Transient synovitis (or irritable hip) is a common self limiting cause of hip pain and limping in children. It accounts for around 0.5% of all paediatric admissions to hospital. The symptoms are due to an arthralgia secondary to inflammation of the synovium.
Transient synovitis is benign form of synovial irritation of an unknown cause; but there may be some form of reaction to trauma or viral illness, such as a recent respiratory infection.
Clinical features of Transient Synovitis:
The age of onset is usually 3 – 10 years of age (with an average or peak around 5-6 years); M>F; 5% are bilateral; pain is in hip and groin region; onset is rapid over a day or two; 50% are acute; the pain can be referred to medial knee or down thigh; tender to palpation; may have muscle spasm; hip range of motion is limited and painful on both active and passive movement; limp can be pronounced; there is occasionally a low grade fever; often cannot bear weight on affected site; x-ray is typically normal or with a slight joint space widening.
Sensitive test is the ‘leg roll’: patient lying supine and the leg is rolled to medially and laterally rotate the limb to produce pain in the hip.
The diagnosis often one of exclusion of other causes. Ultrasound can identify fluid inside joint to rule out infection or other causes.
Differential diagnosis: soft tissue injury; infectious arthritis; Perthe’s disease; developmental dysplasia of the hip (if missed at birth); slipped capital femoral epiphysis; Juvenile Idiopathic Arthritis
The most important differential is to rule out infectious or septic arthritis as early as possible. Kocher et al (1999) reported on the differentiation:
Patients who had septic arthritis differed significantly (p < 0.05) from those who had transient synovitis with regard to the erythrocyte sedimentation rate, serum white blood-cell count and differential, weight-bearing status, history of fever, temperature, evidence of effusion on radiographs, history of chills, history of recent antibiotic use, hematocrit, and gender. Patients who had true septic arthritis differed significantly (p < 0.05) from those who had presumed septic arthritis with regard to history of recent antibiotic use, history of chills, temperature, erythrocyte sedimentation rate, history of fever, gender, and serum white blood-cell differential. Four independent multivariate clinical predictors were identified to differentiate between septic arthritis and transient synovitis: history of fever, non-weight-bearing, erythrocyte sedimentation rate of at least forty millimeters per hour, and serum white blood-cell count of more than 12,000 cells per cubic millimeter (12.0 x 109 cells per liter). The predicted probability of septic arthritis was determined for all sixteen combinations of these four predictors and is summarized as less than 0.2 percent for zero predictors, 3.0 percent for one predictor, 40.0 percent for two predictors, 93.1 percent for three predictors, and 99.6 percent for four predictors. The chi-square test for trend and the area under the receiver operating characteristic curve indicated excellent diagnostic performance of this group of multivariate predictors in identifying septic arthritis.
Caird et al (2006) reported:
This prospective study of children who presented with findings that were highly suspicious for septic arthritis of the hip builds on the work of previous authors. We found fever (an oral temperature >38.5°C) was the best predictor of septic arthritis followed by an elevated C-reactive protein level, an elevated erythrocyte sedimentation rate, refusal to bear weight, and an elevated serum white blood-cell count. In our study group, a C-reactive protein level of >2.0 mg/dL (>20 mg/L) was a strong independent risk factor and a valuable tool for assessing and diagnosing children suspected of having septic arthritis of the hip.
Treatment of Transient Synovitis:
This is usually self-limiting, lasting 3-10 days; range of motion may need 2-3 weeks before it returns to normal. Heat and gentle massage may help somewhat with symptoms.
Monitor for any changes in temperature (increase is indicative of another problem).
Paracetamol or NSAID’s used for symptomatic relief.
Crutches may be needed to ambulate if pain relief not successful to allow continued walking. The worst cases may need short term bed rest.
Recurrence is uncommon.
Recovery almost always complete with generally no sequalae; thought there is a controversial relationship if transient synovitis increases the risk for Legg-Calvé-Perthes disease; some may develop coxa magna (enlargement and deformity of the head of the femur).
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