Analysis of a Unilateral Bridging Cage for Lumbar Interbody Fusion: 2-Year Clinical Results and Fusion Rate with a Focus on Subsidence

Characteristics of interbody bone graft fusion after transforaminal lumbar interbody fusion according to intervertebral space division

BACKGROUND

According to intervertebral space division, the characteristics of interbody bone graft fusion after transforaminal lumbar interbody fusion (TLIF) were assessed via computed tomography (CT) scan to provide a theoretical basis for selecting the bone grafting site of interbody fusion.

METHODS

The medical records of 57 patients with lumbar spinal stenosis and disc herniation treated with TLIF were analysed retrospectively. In total, 57 segments received lumbar interbody fusion. A thin-layer CT scan was performed to evaluate fusion in each zone of the fusion space.

RESULTS

The fusion rates were 57.89% (n = 33) in the anterior cage zone, 73.68% (n = 42) in the posterior cage zone, 66.67% (n = 38) in the decompression zone, 26.32% (n = 15) in the contralateral decompression zone and 94.74% (n = 54) in the inner cage zone. There were significant differences among the fusion rates of the five zones (P < 0.001). Further pairwise comparison revealed that the fusion rates in the inner cage significantly differed from the anterior and posterior cages and decompression and contralateral decompression zones (P = 0.001, 0.002, 0.001 and 0.001, respectively).

CONCLUSION

We think the central cage zone (i.e., inner cage) should be the focus of bone grafting. Although there is small volume of bone graft on the posterior cage zone, the fusion rate is relatively high, only secondary to the inner cage zone. The fusion rate is of the contralateral decompression zone is lower although there is a bone graft.

Radiographic Analysis of Pedicle Screw Retractor-Assisted Transforaminal Lumbar Interbody Fusion for Single-Segment Spondylolisthesis in Adults: A Retrospective Study and Technical Note

Objectives

The objective of this study was to introduce a retractor that can be temporarily installed on unilateral pedicle screws to achieve distraction‐reduction and nerve root protection, and to analyze the efficacy and safety of retractor‐assisted transforaminal lumbar interbody fusion (TLIF) in the treatment of lumbar spondylolisthesis.

Methods

This was a retrospective study of 125 patients who underwent retractor‐assisted TLIF for single‐segment spondylolisthesis from November 2017 to February 2021. Based on morphology, patients were divided into degenerative (N = 66) and isthmic groups (N = 59). Differences in demographics and preoperative characteristics between the groups were analyzed using the independent samples t‐test and χ² test. Changes in radiographic parameters (disc height, foramen height, spondylolisthesis degree, slippage length, and segmental lordosis) before and after surgery were compared using the paired samples t‐test. Logistic regression analysis was performed to analyze the relationship between facet joint angle (FJA) and degenerative lumbar spondylolisthesis (DLS).

Results

Unilateral screw retractor‐assisted TLIF significantly corrected spondylolisthesis and improved disc height and segmental lordosis (p < 0.05). There was no significant difference in foramen height between the two sides before and after operation (pre: 15.81 ± 3.58 mm vs 15.69 ± 3.68 mm, p = 0.599; post: 18.65 ± 2.31 mm vs 18.74 ± 2.26 mm, p = 0.516). The degree of spondylolisthesis in the DLS group before surgery was significantly lower than that in the isthmic spondylolisthesis group (17.70 ± 5.62% vs 25.18 ± 9.73%, p < 0.001), whereas a similar degree of correction could be achieved after surgery (5.91 ± 3.12% vs 7.16 ± 5.69%, p = 0.135). FJAs from L3/4 to L5/S1 were significantly smaller in patients with DLS than those in with isthmic spondylolisthesis (p < 0.05). Patients with facet sagittalization were more likely to have DLS (β: −0.101, odds ratio [OR]:0.904, 95% confidence interval [CI]: 0.874–0.934, p < 0.001), while the cut‐off FJA of L4/5 for predicting L4 spondylolisthesis was 53.19.

Conclusions

Pedicle screw retractor‐assisted TLIF is effective and safe in treating both degenerative and isthmic lumbar spondylolisthesis. The unilateral retractor has the capacity to maintain the disc height achieved by paddle distractors, which optimizes the nerve protection and distractor placement. Patients with an FJA on L4/5 <53.19 were more likely to have DLS.

Minimally invasive transforaminal lumbar interbody fusion with expandable articulating interbody spacers significantly improves radiographic outcomes compared to static interbody spacers

Background

The goal of minimally invasive transforaminal lumbar interbody fusion (MI TLIF) is to restore and maintain disc height and lordosis until arthrodesis occurs, while minimizing muscle disruption and improving recovery time. The purpose of this study was to compare the radiographic outcomes in patients treated with an articulating expandable spacer in MI TLIF to more traditional static spacers.

Methods

This was a multi-site, multi-surgeon, Institutional Review Board-exempt, retrospective clinical study from a prospectively collected database. It included 48 patients with a diagnosis of degenerative disc disease (DDD) at one level from L2 to S1 with or without Grade 1 spondylolisthesis who underwent MI TLIF using either an articulating expandable or static interbody spacer. Twenty-seven patients were in the banana-shaped articulating expandable interbody spacer (ALTERA^®, Globus Medical, Inc., Audubon, PA, USA) group, while 21 patients were in the static interbody spacer group. Both groups had supplemental posterior pedicle screw and rod fixation. Radiographic records were assessed for disc height, neuroforaminal height, and lordosis at baseline, 3 and 6 months, and final follow-up.

Results

The articulating expandable spacer group displayed significantly greater improvement in anterior disc height from baseline compared to the static spacer group at 6 weeks, 3 and 6 months, and final follow-up by averages of 2.6 mm (79%), 2.8 mm (92%), 3.4 mm (105%), and 3.8 mm (139%), respectively (P<0.05). Mean increases in posterior disc height were significantly greater in the expandable group compared to the static group by 1.2 mm (65%) and 1.7 mm (104%) at 6 months and final follow-up, respectively (P<0.05). Articulating expandable spacers produced significantly greater average improvement by 4.0 mm in neuroforaminal height from baseline to final follow-up compared to static spacers (P<0.05). Increases in intervertebral angle from baseline were significantly greater in the expandable group than in the static group at 3 and 6 months, and final follow-up by averages of 2.5°, 2.8°, and 3.1°, respectively (P<0.05). The articulating expandable spacer group resulted in significantly greater improvements in lumbar lordosis from baseline to 3 and 6 months than the static spacer group by 4.4° and 4.0°, respectively (P<0.05).

Conclusions

MI TLIF with articulating expandable interbody spacers provides significant restoration and maintenance of disc height, neuroforaminal height, and lordosis compared to static spacers in this comparative cohort. Long-term clinical outcomes are needed to correlate with these radiographic improvements.

Cage or Pelvic Graft-Study on Bony Fusion of the Ventral Thoracic and Lumbar Spine in Traumatic Vertebral Fractures

Background and Objectives: Stabilization of the spine by cage implantation or autologous pelvic bone graft are surgical methods for the treatment of traumatic spine fractures. These methods serve to stably re-adjust the spine and to prevent late detrimental effects such as pain or increasing kyphosis. They both involve ventral interventions using interbody fusion to replace the intervertebral disc space between the vertebral bodies either by cages or autologous pelvic bone grafts. We examined which of these methods serves the patients better in terms of bone fusion and the long-term clinical outcome. Materials and Methods: Forty-six patients with traumatic fractures (12 cages; mean age: 54.08/34 pelvic bone grafts; mean age: 42.18) who received an anterior fusion in the thoracic or lumbar spine were included in the study. Postoperative X-ray images were evaluated, and fusion of the stabilized segment was inspected by two experienced spine surgeons. The time to discharge from hospital and gender differences were evaluated. Results: There was a significant difference of the bone fusion rate of patients with autologous pelvic bone grafts in favor of cage implantation (p = 0.0216). Also, the stationary phase of patients who received cage implantations was clearly shorter (17.50 days vs. 23.85 days; p = 0.0089). In addition, we observed a significant gender difference with respect to the bony fusion rate in favor of females treated with cage implantations (p < 0.0001). Conclusions: Cage implantations after spinal fractures result in better bony fusion rates as compared to autologous pelvic bone grafts and a shorter stay of the patients in the hospital. Thus, we conclude that cage implantations rather than autologous pelvic bone grafts should be the preferred surgical treatment for stabilizing the spine after fracture.

Salvage Oblique Lateral Interbody Fusion for Pseudarthrosis after Posterior/Transforaminal Lumbar Interbody Fusion: A Technical Note

OBJECTIVE

This study aims to demonstrate the efficacy of salvage oblique lumbar interbody fusion (OLIF) surgery for pseudarthrosis after posterior/transforaminal lumbar interbody fusion (PLIF/TLIF).

METHODS

The study group were patients with leg or back pain induced by pseudarthrosis after PLIF/TLIF. These patients underwent salvage OLIF surgeries in our institutions between July 2015 and Oct 2019. We retrospectively evaluated their clinical and radiographic outcomes.

RESULTS

Seven consecutive patients (all male; mean age 68.4 ± 9.3 years, range 53-81 years) were included in this study. There was no intraoperative complications in all cases. Six of 7 patients achieved bone union (at average 33.4 months follow-up) and had a successful postoperative course. Only 1 patient failed to gain bony fusion and required additional revision surgery due to progression of sagittal and coronal malalignment at 18 months after salvage OLIF surgery.

CONCLUSIONS

The salvage OLIF approach was useful option for pseudarthrosis after PLIF/TLIF. It enabled us to build a rigid anterior support, allowed for extensive curettage of intervertebral scar tissue, and reduced the rate of the complications associated with dealing with posterior scar tissue.

A Biomechanical Model for Testing Cage Subsidence in Spine Specimens with Osteopenia or Osteoporosis Under Permanent Maximum Load

BACKGROUND

Intervertebral fusions in cases of reduced bone density are a tough challenge. From a biomechanical point of view, most current studies have focused on the range of motion or have shown test setups for single-component tests. Definitive setups for biomechanical testing of the primary stability of a 360° fusion using a screw-rod system and cage on osteoporotic spine are missing. The aim of this study was to develop a test stand to provide information about the bone-implant interface under reproducible conditions.

METHODS

After pretesting with artificial bone, functional spine units were tested with 360° fusion in the transforaminal lumbar interbody fusion technique. The movement sequences were conducted in flexion/extension, right and left lateral bending, and right and left axial rotation on a human model with osteopenia or osteoporosis under permanent maximum load with 7.5 N-m.

RESULTS

During the testing of human cadavers, 4 vertebrae were fully tested and were inconspicuous even after radiological and macroscopic examination. One vertebra showed a subsidence of 2 mm, and 1 vertebra had a cage collapsed into the vertebra.

CONCLUSIONS

This setup is suitable for biomechanical testing of cyclical continuous loads on the spine with reduced bone quality or osteoporosis. The embedding method is stable and ensures a purely single-level setup with different trajectories, especially when using the cortical bone trajectory. Optical monitoring provides a very accurate indication of cage movement, which correlates with the macroscopic and radiological results.

Posterior Lumbar Interbody Fusion Versus Transforaminal Lumbar Interbody Fusion: Finite Element Analysis of the Vibration Characteristics of Fused Lumbar Spine

OBJECTIVE

Previous studies have investigated biomechanical characteristics of the lumbar spine after different types of lumbar interbody fusion surgery under static loadings. However, very few have dealt with the whole-body vibration (WBV) condition that is typically present in vehicles. The aim of this study was to compare the influence of posterior lumbar interbody fusion (PLIF) and transforaminal lumbar interbody fusion (TLIF) on dynamic responses of the fused lumbar spine to vertical WBV.

METHODS

The PLIF and TLIF procedures with bilateral pedicle screw fixation at L4-L5 level were simulated by modifying a previously validated intact lumbar L1-S1 finite element model. The PLIF and TLIF models were subjected to a sinusoidal vertical load with a compressive follower preload, and computed for transient dynamic analysis. The obtained dynamic responses for the models at the fused and adjacent levels were collected and compared.

RESULTS

The results showed that the contact force between endplate and cage was higher in the PLIF model than in the TLIF model, indicating that PLIF allowed for higher compressive load across the anterior structure. At fused L4-L5 level, the TLIF led to a higher stress in the endplate and posterior BPSF system than the PLIF. At adjacent L3-L4 level and L5-S1 level, the computed dynamic responses, in terms of stress and deformation, for the PLIF and TLIF models showed very few differences.

CONCLUSIONS

This study may be helpful to quantify dynamic mechanical properties of the fused lumbar spine, and better understand biomechanical differences between the PLIF and TLIF procedures during vibration.

Oblique insertion of a straight cage during single level TLIF procedure proves to be non-inferior in terms of restoring segmental lordosis

Introduction

With increasing relevance of the postoperative spinopelvic alignment, achieving optimal restoration of segmental lordosis (SL) during transforaminal lumbar interbody fusion (TLIF) has become increasingly important. However, despite the easier insertion of the straight cage, its potential to restore SL is still considered inferior to the preferred insert-and-rotate technique with a banana-shaped cage.

Research question

To determine, if simple oblique insertion of a straight cage allows for an equally effective restoration of SL, but reduces risk for intraoperative cage subsidence requiring revision surgery.

Material and methods

The authors retrospectively identified 81 patients who underwent single-level TLIF between 11/2017-03/2020. 40 patients were included in the straight cage group, 41 patients in the banana cage group. The authors determined pre- and postoperative SL from plain lateral radiographs. Bone density was analyzed on computed tomographs using Hounsfield unit (HU) values.

Results

Both cage types were equally effective in restoring SL. However, 7.3% in the banana cage group, but none in the straight cage group, had to undergo revision surgery due to intraoperative cage subsidence. This was related to reduced bone density with lower HU values.

Discussion

With an extended dorsal release, the straight cage may be equally effective in restoring SL. Since no repositioning is needed after oblique insertion, the straight cage might cause less intraoperative endplate violation.

Conclusion

Provided an adequate surgical technique, both cage types might be equally effective in restoring SL after one-level TLIF surgery. However, the straight cage might represent the safer alternative in patients with reduced bone quality.

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Straight cage in single-level TLIF equally effective in restoring segmental lordosis.

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Straight cage might cause less revisions due to intraoperative cage subsidence.

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Straight cage might be safer in patients with reduced bone quality.

Load Sharing and Endplate Pressure Distribution in Anterior Interbody Fusion Influenced by Graft Choice

BACKGROUND

Cage subsidence is a known complication of spinal fusion. Various aspects of cage design have been investigated for their influence on cage subsidence, whereas the potential contribution of graft material to load sharing is often overlooked. We aimed to determine whether graft in the aperture affects endplate pressure distribution.

METHODS

The pressure distributions of a polyetheretherketone interbody cage with 3 different aperture graft conditions were evaluated: empty, demineralized bone matrix, and supercritical CO₂-treated allograft bone crunch (SCCO₂).

RESULTS

Graft materials contributed as much as half the load transmission for SCCO₂, whereas demineralized bone matrix contributed one third. Endplate areas in contact with the cage demonstrated decreased areas within the highest-pressure spectrum with SCCO₂ graft materials compared with empty cages.

CONCLUSIONS

Graft choice plays a role in reducing peak endplate pressures. This finding is relevant to implant subsidence, as well as graft loading and remodeling.