Spinal Operative Exposure

Spinal disorders, such as degenerative disc disease and spondylolistheses, are treated with interbody fusion. To accomplish this, the spine can be exposed through anterior, transforaminal, oblique, lateral, and posterior approaches. The vascular surgeon becomes critical, however, to the success of the orthopedist or neurosurgeon for the anterior approach to the spinal column, ^, which was first described in the 1930s. While there is controversy regarding when to intervene on back pain, what pathology is most amenable to an anterior approach, and whether one approach offers substantial postoperative benefits over others, the anterior approach is generally considered less invasive than the posterior approach. Specifically, anterior spine exposure obviates the need for paraspinal muscle dissection and encountering the spinal cord and cauda equina. As compared to the posterior approach, the anterior approach is associated with less blood loss, fewer transfusions, and shorter operative times.

Anterior spine exposure takes advantage of the potential space between the peritoneal contents and kidney, and the quadratus lumbar and psoas muscles. From the vascular surgeon’s perspective, the goal is to provide the spine surgeon with adequate vertebral side-to-side exposure so that discectomy, decompression, and/or partial corpectomy can be safely performed and implants accurately inserted on the basis of the disc space midpoint. Given that there is potential for major vessel injury, most centers have adopted a two-team (vascular and spine surgeon) approach to minimize morbidity and to maximize optimal operative exposure for reconstructive spinal surgery. These vascular surgeons, functioning as “access surgeons,” have improved patient outcomes, with vascular co-surgeons being associated with decreased intraoperative blood loss, operative time, and length of stay.

In the United States, the incidence of spinal disorders, such as degenerative disc disease, disc herniation, and slipped discs, and subsequent operative management is increasing over time. Therefore, it is possible that the demand for vascular surgeons may increase. This chapter explores anterior spine exposure from a vascular surgeon’s perspective.

Clinical Presentation, Diagnostic Evaluation, and Risk Assessment

Patients present to their spine surgeons with complaints of low back pain, and often have failed pharmacologic and nonpharmacologic (e.g. acupuncture, massage, cognitive behavioral therapy) management, and procedural interventions (e.g. glucocorticoid injections). These surgical candidates will also often have severe or progressive neurologic deficits, and experience decreased health-related quality of life and increased physical disability and depression. In contrast to the patients that the vascular surgeon commonly encounters, patients requiring spine surgery infrequently have atherosclerotic disease. Patients with spine disorders are generally 50 to 70 years of age, female and normal weight. About 40% of the population will be overweight or obese, which is sometimes the result of inactivity secondary to pain. However, as compared to patients undergoing posterior fusion, the patient undergoing anterior fusion is relatively younger and healthier, which may be partly due to a selection bias towards candidates suitable for abdominal surgery.

Despite the low prevalence of atherosclerotic disease, the diagnostic evaluation still includes a peripheral vascular history and physical since anterior spine exposure involves extensive mobilization of major arteries and veins within the abdomen/pelvis. As usual, a history of claudication or any abnormality in the peripheral pulse findings should prompt noninvasive testing. Routine noncontrast imaging of the spine frequently shows aortic calcification or aneurysmal changes. Occasionally, further testing such as duplex ultrasonography and/or computed tomography angiography is required for severe aortoiliac occlusive disease or aortic aneurysmal disease. Knowledge of peripheral pulses is also important as open retroperitoneal anterior spine exposure sometimes leads to temporary vessel occlusion from retraction, which for some may result in thromboembolic events (see Ch. 22 , Vascular Laboratory: Arterial Duplex Scanning and Ch. 29 , Computed Tomography).

Diagnostic evaluation also includes an examination of the patient’s thorax, abdomen, and flank for signs of previous chest or abdominal procedures, the presence of which may influence incision placement. For instance, the lower lumbosacral spine can be well exposed via a right retroperitoneal approach for reoperation at similar disc level, or if there has been prior abdominal surgery with a lower quadrant incision. Lastly, it is wise to anticipate significant anterior spinal scarring with an increased incidence of complications if the procedure is done in the setting of discitis, previous posterior spinal surgery, or if the exposure is one disc level proximal or distal to one that has been previously exposed.

Fortunately, the overwhelming majority of patients needing anterior spine exposure are relatively healthy and do not require any other preoperative testing except as mentioned previously. However, older patients may need preoperative cardiac stress testing or pulmonary function studies, particularly if the procedure requires thoracic spine exposure. It is also paramount to counsel patients regarding the complications of this vascular exposure, which include injury to vasculature, bowel or ureter, deep venous thrombosis, surgical site infection, hematoma, seroma, lymphedema, vein stenosis, incisional hernia, nerve injury, and retrograde ejaculation.

Surgical Treatment

It is beyond the scope of this chapter to discuss the indications for and contraindications to interbody fusion from the perspective of spine surgeons. Rarely the vascular surgeon may advise against surgery if the patient is morbidly obese, or has a history of multiple prior abdominal surgeries, dense aortoiliac calcification, acute/subacute iliofemoral deep vein thrombosis, or solitary kidney. A consistent finding across studies is that morbid obesity is associated with an increased risk of complications, and in these unusual cases, the risks of surgery may exceed the benefits until significant weight loss has been addressed.

Operative Planning and Surgical Exposure Options

Anterior spine exposure for interbody fusion is performed with the patient in either the supine or lateral decubitus position, depending upon disc level(s) of interest. Sometimes, the patient is proned intraoperatively to combine anterior fixation with posterior fixation (i.e. circumferential fixation). In the majority of procedures, the disc space(s) of interest is exposed by dissection and mobilization of the overlying vessels from left to right across the midline via a left thoracotomy for thoracic spine procedures or via the left retroperitoneal space for lumbosacral spine procedures. No single approach lends itself to all circumstances; therefore, it is wise to become comfortable with the relationship of the target disc level(s) to overlying skin and bony structures such as ribs, costal margin, and anterior superior iliac spine. Further, an appropriately placed incision will minimize soft tissue dissection and extent of vessel mobilization. Palpation of pedal pulses before and after the procedure is also prudent because temporary arterial retraction that accompanies disc exposure and spinal instrumentation may result in arterial injury and thrombosis.

Thoracic Spine Exposure

Thoracic spine exposure requires the least amount of vessel dissection because the interbody implants are designed to be placed from a more lateral position, unlike lumbosacral spine exposures in which the implants are usually positioned from a true anterior approach. Therefore, a left (occasionally right) thoracotomy with the lung deflated is employed for thoracic spine procedures. Very proximal thoracic spine procedures that involve disc pathology from T1 to T3 are usually approached posteriorly except in unusual circumstances that may require medial claviculectomy or mini-sternotomy. A right thoracotomy facilitates T3 to T6 exposure, and a left thoracotomy is utilized for procedures that involve T7 to T12 disc pathology. It is also possible to obtain spine exposure through the L2 vertebra from a low thoracotomy if needed.

Thoracolumbar (T12–L2), lumbar (L2–L5), and lumbosacral (L5–S1) spine exposures necessitate more extensive mobilization of major abdominal and pelvic vessels and risk injury to other vital structures within the operative field. Various surgical approaches including open retroperitoneal, laparoscopic transperitoneal, endoscopic retroperitoneal, and endoscopic lateral trans-psoas have been used for anterior interbody fusion to minimize vessel dissection and surgical morbidity without compromising anterior spine exposure. No matter the approach, the key advantages of anterior spine exposure are direct access to and superb visualization of the intervertebral disc level of surgical interest.

Lumbosacral Spine Exposure

The surgical approach for anterior interbody fusion of the lumbosacral spine can pass either through the abdominal cavity or outside the peritoneal contents in an extraperitoneal plane of dissection (see Ch. 56 , Abdominal Vascular Exposures). Abdominal approaches include transperitoneal, transperitoneal laparoscopic, and anterior retroperitoneal.

Transperitoneal exposure

Transperitoneal lumbosacral spine exposure requires extensive mobilization of the midgut and hindgut out of the operative field. This can be a demanding exercise, particularly in obese patients or in those who have dense adhesions as a result of a prior abdominal procedure or inflammatory process. Furthermore, the transperitoneal approach is associated with prolonged postoperative ileus, third-space fluid sequestration, and an increased risk of retrograde ejaculation in male patients.

Transperitoneal laparoscopic exposure

Transperitoneal laparoscopic interbody spine fusion has been evaluated as a method to minimize abdominal wall vascular and urologic complications. However, studies have shown that the approach offers minimal to no benefit above open anterior retroperitoneal exposure. ^, In a prospective, nonrandomized study that directly compared laparoscopic L4–L5 interbody fusion to an open approach, there was no difference in operating time, blood loss, or length of hospital stay for single-level fusions. However, for multi-level fusions, laparoscopic procedures took 25 minutes longer and were associated with more complications. For 16% of patients the laparoscopic approach offered inadequate spine exposure. Many of the perceived advantages of a laparoscopic approach have not been realized in clinical practice and vascular anatomy variability significantly limits its applicability. Another minimally invasive technique, the endoscopic lateral trans-psoas approach, does minimize vessel dissection, but similarly has poor postoperative outcomes with an increased risk of groin/thigh numbness and pain from manipulation of the genitofemoral nerve coursing along the psoas muscle.

Anterior retroperitoneal exposure

Despite a working knowledge of laparoscopic techniques, the open approach via anterior retroperitoneal lumbosacral spine exposure is favored. Open anterior retroperitoneal approach for lumbosacral spine exposure has advantages similar to those that have been described for retroperitoneal aortoiliac vascular procedures. Single-level or multilevel disc exposure can be performed in an expeditious manner with minimal intraoperative complications. Vital structures can be thoroughly mobilized out of harm’s way to facilitate complete discectomy and, in theory, better interbody fusion.

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