What imaging study is ordered in a patient with suspected septic arthritis?
None, or at most any cross-sectional imaging study to confirm the presence of a joint effusion. No imaging study has sufficient sensitivity to fully exclude this important diagnosis.
If septic arthritis is suspected, then the only way to exclude joint space infection is to proceed with joint aspiration (arthrocentesis).
Typically, this can be done in the office or at the bedside (such as of the shoulder, elbow, knee, and ankle joint), although some joints (hip and unusual sites like the sacroiliac joints) may benefit from an image-guided arthrocentesis using either fluoroscopic, sonographic, or rarely CT guidance.