Anterior Retroperitoneal Approach to the
Lumbar Spine
This approach is used mainly for procedures on the L5/S1 disc space. These include fusion operations for degenerative disease, debridement and fusion of spinal tuberculosis, and insertion of disc prostheses. Although the approach can be used at higher levels the anterolateral retroperitoneal approach may be preferred in such cases.
Position of the Patient
Position the patient lying flat and supine on a radiolucent table.
Landmarks and Incisions
The landmarks on the anterior abdominal wall used for surgery vary dependant on the disc level or levels to be approached. The landmark for access to the L5-S1 disc is usually distal to the midway mark between the umbilicus and symphysis. This is not directly over the disc space being distal to it. A more distal incision is required for the L5-S1 disc because of its downward orientation. The anterior landmark for the L4-5 disc is generally located a few centimeters from the umbilicus, and the L3-4 landmark is a few centimeters proximal to the umbilicus. The final localization should be done by fluoroscopy prior to the incision as the disc level may vary.
A transverse incision directly over the disc space can be used if only one level is to be treated. The more versatile incision for one or more levels is a midline longitudinal or slight oblique incision (Fig. 6-23).14
Internervous Plane
An interval just medial to the rectus abdominis and under the rectus is developed. The rectus is innervated segmentally.
Superficial Surgical Dissection
Deepen the incision down to the ventral rectus fascia (Fig. 6-24). Divide the rectus fascia longitudinally on the medial edge of the muscle (Fig. 6-25). Identify the medial edge of the muscle and the lift up the rectus and retract it to expose the dorsal rectus fascia and the arcuate line (Fig. 6-26). Identify and preserve the inferior epigastric vessels. Use blunt dissection to
 |
 |
Figure 6-23 The landmarks for an anterior minimally invasive retroperitoneal approach are shown. The final localization should be done radiographically prior to the incision as the disc level may vary. The incisions can be transverse, longitudinal, or slightly oblique. The incisions for L3-4 and L4-5 are generally performed directly over the disc level, whereas the L5-S1 disc must be approached through a more distal incision given the downward orientation of the disc.
 |
 |
Figure 6-24 The incision is continued to the ventral fascia of the rectus abdominis. The midline can be identified by the crisscrossing fibers of the fascia.
Deep Surgical Dissection
Continue the blunt dissection toward the left lower quadrant, to encounter the retroperitoneal fat; underneath it, the psoas muscle can be seen. At this point, branches of the genitofemoral nerve are readily identified lying on the psoas and just medial is the common iliac artery. Choose retractors appropriate to the direction and size of the incision (Fig. 6-28). Identify the ureter on the underside of the peritoneum. Retract the peritoneum and ureter medially and identify the common iliac vein just dorsal to the artery and crossing from proximal-medial to distal-lateral. Caution must be used not to damage the thin walls of the vein, as it is easily the most fragile structure of this approach. Using blunt dissection, push the soft tissues in front of the L5-S1 disc and sacral promontory medially to expose the middle sacral vein(s) (Fig. 6-29). The veins require clipping, cauterizing, and ligating to divide them and mobilize the left iliac vein.
 |
 |
Figure 6-25 The rectus fascia is cut longitudinally on the medial edge of the muscle.
 |
 |
Figure 6-26 The medial edge is identified and the rectus is lifted up and retracted to expose the dorsal fascia and the arcuate line.
 |
 |
Figure 6-27 The epigastric vessels are identified and preserved. Blunt dissection is used to develop a plane dorsal to the rectus abdominis and toward the lower quadrant. If exposing proximal to L5, the fascia of the arcuate line is divided.
 |
 |
Figure 6-28 Continuing the blunt dissection toward the left lower quadrant, retroperitoneal fat is eventually encountered; underneath it, the psoas muscle can be seen. At this point, branches of the genitofemoral nerve are readily identified lying on the psoas and just medial is the common iliac artery.
To expose the L4-5 disc, the dissection is moved proximal to the iliac vessels. Develop a plane between the psoas and the iliac vessels by blunt dissection. Identify and ligate the ascending iliolumbar vein before retracting the iliac vein.15
Dang
Nerves
The presacral plexus of nerves is critically important to sexual function. Dissection should be gentle and blunt with all the soft tissues anterior to the disc moved as a unit with the retroperitoneum. Bipolar cautery should be used selectively.
The sympathetic chain can be found medial and deep to the psoas on the lateral vertebral body particularly when exposing proximal to L5.
Arteries and Veins
The aorta and inferior vena cava are tethered to the anterior surface of the lumbar vertebrae by the lumbar vessels. These smaller vessels must be ligated and cut to allow the great vessels to be lifted forward off the lumbar vertebrae, exposing the L4-5 disc space (see Fig. 6-12). It is important to dissect these vessels carefully, without cutting them flush with the aorta. If the vessels are cut flush, there will be, in effect, a hole in the aorta, and the bleeding may be extremely difficult to control. Mobilization of the venous structures should be undertaken very carefully, because they are fairly fragile and easily traumatized. Damage to these vessels may result in thrombosis; mobilization and retraction should be kept to a minimum.
Special Structures
The ureter can be mobilized lateral or medial with the retroperitoneal approach. It is generally easier to let the ureter be moved medially with the rest of the retroperitoneum. It can be identified by inducing peristalsis by gently pinching it with a pair of nontoothed forceps.
How to Enlarge the Approach
The retroperitoneal approach can expose from the distal aspect of T11 to S1. Exposing more proximal discs requires control and division of the segmental vessels to mobilize the aorta and vena cava.
 |
 |
Figure 6-29 The soft tissues in front of the L5-S1 disc and sacral promontory are bluntly pushed laterally to expose the middle sacral vein(s).
