by Curt Freudenberger, MD; Emily M. Lindley, PhD; Douglas W. Beard, MD; W. Carlton Reckling, MD; Allison Williams, PhD; Evalina L. Burger, MD; Vikas V. Patel, MD
Over the past 2 decades, posterior lumbar interbody fusion (PLIF) with pedicle screw instrumentation has gained popularity. Anterior fusion techniques, however, have evolved over time and currently allow for minimally invasive anterior retroperitoneal diskectomy, interbody graft placement, and rigid instrumentation. A direct comparison of anterior lumbar interbody fusion (ALIF) with anterior tension band plating to that of instrumented PLIF has not been previously reported.
This retrospective uncontrolled cohort comparison included 59 patients with low back pain and 1- or 2-level lumbar degenerative disk disease from L3 to S1 who underwent PLIF with pedicle screw instrumentation or ALIF with anterior tension band plating. Outcome measures included estimated blood loss, surgical time, radiographic evidence of fusion at 6 to 9 months postoperatively, and pre- and postoperative Oswestry Disability Index scores. Fusion rates for the 2 procedures were similar. Posterior lumbar interbody fusion patients had significantly higher estimated blood loss and longer surgical time than ALIF-ATB patients. Oswestry Disability Index scores were similar between the 2 groups at all postoperative time points, except at 3 months postoperatively when PLIF patients had lower scores than ALIF-ATB patients. These findings suggest that ALIF-ATB has similar fusion and functional outcomes as PLIF, but with shorter surgical time and decreased blood loss.
Spinal fusion is commonly performed together with rigid instrumentation to treat various lumbar spine disorders. Current methods of fixation include posterior pedicle screw instrumentation with posterior lumbar interbody fusion (PLIF) or transforaminal lumbar interbody fusion (TLIF), posterior pedicle screw instrumentation with anterior lumbar interbody fusion (ALIF), and anterior plate and screw instrumentation with ALIF. Over the past 20 years, PLIF with pedicle screw instrumentation has gained popularity in the spine community, and may therefore be considered a standard for fusion to which alternative treatment methods can be compared; however, anterior fusion techniques have evolved and currently allow for minimally invasive anterior retroperitoneal diskectomy, interbody graft placement, and rigid instrumentation.
It is unclear whether there are comparative advantages between instrumented anterior and instrumented posterior fusions. Recently, Glassman et al1 found a greater improvement at 1 year for ALIF patients as compared to posterolateral spinal fusion, PLIF/TLIF, or 360° fusion patients; and a greater improvement at 2 years for both ALIF and posterolateral spinal fusion over the PLIF/TLIF patients. The addition of a posterior procedure to stand-alone ALIF or instrumented ALIF for the purpose of achieving a circumferential fusion may or may not provide superior mechanical stability.2,3 After treating thoracolumbar injury patients with anterior spinal decompression and stabilization, Dunn4 found greater neurological recovery in these patients than in those treated with posterior instrumentation alone. This is likely due to better anterior decompression of the spinal canal and anterior column stabilization; however, less retraction of the paravertebral muscles and poor placement of pedicle screws may also play a role in favorable outcomes for the anterior approach.5
Each surgical approach has unique complications that can influence the success of lumbar fusion surgery. Risks associated with pedicle screw placement in lumbar and lumbosacral fusion include deep infection, neurological damage, and loss of correction due to instrumentation or fixation failure.6 While the posterior approach is associated with greater neurological and dura-related injuries, the ALIF approach has a higher incidence of ileus and deep vein thrombosis.7 Studies have also found that patient demographics can be predictive of outcome complications. Demographic factors that reportedly influence ALIF functional outcomes include postoperative compensation claim, age, and obesity.8 Conversely, a study of PLIF patients found that older age was not associated with increased complications, blood loss, or operative time; however, PLIF in older patients was associated with longer hospital stays, more conservative fusion strategies, and fewer repeat procedures.9 Consistent with diminished bone quality with age, greater bone mineral density is significantly correlated with both successful pedicle screw instrumentation and bony union in the elderly.10
While the current literature explores the outcomes of posterior and anterior fusion methods with and without instrumentation, a direct comparison of ALIF with anterior plating to instrumented PLIF has not been previously reported. Thus, the purpose of the present study was to retrospectively compare the outcomes of ALIF with plate fixation to the accepted PLIF with pedicle screw instrumentation, with regard to surgical time, blood loss, radiographic evidence of fusion, and function.
Materials and Methods
This study was a retrospective comparison of 59 patients who underwent either PLIF with pedicle screw instrumentation (n = 29) or ALIF with anterior plating (n = 30) (Anterior Tension Band Plate; Synthes Spine, Paoli, Pennsylvania) at 2 independent orthopedic spine surgery centers between 2004 and 2006. Patient data were obtained from demographics, operative logs, and clinical records. Outcome measures included estimated blood loss, surgical time, radiographic evidence of fusion, and pre- and postoperative Oswestry Disability Index (ODI) scores. Complications were also recorded.
Patient Selection Criteria
All patients presented with 1- or 2-level lumbar degenerative disk disease from L3 to S1. The diagnosis was based on the patient’s history, clinical symptoms, physical findings, functional deficits, and radiographic confirmation. Although not universal, radiographs were augmented with computed tomography (CT), diskography, and/or magnetic resonance imaging (MRI). All patients reported low back pain with or without associated radiculopathy, were symptomatic for a minimum of 6 months, and had failed nonoperative interventions including physical therapy, medications, and/or spinal injections. Positive diagnostic imaging included > 1 of the following findings on radiographs, MRI, diskography, or CT: 1) disk-space collapse or desiccation; 2) osteophyte formation at endplates or facet joints; 3) scarring or thickening of the ligamentum flavum, annulus fibrosis, or facet joint capsule; 4) herniated nucleus pulposus; and 5) spondylolisthesis no greater than grade I. Patients who underwent prior fusion surgery or had pathology at > 2 levels were excluded from this analysis; patients who underwent prior decompressions or those with grade I spondylolisthesis were not excluded.
Posterior lumbar interbody fusion surgery included a posterior midline incision, decompression of the spinal canal if needed, and bilateral diskectomy followed by insertion of allograft bone spacer, local bone, and bone morphogenetic protein into the interbody space, with additional local bone placed in the posterolateral space and pedicle screw instrumentation. Anterior lumbar interbody fusion with anterior tension band was performed through a minimally invasive transverse, para-midline incision and a retroperitoneal approach by a general/vascular surgeon. After exposure, complete diskectomy was performed, followed by insertion of allograft bone spacer and bone morphogenetic protein into the interbody space and application of the anterior tension band plate. At both locations, each orthopedic surgeon (D.W.B., W.C.R.) used a separate general surgeon. Lumbar bracing was provided for the first 6 weeks postoperatively and activity advancement was based on progress in the physical therapy regimen.
Radiograph Outcome Measurements
Anteroposterior and lateral radiographs obtained 6 to 9 months postoperatively were evaluated for evidence of fusion. Solid fusion was defined as bridging bone across adjacent vertebral bodies, an absence of motion at the fusion site, <5° of angulation or < 3 mm of translation on flexion extension views, absence of progressive listhesis when compared to prior studies, and absence of radiolucent lines on each endplate of the fusion level. Partial fusion was defined as evidence of initial bony bridging that had yet to fully develop. Minimal fusion was noted when there was no evidence of bony bridging across vertebral bodies.
Statistical analyses were performed using SPSS 16.0 software (SPSS, Chicago, Illinois). For continuous variables, comparisons between groups were made using independent sample t tests and the Mann-Whitney U test. The chi-square statistic was performed to assess differences among categorical variables. To account for multiple comparisons, a Bonferroni correction was applied.
Patient demographic results are presented in Table 1. Data were available for 59 patients. The PLIF and ALIF-ATB groups both comprised of 11 men (37.9%) and 18 women (62.1%). Sex identification was missing for 1 patient in the ALIF-ATB group. The mean body mass index (BMI) for the PLIF group was 28.5 and for the ALIF-ATB group was 27.6. No statistically significant differences were found between groups for sex or BMI (P >.05 for both). A statistically significant difference was found for age. The mean age for the PLIF group was 58 years and for the ALIF-ATB group was 40 years (P <.001).
A significant difference between the PLIF and ALIF-ATB groups was found for surgical time (P <.001; Table 2). Mean and median surgical times for the PLIF group were 164 minutes and 159 minutes, respectively. Mean and median surgical times for the ALIF-ATB group were 114 minutes and 104 minutes, respectively. The PLIF group had significantly higher estimated blood loss values than the ALIF-ATB group (P = .011; Table 2). Mean and median estimated blood loss for the PLIF group were 341 mL and 250 mL, respectively. Mean and median estimated blood loss for the ALIF-ATB group were 212.5 mL and 112.5 mL, respectively.
Radiographic analyses of PLIF patients at 6 to 9 months postoperatively revealed that 2 patients (7.4%) displayed minimal fusion, 8 (29.6%) displayed partial fusion, and 17 (63%) achieved solid fusion (Table 3). In the ALIF-ATB group, 2 patients displayed minimal fusion (7.7%), 9 (34.6%) displayed partial fusion, and 15 (57.7%) achieved solid fusion. No statistically significant difference between the groups was found regarding fusion (P = .921).
Oswestry Disability Index sum scores for the PLIF and ALIF-ATB groups were compared preoperatively and at 4 postoperative intervals: <6 weeks, 6 to 12 weeks, 3 to 4 months, and 12 to 18 months (Table 4). Mean preoperative sum scores were 20.2 for the PLIF group and 24.3 for the ALIF-ATB group. This difference was not statistically significant (P = .75). Differences between the groups were also not statistically significant at <6 weeks (P = .057), 6 to 12 weeks (P = .21), or 1 year (P = .788). The magnitude of difference between the groups for ODI scores was greatest 3 months postoperatively, with a mean of 10.8 for the PLIF group and 20.3 for the ALIF-ATB group; however, after correcting for multiple comparisons, this difference was not statistically significant (P >.007).
Among the anterior tension band population there were a total of 4 complications, each in different patients: 2 intraoperative common iliac vein injuries and repairs (estimated blood loss 800 and 1000), 1 postoperative thrombus, and 1 ileus. Two patients in the PLIF group required reoperations for hematoma evacuation, and a third patient required reoperation for hardware revision due to a poorly placed pedicle screw. All complications resulted in no long-term sequelae.
Surgical techniques that use anterior approaches include traditional open ALIF, mini-open ALIF, and laparoscopic ALIF. In a review by Inamasu and Guiot, 11 there were no significant differences between these alternatives with regard to operative time, blood loss, and length of hospital stay; there was, however, a greater incidence of retrograde ejaculation with laparoscopic ALIF. Mini-open ALIF is also associated with vascular injury and postoperative retrograde ejaculation.12 Aortic erosion and laceration have been attributed to prominent anterior plating.13 While surgical fusion for the treatment of low back pain qualitatively improves one’s sex life, complications from anterior approaches can include disturbed orgasm and genital sensation in women and disturbed ejaculation and genital sensation in men.14 When augmented with either anterior or posterior instrumentation, the rigidity of ALIF increases.15 Regardless of technique, the addition of anterior plating to an ALIF improves biomechanical fixation, although it appears to be a less rigid construct in the flexion-extension range of motion when compared to pedicle or translaminar facet screws with a posterior approach.16 This finding, however, is not necessarily clinically significant. In the present study, the mini-open technique was complicated by 2 vein injuries that did not result in retrograde ejaculation. With regard to fixation and radiographic fusion rates, PLIF with instrumentation and ALIF with anterior plating appeared to be similar.
During an anterior approach, the great vessels are encountered. Although this may not result in a vascular laceration, such manipulation can have untoward complications. Vascular compression of the left iliac vessels occurs during 57% of L4-5 approach procedures.17 Variation in the surgical anatomy of the great vessels bifurcation in relation to vertebral body level is well described and may help predict the risk of vascular complications.18 When common iliac occlusion or acute vasospasm occurs, it can be associated with a prior history of vascular disease and smoking; furthermore, surgical outcome complications following ALIF, such as pseudoarthrosis, are associated with patients who smoke >1 pack of cigarettes per day.19,20 The vascular injuries in the present study were not age dependent, although no statement can be made about the presence of vascular disease.
In the present retrospective comparison, patients who underwent ALIF with anterior plating had fusion rates similar to those of patients who underwent PLIF with pedicle screw instrumentation. Postoperative functional outcomes were also similar between the 2 groups, except at 3 months when ODI scores were higher in the ALIF-ATB group; however, this difference was not significant after correction for multiple comparisons. In addition, the ALIF-ATB group was associated with decreased blood loss, shorter surgical time, and a younger patient population than the PLIF group. The greater blood loss with PLIF (250 mL vs 112.5 mL in the ALIF-ATB group) typically results from the extensive muscle dissection encountered in the traditional posterior approach or from epidural bleeding encountered at the time of the diskectomy. It is not clear, however, whether the greater blood loss in the PLIF patients was clinically significant, as we did not track the need for transfusions in these patients. The shorter surgical time associated with the anterior approach likely reflects the experience of the approach surgeon and the minimal dissection necessary in navigating among the great vessels at the anterior lumbar spine. Additional anterior approach advantages include ease of diskectomy and interbody graft placement, ease of instrumentation when compared to pedicle screw placement, and avoidance of nerve root manipulation.
While these findings suggest that ALIF with anterior plating may be as effective as PLIF for the treatment of lumbar degenerative disk disease, this study has several limitations, particularly those common to all retrospective reviews. Given that the patients in this study were not randomly assigned to a surgical technique, they were not paired identically. For example, the ALIF-ATB group was younger than the PLIF group, most likely due to the surgeons’ concern with using an anterior approach in older patients. It is also possible that some of the patients would not have been truly equal candidates for either procedure. Patients with radiculopathy were probably more likely to be treated with the posterior approach to allow for decompression of the neutral elements than patients with purely mechanical back pain. One could also argue that including a larger number of patients may increase the power of the study and show differences in fusion outcomes between the 2 groups. Despite these limitations, we feel this study provides a useful preliminary retrospective comparison of ALIF with anterior plating to the “standard” PLIF lumbar fusion technique.
Patients in the ALIF-ATB group had similar fusion and functional outcomes as patients in the PLIF group, but with significantly shorter surgical time and decreased blood loss. While surgeons may be uncomfortable with subjecting an older patient to an anterior approach, in the absence of documented concerns regarding abdominal aortic aneurysms or friable calcified vessels, these advantages may make ALIF with anterior plating more appropriate for older patients. Prospective studies of this patient population are needed before this recommendation can be asserted.
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