Lateral Cage Research Articles

Maximizing screw length in expandable lateral lumbar interbody spacers with integrated fixation may obviate the need for supplemental pedicle screws.

Lateral lumbar interbody fusion (LLIF) is a minimally invasive surgical technique that provides a wide footprint interbody cage for correction of lumbar coronal and sagittal deformity. Traditional spinal interbody fusion procedures utilize pedicle screws and rods for additional stability. An expandable lateral titanium interbody cage with an integrated lateral fixation (eLLIFp) device provides a stand-alone LLIF that is intended to function autonomously. This may reduce the complexity of the surgery and the potential risks associated with supplemental posterior instrumentation. The minimum-acceptable screw length to promote adequate biomechanical fixation and stability for a stand-alone eLLIFp has not been determined. To investigate the effective ratio (of screw length/cage length) of a stand-alone eLLIFp construct that provides adequate biomechanical fixation and stability as compared to the eLLIFp with supplemental bilateral pedicle screw-rod fixation. In vitro cadaveric biomechanical testing and finite element modeling. Eight fresh-frozen human cadaveric lumbar spine specimens (L2-5) were used. Range-of-motion (ROM) measurements of intact and treated specimens with simulated stresses within the construct and surrounding bone during flexion-extension (FE), lateral bending (LB), and axial rotation (AR). Specimens with similar age and DEXA scores were selected. ROM of intact specimens was measured before treatment with LLIF at L3-4. Specimens were treated with expandable lateral cages with integrated fixation (stand-alone eLLIFp) or eLLIFp with supplemental posterior fixation using bilateral pedicle screws and rods (eLLIFp + BPS). ROM was measured using a custom-built 6-degrees-of-freedom motion simulator (±7.5Nm) and normalized as a percentage of intact. Four patient-specific lumbar functional spinal unit finite element models (FEMs) were developed, validated, and then instrumented with eLLIFp stand-alone devices. The integrated screw lengths were varied to achieve screw-to-cage length ratios of 0.6, 0.75 and 0.9. Stresses were compared among the constructs under a 7.5Nm pure moment load in FE, LB, and AR. The stand-alone and posteriorly supplemented eLLIFp constructs were not sensitive to the ratio during FE and LB (with only a 4-9% change in motion trends from low-to-high ratios, relative to intact). Independent of ratio, these constructs had minimal differences in FE and LB motion. However, during AR both constructs were sensitive to the ratio showing greater stability and less variability in performance with higher ratios (≥0.65). Regression analysis revealed that posteriorly supplemented eLLIFp constructs had a linear 13% reduction in AR motion as the ratio increased from low-to-high (p<0.05). AR also imposed the highest stresses on the eLLIFp and these stresses increased with higher ratios (maximum stress 259MPa for ratio 0.9 during AR), yet implant failure was improbable because of the material properties of the titanium alloy used. Similarly, surrounding bone stresses were higher during AR and longer screws reduced these stresses (63MPa with a 0.6 ratio compared to 38MPa with a 0.9 ratio). Independent of screw-to-cage length ratio, eLLIFp had comparable reduction of FE and LB motion with or without posterior fixation. For eLLIFp with and without posterior fixation, torsional performance and repeatability increased with screw-to-cage length ratio. Torsional stability was comparable between stand-alone eLLIFp with high ratios (≥ 0.65) and posteriorly supplemented eLLIFp with low ratios (0.55). However, a threshold screw-to-cage length ratio for optimizing the clinical performance of eLLIFp cannot be prescribed. Implant stress findings reinforced torsion as the critical loading condition. Surrounding bone stress decreased as the screw length increased, indicating the benefit of using longer screws. Surgeons using eLLIFp should consider longer screw lengths based on anatomical considerations. eLLIFp cages can be used as a stand-alone device in appropriately selected patients. This avoids the morbidity and cost associated with futher supplemental posterior fixation. Surgeons using eLLIFp should consider using longer screws to optimize fixation.

EFFECT OF SPINAL FUSION ON BIOMECHANICS OF FACET JOINTS: SYNCHRONIZED SPATIO-TEMPORAL AND MECHANICAL ANALYSIS

ObjectivesUnderstanding lumbar facet joint involvement and biomechanical changes post spinal fusion is limited. This study aimed to establish an in vitro model assessing mechanical effects of fusion on human lumbar facet joints, employing synchronized motion, pressure, and stiffness analysis.Methods and ResultsSeven human lumbar spinal units (age 54 to 92, ethics 15/YH/0096) underwent fusion via a partial nucleotomy model mimicking a lateral cage approach with PMMA cement injection. Mechanical testing pre and post-fusion included measuring compressive displacement and load, local motion capture, and pressure mapping at the facet joints. pQCT imaging (82 microns isotropic) was carried out at each stage to assess the integrity of the vertebral endplates and quantify the amount of cement injected.Before fusion, relative facet joint displacement (6.5 ± 4.1 mm) at maximum load (1.1 kN) exceeded crosshead displacement (3.9 ± 1.5 mm), with loads transferred across both facet joints. After fusion, facet displacement (2.0 ± 1.2 mm) reduced compared to pre-fusion, as was the crosshead displacement (2.2 ± 0.6 mm). Post-fusion loads (71.4 ± 73.2 N) transferred were reduced compared to pre-fusion levels (194.5 ± 125.4 N). Analysis of CT images showed no endplate damage post-fusion, whilst the IVD tissue: cement volume ratio did not correlate with the post-fusion behaviour of the specimens.ConclusionAn in vitro model showed significant facet movement reduction with stand-alone interbody cage placement. This technique identifies changes in facet movement post-fusion, potentially contributing to subsequent spinal degeneration, highlighting its utility in biomechanical assessment.Conflicts of interestNoneSources of fundingThis work was funded by EPSRC, under grant EP/W015617/1.

Novel Use of Bilateral Prone Transpsoas Approach for the Treatment of Transforaminal Interbody Fusion Pseudarthrosis and Interbody Cage Subsidence.

Pseudarthrosis is a complication after transforaminal lumbar interbody fusion (TLIF) that leads to recurrent symptoms and potential revision surgery. Subsidence of the interbody adds to the complexity of surgical revision. In addition, we report a novel technique for the treatment of TLIF pseudarthrosis with subsidence and propose an approach algorithm for TLIF cage removal. Cases of reoperation for TLIF pseudarthrosis were reviewed. We report a novel technique using a bilateral prone transpsoas (PTP) approach to remove a subsided TLIF cage and place a new lateral cage. An approach algorithm was developed based on the experience of TLIF cage removal. The patient was placed in the prone position with somatosensory evoked potential and electromyography monitoring. A PTP retractor was placed using standard techniques on the ipsilateral side of the previous TLIF. After the discectomy, the subsided TLIF cage was visualized but unable to be removed. The initial dilator was closed, and a second PTP retractor was placed on the contralateral side. After annulotomy and discectomy to circumferentially isolate the subsided cage, a box cutter was used to push and mobilize the TLIF cage from this contralateral side, which could then be pulled out from the ipsilateral side. A standard lateral interbody cage was then placed. Retractor time was less than 10 minutes on each side. The patient's symptoms resolved postoperatively. We review illustrative cases of various approaches for TLIF cage removal spanning the lumbosacral spine and recommend an operative approach based on the lumbar level, degree of subsidence, and mobility of the interbody. Bilateral PTP retractors for TLIF cage removal may be effectively used in cases of pseudarthrosis with severe cage subsidence. Careful consideration of various factors, including patient surgical history, body habitus, and intraoperative findings, is essential in determining the appropriate treatment for these complex cases.

Cage subsidence-Amultifactorial matter!

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 afocus on the hypothesis that the larger surface area of lateral cages results in lower subsidence rates. This study retrospectively reviewed 194patients who underwent interbody fusion between 2016 and 2019 with aprimary 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. Medical records were reviewed for 194patients 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 asignificant 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). Cage subsidence is acommon 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.

Extreme Lateral Interbody Fusion (XLIF) with Lateral Modular Plate Fixation: Preliminary Report on Clinical and Radiological Outcomes.

The lateral transpsoas approach (extreme lateral interbody fusion, or XLIF) allows surgeons to use various lordotic cage sizes to help restore intervertebral disk height, correct sagittal alignment, and improve fusion rates. The use of standalone devices has consistently raised doubts due to the high risk of complications and inadequate functional recovery that a circumferential arthrodesis can support. The recent introduction of a novel XLIF cage with adapted lateral plate fixation (XLPF) may further enhance the structural rigidity, consolidating the cage and plate into a singular modular entity. Nine patients from our surgical centers underwent a procedure of 1-level XLIF with XLPF in selected cases. We observed that XLPF does not extend the intraoperative footprint and provides immediate rigidity to the anterior column without any additional risk of complications and with minimal increased time compared to the traditional cage implant procedure. Although it has been shown that the use of interbody fusion cages with supplemental posterior fixation improves stabilization in all directions, the technique of standalone lateral cages may also have a place in spine surgery in that the stability may be sufficient in selected cases, such as junctional syndrome and in some forms of degenerative scoliosis.

Cage Obliquity and Radiological Outcomes in Oblique Lateral Interbody Fusion.

Retrospective radiological study. This study aimed to examine whether cage obliquity affects radiological outcomes in oblique lateral interbody fusion (OLIF). The OLIF cage enters the disk space in the oblique direction and is then turned to the true orthogonal orientation. However, orthogonal cage placement is often hindered by cage rotation limitations. Few studies have examined the degree of cage obliquity and its effects in OLIF. This study involved 171 levels in 118 consecutive patients who underwent OLIF between L2-L3 and L4-L5 with a minimum two-year follow-up. Cage obliquity was divided into three groups on postoperative axial computed tomography images; cage obliquity <10° (group 1), cage obliquity ≥10° and <20° (group 2), and cage obliquity ≥20° (group 3). The radiological outcomes included anterior/posterior disk height, intervertebral disk angle, foraminal height, fusion, and cage subsidence. Postoperative complications related to cage obliquity were examined. The mean cage obliquity of the 171 cages was 11.3±6.9°. Cage obliquity was greater at the L4-L5 level (13.4±6.4°) than at other levels (L2-L3 and L3-L4: 6.5±7.0° and 10.1±6.2°, respectively) ( P <0.05). There were no significant differences in radiological outcomes among the groups. There were two cases of postoperative contralateral neurological symptoms in group 3. Our study showed that the orthogonal cage rotation in OLIF achieved adequate lateral cage placement. Although accurate cage rotation can be limited at the lower lumbar segments, radiological outcomes were not affected by cage obliquity.

Biomechanical comparison of subsidence performance among three modern porous lateral cage designs

BackgroundCage subsidence remains a major complication after spinal surgery. The goal of this study was to compare the subsidence performance of three modern porous cage designs. MethodsThree porous cages were evaluated: a porous titanium cage, a porous polyetheretherketone cage and a truss titanium cage. Mechanical testing was performed for each cage per the American Society for Testing and Materials F2077 and F2267 standards to evaluate cage stiffness and block stiffness, and per a novel clinically relevant dynamic subsidence testing method simulating cyclic spine loading during 3-months postoperatively to evaluate the subsidence displacement. FindingsThe porous polyetheretherketone cage demonstrated the lowest cage stiffness (21.0 ± 1.1 kN/mm), less than half of both titanium cages (truss titanium cage, 49.1 kN/mm; porous titanium cage, 43.6 kN/mm). The block stiffness was greatest for the porous titanium cage (2867.7 ± 105.3 N/mm), followed by the porous polyetheretherketone (2563.4 ± 72.9 N/mm) and truss titanium cages (2213.7 ± 21.8 N/mm). The dynamic subsidence displacement was greatest for the truss titanium cage, which was 1.5 and 2.5 times the subsidence displacement as the porous polyetheretherketone and porous titanium cages respectively. InterpretationsSpecific porous cage design plays a crucial role in the cage subsidence performance, to a greater degree than the selection of cage materials. A porous titanium cage with body lattice and microporous endplates significantly outperformed a truss titanium cage with a similar cage stiffness in subsidence performance, and a porous polyetheretherketone cage with half of its stiffness.

33. Comparison of the biomechanics of lumbar spine instrumented with standalone interbody fixation constructs vs interbody with supplemental fixation: a finite element investigation

<h3>BACKGROUND CONTEXT</h3> Low fusion rates and cage subsidence have been reported as the main drawbacks of lumbar fixation with static interbody cages. Although several clinical and biomechanical studies have evaluated the efficacy of 360 interbody fixation constructs (anterior cage plus posterior fixation), no study has reported the biomechanical comparison between such constructs and more novel techniques which use standalone fixation implants. A cadaver validated computational model of lumbar spine was used to compare the biomechanics of spine instrumented with 360 fixations vs standalone cage and screw and cage with lateral plate systems. <h3>PURPOSE</h3> To compare the mechanical stability of different interbody fixation techniques in lumbar spinal segments with standalone interbody vs static cage with posterior fixation or lateral plate system. <h3>STUDY DESIGN/SETTING</h3> Finite element modeling. <h3>OUTCOME MEASURES</h3> Range of motion across instrument segments and load sharing on vertebral endplate. <h3>METHODS</h3> An experimentally validated finite element (FE) model of L1-pelvic segment was used to simulate ALIF and LIF lumbar fixation techniques including: ALIF cage at L5-S1 plus posterior screw-rod fixation (360 construct) vs ALIF standalone (screw through the cage). LIF cage at L4-L5 vs LIF cage with integrated two-hole lateral plate system. 4WEB Medical's Truss ALIF (27mm x 25mm), Lateral Truss (22mm X 5mm) cages and 2-hole integrated plate systems were used for simulation of the surgical procedure. For 360 constructs, a generic posterior rod and screw system was used. All models were subjected to a 400N compressive pre-load followed by an 8Nm moment to simulation flexion-extension, left and right bending and axial rotation motions. The segmental kinematics and the load sharing at the inferior endplate were compared among cases. <h3>RESULTS</h3> The segmental motion in standalone ALIF construct was 1.1°(Flex-Ext), 0.9° (LB) and 0.4° vs 0.8°, 0.8° and 0.6° in 360 ALIF in the same planes of motion. When comparing lateral cases, the motions were 1.2° (Flex-Ext), 1.4° (LB) and 0.5° (AR) in lateral cage with plate vs 0.9°, 1.0° and 0.8° in the 360 lateral construct for the same loads. The peak stresses in extension for the LIF stand-alone cage were somewhat higher than the posterior instrumented cases, but not significant. When comparing the mechanical stress on the inferior endplate of the index segment, the standalone ALIF had almost 20% higher peak stress compared to the 360 ALIF. In the lateral construct, the cage-plate segment experienced 15% lower stresses on the endplate compared to the 360 lateral construct. <h3>CONCLUSIONS</h3> Our data suggest that standalone ALIF cage with screw through the cage is able to provide kinematic stability in the fixation construct comparable to the cage plus posterior fixation, although the 360 construct is able to provide slightly more stability in the sagittal plane. Also, the standalone cage results in higher stresses applied to the endplate compared the cage in 360 constructs. The lateral cage with integrated plate had superior stability in axial rotation compared to the 360 lateral construct. The loads on the endplate were also slightly lower compared to the 360-fixation case. Standalone ALIF and LIF with lateral plate are biomechanically effecient alternatives to 360-fixation constructs at least under the controlled conditions analyzed in the present study. Clinical data are required to support the findings and define the further role and application of standalone cages. <h3>FDA DEVICE/DRUG STATUS</h3> 4WEB ALIF Truss System (Approved for this indication), 4WEB Lateral Plate System (Approved for this indication), 4WEB Lateral Truss System (Approved for this indication)

A Modified Anterior Column Realignment With Partial Anterior Longitudinal Ligament Release in Oblique Lateral Interbody Fusion.

Retrospective radiological analysis. To demonstrate the radiological outcome after a modified anterior column realignment (mACR) with partial anterior longitudinal ligament (ALL) release in oblique lateral interbody fusion (OLIF). Anterior column realignment (ACR) remains a powerful sagittal correction technique in minimally invasive adult spinal deformity surgery and is often combined with posterior column osteotomy (PCO) to achieve more lordosis. OLIF is ideal for ACR because the anterior-to-psoas corridor typically involves the anterolateral half of the disk. This study included 112 operated disk levels of 101 consecutive patients who underwent OLIF between L2-L3 and L4-L5 using a 12° lateral cage. The mACR was performed at 73 (65.2%) levels with 30% to 50% sectioning of the ALL. Each operated level was grouped according to the mACR and additional PCO as: (1) no mACR, OLIF only (n=39); (2) mACR with no PCO (n=18); (3) mACR with grade 1 PCO (n=27); (4) mACR with grade 2 PCO (n=22); or (5) mACR with grade 3 PCO (n=6). At the last follow-up, the mean disk lordotic angles were 10.9±2.9°, 12.6±3.0°, 13.3±3.9°, 16.7±3.2°, and 16.8±2.4° in the no mACR, mACR with no PCO, mACR with grade 1 PCO, mACR with grade 2 PCO, and mACR with grade 3 PCO groups, respectively ( P <0.001). The mean increases in disk lordotic angle were 5.8±4.1°, 12.1±6.1°, 13.5±8.7°, 15.8±6.7°, and 17.9±6.2° in each group, respectively ( P <0.001). ACR can be performed with partial ALL release under direct vision in OLIF without deep dissection into the ventral disk space. The mACR in OLIF is a simple, safe, and effective technique for anterior column lengthening. 4.

Expandable Lateral Lumbar Cages With Integrated Fixation: A Viable Option for Rostral Adjacent Segment Disease.

Adjacent segment disease (ASD) above a previous posterior lumbar instrumented fusion can be managed with minimally invasive lateral lumbar interbody fusion. Earlier procedures with stand-alone lateral cages risked nonunion, and lateral cages with separate lateral plates risked lumbar plexus injury and vertebral fracture. We investigated clinical and radiographic outcomes of an expandable lateral titanium interbody cage with an integrated lateral fixation (eLLIFp) device as a stand-alone treatment for symptomatic ASD above a previous posterior lumbar fusion and performed a comparative cost analysis of eLLIFp to alternative operations for ASD. In this prospective, observational study, patients with ASD above 1-, 2-, 3-, or 4-level instrumented posterior fusions underwent surgery with lateral expandable titanium cage(s) with an integrated lateral plate with single screws into each adjacent vertebra from August 2017 to August 2019. Multimodality intraoperative neural monitoring was performed. Patient-reported outcomes, computed tomography outcomes, and total costs were analyzed. A total of 33 patients received 35 eLLIFp cages. All clinical outcomes improved significantly. The eLLIFp cages added 2.2° segmental lordosis and 2.7 mm posterior disc height. Interbody fusion rate was 94% at 12 months. There were 2 neurologic complications (6%): 1 patient reported transient anterior thigh numbness and 1 had mild persistent L4 radiculopathy. No cage subsidence, cage migration, screw loosening, or vertebral fracture occurred. No revision lateral surgery, posterior decompression, or supplemental posterior fixation was required. The total eLLIFp cost (AU$19,715) was lower than the cost for all other procedures. eLLIFp provided a minimally invasive, low morbidity, cost-effective, and robust alternative to traditional posterior construct extension surgery for rostral lumbar ASD in selected patients with 1- to 2-level stenosis and minimal deformity. Traditional ASD treatment involves substantial risks and expense. eLLIFp should be considered a safe, effective, and lower cost alternative to posterior construct extension surgery.

Choice of Spinal Interbody Fusion Cage Material and Design Influences Subsidence and Osseointegration Performance

The objective of the study was to quantify the effect of cage material (titanium-alloy vs. polyetheretherketone or PEEK) and design (porous vs. solid) on subsidence and osseointegration. Three lateral cages (solid PEEK, solid titanium, and 3-dimension-printed porous titanium cages) were evaluated for cage stiffness, subsidence compression stiffness, and dynamic subsidence displacement under simulated postoperative spine loading. Dowel-shaped implants made of grit-blasted solid titanium alloy (solid titanium) and porous titanium were fabricated using commercially available processes. Samples were processed for mechanical push-out testing and polymethylmethacrylate histology following an established ovine bone implantation model. The solid titanium cage exhibited the greatest stiffness (57.1±0.6kN/mm), followed by the porous titanium cage (40.4±0.3kN/mm) and the solid PEEK cage (37.1±1.2kN/mm). In the clinically relevant dynamic subsidence, the porous titanium cage showed the least amount of subsidence displacement (0.195±0.012mm), significantly less than that of the solid PEEK cage (0.328±0.020mm) and the solid titanium cage (0.538±0.027mm). Bony on-growth was noted histologically on all implant materials; however, only the porous titanium supported bony ingrowth with marked quantities of bone formed within the interconnected pores through 12weeks. Functional differences in osseointegration were noted between groups during push-out testing. The porous titanium showed the highest maximum shear stress at 12weeks and was the only group that demonstrated significant improvement (4-12weeks). The choice of material and design is critical to cage mechanical and biological performances. A porous titanium cage can reduce subsidence risk and generate biological stability through bone on-growth and ingrowth.

Comparison of Navigated Expandable Vertebral Cage with Conventional Expandable Vertebral Cage for Minimally Invasive Lumbar/Thoracolumbar Corpectomy.

Background and Objectives: The thoracolumbar burst fracture is one of the most common spinal injuries. If the patient has severe symptoms, corpectomy is indicated. Currently, minimally invasive corpectomy with a navigated expandable vertebral cage is available thanks to spinal surgical technology. The aim of this study is to retrospectively compare clinical and radiographic outcomes of conventional and navigational minimally invasive corpectomy techniques. Materials and Methods: We retrospectively evaluated 21 patients who underwent thoracolumbar minimally invasive corpectomy between October 2016 and January 2021. Eleven patients had a navigated expandable cage (group N) and 10 patients had a conventional expandable cage (group C). Mean follow-up period was 31.9 months for group N and 34.7 months for group C, ranging from 12 to 42 months in both groups. Clinical and radiographic outcomes are assessed using values including visual analogue scale (VAS) for back pain and Oswestry disability index (ODI). This data was collected preoperatively and at 6, 12, and 24 months postoperatively. Results: Surgical time and intraoperative blood loss of both groups were not significantly different (234 min vs. 267 min, 656 mL vs. 786 mL). Changes in VAS and ODI were similar in both groups. However, lateral cage mal-position ratio in group N was lower than that of group C (relative risk 1.64, Odds ratio 4.5) and postoperative cage sinking was significantly lower in group N (p = 0.033). Conclusions: Clinical outcomes are not significantly different, but radiographic outcomes of lateral cage mal-position and postoperative cage sinking were significantly lower in the navigation group.

Incidence et facteurs de risque de la migration des cages latérales après le premier temps d’arthrodèse intersomatique antéro-latérale circonférentielle

BackgroundLateral lumbar interbody fusion (LLIF) is a novel, minimally invasive technique for the surgical treatment of lumbar diseases. The aim of this study was to identify the incidence and risk factors of lateral cage migration (LCM) occurred after the first-stage LLIF. HypothesisThe hypothesis was that LCM occurred after the first-stage LLIF was associated with some demographic characteristics, surgical variables and radiographic parameters. Patients and methodsBetween June 2016 and August 2020, 335 patients (901 levels) underwent staged LLIF were retrospectively reviewed. Patients were classified into LCM and non-LCM group based on the experience of LCM before the second-stage posterior instrumentation. 100 patients in non-LCM were randomly sampled as a control group. Incidence of LCM was determined; demographic characteristics, surgical variables and radiographic parameters associated with LCM were compared between the LCM and control group. Univariate analyses and multivariable logistic regression analysis were used to identify the risk factors. ResultsLCM occurred after the first-stage LLIF was found in 19 (5.7%) patients. Bony endplate injury (OR, 106.255; 95% CI, 1.265–8924.765; p=0.039) and greater preoperative range of motion (ROM) (OR, 2.083, 95% CI, 1.068–4.066, p=0.031) were high-risk factors for LCM. LCM occurred mainly 3 days later after the first-stage LLIF, while 4 cases experienced severe neural symptoms, intolerable low back pain and finally underwent reoperation. DiscussionLCM occurred after the first-stage LLIF was significantly associated with bony endplate injury and greater preoperative ROM. Second-stage posterior fixation should be performed as soon as possible or a supplement lateral fixation/self-locking cage should be used in high-risk patients. Level of EvidenceIV.

Comparison of surgical outcomes between oblique lateral interbody fusion (OLIF) and anterior lumbar interbody fusion (ALIF)

ObjectiveAlthough oblique lateral interbody fusion (OLIF) utilizes the similar approach in anterior lumbar interbody fusion (ALIF), OLIF is essentially a lateral lumbar interbody fusion (LLIF). Therefore, OLIF may have advantages in LLIF that the lateral cage can achieve greater restoration of the disc height and angle. We aimed to compared the surgical outcomes between OLIF and ALIF. MethodsThis study involved 47 consecutive patients who underwent a single-level OLIF and 45 consecutive patients who underwent a single-level ALIF at L2-L5 levels. Radiological measurements included the changes of anterior/posterior disc height, coronal/sagittal disc angle, foramen cross-sectional area (CSA), cage position from the anterior margin of the lower vertebra, fusion rate, and cage subsidence using the serial radiographs and computed tomography preoperatively and at the postoperative 1-year follow-up. Clinical outcomes were assessed by visual analog scale (VAS) for back/leg pain, Oswestry disability index (ODI), and the occurrence of perioperative complications. ResultsThe baseline radiological and clinical parameters were similar between the OLIF and ALIF groups (all P > 0.05). At postoperative 1 year, the mean anterior disc height was higher in the OLIF group than the ALIF group (11.4 ± 1.9 mm vs. 9.6 ± 2.6 mm, P = 0.021). The mean sagittal disc angle was also greater in the OLIF group than the ALIF group (10.9 ± 4.4° vs. 8.9 ± 5.8°, P < 0.001). The mean cage position was 5.8 ± 2.1 mm in the OLIF group and 8.7 ± 2.3 mm in the ALIF group (P < 0.001). There was no difference in the postoperative changes of coronal disc angles, foramen CSA, fusion rate, cage subsidence, VAS for back/leg pain, ODI, and the occurrence of perioperative complications between the OLIF and ALIF groups (all P > 0.05). ConclusionsOLIF showed a greater increase in disc height and segmental lordosis than ALIF with comparable complications. OLIF is a meaningful progress from ALIF.

16. Evaluation of the cage subsidence performance of three porous lateral cage designs

<h3>BACKGROUND CONTEXT</h3> Interbody cage subsidence remains a major complication after lumbar spine fusion surgery, particularly in lateral or other procedures that rely on indirect decompression. Porous cages are believed to reduce the risk of cage subsidence. Multiple porous cage designs exist, including 3D printed (3DP) titanium cages with body lattice and microporous endplates, 3DP titanium cages with a truss structure, and PEEK cages with surface porosity. Currently, there is a lack of carefully-controlled biomechanics studies to evaluate their relative performance. <h3>PURPOSE</h3> To evaluate the resistance to subsidence of three representative porous cage designs using ASTM standardized testing methods, as well as clinically relevant dynamic subsidence testing methods. <h3>STUDY DESIGN/SETTING</h3> Mechanical testing using foam blocks. <h3>PATIENT SAMPLE</h3> Three porous cage designs were included: a 3DP cage with stress-optimized body lattice and microporous endplates (stress-optimized titanium cage), a 3DP titanium cage with truss structure (truss titanium cage) and a PEEK cage with surface porosity (porous PEEK cage). All cage designs have the similar dimensions. N=5 testing constructs were used per cage design/loading mode. For titanium cages, one single cage was reused for all constructs. For PEEK cages, a new cage was used in each construct. <h3>OUTCOME MEASURES</h3> For ASTM F2267 static subsidence testing, the block stiffness at the implant-foam interface was reported. The greater the block stiffness, the more force was required to generate the same displacement. For the clinically relevant dynamic subsidence testing, the post-test subsidence displacement was reported, measured as the amount of displacement that each cage sank into the test block surface after a simulated 3-month period of physiologically relevant loading. <h3>METHODS</h3> Static subsidence testing per the ASTM F2267 standard, and novel dynamic subsidence testing, consisting of a physiologically relevant cyclic compressive load, were performed for each cage design to evaluate subsidence performance. Surface-conforming polyurethane foam test blocks that simulated the adjacent vertebral bodies were used in both the static and dynamic subsidence tests. All testing was performed on a calibrated servohydraulic load frame. Testing results were compared between three designs using one-way ANOVA with Bonferroni correction for post-hoc analysis. <h3>RESULTS</h3> In ASTM F2267 static compression testing, the stress-optimized titanium cage showed a significantly greater (27%) block stiffness of 2690.9 ± 92.7 N/mm than that of the truss titanium cage (2118.3 ± 19.9 N/mm, p<0.001), as well as 17.7% greater than that of the porous PEEK cage (2284.7 ± 64.5 N/mm, p=0.001). The porous PEEK cage also significantly outperformed the truss titanium cage (p=0.001) by 8%. In the clinically relevant dynamic subsidence testing, the truss Ti-cage showed the greatest amount of subsidence displacement of 0.141±0.007mm, significantly greater than that of the stress-optimized titanium cage by 153.3% (0.056±0.008mm, p<0.001) and that of the porous PEEK cage by 65.6% (0.085±0.004mm, p<0.001). The stress-optimized titanium cage showed a significantly lower subsidence displacement than that of the porous PEEK (p<0.001) by 34.6%. <h3>CONCLUSIONS</h3> Despite the common conception that porous cage design can reduce the risk of subsidence, the specific design rationale is worthy of rigorous investigation. Under the ASTM F2267 standard static subsidence testing and clinically relevant dynamic subsidence testing conditions, a 3DP titanium cage with a stress-optimized body lattice and microporous endplates showed the best subsidence performance, followed by the porous PEEK cage, and then the 3DP truss titanium cage design. <h3>FDA DEVICE/DRUG STATUS</h3> Modulus XLIF (Approved for this indication), Cohere XLIF (Approved for this indication), LATERAL SPINE TRUSS SYSTEM (Approved for this indication)

Incidence and risk factors of lateral cage migration occurred after the first-stage lateral lumbar interbody fusion surgery

BackgroundLateral lumbar interbody fusion (LLIF) is a novel, minimally invasive technique for the surgical treatment of lumbar diseases. The aim of this study was to identify the incidence and risk factors of lateral cage migration (LCM) occurred after the first-stage LLIF. HypothesisThe hypothesis was that LCM occurred after the first-stage LLIF was associated with some demographic characteristics, surgical variables and radiographic parameters. Patients and methodsBetween June 2016 and August 2020, 335 patients (901 levels) underwent staged LLIF were retrospectively reviewed. Patients were classified into LCM and non-LCM group based on the experience of LCM before the second-stage posterior instrumentation. 100 patients in non-LCM were randomly sampled as a control group. Incidence of LCM was determined; demographic characteristics, surgical variables and radiographic parameters associated with LCM were compared between the LCM and control group. Univariate analyses and multivariable logistic regression analysis were used to identify the risk factors. ResultsLCM occurred after the first-stage LLIF was found in 19 (5.7%) patients. Bony endplate injury (OR, 106.255; 95% CI, 1.265–8924.765; p=0.039) and greater preoperative range of motion (ROM) (OR, 2.083, 95% CI, 1.068–4.066, p=0.031) were high risk factors for LCM. LCM occurred mainly 3 days later after the first-stage LLIF, while 4 cases experienced severe neural symptoms, intolerable low back pain and finally underwent reoperation. DiscussionLCM occurred after the first-stage LLIF was significantly associated with bony endplate injury and greater preoperative ROM. Second-stage posterior fixation should be performed as soon as possible or a supplement lateral fixation/self-locking cage should be used in high-risk patients. Level of evidenceIV.

Load Share Mapping for Traditional PEEK vs Novel Hybrid PEEK With Expandable Porous Mesh Intervertebral Devices.

A successful intervertebral fusion requires biomechanical stability created by the structural support of the interbody device and loading of the bone graft material to accelerate mechanotransduction and bone remodeling. The objective of this study was to generate a quantitative map of the contact area and stress profile for 2 implant designs; a rigid monolithic polyetheretherketone (PEEK) lateral cage (MPLC), and a unique hybrid interbody design, which includes PEEK terminal supports surrounding an expandable porous mesh (P+EPM) that serves to contain bone graft. The construct for each test consisted of a device sandwiched between 2 flat or shaped Grade 15 foam blocks. Pressure sensitive film and thin film sensors were placed between the device and each of the foam blocks. A series of each implant type was compressed at a rate 0.1 mm/second for 2 loads (1100 N and 2000 N) with and without bone graft. Device and bone graft contact area were analyzed for each test condition and corresponding load profiles were quantified and mapped. P+EPM demonstrated 34% greater graft volume than MPLC resulting in a 28% larger area for bone exchange when filled. The load profiles for all applied loading paradigms for P+EPM demonstrated significant direct loading on the bone graft contained within the mesh, resulting in at least 170% greater loaded area than MPLC. Furthermore, the P+EPM demonstrated load sharing with the terminal PEEK supports. MPLC for all loading conditions demonstrated negligible bone graft loading. P+EPM allows for an optimized contact area for bone exchange and graft incorporation. The load profiles confirmed that the filled mesh does not stress shield terminal PEEK supports and will load share. The expandable, compliant, porous mesh provides a greater multiplanar area for bone exchange and allows for direct contact with the viscoelastic vertebral endplates, improving the endplate and graft interface mechanics.

The feasibility of computer-assisted 3D navigation in multiple-level lateral lumbar interbody fusion in combination with posterior instrumentation for adult spinal deformity.

The lateral lumbar interbody fusion (LLIF) technique is used to treat many common spinal degenerative pathologies including kyphoscoliosis. The use of spinal navigation for LLIF has not been broadly adopted, especially in adult spinal deformity. The purpose of this study was to evaluate the feasibility as well as the intraoperative and navigation-related complications of computer-assisted 3D navigation (CaN) during multiple-level LLIF for spinal deformity. Retrospective analysis of clinical and operative characteristics was performed for all patients > 18 years of age who underwent multiple-level CaN LLIF combined with posterior instrumentation for adult spinal deformity at the University of Michigan between 2014 and 2020. Intraoperative CaN-related complications, LLIF approach-related postoperative complications, and medical postoperative complications were assessed. Fifty-nine patients were identified. The mean age was 66.3 years (range 42-83 years) and body mass index was 27.6 kg/m2 (range 18-43 kg/m2). The average coronal Cobb angle was 26.8° (range 3.6°-67.0°) and sagittal vertical axis was 6.3 cm (range -2.3 to 14.7 cm). The average number of LLIF and posterior instrumentation levels were 2.97 cages (range 2-5 cages) and 5.78 levels (range 3-14 levels), respectively. A total of 6 intraoperative complications related to the LLIF stage occurred in 5 patients. Three of these were CaN-related and occurred in 2 patients (3.4%), including 1 misplaced lateral interbody cage (0.6% of 175 total lateral cages placed) requiring intraoperative revision. No patient required a return to the operating room for a misplaced interbody cage. A total of 12 intraoperative complications related to the posterior stage occurred in 11 patients, with 5 being CaN-related and occurring in 4 patients (6.8%). Univariate and multivariate analyses revealed no statistically significant risk factors for intraoperative and CaN-related complications. Transient hip weakness and numbness were found to be in 20.3% and 22.0% of patients, respectively. At the 1-month follow-up, weakness was observed in 3.4% and numbness in 11.9% of patients. Use of CaN in multiple-level LLIF in the treatment of adult spinal deformity appears to be a safe and effective technique. The incidence of approach-related complications with CaN was 3.4% and cage placement accuracy was high.

P17. Investigating the effects of cage width and placement on subsidence performance using anatomically representative models

BACKGROUND CONTEXT Previous studies have identified geometric mismatch between the endplate and interbody as a main risk factor for subsidence. A proper selection of the cage width and placement can potentially reduce the risk of subsidence. Existing studies using surrogate vertebral bodies to evaluate the subsidence performance of interbody cages often omit the morphology of the endplate, which can vary markedly across patients. PURPOSE To comprehensively evaluate the effects of cage width and placement on the subsidence performance using anatomically representative test blocks that cover a different range of endplate concavity depths. STUDY DESIGN/SETTING Surrogate models were fabricated using 15 pcf polyurethane foam representative of the anatomy of a L5 vertebral body. Specifically, an elliptical cylinder was used as the base geometry to capture the overall anatomy of superior half of L5 vertebral body. The major and minor axes were taken from averaged population data (52mm, 36mm). Next, deviations of the shape in the radial direction was included to represent the anterior part, vertebral foramen, left and right pedicles. Lastly, an endplate concavity was created by removing from the endplate surface a concentric ellipsoid with varying depths (1, 2, 3 and 4mm) to simulate different endplate morphology. Lateral cages of two different widths (18mm or 22mm; Modulus XLIF), placed anteriorly or centrally, were assessed for construct stiffness, an indicator of the device's propensity to subside, in static compression per ASTM F2267 standards. PATIENT SAMPLE Sixteen combinations (4 depths, 2 widths, 2 placements) were tested. Five samples were tested in each combination. OUTCOME MEASURES Stiffness measured per ASTM F2267 testing standards was used as the indicator of subsidence performance, with a greater stiffness representing a better resistance to subsidence. METHODS Multiple linear regression was used to examine the role of each variable in subsidence performance. RESULTS Endplate concavity depth and cage width were identified as significant factors to subsidence performance. For each 1mm increase in the endplate concavity depth (more geometric mismatch), a decrease of 634.4 N/mm was observed (p CONCLUSIONS Endplate morphology plays a critical role in the evaluation of subsidence performance of interbody cages. Therefore, using anatomically representative endplate models is recommended. Using a wider cage can mitigate the risk of subsidence, particularly with more concave endplates. FDA DEVICE/DRUG STATUS Modulus XLIF (Approved for this indication).

The Impact of Vertebral End Plate Lesions on the Radiological Outcome in Oblique Lateral Interbody Fusion.

Study Design:Retrospective case-control study.Objectives:Vertebral end plate (EP) lesions include Modic changes, Schmorl’s nodes, EP erosion, EP sclerosis, and so on. While previous studies have mostly focused on the association between vertebral EP lesions and low back pain, few studies evaluated the influence of vertebral EP lesions on the radiological outcomes in lumbar interbody fusion.Methods:This study included a total of 125 operated disc levels from 86 consecutive patients who underwent a 1- or 2-level oblique lateral interbody fusion (OLIF) and had more than 1-year regular follow-up. The presence of vertebral EP lesions, changes in disc heights/angle, cage subsidence, and fusion grade were examined. The associations between vertebral EP lesions and radiological parameters were analyzed.Result:The presence of Modic changes, Schmorl’s node, EP cartilage erosion, and EP sclerosis were found in 72 (57.6%), 26 (20.8%), 31 (24.8%), and 44 (35.2%) disc levels, respectively. The mean anterior disc height increased from 6.9 ± 3.8 mm to 13.1 ± 2.7 mm (P < .001) and the mean segmental angle increased from 2.9° ± 5.8° to 9.2° ± 4.8° (P < .001) at the last follow-up. The overall fusion rate was 98.4% (123/125) and cage subsidence rate was 7.2% (9/125). All radiological parameters and cage subsidence rate were not different regardless of vertebral EP lesions.Conclusions:Vertebral EP lesions did not affect the overall radiological outcome in 1- or 2-level OLIF. These results come from the stable contact between lateral cage and peripheral rim of vertebral EP.