In 40 children with unilateral Perthes' disease, we measured the physeal slope, the angle between the physeal plane and the axis of the femoral shaft, from radiographs taken early in the disease. Thirty-seven of the 40 hips were classified as Catterall grades III and IV. Heat-at-risk signs were present in 23. We found no statistically significant difference 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 Catterall (p = 0.56) or lateral pillar (p = 0.67) gradings.

The variability in measurement of angles in congenital scoliosis is not known, but it is postulated that it is larger than that in adolescent idiopathic scoliosis due to skeletal immaturity, incomplete ossification, and anomalous development of the end-vertebrae. To determine this variability, we selected 54 radiographs of adequate quality showing 67 scoliotic curves from children with congenital scoliosis. The end-vertebrae were preselected. Each curve was measured by the Cobb method on two separate occasions by six different observers, using the same goniometer and marker. The intraobserver variability was +/- 9.6 degrees and the interobserver variability +/- 11.8 degrees. If 'significant progression' is to be used as a criterion for surgical fusion in congenital scoliosis, there should be at least a 23 degrees increase, the entire range of the interobserver variability, in the curvature to ensure that the perceived increase is not due to variability in measurement.