First, we will review the flexor carpi ulnaris anatomy. The flexor carpi ulnaris muscle originates from two heads. The humeral head originates from the medial epicondyle of the humerus, while the ulnar head originates from the medial margin of the olecranon and upper posterior border of the ulna. It then travels to the pisiform bone and inserts by the ligaments of the hamate and 5th metacarpal bone. The flexor carpi ulnaris is innervated by the ulnar nerve. It flexes the hand at the wrist joint and adducts the hand. Now we will review the cross-sectional anatomy of the flexor carpi ulnaris muscle. The flexor carpi ulnaris is highlighted here. The injection will be performed in the proximal forearm. The flexor carpi ulnaris muscle is located deep to the basilic vein and superficial to the ulnar nerve. The tip of the needle has been placed in the flexor carpi ulnaris muscle, traveling from medial to lateral. Note the location of the basilic vein. Also note the ulnar nerve is located deep to the flexor carpi ulnaris muscle. Lets discuss the anatomy we expect to see in ultrasound. Note the position of the ulna. Outlined here is the flexor carpi ulnaris. Also note the location of the ulnar nerve, deep to the flexor carpi ulnaris muscle. Again, complete injection preliminary steps prior to beginning the procedure. Take time before the procedure to set up the room and make sure that you have adequate assistance. Collect equipment and position the patient. You will first need to orient yourself by scanning the target muscle region. The target muscle, flexor carpi ulnaris, is circled in red here. Using color flow doppler imaging, identify the vasculature to avoid during the injection. Here the needle is being inserted from medial to lateral to the flexor carpi ulnaris muscle. The needle remains superficial to the vascular bundle and ulnar nerve. Electrical stimulation can now be used to ensure proper needle tip positioning. Three key images are needed to confirm needle placement. These include the cross-sectional view of the target muscle, cross-sectional view of the vasculature adjacent to the target muscle, and length of the needle traversing to the target muscle. Once needle position is confirmed, botulinum toxin is injected into the target muscle. Finally, the needle is withdrawn, and post-injection scanning may be conducted to assess for hematomas.

anatomy

injection technique

flexor carpi ulnaris muscle

ulnar nerve

botulinum toxin