Revision lumbar surgery is a technically challenging operation that requires careful planning and patient selection. In the case of previous interbody fusion, there are particular considerations the surgeon needs to address when planning a revision operation, such as the approach taken at the index surgery. Compared with posterolateral fusions, interbody fusions may be more challenging, as a more complicated dissection involving the thecal sac and nerves may be required owing to cage migration or the need to remove the cage from within the disk space. Indications for revision of interbody fusion include, but are not limited to excessive graft subsidence, pseudoarthrosis, graft extrusion, and infection. Factors that need to be taken into account include type of interbody cage used, spinal levels involved, presence or absence of bony fusion, and presence or absence of posterior supplementation. In this chapter, we review the various interbody fusion techniques, potential complications requiring revision, and treatment options.
Interbody Fusion Techniques
Posterior Lumbar Interbody Fusion and Transforaminal Lumbar Interbody Fusion
Posterior lumbar interbody fusion (PLIF) and transforaminal lumbar interbody fusion (TLIF) are widely accepted procedures for achieving interbody arthrodesis. They use either a direct posterior (PLIF) or a posterolateral (TLIF) approach to enter the disk space. TLIF most commonly involves a unilateral approach via the foramen with insertion of a single oblique or banana-shaped cage. Some surgeons utilize a bilateral approach with placement of two cages obliquely. PLIF traditionally involves a wide laminectomy and at least partial facetectomies with orthogonal placement of a cage on each side of the vertebral disk spaces. Because of the posterolateral approach used in TLIF, less dural sac and exiting nerve root retraction is necessary than in PLIF. These procedures can be performed with a traditional open or minimally invasive approach.
Graft extrusion after PLIF or TLIF has been widely reported in the literature, with an incidence ranging from 0.35% to 6% ( Fig. 21.1 ). Bakhsheshian et al . reported their series of 513 patients undergoing minimally invasive TLIF and found 5 cases of graft extrusion. Of these 5 cases, 2 patients were asymptomatic and did not require surgery. Three patients had evidence of neurologic decline and underwent revision surgery. Similarly, Zhao et al. reported their series of 512 patients undergoing mini-open TLIF, with 6 patients having graft extrusion. They reported that small cages, rectangular cage shape, and multi-level procedures increased the risk of cage extrusion. Furthermore, the presence of linear endplates as opposed to concave presented a higher likelihood of extrusion. Other studies have reported similar risk factors.
Currently no direct comparative studies are investigating the rates of graft extrusion in open TLIF versus minimally invasive TLIF. Several studies have examined the relationship between unilateral versus bilateral pedicle screw fixation in TLIF. Although the data are not yet conclusive, it does appear that there may be a higher rate of cage migration in patients with unilateral pedicle screw fixation, suggesting that bilateral screws provide greater stability to the graft.
Lateral Lumbar Interbody Fusion
Lateral lumbar interbody fusion (LLIF) is a technique that was first described in 2006 by Ozgur et al., although variations of this technique have existed prior to that report. This procedure classically involves a retroperitoneal transpsoas approach to access the disk space orthogonally. It has been an increasingly popular technique that offers the advantages of a less-invasive approach with minimal blood loss, as well as providing an alternative means of achieving a more robust diskectomy with placement of a larger cage than with PLIF or TLIF. LLIF has been utilized both in a stand-alone fashion, as well as with posterior pedicle screw fixation or lateral plate fixation.
Overall reported rates of graft extrusion in LLIF have been low ( Fig. 21.2 ), although there are several case reports in the literature. However, larger case series describe graft subsidence to be a bigger complication of LLIF. Le et al. reported a 14.3% rate of radiographic subsidence and a 2.1% rate of clinical subsidence in a group of 140 LLIF patients, and noted that increasing construct length was associated with higher subsidence rates. Many cases of reported subsidence did require revision surgery, although the nature of the surgery has been inconsistently reported. In addition, the definition of subsidence has varied among authors. Several studies report associated vertebral body fractures. Owing to the heterogeneity of subsidence, some studies advocate conservative management, whereas other authors advocate for either placement of posterior instrumentation in cases with stand-alone cages, or supplementation with vertebroplasty/kyphoplasty in cases of vertebral body fracture.
Anterior Lumbar Interbody Fusion
Anterior lumbar interbody fusion (ALIF) is a technique that provides direct access to the anterior spine. It is typically performed by a vascular or general surgeon using either a transperitoneal or, more commonly, a retroperitoneal approach to expose the anterior disk space. With this approach, a robust diskectomy can be performed and a large interbody cage placed. ALIF can be performed as a stand-alone, with integral fixation, anterior plate fixation, or with posterior supplemental fixation. Although graft extrusion and implant migration have been described, they are relatively rare with the use of modern techniques. However, subsidence has been reported commonly, particularly in stand-alone ALIF ( Fig. 21.3 ).
Axial Lumbar Interbody Fusion
Axial lumbar interbody fusion (AxiaLIF) is a minimally invasive percutaneous technique that can achieve fusion at L5-S1, or from L4-S1. This technique utilizes a small paracoccygeal incision that gives access to the presacral area with serial dilation, allowing for diskectomy, placement of interbody graft to promote fusion, and placement of a threaded rod to serve as the interbody fixation device. Although AxiaLIF has reported good fusion rates, there is a risk of rectal or bowel injuries. There is a reported revision rate of 8.8% owing to pseudoarthrosis at 3-year follow-up. Revision techniques, including anterior and posterior approaches with or without removal of the AxiaLIF implant, have been described.
Many cases of pseudoarthrosis or graft extrusion can be managed with nonoperative treatment. In asymptomatic patients, serial imaging may be the appropriate management. However, cases of progressive migration or development of deformity will likely warrant operative intervention, even with a lack of symptoms.
For those cases of simple graft symptomatic subsidence or pseudoarthrosis in which surgery is needed, a posterior approach can frequently be utilized. These would be cases in which alignment correction or increased foraminal height are not needed. Particularly in instances where only stand-alone ALIF or LLIF cages were utilized, supplementation with posterior pedicle screws and posterolateral fusion can be efficacious to provide additional stability to the involved segments, eventually leading to adequate bony fusion. This approach provides the advantage of being relatively simple to perform using a straightforward standard technique. Posterior approaches are also indicated in posterior graft extrusions, both to remove the mal-positioned graft and to perform a redo interbody fusion with additional pedicular fixation.
Anterior approaches to the lumbar spine can be helpful in multiple instances of interbody failure. They can be particularly helpful in revision of anterior graft extrusions. Whereas TLIF cages are more likely to retropulse, they can extrude anteriorly as well. Similarly, ALIF and LLIF grafts can also extrude anteriorly. In cases of LLIF, this may become more common with release of the anterior longitudinal ligament. In the case of graft extrusion anteriorly, computed tomography (CT) angiography and consultation with a vascular surgeon should be strongly considered to evaluate proximity to the great vessels. However, the morbidity with this approach should also be considered against the risk of nonoperative intervention, as anteriorly migrated grafts may rarely cause significant morbidity such as pseudoarthrosis or delay injury to the great vessels on their own. The retroperitoneal transpsoas approach has also been described in revision of interbody cages. In cases of lateral extrusion of LLIF cages, a repeat lateral surgery can be performed to access the cage.
Endoscopic approaches to the spine are relatively new, but are being performed for lumbar diskectomy, foraminotomy, and interbody fusions. In conjunction with this increasing popularity, endoscopic approaches are being investigated for their utility in revision surgery. McGrath et al. described a case in which a patient with a previous TLIF had cage retropulsion causing symptomatic nerve compression. The patient was also noted to have a solid bony interbody fusion. The authors elected to perform an endoscopic interlaminar partial resection of the interbody cage, resulting in decompression of the lateral recess and complete resolution of symptoms. In the setting of a solid fusion, this procedure allowed for avoidance of a more extensive procedure requiring removal of the interbody cage.