Irritable hip

Overview

Irritable hip, or transient synovitis, is the most common cause of acute hip pain and limp in young children. It is a self-limiting, non-infective inflammation of the hip. It is a diagnosis of exclusion, and the main task is to rule out septic arthritis.

Aetiology and pathology

  • Cause unknown. Often follows a viral upper respiratory infection.
  • Sterile synovial inflammation and a small effusion.
  • Peak age 3 to 8 years, with boys more often affected than girls.

Clinical features

  • Acute limp or hip, thigh or knee pain. Hip pathology often refers pain to the knee.
  • The child is usually well, afebrile or mildly febrile, and can bear some weight.
  • Hip held in flexion, abduction and external rotation, the position of greatest capsular volume.
  • Mild restriction of internal rotation. A child who will not allow any movement is more worrying.
  • Differential diagnosis includes septic arthritis, osteomyelitis, Perthes disease, slipped capital femoral epiphysis, toddler’s fracture, juvenile idiopathic arthritis, leukaemia and non-accidental injury.

Investigations

  • Kocher criteria predict septic arthritis.
  • History of fever above 38.5 degrees.
  • Non-weight-bearing.
  • ESR of 40 mm per hour or more.
  • Serum white cell count above 12 x 109 per litre.
  • In the original series the probability of septic arthritis was below 0.2 percent with no predictors, 3 percent with one, 40 percent with two, 93 percent with three and 99.6 percent with four.
  • Validation in a new population showed somewhat lower accuracy that remained clinically useful.
  • CRP above 20 mg per litre was later added as a strong independent predictor.

Imaging

  • AP pelvis and frog-leg lateral radiographs to exclude Perthes disease, slipped capital femoral epiphysis, fracture and tumour.
  • Ultrasound confirms an effusion and guides aspiration. It cannot separate sterile from infected fluid.
  • MRI is useful when osteomyelitis or pyomyositis is suspected.

Management

  • Low risk children are managed with rest, NSAIDs and review within 24 to 48 hours.
  • Clear advice to return if fever develops or the child stops weight bearing.
  • Intermediate or high risk children need ultrasound guided aspiration. Send fluid for Gram stain, cell count and culture.
  • Suspected septic arthritis requires urgent arthrotomy or arthroscopic washout and intravenous antibiotics.
  • Symptoms usually settle within 1 to 2 weeks.

Complications

  • Recurrence in a minority of children.
  • A small proportion later develop Perthes disease, so persistent or recurrent symptoms need repeat radiographs.
  • Missed septic arthritis may lead to avascular necrosis, physeal arrest and joint destruction.

Exam traps

  • State the Kocher criteria and the probabilities.
  • Remember the prediction rule supports clinical judgement and does not replace it.
  • Always examine the spine, knee and abdomen in a limping child.
  • Do not label a child under 2 or over 10 years with transient synovitis without careful exclusion of other causes.

References

1. Kocher MS, Zurakowski D, Kasser JR. Differentiating between septic arthritis and transient synovitis of the hip in children, an evidence-based clinical prediction algorithm. J Bone Joint Surg Am. 1999, 81(12), 1662-70.

2. Kocher MS, Mandiga R, Zurakowski D, Barnewolt C, Kasser JR. Validation of a clinical prediction rule for the differentiation between septic arthritis and transient synovitis of the hip in children. J Bone Joint Surg Am. 2004, 86(8), 1629-35.

3. Caird MS, Flynn JM, Leung YL, Millman JE, D’Italia JG, Dormans JP. Factors distinguishing septic arthritis from transient synovitis of the hip in children. A prospective study. J Bone Joint Surg Am. 2006, 88(6), 1251-7.

Reviewed by Professor Phong Tran, Head of Orthopaedic Surgery, Western Health. Last updated 17 October 2026.