Classification of Perthe's disease

Classification of Perthe's disease

A fourfold classification of the condition in relation to extent of the involvement of the femoral head has been proposed by Catterall:

• grades of involvement are as follows:
  • I - central involvement
  • II - central involvement with collapse
  • III - nearly whole head involvement
  • IV - whole head involvement
    
    
• but the reliability and prognostic value is limited (1)
• this classification was supplemented with “head at risk signs”
  • these were associated with a poorer prognosis
  • signs include:
    • Gage's sign - a radiolucent defect between the lateral epiphysis and metaphysis
    • calcification lateral to the epiphysis
    • metaphyseal cysts
    • lateral subluxation
    • horizontal growth plate (2)

An alternative classification based on the height of the lateral pillar of the epiphysis of the femoral head (as seen on an AP x-ray view) in the early fragmentation phase has been described by Herrring in 1992.

• the three choices include:
  • the lateral pillar is intact
  • at least 50% of the lateral pillar remains standing
  • less than 50% of the lateral pillar remains standing (1)
    
    
• this has a greater prognositic value and also a greater inter-observer reliability than the Catterall classification
• predictive value is higher when the patient's age at the onset of the disease is also taken into consideration (1).

Reference:

1. Nelitz M, Lippacher S, Krauspe R, Reichel H. Perthes Disease Current Principles of Diagnosis and Treatment Dtsch Arztebl Int. 2009 July; 106(31-32): 517–523.
2. The Pediatric Orthopaedic Society of North America (POSNA) 2012. Legg-Calve-Perthes Syndrome