First, we will review the flexor digitorum superficialis anatomy. It originates from two heads. The humeral ulnar head is located at the medial epicondyle of the humerus and the coronary process of the ulna. The radial head is located anterior to the surface of the rabius below the radial tuberosity. It then travels by four long tendons to insert onto the sides of the middle phalanx of the ulnar four digits. The flexor digitorum superficialis is innervated by the median nerve. It flexes the middle and proximal phalanges of the four ulnar digits and also assists with flexing the wrist. The four slips of the flexor digitorum superficialis are located using surface anatomy. This technique was described in an article published in Muscle & Nerve titled Flexor Digitorum Superficialis, Locations of Individual Muscle Bellies for Botulinum Toxin Injection. First, locate the medial epicondyle. Locate the pisiform bone. Draw a landmarking line between the medial epicondyle and pisiform. Mark the halfway point between the medial epicondyle and pisiform on the landmarking line. A second point is marked three-fourths of the distance between the medial epicondyle and pisiform on the landmarking line. A point is marked at 7 millimeters and 17 millimeters lateral to the halfway point of the landmarking line. A point is marked at 6 millimeters and 14 millimeters lateral to the three-fourths point of the landmarking line. The slips of the middle finger and ring finger are located lateral to the halfway point of the landmarking line, and the index finger and small finger slips are located lateral to the three-fourths point of the landmarking line. Now we will review the cross-sectional anatomy of the ring finger and middle finger slips of the Flexor Digitorum Superficialis. The Flexor Digitorum Superficialis is highlighted here. The injection of the ring finger and middle finger slips will be performed in the mid-forearm. The Flexor Digitorum Superficialis is located deep to the brachioradialis and palmaris longus muscles. The medial antebrachial vein may be found anterior to the Flexor Digitorum Superficialis muscle. Several structures lie posteriorly to the Flexor Digitorum Superficialis and from medial to lateral include the ulnar nerve, ulnar artery, and median nerve. The radial artery and superficial branch of the radial nerve are located lateral to the target muscle. The needle has been inserted at the halfway point of the landmarking line and directed seven millimeters to the ring finger slip of the Flexor Digitorum Superficialis. The needle is then advanced approximately ten millimeters to the middle finger slip. Let's discuss the anatomy we expect to see on ultrasound. Note the superficial position of the Flexor Digitorum Superficialis. The neurovascular bundle is located posterior to the target muscle. Let's review the cross-sectional anatomy of the small finger and index finger slips of the Flexor Digitorum Superficialis. The injection of the small finger and index finger slips will be in the distal forearm. Located medially is the ulnar artery and nerve. The median nerve is lateral to the target muscle. The needle has been inserted at the three-fourths point of the landmarking line and directed six millimeters to the small finger slip of the Flexor Digitorum Superficialis. The needle is then advanced approximately eight millimeters to the index finger slip. Let's discuss the anatomy we expect to see on ultrasound. The Flexor Digitorum Superficialis is highlighted here. Located medially is the neurovascular bundle. The median nerve is lateral to the target 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. We will start the procedure by marking the four slips of the Flexor Digitorum Superficialis. Locate the medial epicondyle and pisiform bone. Draw a landmarking line between the medial epicondyle and pisiform. Mark the halfway point between the medial epicondyle and pisiform on the landmarking line. A second point is marked three-fourths of the distance between the medial epicondyle and pisiform on the landmarking line. A point is marked at 7 millimeters and 17 millimeters lateral to the halfway point of the landmarking line. A point is marked at 6 millimeters and 14 millimeters lateral to the three-fourths point of the landmarking line. We will now demonstrate the injection procedure for the middle finger and ring finger slips of the Flexor Digitorum Superficialis. You will first need to orient yourself by scanning the target muscle region. The target muscle, Flexor Digitorum Superficialis, is circled in red. Using Color Flow Doppler imaging, identify the vasculature to avoid during the injection. The needle is inserted at the halfway point of the landmarking line and directed 7 mm lateral to the ring finger slip of the flexor digitorum superficialis 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 approximately 10 mm to the middle finger slope. 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. We will now demonstrate the injection procedure for the index finger and small finger slips of the flexor digitorum superficialis. You will first need to orient yourself by scanning the target muscle region. The target muscle, flexor digitorum superficialis, is circled in red. Using Color Flow Doppler imaging, identify the vasculature to avoid during the injection. The needle is inserted at the 3 force point of the land marking line and directed 6mm lateral to the small finger slip of the flexor digitorum superficialis muscle. 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 approximately 8 mm 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.

anatomy

injection procedures

flexor digitorum superficialis muscle

ultrasound guidance

needle placement