Analgesic Efficacy and Motor-Sparing Properties of Superior Trunk Block versus Interscalene Brachial Plexus Block with Liposomal Bupivacaine for Shoulder Arthroscopy: A Randomized Controlled Trial

Background: The interscalene brachial plexus block (ISB) is widely regarded as the most commonly used regional anesthesia technique for perioperative analgesia in arthroscopic shoulder surgery; however, it is associated with a high incidence of phrenic nerve paresis and profound, often complete, motor blockade of the upper extremity. In contrast, the superior trunk block (STB) represents an anatomically targeted alternative specifically designed to preserve distal motor function while maintaining effective surgical anesthesia. This randomized comparative study evaluated the motor-sparing profile of an identical liposomal bupivacaine–based admixture administered via either STB or ISB, as well as their comparative analgesic effects. Patients and Methods: In this prospective, randomized, participant- and outcome-assessor-blinded, active-controlled trial, 68 patients undergoing elective arthroscopic shoulder surgery were randomly assigned to receive either ultrasound-guided ISB (n = 35) or STB (n = 33). Both groups received a 20 mL admixture containing 10 mL of liposomal bupivacaine (133 mg) and 10 mL of 0.9% normal saline. The primary outcomes were postoperative pain intensity measured by the visual analogue scale (VAS; range 0– 10 cm) at rest and during activity at 30 min, 6 h, 12 h, and 24 h. Secondary outcomes included the modified Bromage scale (MBS; range 0– 4) for upper extremity motor function (assessed by shoulder abduction, elbow flexion, and elbow extension) and the University of California at Los Angeles (UCLA) shoulder score (range 2– 35) for early functional assessment at 24 h. No block-related complications were observed in either group. Results: No statistically significant differences were observed in either resting or activity VAS scores between the two groups at any postoperative time points (all P > 0.0125 after Bonferroni correction). Crucially, the STB group achieved significantly higher MBS scores compared to the ISB group (median difference 0.00, 95% CI: 0.00 to 1.00; Z = − 2.706, P = 0.007), demonstrating a profound motor-sparing effect on the upper extremity. Early shoulder function at 24 h was comparable between the two groups, with an identical median UCLA score of 30.00 in both cohorts (median difference − 1.00, 95% CI: − 3.00 to 1.00; Z = 0.858, P = 0.391). Conclusion: Ultrasound-guided superior trunk block with a liposomal bupivacaine admixture provides postoperative analgesia comparable to the traditional interscalene approach, with no statistically significant differences in VAS scores observed between the two groups. Crucially, the superior trunk approach offers a significant clinical advantage by preserving upper extremity motor function, making it an optimized regional anesthetic technique aligned with modern enhanced recovery after surgery (ERAS) principles. Keywords: liposomal bupivacaine, superior trunk block, interscalene brachial plexus block, shoulder arthroscopy, motor-sparing anesthesia, enhanced recovery after surgery (ERAS)