Severity of disease

It is unusual for the whole of the femoral head to be involved in Perthes Disease. Several grading systems have been developed to measure the extent of involvement. The extent of disease is graded, based on the appearance of plain x-rays of the hip joint. Severity of disease and age will dictate treatment.

Grading of severity based on x-ray appearance of affected hip

In simple terms the greater the proportion of the femoral head involved the more likely deformity is to develop. These children may be described as being in the ‘head at risk’ category in the medical evidence. This means they are at risk of developing deformity of the femoral head. Because of this risk these children are most likely to have surgical treatment or other treatments that significantly limit their mobility.

The following grading systems may be may be used to describe severity in the medical evidence -:

• Catteral Classification – x-ray appearance is graded from I to IV (I being mild and IV being severe).
• Salter-Thomson Classification – simplifies the Catteral classification into two groups -:
• Group A includes Catteral I and II and means less than 50% of the ball is involved.
• Group B includes Catteral III and IV and means more than 50% of the ball is involved. If less than 50% of the ball is involved the prognosis is good and if more than 50% is involved the prognosis is potentially poor.
• Herring Classification - measures part of the femur on the X-ray called the lateral pillar. There are three grades, grade A, B and C with grade A being the most normal looking x-ray appearance with the best prognosis and group C being the most abnormal with a worse prognosis.