In a PA coccyx projection, where should the central ray be directed?

In a PA (posteroanterior) coccyx projection, the central ray should be directed just below the sacrococcygeal joint. This positioning is crucial because it ensures that the coccyx, which is a small triangular bone at the end of the vertebral column, is adequately captured in the radiograph. By directing the central ray below the sacrococcygeal joint, you precisely target the area of interest, allowing for clear visualization of the coccyx and any potential abnormalities.

Positioning the central ray correctly at this specific point also helps to minimize distortion and ensures that the image is not affected by overlapping structures. This alignment is essential for accurate diagnostics and treatment planning in cases where the coccyx might be fractured or otherwise pathological. Other options, such as directing the central ray at the level of the ASIS, the pubic symphysis, or L5-S1, would not provide the optimal view of the coccyx, leading to inadequate imaging for clinical evaluation.