What method is used to measure for a lateral lumbar X-ray?

To correctly position for a lateral lumbar X-ray, the landmark used is 1 inch above the iliac crest. This reference point is critical because the iliac crest generally corresponds to the L4-L5 intervertebral disc space. Positioning the X-ray beam 1 inch above the iliac crest ensures that all necessary lumbar vertebrae (L1-L5) are included in the film, providing a comprehensive view of the lumbar region that prevents obstructions and captures the desired anatomical details.

Using the iliac crest itself or any other reference point such as the bottom of the lumbar spine would not provide as accurate a measurement, possibly leading to films missing vital aspects of the lumbar area or including unnecessary anatomy outside of the region of interest. Therefore, the selection of the 1 inch above the iliac crest is a standard practice in radiography to achieve optimal imaging results.