Transsacral
block was first performed by Pauchet and L”wen in 1909.
The five
pairs of sacral and one pair of coccygeal nerves arise at the level of T12 and
L1, course downward within the cauda equina, and, after reaching the sacral
canal, exit their respective intervertebral foramina. At that point, they
immediately divide into anterior and posterior primary divisions.
The
posterior primary divisions of the upper four sacral nerves pass posteriorly
through the posterior sacral foramina, while those of the fifth sacral and the
coccygeal nerves emerge through the sacral hiatus. The upper three
posterior divisions then divide into medial branches, which supply the musculi
multifidi and lateral branches, which from the posterior sacral plexus
supplying the skin on the medial part of the gluteus maximus. The
posterior primary divisions of the lower two sacral nerves and that of the
coccygeal nerve unite to form the posterior anococcygeal nerve, which supplies
the skin over the coccyx.
The anterior
primary divisions of the upper four sacral nerves pass anteriorly into the
pelvis through the anterior sacral foramina; that of the fifth emerges from the
sacral hiatus and passes anteriorly. The anterior division of the
coccygeal nerve also passes anteriorly below the rudimentary transverse process
of Co1. The anterior primary divisions then take part in the formation of
the sacral plexus and the pudendal plexus.
The
transsacral block is indicated for diagnostic, prognostic or therapeutic
purposes in pain syndromes of the pelvis and perineum, especially those caused
by malignancy. Hypertonic bladder in paraplegics can be treated with a
bilateral block of S2-3.
Position. The patient is in a prone
position, usually with a pillow under the pelvis.
Landmarks. The posterior superior iliac
spine, the most posteromedial point of the iliac crest, is located. The
sacral cornua are then identified. These landmarks are situated at the
level of the second and fifth sacral foramina, respectively.
Procedure. After a sterile prep, the
above landmarks are identified. A skin wheal is raised 1 cm medial and
inferior to the posterior superior iliac spine. This overlies the second
sacral foramen. A second skin wheal is raised 1 cm medial and inferior to
the sacral cornu, which overlies the fifth sacral foramen. The distance
between the two wheals is then divided into three equal parts by raising two
intermediate wheals overlying the third and fourth sacral foramina. The
first foramen is then located by raising a wheal 2 cm superior to the second
sacral foramen. All five should form a straight line parallel to the
midline.
For
injections involving the first and second sacral foramina, 8-cm 22-gauge
needles are used, while 5-cm 22-gauge needles are used for the other sacral
foramina. At each of the five foramina, a needle is introduced
perpendicularly with a slight medial and inferior direction.
After the
posterior surface of the sacrum is contacted, each needle is marked by
measuring off a depth of 1.5 cm for the first sacral nerve, 1 cm for the second
sacral nerve and 0.5 cm for the remaining nerves from the skin at each
respective point. The needle is then withdrawn slightly and reinserted with
a controlled fanwise movement until it advances to the measured depth.
Paresthesia can be elicited at that point.
If the
needles have been properly placed, they will be in a straight line. After
negative aspiration for blood, CSF or a dose of air, 5-10 ml local anesthetic
for the first sacral nerve and 5 ml for the other nerves in injected at each
site. For neurolytic block, 1-3 ml is injected to each sacral
foramen. Fluoroscopy may be employed to locate the foramina by taking
antero-posterior and lateral views with the needles in place.
Possible
complications are intravascular injection, subarachnoid or epidural injection
or perforation of the pelvic viscera.