CASE                               17                               

During the course of examination of finger injuries in the emergency room, it is important to be facile with the placement of local anesthetic. This local anesthetic may be administered in the form of flexor sheath block, a web space block, or a digital nerve block which is administered at the level of the metacarpal neck often referred to as the metacarpal block.

The correct relationship of the digital nerve to the vessels at the level of the proximal phalanx would be which of the following?

1. The proper digital vessel is volar to the digital nerve

2. The digital nerve and the vessel run side by side

3. The digital nerve lies volar to the vessel

4. The exact relationship is undefined and can vary from digit to digit

Discussion

The correct answer is (C). At the level of the base of the palm, the digital vessels, after they come off the superficial arch, lie volar to the digital nerves which are common digital nerves. At the level of the metacarpal necks, the common digital

nerve then divides into proper digital nerves which supply contiguous sides of each web space. Shortly thereafter, the digital nerves and vessels change relationships so that by the time the digital nerve is at the level of the proximal phalanx, the nerve comes to lie volar to the vessel.

During the course of placement of local anesthetic for the management of an index finger laceration over the proximal phalanx of the index finger, you place a lidocaine block at the level of the metacarpal neck. The patient’s laceration extends on to the dorsal surface of the proximal phalanx of the index finger. The suturing of the volar aspect of the laceration is accomplished uneventfully. As you are suturing the dorsal aspects of the laceration over the index finger proximal phalanx, the patient experiences considerable pain.

The most likely reason for this patient’s discomfort is which of the following?

1. The local anesthetic that you placed on the volar side has worn off.

2. The patient has aberrant nerve supply.

3. The patient is simply experiencing nervous anxiety.

4. Sensory supply to the dorsal aspect of the proximal phalanx of the index finger comes from terminal branches of the radial sensory nerve, which need to be anesthetized separately during the course of performance of the procedure on the dorsal aspect of the proximal phalanx of the index finger.

Discussion

The correct answer is (D). Digital nerves reliably supply the entire volar aspect of all the fingers as well as the thumb. In the fingers, sensory supply to the dorsal aspect of the finger distal to the PIP articulation in most studies appears to be performed by a digital branch, which arises from the radial digital nerve of the finger. However, the dorsal aspect of the proximal phalanx of the index finger and the dorsal aspect of the proximal phalanx of the small finger, respectively, receives cutaneous nerve supply from terminal branches of the radial sensory nerve and the dorsal cutaneous branch of the ulnar nerve, respectively. In performing procedures over the dorsal aspect of these fingers at this level, it is vital to separately anesthetize these nerve branches prior to performing the procedure.

Objectives: Did you learn...?

Describe the anatomy of the neurovascular structures of the hand?