summary Transient Synovitis of Hip is inflammation of the synovium and a common cause of hip pain in pediatric patients that must be differentiated from septic arthritis of the hip. Diagnosis is one of exclusion and can be suspected in a patient with hip pain with low CRP and near normal synovial WBC count. Treatment is usually anti-inflammatories and observation given self-limiting nature. Epidemiology Incidence most common cause of hip pain in the pediatric population 3% of children between 3-10yo recurrence rate is as high as 20% Demographics most common in children aged 4-8 years old male-to-female ratio is 2:1 Anatomic location can affect any major joint but most commonly affects the hip joint Risk factors the exact cause of transient synovitis is largely unknown, however, may be related to viral infection (upper respiratory) bacterial infection (poststreptococcal toxic synovitis) trauma higher interferon concentration allergic reaction Etiology Pathophysiology pathoanatomy non-specific inflammation and hypertrophy of the synovial lining/membrane Presentation History recent upper respiratory infection or trauma Symptoms mild or absent fever acute or insidious onset of groin/thigh pain refusal to bear weight on the affected extremity usually improves during the day (child can walk with a limp later in the day) muscle spasms Physical exam inspection hip presents in flexion, abduction, and external rotation (position with least amount of intracapsular pressure) usually does not have a toxic appearance motion mild to moderate restriction of hip internal rotation is the most sensitive range-of-motion restriction a painless arc of motion is more likely synovitis rather than septic arthritis neurovascular toe-walking, cavus foot, or clawing of the toes may suggest a neurological cause of limp provocative tests log-rolling leg can detect involuntary muscle guarding non-tender motion of lumbar spine and ipsilateral knee Imaging Radiographs recommended views AP, lateral or frog leg hip views optional radiographs spine films findings usually normal Ultrasonography indications history and physical examination suspicious for septic arthritis findings accurate for detecting intracapsular fluid/effusion may show synovial membrane thickening sensitivity/specificity difficult to distinguish transient synovitis from septic arthritis, but infection less likely if effusion absent MRI indications suspicion for myositis or osteomyelitis significantly elevated lab values Studies Serum labs WBC may be slightly elevated CRP < 20 mg/l most important factor to RULE OUT septic arthritis ESR usually less than 20 mm/h Invasive studies synovial fluid aspiration if concern for septic arthritis based on clinical judgment or Kocher criteria assume it is septic arthritis if synovial WBC is >50,000 Differential Hip septic arthritis Osteomyelitis SCFE Treatment Nonoperative NSAIDS and close observation indications low clinical suspicion of septic arthritis modalities treat the patient with IV or PO NSAIDS and observe over 24 hours minimize walking for 24 hours consider traction to enforce rest outcomes if symptoms improve with NSAIDS, more likely to be transient synovitis symptom resolution in under 1 week from the date of presentation Complications Recurrence ~ 20% Legg-Calve-Perthes reported as 0-10% incidence however his is controversial as most series show no long term sequelae Prognosis Natural history of disease usually benign marked improvement, usually in 24-48 hours complete resolution of symptoms will usually occur in 1-2 weeks