How femoral rotation affects the neck-shaft angle in 3-dimensional femoral imaging model.

OBJECTIVE

This study aims to evaluate how femoral rotation affects the neck-shaft angle (NSA) in 3D imaging and to compare femoral anteversion measurements along the mechanical axis (AV-MA) and anatomical axis (AV-AA).

METHODS

Thirty embalmed cadaveric femurs were CT scanned to measure anatomical parameters. A 3D model was created for each femur, and the mechanical, shaft, and neck axes were defined. NSA was measured from 2D images at varying degrees of femoral rotation around the mechanical axis. The smallest NSA (True-NSA) indicated the perpendicular X-ray beam to the neck axis and represented AV-MA. AV-AA was measured using axial CT scans. Each measurement was repeated three times for accuracy.

RESULTS

Fifteen right and 15 left femurs were included, with a mean age of 73.2 years. The average AV-MA was 23.0° (SD 7.7), while the mean AV-AA was 5.6° (SD 5.6), with a significant difference of 17.3° (p < 0.001). The mean NSA in the AP view was 127.8° (SD 4.8), and the True-NSA was 124.6° (SD 5.1), with a significant mean difference of 3.1° (p = 0.0018).

CONCLUSIONS

Femoral rotation significantly affects NSA measurements in 3D imaging. The True-NSA, obtained using a perpendicular X-ray beam, provides a more accurate representation than the standard AP view. There is also a significant difference between femoral anteversion measurements along the mechanical and anatomical axes, emphasizing the need for careful consideration of measurement techniques in clinical assessments.