This anatomical study shows that an ultrasound-guided TAP injection cephalad to the iliac crest is likely to involve the T10-L1 nerve roots, and implies that the technique may be limited to use in lower abdominal surgery.

Previous descriptions of the thoracolumbar spinal nerves innervating the anterior abdominal wall have been inconsistent. With modern surgical and anesthetic techniques that involve or may damage these nerves, an improved understanding of the precise course and variability of this anatomy has become increasingly important. The course of the nerves of the anterior abdominal is described based on a thorough cadaveric study and review of the literature. Twenty human cadaveric hemi-abdominal walls were dissected to map the course of the nerves of the anterior abdominal wall. Dissection included a comprehensive tracing of nerves and their branches from their origins in five specimens. The branching pattern and course of all nerves identified were described. All thoracolumbar nerves that innervate the anterior abdominal wall were found to travel as multiple mixed segmental nerves, which branch and communicate widely within the transversus abdominis plane (TAP). This communication may occur at multiple locations, including large branch communications anterolaterally (intercostal plexus), and in plexuses that run with the deep circumflex iliac artery (DCIA) (TAP plexus) and the deep inferior epigastric artery (DIEA) (rectus sheath plexus). Rectus abdominis muscle is innervated by segments T6-L1, with a constant branch from L1. The umbilicus is always innervated by a branch of T10. As such, identification or damage to individual nerves in the TAP or within rectus sheath is unlikely to involve single segmental nerves. An understanding of this anatomy may contribute to explaining clinical outcomes and preventing complications, following TAP blocks for anesthesia and DIEA perforator flaps for breast reconstruction.

Abdominal surgery can cause significant postoperative pain and associated morbidity. Systemic opioids often contribute to side-effects such as sedation, respiratory depression, nausea and vomiting. Postoperative epidural analgesia offers superior analgesia and reduced pulmonary morbidity compared to systemic analgesia 1 , however several reports have alluded to a recent decline in its utilisation following abdominal surgery 2-4. This has occurred on a background of large clinical trials that have failed to demonstrate improved survival following major surgery 1,5 and large studies focusing on morbidity due to epidural analgesia 6-8. Although neurological disability following central neuraxial block is rare, medicolegal concerns can dominate clinical decision-making regarding anaesthesia options. Postoperative epidural analgesia requires ongoing clinical care and surveillance, whereas systemic opioids may have less demand on clinical resources. Furthermore, there is a current trend towards minimally invasive surgical procedures, hence an increasing role for emerging less invasive analgesia techniques. One less invasive analgesic technique is transversus abdominis plane (TAP) block. This technique involves injection of local anaesthetic into the fascial plane between internal oblique and transversus abdominis muscles, where the thoracolumbar nerves T6 to L1 course before innervating the anterior abdominal wall 9. Results from three randomised control trials, utilising anatomical landmark techniques have

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