Sub-Omohyoid Fascial Plane Block as a Diaphragm-Sparing Approach for Shoulder Analgesia: A Narrative Review.

Shoulder surgery often requires effective regional analgesia, but interscalene brachial plexus block, the current reference technique, is frequently associated with hemidiaphragmatic paresis and upper-extremity motor blockade. These limitations have driven interest in diaphragm-sparing approaches that preserve respiratory and functional recovery. The sub-omohyoid fascial plane block (SOFPB) is an emerging ultrasound-guided interfascial concept that targets the fascial compartment deep to the omohyoid muscle near the superior trunk-suprascapular nerve complex. In this narrative review, SOFPB is considered as an operational umbrella term for closely related sub-omohyoid approaches rather than as a fully standardized single technique. This review summarizes the anatomical rationale, sonoanatomy, proposed mechanisms, technical considerations, and available clinical evidence for SOFPB and related sub-omohyoid approaches in shoulder surgery. Current evidence suggests that sub-omohyoid approaches may provide clinically meaningful analgesia through suprascapular nerve involvement, partial superior trunk coverage, and variable interfascial spread while potentially reducing phrenic nerve exposure compared with conventional interscalene block. However, direct evidence remains limited and heterogeneous, with inconsistent nomenclature, variable injectate volumes, and insufficient standardized assessment of diaphragmatic function, motor preservation, and patient-centered outcomes. Cadaveric dye studies provide anatomical plausibility but should be interpreted as indirect and hypothesis-generating evidence rather than proof of clinical efficacy or respiratory safety. Therefore, SOFPB should currently be regarded as a promising but unvalidated addition to the spectrum of diaphragm-sparing shoulder blocks rather than a replacement for established techniques. Future anatomical imaging studies, dose-finding trials, and head-to-head randomized comparisons are needed to define its optimal role in contemporary shoulder regional anesthesia.