The Oval-like Cross-section of Femoral Neck Isthmus in Three-dimensional Morphological Analysis

Objectives: To investigate the cross-section shape of the femoral neck isthmus (FNI) in three-dimensional reconstruction model of the femoral neck. Methods: From December 2009 to December 2012, computed tomography (CT) data of bilateral hip joint from 200 consecutive patients (137 males and 63 females, 69.41 +/- 9.21 years old, ranged from 50-85 years old) who underwent surgical treatments for proximal femoral fracture were retrospectively reviewed. The 3D model of the proximal femur was reconstructed, and the "inertia axis" method, which was applied to measure the long and short axes of the cross-section of the FNI, was established. The cross-sectional area and perimeter were calculated by a formula using the length of the long and short axes and then compared with the actual measured values by the software. Correlation between the descriptive parameters of the FNI cross-section (area, perimeter, and eccentricity) and patients' demographics (age, height, and weight) was analyzed. Stepwise linear regression analysis was used to determine the main relevant factors. Results: The ICC results showed excellent data reproducibility ranged from 0.989 to 0.996. There was no significant difference in the cross-sectional area of the FNI between the actual measured values and the predicted values using the formula (732.83 +/- 126.74 mm(2) vs 731.62 +/- 128.15 mm(2), P = 0.322). The perimeter using the two methods showed narrow while significant difference (97.86 +/- 8.60 mm vs 92.84 +/- 8.65 mm, P < 0.001), the actual measured values were about 5 mm greater than the predicted values. The parameters (area, perimeter, and eccentricity) were significantly larger in male than female (P < 0.001). A positive correlation between the cross-sectional area, perimeter, height, and weight was observed. The stepwise linear regression analysis showed that the regression equation of the FNI area was as follows: Y = -1083.75 + 1033.86 x HEIGHT + 1.92 x WEIGHT, R-2 = 0.489. Conclusion: The cross-section shape of the FNI appears to be oval-like in the 3D model, which is separated according to the inertia axis, and the findings proposed an anatomical basis for the further study of the spatial configuration of cannulated screws in the treatment of femoral neck fractures.