The sympathetic trunks are paired chains of ganglionated nerve strands descending anterior to the vertebral column. They start separately at the base of the skull as plexuses around the internal carotid artery on each side and they end at the coccygeal bone where they fuse as the ganglion impar.

The sympathetic trunks are part of the autonomic nervous system. On each side white rami run from the spinal cord to the sympathetic trunk, and gray rami run from the sympathetic trunk to each spinal nerve.

The inferior cervical ganglion of the sympathetic trunk is oftentimes fused with the first thoracic paravertebral ganglion. The fused ganglion is called “the stellate ganglion”.

The sympathetic trunk descends anterior to the longus colli muscle, which is anterior to the transverse processes of the cervical vertebral bodies. The longus colli muscle origins from the anterior tubercles and transverse processes of vertebrae C3-T3 and inserts on the anterior tubercles of transverse processes C5-C6 and the anterior surfaces of the vertebral bodies C2-C4 and atlas.

Bendtsen TF, L

It is important to visualize the inferior gluteal artery medially next to the sacral margin. It indicates the correct level of needle insertion and it is a safeguard that allows you to avoid piercing the artery during needle insertion.

Reflex dystrophia of the upper limb.

The curved array probe is placed on the upper half of the line connecting the posterior superior iliac spine and the ischial tuberosity. In this position the iliac bone line is a continuous hyperechoic line (see next page).

From this starting position the probe is parallel shifted infero-medially until the continuity of the iliac bone is disrupted. It is disrupted because the probe reaches the pelvic opening where the sacral plexus exits the pelvis – the greater sciatic foramen (see second next page).

With a slight caudal tilt of the probe, the sacral plexus becomes visible underneath the piriformis muscle (see second next page).

The needle is inserted from the lateral end of the probe and the needle tip is advanced until it reaches the target lumbar plexus (see second next page). Electrical nerve stimulation can be used to confirm the endpoint.

10-15 mL of local anaesthetic is injected in the fascial space between the piriformis muscle and the strong pelvic fascia.

After removal of the gluteus minimus muscle, the major part of the iliac bone is exposed. The superior gluteal artery runs across the iliac bone.

In the starting position of the probe the characteristic continuous, hyperechoic iliac bone is visualized.

The needle penetrates the gluteus maximus and the piriformis in order to reach the target sacral plexus in the greater sciatic foramen between the sacral bone and the ischial bone.

Removal of the piriformis muscle reveals the sacral plexus as it emerges from the greater sciatic foramen.

The ultrasound guided sacral plexus block – the socalled parasacral shift (PSPS) is indicated for

– surgical anaesthesia of the hip combined with a lumbar plexus block

– postoperative analgesia after major hip surgery combined with a lumbar plexus block

– proximal sciatic blockade as an alternative to the subgluteal approach to block the sciatic nerve