Does the Femoral CCD Angle Measurement in a Standard AP Projection Correlate with the True Anatomical Shape of the Femur?

Abstract

PURPOSE OF THE STUDYThis study aims to ascertain whether a high anteversion of the femoral neck can influence the measurement of the caputcollum-diaphyseal (CCD) angle on a plain anteroposterior (AP) radiograph of the proximal femur. MATERIAL AND METHODSWe developed a new method of measuring the CCD angle and femoral neck version of the femur. This was done with the use of a computer program that utilised the measurement of the entire visualised area of femoral neck and shaft to calculate their long axis. Using this method, we measured the CCD angle and femoral neck version (FNV) of 100 photographed cadaveric femurs in two projections: The condylar line (CL) projection and the femoral neck (FN) projection. The same method was applied to 50 radiographs of the same femurs. The femurs were divided into three groups depending on the femoral neck version: Retro (FNV of <0°), Normal (FNV of 0-15°) and Ante (FNV of >15°) RESULTSWe found a statistically significant difference in the CCD angle measured in the FN and CL projections in the Normal and Ante groups but not in the Retro group. There is a significant correlation between the increase in FNV and the difference between the measured CCD values in the FL and CL projections. The femoral neck version of our cadaveric femurs varied from -14. 4° to 31. 5° which is a range of more than 35°. CONCLUSIONSFrom the results, it is clear that with an increase in femoral neck anteversion, there is a statistically significant difference in the CCD angle measured between the two projections. This difference can be up to almost 10°. Surgeons should be aware of the limitation of the AP projection when planning for surgery on the hip.