8 – Sonoanatomy: The parasacral parallel shift

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

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Iliac bone line (red arrows), gluteus medius (white asterix), gluteus maximus (cyan asterix), M = medial, L = lateral

9 – Sonoanatomy: The sacral plexus

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

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Sacral plexus (yellow shadow), piriformis (triangular brown shadow), gluteus maximus (cyan asterix), surface of sacral bone (green arrows), surface of iliac bone (red arrows), needle (red), M = medial, L = lateral

10 – Sonoanatomy: The inferior gluteal artery

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

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Sacral plexus (red arrow), inferior gluteal artery (red shadow), iliac bone (magenta asterix), sacral bone (green asterix), piriformis (white asterix), L = lateral, M = medial

12 – References

Bendtsen TF, Lönqvist PA, Jepsen KV, Petersen M, Børglum J: Preliminary results of a new ultrasound-guided approach to block the sacral plexus: The parasacral parallel shift. Br J Anaesth 107(2): 278-80 (2011)

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7 – Scanning technique for the parasacral parallel shift

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

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The curved array probe is placed on the upper half of the blue line connecting the posterior superior iliac spine and the greater trochanter. From this position the probe is parallel shifted infero-medially (red arrow)

8 – References

Sauter A, Ullensvang K, Bendtsen TF, Børglum J: The “Shamrock Method” – a new and promising technique for ultrasound guided lumbar plexus block. (2013)

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