What Do Anterior and Posterior Mean?

What it means

Doctors use direction words so everyone describes locations the same way. Anterior means front and posterior means back, as if the person were standing upright and facing you. The words work the same way for the whole body and for a single part of it, such as the front or back wall of the womb, or the front or back of the knee.

On a report, these words tell the reader exactly which part of an organ, bone or joint is being described, so the next doctor or surgeon can find the same spot. Other common direction words include superior (above), inferior (below), medial (toward the middle), lateral (toward the side), proximal (closer to the trunk) and distal (further away). They are often combined, as in "posterolateral", meaning toward the back and side.

On X-ray reports, "AP" and "PA" describe the direction the X-ray beam travelled: front-to-back or back-to-front. This is about how the picture was taken, not a finding. A chest X-ray taken AP, often done in bed when someone is unwell, can make the heart look a little larger than it really is, which the radiologist takes into account.

Where you may see it

• MRI and CT reports describing joints, the spine or organs
• Surgical and examination notes
• X-ray technique lines, such as "AP and lateral views" or "PA chest"
• Ultrasound reports, such as "posterior wall of the bladder" or "anterior placenta" in pregnancy scans
• Spine MRI reports, such as "posterior disc bulge"