Chapter 84
Operative Exposure for Spinal Reconstructive Surgery
Jeffrey L. Ballard, Gregory D. Carlson
Anterior lumbar interbody fusion (ALIF) was first described by Carpenter1 in 1932 and promoted by Hogson and Stock2 in 1956 for definitive treatment of more anteriorly oriented spine pathology and to avoid posterior element injury. The originally described procedure, which required significant operative exposure and was considered to be quite invasive, has undergone a number of modifications that have minimized the extent of required surgical exposure. These surgical modifications have made the anterior approach to the lumbosacral (ALIF) as well as the thoracic (anterior thoracic interbody fusion [ATIF]) spine a widely accepted technique for spinal arthrodesis.
Anterior spine exposure for interbody fusion, performed with the patient in either supine or lateral decubitus position depending upon disk level(s) of interest, is usually combined with supplemental posterior fixation with the patient prone to increase the rate of complete spinal fusion. A number of different implants are used to effect anterior interbody fusion (AIF); however, description of them is beyond the scope of this chapter. Advantages of AIF from the orthopedic perspective include preservation of posterior elements, decreased incidence of nerve injury, and avoidance of epidural scarring.3 From the vascular surgeon’s perspective, the key to successful AIF is to provide the spine surgeon with adequate surgical exposure so that diskectomy, decompression, and partial corpectomy (if needed) can be safely performed from vertebra side-to-side and so that implants can be accurately inserted on the basis of the center of the disk space.
AIF for lumbosacral (LS) spine pathology was originally performed through an open retroperitoneal exposure with a large incision, extensive tissue manipulation, and significant patient morbidty.3 This retroperitoneal approach for ALIF takes advantage of the potential space between the peritoneal contents and kidney and the quadratus lumbar and psoas muscles to afford excellent anterior lumbosacral spine exposure. Other surgical approaches, such as mini–open retroperitoneal, endoscopic retroperitoneal, and endoscopic lateral transpsoas, have also been used to capitalize on the retroperitoneal approach but to minimize surgical morbidity without compromising anterior spine exposure.3–18 Laparoscopic transperitoneal spine exposure also has it proponents.6,8,9,11 However, all the previously mentioned surgical approaches eventually necessitate dissection and mobilization of the thoracic aorta, abdominal aorta, and/or iliac arteries with accompanying major venous structures depending on the disk level(s) of interest.
Notwithstanding the potential for major arterial or venous injury that could occur during anterior spine exposure, there is also the potential for significant injury to other vulnerable structures that are encountered during spine exposures.4 Recognition of these possible complications has been the impetus for most centers of excellence to develop a two-team (vascular surgery plus either orthopedic surgery or neurosurgery) approach to minimize morbidity and to maximize optimal operative exposure for reconstructive spinal surgery. This chapter further explores the multifaceted world of anterior spine exposure from a vascular surgeon’s perspective.
Clinical Presentation, Diagnostic Evaluation, and Risk Assessment
In contrast to the characteristic patient with atherosclerotic disease that a vascular surgeon encounters, the patient needing anterior spine exposure is often younger, has few to no risk factors for peripheral arterial disease (PAD), and, not infrequently, is overweight due to inactivity. The patient often has associated radiculopathy, a long-standing pain syndrome that may be managed by many different specialists, and many have had a traumatic work-related injury. In short, the typical patient requiring AIF presents with a number of complicating issues that are not related to peripheral arterial disease.
Lumbosacral spine exposure involves extensive mobilization of major arteries within the abdomen/pelvis as well as their accompanying major veins; therefore, a history of claudication or any abnormality in the peripheral pulse findings should be first evaluated by noninvasive testing. Occasionally, further invasive testing such as arteriography and/or computed tomography is required for severe aortoiliac occlusive disease or aortic aneurysmal disease. Significant aortoiliac artery calcification can be problematic regarding placement of retractors and increases the potential risk of arterial injury or dissection. Extent of arterial calcification can be evaluated with plain radiographs or computed tomography if this diagnosis is suggested by noninvasive testing results. The bottom line here is to have an accurate assessment of peripheral pulses prior to surgery because temporary vessel occlusion is part and parcel of mini–open retroperitoneal anterior spine exposure.
Besides a thorough peripheral pulse examination, it is wise to examine the patient’s thorax, abdomen, and flank for signs of previous chest or abdominal procedures, presence of which may influence subsequent incision placement. For instance, the lower lumbosacral spine can be well exposed via a right retroperitoneal approach if the procedure is a “redo” on, if the adjacent proximal or distal disk level will now be exposed, or if there has been prior abdominal surgery with incisions in the left upper or lower quadrant. In our experience, patients undergoing ALIF (particularly the younger ones) are often focused on incision position and length; therefore it is prudent to discuss the proposed incision prior to surgery because omission of this minor detail can be very problematic for both surgeon and patient in the postoperative period. Incision length may need to be extended to facilitate adequate spine exposure if there is significant calcific atherosclerotic disease or when the patient has a large body habitus.
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. Needless to say, it is paramount to thoroughly discuss possible complications of surgery with the patient, including but not limited to major artery/vein injury, bowel or ureter injury, deep venous thrombosis, wound infection/seroma, nerve injury, and erectile dysfunction (usually retrograde ejaculation as opposed to impotence) due to disruption of the intermesenteric nerve plexus and superior hypogastric nerve plexus, which course over the left common iliac artery origin.4 Lastly, it is wise to note that there is often significant anterior spinal scarring with an increased incidence of complications if the procedure is done in the setting of infection of previous posterior laminectomy or if the exposure is one disk level proximal or distal to one that has been previously exposed.
Surgical Treatment
It is beyond the scope of this chapter to discuss the indications for and contraindications to ALIF and ATIF from an orthopedic perspective, and in this clinical setting, the vascular surgeon must rely upon the expertise of the orthopedic colleague to ensure that surgical indications are sound. Rarely have we advised against surgery after a thorough orthopedic and vascular preoperative assessment except in the occasional case of a grossly morbidly obese patient. In these unusual cases the risks of surgery far exceed the benefits until significant weight loss has been addressed. Nonetheless, we do have significant experience with successful AIF even in patients with body mass index (BMI) higher than 30. The following paragraphs discuss operative planning, options, and relevant surgical anatomy, describe various spine level exposures, and explore results and complications of anterior spine exposure.
Operative Planning and Surgical Exposure Options
In the majority of procedures the disk space(s) of operative interest are 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 disk level(s) to overlying skin and bony structures such as ribs, costal margin, and anterior superior iliac spine, because the 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 occlusion often accompanies disk exposure and spinal instrumentation.
Once the disk level or levels of interest are fully exposed, we have found it wise to remain present in the operating room to assist the orthopedic surgeon with diskectomy and spinal fusion. Major vascular injuries typically occur when sharp curettes, rongeurs, drill bits, and so on, are being used. Prompt, potentially life-saving, vessel repair can be performed only if the vascular surgeon remains close at hand. Finally, and particularly in teaching institutions, thoracic and retroperitoneal exposure of major arterial and venous structures provides an excellent opportunity for vascular surgery residents to obtain open surgical training and to learn how to safely and effectively manipulate blood vessels.
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 in lumbosacral spine exposures, in which the implants are usually positioned from a true anterior approach. Therefore, a mini-open left or, occasionally, right, thoracotomy with the lung deflated is commonly employed for procedures that are limited to the thoracic spine. Very proximal thoracic spine procedures that involve disk pathology from T1 to T3 are usually approached posteriorly except in unusual circumstances that may require medial claviculectomy or mini-sternotomy. This chapter does not discuss these uncommon cases. A limited right thoracotomy facilitates spine access and exposure from T3 to T6, and a limited left thoracotomy is usually utilized for procedures that involve disk pathology from T7 to T12, although one can also obtain spine exposure through the L2 vertebra from a low thoracotomy if needed. These exposures are further discussed in subsequent paragraphs.
Thoracolumbar (T12-L2), lumbar (L2-L5), and lumbosacral (L5-S1) spine exposures necessitate more extensive mobilization of major abdominal and pelvic vessels and risks injury to other vital structures within the operative field.4 Various surgical approaches including mini–open retroperitoneal, laparoscopic transperitoneal, endoscopic retroperitoneal, and endoscopic lateral transpsoas have been used for ALIF to minimize vessel dissection and surgical morbidity without compromising anterior spine exposure.4–18 No matter the approach, the key advantages of anterior spine exposure, which are explored further in this chapter, are direct access to and superb visualization of the intervertebral disk level of surgical interest.
Lumbosacral Spine Exposure
The surgical approach for ALIF can pass either through the abdominal cavity or outside the peritoneal contents in an extraperitoneal plane of dissection.
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.6,12–15 Sasso et al15 found a tenfold higher risk of retrograde ejaculation when they compared transperitoneal with retroperitoneal L4 to S1 spine exposure. Mini–open anterior retroperitoneal lumbosacral spine exposure has advantages similar to those that have been described for retroperitoneal aortoiliac vascular procedures.19 This is particularly true in regards to length of hospital stay, postoperative ileus, and perioperative complications.
Transperitoneal Laparoscopic Exposure.
Transperitoneal laparoscopic interbody spine fusion has been evaluated as a method to minimize open surgical morbidity and potential abdominal wall complications.6,8,9,16 Katkhouda et al16 compared the safety and efficacy of the laparoscopic approach for single- and multilevel degenerative disk procedures. Twenty-four consecutive laparoscopic transperitoneal interbody lumbar fusions were evaluated prospectively (18 single-level procedures were compared with 6 multilevel procedures). Results of the laparoscopic multilevel procedures were further compared with those of 12 mini-open multilevel operations. Twenty of 24 procedures were completed laparoscopically. Four procedures were converted to open procedures to control bleeding from an iliac vein laceration in three patients and a mesenteric tear in the fourth. Overall results were decidedly worse for multilevel laparoscopic procedures than those in the matched open group.
Another prospective, nonrandomized study directly compared laparoscopic with open mini–anterior L4 to L5 retroperitoneal lumbar interbody fusion in 50 consecutive patients.8 Twenty-five patients underwent anterior laparoscopic interbody fusion, and 25 had open mini-ALIF. There was no statistical difference in operating time, blood loss, or length of hospital stay between the two groups for single-level fusions. However, laparoscopic procedures took 25 minutes longer (P = 0.035) than open procedures for multilevel fusions. The rate of complications was significantly higher in the laparoscopic group (20% vs. 4%), and in 16% of patients undergoing laparoscopic surgery there was inadequate spine exposure. Other writers have commented that the perceived advantages of a laparoscopic approach do not pan out in clinical practice and that variability in vascular anatomy significantly limits its applicability.6–9 Finally, the endoscopic lateral transpsoas approach does minimize vessel dissection but has increased risk of groin/thigh numbness and pain from manipulation of the genitofemoral nerve coursing along the psoas muscle.5
Anterior Retroperitoneal Exposure.
Despite a working knowledge of laparoscopic techniques, we continue to favor open mini-ALIF via anterior retroperitoneal lumbosacral spine exposure, if possible, for the following reasons. Our current experience demonstrates few overall complications for this approach in comparison with other spine exposure techniques.18 Single-level or multilevel disk 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 diskectomy and, in theory, better interbody fusion. Finally, the surgical approaches described in the following paragraphs facilitate the spine surgeons’ need to have direct anterior access to the lumbosacral spine.
Relevant Surgical Anatomy
Thoracic Spine Exposure
Patient positioning for exposure of the thoracic spine is similar to the position that is often used for open thoracoabdominal aortic aneurysm repair.20 After central venous and radial arterial line placement and dual-lumen endotracheal intubation, the patient is placed in a right or left lateral decubitus position, with the hips perpendicular to the floor. A beanbag device is helpful to support the patient’s position on the operating table, and the patient’s flank should be positioned over the kidney rest. The free upper extremity can be passed across the upper chest and supported on a cushioned Mayo stand. Care should be taken to ensure that padding of the lower extremities is appropriate and that there is no external pressure on the feet or that the feet are severely plantar flexed. Transcranial motor evoked potential (TCMEP) monitoring and somatosensory evoked potential (SSEP) monitoring of the posterior tibial nerve, with the ulnar nerve as control, is used for all of our spine procedures.
The rib interspace to be entered after the lung is deflated depends primarily on the extent of thoracic spine that is to be exposed, and there is no need to divide the costal margin in the vast majority of cases. In general, the best operating exposure for the spine surgeon is afforded by entering the chest two intercostal levels proximal to the disk level of interest. We occasionally remove the lower rib to facilitate access at multiple disk levels and then morselize the rib for use as bone graft during the procedure. However, removal of the rib facilitates spine visualization at the potential cost of increased postoperative pain, which can be relieved with a multilevel intercostal block. Intraoperative fluoroscopy is vital to identify the appropriate disk space(s) and to limit the extent of surgical dissection. For proximal thoracic spine exposure via a right thoracotomy, incision of the parietal pleura along the lateral aspect of the thoracic vertebra and limited division of ipsilateral intercostal arteries/veins facilitates anterior exposure of the disk space(s) as needed. Venous tributaries coursing into the azygos vein should be divided as needed to prevent injury and troublesome bleeding. These maneuvers are generally all that is needed for proximal thoracic spine exposure, and it is in the rare circumstance that one would encounter the esophagus or the vagus nerve, which courses parallel and medial to the azygos vein in the proximal chest.
From the left side, for mid-to-distal anterior thoracic spine exposure, the approach is similar to that already described, except that the descending thoracic aorta is encountered as one dissects across the anterior surface of the thoracic vertebra and disk space. After limited division of ipsilateral intercostal arteries/veins, the descending thoracic aorta can be retracted medially with Omni-Tract (Integra Lifesciences, Minneapolis, Minn) renal vein retractors to minimize the risk of arterial injury. Preservation of the blood supply to the spinal cord is critical; therefore, it is wise to ligate intercostal arteries close to the aorta to preserve potential collateral vessels. Brockstein and associates21 have stressed the importance of the arteria radicularis magna (artery of Adamkiewicz) in providing circulation to the anterior spinal artery. This vessel is a branch of either a distal intercostal or a proximal lumbar artery. It has been identified as proximal as T5 and as distal as L4.21 However, the artery generally arises between the T8 and L1 vertebral levels. Therefore, it is unwise to ligate any large intercostal or proximal lumbar artery unless it is absolutely necessary to do so for adequate disk space exposure. Finally, the diaphragm can be divided in a limited fashion just lateral to its central tendinous portion to extend the dissection distally to facilitate exposure through the L1 to L2 disk space. Alternatively, these disk spaces can be exposed from the chest by “hooking” the central tendinous portion of the diaphragm with a renal vein retractor, pulling caudad, and performing very limited dissection of the diaphragmatic attachments to the proximal lumbar vertebral bodies.
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