Modified lateral block of the suprascapular nerve: a safe approach and how much to inject? A morphological study

This paper presents an evaluation of a modified lateral suprascapular nerve block with easy orientation, low risk of displacement of the needle, and with an assessment of 2 different volumes to propose an ideal volume for a successful block.

Both shoulders of 34 cadavers were investigated. Insertion point of the needle was determined in the angle of the lateral end of the clavicle, acromion, and the spine of the scapula. The needle was directed toward the medial, dorsal, and caudad direction. Ten mL of diluted contrast agent for computerized tomography was injected in the 34 right sides (group A) and 5 mL in the 34 left sides (group B). Immediately after injection, all shoulders were investigated by computerized tomography scans and 3-dimensional reconstruction to document the constrast dissemination. Five sides of each group were injected with colored contrast and dissected after computerized tomography investigation.

Group A showed a distribution to the entire supraspinous fossa in all cases and the contrast was pressed out of the suprascapular notch in 4 cases with a maximal extension into the axillary fossa in 3 cases. In group B, the supraspinous fossa was filled in 24 cases, with a maximal extension to the axillary fossa in 2 cases. In 9 cases, the contrast agent stayed in the lateral half of the supraspinous fossa. In 1 case we had a medial spread only which still surrounded the suprascapular notch, in another case a superficial spread with misplacement of the needle.

Based on this cadaver study, the lateral modified approach appears to be a safe technique for a suprascapular nerve block, which might be preferred as a single shot technique. A 5 mL volume appears sufficient to fill the supraspinous fossa and to reach the suprascapular nerve, which branches in this anatomical compartment.