Anatomical Study of Abdominal Wall Muscle Innervation to Optimize Retroperitoneal Vascular Approach.

Introduction: Different surgical approaches are used in aortic surgery. Retroperitoneal approaches can result in abdominal wall weakness and flank bulging. These approaches often require dissection of the anterolateral or anteromedial muscles of the abdominal wall. During dissection, the underlying nerves are at great risk of injury, which induces significant complications in abdominal wall muscles. Few studies have been conducted to minimize the risk of injury to these nerves.

Objectives: This study aims to describe the trajectory of abdominal muscle motor nerves and their relationship to ribs and other anatomical landmarks. The secondary objective is to optimize surgical approaches by preserving the nerves.

Method: We conducted 12 dissections on fresh cadavers. Nerve trajectories, the communication between the intercostal nerves (9^th-10^th-11^th) and the subcostal nerve (12^th), and the distance from the nerve to the estimated projection point of intersection with the abdominal midline, umbilicus, and iliac crest were recorded.

Results: Our dissections identified the 12^th subcostal nerve as the largest nerve. The 11^th intercostal nerve exhibits more accessory branches than other nerves. Multiple communications and branches were observed between the 10th and 11^th intercostal nerves and between the 11^th and 12^th nerves in the region from the anterior axillary line (AAL) to the mid-clavicular line. The estimated projection point of intersection with the midline was 7.92 ± 1.24 cm supraumbilical for the ninth intercostal nerve, 3.92 ± 1.18 cm supraumbilical for the 10th, 1.08 ± 1.52 cm at the umbilical level for the 11^th, and -3.33 ± 0.83 cm infraumbilical for the subcostal nerve. The distance between the iliac crest and the iliohypogastric nerve (IHN) in the lateral jackknife position was 2.54 ± 0.65 cm. The 11^th nerve had an angle in relation to the rib between -45° and -10° (average: -24.6°), and the 12^th nerve had a similar angle between -30° and 0° (average: -18.3°). For the 11^th nerve, the distance was between 0 and 5.5 cm (average: 2.92 cm); for the 12^th nerve, it was between 0 and 3.0 cm (average: 1.71 cm).

Conclusions: To preserve the 11^th nerve, the optimal approach is a straight incision starting from the upper edge of the 11^th rib toward the midline, 4 cm above the umbilicus; for the 12^th nerve, the optimal approach is a straight incision starting from the upper edge of the 12^th rib toward the midline, 1 cm below the umbilicus; for the IHN, the optimal approach is an incision close to the iliac crest at a distance <1.5 cm. The estimated projection point of intersection between the nerve directions toward the midline can indicate the anatomical trajectory of nerves. A nerve projection toward the midline can provide valuable information about the anatomical location of a nerve. This study has utility in optimizing surgical approaches. A clinical study can confirm these anatomical results.