Long-term radiographic outcomes of expandable versus static cages in transforaminal lumbar interbody fusion

Expandable Cages for Lumbar Interbody Fusion: A Narrative Review

Lumbar fusion surgery for treating degenerative spinal diseases has undergone significant advancements in recent years. In addition to posterior instrumentation, anterior interbody fusion techniques have been developed along with various cages for interbody fusion. Recently, expandable cages capable of altering height, lordotic angle, and footprint within the disc space have garnered significant attention. In this manuscript, we review the current status, clinical outcomes, and future prospects of expandable cages for lumbar interbody fusion based on the existing literature. Expandable cages are suitable for minimally invasive spinal surgeries. Small-sized cages can be inserted and subsequently expanded to a larger size within the disc space. While expandable cages generally demonstrate superior clinical outcomes compared to static cages, some studies have suggested comparable or even poorer outcomes with expandable cages than static cages. Careful interpretation through additional long-term follow-ups is required to assess the utility of expandable cages. If these shortcomings are addressed and the advantages are further developed, expandable cages could become suitable surgical instruments for minimally invasive spinal surgeries.

Sagittal Alignment in the Degenerative Lumbar Spine: Surgical Planning

➤ Sagittal alignment of the spine has gained attention in the field of spinal deformity surgery for decades. However, emerging data support the importance of restoring segmental lumbar lordosis and lumbar spinal shape according to the pelvic morphology when surgically addressing degenerative lumbar pathologies such as degenerative disc disease and spondylolisthesis.➤ The distribution of caudal lordosis (L4-S1) and cranial lordosis (L1-L4) as a percentage of global lordosis varies by pelvic incidence (PI), with cephalad lordosis increasing its contribution to total lordosis as PI increases.➤ Spinal fusion may lead to iatrogenic deformity if performed without attention to lordosis magnitude and location in the lumbar spine.➤ A solid foundation of knowledge with regard to optimal spinal sagittal alignment is beneficial when performing lumbar spinal surgery, and thoughtful planning and execution of lumbar fusions with a focus on alignment may improve patient outcomes.

Early Experience With Uniplanar Versus Biplanar Expandable Interbody Fusion Devices in Single-Level Minimally Invasive Transforaminal Lumbar Interbody Fusion

OBJECTIVE

To compare the early radiographic and clinical outcomes of expandable uniplanar versus biplanar interbody cages used for single-level minimally invasive transforaminal lumbar interbody fusion (MIS-TLIF).

METHODS

A retrospective review of 1-level MIS-TLIFs performed with uniplanar and biplanar polyetheretherketone cages was performed. Radiographic measurements were performed on radiographs taken preoperatively, at 6-week follow-up, and 1-year follow-up. Oswestry Disability Index (ODI) and visual analogue scale (VAS) for back and leg at 3-month and 1-year follow-up.

RESULTS

A total of 93 patients (41 uniplanar, 52 biplanar) were included. Both cage types provided significant postoperative improvements in anterior disc height, posterior disc height, and segmental lordosis at 1 year. No significant differences in cage subsidence rates were found between uniplanar (21.9%) and biplanar devices (32.7%) at 6 weeks (odds ratio, 2.015; 95% confidence interval, 0.651-6.235; p = 0.249) with no additional instances of subsidence at 1 year. No significant differences in the magnitude of improvements based on ODI, VAS back, or VAS leg at 3-month or 1-year follow-up between groups and the proportion of patients achieving the minimal clinically important difference in ODI, VAS back, or VAS leg at 1 year were not statistically significantly different (p > 0.05). Finally, there were no significant differences in complication rates (p = 0.283), 90-day readmission rates (p = 1.00), revision surgical procedures (p = 0.423), or fusion rates at 1 year (p = 0.457) between groups.

CONCLUSION

Biplanar and uniplanar expandable cages offer a safe and effective means of improving anterior disc height, posterior disc height, segmental lordosis, and patient-reported outcome measures at 1 year postoperatively. No significant differences in radiographic outcomes, subsidence rates, mean subsidence distance, 1-year patient-reported outcomes, and postoperative complications were noted between groups.

Cage subsidence-A multifactorial matter!

STUDY DESIGN

Retrospective cohort study OBJECTIVE: Wider cages are associated with improved decompression and reduced subsidence, but variation in cage physical properties limits consistent outcome analysis after thoracolumbar interbody fusion. This study investigated cage subsidence and its relationship to lateral and posterior approaches with a focus on the hypothesis that the larger surface area of lateral cages results in lower subsidence rates.

METHODS

This study retrospectively reviewed 194 patients who underwent interbody fusion between 2016 and 2019 with a primary outcome of cage subsidence. Secondary outcomes were cage distribution (patients, approaches, expandability), cage dimensions, t‑scores, length of hospital stay, blood loss, surgical time, and pelvic incidence-lumbar lordosis (PI-LL) mismatch.

RESULTS

Medical records were reviewed for 194 patients receiving 387 cages at 379 disc levels. Subsidence was identified in 35.1% of lateral cages, 40.9% of posterior cages, and 36.3% of all cages. Lower surface area (p = 0.008) and cage expandability were associated with subsidence risk. Lower anteroposterior cage length proved to be a significant factor in the subsidence of posteriorly placed cages (p = 0.007). Osteopenic and osteoporotic patients experienced cage subsidence 36.8% of the time compared to 3.5% of patients with normal t‑scores (p = 0.001). Cage subsidence correlated with postoperative deterioration of the PI-LL mismatch (p = 0.03). Patients receiving fusion augmentation with bone morphogenic protein experienced higher fusion rates (p < 0.01).

CONCLUSION

Cage subsidence is a common complication that can significantly impact operative outcomes following thoracolumbar interbody fusion. Low t‑scores, smaller surface area, cage expandability, and lower cage length in posterior approaches contribute significantly to cage subsidence.

The Use of Dual Direction Expandable Titanium Cage With Biportal Endoscopic Transforaminal Lumbar Interbody Fusion: A Technical Consideration With Preliminary Results

Objective: Expandable cage technology has emerged for lumbar interbody fusion to restore intervertebral disc space height and alignment through a narrow surgical corridor. The purpose of this study is to present the technique of biportal endoscopic transforaminal lumbar interbody fusion (TLIF) using dual direction expandable cage and provide early clinical results.Methods: We performed the biportal endoscopic TLIF using a dual direction expandable titanium cage for height restoration and a larger footprint in 10 patients. Clinical parameters including Oswestry Disability Index (ODI), visual analogue scale (VAS), and complications were retrospectively analyzed. Also, we investigated radiologic parameters using preoperative and postoperative x-ray images.Results: We successfully inserted dual direction expandable cages during biportal endoscopic TLIF. There was no significant subsidence or collapse of the expandable cages during the 6-month follow-up period. Lumbar lordosis and disc height were significantly increased after surgery. ODI and VAS scores were significantly improved at 6 months after surgery.Conclusion: In this report, we describe the first use of a dual direction expandable interbody TLIF cage that expands in both width and height in biportal endoscopic TLIF surgery. Early clinical and radiographic outcomes of this TLIF technique may be favorable in early 6-month follow-up.

Static versus Expandable Interbody Fusion Devices: A Comparison of 1-Year Clinical and Radiographic Outcomes in Minimally Invasive Transforaminal Lumbar Interbody Fusion

STUDY DESIGN

Retrospective cohort study.

PURPOSE

To compare the radiographic and clinical outcomes of static versus expandable interbody cages in transforaminal lumbar interbody fusion using minimally invasive surgery (MIS-TLIF).

OVERVIEW OF LITERATURE

Expandable interbody cages may potentially improve radiographic and clinical outcomes following MIS-TLIF compared to static pages, but at a potentially higher cost and increased rates of subsidence.

METHODS

A retrospective chart review of 1- and 2-level MIS-TLIFs performed from 2014 to 2020 was reviewed. Radiographic measurements were obtained preoperatively, 6 weeks postoperatively, and at final follow-up. Patient-reported outcome measures (PROMs) including the Oswestry Disability Index, Visual Analog Scale (VAS) back, and VAS leg were evaluated. Multivariate linear regression analysis determined the effect of cage type on the change in PROMs, controlling for demographic characteristics. Alpha was set at 0.05.

RESULTS

A total of 221 patients underwent MIS-TLIF including 136 static and 85 expandable cages. Expandable cages had significantly greater anterior (static: 11.41 mm vs. expandable: 13.11 mm, p <0.001) and posterior disk heights (static: 7.22 mm vs. expandable: 8.11 mm, p <0.001) at 1-year follow-up. Expandable cages offered similar improvements in segmental lordosis at 6 weeks (static: 1.69° vs. expandable: 2.81°, p =0.243), but segmental lordosis was better maintained with expandable cages leading to significant differences at 1-year follow-up (static: 0.86° vs. expandable: 2.45°, p =0.001). No significant differences were noted in total complication (static: 12.5% vs. expandable: 16.5%, p =0.191) or cage subsidence rates (static: 19.7% vs. expandable: 22.4%, p =0.502) groups at 1-year follow-up.

CONCLUSIONS

Expandable devices provide greater improvements in radiographic measurements including anterior disk height, posterior disk height, and segmental lordosis, but this did not lead to significant improvements in PROMs, complication rates, subsidence rates, or subsidence distance.

Comparison of the efficacy of expandable interbody fusion cage (EXP-IFC) and non-expandable interbody fusion cage (NE-IFC) in MIS-TLIF for lumbar degenerative diseases: A systematic retrospective study on 62 patients

OBJECTIVES

To investigate the clinical and radiographic outcomes of EXP-IFC in single-level MIS-TLIF.

METHODS

This study included patients aged ≥18 years who received a single-level MIS-TLIF procedure with at least 1 year of follow-up. Outcome measures: clinical features, preoperative and neurological complications. Imaging analysis included disc height (DH) restoration, surgical and contralateral side foraminal height (FH), lumbar lordosis angle (LL), segmental lordosis (SL). Visual analog scale (VAS) score for low back pain (VAS-LBP) and leg pain (VAS-LP), Oswestry Disability Index (ODI) and Japanese Orthopaedic Association (JOA) score were used to evaluate clinical outcomes. Statistical analysis was performed using independent sample t-test and sample t-test. The significance was set to p < 0.05 in univariate analysis.

RESULTS

A total of 62 patients undergoing single level MIS-TLIFs between January 2017 and January 2019 were included, with 32 NE-IFC 46.9% female, mean age 54.86 ± 11.65, mean body mass index (BMI) 24.59 ± 3.63) and 30 EXP (40% female, mean age 58.32 ± 12.99, mean BMI 24.45 ± 2.76) with no significant differences in demographics. There were no significant differences between two groups in Operative time (OT), Estimated blood loss (EBL) and Length of stay (LOS). No significant differences were found in VAS-LBP, VAS-LP, JOA and ODI in post-operation and the last follow-up between the two groups. The imaging outcome demonstrated that the mean increase in DH was significantly greater for the patients with EXP-IFC than those with NE-IFC group at 1 year follow-up (8.92 ± 0.51 mm EXP-IFC vs. 7.96 ± 0.96 mm NE-IFC, p < 0.001). The mean change in FH of operative and contralateral sides were observed to be significantly higher for the patients with EXP-IFC at 1 year follow-up (operative side:17.67 ± 2.29 mm EXP-IFC vs. 16.01 ± 2.73 mm NE-IFC, p = 0.042; contralateral side:17.32 ± 2.26 mm EXP-IFC vs. 16.10 ± 2.32 mm NE-IFC, p < 0.001), but changes in LL and SL were not significantly different. At the last follow-up, we did not find any significant difference in the fusion rate between the two groups.

CONCLUSION

Our results indicated that there may be no significant difference in short-term clinical outcomes between EXP-IFC and NE-IFC, but the use of EXP-IFC in MIS-TLIF can provide a significant restoration of disc height, and neural foraminal height compared to NE-IFC.

Spinal stability analysis of lumbar interbody fusion according to pelvic type and cage angle based on simplified spinal model with various pelvic indices

Recently, the objectives of lumbar interbody fusion (LIF) have been extended to include the correction of broader/relative indications in addition to spinal fixation. Accordingly, LIF must be optimized for sagittal alignment while simultaneously achieving decompression. Therefore, a representative model classified into three pelvic types, i.e., neutral pelvis (NP), anterior pelvis (AP), and retroverted pelvis (RP), was selected according to the pelvic index, and LIF was performed on each representative model to analyze Lumbar lordosis (LL) and the corresponding equivalent stress. The finite element (FE) model was based on a sagittal 2D X-ray image. The calculation efficiency and convergence were improved by simplifying the modeling of the vertebral body in general and its posterior portion in particular. Based on the position of the pelvis, according to the pelvic shape, images of patients were classified into three types: AP, RP, and NP. Subsequently, representative images were selected for each type. The fixation device used in the fusion model was a pedicle screw and a spinal rod of a general type. PEEK was used as the cage material, and the cage shape was varied by using three different cage angles: 0°, 4°, and 8°. Spinal mobility: The pelvic type with the highest range of motion (ROM) for the spine was the NP type; the AP type had the highest LL. Under a combination load, the NP type exhibited the highest lumbar flexibility (LF), which was 2.46° lower on average compared to the case where a pure moment was applied. Equivalent stress on the spinal fixation device: The equivalent stress acting on the vertebrae was lowest when cage 0 was used for the NP and AP type. For the RP type, the lowest equivalent stress on the vertebrae was observed when cage 4 was used. Finally, for the L5 upper endplate, the stress did not vary significantly for a given type of cage. In conclusion, there was no significant difference in ROM according to cage angle, and the highest ROM, LL and LF were shown in the pelvic shape of NP type. However, when comparing the results with other pelvic types, it was not possible to confirm that LF is completely dependent on LL and ROM.

History and Evolution of the Minimally Invasive Transforaminal Lumbar Interbody Fusion

The minimally invasive transforaminal lumbar interbody fusion (MIS-TLIF) is a popular surgical technique for lumbar arthrodesis, widely considered to hold great efficacy while conferring an impressive safety profile through the minimization of soft tissue damage. This elegant approach to lumbar stabilization is the byproduct of several innovations throughout the past century. In 1934, Mixter and Barr's paper in the New England Journal of Medicine elucidated the role of disc herniation in spinal instability and radiculopathy, prompting surgeons to explore new approaches and instruments to access the disc space. In 1944, Briggs and Milligan published their novel technique, the posterior lumbar interbody fusion (PLIF), involving continuous removal of vertebral bone chips and replacement of the disc with a round bone peg. The following decades witnessed several PLIF modifications, including the addition of long pedicle screws. In 1982, Harms and Rolinger sought to redefine the posterior corridor by approaching the disc space through the intervertebral foramen, establishing the transforaminal lumbar interbody fusion (TLIF). In the 1990s, lumbar spine surgery experienced a paradigm shift, with surgeons placing increased emphasis on tissuesparing minimally invasive techniques. Spurred by this revolution, Foley and Lefkowitz published the novel MIS-TLIF technique in 2002. The MIS-TLIF has demonstrated comparable surgical outcomes to the TLIF, with an improved safety profile. Here, we present a view into the history of the posterior-approach treatment of the discogenic radiculopathy, culminating in the MIS-TLIF. Additionally, we evaluate the hallmark characteristics, technical variability, and reported outcomes of the modern MIS-TLIF and take a brief look at technologies that may define the future MIS-TLIF.

Does the application of expandable cages in TLIF provide improved clinical and radiological results compared to static cages? A meta-analysis

Purpose

This study aimed to provide a direct meta-analysis of the evidence comparing outcomes between expandable cages and static cages in patients with transforaminal lumbar interbody fusion (TLIF).

Methods

A search of relevant materials from databases was performed from inception to March 7, 2022. Clinical and radiological outcomes were included.

Results

Ten studies (1,440 patients) were included. The anterior disc height and foraminal height for expandable cages were substantially higher than those for static cages at the final follow-up (P < 0.0001; P = 0.05). In comparison with static cages, although not statistically significant, expandable cages showed beneficial results, including an increase in posterior disc height and segmental lordosis. There were no statistically significant differences in segmental lordosis, lumbar lordosis, pelvic parameters, cage subsidence, or fusion rates (P > 0.05). Oswestry disability index scores for expandable cages were substantially lower than those for static cages at the final follow-up (P = 0.0007). Interestingly, although the preoperative visual analog scores for back and leg pain were significantly higher in the expandable group than in the static group (P < 0.0001; P = 0.008), there was no significant difference between the static and expandable groups during the final follow-up (P = 0.51; P = 0.85).

Conclusions

Expandable cages are associated with improved functional outcomes and restored postoperative disc and foraminal heights in patients with TLIF. In addition, no statistically significant differences were observed in segmental lordosis, lumbar lordosis, pelvic parameters, cage subsidence, or fusion rate.

What Affects Segmental Lordosis of the Surgical Site after Minimally Invasive Transforaminal Lumbar Interbody Fusion?

PURPOSE

This study was undertaken to identify factors that affect segmental lordosis (SL) after minimally invasive transforaminal lumbar interbody fusion (MIS-TLIF) by comparing patients whose postoperative SL increased with those whose decreased.

MATERIALS AND METHODS

Fifty-five patients underwent MIS-TLIF at our institute from January 2018 to September 2019. Demographic, pre- and postoperative radiologic, and cage-related factors were included. Statistical analyses were designed to compare patients whose SL increased with decreased after surgery.

RESULTS

After surgery, SL increased in 34 patients (group I) and decreased in 21 patients (group D). The index level, disc lordosis, SL, lumbar lordosis, proximal lordosis (PL), and Y-axis position of the cage (Yc) differed significantly between groups I and D. The cage in group I was more anterior than that in group D (Yc: 55.84% vs. 51.24%). Multivariate analysis showed that SL decreased more significantly after MIS-TLIF when the index level was L3/4 rather than L4/5 [odds ratio (OR): 0.46, p=0.019], as preoperative SL (OR: 0.82, p=0.037) or PL (OR: 0.68, p=0.028) increased, and as the cage became more posterior (OR: 1.10, p=0.032).

CONCLUSION

Changes in SL after MIS-TLIF appear to be associated with preoperative SL and PL, index level, and Yc. An index level at L4/5 instead of L3/4, smaller preoperative SL or PL, and an anterior position of the cage are likely to result in increased SL after MIS-TLIF.

Comparison of Long-Term Efficacy of MIS-TLIF Intraoperative Implants in Patients with Osteoporosis

Osteoporosis and degenerative spinal disease are still an unsolvable surgical problem. It is still difficult to solve the complications related to postoperative osteoporosis, such as cage subsidence, displacement, and retraction. Expandable interbody cage is a recent innovation and an increasingly popular alternative to standard static cage. However, the clinical efficacy of MIS-TLIF combined with expandable cage for the treatment of osteoporosis has limited reports. The purpose of this paper was to analyze the efficacy of MIS-TLIF with expandable cage in patients with degenerative lumbar disease with osteoporosis. Patients with osteoporosis who received single-level MIS-TLIF and were followed up for at least 1 year were included. The outcome measures are as follows: clinical features, perioperative period, and neurological complications. JOA score and VAS pain score were used to analyze the improvement of patients’ function. Imaging analysis included segmental lordosis (SL), lumbar lordosis (LL), intervertebral disc height (DH), and the ratio of cage height to preoperative DH (RCD). The final data analysis included 284 patients with osteoporosis. 178 patients used static cages, and 106 patients used expandable cages. There was no significant difference in baseline characteristics, surgical indexes, and JOA and VAS scores between the two groups. There was no difference in SL or LL between static group and expandable group. There was no significant difference in preoperative DH between the two groups. The RCD in the expansion group was significantly lower than that in the static group. The intraoperative and postoperative sedimentation rate in the static group was significantly higher than that in the expandable group. The use of expandable cages in MIS-TLIF has shown good results for the treatment of degenerative lumbar diseases with osteoporosis. Through appropriate surgical techniques, the expandable cage can reduce the risk of cage sinking.

Radiographic and clinical outcomes in one- and two-level transforaminal lumbar interbody fusions: a comparison of bullet versus banana cages

OBJECTIVE

The aim of this study was to determine whether cage morphology influences clinical and radiographic outcomes following short-segment transforaminal lumbar interbody fusion (TLIF) procedures.

METHODS

The authors retrospectively reviewed one- and two-level TLIFs at a single tertiary care center between August 2012 and November 2019 with a minimum 1-year radiographic and clinical follow-up. Two cohorts were compared based on interbody cage morphology: steerable "banana" cage or straight "bullet" cage. Patient-reported outcome measures (PROMs), radiographs, and complications were analyzed.

RESULTS

A total of 135 patients with 177 interbody levels were identified; 45 patients had 52 straight cages and 90 patients had 125 steerable cages. Segmental lordosis increased with steerable cages, while it decreased with straight cages (+3.8 ± 4.6 vs -1.9 ± 4.3, p < 0.001). Conversely, the mean segmental lordosis of adjacent lumbar levels decreased in the former group, while it increased in the latter group (-0.52 ± 1.9 vs +0.52 ± 2.1, p = 0.004). This reciprocal relationship results in global sagittal parameters, including pelvic incidence minus lumbar lordosis and lumbar distribution index, which did not change after surgery with either cage morphology. Multivariate analysis confirmed that steerable cage morphology, anterior cage positioning, and less preoperative index-level segmental lordosis were associated with greater improvement in index-level segmental lordosis. PROMs were improved after surgery with both cage types, and the degree of improvement did not differ between cohorts (p > 0.05). Perioperative and radiographic complications were similar between cohorts (p > 0.05). Overall reoperation rates, as well as reoperation rates for adjacent-segment disease within 2 years of surgery, were not significantly different between cohorts.

CONCLUSIONS

Steerable cages are more likely to lie within the anterior disc space, thus increasing index-level segmental lordosis, which is accompanied by a reciprocal change in segmental alignment at the adjacent lumbar levels. The converse relationship occurs for straight cages, with a kyphotic change at the index levels and reciprocal lordosis occurring at adjacent levels.

Expandable vs. Static Transforaminal Lumbar Interbody Fusion Cages: 1-year Radiographic Parameters and Patient Reported Outcomes

BACKGROUND

Expandable transforaminal lumbar interbody fusion (TLIF) cages capable of multidirectional in situ expansion have gained popularity as they increase axial surface area for fusion and may enhance lordotic correction through a traditional MIS surgical corridor.

OBJECTIVE

To evaluate and compare the radiographic and clinical outcomes between a novel expandable vs. static MIS TLIF cage for the treatment of degenerative disc disease.

STUDY DESIGN

A single center retrospective review of 120 consecutive adult patients undergoing 1 or 2-level MIS TLIF with an expandable (n=60) or static cage was performed between 2015-2019. Preoperative and 1-year postoperative radiographic and clinical outcomes were assessed by upright flexion/extension radiographs and serial confidential surveys.

RESULTS

120 patients (mean age 63.5 years, 60.0 % female) undergoing 1 and 2-level MIS TLIF met inclusion criteria. A statistically significant reduction of spondylolisthesis, restoration of foraminal, anterior and posterior disc height was achieved in both cohorts, but greater in the ECC (all p<0.05). Comparable rates of fusion, 93% and 91% were observed in the ECC and SCC. A significant reduction in NRS back and ODI scores were observed in both cohorts but more pronounced in the ECC (5.9±2.4 to 2.2±1.9 and 37.3±16.2 to 17.1±15.2) vs. SCC (6.2±2.8 to 3.2±2.5 and 41.8±16.1 to 24.3±17.5) (p<0.05). One instance of cage migration requiring reoperation occurred in the ECC.

CONCLUSIONS

Taken together, these radiographic and clinical findings suggest an expandable cage placed through an MIS corridor represents a safe, equitable and efficacious alternative to a static TLIF in adults with degenerative lumbar pathology.