OBJECT: The thoracolumbar junction is frequently accessed through an anterolateral approach with the incision and muscle dissection extending from the lower thoracic region to the lateral border of the rectus abdominis muscle. This approach is frequently associated with the subsequent development of an unsightly and uncomfortable relaxation of the ipsilateral abdominal wall, or flank bulge, caused by denervation injury to the intercostal nerves. However, the etiology of this complication is not widely recognized by spine surgeons. The object of this study was to better define the relevant anatomy and innervation of the anterolateral abdominal wall musculature. METHODS: The authors performed 32 cadaveric dissections and 6 intraoperative electromyography (EMG) evaluations. RESULTS: The cadaveric dissection studies and intraoperative EMG evaluations provided detailed anatomy of the anterolateral abdominal wall and its innervation. Cadaveric dissections revealed that the most significant intercostal nerve contributions to the anterolateral abdominal wall arise from T11 and T12. Electrophysiological confirmation of these findings was accomplished through intraoperative stimulation in 6 patients undergoing anterolateral retroperitoneal approaches to the thoracolumbar junction. The authors confirmed T11 and T12 innervation of the anterolateral abdominal wall musculature by direct intraoperative EMG recording in all 6 patients. CONCLUSIONS: The authors classified the 3 potential zones of injury that can be affected during an anterolateral approach to the thoracolumbar junction. Modifications to the operative technique are suggested to avoid the complication of flank bulge. The most significant intercostal nerve contributions to the anterolateral abdominal wall arise from T11 and T12.
OBJECT: The thoracolumbar junction is frequently accessed through an anterolateral approach with the incision and muscle dissection extending from the lower thoracic region to the lateral border of the rectus abdominis muscle. This approach is frequently associated with the subsequent development of an unsightly and uncomfortable relaxation of the ipsilateral abdominal wall, or flank bulge, caused by denervation injury to the intercostal nerves. However, the etiology of this complication is not widely recognized by spine surgeons. The object of this study was to better define the relevant anatomy and innervation of the anterolateral abdominal wall musculature. METHODS: The authors performed 32 cadaveric dissections and 6 intraoperative electromyography (EMG) evaluations. RESULTS: The cadaveric dissection studies and intraoperative EMG evaluations provided detailed anatomy of the anterolateral abdominal wall and its innervation. Cadaveric dissections revealed that the most significant intercostal nerve contributions to the anterolateral abdominal wall arise from T11 and T12. Electrophysiological confirmation of these findings was accomplished through intraoperative stimulation in 6 patients undergoing anterolateral retroperitoneal approaches to the thoracolumbar junction. The authors confirmed T11 and T12 innervation of the anterolateral abdominal wall musculature by direct intraoperative EMG recording in all 6 patients. CONCLUSIONS: The authors classified the 3 potential zones of injury that can be affected during an anterolateral approach to the thoracolumbar junction. Modifications to the operative technique are suggested to avoid the complication of flank bulge. The most significant intercostal nerve contributions to the anterolateral abdominal wall arise from T11 and T12.