Undercut macrostructure topography on and within an interbody cage improves biomechanical stability and interbody fusion

BACKGROUND CONTEXTThe interface and interactions between an interbody cage, graft material, and host bone can all participate in the fusion. Shortcomings of Poly(aryl-ether-ether-ketone) interbody cages have been addressed with novel titanium surfaces. Titanium surfaces paired with macroscale topography features on the endplates and within the aperture may provide additional benefits.PURPOSETo evaluate the influence of cage design parameters on interbody fusion in a large animal preclinical model.STUDY DESIGN/SETTINGA comparative preclinical large animal model was performed to evaluate how macroscale topography features of an interbody cage can facilitate early integration between the host bone, graft material, and interbody cage and these effects on biomechanical stability and fusion.METHODSForty single level interbody fusions (L4–L5) using iliac crest autograft and bilateral pedicle screw fixation were performed in adult sheep to evaluate the effect of undercut macrostructure topography features of an interbody cage on the endplates and within the aperture. Fusions were evaluated at 6 and 12 weeks (n=10 per group) using radiography, microcomputed tomography, biomechanical integrity, and histology endpoints.RESULTSThe presence of the undercut macrostructures present on the endplates and within the aperture statistically improved biomechanical integrity at 6 and 12 weeks compared with controls. Microcomputed tomography and histology demonstrated bony interdigitation within the endplate and aperture features contributing to the improvement in properties.CONCLUSIONSThe present study demonstrates that Poly(aryl-ether-ether-ketone) implants with titanium surfaces can be augmented by undercut macrostructures present on the endplates and within the aperture to provide opportunities for a series of anchoring points that, with new bone formation and remodelling, result in earlier and improved biomechanical integrity of the treated level.CLINICAL SIGNIFICANCEThis preclinical study showed that bone interdigitation with the undercut macrostructures present on the endplates and within the aperture resulted in improved fusion and biomechanical stability in a clinically relevant spinal fusion model. Future clinical study is warranted to evaluate such implants’ performance in humans.     

Subsidence and fusion performance of a 3D-printed porous interbody cage with stress-optimized body lattice and microporous endplates - a comprehensive mechanical and biological analysis

BACKGROUND CONTEXTCage subsidence remains a serious complication after spinal fusion surgery. Novel porous designs in the cage body or endplate offer attractive options to improve subsidence and osseointegration performance.PURPOSETo elucidate the relative contribution of a porous design in each of the two major domains (body and endplates) to cage stiffness and subsidence performance, using standardized mechanical testing methods, and to analyze the fusion progression via an established ovine interbody fusion model to support the mechanical testing findings.STUDY DESIGN/SETTINGA comparative preclinical study using standardized mechanical testing and established animal model.METHODSTo isolate the subsidence performance contributed by each porous cage design feature, namely the stress-optimized body lattice (vs. a solid body) and microporous endplates (vs. smooth endplates), four groups of cages (two-by-two combination of these two features) were tested in: (1) static axial compression of the cage (per ASTM F2077) and (2) static subsidence (per ASTM F2267). To evaluate the progression of fusion, titanium cages were created with a microporous endplate and internal lattice architecture analogous to commercial implants used in subsidence testing and implanted in an endplate-sparing, ovine intervertebral body fusion model.RESULTSThe cage stiffness was reduced by 16.7% by the porous body lattice, and by 16.6% by the microporous endplates. The porous titanium cage with both porous features showed the lowest stiffness with a value of 40.4±0.3 kN/mm (Mean±SEM) and a block stiffness of 1976.8±27.4 N/mm for subsidence. The body lattice showed no significant impact on the block stiffness (1.4% reduction), while the microporous endplates decreased the block stiffness significantly by 24.9% (p<.0001). All segments implanted with porous titanium cages were deemed rigidly fused by manual palpation, except one at 12 weeks, consistent with robotic ROM testing and radiographic and histologic observations. A reduction in ROM was noted from 12 to 26 weeks (4.1±1.6° to 2.2±1.4° in lateral bending, p<.05; 2.1±0.6° to 1.5±0.3° in axial rotation, p<.05); and 3.3±1.6° to 1.9±1.2° in flexion extension, p=.07). Bone in the available void improved with time in the central aperture (54±35% to 83±13%, p<.05) and porous cage structure (19±26% to 37±21%, p=.15).CONCLUSIONSBody lattice and microporous endplates features can effectively reduce the cage stiffness, therefore reducing the risk of stress shielding and promoting early fusion. While body lattice showed no impact on block stiffness and the microporous endplates reduced the block stiffness, a titanium cage with microporous endplates and internal lattice supported bone ingrowth and segmental mechanical stability as early as 12 weeks in ovine interbody fusion.CLINICAL SIGNIFICANCEPorous titanium cage architecture can offer an attractive solution to increase the available space for bone ingrowth and bridging to support successful spinal fusion while mitigating risks of increased subsidence.     

3D-printed titanium cages without bone graft outperform PEEK cages with autograft in an animal model

BACKGROUND CONTEXTModernization of 3D printing has allowed for the production of porous titanium interbody cages (3D-pTi) which purportedly optimize implant characteristics and increase osseointegration; however, this remains largely unstudied in vivo.PURPOSETo compare osseointegration of three-dimensional (3D) titanium cages without bone graft and Polyether-ether-ketone (PEEK) interbody cages with autologous iliac crest bone graft (AICBG).STUDY DESIGNAnimal study utilizing an ovine in vivo model of lumbar fusion.METHODSInterbody cages of PEEK or 3D-pTi supplied by Spineart SA (Geneva, Switzerland) were implanted in seven living sheep at L2-L3 and L4-L5, leaving the intervening disc space untreated. Both implant materials were used in each sheep and randomized to the aforementioned disc spaces. Computed tomography (CT) was obtained at 4 weeks and 8 weeks. MicroCT and histological sections were obtained to evaluate osseointegration.RESULTSMicroCT demonstrated osseous in-growth of native cancellous bone in the trabecular architecture of the 3D-pTi interbody cages and no interaction between the PEEK cages with the surrounding native bone. Qualitative histology revealed robust osseointegration in 3D-pTi implants and negligible osseointegration with localized fibrosis in PEEK implants. Evidence of intramembranous and endochondral ossification was apparent with the 3D-pTi cages. Quantitative histometric bone implant contact demonstrated significantly more contact in the 3D-pTi implants versus PEEK (p<.001); region of interest calculations also demonstrated significantly greater osseous and cartilaginous interdigitation at the implant-native bone interface with the 3D-pTi cages (p=.008 and p=.015, respectively).CONCLUSIONS3D-pTi interbody cages without bone graft outperform PEEK interbody cages with AICBG in terms of osseointegration at 4 and 8 weeks postoperatively in an ovine lumbar fusion model.CLINICAL SIGNIFICANCE3D-pTi interbody cages demonstrated early and robust osseointegration without any bone graft or additive osteoinductive agents. This may yield early stability in anterior lumbar arthrodesis and potentially bolster the rate of successful fusion. This could be of particular advantage in patients with spinal neoplasms needing post-ablative arthrodesis, where local autograft use would be ill advised.     

Comparison in the same intervertebral space between titanium-coated and uncoated PEEK cages in lumbar interbody fusion surgery

BackgroundsDisadvantages of polyetheretherketone (PEEK) cages are their smooth and hydrophobic surfaces and their lack of osteoconductivity. Titanium (Ti) coated PEEK cage has been innovated to overcome these potential concerns. However, few well-designed studies have investigated the efficacy of Ti-coated PEEK cage on interbody fusion in humans. This study aimed to evaluate the efficacy of Ti coating on bone ongrowth at bone–implant surface by simultaneously comparing Ti-coated and uncoated PEEK cages in the same intervertebral space.MethodsThis study is a prospective comparative study for the two different cages. Twenty-six subjects who underwent one-level instrumented posterior lumbar interbody fusion (PLIF) were included. Two PEEK cages [a plasma-sprayed Ti-coated (PTC-PEEK) and an uncoated PEEK cage] were inserted in the same intervertebral space. Fusion rates, cage subsidence, and vertebral cancellous condensation (VCC) around the cage, which indicates bone growth on the surface of each cage, were assessed by thin-slice computed tomography (CT) immediately (within 1 week) and at 3 months postoperatively. A functional radiograph was obtained at 3 and 12 months postoperatively.ResultsTwenty-three subjects showed solid fusion at 3 months postoperatively (fusion rate, 88%). Cage subsidence was not observed. VCC was often observed around the PTC-PEEK cage as evaluated by completely synchronized CT images between immediately and at 3 months postoperatively. Quantified VCC around the cage was significantly larger in the PTC-PEEK cage than in the uncoated PEEK cage (P = 0.01).ConclusionsThe Ti-coated PEEK cage exhibits radiographic signs, suggesting bone ongrowth, as represented by VCC around the cage compared with that around the uncoated PEEK cage. The Ti-coated PEEK cage has the potential to promote solid fusion and to improve clinical outcomes in lumbar interbody fusion surgery.     

Failure of a polyether-ether-ketone expandable interbody cage following transforaminal lumbar interbody fusion

Purpose

Expandable cages are a more recent option for maintaining or restoring disc height and segmental lordosis with transforaminal lumbar interbody fusion (TLIF). Complications associated with expandable cages have not yet been widely reported. We report a case of postoperative failure of a polyether-ether-ketone (PEEK) expandable interbody device used during TLIF.

Methods

A 50-year-old man presented with severe back and right leg pain after undergoing L4-5 and L5-S1 TLIFs with expandable cages and L3-S1 posterior instrumented fusion. Imaging showed retropulsion of a portion of the interbody cage into the spinal canal causing nerve compression. Displacement occurred in a delayed manner. In addition, pseudoarthrosis was present.

Results

The patient underwent re-exploration with removal of the retropulsed wafer and redo fusion.

Conclusions

Expandable cages are a recent innovation; as such, efficacy and complication data are limited. As with any new device, there exists potential for mechanical failure, as occurred in the case presented.

     

Bony ingrowth potential of 3D-printed porous titanium alloy: a direct comparison of interbody cage materials in an in vivo ovine lumbar fusion model

Background Context

There is significant variability in the materials commonly used for interbody cages in spine surgery. It is theorized that three-dimensional (3D)-printed interbody cages using porous titanium material can provide more consistent bone ingrowth and biological fixation.

Relation between radiological assessment and biomechanical stability of lumbar interbody fusion in a large animal model

Purpose

To relate the progress of vertebral segmental stability after interbody fusion surgery with radiological assessment of spinal fusion.

Methods

Twenty goats received double-level interbody fusion and were followed for a period of 3, 6 and 12 months. After killing, interbody fusion was assessed radiographically by two independent observers. Subsequently, the lumbar spines were subjected to four-point bending and rotational deformation, assessed with an optoelectronic 3D movement registration system. In addition, four caprine lumbar spines were analysed in both the native situation and after the insertion of a cage device, as to mimic the direct post-surgical situation. The range of motion (ROM) in flexion/extension, lateral bending and axial rotation was analysed ex vivo using a multi-segment testing system.

Results

Significant reduction in ROM in the operated segments was already achieved with moderate bone ingrowth in flexion/extension (71 % reduction in ROM) and with only limited bone ingrowth in lateral bending (71 % reduction in ROM) compared to the post-surgical situation. The presence of a sentinel sign always resulted in a stable vertebral segment in both flexion/extension and lateral bending. For axial rotation, the ROM was already limited in both native and cage inserted situations, resulting in non-significant differences for all radiographic scores.

Discussion

In vivo vertebral segment stability, defined as a significant reduction in ROM, is achieved in an early stage of spinal fusion, well before a radiological bony fusion between the vertebrae can be observed. Therefore, plain radiography underestimates vertebral segment stability.     

A novel narrow surface cage for full endoscopic oblique lateral lumbar interbody fusion: A finite element study

ObjectiveTo evaluate the mechanical response of a narrow surface cage that we designed for full endoscopic oblique lateral lumbar interbody fusion (FE-OL-LIF).MethodsA finite element (FE) model of lumbar spine was developed and validated. To simulate the FE-OL-LIF, the functional spinal unit (FSU) L4-L5 was assembled with a narrow surface polyetheretherketone (PEEK) cage, two rods and four screws. 500N load combined with 7.5Nm moment was applied to the surgical models. Effect of the cage width on the stress was studied.ResultsRange of motion (ROM) in the surgical models significantly decreased by 88% in flexion, 91% extension, 85% in right and left lateral bending, 75% in right and left axial rotation as compared to the intact model. Width of the cage slightly decreased the ROM in all loading scenarios. Flexion produced the highest stress in the cages and endplates. In all loading cases, the maximum stresses of cages and endplates were both lower than their yield stress.ConclusionsIn engineering analysis, the novel narrow-surface cage had a strength to support spine activities. 9 mm width cage was recommended in FE-OL-LIF. This study provided engineering evidence and technical advice to improve the design of minimally invasive cage. Fatigue test and cadaver trial shall be improved.     

扩张式椎间融合器在腰椎融合术中的应用

目的探讨扩张式椎间融合器（expanding cage,EC）在腰椎融合术中应用的适应性、技术要点和疗效。方法本组47例患者,均行后路扩张式椎间融合术（PELIC）。术前分别诊断为腰椎管狭窄、腰椎间盘突出、腰椎滑脱和退变性腰椎不稳,经非手术治疗无效后,以手术对椎管及神经根管减压,用EC融合固定并植骨。术前、术后对患者的腰疼情况进行视觉痛觉自我评定尺（VAS）评分。结果所有患者术前症状消失,术中未发生神经损伤,随访最长时间为61个月,最短53个月,平均57．3个月,无假关节形成,无明显椎体塌陷。结论EC在腰椎融合术应用中具有融合可靠、症状改善明显等优点。     

颈椎椎体间融合器在颈椎病外科治疗中的应用

目的探讨应用颈椎椎体间融合器治疗脊髓型颈椎病的临床疗效。方法回顾性总结分析我院2002年3月~2005年2月间应用颈椎椎体间融合器治疗的38例脊髓型颈椎病患者的临床及影像学资料,观察椎体间隙高度、颈椎生理曲度及融合情况。结果平均随访10个月时,36例获得骨性融合,融合率达95%,优良率达87%,颈椎生理曲度及融合节段的椎间隙高度恢复及维持满意。结论颈椎椎体间融合器应用能使融合节段获得即刻的稳定性,恢复并维持颈椎生理曲度及融合节段的椎间隙高度,是治疗脊髓型颈椎病的有效方法。     

聚醚醚酮颈椎椎间融合器的临床应用及疗效评价

[目的]评价聚醚醚酮椎间融合器在颈前路经椎间隙减压融合术中的临床应用及疗效。[方法]采用颈前路经椎间隙减压、聚醚醚酮椎间融合器植入固定融合术治疗颈椎病及颈椎间盘突出症45例，术后定期随访颈椎X线片，观察手术椎节的稳定性、融合情况、椎间隙高度恢复以及患者神经功能改善。[结果]随访6～12个月，手术节段稳定，椎间高度恢复满意，术后6个月绝大多数病例获得满意骨性融合。神经功能改善率45％～100％，平均84％。[结论]聚醚醚酮椎间融合器具有生物相容性好、弹性膜量小、x线透光等优点，有助于重建并维持椎间高度和生理曲度，促进植骨融合。     

The in vitro stabilising effect of polyetheretherketone cages versus a titanium cage of similar design for anterior lumbar interbody fusion

This biomechanical study was performed to test the primary segmental in vitro stabilising effect of a standard and large footprint radiolucent poly-ether-ether-ketone (PEEK) box cage versus a titanium box cage for anterior lumbar interbody fusion. Eighteen L2-L3 and sixteen L4-L5 cadaveric motion segments were divided into three groups and received a titanium cage or a radiolucent PEEK cage with standard or large footprint. All specimens were tested in three testing conditions: intact, stand-alone anterior cage and finally with supplemental translaminar screw fixation. Full range of motion and neutral zone measurements were determined and anterior cage pull out force was tested. The titanium design was significantly more effective in reducing the range of motion only in axial rotation. The larger footprint radiolucent cage did not increase stability as compared to the standard footprint. The titanium cage pull out force was significantly (P=0.0002) higher compared to both radiolucent cage constructs. Clinical relevance: Supplemental posterior fixation is strongly recommended to increase initial stability of any anterior interbody fusion cage construct. Although the biomechanical stability necessary to achieve spinal fusion is not defined, the radiolucent designs tested in this study, with a standard footprint as well as with a larger footprint, may be insufficiently stabilised with translaminar screws as compared to the titanium implant. Supplemental pedicle screw fixation may be required to obtain adequate stabilisation in the clinical setting.     

The influence of cage positioning and cage type on cage migration and fusion rates in patients with monosegmental posterior lumbar interbody fusion and posterior fixation

In posterior lumbar interbody fusion, cage migrations and lower fusion rates compared to autologous bone graft used in the anterior lumbar interbody fusion procedure are documented. Anatomical and biomechanical data have shown that the cage positioning and cage type seem to play an important role. Therefore, the aim of the present study was to evaluate the impact of cage positioning and cage type on cage migration and fusion. We created a grid system for the endplates to analyze different cage positions. To analyze the influence of the cage type, we compared “closed” box titanium cages with “open” box titanium cages. This study included 40 patients with 80 implanted cages. After pedicle screw fixation, 23 patients were treated with a “closed box” cage and 17 patients with an “open box” cage. The follow-up period averaged 25 months. Twenty cages (25%) showed a migration into one vertebral endplate of <3 mm and four cages (5%) showed a migration of ≥3 mm. Cage migration was highest in the medio-medial position (84.6%), followed by the postero-lateral (42.9%), and the postero-medial (16%) cage position. Closed box cages had a significantly higher migration rate than open box cages, but fusion rates did not differ. In conclusion, cage positioning and cage type influence cage migration. The medio-medial cage position showed the highest migration rate. Regarding the cage type, open box cages seem to be associated with lower migration rates compared to closed box cages. However, the cage type did not influence bone fusion.     

纳米羟基磷灰石/聚酰胺66复合材料融合器行经椎间孔腰椎椎体间融合术的影像学研究

目的:将纳米羟基磷灰石/聚酰胺66(n-HA/PA66)复合材料融合器应用于经椎间孔腰椎椎体间融合术,探讨其在恢复、维持腰椎曲度和椎间高度及融合率等方面的作用及意义.方法:将2012年2月至7月符合纳入和排除标准的50例退行性腰椎疾病的患者(其中腰椎间盘突出症32例,腰椎滑脱18例),应用n-HA/PA66复合材料融合器进行经椎间孔腰椎椎体间融合术治疗,其中男34例,女16例;年龄22～64岁,平均52.16岁.术前、术后1周及术后2、4、6、8个月,分别行腰椎X线检查、腰椎三维重建CT;根据腰椎X线,测量术前、术后不同时期的腰椎曲线指数、相对椎间隙高度、Taillard指数、节段前凸角和全腰椎前凸角,并对其进行分析.结果:所有患者获得随访,时间8～13个月,平均11.32个月.术后1周腰椎曲线指数、相对椎间隙高度、Taillard指数、节段前凸角和全腰椎前凸角与术前比较差异均有统计学意义,而术后不同时期比较差异均无统计学意义.腰椎融合时间为4～8个月.结论:n-HA/PA66复合材料融合器能较好地恢复、维持腰椎正常序列、矢状面力线及稳定性,而且融合率更高、并发症少.     

Failure of a polyether-ether-ketone expandable interbody cage following transforaminal lumbar interbody fusion

Purpose

Expandable cages are a more recent option for maintaining or restoring disc height and segmental lordosis with transforaminal lumbar interbody fusion (TLIF). Complications associated with expandable cages have not yet been widely reported. We report a case of postoperative failure of a polyether-ether-ketone (PEEK) expandable interbody device used during TLIF.

Methods

A 50-year-old man presented with severe back and right leg pain after undergoing L4-5 and L5-S1 TLIFs with expandable cages and L3-S1 posterior instrumented fusion. Imaging showed retropulsion of a portion of the interbody cage into the spinal canal causing nerve compression. Displacement occurred in a delayed manner. In addition, pseudoarthrosis was present.

Results

The patient underwent re-exploration with removal of the retropulsed wafer and redo fusion.

Conclusions

Expandable cages are a recent innovation; as such, efficacy and complication data are limited. As with any new device, there exists potential for mechanical failure, as occurred in the case presented.

     

Porous Titanium‐6 Aluminum‐4 Vanadium Cage Has Better Osseointegration and Less Micromotion Than a Poly‐Ether‐Ether‐Ketone Cage in Sheep Vertebral Fusion

Interbody fusion cages made of poly‐ether‐ether‐ketone (PEEK) have been widely used in clinics for spinal disorders treatment; however, they do not integrate well with surrounding bone tissue. Ti‐6Al‐4V (Ti) has demonstrated greater osteoconductivity than PEEK, but the traditional Ti cage is generally limited by its much greater elastic modulus (110 GPa) than natural bone (0.05–30 GPa). In this study, we developed a porous Ti cage using electron beam melting (EBM) technique to reduce its elastic modulus and compared its spinal fusion efficacy with a PEEK cage in a preclinical sheep anterior cervical fusion model. A porous Ti cage possesses a fully interconnected porous structure (porosity: 68 ± 5.3%; pore size: 710 ± 42 μm) and a similar Young's modulus as natural bone (2.5 ± 0.2 GPa). When implanted in vivo, the porous Ti cage promoted fast bone ingrowth, achieving similar bone volume fraction at 6 months as the PEEK cage without autograft transplantation. Moreover, it promoted better osteointegration with higher degree (2‐10x) of bone‐material binding, demonstrated by histomorphometrical analysis, and significantly higher mechanical stability (P < 0.01), shown by biomechanical testing. The porous Ti cage fabricated by EBM could achieve fast bone ingrowth. In addition, it had better osseointegration and superior mechanical stability than the conventional PEEK cage, demonstrating great potential for clinical application.     

Solis cage (PEEK) for anterior cervical fusion: preliminary radiological results with emphasis on fusion and subsidence.

BACKGROUND CONTEXT: Recent literature has raised some apprehensions with regard to the usage of cervical cages. PURPOSE: Radiological review of cases performed at our institution with a novel cage made of polyetheretherketone (PEEK). STUDY DESIGN: Retrospective study. METHODS: A retrospective review of the first 15 consecutive cases of single-level anterior cervical interbody fusion using the Solis cage (PEEK material) for cervical spondylotic radiculopathy or myelopathy was performed. The follow-up ranged from 12 to 35 months (average 18 months). Anteroposterior and lateral radiographs were taken immediately after the surgery and at intervals of 3, 6, 12, and 24 months after surgery. Anterior disc height (ADH), posterior disc height (PDH), interbody height ratio (IBHR), distance between the posterior margin of the cage and the posterior wall of the vertebral body (D-CPW), and interbody angle (IBA) were measured on the lateral radiographs and compared. Fusion was assessed by examining for trabecular continuity, bridging of bone across the disc space, and sclerosis at the vertebral end plates on both sides. The parameters assessed were time for fusion, subsidence, segmental sagittal alignment of the operated segment, and presence/absence of migration of the cage. Data were analyzed using the Mann-Whitney nonparametric test. RESULTS: Fusion was evident at 3-6 months postsurgery in all cases except one (93.33% fusion rate at 6 months). At the last follow-up, fusion was maintained in all cases. The immediate postoperative ADH and PDH was significantly greater than the respective preoperative values and was maintained at the last follow-up though there was a significant amount of subsidence when the follow-up radiographs were compared with the immediate postoperative X-rays. The immediate postoperative IBHR was significantly greater than the preoperative IBHR, and was maintained at the last follow-up, but not statistically significant. The immediate postoperative IBA (lordotic angle) was greater than the preoperative IBA but was not statistically significant. The IBA at the last follow-up was lesser than the preoperative value but with no statistical significance. The IBA measured at the last follow-up was less than the value at the immediate postoperative period, but not statistically significant. There was no migration or extrusion of the cage at latest follow-up. CONCLUSIONS: The high fusion rate, low subsidence, stability provided by the cage, and facilitation of radiological assessment are the result of the physical properties of the PEEK material as well as the design of the cage.     

Evaluation of a polyetheretherketone (PEEK) titanium composite interbody spacer in an ovine lumbar interbody fusion model: biomechanical,microcomputed tomographic,and histologic analyses

Background Context

The most commonly used materials used for interbody cages are titanium metal and polymer polyetheretherketone (PEEK). Both of these materials have demonstrated good biocompatibility. A major disadvantage associated with solid titanium cages is their radiopacity, limiting the postoperative monitoring of spinal fusion via standard imaging modalities. However, PEEK is radiolucent, allowing for a temporal assessment of the fusion mass by clinicians. On the other hand, PEEK is hydrophobic, which can limit bony ingrowth. Although both PEEK and titanium have demonstrated clinical success in obtaining a solid spinal fusion, innovations are being developed to improve fusion rates and to create stronger constructs using hybrid additive manufacturing approaches by incorporating both materials into a single interbody device.

Comparison of fusion rates following transforaminal lumbar interbody fusion using polyetheretherketone cages or titanium cages with transpedicular instrumentation

Purpose

Compared to titanium cage, polyetheretherketone (PEEK) cage with pedicle screw fixation has been increasingly used in transforaminal lumbar interbody fusion (TLIF). However, there is insufficient evidence supporting the superiority of PEEK cages over titanium cages as optimal TLIF spacers. The aim of this study was to compare the clinical and radiographic outcomes of patients at a 2-year follow-up after undergoing instrumented TLIF in which either a PEEK cage or a titanium cage was implanted.

Materials and methods

We retrospectively analyzed prospectively collected 48 patients who underwent single-level TLIF in which the first 23 patients received a titanium cage and the 25 patients received a PEEK cage. Patient demographics, clinical outcomes, and radiographic imaging were studied.

Results

Improvement of clinical outcomes was comparable between the two groups. Based on the criteria using computed tomography, 96 % in the Titanium group and 64 % in the PEEK group showed fusion at 12 months. At 24 months, fusion rate in the Titanium group was increased to 100 %, while PEEK group showed 76 % of fusion rate. In the PEEK group, vertebral osteolysis was noted in 60 % of the cases with nonunion. This abnormal finding was not observed in the Titanium group. Vertebral osteolysis was significantly associated with nonunion.

Conclusions

The superiority of PEEK cages over titanium cages for bony fusion was not demonstrated. Additionally, we found unfavorable radiographic findings in the cases with a PEEK cage, which may lead to nonunion. Improvement in biocompatibility of a PEEK cage will be needed to increase the fusion rate.     

Primary stability of anterior lumbar stabilization: interdependence of implant type and endplate retention or removal

This is a comparative in vitro biomechanical study of the primary stability of an anterior lumbar interbody stabilization. The objective was to compare the stability of a interbody stabilizing titanium cage with and without the retention of the bordering vertebral endplates, as well as to compare the titanium cage with a tricalcium phosphate block when the endplates are removed. An adequate blood supply is critical for interbody fusion, which suggests surgical treatment of the bordering endplates. On the other hand, primary stability is improved by the retention of the endplates. Furthermore, bone substitute materials are finding more frequent use due to complications associated with autologous bone grafts. Ten bovine lumbar spine motion segments (average age 6 months) were investigated. Pure bending loadings as well as eccentric axial compression loadings were applied. A titanium cage and tricalcium phosphate block, were tested in conjunction with an anterior augmentation (MACS). Range of motion, neutral zone (NZ) and bending stiffness were measured under pure bending to 10 Nm, and bending stiffness under axial loads of up to 1500 N. Range of motion of both implants in flexion-extension was significantly smaller than physiologic (cage without endplates 4.3°, cage with 2.8°, block without 3.4°, and physiologic 6.6°, all p<0.001). The cage with endplates and the block without endplates were both significantly stiffer than physiologic in all directions except left lateral bending. The block without endplates and the cage with endplates were both stiffer than the cage without endplates. The results suggest that the use of the bone substitute block provides better stability than the cage when the endplates are removed.