POSITION

The patient is in the supine position with the hip and knee joint slightly flexed and the hip joint abducted. A bump is placed under the low back at the level of the anterior superior iliac spine (ASIS) to form the lumbar lordotic curve.

INCISION

A curved incision is made just at the lateral aspect of the rectus sheath. The umbilicus corresponds to the L3–4 disc. The superior iliac crest is at the L4–5 level. The L5–S1 level is located midway between the umbilicus and the pubic symphysis.

The incision starts from 4–5 cm superior to the umbilicus, and reaches to 5–6 cm superior to the pubic symphysis (Fig. 27-1).

Fig. 27-1 Skin incision for the approach. The umbilicus corresponds to L3–4 intervertebral disc level, and the superior iliac crest is at the L4–5 level. The L5–S1 level is located midway between the umbilicus and pubic symphysis.

RECTUS MUSCLE INCISION

The anterior rectus sheath is incised (Figs. 27-2 and 27-3). During the incision, superficial epigastric vessels may be encountered and sacrificed. The rectus muscle is mobilized and retracted medially to expose the posterior sheath (Figs. 27-4 and 27-5). The inferior epigastric vessels lie between the abdominal wall muscles and the transversalis fascia.¹ Because of their lateral position, they are rarely at risk during a midline approach but may be injured during a more lateral approach. Otherwise the rectus muscle can be split and the posterior sheath approached between the muscle fibers.

Fig. 27-2 Anterior rectus sheath incision.

Fig. 27-3 The anterior rectus sheath is seen after the subcutaneous tissue is retracted.

Fig. 27-4 Rectus muscle mobilization. The rectus muscle is mobilized medially, and the posterior sheath of rectus muscle is exposed (right side is cephalad).

Fig. 27-5 Exposure of the posterior sheath of the rectus muscle.

After the rectus muscle is swept away, the posterior rectus sheath is grasped and carefully incised to prevent cutting through the peritoneum (Figs. 27-6 and 27-7). The incision of the posterior sheath provides the entry into the retroperitoneal space. The retroperitoneal fat tissue lies between the posterior sheath and the peritoneum.

Fig. 27-6 After the posterior sheath is incised, the retroperitoneal fat tissue is exposed.

Fig. 27-7 After the posterior rectus sheath is retracted, the peritoneum is seen.

RETROPERITONEAL DISSECTION

Once the peritoneum is identified, it is swept off the abdominal wall with a blunt dissection (Figs. 27-8 and 27-9). An alternative method is to incise the fibers of the transversalis fascia below the arcuate line.² The blunt dissection allows the surgeon to find the plane between the peritoneum and the transversalis fascia, which can be incised rostrally.

Fig. 27-8 Peritoneal membrane is pushed away from the vertebral body.

Fig. 27-9 Schematic view of retroperitoneal finger dissection.

The retroperitoneal fat and intra-abdominal contents are retracted medially, exposing the psoas muscle. A Dever retractor with a wet laparotomy sponge is used for this retraction.

The genitofemoral nerve is seen on the surface of the psoas muscle. The ureter usually can be identified to cross the common iliac artery from lateral to mediocaudal as the peritoneum is lifted away from the psoas. Great care needs to be taken to prevent injury to these structures.

L5 BODY EXPOSURE

The L5 vertebral body is approached by mobilizing the great vessels at the bifurcation. Because the vascular anatomy at this level is somewhat varied, the surgeon should confirm the level of the L5–S1 disc space with an intraoperative x-ray. The bifurcation of the vena cava occurs lower than that of the aorta and is usually located above the L5–S1 disc space (Fig. 27-10).³ The aortic bifurcation usually is immediately anterior to the body of the L4 vertebrae, and the origin of the common iliac veins is observed mainly at the L5 body.

Fig. 27-10 Exposure of L5–S1 disc space. Overlying superior hypogastric plexus and soft tissue are dissected away from the disc surface.

The vena cava bifurcation is to the right of the aorta, and the left common iliac vein passes through the aortic bifurcation. In the lower lumbar spine levels, care must be taken to identify all branches of the common iliac arteries and veins. The left common iliac vein, which is commonly injured, crosses at the L4–5 disc space. Ligating all branches will allow for the vessels to be mobilized to access the spine. The middle sacral artery and vein are routinely ligated during the operation to facilitate exposure. The sacral artery arises from the dorsal surface of the aorta just proximal to its bifurcation (Fig. 27-11). It is recommended that either vascular clamps or suture ligation are used to achieve this, and that the use of monopolar cautery is kept to a minimum. The use of electrocautery can cause damage to the superior hypogastric plexus, which in males can result in retrograde ejaculation.

Fig. 27-11 Dissection method for superior hypogastric plexus.

Once the vessels have been identified, Wiley vein retractors can be used or rubber shaded pins can be placed into the vertebral bodies to hold the vessels clear of the operative level.

VASCULAR MOBILIZATION

The dissection is carried anterior and medial to the left common iliac vessels. The middle sacral artery and vein may be taken with ligation. The left iliac vein needs to be widely mobilized to allow placement of the retractor against the left lateral edge of the spine.⁴

The bifurcation of the abdominal aorta varies from the upper L4 body to the upper L5 body. Rarely can bifurcation be positioned on the lower L5 body. The level of the inferior vena cava confluence is slightly lower than the aortic bifurcation, ranging from the upper L5 to the lower L5 body.

The L5 approach is easy to perform in patients with a high-lying bifurcation (Fig. 27-12). The bilateral retraction of common iliac vessels provides adequate exposure of the L5 vertebral body.

Fig. 27-12 High-lying bifurcation. Common iliac branches are retracted bilaterally.

For patients with bifurcation on the L4–5 disc level, an upward retraction of the bifurcation point of great vessels is necessary (Fig. 27-13).

Fig. 27-13 Bifurcation at L4–5 disc level. Bifurcation point is retracted cephalad and two branches bilaterally.

In cases of low-lying bifurcation, the retraction of the aorta and vena cava is accomplished from the left to the right side to expose the L5 vertebral body (Fig. 27-14). For the vena cava to be retracted, the iliolumbar vein and fifth lumbar vein should be searched out and ligated. The iliolumbar vein makes a tethering effect on the common iliac vein. For the L5 segmental vessels and iliolumbar vein to be found, the medial margin of the psoas muscle should be retracted to the lateral side. When the tumor infiltrates the vertebral body, the periosteum and anterior longitudinal ligament (ALL) slacken, causing adhesion between the ALL and overlying vessels. The dissection of the vessels may be difficult.

Fig. 27-14 Low-lying bifurcation. Two great vessels are retracted to right side.

L4 BODY EXPOSURE

For exposure of the L4 vertebral body, the psoas muscle is retracted to expose the L4 segmental vessels. Segmental vessels are cut and dissected from the vertebral body.

The great vessels and the superior hypogastric plexus are retracted in the medial direction (Figs. 27-15 to 27-17). For easy retraction of the great vessels, the L5 segmental vessels and iliolumbar vein may be ligated (see Fig. 27-15).

Fig. 27-15 Exposure of L4 vertebral body. L4 segmental vessels are ligated and transected. The aorta is retracted to midline. If necessary, the iliolumbar vein and ascending lumbar vein may be sacrificed.

Fig. 27-16 L4 body in surgical field, with the greater vessels retracted.The L3–4 intervertebral disc is partially incised.

Fig. 27-17 After L4 corpectomy, the ventral dura is seen.

Before the L4 corpectomy is performed, the adjacent discs are removed. The L3–4 intervertebral disc and the L4–5 intervertebral disc are removed and the L4 vertebral body is approached. With the monopolar coagulator, the ALL is coagulated and resected (see Fig. 27-16). Vertebral body removal is performed with a punch and drill. After the posterior cortex of the vertebral body is removed, the ventral dura is seen. From the dural sac, the origin of the nerve root can be seen.

UPPER LEVEL APPROACH

This approach also may be used for the L2–4 levels. This requires the mobilization of the vena cava and aorta to one side for access to these levels. Even after mobilization of the vessels, the exposure generally is not as good as that of the flank incision. When extensive debridement and reconstruction are needed, the flank incision is preferred because it allows more exposure lateral to the great vessels. In the upper lumbar spine, it is critical to ligate all segmental vessels around the operative level or levels. This will allow the surgeon to work safely without causing unnecessary bleeding.