DEFINING THE CROSS-SECTIONAL ANATOMY IMPORTANT TO INTERSCALENE BRACHIAL-PLEXUS BLOCK WITH MAGNETIC-RESONANCE-IMAGING

Background and Objectives. Interscalene brachial plexus block is a use ful technique to provide anesthesia and analgesia for the shoulder and proximal upper extremity. The initial needle direction at the intersc alene groove has been described as being ''perpendicular to the skin i n every plane'' (1). A cross-sectional (axial) approach may offer a mo re easily conceptualized directed needle placement. The purpose of thi s study is to define the cross-sectional anatomy and idealized needle angles important to interscalene brachial plexus block. Methods. Follo wing IRB approval, 50 patients were studied. Cross-sectional volume co il T1-weighted magnetic resonance images (MRI) were obtained from 50 p atients undergoing cervical region imaging for other reasons. At the i nterscalene groove, a simulated needle path to contact the ventral ram i or trunks of the brachial plexus was approximated at the level of C6 or C6-C7 interspace. The angle of this needle path intersecting the s agittal plane was recorded for each patient. Results. The mean angle o f the simulated needle path relative to sagittal plane was determined to be 61.1 +/- 6.1 degrees (range, 50-78 degrees). In 13 of 50 (26%) M RT scans, the cervical nerve roots were not visualized at the level of C6 and were measured at the C6-C7 level. Conclusions. These findings suggest initial needle placement at the interscalene groove should be angled less perpendicularly relative to the sagittal plane than is oft en observed. A cross-sectional approach enables more practical visuali zation of initial needle placement. A more accurate initial needle pla cement may minimize the number of needle passes necessary to contact t he nerve roots, thereby more efficiently obtaining a successful block.