Interbody Fusion Cages Research Articles

Stand-alone polyetheretherketone cages for anterior cervical discectomy and fusion for successive four-level degenerative disc disease without plate fixation.

Background:Anterior cervical discectomy with fusion became the most frequently performed technique for the treatment of symptoms related to cervical disc prolapse. Multilevel anterior cervical discectomy has been combined with anterior cervical plate application to help maintain the cervical lordosis and enhance fusion. This was associated with more soft-tissue separation and retraction with increased incidence of surgically related complications and postoperative dysphagia.Aim of the Study:The aim of this study is to evaluate the safety and efficacy of the stand-alone cervical polyetheretherketone (PEEK) cages in four-level discectomy and to determine if it is possible to avoid anterior plate fixation and to achieve satisfactory outcomes.Methodology:This is a retrospective study which was performed between June 2011 and December 2018 at one institute. The clinical and radiological data were collected from patients who underwent successive four-level anterior cervical discectomy and fusion with PEEK cages for degenerative cervical disc disease without plate fixation.Results:This study included 66 patients, 35 males and 31 females. The follow-up period was 24 months. Mean Japanese Orthopedic Association scores were 13.3 ± 1.41 preoperative and 15.9 ± 0.86 postoperative (P = 0.046). The cervical curvature index “Ishihara” (ICI) was 9.9 ± 5.90 preoperative and the mean of ICI was 10.5 ± 6.65 postoperative, which is insignificant, P = 0.7). The lordotic curvature according to these results was preserved till the end of the year and half of the follow-up period postoperative.Conclusion:Consecutive four-level anterior discectomy with PEEK cage interbody fusion without plate and screw is a safe and effective procedure in the absence of instability, and it may be a reliable alternative for the treatment of multilevel cervical disc.

Dynamically Crystalizing Liquid-Crystal Elastomers for an Expandable Endplate-Conforming Interbody Fusion Cage.

Degenerative disc disease (DDD) is the leading cause of low back pain and radiating leg pain. DDD is commonly treated surgically using spinal fusion techniques, but in many cases failure occurs due to insufficient immobilization of the vertebrae during fusion. The fabrication and demonstration of a 3D-printed semi-crystalline liquid crystal elastomer (LCE) spinal fusion cage that addresses these challenges in particular subsidence are described. During implantation of the fusion cage, the LCE is rubbery and capable of deforming around and conforming to delicate anatomy. In the hours following implantation, the device crystallizes into a rigid, structural material with the modulus increasing tenfold from 8 to 80 MPa. In the crystalline regime, a 3D-printed prototype device is capable of enduring 1 million cycles of physiologic compressive loading with minimal creep-induced ratcheting. Effects of LCE molecular architecture on the rate and magnitude of modulus increase, material processability, and mechanical properties are explored. This fundamental characterization informs a proof-of-concept device-the first bulk 3D printed LCE demonstrated to date. Moreover, the novel deployment strategy represents an exciting new paradigm of spinal fusion cages, which addresses real clinical challenges in expandable interbody fusion cages.

Correlation analysis between the pulmonary function test and the radiological parameters of the main right thoracic curve in adolescent idiopathic scoliosis

BackgroundScoliosis causes thoracic deformities, and it is necessary to assess these changes in pulmonary function test (PFT). To determine how measurements of spinal and thoracic cage deformities are related to pulmonary function.MethodsSeventy-two patients with main right thoracic curvature in adolescent idiopathic scoliosis (AIS) underwent a PFT and a radiological parameter evaluation of spinal and thoracic cage deformities. Simple and multiple linear regressions were also used to note whether a combination of variables might better predict PFT values. Means were compared using the two-sample t test or one-way ANOVA with Tukey’s multiple comparison methods.ResultsForced vital capacity (FVC)% predicted had significantly negative correlations with main thoracic curve Cobb (MT-Cobb) (R2 = 0.648, p < 0.001), main thoracic curve-rib hump (MT-RH) (R2 = 0.522, p < 0.001), main thoracic curve apical vertebral body-to-rib ratio (MT-AVB-R) (R2 = 0.536, p < 0.001), and main thoracic curve apical vertebra translation (MT-AVT) (R2 = 0.383, p < 0.001). Multiple regression analysis was performed with FVC% predicted as the dependent variable and MT-Cobb, MT-RH, MT-AVB-R, and MT-AVT as the independent variables. MT-Cobb, MT-RH, MT-AVB-R, and MT-AVT were factors with a significant effect on FVC% predicted (p < 0.001). For 45 patients who had preoperative FVC impairment (FVC% predicted < 80%), their MT-Cobb averaged 76.71°. Twenty-seven patients with normal preoperative FVC (FVC% predicted ≥ 80%) had a smaller mean MT-Cobb of 52.03° (p < 0.001). In other radiological parameters, the impaired FVC group had a MT-AVT of 54.29 mm compared to 38.06 mm for the normal FVC group (p < 0.001). MT-AVB-R averaged 2.92 for the impaired FVC group and 1.78 for the normal FVC group (p < 0.001). MT-RH averaged 28.79 mm for the impaired group and 16.62 mm for the normal group (p < 0.001). Further stratification of preoperative PFT results is divided into three groups. The three groups also showed significant differences in MT-Cobb, MT-RH, MT-AVB-R, and MT-AVT (p < 0.001).ConclusionSevere scoliosis leads to an increased degree of thoracic deformity, which increases the risk of lung damage in AIS. Moreover, a more accurate assessment of pulmonary function is achieved through radiological parameters and PFTs.

Clinical outcomes for anterior cervical discectomy and fusion with silicon nitride spine cages: a multicenter study.

Intervertebral spacers made of silicon nitride (Si3N4) are currently used in cervical and thoracolumbar fusion. While basic science data demonstrate several advantages of Si3N4 over other biomaterials, large-scale clinical results on its safety and efficacy are lacking. This multicenter retrospective study examined outcomes for anterior cervical discectomy and fusion (ACDF) using Si3N4 cages. Results were compared to compiled metadata for other ACDF materials. Pre-operative patient demographics, comorbidities, changes in visual analog scale (VAS) pain scores, complications, adverse events, and secondary surgical interventions were collected from the medical records of 860 patients who underwent Si3N4 ACDF at four surgical centers. For comparison, MEDLINE/PubMed and Google Scholar searches were performed for ACDF using other cage or spacer materials. Nine studies with 13 cohorts and 736 patients met the inclusion criteria for this control group. Overall, the mean last-follow-up for all patients was 319±325 days (10.6±10.8 months), with the longest follow-up being 6.5 years. In comparison to the metadata, patients from the Si3N4 groups were older (57.9±12.2 vs. 56.8±11.1 y, P=0.06) and had higher BMI values (30.0±6.3 vs. 28.1±6.5, P<0.01), but gender and smoking were not different. The Si3N4 patients reported significant improvements in VAS pain scores at last follow-up (i.e., pre-op of 71.0±22.1 vs. follow-up of 36.4±31.5, P<0.01). Although both preoperative and last-follow-up pain scores were higher for Si3N4 patients than the control, the overall change in scores (ΔVAS) was similar. From pre-op to last-follow up, ΔVAS values were 35.4±34.3 for patients receiving the Si3N4 implants versus 34.4±27.3 for patients from the meta-analysis (P=0.56). The complication and reoperation rate for the Si3N4 and the metadata were also comparable (i.e., 7.39% and 0.31% versus 9.79% and 0%, P=0.17 and 0.25, respectively). ACDF outcomes using Si3N4 implants matched the clinical efficacy of other cage biomaterials.

Biomechanical Analysis of Spinal Fusion Cage for Lumbar Vertebrae

Lumbar spinal fusion or lumbar interbody fusion is a surgical procedure done by putting the cages implant between the lumbar vertebra supported by rods and screws to hold the vertebra. This procedure is commonly used to treat disc degeneration diseases and other medical conditions. However, failure of the subcutaneous vertebral endplate has been identified to increase the possibility of biomechanical instability. There are broad range of designs and material types of the spinal implant cages that can be used in spinal fusion. Posterior lumbar interbody fusion (PLIF) cage is used to preserve stability and stimulate fusion between vertebrae. There are four different types of biomaterials that can be used to produce the cage namely as metal, ceramic, polymer and composite. The objective of this project is to examine the interbody fusion effects of a several type of cage’s materials. A 3D finite element model of third (L3) and fourth lumbar (L4) vertebrae with interbody fusion made up of different types of cage’s materials namely as Polyether ether ketone (PEEK), poly lactic acid (PLA), Cobalt Chromium, Titanium Alloy and Stainless Steel were developed and analysed. A fusion model developed based on the respective surgical protocols. The resulting stress and displacement within the cage at the vertebra were measured under different types of compressive loadings and motions. The results indicated an important effects of the material properties on flexibility in extension, axial rotation and lateral bending. Titanium Alloy have been identified as a good material for the metal categories, while for the composite categories PLA (Polylactic acid) has also been simulated as the best alternative material with cheaper material and lower production costs.

Surface Modification Strategies to Improve the Osseointegration of Poly(etheretherketone) and Its Composites.

In the last 5 years, a wide variety of surface modification strategies are explored to improve the integration of poly(etheretherketone) (PEEK) implants with bone. Since PEEK does not support bone on-growth, its surface properties need to be tailored to promote osteogenesis at the bone-implant interface. Surface modifications applied to achieve this response range from simple surface morphology changes to the deposition of osteoconductive coatings. Of the many methods, titanium and/or hydroxyapatite coatings, extrusion to create surface pores, and an accelerated neutral atom beam treatment have been approved by the U.S. Food and Drug Administration to improve the integration of PEEK spinal cages. The success of these surface modifications brings hope for the clinical translation of other techniques in the future, but there are several limitations that may be preventing other treatments from reaching the clinic. This review describes numerous strategies that have been applied to PEEK-based implants for improving their osseointegration and enhancing their antibacterial properties. The review concludes with a discussion about future directions for the field and provides suggestions for advancing clinical translation of surface-modified PEEK implants to improve the lives of patients in need of these implants.

Endplate Changes with Polyetheretherketone Cages in Posterior Lumbar Interbody Fusion.

Study DesignA retrospective radiographic analysis.PurposeThe aim of the current study is to assess endplate changes after the use of polyetheretherketone (PEEK) cages in posterior lumbar interbody fusion (PLIF).Overview of Literature A few recent reports had revealed endplate abnormalities due to PEEK cages, which may lead to nonunions.MethodsA retrospective computed tomography (CT)-based analysis of the endplate cavities and fusion status following PLIFs with PEEK cages was conducted by two independent observers. The term “cavity” was used to describe the endplate changes. The vertebral endplate cavities were assessed according to the size, multiplicity, location, and presence or absence of sclerosis.ResultsThere were 86 fixed levels in 65 consecutive patients, with a mean age of 35.44±19.60 years. The mean follow-up was 16.5±10.1 months (range, 6–57 months). Definite fusion was seen in 56 levels (65.12%) by observer 1 versus 44 levels (51.16) by observer 2. The strength of agreement was moderate. Endplate cavities were observed in 42 levels (48.84%) by observer 1 versus 47 levels (54.65%) by observer 2, with fair agreement. The strengths of agreement for the locations, multiplicity, and size were moderate, fair, and poor, respectively. Neither age, sex, etiology, levels, nor follow-up period was significantly associated with the presence of cavities. With regard to fusions, the nonunions detected by observer 1 were significantly associated with the presence of cavities (p<0.0001). However, those detected by observer 2 were nearly significant (p=0.05).ConclusionsThere was a high rate of unfavorable radiographic findings in the form of endplate cavities in PLIF cases with PEEK cages. A more comprehensive classification for the assessment of fusions and endplate cavities should be formulated. We strongly recommend further CT-based studies with larger sample size and longer follow-up periods.

Novel PEEK Copolymer Synthesis and Biosafety - I: Cytotoxicity Evaluation for Clinical Application.

In this research, we synthesized novel polyetheretherketone (PEEK) copolymers and evaluated the biosafety and cytotoxicity of their composites for spinal cage applications in the orthopedic field. The PEEK copolymers and their composites were prepared through a solution polymerization method using diphenyl sulfone as a polymerization solvent. The composite of PEEK copolymer showed good mechanical properties similar to that of natural bone, and also showed good thermal characteristics for the processing of clinical use as spine cage. The results of an in vitro cytotoxicity test did not show any evidence of a toxic effect on the novel PEEK composite. On the basis of these cytotoxicity test results, the PEEK composite also proved its in vitro biosafety for application to an implantable spine cage.

Design and Biomechanical Verification of Additive Manufactured Composite Spinal Cage Composed of Porous Titanium Cover and PEEK Body

Incidents of lumbar degenerative diseases, such as spinal stenosis and degenerative spondylolisthesis, are increasing due to the aging population, and as a result, posterior lumbar interbody fusion (PLIF) is widely used. However, the interbody fusion cage used in the fusion surgery has been reported to cause subsidence in the fusion cage of the titanium material and bone nonunion in the case of the polyetheretherketone (PEEK) material cage. Therefore, we aim to reduce the possibility of subsidence of the spinal fusion cage through its elastic modulus difference with the cortical bone of the vertebral body. For the vertebral end plate, which is related to the fusion rate, we also aim to design a new composite vertebral cage, which integrates a cover of porous structure using the additive manufacturing method of titanium alloy to fabricate a prototype, and to biomechanically verify the prototype. The method was as follows. In order to find a similar pore size of human cancellous bone, the pore size was adjusted and the results were measured with SEM. The pore size of each surface was measured individually and the mean value was calculated. Next, an animal experiment was conducted to confirm the degree of fusion of each structural type, and prototypes of various structures were fabricated. The degree of fusion was confirmed by a push down test. A prototype of the fusion cage composed of titanium and PEEK material was fabricated, and the possibility of subsidence by existence of porous structure was confirmed by using the lumbar spine finite element model. Then, the prototype was compared with the composite fusion cage developed by ASTM F2077 and ASTM F2267 methods, and with the commercial PEEK and titanium cages. As a result, the correlation between bone fusion and the porous structure, as well as size of the spine fusion cage composing the composite for porous structure and elasticity, was confirmed. Type 3 structures showed the best performance in bone fusion and the pore size of 1.2 mm was most suitable. In addition, the likelihood of subsidence of a cage with a porous structure was considered to be lower than that of a cage with a solid structure. When the new composite cage combined with two composites was compared with commercial products to verify, the performance was better than that of the existing PEEK material. The subsidence result was superior to the titanium product and showed similar results to PEEK products. In conclusion, the performance value was superior to the existing PEEK material, and the subsidence result was superior to the titanium product and was similar to the PEEK product, and thus, performance-wise, it is concluded that the PEEK product can be completely replaced with the new product.

Does annealing improve the interlayer adhesion and structural integrity of FFF 3D printed PEEK lumbar spinal cages?

Polyaryletheretherketone (PEEK) has been commonly used for interbody fusion devices because of its biocompatibility, radiolucency, durability, and strength. Although the technology of PEEK Additive Manufacturing (AM) is rapidly developing, post-processing techniques of 3D printed PEEK remain poorly understood. AM of PEEK has been challenging because of its high melt temperature (over 340 °C) and requires specialized equipment which was not commercially available until recently. A lumbar fusion cage design, used in ASTM interlaboratory studies, was 3D printed with a medical grade PEEK filament via Fused Filament Fabrication (FFF) under two different print speeds. PEEK cages were then annealed above the PEEK's glass transition temperature, at 200 °C or 300 °C. AM cages were CT scanned to determine the porosity before and after annealing. Mechanical tests were conducted on cages according to ASTM F2077 (ASTM F2077, 2014). SEM images helped to evaluate the cages' surface morphology before and after heat treatment. It was observed that annealing did not produce markedly better mechanical properties at either temperature, however, it had an effect on the cages’ mechanical properties at lower printing speed under all loading conditions. Although the structure of the pores changed after annealing, annealing conditions examined here as a post-processing method were not able to decrease the undesired porosity formed during the 3D printing process or change the failure mechanism, which is due interlayer debonding.

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.

254. 3D spinal alignment, thoracic volume and pulmonary function in surgical correction of AIS: a five-year follow-up study

BACKGROUND CONTEXT Surgical correction of adolescent idiopathic scoliosis is advocated for severe curves to preserve or improve pulmonary function, prevent progressive deformity and pain, and improve self-appearance. Restoration of sagittal and 3D alignment, in particular thoracic kyphosis (TK), has become increasingly emphasized in efforts to improve pulmonary function, thoracic volumes, provide improved sagittal balance, and prevent adjacent segment degeneration and deformity. PURPOSE To study the effects of thoracic kyphosis restoration in AIS type 1 and 2 curves on postoperative thoracic volume and pulmonary function. STUDY DESIGN/SETTING Retrospective review of prospective multicenter database. PATIENT SAMPLE Thirty-nine AIS patients with Type 1 and 2 curves with 5Y postoperative stereo-radiographic data and pulmonary function tests (PFTs). OUTCOME MEASURES Five-year spinal and rib cage measures and PFTs. METHODS A multicenter prospective registry of patients undergoing surgical correction of Type 1- and 2- AIS curves was queried for patients with 5-year postoperative visits including stereoradiographic assessment and PFTs. 3-dimensional (3D) radiographic analysis was performed to assess spinal alignment and chest wall dimensions at preoperative, first erect and 5 year postoperative time points. Variables were analyzed between time points with a one-way ANOVA and post-hoc Tukey analysis, and between variables with linear regression analysis. RESULTS A total of 39 patients met the inclusion criteria (37F, age 14.4±2.2). 3D spine alignment analyses demonstrated significant reduction in pre-op to 1st erect upper thoracic (41.3° to 11.6°), mid-thoracic (48.6° to 9.55°) and lumbar Cobb angles (19.7° to 8.9°), an increase in TK:T2-12 (20.0° to 39.8°) and TK:T5-12 (9.8 to 28.2°), and reduction in proximal and mid-thoracic apical vertebral rotation (9.5° to 2.1°) from preoperative to 1st erect postoperative (p 0.05 for all). 3D rib cage analysis demonstrated there was a small reduction in maximal depth (144 mm to 138 mm), maximum width (235 mm to 232 mm), and increase in thoracic height (220 mm to 230 mm, p CONCLUSIONS While thoracic kyphosis increases, coronal Cobb and apical vertebral rotation decrease postoperatively, these do not directly influence chest wall volume. Chest wall volume continues to increase between from first erect to 5 years due to presumed growth, which corresponds with an improvement in FEV1 and FVC at 5 year follow-up. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs.

251. Additive manufactured Ti-6Al-4V/polyetheretherketone composite porous cage for interbody fusion: bone growth and biocompatibility evaluation in a porcine model

BACKGROUND CONTEXT Several materials have been used to manufacture the cages, the most common being polyetheretherketone (PEEK) and titanium (Ti) alloy (Ti–6Al–4V). Each material has its advantages and disadvantages. PURPOSE The purpose is to utilize the advantages of each material in combination with additive manufacturing technology to develop a new porous Ti alloy/PEEK composite interbody cage. STUDY DESIGN/SETTING In vitro mechanical tests and cell biocompatibility study; in vivo posterior instrumented interbody fusion porcine model. PATIENT SAMPLE In vitro cell culture analysis for Porous Ti alloy/PEEK composite cages. In vivo animal study used 20 female pigs through an anterior intervertebral lumbar fusion and posterior pedicle screws augmentation. Each level was randomly implanted with one of five testing cages. OUTCOME MEASURES In vitro mechanical tests for shear strength of the interface layer. In vitro cell culture analysis for alkaline phosphatase (ALP) activity, ALP and osteocalcin mRNA expression for in vitro study. Micro–computed tomography (CT), back-scattered-electrons SEM (BSE-SEM) and histological analyses for in vivo study. METHODS In vitro and in vivo study compared 5 groups of cages. The first was a commercialized pure PEEK cage (group 1). The second was a Ti alloy/PEEK composite cage with nonporous Ti alloy end plates (group 2). The third, fourth, and fifth groups were composite cages with porosity of 40%, 60%, and 80% (groups 3, 4, and 5), respectively. Mechanical tests, alkaline phosphatase activity and mRNA expression, osteocalcin mRNA expression, SEM were performed for in vitro study. Micro–computed tomography (CT), back-scattered-electrons SEM (BSE-SEM) and histological analyses were performed for in vivo study. RESULTS The shear strength reached 33.4 MPa at the Ti alloy/PEEK interface. ALP activity and ALP mRNA expression were positively correlated with the porosity rate and peaked at 60% porosity. Micro-CT and BSE-SEM demonstrated that structures with high porosities, especially 60% and 80%, facilitated more bone formation inside the implant but not outside the implants. Histological analysis also showed that bone formation was better in Ti alloy groups than in the PEEK group. CONCLUSIONS In vitro cell culture showed higher porous structure exhibited superior bone growth. Micro-CT and histological analyses showed improved bone growth in high-porosity composite cage groups. Composite cage implant takes the biological advantages of Ti alloy porous end plates and the mechanical and radiographic advantages of PEEK central core to incorporate as a single implant suitable for intervertebral fusion. FDA DEVICE/DRUG STATUS Unavailable from authors at time of publication.

Reoperation rate after anterior cervical discectomy and fusion using standalone cages in degenerative disease: a study of 2,078 cases

BACKGROUND CONTEXTOver the last two decades, there has been a rapid increase in the use of cervical spine interbody fusion cages. Reoperation rate remains an important determinant of procedural efficacy and safety. PURPOSETo evaluate the rate and reasons for reoperations in cervical spondylosis patients undergoing anterior decompression and fusion using stand-alone cervical interbody fusion cages. STUDY DESIGNA retrospective study of 2,078 consecutive cases of degenerative cervical spine disease undergoing fusion using stand-alone cages. PATIENT SAMPLEBetween January 2005 and December 2014, 2,078 patients underwent anterior cervical decompression and fusion using stand-alone cages in our institution. OUTCOME MEASURESThe reoperations were analyzed and classified into early (during the first 90 days postoperatively) and late (after 90 days) reoperations. The rate and the causes of reoperation in both groups were reported and the results were compared. METHODSIn 1,558 patients, a short segment fusion (≤2 levels) was performed, while the remaining 520 patients underwent a long segment fusion (≥3 levels). RESULTSThe overall incidence of reoperation was 5.63%. The rate of early reoperations was 2.07%, mostly due to postoperative hematoma, and the rate of late reoperations was 3.56%, mostly due to adjacent segment disease. Revision due to pseudarthrosis was performed in 0.58% of cases. The early reoperation rate was significantly higher in the group with a long segment fusion, while the late reoperation rate was significantly higher in patients undergoing a short segment fusion. CONCLUSIONFollowing anterior cervical decompression and fusion with a stand-alone cage, the overall incidence of symptomatic pseudarthrosis is low. Patients undergoing long segment fusion should be closely observed in the early postoperative period as they have a higher early complication rate. On the other hand, long segment fusions have a lower incidence of adjacent segment disease over the years.

Size effects on geometrical accuracy for additive manufacturing of Ti-6Al-4V ELI parts

A comprehensive investigation of the size and geometry dependency of the dimensional accuracy of direct metal laser sintering (DMLS) for Ti-6Al-4V ELI is presented. For features such as walls, squares, tubes, and rods with different sizes, the percent error significantly increases with decreasing the feature size. The polynomial function a t-b is suggested to describe this size dependency of the dimensional error where a and b are parameters depending on the geometry, material, and DMLS process parameters. This function is used to successfully predict the dimensional error in DMLS of two spinal cages. Therefore, these functions can be used to account for these errors in DMLS by design change or by adjusting DMLS scaling factors. Furthermore, the inconsistency of the DMLS-manufactured dimensions within the feature is shown to be in the same range of the dimensional inconsistency for features located at different positions on the build platform, implying that the location of the feature on the build platform has a negligible effect on the dimensional accuracy. Finally, it is shown that the error in the position accuracy of DMLS-manufactured features is negligible when the size dependency of the dimensional features is considered in the measurements.

Does implantation site influence bone ingrowth into 3D-printed porous implants?

BACKGROUND CONTEXTThe potential for osseointegration to provide biological fixation for implants may be related to anatomical site and loading conditions. PURPOSETo evaluate the influence of anatomical site on osseointegration of 3D-printed implants. STUDY DESIGNA comparative preclinical study was performed evaluating bone ingrowth in cortical and cancellous sites in long bones as well as lumbar interbody fusion with posterior pedicle screw stabilization using the same 3D-printed titanium alloy design. METHODS3D-printed dowels were implanted in cortical bone and cancellous bone in adult sheep and evaluated at 4 and 12 weeks for bone ingrowth using radiography, mechanical testing, and histology/histomorphometry. In addition, a single-level lumbar interbody fusion using cages based on the same 3D-printed design was performed. The aperture was filled with autograft or ovine allograft processed with supercritical carbon dioxide. Interbody fusions were assessed at 12 weeks via radiography, mechanical testing, and histology/histomorphometry. RESULTSBone ingrowth in long bone cortical and cancellous sites did not translate directly to interbody fusion cages. While bone ingrowth was robust and improved with time in cortical sites with a line-to-line implantation condition, the same response was not found in cancellous sites even when the implants were placed in a press fit manner. Osseointegration into the porous walls with 3D porous interbody cages was similar to the cancellous implantation sites rather than the cortical sites. The porous domains of the 3D-printed device, in general, were filled with fibrovascular tissue while some bone integration into the porous cages was found at 12 weeks when fusion within the aperture was present. CONCLUSIONAnatomical site, surgical preparation, biomechanical loading, and graft material play an important role in in vivo response. Bone ingrowth in long bone cortical and cancellous sites does not translate directly to interbody fusions.

Safety and performance of a novel articulating cage for transforaminal lumbar interbody fusion in the setting of intraoperative spinal navigation

ObjectiveTransforaminal lumbar interbody fusion (TLIF) has been described as safe and effective procedure for the treatment of low back pain. However, only a few retrospective articles describing articulating cages exist in literature. The aim of this study was to assess the clinical and radiological results, as well as patient safety and complications by using a novel articulating TLIF cage. Patients and MethodsOut of 50 patients, 49 were included in this prospective study. Under computer tomography (CT) guided spinal navigation the TLIF procedure was performed. Clinical outcome scores visual analog scale (VAS), Oswestry disability index (ODI) and short form-36 health survey questionnaire (SF-36) were obtained preoperatively, 6 and 12 months after surgery. Radiological data were acquired preoperatively, after 6 weeks, as well as 6 and 12 postoperatively and included measurements for disc height (anterior/posterior), foraminal height, segmental and global lumbar lordosis. Results71% of the included patients have undergone previous lumbar surgery. In total, 80 SYNCHRO® cages have been implanted. The clinical results revealed a highly significant improvement of VAS, ODI and SF-36 after 6 and 12 months, compared to baseline levels (p < 0.05). Radiological analysis revealed a significant increase in anterior and posterior disc height, foraminal height, segmental and global lumbar lordosis postoperatively (p < 0.05). 47 out 49 patients (96%) showed evidence for fusion at the 12 months follow-up. Cage dislocation was found in 1 of 80 implanted cages (1%), which required revision surgery. Two dural tears occurred intraoperatively, which have been fixed. Another two patients needed surgical revision due to infection. The overall complication rate was 10% (n = 5/49). ConclusionsThe current study delineates satisfactory clinical and radiological results by using a novel articulating TLIF-cage. The implant-related complication rate was acceptable with low revision rate.

Biomechanical study of proximal adjacent segment degeneration after posterior lumbar interbody fusion and fixation: a finite element analysis

PurposeTo investigate the biomechanical changes in the proximal adjacent segment with different grades of degeneration after posterior lumbar interbody fusion (PLIF).MethodsWe created three finite element models of the L3–5 with different grades of degeneration (healthy, mild, and moderate) at the L3–4 that were developed by changing the disc height and material properties of the nucleus pulposus. The L4–5 were operated by interbody fusion cages and pedicle screws. All models were loaded with a compressive pre-load of 400 N and a bending moment of 10 N a in three planes to recreate flexion, extension, lateral bending, and axial rotation. The range of motion (ROM), nucleus pressure, and annulus fibrosus pressure of the L3–4 were evaluated.ResultsThe ROM, nucleus pressure, and annulus fibrosus pressure increased at the L3–4 after PLIF. As the degeneration progressed in the L3–4, the ROM of the L3–4 decreased while the nucleus pressure and annulus fibrosus pressure increased.ConclusionsAdjacent segment degeneration (ASD) may be related to the ROM and intradiscal pressure after PLIF. However, as the degeneration of the proximal adjacent segment increases, the ROM in the proximal adjacent segment gradually decreases, but the pressure on the nucleus pulposus and annulus fibrosus gradually increases. Degeneration of the proximal adjacent segment before operation is a risk factor for the ASD after PLIF.

3D printed porous Ti6Al4V cage: Effects of additive angle on surface properties and biocompatibility; bone ingrowth in Beagle tibia model

Similar mechanical properties to native bone, excellent biocompatibility and osseointegration are key factors for interbody fusion cage. In the present study, porous Ti6Al4V cage with computer designed macro- and micro-architecture was reproduced by selective laser melting (SLM). Dense Ti6Al4V discs with six different angles were fabricated to investigate the effects of additive angle (inevitable in SLM manufacturing) on surface properties and biocompatibility. As angle increased, both surface roughness and hydrophobicity increased due to increases in the number of unmelted metallic particles. In the early stage of cell culture, more elongated MC3T3E1 cells were observed at higher additive angle, but cell adhesion and proliferation with different angle did not show statistically differences. Bullet-shaped Ti6Al4V cage with opened window, porosity of 70% and pore size of 600 μm revealed elastic modulus of 0.51 ± 0.04 GPa and ultimate compressive strength of 94.7 MPa at 0.29% strain, which is comparable with the commercialized polyetheretherketone cage. In vivo evaluation of Beagle tibia model through histological analysis showed that the cylindrical porous body with same porosity and pore size achieved similar bone ingrowth as commercialized porous tantalum implant at 4 and 12 weeks, indicating SLM fabricated porous Ti6Al4V cage holds great potential for spinal fusion.

Does nanoscale porous titanium coating increase lumbar spinal stiffness of an interbody fusion cage? An in vivo biomechanical analysis in an ovine model

BackgroundQuantitative objective measures to determine fusion achievement further enable the comparison of new technologies, such as interbody cage surface enhancement. Our aims were to compare in vivo biomechanical responses of ovine L4/5 lumbar motion segments with two cages: 1) Polyetheretherketone or 2) Polyetheretherketone with a nanosurfaced titanium porous scaffold from Nanovis, Inc. MethodsFourteen Merino sheep randomly received either 1) standard Polyetheretherketone cage or 2) Nanocoated Polyetheretherketone cage at L4/L5 with autologous bone graft. At baseline and one-year follow-up, dynamic spinal stiffness was quantified in vivo using a validated mechanical assessment at 2 Hz, 6 Hz, and 12 Hz. The dorsoventral secant stiffness (ky = force/displacement, N/mm) and L4-L5 accelerations were determined at each frequency. A repeated measures analysis of variance with Bonferonni correction was used to evaluate within and between group differences among the biomechanical variables. FindingsBoth implants increased spinal stiffness at 2 Hz (21 and 39%, respectively, p < .005), and at 6 Hz (12 and 27%, p < .0001). Significantly greater spinal stiffness was observed with Nanocoated Polyetheretherketone at one-year for both frequencies (p < .05). No significant differences were observed at 12 Hz within or between groups. L4-L5 dorsoventral accelerations were significantly decreased one year following cage placement only with Nanocoated Polyetheretherketone (p < .05) and greater reductions in acceleration were observed with Nanocoated Polyetheretherketone compared to standard Polyetheretherketone (p < .05). InterpretationBoth cages increased spinal stiffness, yet, nanosurfaced cages resulted in greater spinal stiffness changes and decreases in L4-L5 accelerations. These findings may assist in clinical decision making and post-operative recovery strategies.