To review concepts of a standalone endoscopically assisted lumbar interbody fusion as a simplified method to treat spinal instability.
MacNab outcomes and complications were analyzed in a series of 48 consecutive patients who underwent standalone lordotic endoscopic wedge lumbar interbody fusion (LEW-LIF) for advanced lumbar disc degeneration, spinal stenosis, and spondylolisthesis.
Forty-two of the 48 patients (77.8%) did well with
Standalone LEW-LIF was associated with favorable clinical outcomes in the majority of patients. Patient-related predictors of less favorable outcomes considering normal variations as well as patho-anatomy may aid in the development of next-generation implants.
Minimally invasive spinal surgeries (MISS) have become commonplace in the treatment of spinal stenosis and instability related symptomatic neurogenic low back and leg pain in patients who have failed nonoperative care. These procedures have drastically reduced hospitalization stays with a lower rate of medical complications [
The rationale for MISS anterior column reconstruction with the placement of a single oblique interbody fusion cage is straight forward. It allows stabilization of the diseased lumbar spinal motion segment while restoring neuroforaminal height and promoting bony ingrowth [
The advantages of a standalone lordotic endoscopic wedge lumbar interbody fusion (LEW-LIF) with transforaminal implantation of a single oblique interbody fusion device are apparent. This conceivably less burdensome surgery would simplify recovery for most patients with a significant reduction in postoperative complications, and utilization of pain killer to be expected [
For these reasons, the authors started performing standalone LEW-LIF procedure for advanced lumbar disc degeneration, spinal stenosis, and instability using a single oblique threaded expandable cage. Although the majority of patients did well with the procedure, it became clear after an initial learning curve of this series of 48 patients that certain patient-related and anatomic factors appeared to drive less favorable outcomes. Therefore, the purpose of this study was to analyze further these factors with the intent of identifying appropriate patient selection criteria for the procedure.
In 2007, the Center for Advanced Spine Care of Southern Arizona established an outpatient spinal surgery program for the treatment of lumbar herniated disc and spinal stenosis. With the advancement of videoendoscopic equipment, bony decompression became more feasible broadening the indication to treat spinal stenosis. These advancements provided the foundation for the development of a full-endoscopic decompression procedure popularized by Ruetten and colleagues [
Patients considered not suitable for the transforaminal endoscopically assisted intervertebral fusion procedure were stratified according to the following exclusion criteria: (1) Segmental instability with greater than grade II spondylolisthesis or translational motion of greater than 8 mm on preoperative extension-flexion radiographs, (2) severe central stenosis (less than 100 mm2) [
All patients in this consecutive case series provided informed consent and IRB approval was obtained (CEIFUS 106-19).
The surgical procedure employs the endoscopic transforaminal approach using the “outside-in” technique, in which the working sheath is placed into the lower portion of the neuroforamen, thus, aiding in the retraction and avoiding the exiting nerve root. During the interbody fusion procedure and for preparation of the endplate the cannula tip or the endoscope can be positioned in the disc space utilizing “inside-out” techniques for discectomy and endplate preparation. The modified endoscopic decompression technique applied by the author [
In some cases, the foraminoplasty was expanded by partial resection of the superomedial pedicle wall of the distal pedicle. This was often necessary to prepare the introitus for the interbody fusion cage to promote parallel alignment of the implant with the vertebral interspace and to avoid rostral migration of the cage insertion point into the axilla between the exiting and traversing nerve root. Cannulated paddle shavers were used to remove disc tissue and to decorticate the endplates without going through the subchondral bone to minimize implant subsidence. The interbody fusion was done using the VariLift-L interbody fusion system with one oblique positioned cage. The round expandable implants are available in sizes from 10 to14 mm with the final expanded outer diameter typically being 3 to 4 mm larger than its starting size before the expansion maneuver. The implant’s outer diameter is 4 mm smaller at the tip than at the end of the implant’s body. Under fluoroscopic guidance, the sizing tap is inserted into the intervertebral disc space by turning it clockwise. The posterolateral insertion trajectory in the axial plane is typically between 40° to 60° of the midsagittal vertical plumb line but essentially dictated by the patient’s vertical alignment of the intervertebral discs with the iliac crest. The expandable implant should be sized snug. After successful placement and expansion of the implant, local bone- and cancellous allograft was inserted into the cage’s central graft chamber via the inserter.
Typically, patients returned for clinical follow-up at 2, and 6 weeks postoperatively, and at 3, 6, 12, and 24 months, respectively. Primary clinical outcome measures were reductions in the visual analogue scale (VAS) [
Failure to cure following a well-executed standalone LEW-LIF surgery with minimal or no pain relief was not considered a complication. Likewise, sequelae including extravasation of irrigation fluid into the spinal canal or in the subcutaneous tissues causing spinal headaches, or increased incisional pain, or pain from contusion of the ilium during the L5/S1 transforaminal approach, or dysesthetic leg pain from dorsal root ganglion (DRG) irritation were also not considered complications. All complications during the stay at the ASC were recorded. As all patients enrolled in this study were discharged to return home after surgery. At each follow-up visit, patients were asked whether they were treated for any postoperative complications in an emergency room and if any of these visits resulted in an admission to a hospital. Patients were also monitored during regularly scheduled follow-up visits for any signs of unbeknownst or asymptomatic postoperative complications, such as new onset of motor weakness, abnormal sensory function or acute onset of low back pain. In the case of
For the clinical outcome analysis, cross tabulation statistics and measures of association were computed for two-way tables using IBM SPSS Statistics ver. 25.0 (IBM Co., Armonk, NY, USA). Descriptive statistic measures were used to calculate the mean, range, and standard deviation as well as percentages. Crosstabulation methods were used to assess for any statistically significant association between clinical outcome data based on the modified MacNab criteria and VAS scores. Pearson chi-square and Fisher exact test were employed as statistical measures of association. Expected cell counts, continuity corrections, and likelihood ratios were calculated for some analyses. The VAS reductions were compared and tested for statistically significant difference between preoperative and postoperative values using the paired t-test.
Angular cage subsidence (tilt) was determined on intraoperative fluoroscopic and postoperative anteroposterior and lateral views using medical imaging technology Merge picture archiving and communication system (PACS) by Watson Health Imaging, Chicago, IL, USA. Angular measurements were done between horizontal lines drawn along the inferior and superior endplates of the vertebral bodies of the fused lumbar motion segment and additional lines drawn to the most external contact point of the cage with the endplates superiorly and inferiorly on either end of the cage (
Postoperative rehabilitation and supportive care were routinely instituted for all patients. These included active exercise programs prescribed in the postoperative instructions but without formal physical or occupational therapy. Patients were asked whether they developed any new pain syndromes or hitherto unknown conditions that negatively impacted their walking endurance. Patients with dysethetic leg pain due to irritation of the DRG were treated with a combination of oral medication including nonsteroidal anti-inflammatory drugs, gabapentin, or pregabalin, TESI containing a mixture of 1 mL of Depo Medrol Sterile Aqueous Suspension (which contains Methylprednisolone Acetate 20 mg/1 mL and 1 mL of 1% lidocaine), activity modification to a light walking schedule and reduced physical activity program. Patients were advised that narcotic pain medication is not an effective treatment for dysesthetic leg pain due to postoperative DRG irritation. Any unintended aftercare measures were recorded.
Of the 48 patients, 44 patients underwent surgery to alleviate spondylolisthesis-related symptoms (
Clinical outcomes according to MacNab criteria were favorable in the majority of patients with 29 of them having reported
An additional four patients required revision surgery including the same index level. One female patient underwent removal of the standalone expandable fusion cage and placement of cancellous bone allograft into the interspace after it posteriorly extruded following a fall when walking her dog (
This study showed the feasibility of a standalone endoscopically assisted interbody fusion surgery with the LEW-LIF procedure. The majority of patients (37 of 48 patients, 77.08%) had excellent and good outcomes. No significant complications were observed with this outpatient procedure. None of the patients had wound infections, or permanent sensory or motor dysfunction or required admission to a hospital for any reason in the immediate postoperative period. As a result of having mastered the learning curve of the procedure with a case series of 48 patients, the overall rate of failure to cure (
Some pearls of the standalone endoscopic interbody fusion LEW-LIF surgery emerged from this study. First, a generous foraminoplasty with complete resection of the SAP is necessary to mobilize the spinal motion segment and facilitate the introduction of the implant. A partial pediculectomy and resection of obstructing osteophytes of the ring apophysis may aid in that. In turn, these steps may further decrease the rate of DRG irritation. However, improvements in next-generation implant design and instrumentation may also contribute to a decrease in the incidence of this postoperative sequela, which in 25% of the study population required treatment with a TESI. Second, endplate sparing decortication in preparation of the interbody fusion is critical to avoid excessive subsidence of the implant. Osteoporosis may exacerbate this problem. Paddle shavers used during the decortication maneuvers should rest on the opposite ring apophysis when rotated to avoid breaching the subchondral bone of the endplate. Intraoperative observations showed that the inferior endplate of the rostral vertebral body is more susceptible to injury than the superior endplate of the inferior vertebral body during these maneuvers. Third, maximizing intervertebral height is critical to aid in indirect decompression of the foramen and lateral recess opposite from the access side. Under-sizing the implant may contribute to recurrent symptoms and should be avoided. However, oversizing of the implant should also be avoided not to propagate any vertebral fractures.
Analysis of vertical and angular subsidence of the expandable threaded cylindrical cage showed that more postoperative pain and less favorable outcomes are associated with preferential cage subsidence into the superior endplate of the distal vertebral body. The anterolateral placement of a single cage and its subsequent expansion may have led to stress concentration in the small contact area of the expanded portion of the cage. While it is difficult to say whether this stress concentration at the bone-implant interface at the expanded end of the cylindrical cage contributed to mechanical failure of the implant in one patient (
Besides the obvious that performing a standalone LEW-LIF requires hands-on experience with the procedure and is not for the novice endoscopic spine surgeon, this study also shows that adherence to appropriate patient selection criteria is critical to achieving successful outcomes. The authors conclude that patients with multilevel lumbar disease, deformity, osteoporosis, more than grade I spondylolisthesis are at risk for less favorable outcomes than spondylolisthesis patients displaying minimal or no translational motion on extension/flexion radiographs and single rather than multilevel stenosis involvement. Therefore, conclusive preoperative workup of the symptomatic pain generators is essential for selecting patients for standalone LEW-LIF. The senior author, A. Yeung, with 28 years of experience in transforaminal endoscopic decompression since 1991 contributed to the standalone concept of decompression and stabilization in the face of spondylolisthesis. He mainly focused on endoscopic decompression, while saving fusion for failed endoscopic decompression. Approximately 25% of his case series with spondylolisthesis eventually required fusion as a staged procedure after 5 years. Highly vetted patient selection and stratification of the failures allowed Yeung to reduce his fusion rate to 12.5% (personal communication and recent and publications in press). For similar reasons, the third author, J Ramirez, has developed a standalone endoscopic interbody fusion implant following the LEW-LIF concept . a procedure that is reserved for patients with failed endoscopic decompression and spondylolisthesis (personal communication). The importance of preoperative planning of LEW-LIF is equally essential as for removal of herniated discs or spinal stenosis [
Standalone LEW-LIF with the use of a single oblique threaded expandable interbody fusion cage is not only feasible but resulted in
The first author has no direct (employment, stock ownership, grants, patents), or indirect conflicts of interest (honoraria, consultancies to sponsoring organizations, mutual fund ownership, paid expert testimony). The first author is not currently affiliated with or under any consulting agreement with any vendor that the clinical research data conclusion could directly enrich. This manuscript is not meant for or intended to endorse any products or push any other agenda other than the associated clinical outcomes with standalone lordotic endoscopic wedge lumbar interbody fusion. The motive for compiling this clinically relevant information is by no means created and/or correlated to directly enrich anyone due to its publication. However, this publication was intended to substantiate the LEW-LIF concept to facilitate technology advancements.
The views expressed in this article represent those of the authors and no other entity or organization.
Supplementary video clip 1 can be found via
Age distribution of patients undergoing standalone lordotic endoscopic wedge lumbar interbody fusion. Patient’s age ranged from 32 to 88 years of age and averaged 64.9 years. The expected normal age distribution is indicated by the black line. SD, standard deviation.
Intraoperative fluoroscopic posterior-anterior (PA) (A), and lateral (B) view of an 88-year-old male who underwent L4/5 standalone lordotic endoscopic wedge lumbar interbody fusion and was asymptomatic at final follow-up. Change in implant position was measured against 2 horizontal lines drawn along the interior L4 and superior L5 endplate. The cylindrical threaded interbody fusion cage subsided both vertically but also by tilting mostly through the inferior endplate of the rostral vertebral body. Progressive implant subsidence was estimated by measuring the angles between the horizontal lines and additional lines drawn to the outer diameter of the circular cage in contact with the inferior L4 endplate superiorly and the L5 endplate inferiorly. These angles indicated progressive subsidence of the standalone threaded fusion cage in both the coronal (A, C, E) and in the sagittal plane (B, D, F): Intraoperative (A, B) lateral (LAT) subsidence into L4 = 3.65°, into L5 = 3.81°, PA subsidence L4 = 5.78°, into L5 = 6.23°; Three months postoperatively (C, D): LAT subsidence into L4 = 6.25°, into L5 = 5.03°, AP subsidence L4 = 11.14°, into L5 = 6.75°; Eleven months postoperatively (E, F): LAT subsidence into L4 = 7.88°, into L5 = 6.82°, AP subsidence L4 = 7.13°, into L5 = 15.48°.
Intraoperative fluoroscopic (A), and 11 months postoperative lateral (B) view of an 88-year-old male who underwent L4/5 standalone lordotic endoscopic wedge lumbar interbody fusion and was asymptomatic at final follow-up. His imaging studies suggested minimal lateral vertical subsidence. The vertical collapse due to implant subsidence was estimated on lateral radiographs by measuring the distance between horizontal lines placed at the most posterior aspect of the inferior L4 and superior L5 endplates. The distance to additional horizontal lines drawn at the most superior rostral and most inferior distal part of the cage was measured. The progressive distance between these superior and inferior lines were used as an estimate of cage subsidence: intraoperative (A) lateral (LAT) subsidence into L4 = 2.1 mm, into L5 = 4.8 mm, and LAT subsidence at 11 months postoperatively into L4 = 4.0 mm, (B) LAT subsidence into L5 = 5.6 mm.
Follow-up to date of patients undergoing standalone lordotic endoscopic wedge lumbar interbody fusion. The green-shaded area highlights the time period when postoperative dorsal root ganglion (DRG) irritations were treated with transforaminal epidural steroid injections. The orange-shaded area signifies the postoperative interval in which additional- and revision surgeries were performed. The expected normal distribution of follow-up data is indicated by the black line. Most postoperative interventions occurred early on within the first 5 months following surgery. SD, standard deviation.
Preoperative lumbar anteroposterior (AP) (A) and lateral (B) plain films of a 68-year-old female with lateral recess stenosis and retrolisthesis at L3/4 due to adjacent segment disease following a prior L4/5 transforaminal lumbar interbody fusion. The patient underwent uneventful standalone lordotic endoscopic wedge lumbar interbody fusion at L3/4. She did well initially but fell at 6 weeks postoperatively when walking her dog. She developed sudden onset of new back pain and right leg anteromedial thigh pain consistent with L3 radiculopathy. Postoperative AP (C) and lateral (D) plain films showed posterolateral dislocation of the cage with extrusion through the transforaminal surgical tract. The patient improved immediately after removal of the implant and placement of bone graft into the interspace.
Preoperative lumbar anteroposterior (A) and lateral (B) plain films of a 72-year-old female with two level L4/5 and L5/S1 spondylolisthesis. She underwent successful L4/5 standalone lordotic endoscopic wedge lumbar interbody fusion as the first of a planned 2-stage surgery to include the L5/S1 level at a later point after sufficient recovery from the L4/5 fusion. She fell 4 weeks postoperatively and represented with acute onset of leg- and low back pain after an initial postoperative period with good pain relief. Imaging workup (C-F) showed a displaced L5 anterior beak fracture and a displaced fracture of the rostral posterior wall with complete cage subsidence causing severe spinal stenosis. She underwent L3–S1 instrumented fusion with placement of L5–S1 polyetheretherketone interbody fusion cages. The postoperative computed tomography scan serendipitously showed good graft filling of the internal graft chamber of the cage.
Preoperative lumbar anteroposterior (AP) (A) and lateral (B) plain films of a 63-year-old female with spondylolisthesis who underwent standalone lordotic endoscopic wedge lumbar interbody fusion at L4/5 for spondylolisthesis. The patient improved immediately postoperatively and never had any pain through final follow-up. At 3 months postoperatively, fracture of the cage was noticed routine lateral (C) and AP (D) X-rays. Since the patient was asymptomatic, no further treatment was instituted.
Three-dimensional (3D) scatter plot of angular (A) and vertical (B) subsidence of standalone lordotic endoscopic wedge lumbar interbody fusion cages into the inferior endplate of the rostral, and the superior endplate of the distal vertebral body below versus clinical outcomes using MacNab criteria. These 3D scatter plots show that the 6 patients
Descriptive statistics of demographics, preoperative diagnosis, and laterality of surgery
Variable | Frequency | Percent | Valid percent | Cumulative percent |
---|---|---|---|---|
Sex | ||||
Female | 29 | 60.4 | 60.4 | 60.4 |
Male | 19 | 39.6 | 39.6 | 100.0 |
Total | 48 | 100 | 100 | |
Preoperative diagnosis | ||||
Adjacent segment disease | 2 | 4.2 | 4.2 | 4.2 |
Spondylolisthesis | 44 | 91.7 | 91.7 | 95.8 |
Stenosis | 2 | 4.2 | 4.2 | 100.0 |
Total | 48 | 100 | 100 | |
Laterality of decompression | ||||
Bilateral | 12 | 25.0 | 25.0 | 25.0 |
Left | 25 | 52.1 | 52.1 | 77.1 |
Right | 11 | 22.9 | 22.9 | 100.0 |
Laterality of transforaminal implantation | ||||
Left | 36 | 75.0 | 75.0 | 75.0 |
Right | 12 | 25.0 | 25.0 | 100 |
Total | 48 | 100 | 100 |
Level distribution of endoscopic transforaminal procedures
Variable | Frequency | Percent | Valid percent | Cumulative percent |
---|---|---|---|---|
L3/4 fusion | 1 | 2.1 | 2.1 | 2.1 |
L4/5 fusion | 36 | 75.0 | 75.0 | 77.1 |
L4/5 fusion & L3/4 laminoforaminotomy microdiscectomy | 1 | 2.1 | 2.1 | 79.2 |
L4/5 fusion & L5/S1 laminoforaminotomy microdiscectomy | 2 | 4.2 | 4.2 | 83.3 |
L5/S1 | 8 | 16.7 | 16.7 | 100 |
Total | 48 | 100 | 100 |
Clinical outcomes by MacNab
Outcome | Frequency | Percent | Valid percent | Cumulative percent |
---|---|---|---|---|
Excellent | 29 | 60.4 | 60.4 | 60.4 |
Good | 13 | 27.1 | 27.1 | 87.5 |
Fair | 4 | 8.3 | 8.3 | 95.8 |
Poor | 2 | 4.2 | 4.2 | 100 |
Total | 48 | 100 | 100 |
Types of additional surgeries following prior standalone endoscopic transforaminal fusion
Type of additional surgery | Frequency | Percent | Valid percent | Cumulative percent |
---|---|---|---|---|
L3-S1 TLIF | 1 | 2.1 | 2.1 | 2.1 |
L4-S1 TLIF | 3 | 6.3 | 6.3 | 8.3 |
L4/5 laminoforaminotomy | 1 | 2.1 | 2.1 | 10.4 |
L5-S1 lamiotomy rhizotomy | 1 | 2.1 | 2.1 | 12.5 |
L5/S1 laminoforaminotomy rhizotomy | 1 | 2.1 | 2.1 | 14.6 |
L5/S1 laminotomy rhizotomy | 2 | 4.2 | 4.2 | 18.8 |
Patients without additional surgery | 37 | 77.1 | 77.1 | 95.8 |
Revision L3/4 fusion | 1 | 2.1 | 2.1 | 97.9 |
Right laminoforaminotomy rhizotomy | 1 | 2.1 | 2.1 | 100 |
Total | 48 | 100 | 100 |
TLIF, transforaminal lumbar interbody fusion.
Confounding factors observed in patients who underwent transforaminal endoscopic standalone fusion
Confounding factor | Frequency | Percent | Valid percent | Cumulative percent |
---|---|---|---|---|
Adjacent segment | 2 | 4.2 | 4.2 | 4.2 |
Adjacent segment disease, scoliosis | 1 | 2.1 | 2.1 | 6.3 |
Multilevel stenosis | 10 | 20.8 | 20.8 | 27.1 |
Multilevel stenosis, osteoporosis | 1 | 2.1 | 2.1 | 29.2 |
Multilevel stenosis, scoliosis | 4 | 8.3 | 8.3 | 37.5 |
Patients without confounding factors | 22 | 45.8 | 45.8 | 83.3 |
Postlaminectomy syndrome | 2 | 4.2 | 4.2 | 87.5 |
Postlaminectomy syndrome, adjacent level disease | 2 | 4.2 | 4.2 | 91.7 |
Postlaminectomy syndrome, multilevel stenosis | 3 | 6.3 | 6.3 | 97.9 |
Postop adjacent segment disease | 1 | 2.1 | 2.1 | 100 |
Total | 48 | 100 | 100 |
Crosstabulation confounding factors versus MacNab outcomes
Confounding factor | MacNab outcomes |
||||
---|---|---|---|---|---|
Excellent | Good | Fair | Poor | Total | |
Multilevel stenosis, scoliosis | 3 | 1 | 0 | 0 | 4 |
Patients without confounding factors | 17 | 5 | 0 | 0 | 22 |
Adjacent segment | 1 | 1 | 0 | 0 | 2 |
Adjacent segment disease, scoliosis | 1 | 0 | 0 | 0 | 1 |
Multilevel stenosis | 3 | 4 | 2 | 1 | 10 |
Multilevel stenosis, osteoporosis | 0 | 0 | 0 | 1 | 1 |
Postlaminectomy syndrome | 0 | 0 | 2 | 0 | 2 |
Postlaminectomy syndrome, adjacent level disease | 1 | 1 | 0 | 0 | 2 |
Postlaminectomy syndrome, multilevel stenosis | 2 | 1 | 0 | 0 | 3 |
Postoperative adjacent segment disease | 1 | 0 | 0 | 0 | 1 |
Total | 29 | 13 | 4 | 2 | 48 |
Pearson chi-square: 57.278804; asymptotic significance (2-sided)=0.001. Likelihood ratio: 32.738249; asymptotic significance (2-sided)=0.206.