The parasacral region is covered by the gluteus maximus muscle.

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

Removal of the gluteus maximus muscle reveals the emergence of the sciatic nerve from the sacral plexus at the lower border of the piriformis muscle.

The interspace between the sacrum and the transverse process (TP) of L5 is the lumbosacral osteofibrotic tunnel bounded by the ala sacrum inferiorly, the TP L5 cranially, the fifth lumbar neural foramen medially, the lumbosacral ligament anteriorly, and the intertransverse ligament posteriorly.

The lumbosacral ligament typically extends obliquely inferolateral from the TP L5 to the ala sacrum.

Bendtsen TF, S

When the needle penetrates the lumbosacral ligament it enters the psoas compartment which is the fascial space posterior to the psoas major.

The psoas compartment contains the terminal nerves from the lumbar plexus and the lumbossacral trunk that is the sacral plexus component from L4 and L5.

Place the patient in the lateral decubitus position.

Place the low-frequency 6-2 MHz) curved array probe across the iliac crest and parallel shift it medially along the iliac crest until the sacral bone comes into view. In this position the probe is rotated until both the upper margin of the sacral bone and the transverse process of the L5 vertebral body and interspace between the two bony structures come into view.

The intertransverse and lumbosacral ligaments are visualized (see next page).

The needle is inserted with a steep out of plane approach perpendicular to the skin surface and advanced until it penetrates the lumbosacral ligament and a loss-of-resistance is obtained. Electrical stimulation is superfluous.

20 mL of local anaesthetic is injected.

When local anaesthetic is injected into the psoas compartment it spreads behind the muscle up to the level of lumbar vertebra L4 and covers the terminal nerves of the lumbar plexus and the lumbosacral trunk of the sacral plexus.

The psoas compartment can be accessed by inserting the needle between the upper margin of the sacrum and the transverse process (TP) of L5 or between the TP’s L4 and L5.

If the needle is inserted more cranial the psoas major is strongly adherent to the neuraxis and the needle tip enters the fascial space between the anterior and posterior lamina of the psoas major.

The single-injection suprasacral parallel shift (SSPS) lumbosacral plexus block is indicated for:

– preoperative analgesia before hip fracture surgery as an alternative to femoral nerve block

– postoperative analgesia after major hip or proximal thigh surgery