Background and Objectives The aim of this study was to examine whether shoulder rotation increases the length of the posterior longitudinal ligament (PLL) in the lateral decubitus position.

Methods Thirty-four adult male volunteers were placed in the right or left lateral decubitus and flexion position on a horizontal operating table. Thoracic spinal ultrasonography was performed using the paramedian oblique sagittal plane to obtain the optimal ultrasound view for the PLL on the dependent side. The lengths of the PLL were measured at the T6/7 and T9/10 interspaces before and after ipsilateral 30-degree shoulder rotation.

Results In the right lateral decubitus position, the ipsilateral shoulder rotation increased the mean (SD) of the PLL from 7.4 (2.8) to 8.4 (2.6) mm (P = 0.006) at the T6/7 level and from 8.4 (2.9) to 10.6 (2.8) mm (P < 0.0001) at the T9/10 level. Similarly, in the left lateral decubitus position, the ipsilateral shoulder rotation increased the mean (SD) of the PLL from 8.0 (2.6) to 9.1 (2.6) mm (P = 0.001) at the T6/7 level and from 9.3 (2.8) to 11.8 (3.1) mm (P < 0.0001) at the T9/10 level.

Conclusions Shoulder rotation significantly increased the dimension of the acoustic target window for paramedian thoracic epidural access in the lateral decubitus position at both T6/7 and T9/10 levels. Further clinical studies are needed to investigate the effect of shoulder rotation on thoracic epidural access.