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Figure 4. On posteroanterior DXA image, the lesser trochanter is not seen in its entirety, indicating proper internal rotation of the thigh for analysis of the femoral neck at its greatest long-axis measurement. Regions of interest (ROIs) in the proximal femur are applied as defaults by analytic software. Like those in lumbar spine, ROIs may be overridden by the operator, but this should be an unusual operation. It must also be recognized that ROIs are not identical between manufacturers, making comparisons imprecise, particularly as regards the proximal femur. Outer rectangle defines global ROI (often described as "total hip"), narrow transverse rectangle orthogonal to the axis of symmetry constitutes the femoral neck, while the Ward "triangle" is the area of least density in a smaller area within a search area centered on the midline at the inferior edge of the femoral neck rectangle. The longer line is constructed along the axis of symmetry of the femoral neck; it is used in defining the ROI and again may be subject to manual override. A shorter subsidiary line separates "trochanteric region" from "intertrochanteric region"; it uses the Ward triangle as a starting point and is drawn to the base of the greater trochanter. Among these ROIs, femoral neck or "total hip" are best used for risk estimation, while "total hip" is preferred for follow-up because precision is greater given the larger sample size. There is no evidentiary basis to support use of the Ward triangle for risk estimation, and many clinicians might prefer to see this measurement eliminated.
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