Tag: transforaminal lumbar interbody fusion

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Segmental Lordosis After Open Transforaminal Lumbar Interbody Fusion Using Expandable Oblique Versus Static Anterior Banana Cages

Operative Neurosurgery 30:78–89, 2026

This clinical research article compares segmental and lumbar lordosis outcomes after open transforaminal lumbar interbody fusion (TLIF) with posterior column osteotomy using either static anterior “banana” cages or obliquely placed expandable cages. In a single-surgeon retrospective cohort of 210 patients (327 segments), expandable cages produced a significantly greater median change in segmental lordosis (ΔSL) by 2.0° at six months, persisting after multivariate adjustment and propensity matching.

The study also reports inconsistent effects of cage type on overall lumbar lordosis (ΔLL), with subgroup and matched analyses yielding differing results, and found no difference in subsidence or complication rates. Findings emphasize the influence of preoperative segmental lordosis, segment level (notably L5–S1), and construct length on achieved correction, while noting limitations including retrospective design and lack of clinical outcomes.

Expandable Cages: Expandable obliquely placed cages in open transforaminal lumbar interbody fusion (TLIF) with posterior column osteotomy (PCO) produce a significantly greater median increase in segmental lordosis (ΔSL) of 2.0° compared to static anteriorly placed banana cages, representing a 50% increase.

Statistical Robustness: The greater segmental lordosis achieved with expandable cages remained significant after multivariate regression analysis and propensity score matching, confirming the reliability of the finding.

Overall Lumbar Lordosis (ΔLL): No clear advantage was found between cage types regarding the change in overall lumbar lordosis, with results varying depending on the statistical method used.

Surgical Technique Consistency: All surgeries were performed open with a full PCO using a consistent technique, minimizing confounding variables related to surgical approach or technique.

Preoperative Segmental Lordosis Impact: Segments with lower preoperative segmental lordosis (<15°) experienced the greatest increase in lordosis postoperatively, regardless of cage type.

L5-S1 Segment Benefit: Expandable cages were especially favorable at the L5-S1 segment, likely due to anatomical constraints that make insertion of large static cages more challenging at this level.

Complication and Subsidence Rates: No significant differences were observed between cage types in rates of complications, cage subsidence, or spondylolisthesis correction.

Clinical Outcomes Unclear: The study did not assess clinical outcomes, so the impact of the observed radiographic differences on patient-reported outcomes remains unknown.

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Five-year follow-up after minimally invasive transforaminal lumbar interbody fusion versus decompression alone for grade 1 spondylolisthesis: are there any differences in outcomes?

J Neurosurg Spine 43:547–556, 2025

This multicenter, prospective registry study compares 60-month outcomes after minimally invasive transforaminal lumbar interbody fusion (MIS TLIF) versus minimally invasive tubular decompression for Meyerding grade 1 degenerative spondylolisthesis. Patient-reported outcomes (ODI, NRS for back/leg pain, EQ-5D, NASS satisfaction) improved significantly in both cohorts, with MIS TLIF showing greater back-pain reduction and higher satisfaction rates.

Durability differs: MIS TLIF had a markedly lower 5-year reoperation rate than MIS decompression (2.8% vs 15.5%), and multivariable analysis found fusion reduced reoperation odds despite similar long-term PROs. Authors conclude both MIS approaches benefit selected patients, but fusion offers superior reoperation durability.

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Development and internal validation of a risk score for subsidence of expandable spacers in transforaminal lumbar interbody fusion (TLIF) surgery

Brain and Spine 5 (2025) 104322

This study developed and internally validated the Expandable TLIF Subsidence Index (ETSI) to predict risk of cage subsidence after TLIF surgery with expandable spacers. Key risk factors include high ASA score, non-degenerative indication, lower lumbar levels, small cage size, and posterior cage position.

• A risk score (Expandable TLIF Subsidence Index, ETSI) was developed to predict cage subsidence (CS) after transforaminal lumbar interbody fusion (TLIF) using expandable spacers.

• The study analyzed 388 patients (482 levels), finding a 31.7% CS rate at 3 months.

• Independent risk factors for CS included high ASA score, non-degenerative surgical indication, lower lumbar level, small cage size, and posterior cage position.

• The ETSI score ranges from -2 to 6; higher scores indicate higher CS risk (each point increases CS odds by about 2x).

• Modifiable risk factors (cage size and position) can reduce CS risk if addressed during surgery.

• Higher ETSI scores are also associated with increased risk of non-union/pseudarthrosis.

• The ETSI demonstrated moderate predictive performance (AUROC ≈ 0.68).

• The score may aid surgical planning and should be externally validated in future studies.

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A survival analysis for predictors of implant subsidence following 1- or 2-level transforaminal lumbar interbody fusion

J Neurosurg Spine 43:42–51, 2025

This study found that after 1- or 2-level TLIF, aggressive disc height restoration and taller interbody implants significantly increase the risk of implant subsidence, especially in patients with poor bone quality. Surgeons should balance correction goals with subsidence risk, particularly in those with low Hounsfield unit measurements.

• This study analyzed predictors of interbody implant subsidence after 1- or 2-level transforaminal lumbar interbody fusion (TLIF) using a time-to-event (survival) analysis.

• Aggressive disc height restoration and use of taller interbody implants significantly increased the risk of subsidence.

• Poor baseline bone quality, measured by lower Hounsfield units (HU) on CT, was a strong independent predictor for significant (≥4 mm) subsidence.

• Longer fusion constructs (more instrumented levels) also increased the risk of significant subsidence.

• No significant association was found between cage material (titanium vs PEEK), device geometry, or lumbopelvic parameters and subsidence risk.

• Subsidence occurred in 38.2% of levels (≥2 mm) and significant subsidence in 10.4% (≥4 mm) by last follow-up.

• Clinical implications suggest balancing correction goals with subsidence risk, especially in patients with poor bone quality.

• Further multicenter and prospective studies are recommended to validate these findings.

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Segmental and overall lumbar lordosis after single-level minimally invasive transforaminal lumbar interbody fusion: a systematic review and meta-analysis

J Neurosurg Spine 43:70–82, 2025

This systematic review and meta-analysis found that single-level minimally invasive transforaminal lumbar interbody fusion (MI-TLIF) generally preserves segmental and overall lumbar lordosis, with preoperative alignment and use of expandable cages predicting postoperative lordosis. Greater segmental lordosis improvement was associated with reduced leg pain, but clinical outcome correlations were otherwise limited.

• Single-level minimally invasive transforaminal lumbar interbody fusion (MI-TLIF) generally preserves or slightly increases segmental and overall lumbar lordosis.

• Meta-analysis of 35 studies (1935 patients) showed significant but modest increases in segmental lordosis (mean +2.2°) and lumbar lordosis (mean +2.8°) postoperatively.

• Preoperative alignment and use of expandable cages are significant predictors of postoperative lordosis change.

• Greater improvement in segmental lordosis was associated with larger reductions in postoperative leg pain, but no strong correlation with other clinical outcomes was found.

• Most included studies were retrospective case series, with high heterogeneity in surgical technique and reporting.

• No significant association was found between facetectomy type, operative bed, or fixation technique and changes in lordosis.

• The main goal of MI-TLIF is neural decompression and fusion, not alignment correction; alternative approaches may be needed for major lordosis restoration.

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Development and internal validation of a risk score for subsidence of expandable spacers in transforaminal lumbar interbody fusion (TLIF) surgery

Brain and Spine 5 (2025) 104322

This study developed and validated the Expandable TLIF Subsidence Index (ETSI) to predict risk of cage subsidence after TLIF surgery with expandable spacers. Key risk factors include high ASA score, non-degenerative indications, lower lumbar level, small cage size, and posterior cage position. Some risk factors are modifiable.

• A risk score (ETSI) was developed to predict cage subsidence (CS) after TLIF surgery using expandable spacers.

• Independent risk factors for CS include high ASA score, non-degenerative surgical indication, lower lumbar level, small cage size, and posterior cage position.

• ETSI ranges from -2 to 6 points and shows a moderate ability to classify CS risk (AUROC ≈ 0.68).

• Modifiable risk factors (cage size and position) can reduce CS risk if optimized by the surgeon.

• Higher ETSI scores are associated with increased risk of non-union/pseudarthrosis at 3 and 12 months.

• Anterior placement of the cage lowers subsidence risk, while posterior placement increases it.

• The study included 388 patients with a 3-month CS rate of 31.7%.

• The ETSI is the first comprehensive scoring system for CS risk with expandable TLIF cages.

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Sarcopenia Predicts the Development of Early Adjacent Segment Disease After Transforaminal Lumbar Interbody Fusion

Neurosurgery 96:1044–1053, 2025

This study explores whether sarcopenia, measured by psoas morphometrics, predicts early adjacent segment disease (ASD) after transforaminal lumbar interbody fusion (TLIF). Results indicate that decreased psoas area and P:VBR are strong predictors of ASD within three years post-surgery, suggesting implications for surgical decision-making and patient counseling.

• Sarcopenia predicts early adjacent segment disease (ASD) after transforaminal lumbar interbody fusion (TLIF) surgery, as shown by decreased psoas area and P:VBR ratios.

• A retrospective study of 109 patients found that 22 (20.2%) developed ASD within 3 years post-surgery.

• Sarcopenic patients had significantly higher rates of ASD (83.33%) compared to nonsarcopenic patients (7.69%).

• Older age, diabetes, and preoperative ODI are significant predictors of ASD.

• Sarcopenia is a stronger predictor of ASD than spinopelvic parameters like PT, LL, and PI-LL mismatch.

• Identifying sarcopenic patients can guide surgical decisions and postoperative care to prevent ASD.

• The study suggests using psoas morphometrics as a simple tool to identify patients at risk for ASD.

• Further research is needed to validate findings and explore the role of sarcopenia in other surgical approaches.

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Cost-effectiveness of posterior lumbar interbody fusion and/or transforaminal lumbar interbody fusion for grade 1 lumbar spondylolisthesis: a 5-year Quality Outcomes Database study

J Neurosurg Spine 41:596–603, 2024

Posterior lumbar interbody fusion (PLIF) and/or transforaminal lumbar interbody fusion (TLIF), referred to as “PLIF/TLIF,” is a commonly performed operation for lumbar spondylolisthesis. Its long-term cost-effectiveness has not been well described. The aim of this study was to determine the 5-year cost-effectiveness of PLIF/TLIF for grade 1 degenerative lumbar spondylolisthesis using prospective data collected from the multicenter Quality Outcomes Database (QOD).

METHODS Patients enrolled in the prospective, multicenter QOD grade 1 lumbar spondylolisthesis module were included if they underwent single-stage PLIF/TLIF. EQ-5D scores at baseline, 3 months, 12 months, 24 months, 36 months, and 60 months were used to calculate gains in quality-adjusted life years (QALYs) associated with surgery relative to preoperative baseline. Healthcare-related costs associated with the index surgery and related reoperations were calculated using Medicare reimbursement–based cost estimates and validated using price transparency diagnosis-related group (DRG) charges and Medicare charge-to-cost ratios (CCRs). Cost per QALY gained over 60 months postoperatively was assessed.

RESULTS Across 12 surgical centers, 385 patients were identified. The mean patient age was 60.2 (95% CI 59.1–61.3) years, and 38% of patients were male. The reoperation rate was 5.7%. DRG 460 cost estimates were stable between our Medicare reimbursement–based models and the CCR-based model, validating the focus on Medicare reimbursement. Across the entire cohort, the mean QALY gain at 60 months postoperatively was 1.07 (95% CI 0.97–1.18), and the mean cost of PLIF/TLIF was $31,634. PLIF/TLIF was associated with a mean 60-month cost per QALY gained of $29,511. Among patients who did not undergo reoperation (n = 363), the mean 60-month QALY gain was 1.10 (95% CI 0.99–1.20), and cost per QALY gained was $27,591. Among those who underwent reoperation (n = 22), the mean 60-month QALY gain was 0.68 (95% CI 0.21–1.15), and the cost per QALY gained was $80,580.

CONCLUSIONS PLIF/TLIF for degenerative grade 1 lumbar spondylolisthesis was associated with a mean 60-month cost per QALY gained of $29,511 with Medicare fees. This is far below the well-established societal willingness-to-pay threshold of $100,000, suggesting long-term cost-effectiveness. PLIF/TLIF remains cost-effective for patients who undergo reoperation.

 

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Transforaminal lumbar interbody fusion subsidence

J Neurosurg Spine 41:463–472, 2024

The aims of this study were to 1) define the incidence of transforaminal lumbar interbody fusion (TLIF) interbody subsidence; 2) determine the relative importance of preoperative and intraoperative patient- and instrumentation-specific risk factors predictive of postoperative subsidence using CT-based assessment; and 3) determine the impact of TLIF subsidence on postoperative complications and fusion rates.

METHODS All adult patients who underwent one- or two-level TLIF for lumbar degenerative conditions at a multi-institutional academic center between 2017 and 2019 were retrospectively identified. Patients with traumatic injury, infection, malignancy, previous fusion at the index level, combined anterior-posterior procedures, surgery with greater than two TLIF levels, or incomplete follow-up were excluded. Interbody subsidence at the superior and inferior endplates of each TLIF level was directly measured on the endplate-facing surface of both coronal and sagittal CT scans obtained greater than 6 months postoperatively. Patients were grouped based on the maximum subsidence at each operative level classified as mild, moderate, or severe based on previously documented < 2-mm, 2- to 4-mm, and ≥ 4-mm thresholds, respectively. Univariate and regression analyses compared patient demographics, medical comorbidities, preoperative bone quality, surgical factors including interbody cage parameters, and fusion and complication rates across subsidence groups.

RESULTS A total of 67 patients with 85 unique fusion levels met the inclusion and exclusion criteria. Overall, 28% of levels exhibited moderate subsidence and 35% showed severe subsidence after TLIF with no significant difference in the superior and inferior endplate subsidence. Moderate (≥ 2-mm) and severe (≥ 4-mm) subsidence were significantly associated with decreases in cage surface area and Taillard index as well as interbody cages with polyetheretherketone (PEEK) material and sawtooth surface geometry. Severe subsidence was also significantly associated with taller preoperative disc spaces, decreased vertebral Hounsfield units (HU), the absence of bone morphogenetic protein (BMP) use, and smooth cage surfaces. Regression analysis revealed decreases in Taillard index, cage surface area, and HU, and the absence of BMP use predicted subsidence. Severe subsidence was found to be a predictor of pseudarthrosis but was not significantly associated with revision surgery.

CONCLUSIONS Patient-level risk factors for TLIF subsidence included decreased HU and increased preoperative disc height. Intraoperative risk factors for TLIF subsidence were decreased cage surface area, PEEK cage material, bullet cages, posterior cage positioning, smooth cage surfaces, and sawtooth surface designs. Severe subsidence predicted TLIF pseudarthrosis; however, the causality of this relationship remains unclear.

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Do expandable cage size and number of cages matter in transforaminal lumbar interbody fusion at L5–S1?

J Neurosurg Spine 41:209–215, 2024

Expandable transforaminal lumbar interbody fusion (TLIF) cages were designed to address the limitations of static cages. Bilateral cage insertion can potentially enhance stability, fusion rates, and segmental lordosis. However, the benefits of unilateral versus bilateral expandable cages with varying sizes in TLIF remain unclear. This study used a validated finite element spine model to compare the biomechanical properties of L5–S1 TLIF by using differently sized expandable cages inserted unilaterally or bilaterally.

METHODS A finite element model of X-PAC expandable lumbar cages was created and used at the L5–S1 level. This model had cage dimensions of 9 mm in height, 15° in lordosis, and varying widths and lengths. Various placements (unilateral vs bilateral) and sizes were examined under pure moment loading to evaluate range of motion, adjacent-segment motion, and endplate stress.

RESULTS Stability at the L5–S1 level decreased when smaller cages were used in both the unilateral and bilateral cage models. In the unilateral model, cage 1 (the smallest cage) resulted in 47.9% more motion at the L5–S1 level compared to cage 5 (the largest cage) in flexion, as well as 64.8% more motion in extension. Similarly, in the bilateral TLIF model, bilateral cage 1 led to 49.4% more motion at the L5–S1 level in flexion and 73.4% more motion in extension compared to bilateral cage 5. Unilateral insertion of cage 5 provided superior stability in flexion and surpassed cages 1–3 in extension when compared to cages inserted either unilaterally or bilaterally. Reduced motion at L5–S1 correlated with increased adjacent-segment motion at L4–5. Bilateral TLIF resulted in greater adjacent-segment motion compared to unilateral TLIF with the same-size cages. Inferior endplates experienced higher stress during flexion and extension than superior endplates, with this difference being more pronounced in the bilateral model. In bilateral cage placement, stress differences ranged from 46.3% to 60.0%, while they ranged from 1.1% to 9.6% in unilateral cages. Qualitative analysis revealed increased focal stress in unilateral cages versus bilateral cages.

CONCLUSIONS The authors’ study shows that using a large unilateral TLIF cage may offer better stability than the bilateral insertion of smaller cages. While large bilateral cages increase adjacent-segment motion, they also provide a uniform stress distribution on the endplates. These findings deepen our understanding of the biomechanics of the available expandable TLIF cages.

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A comparison of modern-era anterior lumbar interbody fusion and minimally invasive transforaminal lumbar interbody fusion at the lumbosacral junction

J Neurosurg Spine 39:785–792, 2023

Interbody fusion is the primary method for achieving arthrodesis across the lumbosacral junction in the setting of degenerative pathologies, such as spondylosis and spondylolisthesis. Two common techniques are anterior lumbar interbody fusion (ALIF) and posterior transforaminal lumbar interbody fusion (TLIF). In recent years, interbody design and technology have advanced, and most earlier studies comparing ALIF and TLIF did not specifically assess the lumbosacral junction. This study compared changes in radiographic and clinical parameters between patients undergoing modern-era single-level ALIF and minimally invasive surgery (MIS) TLIF at L5–S1.

METHODS Consecutive patients who underwent single-segment L5–S1 ALIF or MIS TLIF performed by the senior authors over a 6-year interval (January 1, 2016–November 30, 2021) were retrospectively reviewed. Upright radiographs were used to determine pre- and postoperative lumbar lordosis, segmental lordosis, disc angle, and neuroforaminal height. Improvements in patient-reported outcome scores (Oswestry Disability Index and SF-36) were also compared.

RESULTS Overall, 108 patients (58 [54%] men, 50 [46%] women; mean [SD] age 57.6 [13.5] years) were included in the study. ALIF was performed in 49 patients, and TLIF was performed in 59 patients. The most common treatment indications were spondylolisthesis (50%, 54/108) and spondylosis (46%, 50/108). The cohorts did not differ in terms of intraoperative (p > 0.99) or postoperative (p = 0.73) complication rates. The mean (SD) hospital length of stay was significantly shorter for patients undergoing TLIF than ALIF (1.3 [0.6] days vs 2.0 [1.4] days, p < 0.001). Both techniques significantly improved L5–S1 segmental lordosis, disc angle, and neuroforaminal height (p ≤ 0.008). ALIF versus TLIF significantly increased mean [SD] segmental lordosis (12.5° [7.3°] vs 2.0° [5.7°], p < 0.001), disc angle (14.8° [5.5°] vs 3.0° [6.1°], p < 0.001), and neuroforaminal height (4.5 [4.6] mm vs 2.4 [3.0] mm, p = 0.008). Improvements in patient-reported outcome parameters and reoperation rates were similar between cohorts.

CONCLUSIONS When treating patients at a single segment across the lumbosacral junction, ALIF resulted in significantly greater increases in segmental lordosis, L5–S1 disc angle, and neuroforaminal height compared with MIS TLIF. Improvements in clinical parameters and reoperation rates were similar between the 2 techniques.

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Minimally Invasive Transforaminal Lumbar Interbody Fusion in the Ambulatory Surgery Center Versus Inpatient Setting: A 1-Year Comparative Effectiveness Analysis

Neurosurgery 93:867–874, 2023

Ambulatory surgery centers (ASCs) have emerged as an alternative setting for surgical care as part of the national effort to lower health care costs. The literature regarding the safety of minimally invasive transforaminal lumbar interbody fusion (MIS TLIF) in the ASC setting is limited to few small case series.

OBJECTIVE: To assess the safety and efficacy of MIS TLIF performed in the ASC vs inpatient hospital setting.

METHODS: A total of 775 patients prospectively enrolled in the Quality Outcomes Database undergoing single-level MIS TLIF at a single ASC (100) or the inpatient hospital setting (675) were compared. Propensity matching generated 200 patients for analysis (100 per cohort). Demographic data, resource utilization, patient-reported outcome measures (PROMs), and patient satisfaction were assessed.

RESULTS: There were no significant differences regarding baseline demographic data, clinical history, or comorbidities after propensity matching. Only 1 patient required inpatient transfer from the ASC because of intractable pain. All other patients were discharged home within 23 hours of surgery. The rates of 90-day readmission (2.0%) and reoperation (0%) were equivalent between groups. Both groups experienced significant improvements in all PROMs (Oswestry Disability Index, EuroQol-5D, back pain, and leg pain) at 3 months that were maintained at 1 year. PROMs did not differ between groups at any time point. Patient satisfaction was similar between groups at 3 and 12 months after surgery.

CONCLUSION: In carefully selected patients, MIS TLIF may be performed safely in the ASC setting with no statistically significant difference in safety or efficacy in comparison with the inpatient setting.

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Clinical Outcomes of Liposomal Bupivacaine Erector Spinae Block in Minimally Invasive Transforaminal Lumbar Interbody Fusion Surgery

Neurosurgery 92:590–598, 2023

Postoperative pain is a barrier to early mobility and discharge after lumbar surgery. Liposomal bupivacaine (LB) has been shown to decrease postoperative pain and narcotic consumption after transforaminal lumbar interbody fusions (TLIFs) when injected into the marginal suprafascial/subfascial plane-liposomal bupivacaine (MSSP-LB). Erector spinae plane (ESP) infiltration is a relatively new analgesic technique that may offer additional benefits when performed in addition to MSSP-LB.

OBJECTIVE: To evaluate postoperative outcomes of combining ESP-LB with MSSP-LB compared with MSSP-LB alone after single-level TLIF.

METHODS: A retrospective analysis was performed for patients undergoing single-level TLIFs under spinal anesthesia, 25 receiving combined ESP-LB and MSSP-LB and 25 receiving MSSP-LB alone. The primary outcome was length of hospitalization. Secondary outcomes included postoperative pain score, time to ambulation, and narcotics usage.

RESULTS: Baseline demographics and length of surgery were similar between groups. Hospitalization was significantly decreased in the ESP-LB + MSSP-LB cohort (2.56 days vs 3.36 days, P = .007), as were days to ambulation (0.96 days vs 1.29 days, P = .026). Postoperative pain area under the curve was significantly decreased for ESP-LB + MSSP-LB at 12 to 24 hours (39.37 ± 21.02 vs 53.38 ± 22.11, P = .03) and total (44.46 ± 19.89 vs 50.51 ± 22.15, P = .025). Postoperative narcotic use was significantly less in the ESP-LB + MSSP-LB group at 12 to 24 hours (13.18 ± 4.65 vs 14.78 ± 4.44, P = .03) and for total hospitalization (137.3 ± 96.3 vs 194.7 ± 110.2, P = .04).

CONCLUSION: Combining ESP-LB with MSSP-LB is superior to MSSP-LB alone for single level TLIFs in decreasing length of hospital stay, time to ambulation, postoperative pain, and narcotic use.

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Comparison of local and regional radiographic outcomes in minimally invasive and open TLIF

J Neurosurg Spine 37:384–394, 2022

Local and regional radiographic outcomes following minimally invasive (MI) transforaminal lumbar interbody fusion (TLIF) versus open TLIF remain unclear. The purpose of this study was to provide a comprehensive assessment of local and regional radiographic parameters following MI-TLIF and open TLIF. The authors hypothesized that open TLIF provides greater segmental and global lordosis correction than MI-TLIF.

METHODS A single-center retrospective cohort study of consecutive patients undergoing MI- or open TLIF for grade I degenerative spondylolisthesis was performed. One-to-one nearest-neighbor propensity score matching (PSM) was used to match patients who underwent open TLIF to those who underwent MI-TLIF. Sagittal segmental radiographic measures included segmental lordosis (SL), anterior disc height (ADH), posterior disc height (PDH), foraminal height (FH), percent spondylolisthesis, and cage position. Lumbopelvic radiographic parameters included overall lumbar lordosis (LL), pelvic incidence (PI)–lumbar lordosis (PI-LL) mismatch, sacral slope (SS), and pelvic tilt (PT). Change in segmental or overall lordosis after surgery was considered “lordosing” if the change was > 0° and “kyphosing” if it was ≤ 0°. Student t-tests or Wilcoxon rank-sum tests were used to compare outcomes between MI-TLIF and open-TLIF groups.

RESULTS A total of 267 patients were included in the study, 114 (43%) who underwent MI-TLIF and 153 (57%) who underwent open TLIF, with an average follow-up of 56.6 weeks (SD 23.5 weeks). After PSM, there were 75 patients in each group. At the latest follow-up both MI- and open-TLIF patients experienced significant improvements in assessment scores obtained with the Oswestry Disability Index (ODI) and the numeric rating scale for low-back pain (NRS-BP), without significant differences between groups (p > 0.05). Both MI- and open-TLIF patients experienced significant improvements in SL, ADH, and percent corrected spondylolisthesis compared to baseline (p < 0.001). However, the MI-TLIF group experienced significantly larger magnitudes of correction with respect to these metrics (ΔSL 4.14° ± 4.35° vs 1.15° ± 3.88°, p < 0.001; ΔADH 4.25 ± 3.68 vs 1.41 ± 3.77 mm, p < 0.001; percent corrected spondylolisthesis: −10.82% ± 6.47% vs −5.87% ± 8.32%, p < 0.001). In the MI-TLIF group, LL improved in 44% (0.3° ± 8.5°) of the cases, compared to 48% (0.9° ± 6.4°) of the cases in the open-TLIF group (p > 0.05). Stratification by operative technique (unilateral vs bilateral facetectomy) and by interbody device (static vs expandable) did not yield statistically significant differences (p > 0.05).

CONCLUSIONS Both MI- and open-TLIF patients experienced significant improvements in patient-reported outcome (PRO) measures and local radiographic parameters, with neutral effects on regional alignment. Surprisingly, in our cohort, change in SL was significantly greater in MI-TLIF patients, perhaps reflecting the effect of operative techniques, technological innovations, and the preservation of the posterior tension band. Taking these results together, no significant overall differences in LL between groups were demonstrated, which suggests that MI-TLIF is comparable to open approaches in providing radiographic correction after surgery. These findings suggest that alignment targets can be achieved by either MI- or open-TLIF approaches, highlighting the importance of surgeon attention to these variables.

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

J Neurosurg Spine 36:918–927, 2022

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.

 

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Minimally Invasive Transforaminal Lumbar Interbody Fusion: Cost of a Surgeon’s Learning Curve

World Neurosurg. (2022) 162:e1-e7

Minimally invasive transforaminal interbody fusion has become an increasingly common approach in adult degenerative spine disease but is associated with a steep learning curve. We sought to evaluate the impact of the learning experience on mean procedure time and mean cost associated with each procedure.

METHODS: We studied the first 100 consecutive minimally invasive transforaminal interbody fusion procedures of a single surgeon. We performed multivariable linear regression models, modeling operating time, and costs in function of the procedure order adjusted for patients’ age, sex, and number of surgical levels. The number of procedures necessary to attain proficiency was determined through a k-means cluster analysis. Finally, the total excess operative time and total excess cost until obtaining proficiency was evaluated.

RESULTS: Procedure order was found to impact procedure time and mean costs, with each successive case being associated with progressively less procedure time and cost. On average, each successive case was associated with a reduction in procedure time of 0.97 minutes (95% confidence interval 0.54e1.40; P < 0.001) and an average adjusted reduction in overall costs of $82.75 (95% confidence interval $35.93e129.57; P < 0.001). An estimated 58 procedures were needed to attain proficiency, translating into an excess procedure time of 2604.2 minutes (average of 45 minutes per case), overall costs associated with the learning experience of $226,563.8 (average of $3974.80 per case), and excess surgical cost of $125,836.6 (average of $2207.66 per case).

CONCLUSIONS: Successive cases were associated with progressively less procedure time and mean overall and surgical costs, until a proficiency threshold was attained.

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Robotic-Assisted vs Nonrobotic-Assisted Minimally Invasive Transforaminal Lumbar Interbody Fusion: A Cost-Utility Analysis

Neurosurgery 90:192–198, 2022

Management of degenerative disease of the spine has evolved to favor minimally invasive techniques, including nonrobotic-assisted and robotic-assisted minimally invasive transforaminal lumbar interbody fusion (MIS-TLIF). Value-based spending is being increasingly implemented to control rising costs in the US healthcare system. With an aging population, it is fundamental to understand which procedure(s) may be most cost-effective.

OBJECTIVE: To compare robotic and nonrobotic MIS-TLIF through a cost-utility analysis.

METHODS: We considered direct medical costs related to surgical intervention and to the hospital stay, as well as 1-yr utilities. We estimated costs by assessing all cases involving adults undergoing robotic surgery at a single institution and an equal number of patients undergoing nonrobotic surgery, matched by demographic and clinical characteristics. We adopted a willingness to pay of $50 000/quality-adjusted life year (QALY). Uncertainty was addressed by deterministic and probabilistic sensitivity analyses.

RESULTS: Costs were estimated based on a total of 76 patients, including 38 undergoing robot-assisted and 38 matched patients undergoing nonrobot MIS-TLIF. Using point estimates, robotic surgery was projected to cost $21 546.80 and to be associated with 0.68 QALY, and nonrobotic surgery was projected to cost $22 398.98 and to be associated with 0.67 QALY. Robotic surgery was found to be more cost-effective strategy, with costeffectiveness being sensitive operating room/materials and room costs. Probabilistic sensitivity analysis identified robotic surgery as cost-effective in 63% of simulations.

CONCLUSION: Our results suggest that at a willingness to pay of $50 000/QALY, robotic assisted MIS-TLIF was cost-effective in 63% of simulations. Cost-effectiveness depends on operating room and room (admission) costs, with potentially different results under distinct neurosurgical practices.

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Does transforaminal lumbar interbody fusion induce lordosis or kyphosis?

J Neurosurg Spine 35:419–426, 2021

Conflicting reports exist about whether transforaminal lumbar interbody fusion (TLIF) induces lordosis or kyphosis, ranging from decreasing lordosis by 3.71° to increasing it by 18.8°. In this study, the authors’ aim was to identify factors that result in kyphosis or lordosis after TLIF.

METHODS A single-center, retrospective study of open TLIF without osteotomy for spondylolisthesis with a minimum 2-year follow-up was undertaken. Preoperative and postoperative clinical and radiographic parameters and cage specifics were collected. TLIFs were considered to be “lordosing” if postoperative induction of lordosis was > 0° and “kyphosing” if postoperative induction of lordosis was ≤ 0°.

RESULTS A total of 137 patients with an average follow-up of 52.5 months (range 24–130 months) were included. The overall postoperative disc angle (DA) and segmental lordosis (SL) increased by 1.96° and 1.88° (p = 0.003 and p = 0.038), respectively, whereas overall lumbar lordosis remained unchanged (p = 0.133). Seventy-nine patients had lordosing TLIFs with a mean SL increase of 5.72° ± 3.97°, and 58 patients had kyphosing TLIFs with a mean decrease of 3.02° ± 2.98°. Multivariate analysis showed that a lower preoperative DA, lower preoperative SL, and anterior cage placement were correlated with the greatest increase in postoperative SL (p = 0.040, p < 0.001, and p = 0.035, respectively). There was no difference in demographics, cage type or height, or spinopelvic parameters between the groups (p > 0.05). Linear regression showed that the preoperative DA and SL correlated with SL after TLIF (R2 = 0.198, p < 0.001; and R2 = 0.2931, p < 0.001, respectively).

CONCLUSIONS Whether a TLIF induces kyphosis or lordosis depends on the preoperative DA, preoperative SL, and cage position. Less-lordotic segments became more lordotic postoperatively, and highly lordotic segments may lose lordosis after TLIF. Cages placed more anteriorly were associated with more lordosis.

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Transforaminal lumbar interbody fusion using a novel minimally invasive expandable interbody cage

J Neurosurg Spine 35:170–176, 2021

The goal of this study was to evaluate the clinical and radiographic outcomes of a novel multidirectional in situ expandable minimally invasive surgery (MIS) transforaminal lumbar interbody fusion (TLIF) cage.

METHODS A retrospective analysis of 69 consecutive patients undergoing a 1- or 2-level MIS TLIF using an expandable cage was performed over a 2-year period. Standard MIS techniques with pedicle screw fixation were used in all cases. Upright lateral dynamic flexion/extension radiographs were reviewed prior to and at 1 year after surgery. Clinical metrics included numeric rating scale for back and leg pain, Oswestry Disability Index, and the SF-12 and VR-12 physical and mental health surveys. Radiographic parameters included anterior and posterior disc height, neuroforaminal height, spondylolisthesis, segmental lordosis, lumbar lordosis, and fusion rate.

RESULTS A total of 69 patients representing 75 operative levels met study inclusion criteria. The mean patient age at surgery was 63.4 ± 1.2 years, with a female predominance of 51%. The average radiographic and clinical follow-ups were 372 and 368 days, respectively. A total of 63 patients (91%) underwent 1-level surgery and 6 patients (9%) underwent 2-level surgery. Significant reductions of numeric rating scale scores for back and leg pain were observed—from 6.1 ± 0.7 to 2.5 ± 0.3 (p < 0.0001) and 4.9 ± 0.6 to 1.9 ± 0.2 (p < 0.0001), respectively. A similar reduction in Oswestry Disability Index from 38.0 ± 4.6 to 20.0 ± 2.3 (p < 0.0001) was noted. Likewise, SF-12 and VR-12 scores all showed statistically significant improvement from baseline (p < 0.001). The mean anterior and posterior disc heights improved from 8.7 ± 1.0 mm to 13.4 ± 1.5 mm (p = 0.0001) and 6.5 ± 0.8 mm to 9.6 ± 1.1 mm (p = 0.0001), respectively. Neuroforaminal height improved from 17.6 ± 2.0 mm to 21.9 ± 2.5 mm (p = 0.0001). When present, spondylolisthesis was, on average, reduced from 4.3 ± 0.5 mm to 1.9 ± 0.2 mm (p = 0.0001). Lumbar lordosis improved from 47.8° ± 5.5° to 58.5° ± 6.8° (p = 0.2687), and no significant change in segmental lordosis was observed. The overall rate of radiographic fusion was 93.3% at 1 year. No perioperative complications requiring operative revision were encountered.

CONCLUSIONS In this series of MIS TLIFs, use of this novel interbody cage was shown to be safe and effective. Significant improvements in pain and disability were observed. Effective and durable restoration of disc height and neuroforaminal height and reduction of spondylolisthesis were obtained, with concurrent gains in lumbar lordosis. Taken together, this device offers excellent clinical and radiographic outcomes via an MIS approach.

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

J Neurosurg Spine 34:471–480, 2021

Potential advantages of using expandable versus static cages during transforaminal lumbar interbody fusion (TLIF) are not fully established. The authors aimed to compare the long-term radiographic outcomes of expandable versus static TLIF cages.

METHODS A retrospective review of 1- and 2-level TLIFs over a 10-year period with expandable and static cages was performed at the University of California, San Francisco. Patients with posterior column osteotomy (PCO) were subdivided. Fusion assessment, cage subsidence, anterior and posterior disc height, foraminal dimensions, pelvic incidence (PI), segmental lordosis (SL), lumbar lordosis (LL), pelvic incidence–lumbar lordosis mismatch (PI-LL), pelvic tilt (PT), sacral slope (SS), and sagittal vertical axis (SVA) were assessed.

RESULTS A consecutive series of 178 patients (with a total of 210 levels) who underwent TLIF using either static (148 levels) or expandable cages (62 levels) was reviewed. The mean patient age was 60.3 ± 11.5 years and 62.8 ± 14.1 years for the static and expandable cage groups, respectively. The mean follow-up was 42.9 ± 29.4 months for the static cage group and 27.6 ± 14.1 months for the expandable cage group. Within the 1-level TLIF group, the SL and PI-LL improved with statistical significance regardless of whether PCO was performed; however, the static group with PCOs also had statistically significant improvement in LL and SVA. The expandable cage with PCO subgroup had significant improvement in SL only. All of the foraminal parameters improved with statistical significance, regardless of the type of cages used; however, the expandable cage group had greater improvement in disc height restoration. The incidence of cage subsidence was higher in the expandable group (19.7% vs 5.4%, p = 0.0017). Within the expandable group, the unilateral facetectomy-only subgroup had a 5.6 times higher subsidence rate than the PCO subgroup (26.8% vs 4.8%, p = 0.04). Four expandable cages collapsed over time.

CONCLUSIONS Expandable TLIF cages may initially restore disc height better than static cages, but they also have higher rates of subsidence. Unilateral facetectomy alone may result in more subsidence with expandable cages than using bilateral PCO, potentially because of insufficient facet release. Although expandable cages may have more power to induce lordosis and restore disc height than static cages, subsidence and endplate violation may negate any significant gains compared to static cages.

 

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