Fig. 2

Illustration showing coronal (A) and axial (B) CT images of a patient with AO/OTA 31 A2 fracture. The central axis of the femoral head and neck was set as the x-axis, the central axis of the femoral shaft was set as the y-axis, the z-axis was perpendicular to the x-axis and y-axis, and the common plane of the x-axis and y-axis was set as the coronal plane. The axial CT plane was angled 130° upward to the femoral head and neck. The RACL of the proximal femur was measured as the length of the remnant lateral cortex on the central axis of the head and neck (blue line). Line 1 (L1) was a line tangential to the lateral wall of the proximal femoral fracture. Point (a) was the intersection of the x-axis and the lateral edge of the cortex, point (b) was a remnant anterior cortical extremity, and point (c) was a remnant posterior cortical extremity. Line 2 (L2) was a straight line passing through points (b) and (c). The γ angle was the angle between L1 and L2. The RACL was further divided into the RAC (d1), the RLC (d0), and the RPC (d2). Red: femoral head and neck, blue: femoral shaft, and green: posterior fragment. AO/OTA, AO Foundation and Orthopaedic Trauma Association, RAC: remnant anterior cortex, RACL: remnant axial cortical length, RLC: remnant lateral cortex, RPC: remnant posterior cortex