First, we will review the flexor digitorum profundus anatomy. It originates at the proximal three-fourths of the anterior medial aspect of the ulna and the ulnar half of the interosseous membrane. It then travels to the anterior surface of the base of the distal phalanx of the four medial fingers. The radial half of the muscle is innervated by the interosseous branch of the median nerve and the ulnar half is innervated by the ulnar nerve. It flexes the distal phalanx of the four medial fingers and also assists with flexing the wrist. Now we will review the cross-sectional anatomy of the flexor digitorum profundus. The flexor digitorum profundus is highlighted here. Injection will be performed in the mid-forearm. The flexor digitorum profundus is located deep to the flexor digitorum superficialis and lateral to the flexor carpi ulnaris. Several structures lie anterior to the flexor digitorum profundus. From medial to lateral, they include the ulnar nerve, ulnar artery, and median nerve. The anterior interosseous artery and nerve are located lateral to the target muscle. The tip of the needle has been placed in the small finger slip of the flexor digitorum profundus muscle. The needle is then advanced from medial to lateral to inject the ring finger slip, middle finger slip, and index finger slip. From medial to lateral, note the location of the bacillic vein, ulnar nerve, ulnar artery, median nerve, and anterior interosseous nerve and artery. Let's discuss the anatomy we expect to see on ultrasound. Note the position of the ulna. The neurovascular bundle is located anterior to the flexor digitorum profundus. Outlined here is the flexor digitorum profundus located between the ulna and neurovascular bundle. 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 digitorum profundus, is circled in red here. Using Color Flow Doppler imaging, identify the vasculature to avoid during the injection. The needle is being inserted from medial to lateral to the small finger slip of the flexor digitorum profundus muscle. 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. The needle is then advanced to the ring finger slip. Electrical stimulation can now be used to ensure proper needle tip positioning. Once needle position is confirmed, botulinum toxin is injected into the target muscle. The needle is then advanced to the middle finger slip. Electrical stimulation can now be used to ensure proper needle tip positioning. Once needle position is confirmed, botulinum toxin is injected into the target muscle. The needle is then advanced to the index finger slip. Electrical stimulation can now be used to ensure proper needle tip positioning. 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.

flexor digitorum profundus muscle

injection procedure

botulinum toxin

ultrasound visualization

electrical stimulation