The Catterall classification of Perthes disease is based on radiographic appearances of the epiphysis and metaphysis visible in osteonecrosis of the femoral head:
-
stage I
- bone absorption changes visible in the anterior aspect of the epiphysis of femoral head
- changes are visible best in frog leg lateral view
- no sclerosis is seen
-
stage II
- further bone resorption with slight femoral head collapse in the anterior aspect of femoral head
- sclerosis
-
stage III
- almost entire femoral head involved in collapse with characteristic head within head appearance
- sclerosis
-
stage IV
- complete collapse of femoral head with flattening and formation of dense sclerosis; additional metaphyseal changes may be visible
- sclerosis
- posterior remodeling