Endplate Surface Research Articles

Endplate Remodeling: a key indicator of cigarette smoke exposure-induced intervertebral disc degeneration in a male rat model

Abstract Recent clinical studies have established a strong association between cigarette smoking and degenerative disc disease. Both in vitro and in vivo research indicated that cigarette smoke disrupts cellular homeostasis in the intervertebral disc (IVD), leading to spatiotemporal remodeling of the extracellular matrix, with a notable reduction in solute diffusivity within the cartilage endplate (CEP). As the CEP serves as a critical mechanical barrier and solute diffusion pathway for the IVD, both roles can be compromised by pathological changes in the tissue. This underscores the need for a more comprehensive examination of endplate remodeling during IVD degeneration, particularly in the context of cigarette smoking and cessation. The objective of this study was to perform a quantitative analysis of the structure-material property relationship changes in the endplate at tissue and cellular levels to determine how endplate mineralization progresses during IVD degeneration in the context of cigarette smoke exposure and cessation, using our previously developed Sprague–Dawley rat model. Our results indicates that cigarette smoke exposure induced endplate remodeling is characterized by a higher CEP histological grade, increased aberrant CEP calcification level, and elevated bony endplate surface flatness score, all of which correlated with an accelerated chondrocyte cell life cycle. Smoke cessation alone was insufficient to reverse the mineralization progression in the endplate. Principal component analysis further identified alterations in endplate morphometry at the tissue level and disruptions in the chondrocyte life cycle at cellular level as key markers of degenerative remodeling. These findings establish endplate remodeling as a key indicator of smoke exposure induced IVD degeneration and inform the development of novel therapeutic strategies aimed at preserving or improving disc health.

Optimization of 3D-printed titanium interbody cage design. Part 2: An in vivo study of spinal fusion in sheep.

3D-printed titanium cage designs can incorporate complex, porous features for bone ingrowth and a greater surface area for minimizing subsidence. In a companion study (Part 1), we determined that increased surface area leads to decreased subsidence; however, it remains unclear how increasing the cage surface area, resulting in a smaller graft aperture, influences fusion. We evaluated the effects of surface area of 3D-printed titanium cages and the use of autologous bone grafts on spinal fusion in sheep. In vivo large animal study in 12 sheep. Interbody fusion was performed in 12 adult sheep at 24 levels (L2-3 and L4-5) using 3D-printed titanium cages with bilateral pedicle screw fixation. The cage designs varied in aperture: standard (low endplate surface area), small (medium endplate surface area), or none (high endplate surface area). These cages were packed with autologous iliac crest bone grafts (ICBG). A fourth group was implanted without bone grafts, using the no-aperture cage. Fusion was evaluated at 16 weeks via manual palpation, microcomputed tomography (microCT), histology, and histomorphometry. Standard, small, and no-aperture cages packed with ICBG resulted in high fusion rates (80%, 100%, and 83%, respectively) at 16 weeks by manual palpation, and these results were not significantly different. Implantation without ICBG was associated with a significantly lower fusion rate (33%, p<.05). Histological, histomorphometry, and microCT results supported the findings obtained by manual palpation; findings from these modalities showed new bone spanning the vertebral endplates in the spines graded as fused by manual palpation. Similar fusion results for standard, small, and no-aperture cage designs packed with ICBG suggest that aperture size does not influence fusion results in the sheep model. However, without ICBG grafting, fusion was significantly decreased, suggesting that graft material is necessary to predictably obtain fusion in this model. When the in vitro subsidence data (companion study, Part 1) is considered with the in vivo fusion data described here, porous 3D-printed titanium cages with maximal surface endplate contact and bone grafting perform favorably, resulting in low subsidence and high fusion rates. 3D-printed porous titanium interbody cages are novel devices with increasing clinical use. The study results show that the aperture size of the interbody cage did not influence fusion in a large animal (sheep) model. The use of bone graft material was the most important variable affecting fusion. These data suggest that the clinical use of 3D Ti cages without graft material should be avoided.

Calcium phosphate complex of recombinant human thrombomodulin promote bone formation in interbody fusion.

Interbody fusion is an orthopedic surgical procedure to connect two adjacent vertebrae in patients suffering from spinal disc disease. The combination of synthetic bone grafts with protein-based drugs is an intriguing approach to stimulate interbody bone growth, specifically in patients exhibiting restricted bone progression. Recombinant human thrombomodulin (rhTM), a novel protein drug characterized by its superior stability and potency, shows promise in enhancing bone formation. A composite bone graft, termed CaP-rhTM, has been synthesized, combining calcium phosphate (CaP) microparticles as a delivery vehicle for rhTM to facilitate interbody fusion.In vitrostudies have demonstrated that rhTM significantly promotes the proliferation and maturation of preosteoblasts at nanogram dosage, while exerting minimal impact on osteosarcoma cell growth. The expression levels of mature osteoblast markers, including osteocalcin, osteopontin, alkaline phosphatase, and calcium deposition were also enhanced by rhTM. In rat caudal disc model of interbody fusion, CaP-rhTM with 800 ng of drug dosage was implanted along with a polylactic acid cage, to ensure structural stability within the intervertebral space. Microcomputed tomography analyses revealed that from 8 to 24 weeks, CaP-rhTM substantially improves both bone volume and trabecular architecture, in addition to the textural integrity of bony endplate surfaces. Histological examination confirmed the formation of a continuous bone bridge connecting adjacent vertebrae. Furthermore, biomechanical assessment via three-point bending tests indicated an improved bone quality of the fused disc. This study has demostrated that rhTM exhibits considerable potential in promoting osteogenesis. The use of CaP-rhTM has also shown significant improvements in promoting interbody fusion.

The influence of lumbar vertebra and cage related factors on cage-endplate contact after lumbar interbody fusion: An in-vitro experimental study

Lumbar interbody fusion (LIF) using interbody cages is an established treatment for lumbar degenerative disc disease, but fusion results are known to be affected by risk factors such as bone mineral density (BMD), endplate geometry and cage position. At present, direct measurement of endplate-cage contact variables that affect LIF have not been fully identified. The aim of this study was to use cadaveric experiments to investigate the dependency between BMD, endplate geometry, cage parameters like type, orientation, position, and contact variables like stress and area. One vertebral body specimen from each of the five lumbar positions was harvested from five male donors. The lower half of each vertebra was potted and placed in a material testing machine (Instron 8874). A spinal cage was clamped to the machine then lowered to bring it into contact against the superior endplate. A lockable ball-joint was used to rotate the cage such that its inferior surface was congruent with the local endplate surface. A pressure sensor (Tekscan) was placed between the cage and endplate to record contact area and the peak and average contact pressures. Axial compression of 400 N was performed for five positions using a straight cage, and in one anterior position using a curved cage. The linear mixed model was utilised to perform data analyses for experimental results with statistical significance set at p < 0.05. The results indicated two trends toward significance for contact area, one for volumetric BMD (vBMD) of the vertebra (p = 0.081), and another for predicted contact area (p = 0.057). Peak contact pressure correlated significantly with vBMD (p = 0.041), and there was a trend between average contact pressure and lateral position of cage (p = 0.051). In addition, predicted contact area correlated significantly with cage orientation (p < 0.001). These results indicated that high vBMD of vertebra and a medially positioned cage led to higher contact pressures. Logically, low vBMD of vertebra and transverse cage orientation increased the contact area between the cage and endplate. In conclusion, the study identified significant influence of vBMD of vertebra, cage position and orientation on cage-endplate contact which may help to inform cage selection and design for LIF.

Tomographic Assessment of Fusion Rate, Implant-Endplate Contact Area, Subsidence, and Alignment With Lumbar Personalized Interbody Implants at 1-Year Follow-Up.

Incongruity between irregularly shaped vertebral endplates and the uniform surfaces of stock interbody fusion cages has been identified as contributing to cage subsidence, pseudarthrosis, and unpredictable alignment. Advances in manufacturing techniques have driven the development of personalized interbody cages (PICs) that can match individual endplate morphology and provide the exact shape and size needed to fill the disc space and achieve the planned correction. This study used computed tomography (CT) imaging to evaluate the implant-endplate contact area, fusion, subsidence, and achievement of planned alignment correction in patients receiving PIC devices. This retrospective study included patients treated for adult spinal deformity at a single site and implanted with PIC devices at L4 to L5 or L5 to S1 for segmental stabilization and alignment correction, who received 1-year postoperative CT images as part of their standard of care. An evaluation using 3-dimensional thin-section scans was conducted. Implant-endplate contact and signs of fusion were assessed in each CT slice across both endplates. The degree of subsidence as well as measures of segmental and global lumbar alignment were also assessed. Fifteen patients were included in the study, with a mean age of 68.2 years. Follow-up ranged between 9 and 14 months. Twenty-six total lumbar levels were implanted; 20 with PIC devices via the anterior lumbar interbody fusion approach, 2 with stock cages via the anterior lumbar interbody fusion approach, and 4 with PIC devices via the transforaminal lumbar interbody fusion approach. CT analysis of PIC-implanted levels found an overall implant-endplate contact area ratio of 93.9%, a subsidence rate of 4.5%, a fusion rate of 100%, and satisfactory segmental and global lumbar correction compared with the preoperative plan. PIC implants can provide nearly complete contact with endplate surfaces regardless of the individual endplate morphology. Subsidence, fusion, and alignment assessments in this tomographic study illustrated results consistent with the benefits of a personalized interbody implant.

Impaired communication at the neuromotor axis during Degenerative Cervical Myelopathy.

Degenerative Cervical Myelopathy (DCM) is a progressive neurological condition characterized by structural alterations in the cervical spine, resulting in compression of the spinal cord. While clinical manifestations of DCM are well-documented, numerous unanswered questions persist at the molecular and cellular levels. In this study, we sought to investigate the neuromotor axis during DCM. We use a clinically relevant mouse model, where after 3 months of DCM induction, the sensorimotor tests revealed a significant reduction in both locomotor activity and muscle strength compared to the control group. Immunohistochemical analyses showed alterations in the gross anatomy of the cervical spinal cord segment after DCM. These changes were concomitant with the loss of motoneurons and a decrease in the number of excitatory synaptic inputs within the spinal cord. Additionally, the DCM group exhibited a reduction in the endplate surface, which correlated with diminished presynaptic axon endings in the supraspinous muscles. Furthermore, the biceps brachii (BB) muscle exhibited signs of atrophy and impaired regenerative capacity, which inversely correlated with the transversal area of remnants of muscle fibers. Additionally, metabolic assessments in BB muscle indicated an increased proportion of oxidative skeletal muscle fibers. In line with the link between neuromotor disorders and gut alterations, DCM mice displayed smaller mucin granules in the mucosa layer without damage to the epithelial barrier in the colon. Notably, a shift in the abundance of microbiota phylum profiles reveals an elevated Firmicutes-to-Bacteroidetes ratio-a consistent hallmark of dysbiosis that correlates with alterations in gut microbiota-derived metabolites. Additionally, treatment with short-chain fatty acids stimulated the differentiation of the motoneuron-like NSC34 cell line. These findings shed light on the multifaceted nature of DCM, resembling a synaptopathy that disrupts cellular communication within the neuromotor axis while concurrently exerting influence on other systems. Notably, the colon emerges as a focal point, experiencing substantial perturbations in both mucosal barrier integrity and the delicate balance of intestinal microbiota.

Effect of a Pericardium Graft Inserted Adjacent to the Endplate in the Ahmed Glaucoma Valve Implantation.

The surface area of encapsulation around the Ahmed glaucoma valve (AGV) endplate is a critical factor in the surgical outcome as it is associated with the degree of IOP reduction. We investigated the surgical outcome of AGV implantation with an additional pericardium graft inserted adjacent to the endplate, with the intent of expanding the surface area of encapsulation. We enrolled 92 patients (92 eyes) who underwent AGV implantation. Of them, 50 patients underwent conventional surgery (termed the without-expansion group), and 42 received an additional an 8 × 6 mm pericardium graft inserted adjacent to the AGV endplate at the sub-Tenon's space (with-expansion). The hypertensive phase was classified as mild (>21 mmHg), moderate (>25 mmHg), and severe (>30 mmHg). Six months post-surgery, the with-expansion group exhibited a lower IOP (14.90 ± 4.27 mmHg) and lower peak IOP (22.29 ± 4.95 mmHg) than the without-expansion group (17.56 ± 4.88 mmHg and 25.06 ± 6.18 mmHg, p = 0.008 and p = 0.021, respectively). The with-expansion group exhibited a relatively low rate of moderate (16.7%) and severe (4.8%) hypertensive phases compared to the without-expansion group (40.0% and 20.0%, with p = 0.014 and p = 0.031, respectively). The additional pericardium graft was associated with a reduced occurrence of moderate hypertensive phase in both univariate and multivariate analysis logistic regression analyses (p = 0.017 and p = 0.038, respectively). Endplate surface area expansion using an additional pericardium graft reduced the occurrence of moderate and severe hypertensive phases, and lower postoperative 6-month IOP could be achieved.

Initiation and accumulation of loading induced changes to native collagen content and microstructural damage in the cartilaginous endplate

BACKGROUND CONTEXTInjury to the cartilaginous endplate (CEP) is linked to clinically relevant low back disorders, including intervertebral disc degeneration and pain reporting. Despite this link to clinical disorders, the CEP injury pathways and the modulating effect of mechanical loading parameters on the pace of damage accumulation remains poorly understood. PURPOSEThis study examined the effect of cyclic loading on the initiation and accumulation of changes to native collagen content (type I, type II) and microstructural damage in the central region of cadaveric porcine CEPs. STUDY DESIGNIn vitro longitudinal study. METHODSOne hundred fourteen porcine cervical spinal units were included (N=6 per group). The study contained a control group (no cyclic loading) and 18 experimental groups that differed by loading duration (1,000, 3,000, 5,000 cycles), joint posture (flexed, neutral), and cyclic peak compression variation (10%, 20%, 40%). Multicolor immunofluorescence staining was used to quantify loading induced changes to type I (ie, subchondral bone) and type II (ie, endplate) native collagen content (fluorescence area, fluorescence intensity) and microstructural damage (pore area [transverse plane], void area along the CEP-bone border [sagittal plane]). RESULTSSignificant main effects of loading duration and posture were observed for fluorescence area and fluorescence intensity of type I and II collagen. In the transverse plane, type II fluorescence area significantly decreased following 1,000 cycles (-12%), but a significant change in fluorescence intensity was not observed until 3,000 cycles (-17%). Type II fluorescence area (-14%) and intensity (-10%) were both significantly less in flexed postures compared to neutral. Similar trends were observed for type I collagen in the sagittal plane sections. Generally, significant changes to fluorescence area were accompanied by the development of microstructural voids along the endplate-subchondral bone border. CONCLUSIONSThese findings demonstrate that microstructural damage beneath the endplate surface occurs before significant changes to the density of native type I and II collagen fibers. Although flexed postures were associated with greater and accelerated changes to native collagen content, the injury initiation mechanism appears similar to neutral. CLINICAL SIGNIFICANCENeutral joint postures can delay the initiation and pace of microdamage accumulation in the CEP during low-to-moderate demand lifting tasks. Furthermore, the management of peak compression exposures appeared relevant only when a neutral posture was maintained. Therefore, clinical low back injury prevention and load management efforts should consider low back posture in parallel with applied joint forces.

Novel 3D printed lattice structure titanium cages evaluated in an ovine model of interbody fusion.

The use of intervertebral cages within the interbody fusion setting is ubiquitous. Synthetic cages are predominantly manufactured using materials such as Ti and PEEK. With the advent of additive manufacturing techniques, it is now possible to spatially vary complex 3D geometric features within interbody devices, enabling the devices to match the stiffness of native tissue and better promote bony integration. To date, the impact of surface porosity of additively manufactured Ti interbody cages on fusion outcomes has not been investigated. Thus, the objective of this work was to determine the effect of implant endplate surface and implant body architecture of additive manufactured lattice structure titanium interbody cages on bony fusion. Biomechanical, microcomputed tomography, static and dynamic histomorphometry, and histopathology analyses were performed on twelve functional spine units obtained from six sheep randomly allocated to body lattice or surface lattice groups. Nondestructive kinematic testing, microcomputed tomography analysis, and histomorphometry analyses of the functional spine units revealed positive fusion outcomes in both groups. These data revealed similar results in both groups, with the exception of bone-in-contact analysis, which revealed significantly improved bone-in-contact values in the body lattice group compared to the surface lattice group. Both additively manufactured porous titanium cage designs resulted in increased fusion outcomes as compared to PEEK interbody cage designs as illustrated by the nondestructive kinematic motion testing, static and dynamic histomorphometry, microcomputed tomography, and histopathology analyses. While both cages provided for similar functional outcomes, these data suggest boney contact with an interbody cage may be impacted by the nature of implant porosity adjacent to the vertebral endplates.

Observations of bony ongrowth and clinical fixation in two retrieved disc replacements.

Total disc replacements utilize textured coatings to maximize bony ongrowth. However, the contribution of direct bony attachment to overall fixation for total disc replacements has not been reported. The goal of the present study was to document the extent of bony attachment to the surfaces of two clinically functional total disc replacements that were securely fixed at the time of revision. Two metal-and-polymeric disc replacements, one cervical and one lumbar, were evaluated following surgical retrieval. The cervical device was retrieved at 8 months and the lumbar device at 28 months post-operative. Both devices were reported well-fixed at the time of removal, with large bone masses attached to one endplate of each device. Visual inspections, non-destructive gravimetric measurements, and surface metrology were performed to assess fixation. These inspections suggested that both devices had been fixed at the time of removal with little in vivo mechanical damage, as surgical extraction damage was noted on both devices and provided imaging showed a lack of device migration. Devices were then embedded and sectioned to evaluate the bone-implant interface. High resolution photographs and contact microradiographs were taken to assess bony attachment. In contrast to initial analysis, these images revealed radiolucent gaps between the endplates and bone masses. Little direct contact between the bone and endplate surface was identified and the original surgical cuts were still visible. Both devices were clinically fixed at the time of removal and neither had complications associated with loosening. However, osseointegration was minimal in one of the devices and altogether absent from the other. The findings of the present study suggest that other factors may influence overall clinical fixation such as the surgical preparation of the vertebral bone or the surface roughness of the treated endplates. Despite the limitations of the present study, this information is unique to the current total disc replacement literature and the ongrowth and fixation of devices should be considered as a topic for future investigation.

Biomechanical evaluation of an osteoporotic anatomical 3D printed posterior lumbar interbody fusion cage with internal lattice design based on weighted topology optimization.

In this study, we designed and manufactured a posterior lumbar interbody fusion cage for osteoporosis patients using 3D-printing. The cage structure conforms to the anatomical endplate's curved surface for stress transmission and internal lattice design for bone growth. Finite element (FE) analysis and weight topology optimization under different lumbar spine activity ratios were integrated to design the curved surface (CS-type) cage using the endplate surface morphology statistical results from the osteoporosis patients. The CS-type and plate (P-type) cage biomechanical behaviors under different daily activities were compared by performing non-linear FE analysis. A gyroid lattice with 0.25 spiral wall thickness was then designed in the internal cavity of the CS-type cage. The CS-cage was manufactured using metal 3D printing to conduct in vitro biomechanical tests. The FE analysis result showed that the maximum stress values at the inferior L3 and superior L4 endplates under all daily activities for the P-type cage implantation model were all higher than those for the CS-type cage. Fracture might occur in the P-type cage because the maximum stresses found in the endplates exceeded its ultimate strength (about 10 MPa) under flexion, torsion and bending loads. The yield load and stiffness of our designed CS-type cage fall into the optional acceptance criteria for the ISO 23089 standard under all load conditions. This study approved a posterior lumbar interbody fusion cage designed to have osteoporosis anatomical curved surface with internal lattice that can achieve appropriate structural strength, better stress transmission between the endplate and cage, and biomechanically tested strength that meets the standard requirements for marketed cages.

The Efficacy of Trabecular Titanium Cages to Induce Reparative Bone Activity after Lumbar Arthrodesis Studied through the 18f-Naf PET/CT Scan: Observational Clinical In-Vivo Study.

Background: Titanium trabecular cages (TTCs) are emerging implants designed to achieve immediate and long-term spinal fixation with early osseointegration. However, a clear radiological and clinical demonstration of their efficacy has not yet been obtained. The purpose of this study was to evaluate the reactive bone activity of adjacent plates after insertion of custom-made titanium trabecular cages for the lumbar interbody with positron emission tomography (PET)/computed tomography (CT) 18F sodium fluoride (18F-NaF). Methods: This was an observational clinical study that included patients who underwent surgery for degenerative disease with lumbar interbody fusion performed with custom-made TTCs. Data related to the metabolic-reparative reaction following the surgery and its relationship with clinical follow-up from PET/CT performed at different weeks were evaluated. PET/CTs provided reliable data, such as areas showing abnormally high increases in uptake using a volumetric region of interest (VOI) comprising the upper (UP) and lower (DOWN) limits of the cage. Results: A total of 15 patients was selected for PET examination. Timing of PET/CTs ranged from one week to a maximum of 100 weeks after surgery. The analysis showed a negative correlation between the variables SUVmaxDOWN/time (r = −0.48, p = 0.04), ratio-DOWN/time (r = −0.53, p = 0.02), and ratio-MEAN/time (r = −0.5, p = 0.03). Shapiro−Wilk normality tests showed significant results for the variables ratio-DOWN (p = 0.002), ratio-UP (0.013), and ratio-MEAN (0.002). Conclusions: 18F-NaF PET/CT has proven to be a reliable tool for investigating the metabolic-reparative reaction following implantation of TTCs, demonstrating radiologically how this type of cage can induce reparative osteoblastic activity at the level of the vertebral endplate surface. This study further confirms how electron-beam melting (EBM)-molded titanium trabecular cages represent a promising material for reducing hardware complication rates and promoting fusion.

Evaluation of the contact surface between vertebral endplate and 3D printed patient-specific cage vs commercial cage

Biomechanical study. To evaluate the performance of the contact surface for 3D printed patient-specific cages using CT-scan 3D endplate reconstructions in comparison to the contact surface of commercial cages. Previous strategies to improve the surface of contact between the device and the endplate have been employed to attenuate the risk of cage subsidence. Patient-specific cages have been used to help, but only finite-element studies have evaluated the effectiveness of this approach. There is a possible mismatch between the CT-scan endplate image used to generate the cage and the real bony endplate anatomy that could limit the performance of the cages. A cadaveric model is used to investigate the possible mismatch between 3D printed patient-specific cages and the endplate and compare them to commercially available cages (Medtronic Fuse and Capstone). Contact area and contact stress were used as outcomes. When PS cage was compared to the Capstone cage, the mean contact area obtained was 100 ± 23.6 mm2 and 57.5 ± 13.7 mm2, respectively (p < 0.001). When compared to the Fuse cage, the mean contact area was 104.8 ± 39.6 mm2 and 55.2 ± 35.1 mm2, respectively(p < 0.001). Patient-specific cages improve the contact area between the implant and the endplate surface, reducing the contact stress and the risk of implant subsidence during LIF surgeries.

Mechanically induced histochemical and structural damage in the annulus fibrosus and cartilaginous endplate: a multi-colour immunofluorescence analysis.

The annulus fibrosus (AF) and endplate (EP) are collagenous spine tissues that are frequently injured due to gradual mechanical overload. Macroscopic injuries to these tissues are typically a by-product of microdamage accumulation. Many existing histochemistry and biochemistry techniques are used to examine microdamage in the AF and EP; however, there are several limitations when used in isolation. Immunofluorescence may be sensitive to histochemical and structural damage and permits the simultaneous evaluation of multiple proteins-collagen I (COL I) and collagen II (COL II). This investigation characterized the histochemical and structural damage in initially healthy porcine spinal joints that were either unloaded (control) or loaded via biofidelic compression loading. The mean fluorescence area and mean fluorescence intensity of COL II significantly decreased (- 54.9 and - 44.8%, respectively) in the loaded AF (p ≤ 0.002), with no changes in COL I (p ≥ 0.471). In contrast, the EP displayed similar decreases in COL I and COL II fluorescence area (- 35.6 and - 37.7%, respectively) under loading conditions (p ≤ 0.027). A significant reduction (-31.1%) in mean fluorescence intensity was only observed for COL II (p = 0.043). The normalized area of pores was not altered on the endplate surface (p = 0.338), but a significant increase (+ 7.0%) in the void area was observed on the EP-subchondral bone interface (p = 0.002). Colocalization of COL I and COL II was minimal in all tissues (R < 0.34). In conclusion, the immunofluorescence analysis captured histochemical and structural damage in collagenous spine tissues, namely, the AF and EP.

Regional distribution of computed tomography attenuation across the lumbar endplate.

The vertebral endplate forms a structural boundary between intervertebral disc and the trabecular bone of the vertebral body. As a mechanical interface between the stiff bone and resilient disc, the endplate is the weakest portion of the vertebral-disc complex and is predisposed to mechanical failure. However, the literature concerning the bone mineral density (BMD) distribution within the spinal endplate is comparatively sparse. The objective of this study is to investigate the three-dimensional (3D) distribution of computed tomography (CT) attenuation across the lumbosacral endplate measured in Hounsfield Units (HU). A total of 308 endplates from 28 cadaveric fresh-frozen lumbosacral spines were used in this study. Each spine was CT-scanned and the resulting DICOM data was used to obtain HU values of the bone endplate. Each individual endplate surface was subdivided into five clinically-relevant topographic zones. Attenuation was analyzed by spinal levels, sites (superior or inferior endplate) and endplate region. The highest HU values were found at the S1 endplate. Comparisons between the superior and inferior endplates showed the HU values in inferior endplates were significantly higher than those in the superior endplates within the same vertebra and the HU values in endplates cranial to the disc were significantly higher than those in the endplates caudal to the disc within the same disc. Attenuation in the peripheral region was significantly higher than in the central region by 32.5%. Regional comparison within the peripheral region showed the HU values in the posterior region were significantly higher than those in the anterior region and the HU values in the left region were significantly higher than those in the right region. This study provided detailed data on the regional HU distribution across the lumbosacral endplate, which can be useful to understand causes of some endplate lesions, such as fracture, and also to design interbody instrumentation.

76. Effect of implant endplate surface topology on subsidence resistance in cervical interbody fixation: comparison of two 3D printed titanium cervical spine fixation devices

<h3>BACKGROUND CONTEXT</h3> Subsidence has become a major concern with the use of interbody fixation devices for single- or multi-level stabilization of cervical spine. Several studies have reported a higher rate of subsidence with titanium vs PEEK devices. Although a known complication whether or not subsidence affects long-term outcomes is not clear. Traditionally, it was believed that increasing the total bone-implant contact area would result in lower incidence and severity of subsidence. With the advent of advance manufacturing technologies we are able to create implants with advanced structural designs and surface topology that can improve subsidence resistance of the interbody device. <h3>PURPOSE</h3> This study is aimed to evaluate subsidence resistance of two 3D-printed titanium cervical interbody devices of the same footprint size, but with different contact surface topology. <h3>STUDY DESIGN/SETTING</h3> Mechanical testing using foam blocks. <h3>OUTCOME MEASURES</h3> Subsidence rate of different interbody constructs. <h3>METHODS</h3> Two cervical 3D-printed titanium interbody fixation devices were used. The first device had a truss design that spans throughout the entire construct and contains a snowshoe style bone interface and the other was an annular interbody device with a large void at the middle of the cage. Both interbody devices were the same dimensions (17mm x 14mm, width x depth). The Truss-based cervical device had 30% less total implant-to-bone contact area compared to the annular device.To mimic mechanical properties similar to human bone density (osteoporotic through normal), 5, 10, 15 and 20 PCF SawBone® foam blocks were utilized for testing. To mimic clinical subsidence, the interbody device was placed over the foam block and compressive displacement was applied to push the device into the foam substrate at the rate of 5mm/min.The test was repeated 6 times for each block/implant combination. The subsidence load at 1 and 2mm displacement was collected for each test combination. To calculate the modulus/stiffness, the ratio of load (normalized to contact area) to axial compression rate of the cage-only construct was calculated. Two-way ANOVA with Sidak-Bonferroni Posthoc was used for multiple comparisons and analysis of statistical significance. <h3>RESULTS</h3> The truss-based interbody device had significantly greater subsidence resistance compared to the annular device at both 1mm and 2mm subsidence rates (p<0.05) across all density blocks. In foam representing osteoporotic bone (5pcf), the truss cage had subsidence resistance load of 212.3N±5N vs 190N ±6N in the predicate cage at 1mm displacement respectively. The corresponding numbers at in rigid bone (20PCF) were 1290N±27N vs 1174N ±8N. <h3>CONCLUSIONS</h3> The truss device with snowshoe design had metal-to-bone contact area of 30% less than the predicate; nevertheless, the truss device demonstrated significantly better resistance to subsidence for all foam densities including those that mimic osteoporotic bone compared to the same size predicate titanium device. The subsidence resistance of the truss cage, despite its smaller contact area for the same footprint size, may be due to the a more efficient distribution of load across the bone / implant interface where the load is uniformly distributed across more of the interbody footprint. The data suggests that the implant's surface contact topology at the endplate plays a greater role than the overall contact area for resisting subsidence. <h3>FDA DEVICE/DRUG STATUS</h3> This abstract does not discuss or include any applicable devices or drugs.

58. Benefits of macroscale topography features on and within interbody cages

BACKGROUND CONTEXT Implant design, material, surfaces, graft and surgical techniques play important roles in the success of interbody fusions and the ability to radiographically assess. PEEK's positive attributes of mechanical properties and radiolucency are maintained using a molecularly bonded submicron deposition of titanium to improve bone on-growth. Novel macroscale topography features on the endplate surfaces and inside the aperture were hypothesized to allow early bone integration and mechanical stability. PURPOSE To evaluate the effect of macroscale topography on a PEEK/Titanium composite cage in a large animal model of interbody fusion. STUDY DESIGN/SETTING Preclinical large animal model. PATIENT SAMPLE Not applicable. OUTCOME MEASURES Not applicable METHODS Lateral L45 interbody fusions were performed in 4-5-year-old ewes using a PEEK/titanium composite cage (Control group) compared to the same cage with macro 3D features on the endplate and inside the aperture (Test group). Iliac crest autograft was placed in the aperture and bilateral pedicle screws and rods for posterior stabilisation. Fusion assessment at 6 and 12 weeks (n=10 per group) included manual palpation, X-rays, mCT, tensile testing and pmMA histology. RESULTS The Test group's manual palpation was 9/10 and 10/10 at 6 and 12 weeks while the control was 4/10 and 7/10 at 6 and 12 weeks. Radiographs and mCT confirmed new bone formation in the aperture of the Control group cages with time while some areas of aperture radiolucency were present. Radiographs and mCT of the Test group cages revealed new bone formation and integration within the topography features on the endplates and inside the aperture which progressed with time. Histology confirmed the radiographic findings in the control group and integration with the host endplates and remodeled bone within the apertures in the Test group. Tensile testing demonstrated nearly a 3-fold statistically significant increase in mechanical properties at both time points for the Test group vs the control group. CONCLUSIONS The macroscale features in the Test group provided multiple opportunities for bone integration between the host endplates and graft within the aperture. Early bony integration translated to a statistically significant increase in mechanical strength compared to the control cage which did not include the same geometric features. Promising data in this clinically relevant animal model warrants further study in humans. FDA DEVICE/DRUG STATUS Shoreline RT (Approved for this indication).

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

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

Three-Dimensional Morphometric Analysis of Lumbar Vertebral End Plate Anatomy

Information on the three-dimensional (3D) shape of vertebral end plates is lacking. Previous studies have analyzed two-dimensional shape; however, 3D data are important because they may help improve our understanding of how differences in shape are related to age, gender, race, size, and other parameters, which may subsequently help improve device design for interbody prosthesis. To study the 3D shape of lumbar vertebral end plates from normal adult lumbar spines and correlate them with age, gender, spinal/end plate level, end plate surface area, concave depth, and size. An invivo analysis was undertaken of lumbar vertebral end plate 3D shape. A total of 136 patients' computed tomography scans were used to create 3D models of the lumbar spine for each patient, which were subsequently analyzed. The shape of the superior end plates is different compared with inferior end plates. Across the lumbar spine (L1-S1), the shape of inferior end plates is similar; however, the shape of the superior end plate varies between spinal levels significantly. There was no clear relationship between age and principal component (PC) shapes but there was a strong correlation between end plate concave depth and end plate PC shape scores. Future interbody (disc replacement and fusion) device designs could use the findings that inferior end plate shape is similar throughout the length of the lumbar spine, whereas superior end plate shape changes. Further, future implants could be level-specific because the present study shows that end plate shape varies through the length of the lumbar spine.

A Practical Positioning Method in End-Plate Surface Distance Measurement with Nano-Meter Precision

End-plate surface distance is important for length value dissemination in the field of metrology. For the measurement of distance of two surfaces, the positioning method is the key for realizing high precision. A practical method with nanometer positioning precision is introduced in consideration of the complexity of positioning laser sources of the traditional methods and new methods. The surface positioning is realized by the combination of laser interference and white light interference. In order to verify the method, a 0.1 mm height step is made, and an experiment system based on the method is established. The principle and the basic theory of the method are analyzed, and the measures to enhance the repeatability from optical and mechanical factors and signal processing methods are presented. The experimental result shows that the surface positioning repeatability is in the order of 10 nm. The measurement uncertainty evaluation shows that the standard uncertainty is 21 nm for a 0.1 mm step. It is concluded that the method is suitable to be applied to the length measurement standard of the lab.