|
Relevant
Anatomy:
Abdominal
muscles: Three layers of muscle form the anterolateral abdominal wall. The external oblique is the outermost; the internal
oblique is the middle layer and the transversus abdominis the innermost.
Deep
muscles: The psoas major muscle is a thick muscle arising from multiple slips attached to inferior border of T12 to L5, a
tendinous arch over the narrow part of L1 to L4 vertebral bodies, and the anterior inferior surface of the transverse process
of L1 to L5. It inserts as a tendon into the lesser trochanter of the femur. The quadratus femoris is a large flat muscle
on the posterior abdominal wall. It originates from aponeurotic fibers of the illiolumbar ligament and posterior part of the
iliac crest. It inserts onto the medial half of lower border of twelfth rib, and through small tendons to the anterior - lateral
surface of the L1 to L4 transverse processes. It is supplied by ventral rami of the subcostal and the upper four lumbar nerves.
Aorta
and iliac veins: The aorta and inferior vena cava are firmly attached to the prevertebral sheath. Ligation of the segmental
arteries and veins allows mobilization of the aorta and inferior vena cava away from the vertebral bodies. The vena cava is
thin walled and fragile compared to the aorta, and a left sided approach is favored. The ascending lumbar vein is inconsistent
in its origin; most commonly it originates from the lateral aspect of the common iliac vein at the level of L5 or S1. It may
be a source of bleeding in the lower lumbar spine.
Sympathetic
plexus: The sympathetic plexus arises from the lumbar splanchic nerves and contributes to celiac plexus, mesenteric plexus
and the superior hypogastric plexus. It is present from the lower border of L 2 to upper border of L5 and crosses the vertebral
bodies on the anteromedial aspect. They lie along the medial margin of the psoas muscle and consist usually of four lumbar
ganglia connected to each other by interganglionic cord. They are continuous above with the thoracic chain and below with
the pelvic sympathetic chain. The sympathetic plexus supplies the wall of bladder, the bladder sphincter, and gives the vasodilator
fibers to erectile tissue of the external genitalia. Injury to sympathetic plexus
during surgery leads to a cooler extremity due to loss of vasoconstrictive affect of the sympathetic system.
Ureters
and kidney: The ureters course down the posterior abdominal wall anterior to the psoas muscle. They generally tend to stay
with the peritoneum as it is swept anteriorly during the approach. The surgeon can identify the ureters by their muscular
wall, and the presence of peristalsis upon being stimulated.
Positioning:
The approach is carried out with the patient in a lateral decubitus position, keeping the left side up. The patient
lies on a bean bag, which is inflated to hold the patient in this position. Care is taken to use an axillary roll and protect
bony prominences and peripheral nerves in both upper and both lower extremities. Using a kidney rest or flexing the table
at the waist increases the distance between the costal margin and the iliac crest. Alternatively, the patient lays on a large
roll placed beneath the waist which will also open up the space between the rib cage and iliac crest. Broad adhesive tape
may be used to secure the patient in this position.
Exposure:
Incision: The skin incision typically starts at the lateral half of the twelfth rib, extending
obliquely downward and anteriorly to the lateral border of the rectus sheath fascia. The twelfth rib may be dissected sub
periosteally and either transected partially or disarticulated. The oblique abdominal muscles are divided along the plane
of their fibers. The transversus abdominis can be cut along the same lines exposing the peritoneal cavity. The peritoneum
is continuous with the transversalis fascia, which extends posteriorly covering the kidneys, the ureters, the peritoneal fat,
the quadratus lumborum and the psoas muscle. Blunt finger dissection just lateral to the erector spinae muscle group will
locate the retroperitoneal plane. The peritoneum and its contents are then swept anteriomedially by hand or with a sponge,
and held retracted. The aorta and iliac artery on the left can now be palpated, identified, and protected in their location
anterior to the spinal column. The psoas muscle is gradually and gently detached from its attachments to the anterior lateral
aspects of the vertebral bodies, allowing it to be retracted posteriorly. This exposes the intervertebral discs and the lateral
and anterior aspects of the vertebral bodies. Segmental vessels traversing the waist of the vertebral bodies are ligated when
exposure to the lateral aspect of the vertebral body is necessary.
For exposure of lower lumbar vertebrae the left common iliac vein may need to be mobilized
and retracted. The illiolumbar or ascending lumbar veins are occasionally in the operative field and may need to be secured.
Potential Complications:
Painful incisional site from neuroma.
Incisional hernias through abdominal musculature.
Hemorrhage from injury to large vessels.
Late hemorrhage from erosion of vessels by prominent anterior hardware.
Dural tears are less frequent than with posterior approaches, but are difficult to repair.
Small tears can be tackled by applying gel foam while larger tears may require repair with free dural grafts, fascial grafts,
or synthetic materials sutured or glued to the leak.
Infection
|
