Which listing produces medial SI edema?

• A. PI
• B. AS
• C. EX
• D. IN

Answer: (C)

The pattern hinges on how the innominate orientation changes which part of the sacroiliac joint bears the load. When the innominate is in external rotation, the contact and stress shift toward the medial aspect of the SI joint, so inflammatory change or edema shows up on that medial side. The other directional positions alter the joint surfaces stressed in different ways, so they don’t produce edema in the medial SI region. In short, external rotation of the innominate concentrates stress medially at the SI joint, leading to medial edema.