Purpose: The objective of this systematic review is to present a comprehensive summary of existing research on the use of 3D printing in spinal surgery. Methods: The researchers conducted a thorough search of four digital databases (PubMed, Web of Science, Scopus, and Embase) to identify relevant studies published between January 1999 and December 2022. The review focused on various aspects, including the types of objects printed, clinical applications, clinical outcomes, time and cost considerations, 3D printing materials, location of 3D printing, and technologies utilized. Out of the 1620 studies initially identified and the 17 added by manual search, 105 met the inclusion criteria for this review, collectively involving 2088 patients whose surgeries involved 3D printed objects. Results: The studies presented a variety of 3D printed devices, such as anatomical models, intraoperative navigational templates, and customized implants. The most widely used type of objects are drill guides (53%) and anatomical models (25%) which can also be used for simulating the surgery. Custom made implants are much less frequently used (16% of papers). These devices significantly improved clinical outcomes, particularly enhancing the accuracy of pedicle screw placement. Most studies (88%) reported reduced operation times, although two noted longer times due to procedural complexities. A variety of 3DP technologies and materials were used, with STL, FDM, and SLS common for models and guides, and titanium for implants via EBM, SLM, and DMLS. Materialise software (Mimics, 3-Matic, Magics) was frequently utilized. While most studies mentioned outsourced production, in-house printing was implied in several cases, indicating a trend towards localized 3D printing in spine surgery. Conclusions: 3D printing in spine surgery, a rapidly growing area of research, is predominantly used for creating drill guides for screw insertion, anatomical models, and innovative implants, enhancing clinical outcomes and reducing operative time. While cost-efficiency remains uncertain due to insufficient data, some 3D printing applications, like pedicle screw drill guides, are already widely accepted and routinely used in hospitals.

Finite element (FE) analyses contribute to a better understanding of the human lumbar spine’s biomechanics and serve as an effective predictive tool. This study aims to present the development of two L1–L5 FE models using literature-based (LBM) and patient-specific (PSM) bone material assignment approaches. The geometry of the lumbar spine was developed based on quantitative computed tomography scans. The LBM and the PSM were compared under pure and combined loads. Various biomechanical parameters were investigated to validate the models. The total range of motion of the LBM in pure flexion-extension, lateral bending, and axial rotation were 30.9°, 29°, and 13.7°, respectively, while for the PSM, it was 31.6°, 28.6°, and 14.1°. The required computational time of the PSM to complete against pure and combined loads were 12.1 and 16.6 times higher on average compared to the LBM. This study demonstrated that both models agree with experimental and in silico results, although the cumulative distribution of the stress and characterization of strain values showed a noteworthy difference between the two models. Based on these findings, the clinically-focused biomechanical FE studies must perceive the differences in internal mechanical parameters and computational demand between the different bone modelling approaches.

Oblique lumbar interbody fusion (OLIF) can provide an ideal minimally invasive solution for achieving spinal fusion in an older, more frail population where decreased bone quality can be a limiting factor. Stabilization can be achieved with bilateral pedicle screws (BPS), which require additional incisions and longer operative time. Alternatively, a novel self-anchoring stand-alone lateral plate system (SSA) can be used, where no additional incisions are required. Based on the relevant literature, BPS constructs provide greater primary biomechanical stability compared to lateral plate constructs, including SSA. This difference is further increased by osteoporosis. Screw augmentation in spinal fusion surgeries is commonly used; however, in the case of OLIF, it is a fairly new concept, lacking a consensus-based guideline. This comparative finite element (FE) study aimed to investigate the effect of PMMA screw augmentation on the primary stability of a stand-alone implant construct versus posterior stabilization in OLIF with osteoporotic bone quality. The biomechanical effect of screw augmentation was studied inside an in-silico environment using computer-aided FE analysis. A previously validated and published L2-L4 FE model with normal and osteoporotic bone material properties was used. Geometries based on the OLIF implants (BPS, SSA) were created and placed inside the L3-L4 motion segment with increasing volumes (1-6 cm³) of PMMA augmentation. A follower load of 400 N and 10 Nm bending moment (in the three anatomical planes) were applied to the surgical FE models with different bone material properties. The operated L3-L4 segmental range of motion (ROM), the inserted cage's maximal caudal displacements, and L4 cranial bony endplate principal stress values were measured. The nonaugmented values for the BPS construct were generally lower compared to SSA, and the difference was increased by osteoporosis. In osteoporotic bone, PMMA augmentation gradually decreased the investigated parameters and the difference between the two constructs as well. Between 3 cm³ and 4 cm³ of injected PMMA volume per screw, the difference between augmented SSA and standard BPS became comparable. Based on this study, augmentation can enhance the primary stability of the constructs and decrease the difference between them. Considering leakage as a possible complication, between 3 cm³ and 4 cm³ of injected PMMA per screw can be an adequate amount for SSA augmentation. However, further in silico, and possibly in vitro and clinical testing is required to thoroughly understand the investigated biomechanical aspects. This study sheds light on the possible biomechanical advantage offered by augmented OLIF implants and provides a theoretical augmentation amount for the SSA construct. Based on the findings, the concept of an SSA device with PMMA augmentation capability is desirable.

To evaluate and compare the biomechanical efficacy of six iliosacral screw fixation techniques for treating unilateral AO Type B2 (Denis Type II) sacral fractures using literature-based and QCT-based bone material properties in finite element (FE) models. Two FE models of the intact pelvis were constructed: the literature-based model (LBM) with bone material properties taken from the literature, and the patient-specific model (PSM) with QCT-derived bone material properties. Unilateral transforaminal sacral fracture was modelled to assess different fixation techniques: iliosacral screw (ISS) at the first sacral vertebra (S1) (ISS1), ISS at the second sacral vertebra (S2) (ISS2), ISS at S1 and S2 (ISS12), transverse iliosacral screws (TISS) at S1 (TISS1), TISS at S2 (TISS2), and TISS at S1 and S2 (TISS12). A 600 N vertical load with both acetabula fixed was applied. Vertical stiffness (VS), relative interfragmentary displacement (RID), and the von Mises stress values in the screws and fracture interface were analysed. The lowest and highest normalised VS was given by ISS1 and TISS12 techniques for LBM and PSM, with 137 % and 149 %, and 375 % and 472 %, respectively. In comparison with the LBM, the patient-specific bone modelling increased the maximum screw stress values by 19.3, 16.3, 27.8, 2.3, 24.4 and 7.8 % for ISS1, ISS2, ISS12, TISS1, TISS2 and TISS12, respectively. The maximum RID values were between 0.10 mm and 0.47 mm for all fixation techniques in both models. The maximum von Mises stress results on the fracture interface show a substantial difference between the two models, as PSM (mean ± SD of 15.76 ± 8.26 MPa) gave lower stress values for all fixation techniques than LBM (mean ± SD of 28.95 ± 6.91 MPa). The differences in stress distribution underline the importance of considering locally defined bone material properties when investigating internal mechanical parameters. Based on the results, all techniques demonstrated clinically sufficient stability, with TISS12 being superior from a biomechanical standpoint. Both LBM and PSM models indicated a consistent trend in ranking the fixation techniques based on stability. However, long-term clinical trials are recommended to confirm the findings of the study.

Following total sacrectomy, lumbopelvic reconstruction is essential to restore continuity between the lumbar spine and pelvis. However, to achieve long-term clinical stability, bony fusion between the lumbar spine and the pelvic ring is crucial. Reduction of the lumbopelvic distance can promote successful bony fusion. Although many lumbopelvic reconstruction techniques (LPRTs) have been previously analyzed, the biomechanical effect of lumbopelvic distance reduction (LPDR) has not been investigated yet. To evaluate and compare the biomechanical characteristics of four different LPRTs while considering the effect of LPDR. A comparative finite element (FE) study. The FE models following total sacrectomy were developed to analyze four different LPRTs, with and without LPDR. The closed-loop reconstruction (CLR), the sacral-rod reconstruction (SRR), the four-rod reconstruction (FRR), and the improved compound reconstruction (ICR) techniques were analyzed in flexion, extension, lateral bending, and axial rotation. Lumbopelvic stability was assessed through the shift-down displacement and the relative sagittal rotation of L5, while implant safety was evaluated based on the stress state at the bone-implant interface and within the rods. Regardless of LPDR, both the shift-down displacement and relative sagittal rotation of L5 consistently ranked the LPRTs as ICR<SRR<FRR<CLR, with ICR being the stiffest for both parameters. LPDR decreased the shift-down displacement values by 25% in CLR, by 61% in SRR, by 15% in FRR, and by 46% in ICR, as well as reduced the relative sagittal rotation values by 21% in CLR, by 73% in SRR, by 11% in FRR, and by 53% in ICR. Considering the stress at the bone-implant interface, without LPDR, the ICR yielded the smallest stress values for flexion, lateral bending, and axial rotation with 131.4 MPa, 68.2 MPa, and 70.3 MPa, respectively, and the second smallest in extension with 36.1 MPa. Due to LPDR, these stress values were reduced by 31% in flexion, by 17% in extension, by 29% in lateral bending, and by 29% in axial rotation. Within the rods, without LPDR, the ICR yielded the smallest stress values for flexion, extension, lateral bending, and axial rotation with 346.5 MPa, 108.0 MPa, 186.2 MPa, and 199.7 MPa, respectively. With LPDR, these stress values were reduced by 16% in flexion, by 9% in extension, by 11% in lateral bending, and by 12% in axial rotation. LPDR significantly improved both lumbopelvic stability and implant safety in all reconstruction techniques after total sacrectomy. LPDR reduced the shift-down displacement of L5, the relative sagittal rotation of L5, and the stress values at the bone-implant interface. Furthermore, in the ICR and SRR techniques, LPDR decreased the peak stress values within the rods. All four investigated LPRTs demonstrated suitability for lumbopelvic reconstruction, with the ICR technique exhibiting the highest lumbopelvic stiffness. LPDR creates a biomechanically advantageous environment following total sacrectomy; therefore, it has the potential to impact the design of custom-made 3D-printed or traditional LPRTs. However, to confirm the findings of the current FE study, long-term clinical trials are recommended.

3D printed anatomical models offer new possibilities in operative medicine, especially in planning complex surgical procedures and patient education. However, the use of such models is not yet widespread, and spinal surgeons' attitudes toward their clinical application remain incompletely understood. The aim of the study is to assess spinal surgeons' attitudes towards 3D-printed anatomical models, with a particular focus on their clinical applications. A multicenter questionnaire-based survey was conducted among 41 spine surgeons from 3 major Hungarian spine centers, generating 1476 evaluative data points. Surgeons rated the utility of conventional imaging (X-ray, CT, MRI) and 3D printed models across multiple clinical domains and case scenarios. Overall, 3D printed models were rated significantly higher than traditional imaging, with a median utility score of 10 [IQR: 8-10] versus 8 [IQR: 7-9] (P < 0.001, r = 0.25). The largest benefit was observed in patient education (median 10 vs. 7, P < 0.001) and surgical planning (median 9 vs. 8, P < 0.001). In complex congenital scoliosis with metal artifacts, 3D models significantly outperformed traditional imaging (median 10 vs. 7, P < 0.001), whereas no difference was observed in degenerative lumbar pathology (median 9 vs. 9, P = 0.99). Perceived utility did not differ significantly by specialty, experience level, case complexity workload or prior exposure to 3D printing (all P > 0.05). Spine surgeons in Hungary perceive 3D printed anatomical models as significantly more useful than traditional imaging, particularly for patient education and complex surgical planning. Their perceived value appears driven primarily by case complexity rather than surgeon demographics or prior experience.