The angle and depth from the insertion point to the brachial plexus (BP) and C_6-7 intervertebral foramen (IF) was examined to prevent critical complications of an interscalene brachial plexus block (ISBPB), such as an epidural or subdural injection of local anesthetics and spinal cord injury.

Thirty patients (female = 12, male = 18), aged 20??4 years, undergoing shoulder or upper limb surgery were examined. ISBPB was performed at the interscalene groove intersecting the extended transverse line from the cricoid cartilage. A needle was then advanced towards the C₆ transverse process (TP) and C_6-7 IF under the C-arm fluoroscopic guidance. The depth and angle of the needle path intersecting the sagittal plane from the skin insertion point to BP, transverse process (TP) and IF were measured.

The mean depth of the needle from the insertion point to BP, TP and IF were 2.6 ± 0.3 cm, 3.2 ± 0.4 cm, 3.7 ± 0.3 cm in the female patients, and 2.7 ± 0.3 cm, 3.6 ± 0.5 cm, 4.1 ± 0.3 cm in the male patients. The mean angle of the needle path at the same point was 56.0 ± 7.2° (range, 42.0-65.0°), 54.2 ± 5.8°, 53.7 ± 4.4° in the female patients, and 59.3 ± 8.3° (45.0-75.0°), 54.0 ± 6.3°, 54.9 ± 4.2° in male patients. There were significant differences in the depth from the skin to the TP and IF between males and females.

These findings are expected to provide a guideline for more accurate needle placement and successful block during ISBPB.