Which listing produces superior SI edema?

• A. PI
• B. AS
• C. EX
• D. IN

Answer: (A)

The amount and location of edema in the SI joint reflect where the joint is under increased mechanical load. A posterior-inferior orientation of the sacrum relative to the ilium concentrates stress on the superior portion of the SI joint. This setup narrows and shears the superior joint space, provoking inflammation and fluid buildup there, so edema shows up at the superior aspect. The other listings shift load to different parts of the joint, leading to edema in other regions rather than the superior area.