Effective range in the proximal shoulder by ultrasound-guided interscalene brachial plexus block.

BACKGROUND

Ultrasound-guided interscalene block (ISB) is a common anesthesia technique for shoulder surgery. However, its effective area remains unclear. Therefore, this study aimed to evaluate the specific area in the proximal aspect of the shoulder affected by ultrasound-guided ISB.

METHODS

A total of 100 consecutive patients who underwent arthroscopic rotator cuff repair under ultrasound-guided ISB in a single institution were included in this study. The effective area of the block was investigated using a pinprick test after surgery along 7 uniquely preset lines: line A extended from the anterolateral corner of the acromion proximally to the proximal edge of the clavicle, line B extended from the coracoid proximally and parallel to line A, line C extended from the coracoid inferiorly and vertically to line B, line D was the bisector of lines B and C, line E extended from the posterolateral corner of the acromion proximally along the scapular spine, line F extended from the posterolateral corner of the acromion inferiorly and vertically to line E, and line G was the bisector of lines E and F. The ratio of the effective range to the distance between the anterolateral corner of the acromion and the proximal edge of the clavicle (A-P distance) was calculated to standardize the physical differences among patients.

RESULTS

Of the 100 patients, 3 demonstrated ineffective supraclavicular nerve block and 59 required local anesthesia on the portal sites in addition to ISB. The average measurements and ratios of the remaining 38 patients were 129.2 ± 36.2 mm and 0.69 ± 0.18 in line A, 106.8 ± 25.5 mm and 0.57 ± 0.13 in line B, 62.4 ± 15.1 mm and 0.34 ± 0.09 in line C, 80.8 ± 22.3 mm and 0.44 ± 0.12 in line D, 65.8 ± 19.3 mm and 0.36 ± 0.11 in line E, 58.2 ± 14.7 mm and 0.31 ± 0.08 in line F, and 58.7 ± 16.1 mm and 0.32 ± 0.09 in line G, respectively. The variability of the ratio was significantly higher in lines A, B, and D than in lines C, E, F, and G.

CONCLUSION

This study demonstrated the effective area in the proximal aspect of the shoulder induced by ultrasound-guided ISB. The effective range in the supraclavicular nerve area is highly variable. These findings can help surgeons determine the range of skin incisions and portal sites for arthroscopic shoulder surgery.