Three-dimensional computed tomography for determination of femoral anteversion in a cerebral palsy model.

Abstract

Previous investigation has proven 3-dimensional (3D) computed tomography (CT) to be a poor method of assessing femoral anteversion in patients with cerebral palsy. However, new advancements in CT software yield the potential to improve upon those dated results. CT was performed on 9 femoral models with varying amounts of anteversion (20 to 60 degrees) and varying neck-shaft angles (120 to 160 degrees). Each model was scanned in 2 holding devices. One holder placed the femur in an ideal position relative to the gantry. The other placed the femur in flexion, adduction, and internal rotation simulating a common lower extremity posture in cerebral palsy. Femoral anteversion was measured on 3D reconstructions by 4 observers on 2 separate occasions. Interobserver and intraobserver reliability, accuracy, and the effect of increasing neck-shaft angle of the measurements were examined and compared with previously published data using the same models. Pearson correlation coefficients between first and second measurements by the same examiner were all above 0.96 regardless of positioning of the femur in the gantry. The correlation coefficients among all examiners were 0.97 regardless of positioning of the femur in the gantry. Accuracy in measurements was comparable using 3D CT techniques with mean differences between the normal and cerebral palsy-positioned models of <3.6 degrees (SD, 3.1 to 3.3 degrees). Accuracy of the study's 3D CT technique in measuring femoral anteversion in cerebral palsy-positioned femurs was significantly more accurate than that of 2D CT (P<0.0001). Recent improvements in processing software and 3D reconstruction have made assessment of femoral anteversion with 3D CT accurate through the studied range of anteversion and neck-shaft angles. Using this technique, high intraobserver and interobserver reliability in the determination of femoral anteversion can be expected regardless of neck-shaft angle or postural deformity. Level II.