Transient synovitis is the self-limiting painful hip condition that occurs due to inflammation of the synovium of the hip for a transient period.
Other named of transient synovitis of the hip are toxic synovitis, irritable hip, transitory coxitis, coxitis fugax, acute transient epiphysitis, coxitis serosa simplex, phantom hip disease and observation hip.
It is a self-limiting condition.
Transient synovitis is usually found in children between 3-10 years old and is the most common cause of pain and limp in that group. But it has been reported to occur in infants and adults as well.
It affects boys twice as often as girls.
Transient synovitis has the highest incidence rate among causes of nontraumatic hip pain in children.
Relevant Anatomy
Hip joint is a ball and socket joint formed by head of femur and acetabulum. The synovium is the inner lining of the capsule of the hip.
[Know more about hip joint anatomy]
Inflammation of synovium is called synovitis.
Cause and Pathophysiology of Transient Synovitis Hip
The exact cause is unknown. A recent viral infection, most commonly an upper respiratory tract infection) or a trauma have been implicated as precipitating events, though the exact relation needs to be seen.
Biopsy of the synovium shows nonspecific inflammation and hypertrophy of the synovial membrane. Increased proteoglycans are found in the synovium.
Clinical Presentation of Transient Synovitis
Most of the children have pain in single hip or groin. the pain may go to the medial thigh. Some children complaint of knee pain as well.
Very young children who are unable to describe the pain may present with unstoppable crying. There would be a history of pain on a change in diapers.
The child may otherwise have a bearable pain and walk with a limp.
In about half of the cases, there would be a history of upper respiratory tract infection like pharyngitis, bronchitis, or otitis media.
There may be no fever or mild fever present. High fever is rare.
On physical examination, the hip may be painful on passive motion and tender on palpation.
The abduction and internal rotation of the affected hip could be normal or slightly restricted. As much as one-third of patients have normal movements.
Involuntary muscle guarding can be ascertained by log-roll test.
The patient lies supine and the examiner gently rolls the limb from side to side. Involuntary muscle guarding is seen on the affected side as compared to other side.
Examination of the knee, the spine, sacroiliac joint, and abdomen is usually normal.
Differential Diagnoses
- Juvenile Idiopathic Arthritis
- Acute Osteomyelitis
- Pediatric Septic Arthritis
- Soft tissue injuries
- Perthes disease in older children
- Lyme arthritis
- Gonococcal arthritis
- Bone tumor
Lab Studies
Inflammatory markers like CRP and ESR are elevated slightly. White blood cell count may be slightly elevated.
In cases where clinical differentiation is difficult, it becomes important to determine if the elevated markers indicate septic arthritis or transient synovitis.
How to Differentiate between Septic Arthritis and transient arthritis?
Various methods of differentiation are described
Kocher Algorithm
There is 99.6% probability of septic arthritis if patients are
- Not able to bear weight over the affected limb
- Had a history of fever
- ESR > 40 mm/hr
- WBC count >12,000 cells/mm
Recent validation studies suggest that this algorithm is not enough to differentiate between transient synovitis and K kingae arthritis.
Therefore it is suggested that blood cultures and nucleic acid amplification assay should be performed in young children presenting with irritation of the hip, even when fever, raised WBC count and a high Kocher score is not present.]
Kocher algorithm has been found a predicted probability of 71% that the patient has septic arthritis.
C-reactive protein
A CRP >20 mg/L is an independent risk factor for septic hip arthritis.
Procalcitonin Levels
This is not done routinely but could be helpful in distinguishing between bacterial infections and inflammatory processes. Procalcitonin levels are low in inflammatory disease but increase in septic arthritis.
If required, Lyme serology, antinuclear antibody, rheumatoid factor, HLA-B27, and tuberculosis skin testing could be done.
Imaging Studies
Xrays
Xrays help to exclude bony lesions like occult fracture or tumor or in some cases Legg Calve Perthes disease.
X-rays are essentially normal in transient synovitis. An anteroposterior and frog lateral view of the pelvis and both hips is advisable. Following radiological signs may be seen though.
- Widening of the medial joint space
- Waldenström sign – Lateral displacement of the femoral epiphyses with surface flattening
- Prominent obturator shadow
- Slight demineralization of the proximal femur.
Medial joint space may be slightly wider in the affected hip
Ultrasound
An ultrasound would show intracapsular effusion but it cannot differentiate from infection
MRI
It helps to differentiate transient synovitis from septic arthritis especially the dynamic contrast-enhanced MRI.
Ultrasound-guided Aspiration
It is done to evaluate the nature of fluid to determine/rule out infection/
It is done in all cases where ultrasonography shows effusion and any of the following is present.
- Temperature > 99.5°F
- ESR > 20 mm/h
- Severe hip pain and spasm
Gram stain, raised WBC count, raised polymorphonuclear cells are seen in septic arthritis
Treatment of Transient Synovitis
Treatment consists of rest, non-weight bearing and drugs for pain when needed. If fever occurs or the symptoms persist, other diagnoses need to be considered.
In cases where the diagnosis is not certain, or the patient is uncomfortable, the patient should be hospitalized for observation
Rest
Bed rest is advised, in a position of comfort. Weight-bearing is discouraged until the limp and pain have resolved.
NSAIDs
NSAIDs are known to shorten the duration of symptom from average 4.5 days to 2 days.
Follow Up
Transient synovitis of the hip should resolve by 7-10 days and if symptoms persist after that, reconsideration of the diagnosis should be done.
All patients should have a repeat x-ray within 6 months to rule out Legg-Calvé-Perthes disease.
Prognosis and Complications
Symptoms of Patients with transient synovitis usually improve within 24-48 hours. 60-75% patients have a complete resolution within 2 weeks.
In the remaining, severity of symptoms may decrease and resolve over several weeks.
4-17% of the cases have a recurrence. Most of the recurrences develop within 6 months.
Approximately 1.5% of patients with transient synovitis develop Legg Calve Perthes disease, Coxa magna or osteoarthritis.
But recent studies have found no such association.
