Paraneural Sheath and Fascial Compartments Surrounding the Brachial Plexus at the Supraclavicular Fossa: A Retrospective Review of High Definition Ultrasound Images Acquired During Selective Trunk Brachial Plexus Blockade

The optimal anatomical plane (relative to the nerve) or the "goal" for local anesthetic (LA) injection during an ultrasound guided (USG) brachial plexus blockade (BPB) at the supraclavicular fossa is currently not known. USG BPB is often described as a "subfascial", "extra fascial", "intracluster", "interfascial", sub-perineural", "intraneural", "corner pocket" or "periplexus" injection. Although this suggests that the local anesthetic is injected into different tissue planes or fascial compartments, even if such planes do exist, as seen in other regions such as popliteal sciatic nerve are not clearly defined at the supraclavicular fossa. However, recently with the use of high definition ultrasound imaging for USG Selective trunk block (SeTB) and principal investigator has often observed distinct paraneural (fascial) sheath and fascial compartments surrounding the brachial plexus at the supraclavicular fossa. These connective tissue layers are also better delineated after the local anesthetic injection. The principal investigator believes these may be the connective tissue layers that previous researchers have referred to in different reports. Currently there are no published data demonstrating the paraneural sheath and fascial compartment surrounding the brachial plexus in-vivo. Principal investigator believes that this fascial layer and compartment influence the spread of LA during USG BPB around the individual elements of the brachial plexus at the supraclavicular fossa and therefore, these anatomical structures have to be delineated so as to improve the safety, success and quality of USG BPB. This study will involve reviewing archived high definition ultrasound images in audio video interleave format from all adult patients who had undergone USG SeTB for surgical anesthesia during upper extremity surgery from January 1, 2020 to June 30, 2021 to define the paraneural sheath and fascial compartments that surround the brachial plexus at the supraclavicular fossa.