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Complications and Avoidance in Lumbar Interbody Fusions
Introduction
As with any surgical procedure, interbody fusions are associated with unique complications. Given the wide variety of approaches utilized when performing an interbody fusion, it is important to recognize common complications associated with each specific technique. Recognition of these complications allows the surgeon to utilize a more protective surgical approach to limit perioperative complications. Furthermore, recognition of common complications better enables the surgeon to inform patients of the risks of potential surgical treatment.
All pressure points should be padded to avoid peroneal neuropathy with pressure on the lateral leg at the proximal fibula. Care must also be made when positioning the patient in the lateral position. The authors do not advocate aggressive “breaking” of the table when lateral interbody fusion is performed. This aggressive “breaking” or bending the bed with the bed and foot of the bed lowered while the fulcrum at the lumbar spine is raised directly or indirectly has resulted in opening of the space between the iliac crest and rib cage. This was performed at the expense of potential stretching of the lumbar plexus and resultant neuropathy (i.e., ipsilateral thigh pain and/or weakness).
At times intraoperative neuromonitoring is utilized in an attempt to minimize neurological complications following interbody fusion. No high level evidence suggests the usage of these techniques results in improved outcome or decreased complications. Triggered electromyography (EMG) is commonly used during transpsoas direct lateral interbody fusion. Identification of motor nerves may decrease the incidence of weakness following surgery; however, it should be noted that this technique cannot accurately identify sensory nerves.
Posterior Lumbar Interbody Fusion
Posterior lumbar interbody fusion (PLIF) is a technically challenging procedure and therefore is associated with increased complication rates compared with other lumbar fusion techniques. Two of the primary complications of PLIF are nerve root injury and incidental durotomy. The reason for higher rates of these specific complications is owing to the significant traction that must be placed on the thecal sac and nerve roots in order to gain access to the intervertebral space. Furthermore, PLIF requires violation of both facet joints to enable adequate exposure for graft placement.
Nerve Root Injury
Arguably the worst complication that commonly occurs with the PLIF procedure is nerve root injury. The current literature is widely variable in reported rates of nerve root injury with incidences ranging from 0.6% to 24%. Davne and Myers reported the lowest rate of nerve root injury at only a 0.6% in their series of 384 PLIF procedures.
Given the high rates and significant morbidity associated with nerve root injury during PLIF, many authors have investigated techniques to lower the rates of this complication. Barnes and colleagues reported a 14% incidence of permanent nerve root injury when using threaded fusion cages compared to a 0% incidence using smaller allograft wedges in their retrospective review of 49 patients. The authors noted their preference for allograft wedges given these findings and their discovery that clinical outcomes were better in the allograft wedge group. Krishna and colleagues noted a 9.7% rate of postoperative neuralgia in patients treated with subtotal facetectomy compared with a 4.9% rate in 226 patients treated with total facetectomy. Although this was not statistically significant, the authors noted their preferred practice of total facetectomy to help prevent nerve root injury. In a separate study, Okuda et al. found a 6.8% rate of postoperative neuralgia with total facetectomy during PLIF.
The aforementioned studies demonstrate the importance of a wide exposure with adequate facetectomy, careful dissection techniques without unnecessary traction of nerve root (especially with canal stenosis at the levels above), and avoidance of oversized grafts in order to minimize the risk of nerve root injury during PLIF. Angled nerve root retractors and direct visualization of the nerve roots at all times can also help prevent neurologic injury during the procedure. A more aggressive total facetectomy can provide an excellent window for graft placement while minimizing the amount of retraction on the nerve root. Triggered EMG, if utilized, may enable assessment of undue retraction during this step of the operation; however, data do not support an improved outcome.
Durotomy
Incidental durotomies are another common complication that occurs at higher rates during PLIF procedures owing to the direct retraction of the thecal sac intraoperatively. Studies have reported rates of durotomies at 9% to 19%, with higher rates occurring during reoperation surgeries owing to dural adhesions. If a durotomy does occur, it can usually be repaired primarily. However, repair may be more difficult when using a minimally invasive technique.
Graft- and Cage-Related Complications
Graft dislodgement and loosening are other complications associated with PLIF, especially during early use of the technique ( Fig. 2.1 ). The cumulative incidence of graft-related complications is less than 5%. However, the rate of this complication is even lower when posterior pedicle screw stabilization is used with the PLIF procedure. Conversely, total facetectomy is associated with a higher incidence of graft extrusion owing to the decreased stability associated with this technique, but is lessened with the use of screw fixation. When graft-related complications are symptomatic, they require revision surgery, which is technically challenging.
Interbody cage type and positioning have been shown to effect rates of migration, with newer technologies being utilized to decrease the incidence of graft dislodgement ( Fig. 2.2 ). Furthermore, subsidence of the implants may also occur after PLIF, which may result in postoperative neuralgia ( Fig. 2.3 ).
Nonunion
Fusion rates after PLIF are generally high, with studies reporting incidences of 95% to 98%. However, there is some reported variability with Rivet et al. achieving a fusion rate of only 74% in 42 patients receiving PLIF.
Other Complications
Other complications, including epidural hematoma (1%), wound infections, and other nonimplant-related complications, seem to occur with a similar frequency in PLIF as in other reconstructive spinal operations. Although adjacent segment disease (ASD) is more of an adverse outcome than complication, some studies have demonstrated earlier rates of ASD and revision surgery compared with other cohorts. However, new surgical techniques have been utilized to prevent this development. Lastly, there is a risk of loss of lumbar lordosis. This was much more relevant with the use of older cages; however, careful attention to detail should minimize this complication.
Anterior Lumbar Interbody Fusion
In contrast to PLIF, the anterior lumbar interbody fusion (ALIF) technique can provide the same interbody support without manipulation of the dural or posterior neural structures. However, the ventral approach required during the ALIF procedure often necessitates significant retraction of the iliac vessels, hypogastric nerves, and peritoneum, which may result in direct injury to these structures. Other complications associated with ALIF include an increased risk of deep vein thrombosis (DVT), abdominal wall hernias, and retrograde ejaculation in men.
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