Anterior Lumbar Interbody Fusion

Indications

Since its original description in 1932,¹ anterior lumbar interbody fusion (ALIF) has been used to address:

• Low-grade spondylolisthesis
• Degenerative disc disease
• Failed posterior spinal fusion

ALIF has also been used in combination with posterior procedures to enhance fusion rates and correct deformity.

Biologic and mechanical advantages inherent to an ALIF procedure include compressive forces transmitted along the anterior column combined with the large cross sectional area and excellent blood supply provided by the vertebral endplates.

Preoperative Planning

Prior to proceeding with ALIF, the surgeon must consider a number of approach- and patient-related factors:

• Coordination with an access surgeon, if needed, for assistance mobilizing the great vessels and maintaining hemostasis until the operative level is visualized and addressed
• Review of magnetic resonance imaging (MRI) to help determine the level of bifurcation of the aorta and iliac vessels, which may assist in planning an anterior approach
• Thorough surgical history
  • Abdominal adhesions and scar tissue may render an anterior approach more difficult
  • Prior vascular surgery may make vessels more friable and difficult to retract
• Gender differences: Males and females need to be counseled differently, as men are at an increased risk for retrograde ejaculation, which has been reported between 1% and 6% in the literature.²

Positioning

The patient is placed in a supine position under general anesthesia. Prior to preparation of the operative field, the intended levels are localized using lateral fluoroscopy to help delineate the incision, as well as the area to include in the sterile surgical field. A nasogastric or orogastric tube is generally placed to help decompress the stomach. It is often helpful to place a lumbar “bump” to exaggerate lumbar lordosis and assist with positioning and access to the caudal lordotic segments.

Approach

The approach used for ALIF procedures can either be transperitoneal or retroperitoneal. The transperitoneal approach has a higher rate of associated retrograde ejaculation,² is more commonly associated with postoperative ileus, and is more difficult in patients who have had prior abdominal surgeries. Therefore, the retroperitoneal approach is more commonly employed.¹³

A left-sided approach is preferred in most cases because the arterial structures can more easily withstand retraction and mobilization than the venous structures encountered with a right-sided approach. Generally, a longitudinal incision is made halfway between the umbilicus and lateral border of the rectus sheath at the level identified by preoperative fluoroscopy. The lateral border of the rectus musculature is identified and retracted medially. Temporary paralysis may be helpful throughout the course of the exposure in order to help retract the rectus musculature.

Once identified, the posterior rectus sheath is divided in-line with the skin incision. The retroperitoneal space is then dissected bluntly to the psoas muscle. Upon encountering the psoas muscle, one should ensure that the ureter is mobilized and protected along with the other peritoneal contents.

The vessels are then identified by palpation and mobilized.

• For L5-S1 procedures, the middle sacral artery should be identified and ligated as the great vessels have bifurcated above the operative site.
• For procedures involving the L4-5 disc space, the common iliac artery and vein must be mobilized in a right to left direction. Prior to mobilization of the common iliac vein, the iliolumbar vein must be identified and ligated in order to avoid unintentional rupture or avulsion. The left-sided L4 segmental vessels may also need to be ligated prior to immobilization.
• For procedures at the L3-4 disc space, the segmental left-sided segmental vessels at L3 and L4 should be identified and ligated prior to mobilization of the aorta and inferior vena cava.

A self-retaining retractor should be used to secure the vessels and abdominal contents in a safe position throughout the remainder of the procedure. Once these structures are secured, the intended disc space is identified and confirmed via intraoperative fluoroscopy.

Techniques

After the disc space is confirmed, a box annulotomy is made in the anterior annulus from the superior to inferior endplate. A Cobb elevator is then placed between the superior endplate and disc, as well as between the disc and the inferior endplate, to remove any residual attachments and allow removal of a large portion of the disc in a single piece. The remainder of the nucleus is removed using a combination of curettes, kerrison and pituitary rongeurs. Unless a neural decompression is necessary, the posterior and lateral portions of the annulus fibrosus should be maintained to help stabilize and compress the implanted interbody device.

After completion of the discectomy, the cartilaginous portion of the endplate is removed with curettes. At this point, care should be taken to preserve the cortical portion of the endplatel removal significantly decreases failure load and stiffness, drastically increasing the propensity for subsidence of the implant.³ In cases where disc space collapse impedes proper preparation and implant insertion, laminar spreaders or commercially available distraction instruments may be used to increase the intervertebral distance.

Once disc space preparation is complete, trials are inserted and viewed under fluoroscopy to determine the implant size necessary to restore the desired intervertebral height and lordosis. The implant is filled with the surgeon’s preferred bone graft or graft substitute and gently malleted into position. The position of the implant is then confirmed via lateral fluoroscopy (Figures 1a-b). A low-profile plate may be used to buttress the interbody implant, augment stability and prevent anterior extrusion.

Figures 1a-b. Anteroposterior (a) and lateral (b) radiographs demonstrating acceptable positioning of an interbody spacer and anterior plate.

The rectus sheath is then closed with a running suture. The subcutaneous layer is closed with absorbable interrupted sutures, and the superficial layer is closed with a subcuticular running suture or staples.

Pearls and Pitfalls

• Due to lumbar lordosis, incisions for approaches to the L4-5 and L5-S1 disc space will likely be just inferior to the level localized on fluoroscopy to ensure adequate access to the disc (Figure 2).

Figure 2. Lateral radiograph localizing the incision for a L5-S1 ALIF procedure. The incision is based just inferior to allow adequate access to the disc space.

• Temporary paralysis may assist in mobilizing the rectus musculature during the exposure.
• In cases of severe intervertebral collapse, the adjacent disc space may be used to template for the ideal sized interbody implant.

Postoperative Care

The patient is encouraged to mobilize as tolerated postoperatively. In some cases, an abdominal binder or lumbar corset may assist in patient comfort. The patient’s diet should be slowly progressed as bowel function returns to avoid postoperative ileus. However, most surgeons will allow advancement to a full regular diet the night of surgery. Early ambulation and sequential compression devices are employed for deep venous thrombosis prophylaxis.

Outcome

Fusion rates with ALIF procedures employing modern devices/interbody implants have been reported between 87% and 100% depending on the implant and grafting substance used.^5-8 More importantly, significant improvement has been demonstrated in clinically validated objective outcomes measures in patients up to 6.5 years after surgery.⁹

Complications

Of the known complications associated with ALIF, vascular injury is likely the most feared. The incidence of vascular injury has been correlated with inflammatory conditions involving the anterior spinal elements and operative level. Additionally, older patients with a tenuous vena cava and revision abdominal approaches are viewed with a heightened awareness for potential complications.

In cases where a vascular complication occurs, damage to a venous structure is more common than an arterial injury because the vessel wall is not as durable as the arterial system. The reported incidence of major intraoperative venous injury is usually less than 4%; the left common iliac vein is the most frequently injured vessel.¹⁰ Arterial injury is encountered much less frequently, with a reported incidence of 0.45%; the left iliac artery is the most commonly affected.¹¹ In most cases, either common hemostasis agents or direct repair allow control of intraoperative vascular injury.

Visceral injury is another complication associated with ALIF. Among the most frequent visceral injuries reported are ureteral injuries, peritoneal tears, and bowel injuries. Though associated rates of these complications vary throughout reports in the literature, each is relatively uncommon but should be considered both intraoperatively and postoperatively.

Retrograde ejaculation results from injury to the superior hypogastric plexus. Risk factors associated with this complication include use of monopolar electrocautery, revision surgery, and the transperitoneal approach. In a review of male patients undergoing ALIF, Sasso reported an incidence of retrograde ejaculation of 1.7% in patients undergoing a retroperitoneal approach, compared with a 13.3% rate in a group undergoing a transperitoneal approach.² Regardless of the approach, male patients with fertility concerns should be counseled on this associated risk prior to surgery.

Postoperatively, deep venous thrombosis (DVT) is a complication that has been reported in 1.6% of anterior lumbar cases.¹² The development of a DVT, likely related to the retraction placed on the mobilized veins intraoperatively, increases concern for pulmonary embolism given the proximal location of the thrombus. Efforts to minimize this complication should center on gentle mobilization and retraction of vessels intraoperatively, combined with early ambulation and the use of sequential compression devices postoperatively.

A final commonly reported complication with ALIF procedures is ileus. The reported incidence of ileus ranges from 0.6% to 5.6% in these cases, and has been associated with the transperitoneal approach, postoperative narcotic use, and previous intra-abdominal procedures.^10,13 Conservative advancement in diet, frequent ambulation, judicious use of narcotics, and nasogastric tube placement are each beneficial in preventing and treating postoperative ileus formation.

References

1. Carpenter N. Spondylolisthesis. Br J Surg 1932;19:374-386.
2. Sasso RC, Burkus KJ, LeHuec JC. Retrograde Ejaculation After Anterior Lumbar Interbody Fusion: Transperitoneal Versus Retroperitoneal Exposure. Spine. 2003;28:1023-1026.
3.  Oxland TR, Grant JP, Dvorak MF, Fisher CG. Effects of endplate removal on the structural properties of the lower lumbar vertebral bodies. Spine. 2003;28:771-777.
4. Burkus JK, Sandhu HS, Gornet MF, et al. Use of rhBMP-2 in Combination with Structural  Cortical Allografts: Clinical and Radiographic Outcomes in Anterior Lumbar Spinal Surgery. J Bone Joint Surg Am. 2005;87:1205-1212.
5. Cheung KM, Zhang YG, Lu DS, Luk KD, Leong JC. Reduction of disc space distraction after anterior lumbar interbody fusion with autologous iliac crest graft. Eur Spine J. 1996;5(5):299-307.
6. Choi JY, Sung KH. Subsidence after anterior lumbar interbody fusion using paired stand-alone rectangular cages. Eur Spine J. 2006 Jan;15(1):16-22. Epub 2005 Apr 21.
7. Pavlov PW, Meijers H, van Limbeek J, et al. Good outcome and restoration of lordosis after anterior lumbar interbody fusion with additional posterior fixation. Orthop Clin North Am. 2004 Jan;35(1):25-32.
8. Sasso RC, Kitchel SH, Dawson EG. A prospective, randomized controlled clinical trial of anterior lumbar interbody fusion using a titanium cylindrical threaded fusion device. Spine J. 2003 Jul-Aug;3(4):289-93.
9. Pfeiffer M, Griss P, Haake M, Kienapfel H, Billion M. Standardized evaluation of long-term results after anterior lumbar interbody fusion. Eur Spine J. 1996;5(5):299-307.
10. Czerwein JK, Thakur N, Miglori SJ, Lucas P, Palumbo M. Complications of Anterior Lumbar Surgery.  J Am Acad Orthop Surg 2011;19:251-258.
11. Brau SA, Delamarter RB, Schiffman ML, Williams LA, Watkins RG: Vascular injury during anterior lumbar surgery. Spine J 2004;4(4):409-412.
12. Baker JK, Reardon PR, Reardon MJ, Heggeness MH: Vascular injury in anterior lumbar surgery. Spine (Phila Pa 1976) 1993;18(15):2227-2230.
13. Santos ER, Pinto MR, Lonstein JE, et al: Revision lumbar arthrodesis for the treatment of lumbar cage pseudoarthro- sis: Complications. J Spinal Disord Tech 2008;21(6):418-421.