Author Contributions
Conceptualization, K.-U.L., S.V., J.C.E. and M.P.L.; methodology, K.-U.L. and M.P.L.; software, K.-U.L. and M.P.L.; validation, K.-U.L., S.V., J.C.E. and M.P.L.; formal analysis, K.-U.L. and M.P.L.; investigation, K.-U.L. and M.P.L.; resources, K.-U.L., S.V. and M.P.L.; data curation, K.-U.L., J.C.E. and M.P.L., writing—original draft preparation, K.-U.L. and M.P.L.; writing—review and editing, K.-U.L., S.V., J.C.E. and M.P.L.; visualization, K.-U.L., S.V., J.C.E. and M.P.L.; supervision, K.-U.L. and M.P.L.; project administration, K.-U.L. and M.P.L.; APC funding acquisition, K.-U.L. All authors have read and agreed to the published version of the manuscript.
Figure 1.
Displayed are eight distinct types of 3D-printed titanium mesh spinal cage implants, each custom-designed for specific spinal surgeries. The implants shown are as follows: (a) Lateral Lumbar Interbody Fusion (LLIF) Cage—designed for lateral approach lumbar fusion surgeries, helping to maintain disc height and spinal alignment while encouraging bone growth; (b,c) Cervical Cages—designed for anterior cervical discectomy and fusion (ACDF) procedures (a) with a buttress plate and (c) with an integrated buttress mechanism, providing stability and promoting bone growth between cervical vertebrae; (d) Corpectomy Cage—applied in corpectomy procedures to replace vertebral bodies removed due to disease or injury, providing structural support and aiding in spinal reconstruction over one or multiple spinal motion segments; (e) Anterior Lumbar Interbody Fusion (ALIF) Cage—used for lumbar fusion surgeries, placed through an anterior approach to maintain disc height and alignment while facilitating bone fusion in the anterior spinal column, (f) Posterior Lumbar Interbody Fusion (PLIF) Cage—used in posterior lumbar fusion surgeries, facilitating the fusion of the lumbar vertebrae and providing stability; and (g,h) Transforaminal Lumbar Interbody Fusion (TLIF) Cages—utilized in lumbar fusion surgeries via a transforaminal approach. These 3D-printed titanium mesh cages are engineered for precision and durability, offering enhanced biocompatibility and osteointegration to improve surgical outcomes and patient recovery.
Figure 1.
Displayed are eight distinct types of 3D-printed titanium mesh spinal cage implants, each custom-designed for specific spinal surgeries. The implants shown are as follows: (a) Lateral Lumbar Interbody Fusion (LLIF) Cage—designed for lateral approach lumbar fusion surgeries, helping to maintain disc height and spinal alignment while encouraging bone growth; (b,c) Cervical Cages—designed for anterior cervical discectomy and fusion (ACDF) procedures (a) with a buttress plate and (c) with an integrated buttress mechanism, providing stability and promoting bone growth between cervical vertebrae; (d) Corpectomy Cage—applied in corpectomy procedures to replace vertebral bodies removed due to disease or injury, providing structural support and aiding in spinal reconstruction over one or multiple spinal motion segments; (e) Anterior Lumbar Interbody Fusion (ALIF) Cage—used for lumbar fusion surgeries, placed through an anterior approach to maintain disc height and alignment while facilitating bone fusion in the anterior spinal column, (f) Posterior Lumbar Interbody Fusion (PLIF) Cage—used in posterior lumbar fusion surgeries, facilitating the fusion of the lumbar vertebrae and providing stability; and (g,h) Transforaminal Lumbar Interbody Fusion (TLIF) Cages—utilized in lumbar fusion surgeries via a transforaminal approach. These 3D-printed titanium mesh cages are engineered for precision and durability, offering enhanced biocompatibility and osteointegration to improve surgical outcomes and patient recovery.
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Figure 2.
This block diagram outlines our comprehensive approach to incorporating 3D printing technology into spine surgery. It begins with an overview of titanium’s key properties, including strength, biocompatibility, and corrosion resistance, and highlights the role of porosity in osteoinduction, osteoconduction, and osteointegration. The customization process is detailed to match patient-specific anatomy. The step-by-step manufacturing process encompasses design and digital CAD modeling, optimization, preparation, 3D printing via SLM or EBM, post-processing, heat treatment, quality control, and sterilization. These steps aim to enhance surface roughness and micro-texturing for optimal cell attachment and bone growth, thereby eliminating the need for bone grafts. The diagram also highlights clinical trial applications in oncology, congenital disorders, and degenerative conditions, while addressing limitations such as accessibility, production challenges, and quality control issues. It discusses payer policies and CMS rulings, focusing on insurance challenges and the impact of Aetna’s policy and CMS decisions on reimbursement. The regulatory environment is explained, covering FDA regulations and point-of-care 3D printing centers. Future directions include advancements in materials, AI integration, and multifunctional implants with expandable capabilities, sensors, and drug delivery systems. The discussion section summarizes the benefits and challenges of 3D-printed titanium cages and outlines future research directions.
Figure 2.
This block diagram outlines our comprehensive approach to incorporating 3D printing technology into spine surgery. It begins with an overview of titanium’s key properties, including strength, biocompatibility, and corrosion resistance, and highlights the role of porosity in osteoinduction, osteoconduction, and osteointegration. The customization process is detailed to match patient-specific anatomy. The step-by-step manufacturing process encompasses design and digital CAD modeling, optimization, preparation, 3D printing via SLM or EBM, post-processing, heat treatment, quality control, and sterilization. These steps aim to enhance surface roughness and micro-texturing for optimal cell attachment and bone growth, thereby eliminating the need for bone grafts. The diagram also highlights clinical trial applications in oncology, congenital disorders, and degenerative conditions, while addressing limitations such as accessibility, production challenges, and quality control issues. It discusses payer policies and CMS rulings, focusing on insurance challenges and the impact of Aetna’s policy and CMS decisions on reimbursement. The regulatory environment is explained, covering FDA regulations and point-of-care 3D printing centers. Future directions include advancements in materials, AI integration, and multifunctional implants with expandable capabilities, sensors, and drug delivery systems. The discussion section summarizes the benefits and challenges of 3D-printed titanium cages and outlines future research directions.
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Figure 3.
Shown is a 3D-printed titanium mesh model employed in a spinal cage and the result of an SEM analysis. The first image (a) shows a Model of a 3D-printed titanium mesh spinal showcasing a proprietary design with a pattern of three distinct pore sizes including hexagonal pores measuring 700 µm in size offering additional stability and support within the mesh, quadratic pores sized at 500 µm, and diamond-shaped pores at 300 µm. These different pores are designed to enhance the mesh’s porosity and osteoconductive properties. The second image (b) shows an SEM image at 1000× magnification, which provides a detailed view of the 3D-printed pore pattern at 1000× magnification. This image highlights the precise arrangement and uniformity of the hexagonal and diamond-shaped pores, demonstrating the high-resolution capabilities of 3D printing technology in creating sophisticated mesh structures. The third image (c) shows another SEM image at 25,000× magnification revealing the surface morphology of the 3D-printed titanium. This image captures the micro-scale texture and topographical details, showcasing the surface roughness and porosity critical for promoting cell attachment and bone integration. These images collectively illustrate the advanced engineering and precision of fabricating 3D-printed titanium mesh spinal cages, emphasizing their potential to enhance spinal fusion outcomes through optimized pore design and surface characteristics.
Figure 3.
Shown is a 3D-printed titanium mesh model employed in a spinal cage and the result of an SEM analysis. The first image (a) shows a Model of a 3D-printed titanium mesh spinal showcasing a proprietary design with a pattern of three distinct pore sizes including hexagonal pores measuring 700 µm in size offering additional stability and support within the mesh, quadratic pores sized at 500 µm, and diamond-shaped pores at 300 µm. These different pores are designed to enhance the mesh’s porosity and osteoconductive properties. The second image (b) shows an SEM image at 1000× magnification, which provides a detailed view of the 3D-printed pore pattern at 1000× magnification. This image highlights the precise arrangement and uniformity of the hexagonal and diamond-shaped pores, demonstrating the high-resolution capabilities of 3D printing technology in creating sophisticated mesh structures. The third image (c) shows another SEM image at 25,000× magnification revealing the surface morphology of the 3D-printed titanium. This image captures the micro-scale texture and topographical details, showcasing the surface roughness and porosity critical for promoting cell attachment and bone integration. These images collectively illustrate the advanced engineering and precision of fabricating 3D-printed titanium mesh spinal cages, emphasizing their potential to enhance spinal fusion outcomes through optimized pore design and surface characteristics.
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Figure 4.
Shown are SEM images of (a) hexagonal pores measuring 700 µm in size with interlaced diamond-shaped pores at 150× magnification, (b) 300× magnification of the same hexagonal pore and (c) a 2000× magnification of the lattice beams whose surface roughness, micro-texturing, and micro-pores typically in the range of a few micrometers play crucial roles in promoting the attachment, proliferation, and differentiation of bone-forming cells. These micropores further increase the surface area and provide additional sites for cellular attachment and ingrowth. The surface roughness appears irregular and textured, with a mix of peaks and valleys, ridges, and grooves resulting from the layer-by-layer additive manufacturing process. These micro-textures create a conducive environment for osteoblasts and other bone cells to adhere more firmly. Depending on the printing direction and parameters, directional patterns may be visible, guiding cellular orientation and spreading, which is beneficial for organized tissue growth. At 2000× magnification, nanoscale roughness can be observed, which provides additional anchoring points for cells and proteins. These tiny irregularities help in the initial cell adhesion processes by increasing the contact points between the cell membrane and the implant surface. The presence of an interconnected porous network allows for better nutrient and waste exchange, facilitating cellular metabolism and promoting a healthy environment for cell proliferation. Titanium also has a surface chemistry characterized by an oxide layer. Titanium naturally forms a thin oxide layer on its surface, which is visible under SEM as a uniform coating ©. This oxide layer enhances biocompatibility and supports protein adsorption, which is critical for cell adhesion. The surface energy of the titanium beams is influenced by their micro-texture and chemistry, making them more hydrophilic. This hydrophilicity is beneficial as it improves the wettability of the surface, allowing bodily fluids to spread more easily, enhancing protein adsorption, and facilitating cell attachment. Occasionally, small particles of unmelted or partially melted titanium powder might be adhered to the surface. These particles can provide additional micro- and nano-scale topographical features that aid in cellular attachment. (d–f) MSC differentiation and morphology are dependent on the surface topography of the device. An in-vitro analysis of cellular differentiation based on surface roughness and coating was performed with fluorescence microscopy images of MSCs cultured on 3D titanium scaffolds for 5 days. Cells were stained with F-actin (red) and nuclei with DAPI (blue) revealing a favorable response of primary mesenchymal stem cells to the 3D architecture of the printed titanium scaffolds eliciting an osteogenic response with different surface treatments.
Figure 4.
Shown are SEM images of (a) hexagonal pores measuring 700 µm in size with interlaced diamond-shaped pores at 150× magnification, (b) 300× magnification of the same hexagonal pore and (c) a 2000× magnification of the lattice beams whose surface roughness, micro-texturing, and micro-pores typically in the range of a few micrometers play crucial roles in promoting the attachment, proliferation, and differentiation of bone-forming cells. These micropores further increase the surface area and provide additional sites for cellular attachment and ingrowth. The surface roughness appears irregular and textured, with a mix of peaks and valleys, ridges, and grooves resulting from the layer-by-layer additive manufacturing process. These micro-textures create a conducive environment for osteoblasts and other bone cells to adhere more firmly. Depending on the printing direction and parameters, directional patterns may be visible, guiding cellular orientation and spreading, which is beneficial for organized tissue growth. At 2000× magnification, nanoscale roughness can be observed, which provides additional anchoring points for cells and proteins. These tiny irregularities help in the initial cell adhesion processes by increasing the contact points between the cell membrane and the implant surface. The presence of an interconnected porous network allows for better nutrient and waste exchange, facilitating cellular metabolism and promoting a healthy environment for cell proliferation. Titanium also has a surface chemistry characterized by an oxide layer. Titanium naturally forms a thin oxide layer on its surface, which is visible under SEM as a uniform coating ©. This oxide layer enhances biocompatibility and supports protein adsorption, which is critical for cell adhesion. The surface energy of the titanium beams is influenced by their micro-texture and chemistry, making them more hydrophilic. This hydrophilicity is beneficial as it improves the wettability of the surface, allowing bodily fluids to spread more easily, enhancing protein adsorption, and facilitating cell attachment. Occasionally, small particles of unmelted or partially melted titanium powder might be adhered to the surface. These particles can provide additional micro- and nano-scale topographical features that aid in cellular attachment. (d–f) MSC differentiation and morphology are dependent on the surface topography of the device. An in-vitro analysis of cellular differentiation based on surface roughness and coating was performed with fluorescence microscopy images of MSCs cultured on 3D titanium scaffolds for 5 days. Cells were stained with F-actin (red) and nuclei with DAPI (blue) revealing a favorable response of primary mesenchymal stem cells to the 3D architecture of the printed titanium scaffolds eliciting an osteogenic response with different surface treatments.
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Figure 5.
The figure shows the workflow for creating personalized surgical plans and implants. This begins with patient imaging (a), such as CT scans and other modalities, which is critical for creating personalized surgical plans and patient-specific implants and instruments. The imaging data is digitally transmitted via a HIPAA-compliant secure portal to the manufacturer. Utilizing this data, along with surgeon inputs and preferences, the manufacturer segments the imaging data using advanced digital technologies, generating personalized surgical plans and implant designs (b). The 3D data, representing the bony anatomy, is used to create 3D geometry, which is then converted into 3D CAD models for implant design (c). Upon surgeon approval of the surgical plan and device design, the manufacturer uses proprietary processes and printing technology to produce the 3D-printed implant. The implants are sterile-packaged in-house for a short and easily manageable chain of custody and delivered to the healthcare facility in time for surgery. This streamlined “just-in-time” process reduces the timeline to five days compared to the typical six to eight weeks. Finally, the patient receives their personalized, patient-specific implant(s), facilitating a customized recovery process.
Figure 5.
The figure shows the workflow for creating personalized surgical plans and implants. This begins with patient imaging (a), such as CT scans and other modalities, which is critical for creating personalized surgical plans and patient-specific implants and instruments. The imaging data is digitally transmitted via a HIPAA-compliant secure portal to the manufacturer. Utilizing this data, along with surgeon inputs and preferences, the manufacturer segments the imaging data using advanced digital technologies, generating personalized surgical plans and implant designs (b). The 3D data, representing the bony anatomy, is used to create 3D geometry, which is then converted into 3D CAD models for implant design (c). Upon surgeon approval of the surgical plan and device design, the manufacturer uses proprietary processes and printing technology to produce the 3D-printed implant. The implants are sterile-packaged in-house for a short and easily manageable chain of custody and delivered to the healthcare facility in time for surgery. This streamlined “just-in-time” process reduces the timeline to five days compared to the typical six to eight weeks. Finally, the patient receives their personalized, patient-specific implant(s), facilitating a customized recovery process.
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Figure 6.
Various clinical applications of 3D-printed custom titanium cages are shown, supported by intraoperative fluoroscopy images. The examples showcase the versatility and effectiveness of these implants in different spinal surgeries: (a) three-level anterior cervical discectomy and fusion (ACDF), (b) multilevel cervical corpectomy stabilized with a buttress plate and posterior supplemental fixation, (c) hybrid cervical corpectomy with ACDF stabilized with a buttress plate, (d) lateral lumbar cages placed through a retroperitoneal approach, and (e) a single-level ACDF. These intraoperative fluoroscopy images highlight the diverse clinical applications of 3D-printed custom titanium cages, showcasing their adaptability and effectiveness in various spinal surgical scenarios.
Figure 6.
Various clinical applications of 3D-printed custom titanium cages are shown, supported by intraoperative fluoroscopy images. The examples showcase the versatility and effectiveness of these implants in different spinal surgeries: (a) three-level anterior cervical discectomy and fusion (ACDF), (b) multilevel cervical corpectomy stabilized with a buttress plate and posterior supplemental fixation, (c) hybrid cervical corpectomy with ACDF stabilized with a buttress plate, (d) lateral lumbar cages placed through a retroperitoneal approach, and (e) a single-level ACDF. These intraoperative fluoroscopy images highlight the diverse clinical applications of 3D-printed custom titanium cages, showcasing their adaptability and effectiveness in various spinal surgical scenarios.
Table 1.
Inclusion and Exclusion Criteria employed in the literature search.
Table 1.
Inclusion and Exclusion Criteria employed in the literature search.
Inclusion Criteria | Exclusion Criteria |
---|
3D-printed titanium interbody spinal fusion cages Personalized spine care 3D-printing technology Titanium implants Intervertebral stability Bone growth promotion Spinal alignment restoration Patient-specific clinical application Osteoinductive and osteoconductive properties Customizable geometry Porosity enhancement Osteointegration Mechanical compatibility Cervical and lumbar spine implants Load-bearing requirements Biomechanical properties Cell attachment Surgical precision and outcomes
| Non-3D-printed implants Non-titanium materials Non-customized spinal fusion cages Generalized or non-personalized treatments Non-specific spinal surgeries Non-advanced manufacturing techniques Traditional manufacturing processes Non-osteoconductive or non-osteoinductive materials Clinical outcomes without reference to 3D-printed titanium Non-spinal applications of 3D printing
|
Table 2.
Key Steps and Characteristics of 3D-Printing Processes via Selective Laser Melting (SLM) and Electron Beam Melting (EBM).
Table 2.
Key Steps and Characteristics of 3D-Printing Processes via Selective Laser Melting (SLM) and Electron Beam Melting (EBM).
Aspect | Selective Laser Melting (SLM) | Electron Beam Melting (EBM) |
---|
Energy Source | High-power laser (usually fiber laser) | High-energy electron beam |
Operating Environment | Inert gas atmosphere (usually argon or nitrogen) | High vacuum |
Powder Material | Metal powder (e.g., titanium, aluminum, steel) | Metal powder (e.g., titanium, cobalt-chrome, nickel alloys) |
Typical Voltage | Not applicable | 60 kV to 150 kV |
Layer Construction | Layer-by-layer melting and solidification with laser | Layer-by-layer melting and solidification with electron beam |
Beam Focus and Control | Optical lenses for focusing and galvanometers for scanning | Electromagnetic lenses for focusing and scanning |
Scanning Speed | High, due to the rapid movement of the laser beam | Generally lower than SLM, dependent on electron beam control |
Resolution | High, with fine feature capability | High, but slightly less than SLM due to beam spread |
Surface Finish | Generally smoother, may still require post-processing | Rougher, often requires post-processing |
Build Rate | Moderate to high, depending on laser power and scan strategy | Generally high, due to the high energy density of the electron beam |
Material Properties | Excellent mechanical properties; can vary with process parameters | Excellent mechanical properties; very consistent |
Typical Applications | Aerospace, medical implants, automotive | Aerospace, medical implants, industrial components |
Complexity of Machine | High, requires precise calibration and control | High, requires a vacuum environment and electron beam control |
Cost | High, both in terms of equipment and operating costs | High, both in terms of equipment and operating costs |
Post-Processing Requirements | May include heat treatment, surface finishing, and removal of support structures | May include heat treatment, surface finishing, and removal of support structures |
Powder Recycling | Possible, with careful handling to avoid contamination | Possible, often easier due to the vacuum environment |
Build Volume | Limited by machine size, but generally available in various sizes | Limited by machine size, but available in various sizes |
Table 3.
Key factors affecting cell attachment, proliferation, and differentiation of MSCs on titanium surfaces with various micro- and nano-scale features.
Table 3.
Key factors affecting cell attachment, proliferation, and differentiation of MSCs on titanium surfaces with various micro- and nano-scale features.
Factors | Description |
---|
Surface Roughness | Irregular and textured surface with a mix of peaks and valleys, ridges, and grooves from the layer-by-layer additive manufacturing process. |
Micro-Texturing | Crucial for promoting attachment, proliferation, and differentiation of bone-forming cells. Creates a conducive environment for osteoblasts and other bone cells to adhere more firmly. |
Micro-Pores | Typically in the range of a few micrometers. Increase surface area and provide additional sites for cellular attachment and ingrowth. |
Printing Direction and Parameters | Directional patterns may be visible, guiding cellular orientation and spreading, which is beneficial for organized tissue growth. |
Nanoscale Roughness (2000× magnification) | Observed nanoscale roughness provides additional anchoring points for cells and proteins, enhancing initial cell adhesion by increasing contact points between the cell membrane and implant surface. |
Interconnected Porous Network | Allows for better nutrient and waste exchange, facilitating cellular metabolism, and promoting a healthy environment for cell proliferation. |
Titanium Surface Chemistry | Characterized by a naturally forming thin oxide layer, visible under SEM as a uniform coating. Enhances biocompatibility and supports protein adsorption, critical for cell adhesion. |
Surface Energy and Hydrophilicity | Influenced by micro-texture and chemistry, making titanium is more hydrophilic. Improves wettability, allowing bodily fluids to spread more easily, enhancing protein adsorption, and facilitating cell attachment. |
Small Particles of Titanium Powder | Occasionally present, providing additional micro- and nano-scale topographical features that aid in cellular attachment. |
MSC Differentiation and Morphology | Dependent on the surface topography of the device. In-vitro analysis at 5 days shows smooth titanium directs MSC differentiation into fibroblast-like cells, whereas rough surfaces promote osteocyte-like differentiation. |
Table 4.
3D-Printing applications in spine surgery.
Table 4.
3D-Printing applications in spine surgery.
Area | Study | Summary |
---|
Oncology | Xiao et al. [126] (2016) | Valuable for pre-operative planning; helps visualize tumor burden and surrounding anatomy |
Xu et al. [129] (2016) | Performed vertebral body replacement after C2 Ewing sarcoma surgery; no complications. |
Kim et al. [131] (2017) | Created a hemi-sacrum post-sacral osteosarcoma resection; no complications; improved symptoms. |
Wei et al. [128] (2017) | Used a sacral replacement prosthesis after sacral chordoma resection; observed asymptomatic instrumental failure and bone-prosthesis ingrowth. |
Choy et al. [132] (2017) | Employed an axial vertebral body device with fixation holes and angled endplates for a T9 primary bone tumor; restored sagittal balance; improved symptoms. |
Li et al. [130] (2017) | Reconstructed multilevel C2–C4 vertebral body after metastatic papillary thyroid carcinoma resection with a self-stabilizing implant; no subsidence at 1 year. |
Mobbs et al. [133] (2017) | Addressed C1/2 chordoma and congenital L5 hemivertebra with occipito-cervical fixation and hemivertebra prosthesis; no imaging abnormalities at 9 and 12 months, despite prolonged operation time. |
Chin et al. [134] (2019) | Achieved posterior instrumentation fixation and osseointegration after en bloc spondylectomy for L1–L3 recurrent giant cell tumor using 3D reconstruction. |
Ahmed et al. [127] (2019) | Referenced 3D models intraoperatively for better tumor visualization and lesion irregularities, minimizing morbidity and achieving negative margins. |
Congenital | Yang et al. [135] (2015) | 3D technology reduced operative time, blood loss, and transfusion volume without affecting LOS, complication rate, screw misalignment, or radiographic outcome; significantly reduced screw misplacement in patients with Cobb angle > 50 degrees (p = 0.02). |
Tu et al. [136] (2019) | Software-aided correction achieved 94% accuracy in screw placement without neurovascular complications. |
Degenerative/Decompression/Fusion | Rosenzweig et al. [137] (2015) | In vitro experiments showed successful culturing of primary articular chondrocytes and nucleus pulposus cells on 3D-printed ABS and PLA scaffolds for osseointegration. |
Lu et al. [138] (2017) | 3D-printed titanium fusion cage used for anterior cervical corpectomy and fusion in 15 patients with cervical spondylotic myelopathy and OPLL; all patients experienced solid interbody fusion and symptom relief. |
Siu et al. [139] (2018) | Customized cages for lumbar radiculopathy and osteoporosis led to symptom resolution at 6 months and CT-confirmed fusion. |
Thayaparan et al. [140] (2018) | Patient-specific titanium atlantoaxial screws demonstrated successful placement and fixation with no neurological issues or implant failures at a 12-month follow-up. |
Ling et al. [123] (2018) | 3D-printed models aided pre-operative planning of “V”-shaped decompressive laminoplasty for multilevel ossification of the ligamentum flavum; successful decompression. |
Choy et al. [141] (2018) | Successful anterior cervical decompression and multi-level fusion with patient-specific 3D-printed titanium implants in complex deformities. |
Mokawem et al. [142] (2019) | Transforaminal or lateral lumbar interbody fusion with silicate-substituted calcium phosphate-packed 3D-printed lamellar titanium cages showed 98.9% fusion success and significantly improved patient outcomes. |
Mobbs et al. [122] (2019) | 3D-printed technology in anterior lumbar interbody fusion provided excellent fit, improved pre-operative planning, restored lumbar lordosis, and reduced operative time, leading to clinical improvement. |
Malone et al. [109] (2022) | 136 levels in 90 patients. The use of bioactive titanium interbody devices with a large surface footprint results in a high fusion rate despite the use of a small volume of low-cost biological material to lower the economic burden inherent to spinal fusion. 3D-pTi interbody cages without bone grafts outperform PEEK interbody cages with grafts. |
Topps et al. [143] (2023) | 90 solid titanium (ST) from 74 patients, and 73 3D-printed (3DPT) interbody levels from 50 patients. both ST and 3DPT cages performed well; however, 3DPT cages were associated with lower rates of subsidence. |
Ham et al. [11] (2023) | 31 consecutive patients who underwent single-level posterior lumbar interbody fusion surgery with two 3D-Ti cages with different designs were inserted: a non-window cage on the left side and a window cage on the right side. Using a non-window 3D-Ti cage during lumbar interbody fusion might be acceptable. |
Duan et al. [13] (2024) | Systematic review reporting 9 studies comparing lumbar interbody fusion with 3D-PPT cages versus PEEK cages for lumbar degenerative disease. Compared to the PEEK cage, the 3DPT cage showed a higher fusion and lower subsidence rate. The 3DPT cage may accelerate fusion, and prevent subsidence. |
Table 5.
Quality Systems (QS) regulations for PoC 3D printing centers.
Table 5.
Quality Systems (QS) regulations for PoC 3D printing centers.
QS-Task | Description |
---|
Process Control [170] | Document 3D printer system parameters, such as calibration, maintenance, and environmental conditions. Implement FDA’s cybersecurity guidance if patient data is transferred during the workflow [177] |
Imaging Quality [170,178] | Ensure imaging used for modeling devices has sufficient resolution, capturing the smallest anatomy of interest on at least three sequential DICOM images. |
Material Documentation [170] | Record chemical names, suppliers, and certificates of analysis for all raw materials, additives, and processing aids. Document the material reuse process to ensure it does not affect device performance. |
Support Structures [170] | Detail the use and removal of support structures to ensure they do not negatively impact the final product. |
Layering and Meshing [170,178] | Optimize layer thickness for the device’s intended use, ensuring the smallest area of interest is captured on at least three consecutive layers. Document the mesh details of 3D model files to maintain accuracy. |
Build Paths | Document the build path and its potential consequences, including fill density and the status of internal voids. |
Post-Processing [170,178] | Ensure post-processing steps enhance utility without affecting the device’s intended use or accuracy. Document all post-processing steps and their impact on material properties. |
Sterilization [179] | Adhere to ISO standards for sterility and biocompatibility. Document sterility processes and validate that they are compatible with the materials used. |
Biocompatibility [179] | Test for biocompatibility of raw materials and the final sterilized product, especially if toxic chemical additives are used. Ensure validation studies for patient-specific cutting guides and implants. |
Table 6.
Best practice recommendations for PoC 3D printing centers.
Table 6.
Best practice recommendations for PoC 3D printing centers.
Task | Considerations |
---|
Internal Regulation [180] | PoC centers should create a Quality Systems (QS) regulations document, detailing training, processes, parameters, and maintenance protocols. QS regulations should align with FDA standards under 21CFR820, even if Premarket Notification or Approval is not required. |
FDA-Cleared Software | Use FDA-cleared and locally validated segmentation and CAD software for creating patient-specific diagnostic anatomic models. The software should meet FDA clearance for the intended indications. |
Accurate Segmentation | Ensure that a radiologist and the ordering physician review and approve the segmentation for 3D-printed models. Document the training and qualifications of all segmentation personnel, including radiology technologists and industrial designers. For oncologic cases, a trained oncologist should segment tumor margins. |
Validated Manufacturing Processes | Establish internal regulation processes, including installation qualification (IQ), operating qualification (OQ), and performance qualification (PQ). Document training for all personnel to ensure proper operation and up-to-date skills. |
Biocompatibility Testing [178] | Devices used in sterile fields must undergo ISO 10993 [181] biocompatibility testing. Due to the complexity and cost, consider outsourcing these validation studies unless the institution has an accredited facility. |
Legal Considerations | Engage with the institution’s legal team to discuss risks and liabilities associated with PoC 3D printing, especially when manufacturing devices previously purchased externally. This increases the hospital’s liability as the legal manufacturer if the implant is printed at the PoC. |