, bronchitis or ear infections.
During a physical examination, the patient might show a limited range of motion, particularly with movements that involve moving the leg away from the body or rotating it inward. The patient’s hip might be flexed (bent), abducted (moved away from the body), and externally rotated (turned outward), as these positions put less pressure on the hip joint. Yet, it’s also possible that a patient with transient synovitis will have a normal range of movement in the hip. Some tests, such as rolling the leg from side to side or the Patrick (or FABER) test, which involves bending and moving the patient’s leg away from the middle of their body and rotating it outward, can be helpful. These tests can indicate a disorder in the hip or, if there’s pain on the opposite side, a problem with the joint that connects the base of the spine (the sacrum) and the pelvis (the ilium).
Testing for Transient Synovitis
If your doctor suspects you might have inflamed hip joint (transient synovitis), septic arthritis, or Lyme arthritis, you will undergo several tests. These are likely to include checks on your white blood cell count, C-reactive protein levels (which signal inflammation), erythrocyte sedimentation rate (measuring how quickly your red blood cells settle at the bottom of a test tube, which can suggest inflammation), hip x-rays, and ultrasound examinations.
A 2017 analysis highlighted key clinical observations that help with diagnosis:
- Being feverish when seeing the doctor is more common in people with septic arthritis (>50%) than in those with transient synovitis (30%) or Lyme disease (23%).
- Refusal to bear weight is common for patients with transient synovitis or septic arthritis (Over 60%), but less so for those with Lyme disease (33%).
- Inflammatory marker levels (erythrocyte sedimentation rate range) differ between the conditions, with the highest levels seen in septic arthritis patients.
- Synovial WBC counts (white blood cell counts in the fluid within your joints) showed a similar trend to the erythrocyte sedimentation rate.
As observed, transient synovitis is usually diagnosed by ruling other conditions out, but the synovial fluid aspiration (insertion of a needle, under ultrasound guidance, into a joint to withdraw fluid) can provide a wealth of diagnostic information.
In terms of additional lab tests, if your C-reactive protein is greater than 2 mg/dL, you are at higher risk of having septic arthritis. However, urinalysis and culture are typically normal. If your levels of procalcitonin (a substance produced by many types of cells in the body, usually in response to bacterial infection) increase, it might suggest septic arthritis
If you live in an area where Lyme disease is prevalent, a routine test for it is not necessary if you have acute, non-traumatic hip pain. However, this test should be performed if your doctor is considering a different diagnosis such as septic or pyogenic arthritis, or if your symptoms are irregular.
In terms of imaging, although an X-ray might appear normal for several months after symptoms appear, they can show certain changes. The joint space of the affected hip may be wider, indicating the presence of fluid. Ultrasound is extremely accurate for detecting this fluid on the hip. If the ultrasound-guided hip aspiration relieves pain and shows certain signs, it would suggest that the patient is more likely to have septic arthritis and not transient synovitis.
If the patient’s symptoms can’t be explained by the results so far, a contrast-enhanced MRI scan can be performed to help tell the difference between transient synovitis and septic arthritis. This scan can show changes in the bone marrow and the synovial tissues (soft tissues inside the joint), which can help to make the right diagnosis.
Finally, there are established guidelines available to help doctors differentiate between septic arthritis and transient synovitis. The diagnostic probability increases if you have a high white blood cell count, can’t or won’t put weight on the affected leg, have a high temperature, or your erythrocyte sedimentation rate is over 40 mm/hour. If none of these factors are present, it’s very unlikely you have septic arthritis of the hip.
Overall, the best predictor of septic arthritis is a high temperature, followed by a C-reactive protein level of over 1 mg/dL, refusal to bear weight, erythrocyte sedimentation rate, and your white blood cell count.
Treatment Options for Transient Synovitis
If you’ve been diagnosed with transient synovitis, which is a temporary inflammation of the joint, your doctor will likely recommend that you rest and avoid any strenuous activities. This not only helps with healing but eases pain as well. You might also be advised to take nonsteroidal anti-inflammatory drugs or NSAIDs, which are a type of medication that can help control pain and reduce inflammation. Using heat or massage therapies can also provide comfort and relief.
In certain situations, particularly when the diagnosis isn’t clear-cut or if there’s concern about your symptoms, you may be admitted to the hospital for continuous observation. This will help the medical team monitor your progress after starting the initial treatment strategies.
Typically, symptoms of transient synovitis start to get better within a day or two. Most people (about 75%) experience complete recovery from symptoms within 1 to 2 weeks. However, a minority of patients may have milder symptoms persisting for several weeks. If you continue to have significant symptoms for a week to ten days after the initial onset, then your doctor might consider other potential diagnoses. If symptoms persist for more than a month, it’s likely that a different medical condition is causing them.
What else can Transient Synovitis be?
When a person comes to the doctor with sudden hip pain, there are several different potential causes that must be considered. Some of these conditions are serious and can lead to major health complications if not spotted and treated fast. These include:
- Bone infection (Osteomyelitis)
- Septic arthritis (infection in a joint)
- Lesions that are either primary (first appearing in the hip) or metastatic (spread from another part of the body)
- LCPD (a childhood hip condition)
- Slipped capital femoral epiphysis (SCFE, a childhood hip condition that occurs when the ball at the head of the thigh bone slips backwards).
On the other hand, there are also other less serious conditions to consider such as:
- Lyme Arthritis (joint inflammation caused by Lyme disease)
- Pyogenic Sacroiliitis (inflammation of the sacroiliac joints due to a bacterial infection)
- Juvenile Rheumatoid Arthritis (a type of arthritis that happens in children).
So, it is very important to remember that sudden hip pain can be a symptom of many different medical conditions, and correct diagnosis is key for effective treatment.
What to expect with Transient Synovitis
Transient synovitis of the hip, a temporary inflammation of the hip joint, has a tendency to recur in about 20% to 25% of patients. It’s important for patients to understand that they have an increased chance for the condition to come back if they’ve had transient synovitis before. A study has shown that for patients who have had this condition before, the likelihood of it recurring is 69% after a year, 13% after two years, and 18% in the long term.
Possible Complications When Diagnosed with Transient Synovitis
The primary issue related to transient synovitis is the return of symptoms.
Main Issue:
- Reoccurrence of symptoms
