Assessment of femoral anteversion in children with cerebral palsy: accuracy of the trochanteric prominence angle test.

Clinical assessment of femoral anteversion (FA) in children with cerebral palsy (CP) is frequently determined by the trochanteric prominence angle test (TPAT). Limited three-dimensional volumetric imaging by axial tomography of the femur was performed before surgery for 35 hips in 20 children with CP. The TPAT was performed before the imaging study for 31 hips in 18 children. The TPAT angle was within 10 degrees of the FA as determined from the computed tomography scans (Murphy technique) for 17 femurs (55%). The most prominent portion of the greater trochanter was located anterior to the femoral neck axis (mean 27 degrees, range 0 degrees-52 degrees) on the three-dimensional images in 34 of 35 hips. A simulated TPAT, measured from the imaging studies, consistently underestimated the FA as determined by the Murphy technique (mean 10 degrees, range 0 degrees-18 degrees). Accurate clinical assessment of FA by the TPAT in children with CP presumes that the prominence of the greater trochanter lies perpendicular to the axis of the femoral neck. Three-dimensional imaging showed the prominence to be anterior, to a variable degree, to the femoral neck axis, which in addition to clinical factors such as obesity compromises the accuracy of this clinical maneuver.