First Carpal Metacarpal Joint Injection
Carpometacarpal (CMC) osteoarthritis of the thumb is very common. The wear and tear of the articular surfaces of the first metacarpal and trapezium are responsible for this condition.
Before you begin, think about the anatomy. Look at your hand and see if you can palpate the anatomic snuffbox. The anatomic snuffbox is bordered by the extensor pollicis brevis tendon (radial side), extensor pollicis longus tendon (ulnar side), radial styloid process, and the base of the first metacarpal.
In this image: CMC osteoarthritis of the thumb is very common.
Which important artery runs through the snuffbox? The radial artery.
The distal border of the snuffbox is created by the base of the first metacarpal. Move your thumb around and try to appreciate the articulation of the first metacarpal and the trapezium (this is the first CMC joint).
Obtain informed consent from the patient.
Gather appropriate equipment needed for the procedure.
First, draw up 0.5cc of 1 or 2% lidocaine into a 3cc syringe.
Then draw up the steroid into the same syringe in order to intermix them. You may use this list of four commonly used steroids as a reference.
Now, position the patient so that they are resting their hand on a comfortable surface with the ulnar side of their palm facing downward.
You may have the patient abduct their thumb to better palpate the extensor pollicus brevis (EPB) and extensor pollicus longus (EPL) tendons.
Cleanse the skin with iodine or an alcohol swab.
In this image: Have the patient rest their hand on a comfortable surface with the ulnar side of their palm facing downward.
Using a 25- or 26-gauge, 1-inch needle, insert the needle toward the ulnar side of the EPB and just proximal to the base of the first metacarpal. Redirect the needle until you are in the joint space. You may need to apply traction to the thumb to help open up the space.
Be sure to aspirate slightly before you inject to ensure that you are not in the deep branch of the radial artery. Once you begin injecting, the medication should flow easily without resistance.
