Relevant Anatomy:
The l5 S1 disc space roughly
corresponds to two-finger breadth above the symphysis pubis.
The rectus femoris is a long flat muscle
that spans the entire length of the abdomen. The two muscles on each side are separated by a linea alba, a relatively avascular
fibrous band. The muscle is supplied by inferior epigastric artery in its lower half; the artery may be injured if the plane
of dissection is not kept strictly midline, however if injured the vessel can be tied off. The deeper surgical dissection
involves separating the aorta and the vena cava from the vertebral body of L4 L5. The aorta divides into Rt. and Lt common
iliac vessel in front of L 4 vertebrae. The Aorta and vena cava are attached firmly to the prevertebral sheath and to dissect
them free the segmental vessels need to be mobilized. The veins in this area are thin walled and fragile as compared to the
arterial structure and so a left sided dissection is preferred. The median sacral artery has its origin from the aorta at
L 4 level, and it runs down in front of sacral promontory to the sacral hollow. There is a diffuse plexus of the parasympathetic
nerves around the aorta running below the aorta on the anterior surface of the sacral promontory. This plexus is responsible
for the sexual activity and damage may result in retrograde ejaculation. The ureters present bilaterally run down over the
posterior abdominal wall in front of the psoas muscle, they may need to be mobilized if the exposure needs to include the
S1 disc
Positioning:
Patient is positioned
supine; hyperextension of lumbar spine can be obtained by positioning over the flexion crease of the table
Exposure:
Incision: A vertical para median
incision (Figure 3, 4) starting about two inch above the umbilicus to about 5 inches below it is used. Alternatively a cosmetic horizontal incision
will also give adequate exposure but will cause rectus abdominis weakness postoperatively due to its transaction.
After the skin and subcutaneous
tissue is incised the anterior rectus sheath (Figure 5) and the rectus abdominis muscle (Figure 6) are retracted towards midline to expose the posterior rectus sheath. The posterior rectus sheath and the abdominal fascia
(Figure 7) form a continuous sheath and should be incised carefully (Figure 8).
The pre peritoneal fat
and the peritoneum is now visible (Figure 9, 10), they are retracted towards midline to expose the retroperitoneal fascia.
The posterior peritoneum
is identified over the sacral promontory.
The aorta, ureter and
the common iliac with their bifurcation should be identified (Figure 11, 12, 13, 14, 15).
To separate the peritoneum
from retroperitoneal structure some amount of saline should be injected in the retroperitoneal space.
The posterior peritoneum
should then be incised and an opening made into the retroperitoneal space (Figure 16).
Cautery should not be
used in this space as it may damage the pre sacral venous plexus and lead to uncontrollable bleeding. The best way to control
bleeding in this region is to pack for some time before resuming the procedure.
A blunt dissection is carried to right of
left iliac artery. The middle sacral artery and vein are then bluntly dissected from left to right, the L 5 – S1 disc
can then be identified by soft texture. An X ray confirmation of the level by inserting smooth pin can be done
Potential Complications:
Damage to presacral plexus of parasympathetic nerve leading to retrograde
ejaculation and impotence in men.
Injury to median sacral artery.
Uncontrolled hemorrhage due to injury to small vessels that are branches
to aorta and inferior vena cave.
Injury to ureters
