Transient Synovitis

Etiology And Epidemiology

The cause of TS is unknown. In the few cases for which biopsy specimens of the synovial membrane have been obtained, histologic examination shows nonspecific inflammation. ^, Considering that many children with TS have had a recent or concurrent upper respiratory or gastrointestinal viral infection and that elevated serum interferon levels have been demonstrated in some patients, TS likely represents a self-limited infection involving the synovial membrane or a postinfectious inflammatory response.

Some investigators have found positive throat culture results for group A Streptococcus or elevated antistreptolysin O titers, or both, for a small number of children with toxic synovitis. ^, However, no single organism has been implicated consistently as the cause of TS. In one series, an increase in antibody concentrations against rubella, enterovirus, Epstein-Barr virus, or Mycoplasma was demonstrated for 67 of 80 children with TS, but there was no unaffected control group; results of viral culture for synovial fluid were negative; and culture samples were not obtained from other sites. In other reports, including one prospective study in which a control group was included and one study in which serologic evidence of acute parvovirus B19 or human herpesvirus 6 infection was sought, no evidence of viral or streptococcal causes was found. ^, Parvovirus B19 DNA has been detected by polymerase chain reaction (PCR) in the sera of a small number of children with TS. In a study of children in a Lyme disease endemic region, 5.2% of children with suspected acute TS of the hip had infectious arthritis due to Borrelia burgdorferi. In a study of 34 Israeli and Spanish children aged 6–27 months of age with culture-proven Kingella kingae arthritis of the hip, TS was the suspected diagnosis in the majority of patients.

TS occurs predominantly in children 18 months to 12 years of age; in various studies, the mean age of occurrence is 5.6–5.9 years. ^{, , ,} Boys are affected approximately twice as often as girls. ^{, , , , ,} Although the annual incidence in the US is unknown, TS frequently is referred to as the most common cause of hip pain in children. The average annual incidence in one study of Swedish children was 0.2%.