Subscapularis Plane Block ‐ A Novel Phrenic Nerve Sparing Single Injection Shoulder Block ‐ An Anatomical Study
Authors: Drake Reese , Vissa Deepti , Johnson Marjorie , Barbeau Michele , Vijayashanker Rakesh Soendekoppam , Ganapathy Sugantha 
Published: November 2023

Introduction

The interscalene block (ISB) is the gold standard regional anesthetic for shoulder surgery, but invariably results in ipsilateral hemi‐diaphragmatic paralysis due to phrenic nerve involvement. Isolated blocks targeting the suprascapular and axillary nerves separately have been shown to be less effective than the gold standard. The specific aim of this study was to develop a novel peripheral block for shoulder surgeries that would avoid phrenic nerve involvement and associated hemi‐diaphragm paralysis, while still providing adequate anesthesia of the targeted nerves to provide a suitable alternative to the gold standard. It was hypothesized that a subscapularis plane block (SPB), as a single injection, would provide a novel technique to block the suprascapular nerve, axillary nerve, and the upper and lower subscapular nerves.

Methodology

Bilateral, ultrasound‐guided (Sonosite M‐Turbo) SPB blocks were performed with a linear probe (13‐6 MHz) on 4 fresh cadavers (n = 8) using 5% dextrose with methylene blue dye as injectate (2 – 10 mLs). With the transducer aligned in the sagittal plane and moving medially, first the head of the humerus was identified, then the bicipital groove, then the coracoid process. Medial to the coracoid process, from superior to inferior, the skin, subcutaneous tissue, deltoid, pectoralis major, pectoralis minor, subscapularis muscles, and subscapular fossa were identified. An insulated Tuohy needle (17 gauge × 80 mm) was used to deposit the injectate above the fascia of the subscapularis muscle. Each cadaver was dissected to note the spread of injectate. The first set of 4 blocks were performed to determine the location of the block, while the second set of 4 blocks were performed to replicate the successful block and standardize the volume used.

Results

Overall, 37.5% of the blocks (3/8) performed were successful in staining all of the target nerves. 37.5% of the blocks (3/8) performed resulted in the injectate spreading along the axillary sheath into the axilla, staining the posterior cord and the lateral cord, but not the suprascapular nerve. 25% of the blocks (2/8) performed resulted in the injectate spreading deep to the subscapularis fascia into the joint. 100% of the blocks spared the phrenic nerve.

Discussion

The angle of the needle appears to factor into the success of the block, as the injectate spread into the axilla when angled more laterally instead of perpendicular to the injection site. Ultrasound visualization of the subscapularis plane in cadavers also contributed to the blocks success rate, as the needle was sometimes inserted deep to the subscapularis fascia, resulting in spread of the injectate to the joint capsule. A single injection, phrenic nerve sparing SPB may be a viable alternative to the gold standard for shoulder surgery anesthetic management. A clinical trial is currently underway to establish the efficacy of the SPB compared to the ISB.