Objective:To study the image features in direction and quantity on CT scans of the axial safety target area of Sawbone femoral neck screw tunnels and possibility of establishing a stable spatial cartesian coordinate system.Methods:After three-dimensional reconstruction of CT data of 40 Sawbone femoral necks, the real axial CT images (perpendicular to the surgical central axis) of each femoral neck were superimposed respectively to get the intersection, called axial safe target area(ASTA). With the anterior cortex of femoral neck basilar seen as a landmark, the spatial rectangular coordinate system ( x, y, z) was established to measure superior-inferior diameters (D-SI), anterior-posterior diameters (D-AP) and the oblique angles. Each intersection was overlapped to the original axial CT images to find coronal position of ASTA boundaries. In addition, coronal CT union (equivalent to anteroposterior X-ray) and sagittal CT union (equivalent to lateral X-ray) were obtained by images in situ superposition method, from which the coronal positions of the isthmus of the perspective boundary (D-SI and D-AP) were determined. The coincidence of the boundary positions of ASTA and those of the perspective isthmus was compared. Pearson correlation coefficients were calculated for the left and right sides respectively to analyze the correlation between D-SI and D-AP. Results:Every ASTA presented an oblique rounded quadrilateral, whose front base was flat and coincided with anterior cortex of femoral neck basilar (FNB). In this coordinate system, D-SI were 35.13±0.51 mm on the left and 30.98±0.82 mm on the right, while D-AP were 26.66±0.39 mm on the left and 27.53±0.72 mm on the right. There was no significant correlation between D-SI and D-AP (left: R=0.43, P=0.060, right: R=0.32, P=0.176, respectively). All the isthmus of X-ray boundary fell at the corresponding ASTA boundary. The oblique angles ranged from 8° to 29°, and all parameters were within the range of normal femoral neck (the anterior cortex of the femoral neck basilar is flat, with a D-SI range of 26-38 mm, a D-AP range of 17-29 mm, and an oblique angle range of 5°-53°). Conclusion:The intersection method can be used to conveniently acquire directional-quantitative-stable individualized ASTA of Sawbone femoral neck. Thus, a stable spatial cartesian coordinate system can be established based on the anterior cortex of femoral neck basilar.