Ultrasound-guided subomohyoid suprascapular nerve block and phrenic nerve involvement: a cadaveric dye study

Abstract

Backgrounds and objectivesThe anterior approach to the subomohyoid suprascapular (SOS) nerve is a new, technically easy and reliable regional anesthesia technique for postoperative shoulder analgesia. However, due to its proximity, the injectate may spread to the brachial plexus and phrenic nerve. The goal of this anatomic study with dye injection in the subomohyoid space and subsequent cadaver dissection was to establish the likely spread of local anesthesia and the extent of brachial plexus and phrenic nerve involvement resulting from ultrasound-guided SOS nerve block.MethodsThe suprascapular nerve (SSN) under the inferior belly of omohyoid muscle in the posterior triangle of the neck was identified. Using a contrast dye, 10 ultrasound-guided SOS nerve injections of 5 mL were done bilaterally, in five fresh cadavers. The area was then dissected to evaluate the spread of the contrast dye in the immediate proximity of the brachial plexus, phrenic and SSN.ResultsThe SSN and omohyoid muscle were easily identified on each cadaver. SOS nerve staining with contrast dye was seen in 90% of dissections. The superior trunk was stained in 90% and the middle trunk was stained in 80% of dissections. The inferior trunk was stained in 20% of dissections. A spread of dye around the SSN was observed in 90% and the phrenic nerve was mildly stained in 20% of the dissections.ConclusionIn-plane ultrasound-guided needle injection with a 5 mL volume for SOS block was sufficient to stain the SSN. This conservative volume involved other parts of the brachial plexus and may potentially spread to the phrenic nerve. Further clinical studies are required for confirmation.

Subomohyoid Anterior Suprascapular Block versus Interscalene Block for Arthroscopic Shoulder Surgery

“…Our findings present consistent evidence of superior trunk blockade when a suprascapular block is performed, indicating that blockade of the superior trunk is a major underlying mechanism to the observed efficacy of suprascapular block. These results provide the clinical correlation of the earlier anatomic studies of Sehmbi et al 17 (who reported 90% staining of the brachial plexus), Laumonerie et al 14 (who reported 100% staining of the superior trunk), and Siegenthaler et al 13 (who reported brachial plexus block even when a 0.1 ml volume of injectate is used). The Downloaded from anesthesiology.pubs.asahq.org by guest on 07/16/2020 consistent spread to the superior trunk observed also offers a plausible explanation for the historical discrepancy in analgesic effects relative to interscalene block observed between the posterior suprascapular block (inferior to interscalene block) [8][9][10] and the suprascapular block (noninferior to interscalene block).…”

“…Owing to anatomical proximity and proximal spread, 15,16 performing an anterior suprascapular nerve block under the inferior belly of the omohyoid muscle in the supraclavicular fossa seems to consistently block the superior trunk and brachial plexus, even when very small local anesthetic volumes are used. [15][16][17] Consequently, we thought that the subomohyoid anterior suprascapular block is another approach to superior trunk block that blocks the majority of shoulder innervation, thus providing postoperative analgesia that is not worse than the interscalene block for shoulder surgery.…”

Diaphragm-sparing nerve blocks for shoulder surgery, revisited

“…In other words, no matter how complete, a targeted suprascapular nerve block still ignores the important roles played by the axillary, lateral pectoral and subscapular nerves in the innervation of the shoulder. A more plausible explanation could be inferred from recent cadaveric studies conducted by Laumonerie et al 44 and Sehmbi et al 45. These authors observed that an anterior suprascapular block with 5–10 mL of a mixture containing methylene blue results in retrograde staining of the upper and middle trunks 44 45.…”

“…A more plausible explanation could be inferred from recent cadaveric studies conducted by Laumonerie et al 44 and Sehmbi et al 45. These authors observed that an anterior suprascapular block with 5–10 mL of a mixture containing methylene blue results in retrograde staining of the upper and middle trunks 44 45. Therefore, the term ‘anterior suprascapular nerve block’ may be somewhat of a misnomer, as LA spread is not solely confined to the suprascapular nerve.…”

“…Therefore, the term ‘anterior suprascapular nerve block’ may be somewhat of a misnomer, as LA spread is not solely confined to the suprascapular nerve. In addition to the brachial plexus, the phrenic nerve was also stained with dye in 20% of cases in both cadaveric reports 45 46. Thus, future investigation should be undertaken to formally quantify the risk of HDP in live patients and to determine if anterior suprascapular nerve blocks could provide surgical anesthesia for shoulder surgery (table 1).…”