With no clear consensus in place regarding the best way to measure a patient’s neck-shaft angle (NSA), researchers compared the reliability and validity of four different methods and shared their findings in Clinical Radiology.
The authors used CT images of 17 patients who had undergone imaging to investigate pain unrelated to their hips to create digitally reconstructed radiographs. The NSA was then measured by three operators using four completely different methods.
Overall, the method that showed the best reliability and validity involved joining the center of the femoral head to the median of the femoral neck base to draw the femoral neck axis. The femoral diaphysis axis is then drawn by joining the median of two lines passing through the medial and lateral edges of the patient’s femoral axis below the lesser trochanter.
This method “was deemed to be the most repeatable” and “showed very high reliability” with intraclass correlation coefficient values between 0.92 and 0.96. It also had the lowest uncertainty among the four methods the authors analyzed.
“The determination of a standardized and repeatable method for the measurement of the NSA is essential in order to decrease the heterogeneity associated with NSA measurement,” wrote lead author A.J. Bizdikian, University of Saint-Joseph in Beirut, Lebanon, and colleagues. “In the present study, the method based on the identification of the exact location of the center of the femoral head in order to later draw the femoral neck axis showed the highest repeatability as well as the lowest bias and global uncertainty.”
The authors did note that only “normal” hips were evaluated for this study. “The same measured parameters on pathological or deformed hips may not be as reliable or repeatable as in normal hips,” they wrote.