In 40 children with unilateral Perthes' disease, we measured the physe
al slope, the angle between the physeal plane and the axis of the femo
ral shaft, from radiographs taken early in the disease, Thirty-seven o
f the 40 hips were classified as Catterall grades III and IV, Head-at-
risk signs were present in 23. We found no statistically significant d
ifference in the physeal slope between the involved and normal hips (p
=0.20), those with or without head-at-risk signs (p=0.96), those with
or without lateral epiphyseal subluxation (p=0.82), and different Catt
erall (p=0.56) or lateral pillar (p=0.67) gradings.