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Exposure Issues in Lumbar Disc Replacement Surgery
Exposure Issues in Lumbar Disc Replacement Surgery Salvador A. Brau, MD, FACS Total lumbar disc replacement must be performed through an anterior approach to the spine. As there are numerous other sources that describe techniques of anterior lumbar exposures, this article focuses on the incidence of significant complications that are to be expected in these operations. Some recommendations are made as to how to possibly avoid or reduce these complications. Preoperative evaluation is important in determining which patients present a greater risk. Intraoperative techniques will be described that help reduce the incidence of these complications. Methods of making an early diagnosis will also be discussed, as well as tactics for managing intraoperative complications. Finally, recommendations are made for reducing and managing problems encountered during revision surgery. Semin Spine Surg 18:72-77 © 2006 Elsevier Inc. All rights reserved. KEYWORDS: lumbar arthroplasty, vascular injury, retrograde ejaculation, ureteral injury, revision strategies
A
pproaches for anterior arthrodesis and arthroplasty are well described,1-5 but the approach for lumbar total disc replacement (TDR) requires wider exposure than the traditional approach for anterior lumbar interbody fusion (ALIF). The inherently greater retraction of the vascular structures is obliged by the true anterior line of approach inherent to the insertion technique of most lumbar disc prostheses. Many ALIF techniques may be performed without either full or straight anterior access. This wider exposure may result in an increase in vascular complications, especially when approaching L4-5, where better than 90% of all vascular injuries have been reported to occur.6 More careful planning and significant experience on the part of the access surgeon are, therefore, necessary if complications are to be avoided.
Preoperative Evaluation As usual, clinical evaluation of the patient is important. Tactile evaluation of the pedal pulses in all patients is mandatory regardless of age. Once confirmed, the location of both the posterior tibial and the dorsalis pedis pulses should be clearly
Spine Access Surgery Associates; Keck School of Medicine–University of Southern California; Geffen School of Medicine–UCLA, Los Angeles, CA. Address reprint requests to Salvador A. Brau, MD, Spine Access Surgery Associates, 1334 Westwood Boulevard, Suite 1D, Los Angeles, CA 90024. E-mail: [email protected].
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1040-7383/06/$-see front matter © 2006 Elsevier Inc. All rights reserved. doi:10.1053/j.semss.2006.03.008
marked for later reference. Should the left pedal pulse diminish or be lost during or after the operation, it is important to know that this pulse was present and clinically normal before the start of the operation, because if it was, then the only reason for a deficit would be a clot or an intimal flap resulting from retraction of the left iliac artery during the procedure. If the pulse is abnormal preoperatively, then the patient needs a vascular evaluation to identify the problem before any lumbar TDR surgery. A judgment would then need to be made as to whether the patient remains a suitable candidate for a disc replacement, or anterior surgery at all. Knowledge of any comorbidities and body mass index is also important as these may increase the likelihood of intraoperative complications. From the standpoint of imaging, the first and perhaps the most important data come from evaluation of the lateral films of the lumbar spine. These radiographs are valuable for three reasons. First, they will show calcifications of the iliac arteries and aorta, which may require more careful mobilization of the vessels and may actually preclude the deployment of an artificial disc. In such cases, an attempt at arthroplasty is prudent as long as an alternative requiring lesser exposure, such as arthrodesis with femoral ring allograft, is presented to the patient beforehand. Second, these films will show any osteophytic activity surrounding the target disc(s), which indicates that there will be more dense inflammatory reaction and fibrosis in the area, making the dissection of the vessels much more difficult. Third, they will show the relationship between the L4-5 disc and the iliac crest as well as the angles
Exposures in lumbar disc replacement surgery
Figure 1 This lateral film of the lumbar spine shows a calcified aorta, osteophytes, and the relationship between the iliac crest and the L4-5 disc space as well as the angles of L5-S1 and L4-5. These findings are helpful in assessing anterior exposure issues and preoperative planning.
of the discs, especially at L5-S1, which will help in determining the exact placement of the incision (Fig. 1). Imaging studies of the vessels, such as radial, color-coded CT scans, and magnetic resonance angiograms (MRA), have not been shown to be helpful in primary cases and are perhaps more valuable in revision surgery. The only other preoperative activity that is important is good communication between the spine and the access surgeon to make sure that all the above steps have been performed and that both are aware of any potential problems.
Intraoperative Techniques to Reduce Complications Arterial The incidence of left iliac artery thrombosis (LIAT) has been shown to be low (0.45%) in a large series of patients, but the sequelae can be catastrophic.6 Early diagnosis is, therefore, of utmost importance if these sequelae are to be avoided. LIAT is a clinical diagnosis more so than a radiological one. If the pedal pulse was normal before surgery, then the only reason for its absence or weakness postoperatively is LIAT or an intimal flap. Pulse evaluation, both iliac and pedal, is mandatory before closing the abdominal incision. In addition, the use of the pulse oxymeter in the toes of the left foot has been shown to be a most sensitive and reliable method of early diagnosis.7 The oxygen saturation value (SaO2) observed before the operation starts should return to that baseline value once the retractors are removed. If the SaO2 does not return to that
73 value, even though it may only be off by a few points, then further evaluation is needed before taking the patient out of the operating room. Segmental arterial pressures using Doppler can be measured in the legs to see if there is a deficit on the left side as compared with the right. In addition, since the patient is already on a radiograph table, an intraoperative angiogram can be performed by the access surgeon. A deficit in the SaO2 alone, however, is indication enough for the access surgeon to attempt a thrombectomy before the patient leaves the operating room. This can be done preferably through the abdominal incision but alternatively through a small left femoral incision. It is not recommended that the patient be sent out of the operating room for an angiogram in the radiograph department. This will only result in unnecessary delays that will increase the time of ischemia, which may result in a compartment syndrome with its associated set of additional complications. Although the etiology of LIAT may be multifactorial, undue stretch of the iliac artery is certainly important while compression of the artery seems to be relatively well tolerated.7 To reduce the incidence of LIAT, it is important to mobilize the left iliac artery far distally toward the femoral canal. This is done quite easily with blunt dissection, since the artery has no significant branches. The result is a reduction of stretch on the artery when retracting it to the right to expose the L4-5 disc space. After retraction is in place, the artery must still be “loose.” If it is tight, then it may be stretched too much and this may cause intimal damage that, although microscopic, will result in release of cytokines that create a thrombogenic situation. In some cases, even after good mobilization, the artery is still too tight, so division of the segmental vessels overlying L4 will be necessary to further reduce the tension by allowing the aorta to move farther to the right. LIAT must be treated by immediate thrombectomy, which should correct the problem in the majority of cases. Delay must be avoided at all costs because younger patients with normal arterial systems do not tolerate ischemia well and may develop significant complications, such as compartment syndrome, after only 2 to 4 hours of ischemia. Return of the SaO2 to baseline values is enough evidence that the thrombectomy has been successful, although intraoperative angiography, an angioscope, or ultrasonography may also be used to document that no further clot remains. If thrombectomy fails, it is because there is an intimal flap or disrupted, previously unrecognized plaque. Both of these require intraoperative angiography to evaluate and treat by open surgical repair, endarterectomy, or stenting. In some cases, bypass surgery may be required to restore the circulation to the left lower extremity. Arterial lacerations are extremely rare and can only be avoided by careful use of sharp instruments such as scalpels, curettes, and drills while preparing the disc space. These lacerations must be repaired with sutures regardless of size and location.
Venous Venous lacerations, on the other hand, are somewhat more common (1.4%).6 To help avoid them, it is important to
S.A. Brau
74 control the ileolumbar vein while exposing L4-5. This vein should be tied, at least proximally, and not just controlled with clips, since the clips have been known to fall off with dire consequences. Although these veins vary in location and number, they can always be found caudal to the L4-5 disc. So if the disc is identified radiographically first, the vein(s), if present, will be found inferior to it, usually coursing posteriorly along the side of the L5 vertebral body. Bear in mind that the branch may arise from the back of the common iliac vein, so it may not be readily apparent. Sometimes this vein dives deeply and in controlling it the lumbosacral plexus can be found near it. Care must be exercised to avoid injury to the extraspinal nerve structures, as with retractors, monopolar cautery, or the like. It is also important to know ahead of time, as indicated by the presence of osteophytes on the radiographs, that the separation of the left common iliac vein from the anterior surface of the spine will be more difficult and may even require sharp dissection. When encountering a situation with increased inflammation and fibrosis, the mobilization of the vein will be more tedious and dangerous and must be performed with extreme care so as not to avulse it while trying to separate it from the prevertebral fascia. In the author’s opinion, the use of sharp-pointed retractors, such as a Hohmann retractor and/or Steinman pins, is best avoided, since during insertion and removal they have been known to cause injury to the vessels. In addition, even while deployed, these retractors tend to create “dead” intervals along the vessels’ path that may create a thrombogenic situation by preventing flow in either direction. They also leave more of the vessels exposed to injury while disc space preparation is going on. More rounded retractors that actually engage the side of the disc space, such as the anterior lumbar access surgery (ALAS) retractor blades (Thompson Surgical Instruments, Inc., Traverse City, MI), offer better protection of the vessels with a more stable retraction system and can be used with any of the available table-held retractor systems. Many, but not all, venous lacerations need to be repaired with sutures. Even relatively large lacerations of 5 to 6 mm in length can be controlled by use of hemostatic agents because this is a low-pressure system. This is especially so in cases where the defect is in a hard to reach area, such as in the inferior wall and toward the right, that may require further mobilization of the vessels and further damage to the already injured vessel with even greater blood loss. Although the bleeding may be profuse, packing the area with dry hemostatic agents and applying pressure for 5 to 7 minutes usually gets the bleeding to stop. If repair becomes necessary, a helpful maneuver is to apply pressure manually or with gauze pads and then release the pressure near the end of the laceration in a rolling motion and grab the edges of the vein with an Allis clamp. This is repeated progressively until the entire laceration is controlled by the Allis clamps and repair can then proceed. Another maneuver is to use sponge sticks to obtain proximal and distal control and then proceed with repair. In nearly all cases, venous lacerations can be controlled without the need to obtain proximal and distal control
of the injured vessel itself. In rare cases, where massive amounts of blood loss are foreseen and the patient is already unstable, it is acceptable to pack the area of the damage to control the bleeding and then ligate the injured vein. Most commonly this would mean tying off the left common iliac vein. It is also possible however to expose proximally and distally to tie off the inferior vena cava and both common iliac veins. This may seem extreme, but it is relatively well tolerated and may be used in a patient salvage situation. Thankfully, the majority of experience with such measures derives from managing life-threatening hemorrhage after penetrating trauma. Repair of the common iliac vein with sutures may increase the incidence of ileofemoral venous thrombosis postoperatively, so anticoagulation may be necessary. Low molecular weight heparin once a day or mini-heparin twice a day may be used initially followed by antiplatelet agents, such as Plavix, for 6 to 8 weeks. In TDR cases the heparin may be started as early as 4 to 8 hours after completion of the procedure and certainly within 24 hours. However, as one can imagine, the potential for a clinically significant epidural hematoma rises with the use of anticoagulants. Thus the patient must be carefully and frequently evaluated during the first 24 to 48 hours postoperatively. Additionally, the spinal surgeon and vascular surgeon should discuss whether and how large of an initial heparin bolus is to be used under the circumstances. Following such interventions, it would be wise to advise the patient and family members of the circumstances, measures taken, and the steps being taken to manage the incremental risks incurred. The author’s own incidence of clinically apparent deep venous thrombosis (DVT) is about 1% in a series of over 2000 arthrodesis and arthroplasty patients, which is surprising, considering the amount of handling and mobilization of the left iliac vein during exposure. DVT prophylaxis, however, remains important and should be performed in all cases. The use of anti-embolism stockings and sequential pressure devices together with early ambulation are important. Prophylactic anticoagulation is used by some, although it does not appear to be a standard for all cases.
Retrograde Ejaculation This much talked about complication in males is largely preventable once it is clear to the surgeon performing the exposure what the exact anatomic location of the superior hypogastric plexus is in the live patient. Graphic depictions and cadaveric dissections are really not very helpful in this and have actually led to the notion that it is better to approach the L5-S1 level from the right to reduce the incidence. In reality, in a large series of close to 1000 male patients undergoing anterior lumbar surgery, the incidence was 0 regardless of the side used for the approach.8 The most important concept to grasp is that the superior hypogastric plexus, much like the ureter, runs with the peritoneum and can be easily elevated from the avascular retroperitoneal plane when the peritoneum is separated anteriorly from the promontory. To do this, you must first identify the iliac artery and start elevating
Exposures in lumbar disc replacement surgery
75 logical consultation be obtained in the operating room for appropriate management. Most injuries can be treated by stenting, which requires placement by cystoscopy, and this can be done before the patient leaves the operating room.
Bowel Injury One reason that the retroperitoneal approach should be used for all cases of TDR is that it virtually eliminates the incidence of bowel injury, which can be catastrophic and which has been known to occur when the spine is exposed via the trans-peritoneal route. In addition, the incidence of ileus is also quite low with the retroperitoneal route. Peritoneal defects noted during the retroperitoneal approach are usually best repaired at the end of the procedure and in some cases need not be repaired at all if closure of the posterior rectus sheath results in adequate sealing of the defect.
Revision Strategies Figure 2 Sympathetic fibers of the superior hypogastric plexus are seen running within the peritoneal sac just above the left iliac vein and are easily elevated from this vessel with careful blunt dissection.
the peritoneum away from it bluntly, with a Kittner or peanut sponge, to expose the iliac vein more medially (Fig. 2). Dissection continues toward the midline, again separating the peritoneum from this vein to expose the promontory and the middle sacral vessels. At this point, the fibers of the plexus can be seen, in all but the most obese patients, traversing inferiorly, as a crow’s foot, within the peritoneum that is being elevated (Figs. 3 and 4). This elevation of the peritoneum continues toward the opposite side until that side of the disc has been exposed. A retractor can then be placed on that side, protecting these fibers and keeping them out of harm’s way. The middle sacral vessels can then be ligated and further exposure of the L5-S1 disc can be performed without fear as long as the retractor remains in place, protecting the nerve fibers from injury (Figs. 5 and 6). These maneuvers should result in a very low incidence of retrograde ejaculation regardless of the side used for the approach.
Revision strategies is a topic of much discussion at present because of the recent approval of the first artificial disc for general use in the United States. Spine and access surgeons who have faced the need to perform revision anterior lumbar surgeries, or who have experience with debridement for infections, fully appreciate the morbidity and mortality issues
Ureteral Injuries Ureteral injuries are rare and mostly associated with revision cases. In primary cases, it is best to allow the ureter to retract with the peritoneum as this structure is elevated away from the retroperitoneal plane. Although occasionally tempting, it is best not to separate the ureter from the peritoneum, keeping it on the left side because this may lead to devascularization with resulting necrosis of a segment. It is also advisable to use Bovie tips that are shielded to prevent arcing that may inadvertently injure the ureter. There is one area of danger, while working on L5-S1, where, between the inferior and right-sided retractors, there is a gap that exposes the ureter to injury while devices are being deployed. Careful observation and awareness of the presence of the ureter in that area will help prevent injury. For any ureteral injury that is discovered during anterior lumbar surgery it is recommended that uro-
Figure 3 Further dissection shows the peritoneal sac more elevated from the vessels and the promontory and middle sacral vessels are now visible. The sympathetic fibers continue to be mobilized with the peritoneum toward the opposite side.
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S.A. Brau
Figure 4 The fibers seen previously are now safely behind the retractor and an additional sympathetic fiber is seen beyond the middle sacral vessels. Further dissection will also elevate this fiber away from the promontory and preserve it from injury.
Figure 5 That additional sympathetic fiber from Fig. 4 has been elevated and is now seen running with the peritoneum as it is being pushed further to the opposite side. The middle sacral vessels have been cauterized and the L5-S1 disc is almost completely exposed.
associated with the need to reposition or remove a disc prosthesis. However, when circumstances leave the treating team and the patient with no reasonable alternative, there are a number of general recommendations that apply to all revisions, while there are specific recommendations that depend on the prior route utilized.9
iliac artery that is otherwise unrecognizable due to scarring and fibrosis. Compression of tissues that result in a drop in saturation will help in this regard. To be forewarned is to be forearmed. Thus having balloon thrombectomy catheters at hand will be helpful in obtaining emergency control of a bleeding area. Percutaneous angioplasty balloons and coated endovascular stents should also be available for rapid deployment via the femoral route, which means that both groins should be prepped and properly draped should the need for these devices arise. In the revision situation ureteral stents should be placed at the outset both to help locate the ureters and to identify any ureteral damage. The stents do not necessarily reduce the incidence of ureteral injury, but they will certainly help identify and repair one if it occurs. Finally, the anesthesia team must be made aware of the potential for sudden and dire amounts of bleeding. Adequate venous access must be in place, along with sufficient blood products available. It almost goes without saying that a “cell
General Recommendations Knowledge of the path taken in the prior approach as well as the device used is extremely important. It is not always obvious what approach was used by just looking at the skin incision. One should also have the correct instruments on hand for extracting the device. The time elapsed since the previous surgery must be known. After 7 to 10 days it may no longer be possible to use the same incision for a revision. In such cases, the retroperitoneal tissues have been found already fused, making it impossible to reopen the retroperitoneal space without entering the peritoneal cavity. Prior operative reports should be obtained and old imaging studies should be evaluated together with new ones. Vascular imaging may be of much greater value than in primary cases. CT angiography, color-coded scanning, and magnetic resonance angiograms and venograms may help identify vessel displacements that may influence decisions on how to remobilize these vessels. This is especially true if there has been anterior extrusion of a core or the entire device at L4-5, where impingement of the vessels may be a factor. When this is the case, a venogram is the study of choice, as it will show the level of obstruction and it will demonstrate the presence of thrombus below such obstruction. If thrombus is detected, an inferior vena cava filter must be inserted before revision to protect the patient against pulmonary embolization once the obstruction is relieved. Use of the pulse oxymeter in the left foot is even more important than in primary cases as it may help localize an
Figure 6 The L5-S1 disc is now fully exposed and the sympathetic plexus is tucked safely behind the retractor that has been engaged on the side of the disc space.
Exposures in lumbar disc replacement surgery saver” should be used in all cases, unless the surgery is being done for an infected device.
Specific Tactical Recommendations by Surgical Level For return to L5-S1 use the opposite retroperitoneal route to the one used before. The use of the right-sided retroperitoneal approach to L5-S1 for primary cases is gaining in popularity because it may make it easier then to go back to L4- at a later date should that become necessary. The trans-peritoneal route is also useful for revisions of L5-S1. This is the least dangerous of all the levels when it comes to revision yet you must still be extremely careful with the left common iliac vein, which is covered in fibrous tissue, is difficult to identify, and is firmly adherent to the promontory. For return to L4-5 you may use the trans-peritoneal approach or a more lateral approach than the one used for the primary procedure. This is the most difficult level to revise for two reasons. There is no longer a plane between the iliac vessels and the anterior surface of the spine, but more importantly, the fibrosis encases the vessels themselves, making them inelastic and subject to laceration on any attempt at mobilization toward the right side. Only very experienced access surgeons should attempt revisions at this level, and then, with great trepidation. For return to L3-4 also use a more lateral approach than the one used previously or go trans-peritoneal. This revision is less dangerous than L4-5 because at this level we are no longer dealing with the iliac vessels as much and the aorta is normally further to the right. Be sure, however, to watch out for stretch on the iliac vessels once the aorta gets pushed to the right to expose the disc space. This could result in intimal damage with a resulting LIAT.
Conclusions Anterior lumbar surgery requires knowledge of and respect for the potential vascular and other complications inherent to the operations. Thorough awareness of these issues, detailed understanding of the surgical anatomy, and collaboration with experienced colleagues are essential to reduce the incidence of complications and to successfully manage them when (not if) they arise. Primary lumbar disc replacements
77 can be performed quickly and efficiently with very few complications once the surgical team has gotten over the learning curve of these procedures and feels comfortable with their ability to expose the spine satisfactorily. The tips presented in this article should be helpful in that regard. The unfortunate reality of the advent of widespread lumbar disc replacement surgery is that some portion of these devices will either displace or fail. For obvious reasons, anterior revisions are best avoided and should be reserved for when there is no other alternative and the device needs to be removed or repositioned. These operations are among the most difficult that a vascular surgeon will attempt and thorough knowledge of the retroperitoneal area and experience with retroperitoneal approaches are of great importance for success. Great patience is necessary because progress will be very slow. Judgment is crucial, especially when it comes to the determination that going any further could do more harm than good. There are times when the procedure needs to be terminated if continuing means increasing the chances that life-threatening massive bleeding may occur.
Acknowledgment Figures 2 to 6 were made possible by an educational grant from Synthes Spine USA, West Chester, PA.
References 1. Mayer HM: Minimally Invasive Spine Surgery—A Surgical Manual. Munich, Springer, 2000 2. Buttner-Janz K: Surgical approach, in Buttner-Janz K, Hochschuler SH, McAfee PC (eds): The Artificial Disk. Berlin, Springer Verlag, 2003 3. Watkins RW (ed): Surgical Approaches to the Spine (ed 2). St. Louis, Springer-Verlag, 2004 4. Brau SA: Anterior approach to the lumbar spine, in Guyer RD, Ziegler JE (eds): Spinal Arthroplasty—A New Era in Spine Care. St. Louis, MO, Quality Medical Publishers, Inc., 2005 5. Brau SA: Mini-open approach to the lumbar spine for anterior lumbar interbody fusion: description of the procedure, results and complications. Spine J 2:216-223, 2002 6. Brau SA, Delamarter RB, Schiffman ML, et al: Vascular injury during anterior lumbar surgery. Spine J 4:409-412, 2004 7. Brau SA, Spoonamore MJ, Snyder L, et al: Nerve monitoring changes related to iliac artery compression during anterior lumbar spine surgery. Spine J 3:351-355, 2003 8. Brau SA: Approach related complications, in Salvage Strategies for Disc Arthroplasty Symposium: Proceedings of the 20th Annual Meeting of the North American Spine Society, Sept 28, 2005, Philadelphia, PA 9. Brau SA: Revision strategies in anterior lumbar surgery, in McAfee P, Geisler FH, Scott-Young M (eds): Complications and Revision Strategies in Lumbar Spine Arthroplasty, Roundtables in Spine Surgery, St. Louis, MO, Quality Medical Publishers, Inc., 2005
A
pproaches for anterior arthrodesis and arthroplasty are well described,1-5 but the approach for lumbar total disc replacement (TDR) requires wider exposure than the traditional approach for anterior lumbar interbody fusion (ALIF). The inherently greater retraction of the vascular structures is obliged by the true anterior line of approach inherent to the insertion technique of most lumbar disc prostheses. Many ALIF techniques may be performed without either full or straight anterior access. This wider exposure may result in an increase in vascular complications, especially when approaching L4-5, where better than 90% of all vascular injuries have been reported to occur.6 More careful planning and significant experience on the part of the access surgeon are, therefore, necessary if complications are to be avoided.
Preoperative Evaluation As usual, clinical evaluation of the patient is important. Tactile evaluation of the pedal pulses in all patients is mandatory regardless of age. Once confirmed, the location of both the posterior tibial and the dorsalis pedis pulses should be clearly
Spine Access Surgery Associates; Keck School of Medicine–University of Southern California; Geffen School of Medicine–UCLA, Los Angeles, CA. Address reprint requests to Salvador A. Brau, MD, Spine Access Surgery Associates, 1334 Westwood Boulevard, Suite 1D, Los Angeles, CA 90024. E-mail: [email protected].
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1040-7383/06/$-see front matter © 2006 Elsevier Inc. All rights reserved. doi:10.1053/j.semss.2006.03.008
marked for later reference. Should the left pedal pulse diminish or be lost during or after the operation, it is important to know that this pulse was present and clinically normal before the start of the operation, because if it was, then the only reason for a deficit would be a clot or an intimal flap resulting from retraction of the left iliac artery during the procedure. If the pulse is abnormal preoperatively, then the patient needs a vascular evaluation to identify the problem before any lumbar TDR surgery. A judgment would then need to be made as to whether the patient remains a suitable candidate for a disc replacement, or anterior surgery at all. Knowledge of any comorbidities and body mass index is also important as these may increase the likelihood of intraoperative complications. From the standpoint of imaging, the first and perhaps the most important data come from evaluation of the lateral films of the lumbar spine. These radiographs are valuable for three reasons. First, they will show calcifications of the iliac arteries and aorta, which may require more careful mobilization of the vessels and may actually preclude the deployment of an artificial disc. In such cases, an attempt at arthroplasty is prudent as long as an alternative requiring lesser exposure, such as arthrodesis with femoral ring allograft, is presented to the patient beforehand. Second, these films will show any osteophytic activity surrounding the target disc(s), which indicates that there will be more dense inflammatory reaction and fibrosis in the area, making the dissection of the vessels much more difficult. Third, they will show the relationship between the L4-5 disc and the iliac crest as well as the angles
Exposures in lumbar disc replacement surgery
Figure 1 This lateral film of the lumbar spine shows a calcified aorta, osteophytes, and the relationship between the iliac crest and the L4-5 disc space as well as the angles of L5-S1 and L4-5. These findings are helpful in assessing anterior exposure issues and preoperative planning.
of the discs, especially at L5-S1, which will help in determining the exact placement of the incision (Fig. 1). Imaging studies of the vessels, such as radial, color-coded CT scans, and magnetic resonance angiograms (MRA), have not been shown to be helpful in primary cases and are perhaps more valuable in revision surgery. The only other preoperative activity that is important is good communication between the spine and the access surgeon to make sure that all the above steps have been performed and that both are aware of any potential problems.
Intraoperative Techniques to Reduce Complications Arterial The incidence of left iliac artery thrombosis (LIAT) has been shown to be low (0.45%) in a large series of patients, but the sequelae can be catastrophic.6 Early diagnosis is, therefore, of utmost importance if these sequelae are to be avoided. LIAT is a clinical diagnosis more so than a radiological one. If the pedal pulse was normal before surgery, then the only reason for its absence or weakness postoperatively is LIAT or an intimal flap. Pulse evaluation, both iliac and pedal, is mandatory before closing the abdominal incision. In addition, the use of the pulse oxymeter in the toes of the left foot has been shown to be a most sensitive and reliable method of early diagnosis.7 The oxygen saturation value (SaO2) observed before the operation starts should return to that baseline value once the retractors are removed. If the SaO2 does not return to that
73 value, even though it may only be off by a few points, then further evaluation is needed before taking the patient out of the operating room. Segmental arterial pressures using Doppler can be measured in the legs to see if there is a deficit on the left side as compared with the right. In addition, since the patient is already on a radiograph table, an intraoperative angiogram can be performed by the access surgeon. A deficit in the SaO2 alone, however, is indication enough for the access surgeon to attempt a thrombectomy before the patient leaves the operating room. This can be done preferably through the abdominal incision but alternatively through a small left femoral incision. It is not recommended that the patient be sent out of the operating room for an angiogram in the radiograph department. This will only result in unnecessary delays that will increase the time of ischemia, which may result in a compartment syndrome with its associated set of additional complications. Although the etiology of LIAT may be multifactorial, undue stretch of the iliac artery is certainly important while compression of the artery seems to be relatively well tolerated.7 To reduce the incidence of LIAT, it is important to mobilize the left iliac artery far distally toward the femoral canal. This is done quite easily with blunt dissection, since the artery has no significant branches. The result is a reduction of stretch on the artery when retracting it to the right to expose the L4-5 disc space. After retraction is in place, the artery must still be “loose.” If it is tight, then it may be stretched too much and this may cause intimal damage that, although microscopic, will result in release of cytokines that create a thrombogenic situation. In some cases, even after good mobilization, the artery is still too tight, so division of the segmental vessels overlying L4 will be necessary to further reduce the tension by allowing the aorta to move farther to the right. LIAT must be treated by immediate thrombectomy, which should correct the problem in the majority of cases. Delay must be avoided at all costs because younger patients with normal arterial systems do not tolerate ischemia well and may develop significant complications, such as compartment syndrome, after only 2 to 4 hours of ischemia. Return of the SaO2 to baseline values is enough evidence that the thrombectomy has been successful, although intraoperative angiography, an angioscope, or ultrasonography may also be used to document that no further clot remains. If thrombectomy fails, it is because there is an intimal flap or disrupted, previously unrecognized plaque. Both of these require intraoperative angiography to evaluate and treat by open surgical repair, endarterectomy, or stenting. In some cases, bypass surgery may be required to restore the circulation to the left lower extremity. Arterial lacerations are extremely rare and can only be avoided by careful use of sharp instruments such as scalpels, curettes, and drills while preparing the disc space. These lacerations must be repaired with sutures regardless of size and location.
Venous Venous lacerations, on the other hand, are somewhat more common (1.4%).6 To help avoid them, it is important to
S.A. Brau
74 control the ileolumbar vein while exposing L4-5. This vein should be tied, at least proximally, and not just controlled with clips, since the clips have been known to fall off with dire consequences. Although these veins vary in location and number, they can always be found caudal to the L4-5 disc. So if the disc is identified radiographically first, the vein(s), if present, will be found inferior to it, usually coursing posteriorly along the side of the L5 vertebral body. Bear in mind that the branch may arise from the back of the common iliac vein, so it may not be readily apparent. Sometimes this vein dives deeply and in controlling it the lumbosacral plexus can be found near it. Care must be exercised to avoid injury to the extraspinal nerve structures, as with retractors, monopolar cautery, or the like. It is also important to know ahead of time, as indicated by the presence of osteophytes on the radiographs, that the separation of the left common iliac vein from the anterior surface of the spine will be more difficult and may even require sharp dissection. When encountering a situation with increased inflammation and fibrosis, the mobilization of the vein will be more tedious and dangerous and must be performed with extreme care so as not to avulse it while trying to separate it from the prevertebral fascia. In the author’s opinion, the use of sharp-pointed retractors, such as a Hohmann retractor and/or Steinman pins, is best avoided, since during insertion and removal they have been known to cause injury to the vessels. In addition, even while deployed, these retractors tend to create “dead” intervals along the vessels’ path that may create a thrombogenic situation by preventing flow in either direction. They also leave more of the vessels exposed to injury while disc space preparation is going on. More rounded retractors that actually engage the side of the disc space, such as the anterior lumbar access surgery (ALAS) retractor blades (Thompson Surgical Instruments, Inc., Traverse City, MI), offer better protection of the vessels with a more stable retraction system and can be used with any of the available table-held retractor systems. Many, but not all, venous lacerations need to be repaired with sutures. Even relatively large lacerations of 5 to 6 mm in length can be controlled by use of hemostatic agents because this is a low-pressure system. This is especially so in cases where the defect is in a hard to reach area, such as in the inferior wall and toward the right, that may require further mobilization of the vessels and further damage to the already injured vessel with even greater blood loss. Although the bleeding may be profuse, packing the area with dry hemostatic agents and applying pressure for 5 to 7 minutes usually gets the bleeding to stop. If repair becomes necessary, a helpful maneuver is to apply pressure manually or with gauze pads and then release the pressure near the end of the laceration in a rolling motion and grab the edges of the vein with an Allis clamp. This is repeated progressively until the entire laceration is controlled by the Allis clamps and repair can then proceed. Another maneuver is to use sponge sticks to obtain proximal and distal control and then proceed with repair. In nearly all cases, venous lacerations can be controlled without the need to obtain proximal and distal control
of the injured vessel itself. In rare cases, where massive amounts of blood loss are foreseen and the patient is already unstable, it is acceptable to pack the area of the damage to control the bleeding and then ligate the injured vein. Most commonly this would mean tying off the left common iliac vein. It is also possible however to expose proximally and distally to tie off the inferior vena cava and both common iliac veins. This may seem extreme, but it is relatively well tolerated and may be used in a patient salvage situation. Thankfully, the majority of experience with such measures derives from managing life-threatening hemorrhage after penetrating trauma. Repair of the common iliac vein with sutures may increase the incidence of ileofemoral venous thrombosis postoperatively, so anticoagulation may be necessary. Low molecular weight heparin once a day or mini-heparin twice a day may be used initially followed by antiplatelet agents, such as Plavix, for 6 to 8 weeks. In TDR cases the heparin may be started as early as 4 to 8 hours after completion of the procedure and certainly within 24 hours. However, as one can imagine, the potential for a clinically significant epidural hematoma rises with the use of anticoagulants. Thus the patient must be carefully and frequently evaluated during the first 24 to 48 hours postoperatively. Additionally, the spinal surgeon and vascular surgeon should discuss whether and how large of an initial heparin bolus is to be used under the circumstances. Following such interventions, it would be wise to advise the patient and family members of the circumstances, measures taken, and the steps being taken to manage the incremental risks incurred. The author’s own incidence of clinically apparent deep venous thrombosis (DVT) is about 1% in a series of over 2000 arthrodesis and arthroplasty patients, which is surprising, considering the amount of handling and mobilization of the left iliac vein during exposure. DVT prophylaxis, however, remains important and should be performed in all cases. The use of anti-embolism stockings and sequential pressure devices together with early ambulation are important. Prophylactic anticoagulation is used by some, although it does not appear to be a standard for all cases.
Retrograde Ejaculation This much talked about complication in males is largely preventable once it is clear to the surgeon performing the exposure what the exact anatomic location of the superior hypogastric plexus is in the live patient. Graphic depictions and cadaveric dissections are really not very helpful in this and have actually led to the notion that it is better to approach the L5-S1 level from the right to reduce the incidence. In reality, in a large series of close to 1000 male patients undergoing anterior lumbar surgery, the incidence was 0 regardless of the side used for the approach.8 The most important concept to grasp is that the superior hypogastric plexus, much like the ureter, runs with the peritoneum and can be easily elevated from the avascular retroperitoneal plane when the peritoneum is separated anteriorly from the promontory. To do this, you must first identify the iliac artery and start elevating
Exposures in lumbar disc replacement surgery
75 logical consultation be obtained in the operating room for appropriate management. Most injuries can be treated by stenting, which requires placement by cystoscopy, and this can be done before the patient leaves the operating room.
Bowel Injury One reason that the retroperitoneal approach should be used for all cases of TDR is that it virtually eliminates the incidence of bowel injury, which can be catastrophic and which has been known to occur when the spine is exposed via the trans-peritoneal route. In addition, the incidence of ileus is also quite low with the retroperitoneal route. Peritoneal defects noted during the retroperitoneal approach are usually best repaired at the end of the procedure and in some cases need not be repaired at all if closure of the posterior rectus sheath results in adequate sealing of the defect.
Revision Strategies Figure 2 Sympathetic fibers of the superior hypogastric plexus are seen running within the peritoneal sac just above the left iliac vein and are easily elevated from this vessel with careful blunt dissection.
the peritoneum away from it bluntly, with a Kittner or peanut sponge, to expose the iliac vein more medially (Fig. 2). Dissection continues toward the midline, again separating the peritoneum from this vein to expose the promontory and the middle sacral vessels. At this point, the fibers of the plexus can be seen, in all but the most obese patients, traversing inferiorly, as a crow’s foot, within the peritoneum that is being elevated (Figs. 3 and 4). This elevation of the peritoneum continues toward the opposite side until that side of the disc has been exposed. A retractor can then be placed on that side, protecting these fibers and keeping them out of harm’s way. The middle sacral vessels can then be ligated and further exposure of the L5-S1 disc can be performed without fear as long as the retractor remains in place, protecting the nerve fibers from injury (Figs. 5 and 6). These maneuvers should result in a very low incidence of retrograde ejaculation regardless of the side used for the approach.
Revision strategies is a topic of much discussion at present because of the recent approval of the first artificial disc for general use in the United States. Spine and access surgeons who have faced the need to perform revision anterior lumbar surgeries, or who have experience with debridement for infections, fully appreciate the morbidity and mortality issues
Ureteral Injuries Ureteral injuries are rare and mostly associated with revision cases. In primary cases, it is best to allow the ureter to retract with the peritoneum as this structure is elevated away from the retroperitoneal plane. Although occasionally tempting, it is best not to separate the ureter from the peritoneum, keeping it on the left side because this may lead to devascularization with resulting necrosis of a segment. It is also advisable to use Bovie tips that are shielded to prevent arcing that may inadvertently injure the ureter. There is one area of danger, while working on L5-S1, where, between the inferior and right-sided retractors, there is a gap that exposes the ureter to injury while devices are being deployed. Careful observation and awareness of the presence of the ureter in that area will help prevent injury. For any ureteral injury that is discovered during anterior lumbar surgery it is recommended that uro-
Figure 3 Further dissection shows the peritoneal sac more elevated from the vessels and the promontory and middle sacral vessels are now visible. The sympathetic fibers continue to be mobilized with the peritoneum toward the opposite side.
76
S.A. Brau
Figure 4 The fibers seen previously are now safely behind the retractor and an additional sympathetic fiber is seen beyond the middle sacral vessels. Further dissection will also elevate this fiber away from the promontory and preserve it from injury.
Figure 5 That additional sympathetic fiber from Fig. 4 has been elevated and is now seen running with the peritoneum as it is being pushed further to the opposite side. The middle sacral vessels have been cauterized and the L5-S1 disc is almost completely exposed.
associated with the need to reposition or remove a disc prosthesis. However, when circumstances leave the treating team and the patient with no reasonable alternative, there are a number of general recommendations that apply to all revisions, while there are specific recommendations that depend on the prior route utilized.9
iliac artery that is otherwise unrecognizable due to scarring and fibrosis. Compression of tissues that result in a drop in saturation will help in this regard. To be forewarned is to be forearmed. Thus having balloon thrombectomy catheters at hand will be helpful in obtaining emergency control of a bleeding area. Percutaneous angioplasty balloons and coated endovascular stents should also be available for rapid deployment via the femoral route, which means that both groins should be prepped and properly draped should the need for these devices arise. In the revision situation ureteral stents should be placed at the outset both to help locate the ureters and to identify any ureteral damage. The stents do not necessarily reduce the incidence of ureteral injury, but they will certainly help identify and repair one if it occurs. Finally, the anesthesia team must be made aware of the potential for sudden and dire amounts of bleeding. Adequate venous access must be in place, along with sufficient blood products available. It almost goes without saying that a “cell
General Recommendations Knowledge of the path taken in the prior approach as well as the device used is extremely important. It is not always obvious what approach was used by just looking at the skin incision. One should also have the correct instruments on hand for extracting the device. The time elapsed since the previous surgery must be known. After 7 to 10 days it may no longer be possible to use the same incision for a revision. In such cases, the retroperitoneal tissues have been found already fused, making it impossible to reopen the retroperitoneal space without entering the peritoneal cavity. Prior operative reports should be obtained and old imaging studies should be evaluated together with new ones. Vascular imaging may be of much greater value than in primary cases. CT angiography, color-coded scanning, and magnetic resonance angiograms and venograms may help identify vessel displacements that may influence decisions on how to remobilize these vessels. This is especially true if there has been anterior extrusion of a core or the entire device at L4-5, where impingement of the vessels may be a factor. When this is the case, a venogram is the study of choice, as it will show the level of obstruction and it will demonstrate the presence of thrombus below such obstruction. If thrombus is detected, an inferior vena cava filter must be inserted before revision to protect the patient against pulmonary embolization once the obstruction is relieved. Use of the pulse oxymeter in the left foot is even more important than in primary cases as it may help localize an
Figure 6 The L5-S1 disc is now fully exposed and the sympathetic plexus is tucked safely behind the retractor that has been engaged on the side of the disc space.
Exposures in lumbar disc replacement surgery saver” should be used in all cases, unless the surgery is being done for an infected device.
Specific Tactical Recommendations by Surgical Level For return to L5-S1 use the opposite retroperitoneal route to the one used before. The use of the right-sided retroperitoneal approach to L5-S1 for primary cases is gaining in popularity because it may make it easier then to go back to L4- at a later date should that become necessary. The trans-peritoneal route is also useful for revisions of L5-S1. This is the least dangerous of all the levels when it comes to revision yet you must still be extremely careful with the left common iliac vein, which is covered in fibrous tissue, is difficult to identify, and is firmly adherent to the promontory. For return to L4-5 you may use the trans-peritoneal approach or a more lateral approach than the one used for the primary procedure. This is the most difficult level to revise for two reasons. There is no longer a plane between the iliac vessels and the anterior surface of the spine, but more importantly, the fibrosis encases the vessels themselves, making them inelastic and subject to laceration on any attempt at mobilization toward the right side. Only very experienced access surgeons should attempt revisions at this level, and then, with great trepidation. For return to L3-4 also use a more lateral approach than the one used previously or go trans-peritoneal. This revision is less dangerous than L4-5 because at this level we are no longer dealing with the iliac vessels as much and the aorta is normally further to the right. Be sure, however, to watch out for stretch on the iliac vessels once the aorta gets pushed to the right to expose the disc space. This could result in intimal damage with a resulting LIAT.
Conclusions Anterior lumbar surgery requires knowledge of and respect for the potential vascular and other complications inherent to the operations. Thorough awareness of these issues, detailed understanding of the surgical anatomy, and collaboration with experienced colleagues are essential to reduce the incidence of complications and to successfully manage them when (not if) they arise. Primary lumbar disc replacements
77 can be performed quickly and efficiently with very few complications once the surgical team has gotten over the learning curve of these procedures and feels comfortable with their ability to expose the spine satisfactorily. The tips presented in this article should be helpful in that regard. The unfortunate reality of the advent of widespread lumbar disc replacement surgery is that some portion of these devices will either displace or fail. For obvious reasons, anterior revisions are best avoided and should be reserved for when there is no other alternative and the device needs to be removed or repositioned. These operations are among the most difficult that a vascular surgeon will attempt and thorough knowledge of the retroperitoneal area and experience with retroperitoneal approaches are of great importance for success. Great patience is necessary because progress will be very slow. Judgment is crucial, especially when it comes to the determination that going any further could do more harm than good. There are times when the procedure needs to be terminated if continuing means increasing the chances that life-threatening massive bleeding may occur.
Acknowledgment Figures 2 to 6 were made possible by an educational grant from Synthes Spine USA, West Chester, PA.
References 1. Mayer HM: Minimally Invasive Spine Surgery—A Surgical Manual. Munich, Springer, 2000 2. Buttner-Janz K: Surgical approach, in Buttner-Janz K, Hochschuler SH, McAfee PC (eds): The Artificial Disk. Berlin, Springer Verlag, 2003 3. Watkins RW (ed): Surgical Approaches to the Spine (ed 2). St. Louis, Springer-Verlag, 2004 4. Brau SA: Anterior approach to the lumbar spine, in Guyer RD, Ziegler JE (eds): Spinal Arthroplasty—A New Era in Spine Care. St. Louis, MO, Quality Medical Publishers, Inc., 2005 5. Brau SA: Mini-open approach to the lumbar spine for anterior lumbar interbody fusion: description of the procedure, results and complications. Spine J 2:216-223, 2002 6. Brau SA, Delamarter RB, Schiffman ML, et al: Vascular injury during anterior lumbar surgery. Spine J 4:409-412, 2004 7. Brau SA, Spoonamore MJ, Snyder L, et al: Nerve monitoring changes related to iliac artery compression during anterior lumbar spine surgery. Spine J 3:351-355, 2003 8. Brau SA: Approach related complications, in Salvage Strategies for Disc Arthroplasty Symposium: Proceedings of the 20th Annual Meeting of the North American Spine Society, Sept 28, 2005, Philadelphia, PA 9. Brau SA: Revision strategies in anterior lumbar surgery, in McAfee P, Geisler FH, Scott-Young M (eds): Complications and Revision Strategies in Lumbar Spine Arthroplasty, Roundtables in Spine Surgery, St. Louis, MO, Quality Medical Publishers, Inc., 2005