Bone Model Research Articles

Estrogen Deficiency alters Vascularization and Mineralization dynamics: insight from a novel 3D Humanized and Vascularized Bone Organoid Model.

Osteoporosis is not merely a disease of bone loss but also involves changes in the mineral composition of the bone that remains. In vitro studies have investigated these changes and revealed that estrogen deficiency alters osteoblast mineral deposition, osteocyte mechanosensitivity and osteocyte regulation of osteoclastogenesis. During healthy bone development, vascular cells stimulate bone mineralization via endochondral ossification, but estrogen deficiency impairs vascularization. Yet, existing in vitro bone models overlook the role of vascular cells in osteoporosis pathology. Thus, here we (1) develop an advanced 3D vascularized, mineralized and humanized bone model following the endochondral ossification process, and (2) apply this model to mimic postmenopausal estrogen withdrawal and provide a mechanistic understanding of changes in vascularization and bone mineralization in estrogen deficiency. We confirmed the successful development of a vascularized and mineralized human bone model via endochondral ossification, which induced self-organization of vasculature, associated with hypertrophy (collagen X), and promoted mineralization. When the model was applied to study estrogen deficiency, we reported the development of distinct vessel-like structures (CD31+) in the postmenopausal 3D constructs. Moreover, during estrogen withdrawal vascularized bone demonstrated a significant increase in mineral deposition and apoptosis, which did not occur in non-vascularized bone. These findings reveal a potential mechanism for bone mineral heterogeneity in osteoporotic bone, whereby vascularized bone becomes highly mineralized whereas in non-vascularised regions this effect is not observed.

Evaluating the value of 3D-printed bone models with fracture fragments connected by flexible rods for training and preoperative planning

BackgroundThe emergence of 3D printing has revolutionized medical training and preoperative planning. However, existing models have limitations, prompting the development of newly designed flexible 3D-printed bone fracture models.MethodsThe designed flexible 3D-printed bone fracture models were evaluated by 133 trauma surgeons with different levels of experience for perceived value as educational tool or as preoperative planning tool.ResultsThe models allowed drilling and showed resistance to manipulation and sterilization. Surgeons found the flexible model helpful for teaching and planning the reduction of fractures, planning and simulating osteosynthesis, understanding fractures, visualizing fractures, and planning surgical approaches.ConclusionsFlexible 3D-printed bone fracture models offer a dynamic and realistic approach to understanding complex fractures, potentially improving surgical training and preoperative planning.

Challenges in detecting various peri-implant bone defects on modified intraoral oblique radiographic projections: evaluation of an artificial mandibular model.

The objective of this study was to evaluate the effectiveness of oblique radiographic projection using the intraoral paralleling technique in detecting various peri-implant bone defects. Artificial mandibular models with appropriate radiopacity were created. An alveolar bone model without bone defects and models with 12 types of peri-implant bone defects (buccal, circumferential, and mixed types with different widths and depths) were created. A total of 273 images were obtained with orthoradial projections and 10-, 20-, and 30-degree oblique projections using a modified receptor holder. Two observers independently evaluated the images to detect bone defects. The grayscale values (GVs) of the peri-implant region and the adjacent area were measured and compared. The relationship between the GV and the observers' results was examined. The area under the curve (AUC) and inter-observer agreement were calculated. Circumferential and mixed bone defects were detected on the orthoradial projections, while buccal defects were not detected. However, the detection of buccal defects was markedly improved using the oblique projections. In particular, the highest detection rates were obtained using the 20-degree oblique projection. There were no significant correlations between the GV and the bone defect detection rate. The AUCs for the two observers were 0.712 and 0.669. The inter-observer agreement was 0.502. Compared with orthoradial projections, the use of oblique projection images greatly improved the ability of observers to detect peri-implant bone defects on the buccal side. The results provide new evidence for the selection of radiographic images in the follow-up of implant treatment.

Comparison of mechanical properties of polyethylene and polyurethane blocks as model materials for in vitro cortical bone modelling

Aims: The aim of this study was to compare polyethylene (PE) and polyurethane (PU) blocks at a density of 60 pcf in terms of flexural strength (FS), elastic modulus (EM), elongation, and hardness in vitro for use in cortical bone modelling. Methods: This in vitro study was conducted at Van Yüzüncü Yıl University Faculty of Dentistry Department of Orthodontics and the testing and laboratory phases of the study were conducted at Van Yüzüncü Yıl University Faculty of Dentistry Research Laboratory. PE (group 1) and PU (group 2) blocks with a density of 60 pcf (0.96 g/cm3) were used in the study. The 3-point bending test was performed on a universal testing machine and FS, EM, elongation, and hardness were measured. A total of 30 samples, 15 in the PU group and 15 in the PE group, were included in the study. Results: The FS and hardness values of PE and PU did not show statistically significant differences (p>0.05). Statistically significant differences were found between the PE and PU groups for EM and elongation values (p<0.05). Conclusion: This study showed that PE blocks can be used in orthodontics for in vitro cortical bone modelling.

Assessment of the proficiency level of novices in distal intramedullary nail interlocking achieved through training with Digitally Enhanced Hands-on Surgical Training (DEHST).

Digitally Enhanced Hands-on Surgical Training (DEHST) platform was introduced to overcome the lack of training capabilities for the challenging task of freehand distal interlocking of intramedullary nails. It demonstrates high perceived realism for surgeons, and novices perform significantly better after DEHST training. However, characterization of how performance improves remained unexplored. The aim of this study was to evaluate the training progression of novices in freehand distal interlocking during five training rounds with DEHST and to compare their performance in a simulated operation against experienced surgeons. Ten novices (Group 1) underwent five DEHST training sessions (approximately one hour in total) and their performance data was acquired and evaluated. The surgical performance of Group 1 was compared with ten surgical experts (Group 2) by performing distal interlocking of a real tibia nail in an artificial bone model in a simulated operation. Time taken, number of X-rays, accuracy of nail hole roundness, and success rates were compared between the groups. Group 1 achieved comparable performance to Group 2 in number of X-rays 26.0 (range 15-40) versus 22.5 (range 16-34), p = 0.281, and accuracy of hole roundness 95.0% (range 91.1-98.0%) versus 93.3% (range 90.7-95.9%), p = 0.087. However, Group 1 needed significantly longer time compared with Group 2, p = 0.001, and furthermore, one participant in Group 1 (10%) failed to hit the nail hole with the drill bit, while 100% of the participants in Group 2 were successful. DEHST appears to be a useful tool to gradually improve the proficiency level of novices and to train relevant practical surgical skills needed for distal interlocking of intramedullary nails. However, further investigations are needed to demonstrate the performance under the conditions of a real operation.

Generating Virtual Bone Scans for the Purpose of Investigating the Effects of Cortical Microstructure.

Evaluating the contribution of microstructure to overall bone strength is tricky since it is difficult to control changes to pore structure in human or animal samples. We developed an open-source program that can generate three-dimensional models of micron-scale cortical bone. These models can be highly customized with a wide array of variable input parameters to allow for generation of samples with high similarity to CT scans of cortical bone or with specific geometric features. The program can generate samples with specific desired porosities (p < 0.001) and minor deviations in pore diameter from human samples: 2.29% (±4.61) using literature values, and 0.87% (±1.39) with optimized values.

Feasibility of Angulated Curettes in Endoscopic Ear Surgery: A Study on Goat Head Temporal Bone Models

Feasibility of Angulated Curettes in Endoscopic Ear Surgery: A Study on Goat Head Temporal Bone Models

Influence of Axial Rotation Between the Femoral Neck and Ankle Joint on Kinematics in Normal Knees: A Cross-Sectional Study.

The effect of axial rotation between the femoral neck and ankle joint (total rotation [TR]) on normal knees is unknown. Therefore, this study aimed to investigate the TR effect on normal knee kinematics. Volunteers were divided into groups large (L), intermediate (I), and small (S), using hierarchical cluster analysis based on TR in the standing position. TR was measured using three-dimensional (3D) bone models generated from CT. A two-dimensional to 3-dimensional registration technique was used to assess the spatial position and femur and tibia orientation during squat. The axial rotation, varus-valgus alignment, and anterior-posterior translation of the femur relative to the tibia were evaluated. Group L had the highest TR, whereas group S had the lowest TR (L: 36.6° ± 6.0°, I: 23.2° ± 3.0°, and S: 13.8° ± 5.1°). Above 50° of flexion, femoral external rotation was greater in group S than in groups L and I. From 40° to 110°, the medial side was more anterior in group L than in groups I and S, whereas the lateral side was more posterior in group S than in groups L and I. Individuals with larger TR had more femur anterior-medial translation relative to the tibia.

Medial patellofemoral ligament reconstruction normalizes patellar kinematics but fails to predict cartilage contact area: A prospective 3D MRI study

AbstractIntroductionThe medial patellofemoral ligament (MPFL) is the main patellar stabilizer in low knee flexion degrees (0–30°). Isolated MPFL reconstruction (MPFLr) is therefore considered the gold standard of surgical procedures for low flexion patellofemoral instabilities (PFIs). Despite excellent clinical results, little is known about the effect of MPFLr on kinematic parameters (KPs) of the patellofemoral joint in vivo. This study investigates the effect of MPFLr on KP of patellofemoral articulation, using a three‐dimensional (3D) in vivo magnetic resonance imaging (MRI) analysis at different flexion and loading positions, and analyzes the correlation of these parameters with the patellofemoral cartilage contact area (CCA).MethodsIn this prospective, matched‐pair cohort study of 30 individuals, 15 patients with low flexion PFI and 15 knee‐healthy individuals were included. Patients were analyzed pre and post‐operatively after MPFLr. MRI images were obtained at 0°, 15° and 30° with and without muscle activation, using a custom‐designed pneumatic loading device. Patellar shift, tilt and rotation were determined in 3D bone and cartilage models of each individual, guaranteeing the highest reliability. Subsequently, the KPs were correlated with patellofemoral CCA.ResultsPatients with low flexion PFI had a leg geometry of 0.5 ± 2.6° valgus and a TTTG of 11.4 ± 4.4 mm. Eleven patients had moderate (Type A/B) and 2 had severe (Type C/D) trochlear dysplasia. Without muscle activation, patients showed significantly increased patellar shift (0–30°; p0° = 0.011, p15° = 0.004 and p30° = 0.015) and tilt (15°; p15° = 0.041). Muscle activation did not compensate for maltracking in these patients, but even increased tilt and shift further in extension (p0° = 0.002 and p0° = 0.001). MPFLr statistically reduced patellofemoral tilt from 0° to 30° flexion during passive flexion and tended to approach the values of knee‐healthy individuals (pext = 0.008, p15° = 0.006 and p30° = 0.003). Post‐operatively, muscle activation led to comparable tilt and shift as in healthy individuals. Tilt, shift and rotation did not correlate with CCA neither in healthy individuals nor in pre‐ or post‐operative patients.ConclusionIsolated MPFLr can normalize patellar shift and tilt in patients with low flexion instability. Considering the influence of muscle activation, passive stabilization through MPFLr seems to be the basic precondition for physiologically active patella stabilization. The investigated KPs as easy‐to‐measure parameters in clinical practice cannot be used to assume normalized CCA for low flexion degrees. Therefore, methodologically demanding methods are still required to calculate the patellofemoral CCA.Level of EvidenceLevel II.

Study and analysis of Ti13Nb13Zr implants in the above knee osseointegration prosthesis

Introduction: Osseointegration is a particular kind of prosthesis that is inserted a short titanium rod or screw into the bone surgically and joined to the prosthetic limb. Experimental part: This study looked at a patient's gait analysis with above-knee amputation wearing an osseointegration prosthesis implant when walking above a force plate. Evaluated the mechanical and fatigue properties of a Ti13Nb13Zr alloy implant. Theoretical part: Drawing and analysis of a femoral bone model with an osseointegration implant using Ansys Workbench 17.2. Results and discussion: The results of the tensile testing showed an ultimate tensile strength of 553 MPa, an average yield strength of 480 MPa, an elongation of 19.66%, and a Young's modulus of 2.73 GPa. Furthermore, a compressive strength of 1010 MPa and a compression yield strength of 700 MPa were found by compression testing. The results of fatigue testing, which were displayed as S-N curves, highlighted the alloy's time-dependent fatigue behavior by showing decreasing fatigue strength with an increase in cycles. The force plate showed a maximum force of 600 N was reported. A strong safety margin was shown by Finite Element Analysis in the bone containing the implant, with safety factors often more than 5 and low deformation (2.4 mm) appropriate for prosthetic uses. A good static design was confirmed by the Von-Mises stress distribution, which was primarily below 46 MPa. Conclusion: Comprehensive results confirm the mechanical feasibility of the Ti13Nb13Zr alloy for prosthetic applications and offer important new information for improving prosthetic design, guaranteeing durability, and improving safety in practical applications.

Data-Efficient Bone Segmentation Using Feature Pyramid- Based SegFormer

The semantic segmentation of bone structures demands pixel-level classification accuracy to create reliable bone models for diagnosis. While Convolutional Neural Networks (CNNs) are commonly used for segmentation, they often struggle with complex shapes due to their focus on texture features and limited ability to incorporate positional information. As orthopedic surgery increasingly requires precise automatic diagnosis, we explored SegFormer, an enhanced Vision Transformer model that better handles spatial awareness in segmentation tasks. However, SegFormer’s effectiveness is typically limited by its need for extensive training data, which is particularly challenging in medical imaging, where obtaining labeled ground truths (GTs) is a costly and resource-intensive process. In this paper, we propose two models and their combination to enable accurate feature extraction from smaller datasets by improving SegFormer. Specifically, these include the data-efficient model, which deepens the hierarchical encoder by adding convolution layers to transformer blocks and increases feature map resolution within transformer blocks, and the FPN-based model, which enhances the decoder through a Feature Pyramid Network (FPN) and attention mechanisms. Testing our model on spine images from the Cancer Imaging Archive and our own hand and wrist dataset, ablation studies confirmed that our modifications outperform the original SegFormer, U-Net, and Mask2Former. These enhancements enable better image feature extraction and more precise object contour detection, which is particularly beneficial for medical imaging applications with limited training data.

The ability of plain radiography to accurately describe the bone surface at the head–neck junction of the femur: a study using human bone models

Abstract In evaluations of a cam deformity on femoroacetabular impingement, the head–neck junction (HNJ) must be accurately assessed. We conducted this study to determine the ability of plain radiography to visualize the end-to-end bone surface of the HNJ. We used six human bone models. Ten examiners evaluated the degree to which attached stainless wire marker at the 1:00, 1:30, and 2:00 radial plane defined in reconstructed computed tomography can be accurately detected on the bone surface on plain radiographies. We employed 13 plain radiographies: the cross-table lateral view, frog-leg lateral view, Espié frog-leg lateral view, false-profile view, modified false-profile view, 30° Dunn view (DV), 45° DV, 60° DV, 90° DV, 30° modified Dunn view (MDV), 45° MDV, 60° MDV, and 90° MDV. Examiners scored the degree to which the radiographic images accurately detected the stainless wire marker on the bone surface of the HNJ on a scale of 1 point (0% match) to 5 points (almost 100% match). The highest score for the 1:00 plane was 4.98 points on the 45° DV. Similarly, the highest scores of the 1:30 and 2:00 planes were 4.98 points for the 45° MDV and 4.68 points for the 90° MDV, respectively. On these bone model studies, the most suitable plain radiography for describing the HNJ at the 1:00, 1:30, and 2:00 planes were both the 45° DV, the 45° MDV, and the 90° MDV, respectively.

Comparative Biomechanical Analysis of Kirschner Wire Fixation in Dorsally Displaced Distal Radius Fractures.

This study aims to evaluate and compare the biomechanical performance of two Kirschner (K) wire configurations-the intra-focal and interfragmentary techniques-for the fixation of dorsally displaced distal radius fractures. The study also assesses the impact of K-wire diameter (1.6 mm vs. 2.0 mm) on mechanical stability. Sixty fresh turkey tarsometatarsus bones were selected and divided into four groups based on the K-wire configuration and diameter used. Fractures were created at standardized locations, and each bone was stabilized using either the intra-focal also known as modified Kapandji (Ka) or interfragmentary technique. Mechanical testing, including axial compression and flexion tests, was performed to assess the biomechanical stability of each configuration. The interfragmentary configuration consistently demonstrated superior biomechanical performance compared to the intra-focal technique. Specifically, the use of 2.0 mm K-wires resulted in significantly higher axial stiffness (13.28 MPa) and load at break (3070 N) compared to the 1.5 mm wires. Confidence intervals further supported the robustness of these findings. The interfragmentary technique, especially with thicker K-wires, provided greater load-bearing capacity and stiffness. The interfragmentary technique with 2.0 mm K-wires offers superior mechanical stability compared to the intra-focal technique, making it the preferred choice for stabilizing comminuted extra-articular distal radius fractures. These findings suggest that adopting this technique may reduce the risk of postoperative complications such as fracture displacement or malunion. Further research involving osteoporotic bone models and clinical trials is recommended to validate these findings in real-world settings.

Personalized Occlusal Guide Guides Panfacial Fracture Repair and Reconstruction.

Restoration of the occlusal relationship is the key point in the treatment of maxillofacial fractures. Poor restoration of the occlusal relationship seriously impacts oral function as well as physical and mental health. This study combines virtual surgical technology with model surgery, uses computed tomography data to establish a maxillofacial bone model, and performs a virtual reduction of fractures. The upper and lower dentition models after reconstruction were intercepted and 3-dimensional printed. After the occlusal relationship was reconstructed by the prosthodontist using the model, an occlusal reduction guide was designed and manufactured based on the reconstructed occlusal relationship to accurately reduce the occlusal relationship in patients with maxillofacial fractures. This study proposes an occlusal guide design process for maxillofacial fractures and optimizes the traditional model surgical process to provide a convenient surgical strategy. This study provides new ideas for the design of personalized surgical guides for maxillofacial fractures.

Developing a 3D bone model of osteosarcoma to investigate cancer mechanisms and evaluate treatments.

Osteosarcoma is the most common primary bone cancer, occurring frequently in children and young adults. Patients are treated with surgery and multi-agent chemotherapy, and despite the introduction of mifamurtide in 2011, there has been little improvement in survival for decades. 3-dimensional models offer the potential to understand the complexity of the osteosarcoma tumor microenvironment and aid in developing new treatment approaches. An osteosarcoma 3D bone core model was developed using human trabecular bone and the chorioallantoic membrane (CAM), to form a functioning vasculature. A tri-culture of cells, stromal cells, macrophages, and the Saos-2 osteosarcoma cell line, were implanted into this model to simulate components of the tumor microenvironment, and mifamurtide was tested in this context. Immunohistochemistry and micro-CT were performed to assess phenotypic and structural effects of implantation. Successful integration and angiogenesis of the bone cores were observed after incubation on the CAM. The 3D bone model also showed similar characteristics to osteosarcoma patient samples including CD68 and CD105 expression. Incubating bone cores with mifamurtide induced a reduction of cellular markers and an increase in bone volume. This 3D bone core model has the potential to investigate osteosarcoma tumor microenvironment and provides a representative model for evaluation of novel therapies.

Breaking the Mould: Comparing 3D-Printed and Composite Bone Models in Orthopaedic Training.

Background and aim Synthetic composite bone models (reinforced solid foam) have become the standardised material used in practical orthopaedic education. However, with discussions regarding whether composite foam truly replicates human bone, there has been a drive to explore other available models. Three-dimensional (3D) printing has risen in both popularity and availability, providing a new option in the creation of anatomically accurate bone models. We designed a pilot study to assess whether a new formulation of synthetic bone provides the same tactile feedback that is essential for training purposes. Method Orthopaedic trainees of various grades across two London hospital trusts were invited to participate in a distal radius fixation workshop. As part of the workshop, trainees were asked to complete the following three tasks on the two different models: Kirschner-wire driving, pilot hole drillingand screw insertion. Participants were blinded in this trialand not informed which model was made via 3D printing or the conventional composite bone. Following completion, participants provided feedback on tactile feedback for each task on each model. Results Twenty-three orthopaedic trainees participated in the workshop, with overall majority agreement in all clinical skills that the 3D-printed model provided better tactile feedback. Three-dimensional models were rated superior in K-wire driving (mean score 7.39 vs 4.82; p<0.001) and pilot hole drilling (7.87 vs 4.96; p<0.001), with no significant difference in screw insertion. Qualitative feedback from testers noted a more anatomical representation of the 3D-printed bone, in addition to an overall better representation of the corticomedullary junction. Conclusion Overall, 3D printed models provide a new high-fidelity and sustainable option when seeking bone models for modern-day orthopaedic training. At present composite bone remains the standard for workshops. However, with the growing availability of 3D-printing models, and as supported by this study, they crucially provide the medium for future orthopaedic surgeons to learn and gain confidence.

Loss of cped1 does not affect bone and lean tissue in zebrafish.

Human genetic studies have nominated cadherin-like and PC-esterase domain-containing 1 (CPED1) as a candidate target gene mediating bone mineral density (BMD) and fracture risk heritability. Recent efforts to define the role of CPED1 in bone in mouse and human models have revealed complex alternative splicing and inconsistent results arising from gene targeting, making its function in bone difficult to interpret. To better understand the role of CPED1 in adult bone mass and morphology, we conducted a comprehensive genetic and phenotypic analysis of cped1 in zebrafish, an emerging model for bone and mineral research. We analyzed two different cped1 mutant lines and performed deep phenotyping to characterize more than 200 measures of adult vertebral, craniofacial, and lean tissue morphology. We also examined alternative splicing of zebrafish cped1 and gene expression in various cell/tissue types. Our studies fail to support an essential role of cped1 in adult zebrafish bone. Specifically, homozygous mutants for both cped1 mutant alleles, which are expected to result in loss-of-function and impact all cped1 isoforms, exhibited no significant differences in the measures examined when compared to their respective wildtype controls, suggesting that cped1 does not significantly contribute to these traits. We identified sequence differences in critical residues of the catalytic triad between the zebrafish and mouse orthologs of CPED1, suggesting that differences in key residues, as well as distinct alternative splicing, could underlie different functions of CPED1 orthologs in the two species. Our studies fail to support a requirement of cped1 in zebrafish bone and lean tissue, adding to evidence that variants at 7q31.31 can act independently of CPED1 to influence BMD and fracture risk.

The Evaluation of Mechanical Properties of Commercial Composite Bones and 3D-Printed Bones Produced Using the CJP Technology

Cadaver bones and artificial bones are utilized to perform preoperative studies and education purposes. Cadaver bones are hard to find, require ethical permissions, and have infection hazards. Therefore, commercial artificial bones are preferred in practice. Nonetheless, since these commercial alternatives are standardly produced in an average size and geometry, it is almost impossible to adapt them to a specific surgical simulation. In addition, these artificial bones have relatively high costs, which limits their accessibility. On the other hand, ColorJet printing (CJP), one of the three-dimensional printing technologies, offers a rapid and cost-effective alternative. However, whether the printed 3D-printed models can mechanically comply with artificial bones is unclear. In this study, 3D-printed bones and artificial commercial composite bones were compared in terms of mechanical properties. Compression tests were applied over 14 printed and 14 composite bones using the ISO 5833 standard. Mechanical properties including stress-strain, load to failure, and elastic modulus were calculated, and these results were compared using the two-sample independent t-test, which is one of the statistical analysis methods. Consequently, there was no significant difference between the bone models in terms of stress and failure load values (p

Effect of screw placement order on range of proximal tibial fragment rotation adjustment and osteotomy gap formation when using manual reduction during tibial plateau levelling osteotomy (TPLO)

AimTo determine the optimal first proximal screw position which permits proximal tibial fragment rotation adjustment while minimising osteotomy gap formation when a manual reduction technique is used for TPLO in dogs.MethodsTPLOs were performed on bone models using Synthes 3.5‐mm TPLO implants with a jig but without the use of an anti‐rotational pin. The osteotomy was held in manual reduction with pointed reduction forceps placed across the proximal tibial fragment while the first three screws were applied. The first two screws were placed in the non‐locking holes of the distal stem of the plate as per manufacturer's screw placement order guidelines. The third screw was placed in one of the three locking screw positions in the head of the plate, denoted as the ‘cranial’, ‘proximal’ and ‘caudal’ screw positions. After the first three screws were placed, the range of possible proximal tibial fragment rotation change (up to 6 mm in each direction) and the resultant cranial and caudal osteotomy gaps were measured.ResultsThe proximal screw position minimises cranial osteotomy gap formation with negative rotation changes to the proximal tibial fragment. The caudal screw position minimises caudal osteotomy gap formation with positive rotation changes to the proximal tibial fragment. Rotation change had a greater effect on cranial osteotomy gaps compared to caudal osteotomy gaps. The cranial screw position had the most limited osteotomy rotation change.ConclusionThe proximal screw position should be placed first in the head of the plate to allow proximal tibial fragment rotation adjustment while minimising osteotomy gap formation when using a manual reduction technique when performing a TPLO.

Optimization of 3D-titanium interbody cage design. Part 1: in vitro biomechanical study of subsidence.

Cage subsidence is a complication of interbody fusion associated with poor clinical outcomes. 3D-printed titanium interbody cages allow for the alteration of features such as stiffness and porosity. However, the influence of these features on subsidence and their biological effects on fusion have not been rigorously evaluated. This 2-part study sought to determine how changes in 3D-printed titanium cage parameters affect subsidence using an in vitro bone model (Part 1) and biological fusion using an in vivo sheep model (Part 2). Biomechanical foam block model. In Part 1 of this study, 9 implant types were tested (8 per implant type). The implant types included 7 3D-printed titanium interbody cages with various surface areas, porosities, and surface topographies, along with 1 standard polyetherether ketone (PEEK) cage and 1 solid titanium cage. Subsidence testing was performed in a standardized foam block model using 2 different densities of foam. Digital imaging correlation was used to determine the relative vertical displacement of the interbody cage-foam block construct. Subsidence decreased as the surface contact area with the bone model increased (all p≤0.01). Increased porous surface topography increased subsidence, while a nonporous surface significantly decreased subsidence (all p<0.001). Subsidence did not differ based on changes in implant porosity (all p≥0.35) or material property/modulus (all p≥0.19). Subsidence was significantly decreased with the higher density foam (p<0.001). The stiffness of the implant was affected by porosity (all p<0.02) and smooth surface topography (p=0.01) but not by lumen size (all p≥0.15). Stiffness did not differ between porous titanium and PEEK implants (p=0.96), which were both less stiff than solid titanium implants (both p <0.001). Surface area negatively correlated with subsidence (r=-0.786, p=0.012) but was not correlated with stiffness (r=0.560, p=0.12). Implant surface area and surface topography greatly influenced interbody subsidence. Apparent stiffness, implant porosity, and material property did not affect subsidence in this in vitro model. Higher foam density also led to lower subsidence than low-density foam. Biological response in the in vivo setting likely also influences clinical subsidence, which is evaluated in the companion study (Part 2). This study provides valuable information regarding the new 3D-printed titanium technology. We showed that cage surface area and surface topography were the implant design parameters that had the greatest influence on the development of interbody subsidence. Moreover, bone mineral density was the factor that had the greatest effect on subsidence prevention. These data support patient optimization before surgery and emphasize the importance of endplate protection during surgery.