Documenting the Density of Innervation in a Sensate Radial Forearm Flap Based on the Lateral Antebrachial Cutaneous Nerve

Abstract

Sir: A left radial forearm innervated flap was elevated for a hemitongue reconstruction but was not needed. The flap, still attached by its vascular pedicle and the lateral antebrachial cutaneous nerve, was returned to the forearm. One month later, we subjected it to sensory testing to see whether (1) the flap retained normal and evenly distributed sensation (demonstrating its suitability as a sensate flap) and (2) the division of overlapping contributions from the superficial radial sensory nerve and the medial antebrachial cutaneous nerve reduced the flap's sensory acuity. The flap measured 10 × 6 cm. It lay to the radial side of the distal forearm, with its lateral border overlying the cephalic vein and its medial third lying medial to the midline of the forearm. By its position, overlapping sensory contributions from the medial antebrachial cutaneous nerve and the DRCN would be expected.1–4 A mirror image of the flap was drawn on the opposite (right) forearm. Each was divided into longitudinal and transverse thirds (Fig. 1) and tested for pain (sharp/dull), temperature (hot/cold), light pressure (Semmes-Weinstein monofilament 10-g, 5.07 strand), and static and moving two-point discrimination.Fig. 1.: Postoperative day 30: the left innervated radial forearm flap is healing satisfactorily. Its image has been marked on the contralateral (right) forearm as a control. Each is divided into nine mirror-image zones.Light pressure, vibration, hot, and cold sensation were present equally in all nine segments of both the flap and control. One-centimeter static two-point discrimination was present in all nine segments of both flap and control. Eight-millimeter static two-point discrimination was equally variable bilaterally (Fig. 2).Fig. 2.: Eight-millimeter static two-point discrimination (+, present; 0, absent).Six-millimeter moving two-point discrimination was present in all nine segments of both flap and control groups. Five-millimeter moving two-point discrimination was equally variable bilaterally (Fig. 3). Sharp-dull discrimination was present bilaterally in all segments except the flap's zone 9.Fig. 3.: Five-millimeter two-point moving discrimination (+, present; 0, absent). Six and 8 mm were present in all zones.The lateral antebrachial cutaneous nerve is the dominant sensory nerve of the lateral forearm, with overlap from the medial antebrachial cutaneous nerve and superficial radial sensory nerve.1–4 The tiny area of sensory loss when the superficial radial sensory nerve is cut suggests a fairly extensive overlap. Because this forearm flap was designed to capture the primary territory of the lateral antebrachial cutaneous nerve and include the cephalic vein, it was centered on a line running between the radial artery and the cephalic vein in the distal forearm.1 Boutros et al. stated that although the lateral antebrachial cutaneous nerve is the dominant sensory nerve of the forearm, 40 percent of the flap is unrepresented by the nerve.4 However, the flap reported by Boutros et al. had its skin paddle extending from the brachioradialis laterally to the flexor carpi ulnaris medially. Boutros et al. stated that for ideal sensation, all three sensory nerves of the forearm should be raised and anastomosed to the lingual nerve stump.4 This is unnecessary: the lateral antebrachial cutaneous nerve flap clearly carries normal sensation. Furthermore, overlapping sensory contributions from the medial antebrachial cutaneous nerve and the superficial radial sensory nerve do not summate in providing normal sensation: the flap is adequately innervated by the lateral antebrachial cutaneous nerve alone. Because the removal of nerves supplying overlapping territory results in no diminution of sensation, we must conclude that this redundancy may have some survival advantages, and that the neurons carrying sensation from overlapping areas by means of different nerves simply project onto the same relay cells in the dorsal column nuclei.1 J. Brian Boyd, M.D. Sarah Sung Kim, B.S. Joachim Granzow, M.D. Tom Liu, M.D. Division of Plastic and Reconstructive Surgery Harbor–University of California, Los Angeles Medical Center David Geffen School of Medicine at University of California, Los Angeles Los Angeles, Calif.