Characteristics

• A transient synovitis.

• The commonest cause of non-traumatic hip pain.

• Usually unilateral with an unknown cause.

• Age range: 9 months to 18 years with a peak at 5 years.

• Many patients have an antecedent illness such as a respiratory-tract infection.

• Important to exclude septic arthritis.

• Consider tuberculosis of the hip in the appropriate clinical settings.

Clinical features

• Presents in a variety of ways including inability to bear weight or a painful hip/thigh/knee.

• Spurious history of trauma.

• Onset may be sudden or gradual over several days.

• Symptoms tend to settle spontaneously after several days.

• Apyrexia.

• On examination passive movements are usually normal.

Radiological features

• Radiographs of the knee, femur and hip are usually normal.

• Occasionally a hip effusion can be seen on the plain radiograph.

• Ultrasound is the imaging modality of choice (> 95% sensitivity). A difference of > 3 mm in joint space between the normal and affected sides should be viewed as pathological.

• Ultrasound is poor at differentiating between a simple effusion, haemorrhage and sepsis.

Management

• Transient synovitis is a diagnosis of exclusion.

• When the diagnosis is unclear, or the patient cannot bear weight, consider septic arthritis.

• Ultrasound guided aspiration of the joint fluid allows definite assessment.

• If the history and examination are consistent with the diagnosis, and investigations, including WCC and ESR, are normal, the patient can often be discharged to the care of a responsible adult with instruction to rest, and simple analgesia.

• Follow-up within 72 hours unless symptoms completely resolve.

• Admission for observation is sometimes needed.