Abstract
Implant-based breast reconstruction is the most commonly used reconstructive modality following mastectomy. Placement of the tissue expander and implant under the pectoralis major muscle is believed to minimize the incidence of capsular contracture, provide adequate soft tissue coverage, and minimize implant visibility and palpability. However, utilization of the submuscular pocket can be associated with discomfort, which may originate from stretching of the cutaneous envelope, distension of the underlying muscle or, rarely, from spasms of the pectoralis major muscle. A case of intractable and involuntary pectoralis major spasms following submuscular implant-based breast reconstruction is presented. An ultrasound-guided pectoral intrafascial plane block is shown to be an effective diagnostic modality, implicating the medial and lateral pectoral nerves in these spasms. The clinical anatomy literature pertaining to the course and branches of the medial and lateral pectoral nerves is reviewed.