Differences in femoral neck shaft angles between anteroposterior X-ray and 3-dimensional CT reconstruction images: report of 265 cases

Abstract

Objective To explore the differences in measurement result of femoral neck shaft angle between anteroposterior X-ray film and 3-dimensional CT reconstruction image, and investigate the main related factors that lead to the differences. Methods The clinical data of 265 lower limbs from 265 patients hospitalized in our center from August 2016 to June 2018 were retrospectively collected from the electronic medical record system of our hospital. The femoral neck shaft angle was measured on the anteroposterior X-ray films and 3-dimensional CT reconstruction images, and the difference was tested. Age, gender, BMI, left and right difference, hip-knee-ankle angle, femoral bowing angle, femoral torsion angle, mechanical lateral distal femoral angle and femoral shaft length were included to establish a statistical model to screen the most important factors leading to the difference. Finally, a control group and an experimental group were set up through the 1:1 propensity score matching to verify the the most important factors. Results The femoral neck shaft angle was (128.02±6.26)° on the anteroposterior X-ray films and (124.22±6.45)° on the 3-dimensional CT reconstruction images, and statistical difference was found between them (P < 0.001), with a difference greater than 3° (accounting for 56.6% of the patients). The established multiple linear regression model (P < 0.001, adjusted R2=0.747) showed that femoral torsion angle (standardized regression coefficient=-0.233, P < 0.001) was the most important factor of the difference. Conclusion There is a difference in the measurement result of femoral neck shaft angle between anteroposterior X-ray film and 3-dimensional CT reconstruction image. Femoral torsion angle is the most important factor. Larger femoral extorsion angle causes larger femoral neck shaft angle measured on the anteroposterior X-ray film.

Keywords

• femoral neck shaft angle
• femoral torsion angle
• 3-dimensional reconstruction image
• x-ray film