Here's how we do an arthrogram of the MCP of the thumb:
Use towels or other material to position the digit to profile the MCP joint like that of an AP radiograph of the thumb.
Obtain a scout image. As you can see, this patient has had prior surgery with a surgical pin in place.
Localize the radial or ulnar aspect of the MCP joint. Injection should be performed on the side contralateral to the area of interest. For example, if there is a suspected radial collateral ligament injury, plan to inject on the ulnar side.
After antiseptic preparation of the skin, drape the area with sterile towels.
Prepare the local anesthetic solution.
Prepare the MR arthrography contrast solution.
Anesthetize the planned needle tract.
We use a 25 gauge butterfly system for the MCP joint. Direct the needle perpendicular to the table and into the joint.
Check your needle position to ensure proper placement before injection.
The MCP joint is small, so approximately 1 ml will be sufficient to distend the joint capsule. As you inject, contrast will distend the joint capsule.
Extravasation indicates capsular/ligamentous injury. Look for contrast extravasation contralateral to the injection site -- in the site of the injury.
Document the intra-articular position of your needle and injection with fluoroscopic spot views.
Remove the needle, and then apply gentle radial and ulnar stress, observing for contrast extravasation.
It is normal to observe a small amount of contrast extravasation along the needle tract at the injection site.