Hip pain in children is always a potentially serious and needs urgent assessment. The main immediate concern is to distinguish infection of the hip joint or pelvic bones from irritable hip. If examination shows a restriction of hip movement or there are x-ray abnormalities, many will have a serious disorder requiring long-term management.

Differential diagnosis

• At any age:
  • Transient synovitis ("irritable hip"); commonest cause of hip pain in a well child¹
  • Trauma
  • Septic arthritis of the hip - always consider this diagnosis, especially in a younger, febrile or unwell child (can destroy a hip joint within hours and is therefore a surgical emergency)
  • Acute osteomyelitis of the proximal femur
  • Tuberculous arthritis
  • Juvenile spondyloarthritis, rheumatoid arthritis and chronic arthritis
  • Bone malignancy
  • Non-accidental injury
• Age under 5 years:
  • Developmental dysplasia of the hip (formerly called congenital dislocation of hip)
  • Infantile coxa vera
  • Acute infective epiphysitis
• Age 5-10 years:
  • Perthes' disease
• Age 10-15 years:
  • Slipped upper femoral epiphysis (also called slipped capital femoral epiphysis)

Investigations

These depend on the likely differential diagnosis:

• Plain X-ray hips (always do both for comparison - and include AP and lateral "frog leg" view).
• Ultrasound - best method of showing hip joint effusion, and may guide the needle if aspiration is appropriate.
• MRI - not often used in clinical practice, but may help if diagnosis unclear or surgery contemplated.

Individual conditions

1. Transient synovitis
   • Summary:
     • Usually has acute onset.²
     • Self limiting condition thought to be due to viral infection or an autoimmune process.
     • Often preceded by a viral upper respiratory tract infection.
     • Twice as common in boys.
   • Presentation:
     • Pain usually not severe but may prevent weight-bearing on the affected leg.
     • Usually no pain at rest and passive movements are only painful at the extreme range of movement.
     • Child is usually well and the ESR is either normal or slightly raised.
   • Management:
     • Includes rest and analgesia, with mobilisation once pain has settled.
     • Symptoms usually resolve within 2 weeks but may recur.
     • There is no evidence of any long term complications.
2. Developmental dysplasia of the hip see Developmental Dysplasia of the Hip record.
   • Summary:
     • Up to 60% of apparently abnormal hips will become normal without treatment after 1 month, leaving the true incidence as 1-2 per 1,000.
   • Risk factors:
     • Female
     • Breech position
     • Caesarean section
     • First born child
     • Prematurity
     • Oligohydramnios
     • Family history
     • DDH is associated with club feet, spina bifida and infantile scoliosis
   • Presentation:
     • Barlow's test, Ortolani's test
     • Asymmetrical skin creases in the thigh or buttock
     • Unequal leg length
     • Reduced hip abduction in flexion (normal is 90 degrees)
     • Reduced distance between greater trochanter and anterior superior iliac spine
3. Septic arthritis - see Septic Arthritis record.
   • Summary:
     • Most often affects hip, knee, ankle, shoulder or elbow.
     • Most often affects children under 2 years.
     • Staphylococcal infection is the most common cause. Haemophilus influenzae arthritis may be associated with concomitant meningitis.
     • Tuberculous infection is increasing, especially in those with contacts in Africa and South Asia.
   • Presentation:
     • Early features are often non-specific.
     • Child often very unwell.
     • Pain often present at rest and there is resistance to attempted movement of the hip.
     • Older children are usually reluctant to weight bear and may be more aware of referred pain in the knee.
     • Hip is kept flexed, abducted and externally rotated.
   • Investigations:
     • Full blood count, ESR, CRP.
     • X-rays, ultrasound.
     • MRI and isotope scans are occasionally required.
     • Joint aspiration under ultrasound control may be tried. Aspiration of pus warrants immediate surgery.
4. Perthes' disease - see Legg Calve Perthes Disease record.
   • Summary:
     • Self-limiting condition with occlusion of blood supply to femoral head causing avascular necrosis.
     • Re-vascularisation and remodelling occur but the femoral head may remain an abnormal shape.
     • Most often affects boys (80%) and those aged 5-10 years.
     • Increased risk with low birth weight, short stature, low socio-economic class and passive smoking.
     • Unilateral in 85% of cases. Other diagnoses should be considered in bilateral cases, e.g. hypothyroidism, epiphyseal dysplasia, Gaucher's disease.
   • Presentation:
     • Gradual onset of pain (may be referred to the knee), limp and restriction of hip movements.
     • More advanced cases may cause leg shortening and proximal muscle wasting.
     • X-rays are initially normal but later show flattening of the superolateral epiphysis and fragmentation.
5. Slipped upper femoral epiphysis see Slipped Upper Femoral Epiphysis record.
   • Summary:
     • Usually occurs at the onset of puberty and most often in children who are either very tall and thin, or short and obese.
     • Other risk factors include Afro-Caribbean, boys, family history.
     • One quarter of cases are bilateral.
   • Presentation:
     • Hip, thigh and knee pain. Often initially a several week history of vague groin or thigh discomfort.
     • May be able to weight bear, but is painful.
     • Flexion of hip often also causes external rotation.
     • May be leg shortening.

Document references

1. Maroo S; Diagnosis of hip pain in children. Hosp Med. 1999 Nov;60(11):788-93. [abstract]
2. Gough-Palmer A, McHugh K; Investigating hip pain in a well child. BMJ. 2007 Jun 9;334(7605):1216-7.

Internet and further reading

• Perry DC, Bruce C; Evaluating the child who presents with an acute limp. BMJ. 2010 Aug 20;341:c4250. doi: 10.1136/bmj.c4250.

Acknowledgements