Superior trunk block (STB) is an increasingly utilized regional anesthesia technique for shoulder and upper extremity surgery that provides effective postoperative analgesia while potentially reducing respiratory complications associated with interscalene brachial plexus block (ISB). The superior trunk of the brachial plexus is formed by the convergence of the C5 and C6 nerve roots and contributes substantially to innervation of the shoulder joint. By targeting the superior trunk distally from the interscalene groove, anesthesiologists can achieve sensory blockade of the shoulder while decreasing unintended anesthetic spread to the phrenic nerve. This approach has generated significant interest as a diaphragm-sparing alternative to ISB, particularly in patients with pulmonary disease or limited respiratory reserve (1).

Ultrasound guidance is essential to accurately perform STB. The superior trunk is generally visualized lateral to the interscalene space beneath the sternocleidomastoid muscle and superior to the clavicle. Following identification of the brachial plexus structures, local anesthetic is deposited around the superior trunk to achieve analgesia for shoulder surgery. Compared with ISB, STB may allow for a more focused anesthetic distribution and lower incidence of complete hemidiaphragmatic paralysis. The technique has become increasingly incorporated into ambulatory orthopedic anesthesia because it supports postoperative pain control and reduces perioperative opioid requirements while supporting enhanced recovery (2).

In addition to respiratory considerations, as a regional anesthesia technique, the superior trunk block must provide adequate analgesia. Several clinical studies have shown it provides analgesia comparable to traditional ISB for arthroscopic shoulder procedures. In a randomized controlled trial by Kang et al., STB delivered noninferior postoperative analgesia compared with ISB while significantly decreasing the incidence of hemidiaphragmatic paralysis (1). Preservation of diaphragmatic function is clinically important because phrenic nerve blockade associated with ISB may produce dyspnea and reduced pulmonary function. These respiratory effects can be particularly problematic in elderly patients and in individuals with chronic obstructive pulmonary disease, obesity, or restrictive lung disease. As a result, the superior trunk block may expand the eligibility of regional anesthesia to higher-risk surgical populations (3).

Although STB reduces the likelihood of phrenic nerve involvement, respiratory complications are not completely eliminated. Kim et al. demonstrated that partial hemidiaphragmatic paresis can still occur depending on anesthetic volume and injection location (2). Consequently, careful ultrasound-guided needle placement and optimization of local anesthetic volume are important for maximizing safety. Additional potential complications include vascular puncture, local anesthetic systemic toxicity, transient neurologic symptoms, and Horner syndrome, though these events are rare based on current data (3).

The increasing popularity of STB reflects broader trends in regional anesthesia favoring motor-sparing and opioid-sparing techniques that support enhanced recovery after surgery protocols. Effective regional analgesia contributes to improved patient satisfaction, earlier mobilization, and shorter hospital stays. Recent comparative studies suggest that STB offers a favorable balance between analgesic efficacy and respiratory preservation when compared with ISB. Nevertheless, further multicenter studies are needed to establish standardized dosing strategies, evaluate long-term neurologic outcomes, and determine the optimal role of STB in various orthopedic procedures. As evidence continues to evolve, the superior trunk block is likely to remain an important advancement in modern regional anesthesia practice.

References

1. Kang R, Jeong JS, Chin KJ, et al. Superior Trunk Block Provides Noninferior Analgesia Compared with Interscalene Brachial Plexus Block in Arthroscopic Shoulder Surgery. Anesthesiology. 2019;131(6):1316-1326. doi:10.1097/ALN.0000000000002919

2. Kim DH, Lin Y, Beathe JC, et al. Superior Trunk Block: A Phrenic-sparing Alternative to the Interscalene Block: A Randomized Controlled Trial. Anesthesiology. 2019;131(3):521-533. doi:10.1097/ALN.0000000000002841

3. El-Boghdadly K, Chin KJ, Chan VWS. Phrenic Nerve Palsy and Regional Anesthesia for Shoulder Surgery: Anatomical, Physiologic, and Clinical Considerations. Anesthesiology. 2017;127(1):173-191. doi:10.1097/ALN.0000000000001668