Transient synovitis is the 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 has historically been termed transitory coxitis, coxitis fugax, acute transient epiphysitis, coxitis serosa seu 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 most common cause of pain and limp in that group. But it has been reported to occur in infants and adults as well.
One of the studies reports the occurrence of about 76 100,000 person-years.
It affects boys twice as often as girls.
Anatomy of Hip Joint
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.
Pain in unilateral hip or groin is the most common presentation. Some children may have report medial thigh or knee pain. Transient synovitis has the highest incidence rate among causes of nontraumatic hip pain in children.
Young children who are unable to describe the pain may present with incessant crying. In other cases changing the diapers could be painful. There may be an associated limp present.
In about 50% cases, a history of upper respiratory tract infection, pharyngitis, bronchitis, or otitis media could be elicited.
Patients either do not have fever or have mildly raised temperature.
Children with transient synovitis are usually afebrile or have a mildly elevated temperature; high fever is rare.
On physical examination, there is mild restriction of abduction and internal rotation but examination could be normal in as much as one third of the cases.
The hip may be painful on passive motion and tender on palpation.
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.
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.
Various methods of differentiation are described
There is 99.6% probabbilty of septic arthritis if patients were
- Had a history of fever
- ESR > 40 mm/hr
- WBC count >12,000 cells/mm
[However, 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.
A CRP >20 mg/L is an independent risk factor for septic hip arthritis.
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.
- Juvenile Idiopathic Arthritis
- Acute Osteomyelitis
- Pediatric Septic Arthritis
- Soft tissue injuries
- Legg-Calvé-Perthes disease
- Lyme arthritis
- Gonococcal arthritis
- Bone tumour
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 demineralisation of the proximal femur.
Medial joint space may be slightly wider in the affected hip
Ultrasound would show intracapsular effusion but it cannot differentiate from infection
It helps to differentiate transient synovitis from septic arthritis especially the dynamic contrast-enhanced MRI.
MRI shows joint effusion, synovial enhancement,synovial thickening and normal signals from adjacent marrow. Contralateral joint effusion is also noted.
Ultrasound guided Aspiration
It is done to evaluate 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..
Treatment of Transient Synovitis
Treatment consists of rest, non-weightbearing and analgesics 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, patient should be hospitalized observation
Bed rest is advised, in a position of comfort. Weight bearing is discouraged until the limp and pain have resolved.
NSAIDs are known to shorten the duration of symptom from qaverage 4.5 days to 2 days.
Those patients who are ebeing treated on OPD basis should be followed next day for a repeat examination.
Transient synovitis of hip should resolve by 7-10 days and if symptoms persist after that, reconsideration of the diagnosis should be done.
All patients should have repeat xray within 6 months to rule out Legg-Calvé-Perthes disease.
Prognosis and Complications of Transient Synovitis
Symptoms of Patients with transient synovitis usually improve within 24-48 hours. 60-75% patients have complete resolution within 2 weeks.
In the remaining, severity of symptoms may decrease and resolve over several weeks.
There is a recurrence rate of 4-17% and most of them develop within 6 months.
Approximately 1.5% of patients with transient synovitis develop Legg Calve Pethes disease, Coxa magna, osteoarthritis.
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