K L Hermann1, N Egund. 1. Department of Radiology, National University Hospital, Copenhagen, Denmark.
Abstract
PURPOSE: To evaluate CT methods of measuring anteversion in the femoral neck with respect to measurement accuracy and with respect to the influence exerted by different femoral shaft positions; and to describe a new CT measurement concept that introduces a mathematical adjustment for different femoral shaft positions. The new technique facilitates the taking of measurements in patients who cannot be correctly positioned in traditional methods. MATERIAL AND METHODS: CT examinations of previously measured anteversions in the femoral neck were reviewed in retrospect in 30 patients with fractures of the femoral neck. The position of the femoral shaft was assessed. A reference angle was compared with direct traditional measurements and with measurements adjusted for the actual position of the femoral shaft by means of a 3D mathematical reconstruction. Reproducibility and inter- and intraobserver variability were assessed in 10 cases. RESULTS: All femurs varied in position within the gantry. The mean difference between the direct CT measurement and the adjusted CT measurement compared to the reference angle were -8.8 degrees (range -35.0-16.3 degrees) and -0.1 degrees (range -1.4-1.4 degrees), respectively. For the adjusted CT method, reproducibility and inter- and intraobserver variability were 1.4 degrees, 1.6 degrees and 1.4 degrees (SD of difference), respectively. CONCLUSION: CT measurement of femoral anteversion in clinical practice can only be accurate when corrected for variation in the position of the femoral shaft.
PURPOSE: To evaluate CT methods of measuring anteversion in the femoral neck with respect to measurement accuracy and with respect to the influence exerted by different femoral shaft positions; and to describe a new CT measurement concept that introduces a mathematical adjustment for different femoral shaft positions. The new technique facilitates the taking of measurements in patients who cannot be correctly positioned in traditional methods. MATERIAL AND METHODS: CT examinations of previously measured anteversions in the femoral neck were reviewed in retrospect in 30 patients with fractures of the femoral neck. The position of the femoral shaft was assessed. A reference angle was compared with direct traditional measurements and with measurements adjusted for the actual position of the femoral shaft by means of a 3D mathematical reconstruction. Reproducibility and inter- and intraobserver variability were assessed in 10 cases. RESULTS: All femurs varied in position within the gantry. The mean difference between the direct CT measurement and the adjusted CT measurement compared to the reference angle were -8.8 degrees (range -35.0-16.3 degrees) and -0.1 degrees (range -1.4-1.4 degrees), respectively. For the adjusted CT method, reproducibility and inter- and intraobserver variability were 1.4 degrees, 1.6 degrees and 1.4 degrees (SD of difference), respectively. CONCLUSION: CT measurement of femoral anteversion in clinical practice can only be accurate when corrected for variation in the position of the femoral shaft.
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