The posterior approach can be undertaken with the patient in either of two positions:

For both positions, use a cold-light headlamp to illuminate the deepest layers around the spine.

The internervous plane lies between the two paraspinal muscles (erector spinae), each of which receives a segmental nerve supply from the posterior primary rami of the lumbar nerves.

Deepen the incision through fat and fascia in line with the skin incision until the spinous process itself is reached. Detach the paraspinal muscles subperiosteally as one unit from the bone, using a dissector, such as a Cobb elevator, or with cautery (Fig. 6-3). Dissect down the spinous process and along the lamina to the facet joint. In a young patient, the tip of the spinous process is a cartilaginous apophysis; it can be split in the midline, making subperiosteal muscle removal easier (Fig. 6-4).

If necessary, dissection can be continued laterally, stripping the facet joint capsule from the descending and ascending facets. To do this, strip the joint capsule in a medial to lateral direction across the posterior aspect of the descending facet; then, continue over the tip of the mamillary process of the more lateral ascending facet. If the transverse processes must be reached, continue dissecting down the lateral side of the ascending facet and onto the transverse process itself (see Fig. 6-4).

Close to the facet joints, in the area between the transverse processes, are the vessels supplying the paraspinal muscles on a segmental basis. These branches of the lumbar vessels frequently bleed as the dissection is carried out laterally. Vigorous cauterization of these



vessels may be necessary to stop the bleeding. Note that the posterior primary rami of the lumbar nerves, which also supply the paraspinal muscles segmentally, run with these vessels. Loss of some of these nerves does not totally denervate the paraspinal muscles, because they are innervated segmentally (see Fig. 6-4).

Remove the ligamentum flavum by cutting its attachments to the superior, or leading, edge of the inferior lamina using either a curette or sharp dissection. Immediately beneath are epidural fat and the blue-white dura. Using blunt dissection and staying lateral to the dura, carefully continue down to the floor of the spinal canal, retracting the dura and its nerve root medially (Figs. 6-5, 6-6, 6-7 and 6-8).

Place the patient in the prone position on a radiolucent table, with the abdomen free and the extremities padded.

Palpate the spinous processes to identify the midline. Fluoroscopy is used to determined the disc level.

The approach splits the fibers of the erector spinae muscle group that are innervated segmentally.

The skin, subcutaneous adipose tissue, and the erector spinae fascia are sharply divided with a knife.

The erector spinae muscle fibers are split by the dilating/retracting tube and abutted against the lamina and medial facet joint.⁷ The distal lamina and ligamentum flavum are resected on the affected side to expose the nerve root over the disc. Some of the medial facet can be resected to decompress the lateral recess. The nerve root is then retracted medially to expose the pathologic disc (Fig. 6-9).

Meticulous positioning of the retractors must be done with landmarks and fluoroscopy because a very small incision is made. Any deviation from the planned course may make it difficult to find the pathology. If the incision is too medial, the spinous processes may impede the proper positioning of the retracting tube. A tube that is angled excessively will make it difficult to work and target the microscope. This can be mitigated by using a tilting operating table. Meticulous hemostasis is important, as the small access port can be obscured easily by excessive bleeding.

The tube/retractor can be repositioned or angled differently to address pathologies in different locations, for example, to access a sequestered disc, a far lateral disc, or to decompress a contralateral spinal stenosis. Larger tubes are available if more exposure is required. In the lordotic spine, a small change in the angle of the tube can permit access to an adjacent level.

The muscles of the lumbar spine are made up of superficial and deep layers. The superficial layer consists of the latissimus dorsi, a powerful muscle of the posterior axillary wall that originates from the spinous processes and inserts into the intertubercular groove of the humerus. The surgically important deep layer consists of the paraspinal muscles and itself is divided into two layers: the superficial portion, which contains the sacrospinalis muscles (erector spinae), and the deep portion, which consists of the multifidus and rotator muscles (Fig. 6-10).

This arrangement is not apparent during surgery, because the approach involves detaching all these muscles in a single mass.

The dorsal lumbar fascia and the supraspinous (supraspinal) ligaments lie between the skin and the

spinous processes. The fascia is a broad, relatively thick, white sheet of tissue that forms a sheath for the sacrospinalis muscles and attaches to the spinous processes (see Fig. 6-10). It extends to the cervical spine, where it becomes continuous with the nuchal fascia of the neck. Medially, it is attached to the spinous processes of the vertebrae, the supraspinous ligaments, and the medial crest of the sacrum. Inferiorly, it is attached to the iliac crests. Laterally, it is continuous with the origin of the aponeurosis of the transversus abdominis and latissimus dorsi muscles.

The supraspinous ligaments extend from vertebra to vertebra, connecting the spinous processes. They blend intimately with the attachment of the dorsal lumbar fascia to the spinous processes (Fig. 6-14).

Further dissection consists of detaching the two layers of muscle from bone. Because these muscles are detached in a single mass, their critical feature, in regard to their surgical anatomy, lies in their blood supply and not in their structure. The segmental lumbar vessels branch directly from the aorta. They wrap around the waist of each vertebral body and then ascend close to the pedicle, where they divide into two branches. One supplies the spinal cord; the other, larger branch then comes directly posteriorly to supply the paraspinal musculature. During the approach, these vessels appear between the transverse processes, close to the facet joints (see Fig. 6-11). They often bleed as dissection is carried out. In addition, the arteries branch within the muscle bodies, frequently creating a very vascular field. For this reason, the dissection should be kept as close to the midline as possible; no major vessels cross the midline, and the plane is safe for use (Fig. 6-13; see Fig. 6-11).

The ligamentum flavum is the most important structure in the deep layer. Consisting of yellow elastic tissue, the ligament takes origin from the leading edge of the lower lamina and inserts into the anterior surface of the lamina above, about halfway up onto a small ridge (Fig. 6-12). The two ligamenta flava, one from each side, meet in the midline, but generally do not fuse; the plane between the ligamentum flavum and the underlying dura fat can be entered most easily at that point. Because of its attachments, the ligamentum flavum is removed best from the leading edge of the lower lamina through sharp dissection or curettage (see Fig. 6-5A).

The major danger in the deep dissection involves damage to the dura. Once the ligamentum flavum is entered, a thin spatula should be placed beneath it to protect the underlying dura from being torn (see Fig. 6-6A). The cord itself and the nerve roots often are difficult to see as a result of bleeding from epidural veins. The veins, which are thin-walled and easy to rupture, even with blunt dissection, can be controlled by direct pressure using a pattie or by bipolar cautery.

Place the patient supine on the operating table (see Fig. 6-14). Make sure that two areas remain bare for incision: one for the abdominal incision, and one for harvesting an anterior iliac crest bone graft. Insert a urinary catheter to keep the bladder empty. Use of mechanical calf compression is recommended to decrease the risk of thromboembolism.

The midline plane lies between the abdominal muscles on each side, segmentally supplied by branches from the seventh to the 12th intercostal nerves. Therefore, this incision can be extended from the xiphisternum to the pubic symphysis.

Deepen the wound in line with the skin incision by cutting through the fat to reach the fibrous rectus sheath. Incise the sheath longitudinally, beginning in the lower half of the incision, to reveal the two rectus abdominis muscles (Fig. 6-16). Separate the muscles with the fingers to expose the peritoneum (Fig. 6-17). Then, pick up the peritoneum carefully between two pairs of forceps and, after making sure that no viscera are trapped beneath it, incise it with a scissors (Fig. 6-18). Extend the incision distally, but take care not to incise the dome of the bladder at the inferior end of the wound. With one hand inside the abdominal cavity to protect the viscera, carefully deepen the upper half of the incision, staying in the midline and cutting through the linea alba, the band of fibrous tissue that separates the two rectus abdominis muscles in the upper half of the abdomen. Complete the exposure by cutting through the peritoneum in the upper half of the wound (Fig. 6-19).

Use a self-retaining Balfour retractor to retract the rectus abdominis muscles laterally and the bladder distally (Fig. 6-20). Perform a routine abdominal exploration. Next, put the operating table in Trendelenburg’s position at 30° and carefully pack the bowel

in a cephalad position, keeping it inside the abdominal cavity. Spread a moist lap pad (swab) over it to prevent loops of bowel from slipping free. It is much safer to keep the bowel within the abdominal cavity, but do not pack it so tightly that vascular compromise is induced. In women, the uterus may be retracted forward with a 0 silk suture placed in its fundus and tied to the Balfour retractor.

Infiltrate the tissue over the anterior surface of the sacral promontory with a few milliliters of saline solution to make dissection easier and to allow identification of the presacral parasympathetic nerves that run down through this area. For the L5-S1 disc space, incise the posterior peritoneum in the midline over the sacral promontory. The sacral artery runs down along the anterior surface of the sacrum and must be ligated or clipped. The ureters should be well lateral to the surgical approach.

Preserve any small nerve fibers that are found. Identify the L5-S1 disc space either by palpating its sharp angle or by inserting a metallic marker and taking a radiograph. The L5-S1 disc space lies below the bifurcation of the aorta; it should be possible to expose it fully without mobilizing any of the great vessels (Figs. 6-21 and 6-22).

Operating on the L4-5 disc space requires a larger exposure; mobilizing the great vessels is necessary, unless the vascular bifurcation occurs much higher. Carefully incise the peritoneum at the base of the sigmoid colon and mobilize the colon upward and to the right to expose the bifurcation of the aorta, the left common iliac artery and vein, and the left ureter. Identify the aorta just above its bifurcation and gently begin blunt dissection on its left side. Identify and ligate the fourth and fifth left lumbar vessels, then divide them. Now, the aorta, vena cava, and left common iliac vessels can be moved to the right, exposing the L4-5 disc space. This exposure is difficult to achieve; a high incidence of venous thrombosis has been reported with anterior surgery at this level. Take care not to injure the left ureter, which crosses the left common iliac vessels roughly over the sacroiliac joint. The ureter may have to be moved laterally, but mobilize it only as much as necessary to reduce the risk of postoperative ischemic stricture formation.

An alternative method is to approach the L4-5 disc space from below, working upward into the apex of the vascular bifurcation. Isolate the left and right common iliac artery, placing umbilicus loops around them. Retract the two arteries cephalad and laterally



to expose the common iliac veins. Dissect into the confluence of the veins and isolate the left common iliac vein with a loop. Gently retract the venous structures to expose the disc space. Use only minimal retraction to avoid injuring the intima, which may lead to venous thrombosis (see Fig. 6-22).

Position the patient lying flat and supine on a radiolucent table.

The landmark for access to the L5-S1 disc is usually distal to the midway mark between the umbilicus and symphysis. A more distal incision is required for the L5-S1 disc because of its downward orientation. The L4-5 disc is generally located a few centimeters from the umbilicus, and the incision is made directly over the disc. L3-4 is a few centimeters proximal to the umbilicus and is also approached with an incision directly over it. The incisions can be transverse if only one level is done or the more versatile incision for one or more level is a midline longitudinal or slight oblique incision (Fig. 6-23).¹³

An interval just medial to the rectus abdominus and under the rectus is developed. The rectus is innervated segmentally.

Continue the incision to the ventral rectus fascia (Fig. 6-24). The rectus fascia is cut longitudinally on the medial edge of the muscle (Fig. 6-25). The medial edge is identified, and the rectus is lifted up and retracted to expose the dorsal fascia and the arcuate line (Fig. 6-26). The inferior 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 (Fig. 6-27).

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. Retractors appropriate to the direction of the incision and size should be determined (Fig. 6-28). The ureter is generally seen on the underside of the peritoneum. The peritoneum and ureter are retracted medially and the common iliac vein is seen just dorsal to the artery and crossing from proximal-lateral to distal-medial. Caution must be used not to damage the thin walls of the vein, as it is easily the most fragile structure of this approach. The soft tissues in front of the L5-S1 disc and sacral promontory are bluntly pushed 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. To expose the L4-5 disc, the dissection is moved proximal to the iliac vessels. A plane between



the psoas and the iliac vessels is developed bluntly. The ascending iliolumbar vein should be identified and ligated/clipped before retracting the iliac vein.¹⁴

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.

The anterior approach to the lumbar spine involves three stages of dissection. The superficial stage consists of cutting the skin and subcutaneous tissues down to the bowel. Below the skin lies the linea alba, a fibrous structure in the midline that is identified most easily in the upper abdomen. Cutting the linea alba in the lower half of the abdomen exposes the rectus muscle, which can be separated by finger pressure. Beneath it is the posterior rectus sheath and peritoneum.

The anatomy of the intermediate stage, which involves packing away the bowel, is the anatomy of the bowel and is not included in this book.

The deep stage of dissection consists of mobilizing the retroperitoneal structures that lie anterior to the L4-5 and L5-S1 disc spaces. These structures include the aorta, vena cava, common iliac vessels, lumbar vessels, ureter, and presacral plexus.

The long, flat rectus abdominis muscle extends along the length of the entire abdomen, split into two muscles in the upper half by the linea alba. The muscle is enclosed in a fascial sheath. Above the umbilicus, the sheath has three elements: the aponeurosis of the internal oblique splits to enclose the rectus muscle; the aponeurosis of the external oblique passes in front of the rectus to form part of the anterior sheath; and the aponeurosis of the transversus abdominis fascia passes behind to form part of the posterior sheath. The inferior margin of the posterior sheath is known as the semicircular line (semicircular fold of Douglas). Below the umbilicus, all three aponeuroses pass anteriorly, leaving a thin film of tissue posteriorly (Figs. 6-31 and 6-32).

The arrangement of the rectus sheath and the linea alba means that, in the upper half of the incision, the approach through fibrous tissue leads directly down to the peritoneum, whereas in the lower half, it leads to the rectus abdominis muscle. Because of this, it is easier to open the abdomen in the lower half of the incision (Fig. 6-33; see Fig. 6-32).

The inferior epigastric artery supplies blood to the lower half of the rectus abdominis muscle. The artery lies between the muscle and the posterior part of the rectus sheath. If the surgical plane remains in the midline, this vessel should escape injury. If the artery is damaged when the rectus muscle is mobilized, it can be tied with impunity.

Deep surgical dissection consists of freeing the distal ends of the aorta and the vena cava from the vertebrae in the L4-5 vertebral area. The aorta divides on the anterior surface of the L4 vertebra into the two common iliac arteries. Just below this bifurcation, the common iliac vessels divide in turn at about the S1 level into the internal and external iliac vessels. The internal iliac is the more medial of the two (Fig. 6-34).

The aorta and vena cava are held firmly onto the anterior parts of the lower lumbar vertebrae by the lumbar vessels. These segmental vessels must be mobilized to permit the aorta and vena cava to be moved (see Fig. 6-13). Because the arterial structures are easier to dissect and more muscular than are the thin-walled venous structures, the preferred approach to the L4-5 disc space is from the left, the more arterial side. The median sacral artery originates from the aorta at its bifurcation at L4 and runs in the midline, over the sacral promontory and down into the hollow of the sacrum (see Fig. 6-34). The lumbosacral disc usually lies in the V that is formed by the two common iliac vessels. Nevertheless, the level at which the vessels bifurcate may vary; on rare occasions, they may have to be mobilized to expose the L5-S1 disc space.

Note that the left common iliac vein lies below the left common iliac artery, whereas the right common iliac artery lies below and medial to the right common iliac vein. Therefore, special care must be taken



when mobilizing the left side of the vascular V, because the vessel closest to the surgery is the thin-walled vein, not the artery (Fig. 6-35; see Fig. 6-34).

A diffuse plexus of nerves exists in the presacral area. The nerves anterior to the L5-S1 disc are part of the superior hypogastric plexus which receives sympathetic innervation from T11 to L3 via the sympathetic chain and a plexus of nerves around the aorta. Injury to these nerves may cause ejaculatory dysfunction in men (retrograde ejaculation). More distally the plexus of nerve has parasympathetic contributions from the pelvic nerves (S2,S3,S4) which are important for erectile function in men. These nerves are more at risk with surgeries anterior to the mid and lower sacrum as well as low rectal and prostate procedures (see Figs. 6-34 and 6-35).¹⁵

The ureter runs down the posterior abdominal wall on the psoas muscle. At the bifurcation of the common iliac artery over the sacroiliac joint, it clings to the posterior abdominal wall, held there by the peritoneum, and should be well lateral to the approach to the L5-S1 disc space. It may have to be mobilized for exposure of the L4-5 disc space (Fig. 6-36; see Fig. 6-35).

Place the patient on the operating table in the semilateral position. The patient’s body should be at about a 45° to 90° angle to the horizontal, facing away from the surgeon. Keep the patient in this position throughout the surgery by placing sandbags under the hips and shoulders or by using a kidney rest brace to hold the patient. The angle allows the peritoneal contents to fall away from the incision. Alternatively, place the patient supine on the operating table and tilt the table at 45° to the horizontal away from the surgeon. This position has the advantage of not putting the psoas muscle on stretch (Fig. 6-37).

The approach can be done with the left or right side up depending on whether the surgeon prefers to work on the “aortic side” or the “caval side.”

No internervous plane is available for use. The three muscles of the abdominal wall (the external oblique, internal oblique, and transversus abdominis) are divided in line with the skin incision. Because all three muscles are innervated segmentally, significant denervation does not occur (Fig. 6-38).

Deepen the incision through subcutaneous fat to expose the aponeurosis of the external oblique



muscle. Divide the aponeurosis of this muscle in the line of its fibers, which is in line with the skin incision. The muscle fibers of the external oblique rarely appear below the level of the umbilicus except in very muscular patients. If they are found there, the muscle should be split in the line of its fibers (Fig. 6-40).

Next, divide the internal oblique muscle in line with the skin incision and perpendicular to the line of its muscular fibers. This division causes partial denervation, but if the muscle is closed properly, postoperative hernias can be avoided (Fig. 6-41). Under the internal oblique muscle lies the transversus abdominis muscle. It, too, should be divided in line with the skin incision to expose the retroperitoneal space (Figs. 6-42, 6-43, 6-47, and 6-48).

Using blunt finger dissection, develop a plane between the retroperitoneal fat and the fascia that overlies the psoas muscle (Fig. 6-44). Gently mobilize the peritoneal cavity and its contents and retract them medially (Fig. 6-45). Carry out this dissection from either the left lower quadrant or the right upper quadrant, depending on the side that needs to be exposed.