Anterior Spine Exposure: Operative Techniques for the Vascular Surgeon

Introduction

The optimal approach to thoracic, lumbar, and sacral spine exposure depends upon the pathology to be addressed, the level or levels being treated, the patient's other comorbid factors, and the experience of the operator and other team members conducting the procedure. Newer approaches to manage degenerative spondylosis, neural decompression, metastatic and primary tumors of the spine, traumatic fractures, osteomyelitis, and congenital anomalies can be more directly managed via an anterior approach to the spine. The responsibility to safely expose the required levels is that of the access surgeon who most often is a vascular surgeon. Thoracic spine exposure may involve a thoracic surgeon and cervical exposure is most often managed by the spine surgeons. Wide exposure may be necessary requiring mobilization of the thoracic or abdominal aorta, vena cava, iliac artery, or veins. In an effort to minimize complications, preoperative considerations, including the presence of atherosclerosis, history of venous thrombosis, reoperative surgery, obesity, and other co-morbid factors, should be included in the planned approach. Communication between the spine specialist and the access surgeon is essential. Familiarity with the various instrumentations is important so that the access provided is adequate for the particular intervention planned. Although slight anterolateral exposure of the intervertebral disc is adequate for some fusions, true anterior exposure is required for disc replacement and fusions with a cage. Major vascular complications can be avoided with meticulous technique and adjunctive use of specialized retractors, which can optimize exposure while minimizing dissection. Noted complications associated with the anterior approach include vascular injury, thromboembolism, injury to the sympathetic nerve plexus resulting in retrograde ejaculation, lymph leak (lymphocele), ureter or bowel injury, ileus, and infection. The incidence of reported vascular injury ranges from under 1% to 24% and almost double that in redo exposures where hardware removal is required. This chapter will present the technique for anterior spine exposure of the more common levels and the principles involved in planning exposure of the spine for instrumentation. Potential complications and their management will be discussed.

Patient Placement

The patient is placed supine on the operating fluoroscopy table. It is imperative that the patient be straight and not rotated. An inflatable airbag behind the lumbar spine can be helpful at times by opening the disc space but should not be routinely inflated. Overinflation can lead to stretching of the vascular structures making them more difficult to mobilize. We prefer to stand on the patient's left side because visualization during exposure of the spine will initially be at an angle from left to right. The fluoroscopy unit is cephalad to the surgeons allowing its intermittent use ( Fig. 65.1 ). An oxygen monitor sensor placed in the left first toe is very useful to monitor return of circulation to the left lower extremity after completion of the procedure ( Fig. 65.2 ). The pulses are examined for comparison at the end of the procedure.

Incision

Incision placement is a very critical component of anterior spine exposure. It must take into account the angle of the intervertebral disc space so that the spine surgeon has visualization of the posterior part of the space, which helps avoid injuring the dura. This will allow thorough discectomy, which is an essential component of the intervention. The level L5 to S1 is particularly critical because the incision is often several centimeters below the location of the disc space ( Fig. 65.3 ). Nevertheless, the space angle should be taken into consideration for any level. Although the anterior and lateral plain x-ray can be used together with skin landmarks ( Fig. 65.4 ), lateral fluoroscopy with the use of a radiopaque marker gives the most precise location for the incision ( Fig. 65.5 ).

For single-level exposure, a transverse incision is preferred. For multiple levels, an up-and-down longitudinal incision is necessary (see Fig. 65.3 ). Generous separation of the subcutaneous tissue medial, superior, lateral, and inferior to the incision allows the skin incision to remain relatively small because it permits movement as necessary. The anterior rectus sheath is then incised in an oblique manner. We prefer to curve the distal medial aspect of the anterior rectus sheath incision across the midline. This releases tension of the linea alba to allow for true anterior exposure. In all instances, the exposure of the posterior rectus sheath, particularly for multiple levels, should be medial to the rectus belly to avoid rectus denervation. The inferior epigastric vessels are carefully preserved. When the exposure is below the semilunar line, the fibers of the transversalis can be bluntly separated laterally to enter the retroperitoneal space. This is most often the case for exposure of the L5 to S1 level ( Fig. 65.6 ). For levels requiring entrance above the semilunar line, the posterior rectus sheath is incised and the peritoneum separated to start entering the retroperitoneal space. The more medial the incision on the posterior rectus sheath, the thinner the peritoneum and the greater likelihood of entering the intraperitoneal space. It is therefore best to keep the incision of the posterior rectus sheath at least 2 to 3 cm from the midline. The peritoneum is then separated from the abdominal wall making sure that as the dissection deepens, it stays anterior to the psoas muscle ( Fig. 65.7 ). Care should be taken to avoid injury to the genitofemoral and the ilioinguinal nerve. The ureter should stay attached to the peritoneum and is retracted medially together with it. Further dissection will depend on the desired level to be exposed. Use of a table-attached retractor is highly recommended ( Fig. 65.8 ).

The access surgeon should remain attentive during the instrumentation by the spine team and re-place the position of the retractors if they are disturbed. This is critical to avoid injury to the surrounding mobilized structures during the actual instrumentation of the spine.