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.
Vascular Injury
Major blood vessel injuries are rare during ALIF. However, vascular injury to the common iliac vessels occurs at a rate of 1% to 7%, with higher rates occurring during exposure of the L5-S1 level. The common iliac vein is very compressible; it lies posterior to the artery such that it can easily be mistaken for soft tissues during exposure. The iliolumbar vein is at higher risk during exposure of the L4-5 level. Some surgeons advocate for controlled ligation of this vessel in all exposures to minimize the risk of inadvertent tearing with retraction. To avoid injury of these vessels, self-retaining retractors should not be used on these vessels during exposure.
Arterial thrombosis secondary to aggressive retraction or arterial injury during ALIF has also been reported. These occur at a rate of 1%. In contrast, DVT occurs in 1% to 11% of patients receiving ALIF, which is higher than in other fusion procedures. Resultant nonfatal pulmonary embolism (PE) was seen at an incidence of 3% in one study. To avoid thrombosis, retraction should not be prolonged and self-retaining retractors should not be used on vessels. It is important to check the lower extremity pulses bilaterally after the procedure. If thrombosis is suspected, an immediate angiogram or venogram should be obtained.
Intraabdominal Complications
Ventral exposure during ALIF is often performed by vascular or general surgeons to decrease the rate of vascular and intraabominal complications. However, gastrointestinal (GI) tract injuries still occur in 2% of all patients receiving ALIF. GI tract injury rates can be lowered by placing packing behind self-retaining retractors. Furthermore, some surgeons advocate for preoperative bowel preparation, including enema, to help decompress the bowel, theoretically decreasing the rate of bowel injury. A nasogastric tube can also be placed preoperatively to facilitate bowel decompression.
Violation of the peritoneum during the retroperitoneal approach or violation of the transversalis fascia during iliac bone graft harvest can lead to the development of postoperative hernias. Although hernias occur in less than 1% of cases, they can lead to bowel obstruction and/or infaction.
Ileus after ALIF is common with reported incidences of 1% to 8%. However, this complication usually resolves within 1 week of the operation. Prolonged ileus should raise suspicion of a postoperative hernia with bowel obstruction.
Retrograde Ejaculation
Retrograde ejaculation as a result of hypogastric plexus injury has been reported in 0.1% to 8% of ALIF procedures performed on male patients. This complication usually occurs after exposure of the L5-S1 level. The mechanism for this complication is secondary to relaxation of the internal sphincter of the bladder with subsequent retrograde flow of ejaculate into the bladder. Avoidance of this complication is possible with good operative technique and anatomical understanding. Inoue et al. noted a decrease in both ileus and retrograde ejaculation with improved surgical technique over the last 13 years in their 27 year study of 350 ALIF patients. Over the last 13 years, no patients had ileus or retrograde ejaculation.
The prevertebral sympathetic plexus runs along the anterolateral edge of the vertebral bodies before traversing over the aortic bifurcation and common iliac vessels and forming the hypogastric plexus. Blunt dissection must be utilized to mobilize the more cephalad prevertebral plexus before the hypogastric plexus can be adequately exposed. Furthermore, aggressive electrocautery should be minimized during the approach of the caudal lumbar spine.
If retrograde ejaculation does occur, patients may be counseled that 25% to 88% of patients suffering from this complication have spontaneous resolution by the end of the second year.
Neurologic Complications
Major neurologic complications during ALIF are rare because the epidural space is not entered and no attempt is made to decompress the neural elements during the procedure. However, injuries to the genitofemoral or ilioinguinal nerves may occur after ALIF, with some authors reporting rates as high as 15%. Injuries to these nerves are characterized by postoperative numbness in the groin and/or medial thigh. This complication is most common in patients who undergo ALIF procedures at the upper lumbar levels. Usually, these nerve palsies resolve spontaneously.
A sympathomimetic dysfunction occurs in 7% to 14% of patients undergoing ALIF procedures. Patients with this complication note that the lower extremity of the side of operation is warmer and possibly more swollen than the contralateral lower extremity. This complication also resolves over time.
Graft- and Cage-Related Complications
Graft collapse after ALIF occurs in 1% to 2% of patients. This complication usually results from excessive removal of subchondral bone from the adjacent vertebral body endplates. This collapse may result in a kyphotic spinal deformity. Graft absorption may also occur, especially in smokers, although this complication is rare.
Graft dislodgement occurs in 1% of patients receiving ALIF. Such graft displacements can be minimized by using a ventral plate or posterior pedicle fixation to enhance stability.
The aforementioned complication may be minimized by the addition of anterior or posterior instrumentation. Biologics may also have both a positive and negative effect. Bone morphogenetic protein-2 (BMP-2) has been demonstrated to result in early osteolysis, which may result in subsidence or graft collapse if performed in a stand-alone ALIF. This may be minimized with the use of posterior instrumentation.
Nonunion
Pseudoarthrosis after ALIF is reported at highly variable rates, ranging from 3% to 58% ( Fig. 2.4 ). Higher rates of nonunion are seen in patients who smoke more than one pack of cigarettes daily. Nonunion may also be minimized with the use of biologics, such as BMP-2, and the addition of spinal instrumentation.
