Pathological process

The whole progression of Perthe's disease takes between 2 and 4 years.

The aetiology is unknown but the following factors may be important:

• repetitive microtrauma
  • the disease is frequently seen in hyperactive children where repetitive microtrauma results in small fractures of the immature femoral head (1)
• vascular insufficiency (1)
• growth plate disruption
• infection and transient synovitis
• hypercoagulability (2)
• a slipped capital femoral epiphysis
• congenital dislocation of the hip

Firstly there is bone death - this appears normal on a radiograph, but is seen on MRI - in association with loss of vascularisation.

Fragmentation follows; the epiphysis may flatten as a result of poor repair of microfractures.

Lastly there is revascularisation, repair and remodelling of the femoral head.

Note that this process is entirely different from the irreversible death of the femoral head in adult avascular necrosis.

Reference:

1. Nelitz M, Lippacher S, Krauspe R, Reichel H. Perthes Disease Current Principles of Diagnosis and Treatment Dtsch Arztebl Int. 2009; 106(31-32): 517–523.
2. Kim HK. Legg-Calve-Perthes disease. J Am Acad Orthop Surg.2010;18(11):676-86