idiopathic, avascular necrosis of the femoral head. It may occur unilaterally or bilaterally and typically manifests between the ages of four and ten. Children experience hip pain on weight-bearing, which often projects to the ipsilateral knee and causes an antalgic gait. Early stages are only detectable on MRI but progress of the disease can be tracked and graded using conventional x-ray. Surgery is performed if x-ray reveals signs that indicate an unfavorable prognosis. The aim of surgical intervention is to cover the femoral head as completely as possible with the hip socket, thus retaining its anatomical position. In mild forms of the disease, reduced weight-bearing and physical therapy are indicated. Important prognostic factors include the age of onset and the extent of femoral head involvement.(LCPD, or Perthes disease) refers to an
Epidemiological data refers to the US, unless otherwise specified.
- Idiopathic disease
- Multiple factors might promote the development and progress of the condition, including: 
This classification possesses the highest clinical relevance because it correlates best with long-term outcome. The crucial criterion in this classification is the height of the lateral third (“lateral pillar”) of the femoral head.
|Modified (Herring) Lateral pillar classification|
|Group A||Height of the lateral pillar is 100% (no involvement)|
|Group B||Height of the lateral pillar is > 50%|
|Group C||Height of the lateral pillar is < 50%|
Other classifications 
of the femoral head due to a mismatch between the rapid growth of the femoral epiphyses and the slower development of adequate blood supply to the area
- Antalgic gait (on weight-bearing leg)
- Pain in the hip or the upper leg, sometimes projecting to the knee
- Restricted range of movement; is usually present, especially regarding internal rotation and abduction, and can cause the child to limp. 
- Hinge abduction: refers to the lateral femoral head bumping into the ventrolateral acetabulum when the leg is abducted, possibly involving pain, a palpable clunk, and restriction in the range of movement
- Contralateral involvement in ∼ 10% of cases 
X-ray (anterior-posterior and frog leg positions )
- Frequently without pathological findings during early stages
- Increased lucency of the femoral head
- Joint space widening
- “Head-at-risk” signs: prognostically unfavorable radiographic signs (as defined by complementary Catterall classification) 
- Lateral calcification
- Lateral subluxation of the femoral head
- Lesions extending to the metaphysis
- Horizontal alignment of the epiphyseal plate
- Gage sign: triangle-shaped osteoporotic area of increased radiolucency of the lateral femoral head
- Crescent sign: subchondral lucency representing a fracture
- See also “Lateral pillar classification” above.
- MRI: indicated if initial imaging is unremarkable but clinical suspicion persists
|Differential diagnosis of pediatric hip pain|
|Disease||Pathophysiology||Clinical features||Diagnostic findings|
|Legg-Calve-Perthes disease|| |
|Developmental dysplasia of the hip|
Pediatric hip pathologies often present as referred pain in the knee! Children or adolescents presenting with nonspecific knee pain and no findings suggestive of knee pathology require prompt assessment of the hip!
Transient synovitis (also known as toxic synovitis) 
- Pathophysiology: nonspecific inflammation and hypertrophy of the synovial membrane
- Clinical features
- Treatment: conservative (e.g., NSAIDs)
The differential diagnoses listed here are not exhaustive.
- Conservative treatment: : limited weight bearing, physical therapy
- Surgery: femoral osteotomy
- Early osteoarthritis of the hip joint due to any of the following: 
We list the most important complications. The selection is not exhaustive.
- Factors associated with a less favorable prognosis include: 
- Older age of onset (≥ 6 years)
- Extensive damage to the femoral head (> 50%)
- Female sex