Enhancing anterior shoulder analgesia with a modified PECS II block during shoulder arthroscopy under regional anesthesia alone: a translational anatomical and clinical feasibility study

Background Regional anesthesia (RA) alone offers important perioperative advantages for shoulder arthroscopy, but conventional interscalene brachial (ISB) and superficial cervical plexus (SCP) blocks may insufficiently cover the anterior shoulder region—especially during biceps, rotator interval, or anterior capsular procedures. This gap likely reflects sensory input from intercostobrachial and pectoral nerves, which are not reliably anesthetized with standard techniques. We therefore hypothesized that a cranially directed modified pectoserratus plane block (PECS II) (second-third intercostal spaces) could enhance anterior analgesia during RA-only shoulder arthroscopy. Methods We conducted a translational feasibility study combining a cadaveric anatomical investigation and a retrospective clinical analysis. Cadaveric dissection of the first three intercostal spaces explored sensory branches relevant to anterior shoulder innervation. Clinically, adult patients undergoing arthroscopic shoulder surgery with anterior surgical steps under RA alone were included. All received ISB and SCP, with or without a modified PECS II block. The primary end point was intraoperative anterior shoulder pain. Secondary outcomes included sedation requirements, need for postanesthesia care unit admission, and the rate of complete RA without supplemental intervention. Results Anatomical findings revealed anterior sensory branches of the intercostobrachial nerve coursing toward the deltopectoral region, with occasional anastomoses to the medial pectoral nerve. Among 46 patients, anterior pain occurred in 56% of the ISB+SCP group vs 7% of the ISB+SCP+modified PECS group (p<0.001). Sedation for pain was required in 56% vs 7%, respectively (p<0.001), and complete RA without supplemental sedation was achieved in 44% vs 93%, respectively (p<0.001). The modified PECS block remained the only independent predictor of pain reduction (adjusted OR 0.0467; 95% CI 0.0057 to 0.38). Conclusions A modified PECS II block performed at the second to third intercostal spaces was associated with improved anterior analgesia and reduced sedation requirements during shoulder arthroscopy under RA alone.