The lateral pectoral nerve provides motor innervation to the pectoralis major. Although this nerve is described as mostly motor, it also has been considered to carry proprioceptive and nociceptive fibers. It arises either from the lateral cord or directly from the anterior divisions of the upper and middle trunks of the brachial plexus, unlike the medial pectoral nerve, which derives from the medial cord. It splits into four to seven branches that pierce the clavipectoral fascia to innervate the entire pectoralis major or its superior portion. The medial and lateral pectoral nerves form a connection, around the axillary artery, called the ansa pectoralis. The lateral pectoral nerve has been described as double, while the medial pectoral nerve has been described as single.
Clinical significance
The lateral pectoral nerve is important in the pain response after breast augmentation and mastectomy, and especially in breast implant surgery, when the implant is inserted by the subpectoral route. The pectoral nerves can be anesthetized intraoperatively by the surgeon under direct vision by three injections - one to block the medial pectoral nerve, the second to block the perforating branches of the medial pectoral nerve, and the third to block the lateral pectoral nerve. An ultrasound-guided pectoral nerve block can also be performed preventively before the operation by an anesthesiologist, experienced in regional anesthesia. It is safe and relies on ultrasound imaging to localize the pectoralis major and minor muscles, the presumed course of the pectoral nerves and the optimal spread of the local anesthetic. Blockade of the lateral pectoral nerve is helpful in cases such as shoulder dislocation and other orthopedic procedures, involving the shoulder. Spasms of the pectoralis major muscle and resulting severe pain may be reduced by pectoral nerve block or neuromuscular relaxation. Decreasing the pectoral muscle tone intraoperatively by neuromuscular relaxation or by a nerve block, can facilitate better cosmetic results during breast augmentation or post-mastectomy breast implantation. “The skin projection point of the neurovascular bundle represents the denervation point.” The NVB may be the guide for local anesthetic applications in order to achieve pectoral muscle denervation. “Routine botulinum toxin infiltration of the chest wall musculature at the time of mastectomy and immediate reconstruction…would paralyze the muscles and reduce the postoperative pain caused by muscle spasm.”
