Lumbar Cage Research Articles

Experimental Analysis of Stress Shielding Effects in Screw Spacers Placed in Porcine Spinal Tissue.

Bone cortical tissues reorganize and remodel in response to tensile forces acting on them, while compressive forces cause atrophy. However, implants support most of the payload. Bones do not regenerate, and stress shielding occurs. The aim is to analyze the biomechanical behavior of a lumbar cage to study the implant's stress shielding. The ASTM E-9 standard was used with the necessary adjustments to perform compression tests on lumbar and thoracic porcine spinal vertebrae. Twelve cases were analyzed: six with the metal prosthesis and six with the PEEK implant. A mathematical model based on the Hertz contact theory is proposed to assess the stress shielding for endoprosthesis used in spine pathologies. The lumbar spacer (screw) helps to reduce the stress shielding effect due to the ACME thread. The best interspinous spacer is the PEEK screw. It does not embed in bone. The deformation capability increases by 11.5% and supports 78.6 kg more than a system without any interspinous spacer.

Analysis Re-Entrant honeycomb auxetic structure for lumbar vertebrae using finite element analysis

Lumbar spinal fusion is a frequent surgical solution among people who are experiencing severe persistent lower back pain. One treatment option is Lateral Lumbar Interbody Fusion (LLIF) surgery. In the medical field, finite element analysis (FEA) can be used to predict the best surgical plan. LLIF surgery involves implanting an interbody cage into the disc space, which may potentially move to regain the disk height while helping stabilize the vertebral bones. In this study, FEA was applied using Mechanical Finder software (MF) to develop a 3D spine model lumbar vertebrae of the fourth and fifth lumbar vertebrae (L4 - L5) with the interbody cage design. The cage was made of polyether ether ketone (PEEK) and designed using Solidworks software. Given the auxetic structure's outstanding energy absorption capabilities, a re-entrant auxetic structure core with a novel sandwich panel was implanted between the lumbar vertebrae L4 and L5, as determined by CT scans using MF software. The model was analyzed in MF to assess the strength and fracture risk analysis of the interbody cage, with the results compared to mechanical properties values obtained by applying compression load (1000 N) to simulate spinal movements. Stress and strain distribution rates were exhibited when applying a force of 1000 N. The findings underscore the relevance of cage design, namely the surface endplate, in mitigating undesirable occurrences associated with cage sinking. To attain enough strength under typical conditions, a lumbar cage with a re-entrant auxetic construction has been proposed.

Do expandable cage size and number of cages matter in transforaminal lumbar interbody fusion at L5-S1? A comparative biomechanical analysis using finite element modeling.

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. 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. 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. 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.

The Combined Effects of RhBMP-2 and Systemic RANKL Inhibitor in Patients With Bone Density Loss Undergoing Posterior Lumbar Interbody Fusion: A Retrospective Observational Analysis With Propensity Score Matching.

The risks of nonunion and subsidence are high in patients with bone density loss undergoing spinal fusion surgery. The internal application of recombinant human bone morphogenic protein 2 (rhBMP-2) in an interbody cage improves spinal fusion; however, related complications have been reported. Denosumab, a human monoclonal antibody targeting the receptor activator of nuclear factor kappa B ligand (RANKL), hinders osteoblast differentiation and function. Therefore, this study aimed to observe the combined effect of the local application of rhBMP-2 in a lumbar cage and systemic RANKL inhibition on postoperative spinal fusion in patients with bone density loss undergoing posterior lumbar interbody fusion (PLIF). This retrospective observational study included 251 consecutive patients with spinal stenosis who underwent PLIF at a single center between 2017 and 2021. Clinical outcomes were assessed, and radiographic evaluations included lumbar flexion, extension, range of motion, and subsidence. Statistical analyses were conducted to identify the combined effect of the treatment and the subsidence and spinal fusion status. One hundred patients were included in the final analysis. Denosumab treatment significantly reduced the rate of osteolysis (p = 0.013). When denosumab was administered in combination with rhBMP-2, the fusion status remained similar; however, the incidences of postoperative osteolysis and postoperative oozing day decreased. The combined use of rhBMP-2 and RANKL inhibition in patients with bone density loss can enhance bone formation after PLIF with fewer complications than rhBMP-2 alone.

Finite element analysis of lattice designed lumbar interbody cage based on the additive manufacturing.

Additive manufacturing (AM) methods, which facilitate the production of complex structures with different geometries, have been used in producing interbody cages in recent years. In this study, the effects of Ti6Al4V alloy interbody lattice designed fusion cages between the third and fourth lumbar vertebrae where degenerative disc diseases occur were investigated using the finite element method. Face centered cubic (FCC), body centered cubic (BCC), and diamond structures were selected as the lattice structure suitable for the interbody cage. A kidney shaped interbody lumbar cage was designed. The designated lattice structures were selected by adjusting the cell sizes suitable for the designed geometry, and the mesh configuration was made by the lumbar lattice structure. 400 N Axial force and 7.5 N.m moments were applied to the spine according to lateral bending, flexion, and torsion. 400 N axial force and 7.5 N.m flexion moment is shown high strain and total deformation then lateral bending and torsion on BCC FCC and diamond lattice structured interbody cages. In addition, the effects of lattice structures under high compression forces were investigated by applying 1000 N force to the lattice structures. When von Mises stresses were examined, lower von Mises stress and strains were observed in the BCC structure. However, a lower total deformation was observed in the FCC. Due to the design of the BCC and the diamond structure, it is assumed that bone implant adhesion will increase. In the finite element analysis (FEA), the best results were shown in BCC structures.

Static Analysis and Design of Innovative Porous Lumbar Interbody Cages

Background: Interbody discs play a major role in maintaining the spine and skeleton structures which may undergo damage. If damage is so severe that the disc cannot be repaired, implants, known as “interbody cages”, should be used. Objectives: The present study aimed to propose a novel design with proper strength and resistance against axial disc torques. Methods: The design and analysis of innovative anatomical cages comprised two stages, namely, cage design according to three different models and finite element analysis (FEA). The designs were based on the spine of a 15-year-old teenager without lumbar disc disease. To model the vertebrae, computed tomography )CT( scans and Digital Imaging and Communications in Medicine (DICOM) files were entered into Mimics Version 10.01 (Materialise Inc., Leuven, Belgium); then, the L4 and L5 spinal segments were modeled. Results: The implants were fixed to the bottom level and subjected to a net force of 1000 N. Additionally, a moment load of 7.5 Nm in flexion, extension, axial rotation, and lateral bending was applied in these three cage models. Considering the application of 1000-N force, maximum and minimum stress and strain distribution rates were presented in three honeycomb, Islamic architecture, and porous gyroid cages. Conclusion: Novel designs for lumbar cages were considered to achieve damping capacity, light weight, and high resistance. Considering the characteristics of the honeycomb, Islamic architecture, and gyroid structures, optimal designs were proposed for lumbar cages to achieve adequate strength and resistance against axial disc torques under normal conditions.

An Analysis of a Decade of Lumbar Interbody Cage Failures in the United States: A MAUDE Database Study.

A retrospective case series. This study aims to assess the rates of lumbar interbody cage failures based on their material and manufacturer. Perioperative lumbar interbody cage malfunctions are underreported events in the spine literature and may result in complications. Although the Food and Drug Administration ensures the safety of these devices under physiological conditions after implantation, these devices may experience nonphysiological conditions during implantation, which may be overlooked. The MAUDE database was examined for reports of lumbar cage device malfunctions from 2012 to 2021. Each report was categorized based on failure type and implant design. A market analysis was performed by dividing the total number of failures per year for each manufacturer by their approximate yearly revenue from spinal implants in the United States. Outlier analysis was performed to generate a threshold value above which failure rates were defined as greater than the normal index. Overall, 1875 lumbar cage malfunctions were identified. Of these, 1230 (65.6%) were cage breakages, 257 (13.7%) were instrument malfunctions, 177 (9.4%) were cage migrations, 143 (7.6%) were assembly failures, 70 (4.5%) were screw-related failures, and 21 (1.1%) were cage collapses. Of the breakages, 923 (74.9%) occurred during insertion or impaction and 97 entries detailed a medical complication or a retained foreign body. Of the migrations, 155 (88.6%) were identified postoperatively, of which 73 (47.1%) detailed complications and 52 (33.5%) required a revision procedure. Market analysis demonstrated that Medtronic, Zimmer Biomet, Stryker, Seaspine, and K2M exceeded the calculated threshold. Lumbar cages with polyether ether ketone core material failed more frequently by breakage, whereas titanium surface cages failed more frequently by migration. Failure rates varied depending on the manufacturer. Most cage breakages identified in the present study occurred intraoperatively during implantation. These findings call for a more detailed Food and Drug Administration evaluation of these intraoperative malfunctions before commercial approval. Level 4.

Clinical and Cost-Effectiveness of Lumbar Interbody Fusion Using Tritanium Posterolateral Cage (vs. Propensity-Matched Cohort of PEEK Cage).

Surgical management of degenerative lumbar spine disorders is effective at improving patient pain, disability, and quality of life; however, obtaining a durable posterolateral fusion after decompression remains a challenge. Interbody fusion technologies are viable means of improving fusion rates in the lumbar spine, specifically various graft materials including autograft, structural allograft, titanium, and polyether ether ketone. This study assesses the effectiveness of Tritanium posterolateral cage in the treatment of degenerative disk disease. Nearest-neighbor 1:1 matched control transforaminal lumbar interbody fusion with PEEK vs. Tritanium posterior lumbar (PL) cage interbody fusion patients were identified using propensity scoring from patients that underwent elective surgery for degenerative disk diseases. Line graphs were generated to compare the trajectories of improvement in patient-reported outcomes (PROs) from baseline to 3 and 12 months postoperatively. The nominal data were compared via the χ2 test, while the continuous data were compared via Student's t-test. The two groups had no difference regarding either the 3- or 12-month Euro-Qol-5D (EQ-5D), numeric rating scale (NRS) leg pain, and NRS back pain; however, the Tritanium interbody cage group had better Oswestry Disability Index (ODI) scores compared to the control group of the PEEK interbody cage at both 3 and 12 months (p=0.013 and 0.048). Our results indicate the Tritanium cage is an effective alternative to the previously used PEEK cage in terms of PROs, surgical safety, and radiological parameters of surgical success. The Tritanium cohort showed better ODI scores, higher fusion rates, lower subsidence, and lower indirect costs associated with surgical management, when compared to the propensity-matched PEEK cohort.

Subsidence of a partially porous titanium lumbar cage produced by electron beam melting technology.

The lumbar intervertebral devices are widely used in the surgical treatment of lumbar diseases. The subsidence represents a serious clinical issue during the healing process, mainly when the interfaces between the implant and the vertebral bodies are not well designed. The aim of this study is the evaluation of subsidence risk for two different devices. The devices have the same shape, but one of them includes a filling micro lattice structure. The effect of the micro lattice structure on the subsidence behavior of the implant was evaluated by means of both experimental tests and finite element analyses. Compressive tests were carried out by using blocks made of grade 15 polyurethane, which simulate the vertebral bone. Non-linear, quasi-static finite element analyses were performed to simulate experimental and physiologic conditions. The experimental tests and the FE analyses showed that the subsidence risk is higher for the device without micro lattice structure, due to the smaller contact surface. Moreover, an overload in the central zone of the contact surface was detected in the same device and it could cause the implant failure. Thus, the micro lattice structure allows a homogenous pressure distribution at the implant-bone interface.

Synthesis of a biocompatible benzophenone-substituted chitosan hydrogel as novel coating for PEEK with extraordinary strong antibacterial and anti-biofilm properties

Chitosan derivatives substituted with benzophenone groups that can be cross-linked by ultraviolet light were synthesized as coatings for PEEK substrates used in the construction of lumbar cages. The IC90 values of the benzophenone-modified chitosan polymers in solution before crosslinking were in the same range as those reported for native chitosan. The resulting hydrogel surface after crosslinking exhibited excellent antimicrobial properties and was highly effective (up to 5 log-fold) against clinically relevant strains of methicillin-resistant S. aureus and E. coli. As a result, the coated surface also significantly reduced biofilm formation. The coatings show good biocompatibility with numerous cell lines as well as low levels of cytotoxicity (ISO 10993–5) and pyrogenicity (ISO 10993–11). The coatings also exhibited strong antioxidant properties toward formed hydroxyl radicals in an in-vitro Fenton reaction. Overall, substitution of chitosan with benzophenone residues is an interesting and important approach to the functionalization of materials used for medical implants that are prone to microbial contamination and mechanical failure. Biocompatible antimicrobial coatings might also be employed in photopatterning methods used in the design of medical devices.

The value of Hounsfield units in predicting cage subsidence after transforaminal lumbar interbody fusion

BackgroundCage subsidence may occur following transforaminal lumbar interbody fusion (TLIF) and lead to nonunion, foraminal height loss and other complications. Low bone quality may be a risk factor for cage subsidence. Assessing bone quality through Hounsfield units (HU) from computed tomography has been proposed in recent years. However, there is a lack of literature evaluating the correlation between HU and cage subsidence after TLIF.MethodsTwo hundred and seventy-nine patients suffering from lumbar degenerative diseases from April, 2016 to August, 2018 were enrolled. All underwent one-level TLIF with a minimum of 1-year follow-up. Cage subsidence was defined as > 2 mm loss of disc height at the fusion level. The participants were divided into 2 groups: cage subsidence group (CS) and non-cage subsidence group (non-CS). Bone quality was determined by HU, bone mineral density of lumbar (BMD-l) and femoral (BMD-f) from dual-emission X-ray absorptiometry (DXA). HU of each vertebra from L1 to L4 (e.g., HU1 for HU of L1) and mean value of the four vertebrae (HUm) were calculated. Visual analog scale (VAS) of back/leg pain and Oswestry disability index (ODI) were used to report clinical outcomes.ResultsCage subsidence occurred in 82 (29.4%) cases at follow-ups. Mean age was 50.8 ± 9.0 years with a median follow-up of 18 months (range from 12 to 40 months). A total of 90.3% patients presented fusion with similar fusion rate between the two groups. ODI and VAS in leg were better in non-CS group at last follow-ups. Using receiver operating characteristic curves (ROCs) to predict cage subsidence, HUm provided a larger area under the curve (AUC) than BMD-l (Z = 3.83, P < 0.01) and BMD-f (Z = 2.01, P = 0.02). AUC for HU4 was larger than BMD-f and close to HUm (Z = 0.22, P = 0.481).ConclusionsCage subsidence may indicate worse clinical outcomes. HU value could be a more effective predictor of lumbar cage subsidence compared with T-score of DXA after TLIF.

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.

Risk factors for cage subsidence and clinical outcomes after transforaminal and posterior lumbar interbody fusion.

Cage subsidence is a very common complication after lumbar interbody fusion. It may compromise vertebral interbody fusion through progressive spinal deformity and consequently cause compression of neural elements. Clinical relevance remains, however, unclear, with few studies on this subject and even less information regarding its correlation with clinical findings. The aim of this study was to identify risk factors for cage subsidence and clinical evaluation after transforaminal (TLIF) and posterior (PLIF) lumbar interbody fusion. A retrospective study in patients submitted to TLIF and PLIF between 2008 and 2017 was conducted. A total of 165 patients were included (123 TLIF and 42 PLIF). Univariate analysis showed an increased risk of cage subsidence in spondylolisthesis comparing with degenerative disk disease (p = 0.007). A higher preoperative lumbar lordosis angle (p = 0.014) and cage placement in L2-L3 (p = 0.012) were associated with higher risk of subsidence. The posterior cage positioning on vertebral endplate was associated with a higher risk of subsidence (p = 0.028) and significant subsidence (p = 0.005), defined as cage migration > 50% of cage height. PLIF presented a higher risk when comparing with TLIF (p = 0.024). Hounsfield unit (HU) values < 135 (OR6; 95% CI [1.95-34]) and posterior positioning (OR7; 95% CI [1.7-27.3]) were independent risk factors for cage subsidence and significant subsidence, respectively, in multivariate analysis. There was a tendency for significant subsidence in degrees ≥ 2 of Meyerding spondylolisthesis (OR4; 95% CI [0.85-21.5]). Significant cage subsidence was not associated with worse clinical results. Other analyzed factors, such as age (p = 0.008), low bone mineral density (BMD) (p = 0.029) and type of surgery (TLIF) (p = 0.004), were associated with worse results. The present study shows that lower BMD and posterior cage positioning are relevant risk factors for lumbar cage subsidence. Low BMD is also a predictor of poor clinical results, so it must be properly evaluated and considered, through HU values measurement in CT scan, a feasible and reliable tool in perioperative planning.

Development of a lumbosacral intervertebral cage prototype for dogs

ABSTRACT: Several surgical procedures aim to decompress and/or stabilize the lumbosacral (LS) joint of dogs; however, the lumbar interbody fusion technique, by using a cage combined with a bone graft, is the most indicated and used in human medicine. No specific implant is available for application to the canine lumbosacral joint. Thus, this study measured lumbosacral discs in large dogs, determined whether a human cage model could fit the dogs’ L7-S1 intervertebral space, and developed a LS cage prototype for dogs. Ten cadaveric lumbosacral spines from adult dog weighing 20-35kg were used. The dogs had died for reasons unrelated to this study. The vertebral body dimensions and the L7-S1 intervertebral space occupied by the intervertebral disc were measured by lateral and ventrodorsal radiographs and by computed tomography in the dorsal, sagittal, and transverse views. Measurements were also taken of the anatomical specimens in the sagittal and transverse planes. After measuring the intervertebral discs, the following mean measures were obtained for L7-S1 discs: height 12.23mm, dorsal thickness 3.3mm, central thickness 4mm, ventral thickness 5.5mm, and width 24.74mm. The human lumbar cage models from brands LDR, Baumer Orthopedics, Stryker, Synthes, and Vertebral Technologies, Inc. and cervical stabilization cages from the brands B-Braun and Stryker were evaluated and were found to be unsuitable for large dogs. Cervical human cages had measurements similar to those found in this study; however, due to their quadrangular shape, the possibility of being introduced surgically through the surgical accesses available for the articulation between L7-S1 in dogs without injuring the cauda equina or the L7 root is small. A cage model was then developed using 3D modelling software. It was designed for insertion via dorsal laminectomy in the lateral portions of the intervertebral space. To avoid cauda equina lesion, the implant model was developed to be placed laterally to the midline. The cage surface is serrated to prevent using the locking screw to fix it, thus avoiding further injury to nerve structures. The serrated surfaces are also designed to avoid cage migration and promote stability. The prototype allows graft placement in the surrounding intervertebral space, which is fundamental for fusion through integration between the cage and the endplates as well as for bone growth between and around the cage. It was also considered studies on humans showing that the lateral regions of the endplates support a more considerable load. Biomechanical and in vivo studies on the developed model are necessary to evaluate the actual degree of distraction, mobility and the long-term rate of fusion between L7 and S1 and its possible impact on the adjacent motor units, combined or not with dorsal fixation techniques.

Design Evaluation and Development of Lumbar Cage

Design Evaluation and Development of Lumbar Cage

Subject-specific finite element analysis of a lumbar cage produced by electron beam melting.

The aim of this study was the analysis of the mechanical behaviour of a partially porous lumbar custom-made cage by means of a subject-specific finite element analysis (FEA). The cage, made of Ti6Al4V ELI alloy, was produced via electron beam melting (EBM) process and surgically implanted in a female subject, 50 years old. The novelty of this study was the customized design of the cage and of its internal structure, which is impossible to obtain with the traditional production techniques. The 3D model of the spine was obtained from the computed tomography (CT) of the patient. Moreover, high-resolution industrial CT was also used to reconstruct a 3D model of the cage, with its real (as-produced) features, such as superficial roughness, morphology of the bulk and of the porous structure. The workflow was divided in several steps: the main finite element analyses were non-linear and quasi-static regarding: the rhombic dodecahedron (RD) unit cell of the porous structure; the device; the whole L4-L5 motion segment with the implanted cage. Stress distribution was calculated under compression load for all models. For the RD unit cell, the maximum stress appeared at the connected cross nodes, where notch effect was present. For the cage subjected to a load of 1 kN, the porous structure did not present any functional failure. For the whole biomechanical system subjected to a physiological load of 360 N, the calculated stress in the bone was smaller than its yield strength value. On the axial view, a zone with higher compressive stresses was present on the L5 vertebral body. This was due to the contact stress between the cage and the vertebra. From the comparison between FE results and the CT images of the spine, bone remodelling was supposed, with the formation of new bone. Graphical abstract Workflow showing the phases of the research.

P34. Multiple anterior bridging bone using newly designed anterior bridging cage (ABC) in posterior lumbar interbody arthrodesis

BACKGROUND CONTEXT A number of spine surgeons place bone graft materials into anterior disc space as well as the void of cages to expect bridging bone at the extra-cage area. However, there have been no lumbar cages enabled to communicate anterior extra-cage grafted bone and intra-cage grafted bone. PURPOSE To introduce the newly designed lumbar cage, anterior bridging cage (ABC) with 4 anterior holes in ogival shape, which design enables to communicate anterior extra-cage grafted bone and intra-cage grafted bone and to first demonstrate the multiple anterior bridging bone (ABB) between anterior extra-cage area and intra-cage area and interconnecting bridging bone between two ABC cages. STUDY DESIGN/SETTING Prospective cohort radiographic study (ClinicalTrials.gov NCTD2485574). PATIENT SAMPLE Consecutive 101 patients with 133 surgical levels were enrolled from May 2015 to Dec 2017. The mean age of patients was 66.44 (95%Cl, 64.94-68.13) and the number of male and female was 31 and 70. OUTCOME MEASURES Bridging scores using post operative 1-year multi-direction computed tomographic (CT) scan and clinical outcomes analysis. METHODS The conventional bilateral transforaminal interbody fusion was performed in all enrolled patients. Anterior bone grafts were prepared by each 6cc volume of half-mixed local auto-bone and artificial or allograft bone at the right and left prepared disc space and then, each ABC cage filled with local auto-bone was inserted bilaterally into disc space. All bridging scores were evaluated in post-operative 1-year CT scan and evaluated by 2 spine surgeons twice. The scores of bridging bone were divided into the intra-cage grafted bridging bone (InGBB, scored 1 to 3 at right and left cages), extra-cage grafted bridging bone (ExGBB, scored 1 to 3 at anterior, posterior, right, left, intermediate area between cages) and anterior bridging bone (ABB, scored 0 to 2 at medial, lateral, superior and inferior holes at each cage). In all area, the higher the score, the more complete bridging bone. Radiographic fusion was determined as if 3 in InGBB and/or in ExGBB were evaluated. RESULTS In reliability assessment, intra-class correlations were ranged 0.82 to 0.87 in InGBB, 0.70 to 0.89 in ExGBB, and 0.65 to 0.81 in ABB and inter-class correlation were 0.77 to 0.78 in InGBB, 0.68 to 0.83 in ExGBB, and 0.56 to 0.74 in ABB. The average scores of InGBBs in right and left sides were 2.43(2.38-2.47) and 2.47(2.44-2.53) resepctively. In ExGBB, the average scores significantly higher in anterior (2.40, 2.35-2.44) compared to posterior (2.11, 2.05-2.17), right (1.48, 1.45-1.55), left (1.50, 1.45-1.55), and intermediate (1.91, 1.83-2.13) (p CONCLUSIONS InGBB and ExGBB demonstrated the acceptable ranges of reliability values. In addition to InGBB, ExGBB was important radiographic findings to determine fusion status and especially, anterior ExGBB was significantly frequent. The ABB score was the highest in a medial hole of the ABC cages and each cage had an average 1.9 holes with complete bridging. Such multiple anterior bridging bones between anterior ExGBB and InGBB as well as interconnecting bridging bone between cages through medial holes might be helpful to sustain stable lumbar interbody fusion process. FDA DEVICE/DRUG STATUS Unavailable from authors at time of publication.

P25. Analysis of cage stability and interbody pressure distribution in compression of cortical bone trajectory fixation

BACKGROUND CONTEXT The compressive stiffness in posterior lumbar interbody fusion (PLIF) secure grafts. The cortical bone trajectory (CBT) fixation is effective for the initial fixation. However, it has been reported that the bone fusion rate of CBT fixation is lower than traditional pedicle screw fixation. One of these factors is less stability of anterior column in CBT fixation, which leads to the cage displacement. PURPOSE In this study, to elucidate the instability of anterior column in CBT fixation, we investigated the experimental initial compressive loading and distribution in CBT fixation. Furthermore, to clarify the cage displacement in CBT fixation, we retrospectively studied the relationship between the initial cage position and displacement in CBT fixation. STUDY DESIGN/SETTING Comparative study using lumbar vertebrae of pigs and human model bones, and retrospective study to clarify cage stability and interbody pressure distribution in compression. METHODS We inserted screws for lumbar vertebrae of pigs and human model bones by traditional trajectory (n=3) and CBT (n=4). Then we placed the pressure measurement film (PRESCALE; Fujifilm, Tokyo, Japan) into the intervertebral space. We analyzed the initial compression loading and distribution. A total of 67 patients (34 men, 33 women, mean age 66.7 years) who underwent CBT fixation using single polyetheretherketone cage in our institution were retrospectively investigated. A total of 114 lumbar cages were analyzed for place in axial plane of intervertebral space using computed tomography (CT) images. Then, we evaluated the range of displacement within 12 months after surgery. RESULTS In the experiment using pig lumbar vertebrae, the average pressure of the anterior column of intervertebral space was significantly lower (p=0.0044) in CBT (0.60±0.01MPa) than traditional trajectory (0.90±0.07MPa), and the compression loading was also significantly lower (p=0.0016) in CBT (12±5N) than traditional trajectory (73±9N). The similar result was observed in the human model bones. In the retrospective study of cage position, cage displacement was observed more frequently in the anterior location (14 cages, 16.3%) than the posterior location (2 cages, 7.1%). However, the cage position was not a significant risk factor for displacement (OR 2.528, 95% CI 0.578-11.75, p=0.227). CONCLUSIONS These findings suggest that the compression power of the anterior column in compression of CBT fixation is insufficient to grasp the cage followed by the cage instability and displacement. FDA DEVICE/DRUG STATUS Unavailable from authors at time of publication.

Application of modified direction-changeable lumbar Cage in transforaminal lumbar interbody fusion

To investigate the effectiveness of modified direction-changeable lumbar Cage in transforaminal lumbar interbody fusion (TLIF). A retrospective analysis was made of 161 patients with single segment L 4 or L 5 isthmic spondylolisthesis treated between January 2013 and December 2015. According to the implantation of Cage, they were divided into trial group (85 cases, modified direction-changeable lumbar Cage implanted in TLIF) and control group (76 cases, traditional nondirection-changeable Cage implanted in TLIF). There was no significant difference in the general data of gender, age, disease duration, slippage segment, and slippage grade between the two groups ( P>0.05). The intraoperative implantation time of Cage, Cage position adjustments times, fluoroscopy times during implantation of Cage, fluoroscopy exposure time, and total operation time were recorded and compared between the two groups. Visual analogue scale (VAS) and Oswestry disability index (ODI) scores were used to evaluate the effectiveness of the patients before operation, and at 3, 6, and 12 months after operation, and the incidence of complications was recorded and analyzed. CT examinations were performed at 6 and 12 months after operation, and lumbar fusion was evaluated by Bridwell criteria. The intraoperative implantation time of Cage, Cage position adjustments times, fluoroscopy times during implantation of Cage, fluoroscopy exposure time, and total operation time in trial group were significant less than those in control group ( P<0.05). All the 161 patients were followed up 12-18 months (mean, 14.3 months). There was 1 case of dural sac tear in the trial group and 1 case of superficial infection in the control group; no complication such as dural tear and infection occurred in other patients. The fusion rate was 76.5% (64/85) in the trial group and 57.9% (44/76) in the control group at 6 months after operation, showing significant difference ( χ 2=6.44, P=0.02); at 12 months after operation, the fusion rate was 96.5% (82/85) in the trial group and 90.8% (69/76) in the control group (including 3 cases of Cage displacement and 4 cases of screw breakage), showing no significant difference in the fusion rate between the two groups ( χ 2=1.54, P=0.26). The VAS and ODI scores of the two groups decreased gradually at 3, 6, and 12 months after operation, and improved significantly when compared with those before operation ( P<0.05). There was no significant difference in VAS and ODI scores between the two groups before and after operation ( P>0.05). Both Cages can obtain the similar effectiveness. The modified direction-changeable lumbar Cage can significantly reduce the fluoroscopy times and radiation dose during TLIF, shorten the operation time, and effectively reduce the radiation exposure of patients and medical staff.

3D printing assisted finite element analysis for optimising the manufacturing parameters of a lumbar fusion cage

The study herein combines the use of fused filament fabrication (FFF) with finite element analysis (FEA) to enhance the understanding of certain manufacturing parameters (i.e. material, infill density, infill pattern, and outer vertical shell) in the design process of a lumbar fusion cage. Three FFF materials with distinct mechanical properties namely polycarbonate (PC), acrylonitrile butadiene styrene (ABS), and polylactic acid (PLA) were tested. Three infill densities (i.e. 25%, 50%, 75%) were investigated along with two different infill patterns (i.e. rectangular and honeycomb). Compressive modulus and compressive yield strength values obtained from standard mechanical analysis were used as input for FEA to assess numerically the mechanical performance of a lumbar fusion cage under physiological static loading. The findings suggest that both infill density and infill pattern influence the quality of the finished part in terms of both printing accuracy and mechanical response. FEA results indicate that both PC and ABS can be safely adopted to fabricate a porous lumbar cage with a 50% honeycomb infill density and a honeycomb infill pattern. This paper demonstrates that 3D printing assisted FEA can be used to predict the performance of a lumbar cage design with varying manufacturing parameters and potentially reduce product design and development time.