Transient synovitis of the hip refers to a self-limiting acute inflammatory condition affecting the synovial lining of the hip. It is considered one of the most common causes of hip pain and limping in young children. Over 90% of hip joint effusions in children tend to be due to transient synovitis 10.
It typically affects young children (3-8-year-olds). There is a recognized increased male predilection.
Patients typically present with hip pain for one to three days, associated with limping or the refusal to bear weight.
Their exact pathogenesis is not well known. Several theories have been proposed. In some situations, it may follow an upper respiratory tract infection. Some have suggested a viral etiology (e.g. related to Parvovirus B-19 and /or Herpes simplex virus 6 infections while others have proposed a post-traumatic etiology with subsequent development of chemical synovitis.
Features are nonspecific although in some cases there may be an increase in medial joint space in the affected hip 5. Hip radiography within 6 months (classically after 4 weeks) to exclude Legg-Calvé-Perthes (LCP) disease is recommended 12.
Useful at demonstrating a joint effusion which is often seen in the anterior recess. Herniation of the synovial membrane through a joint capsular defect (pseudodiverticulum) between the iliopsoas muscle and the anterior border of the joint capsule may be seen in a very small proportion of patients (~2%) 1.
Described features include 6
- symptomatic hip joint effusion
- synovial enhancement
- contralateral joint effusion
- synovial thickening
- signal alterations and enhancement in surrounding soft tissue
- there is usually no signal alteration in the adjacent marrow.
Treatment and prognosis
It is a self-limiting disorder usually has no residual sequelae. Recurrences are possible. Management is usually supportive.
For imaging appearances, possible considerations include
- septic arthritis: on MRI there is often signal abnormality in marrow 8, and classically affects children "younger than 4 years and with a history of fever" while it is "older than 4 years of age and no history of fever" for transient synovitis 11.
For clinical limping there can be much wider differential such as other childhood arthritides (e.g. juvenile rheumatoid arthritis 1, Brucellar arthritis), Perthes disease, epiphysiolysis and osteoid osteoma etc.
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