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ABSTRACT BACKGROUND Spinal instrumentation can be associated with complications, including implant loosening. Hitherto, implant loosening has mainly been attributed to mechanical overload. OBJECTIVE To examine the role of low-grade infections as the cause of implant failure in suspected aseptic implant loosening following spinal instrumentation. METHODS A prospective single center observational study was performed. All patients who had revision surgery following spinal instrumentation between August 2015 and February 2018 were screened. Patients with revision surgery due to screw loosening on the computed tomograhy scan constituted the study group. Patients in which the screws where not loosened but removal was performed for other reasons formed the comparison group. Intraoperative swabs were taken and sonication was performed with the explanted material. Results of microbiological cultivation were analyzed. RESULTS A total of 59 patients were included in the study group and 34 in the comparison group. In the study group in 42.4% of the cultures a bacterium was detected, while in the comparison group only in 17.6%. 84%, and 83.3% of these germs were detected by sonication in the study and comparison group, respectively. The rate of positive cultures was significantly higher in the study group compared to the comparison group (P = .001). The most frequent bacterium cultivated in both groups was Propionibacterium acnes, followed by Staphylococcus species. CONCLUSION For patients with screw loosening a high level of suspicion for a low-grade infection should be raised. Cultures should be performed from the sonication fluid of the explanted devices in all patients with symptomatic screw loosening. Graphical Abstract Graphical Abstract

Intervertebral cages made of Ti6Al4V alloy show excellent osteoconductivity, but also higher stiffness, compared to commonly used polyether-ether-ketone (PEEK) materials, that may lead to a stress-shielding effect and implant subsidence. In this study, a metallic intervertebral fusion cage, with improved mechanical behavior, was manufactured by the introduction of a three-dimensional (3D) mesh structure to Ti6Al4V material, using an additive manufacturing method. Then, the mechanical and biological properties of the following were compared: (1) PEEK, with a solid structure, (2) 3D-printed Ti6Al4V, with a solid structure, and (3) 3D-printed Ti6Al4V, with a mesh structure. A load-induced subsidence test demonstrated that the 3D-printed mesh Ti6Al4V cage had significantly lower tendency (by 15%) to subside compared to the PEEK implant. Biological assessment of the samples proved that all tested materials were biocompatible. However, both titanium samples (solid and mesh) were characterized by significantly higher bioactivity, osteoconductivity, and mineralization ability, compared to PEEK. Moreover, osteoblasts revealed stronger adhesion to the surface of the Ti6Al4V samples compared to PEEK material. Thus, it was clearly shown that the 3D-printed mesh Ti6Al4V cage possesses all the features for optimal spinal implant, since it carries low risk of implant subsidence and provides good osseointegration at the bone-implant interface.

Background Implant‐associated infection remains a serious complication of instrumented spinal surgery. Since biofilm formation on the implant surface is a key factor in the pathogenesis of such infections, current preventive strategies include the use of implants with antibiotic coatings. However, these approaches raise concerns related to antibiotic resistance and cytotoxicity. Ultrafine‐grained (UFG) stainless steel, characterized by nanoscale grain sizes, has demonstrated superior mechanical properties and potential antimicrobial effects. This study aimed to evaluate the antibacterial properties of UFG stainless steel implants against Staphylococcus aureus biofilm formation in both in vitro and in vivo models. Methods UFG and conventional SUS316L stainless steel wires were incubated with bioluminescent Staphylococcus aureus Xen36 for up to 7 days in vitro. Biofilm formation was assessed using crystal violet (CV) staining, colony‐forming unit (CFU) counting, and quantitative PCR (qPCR) for 16S rRNA and luxA genes. In vivo antibacterial effects were evaluated using two mouse models: a subcutaneous pouch model and a postoperative spinal implant infection model. Wires were harvested at 1, 3, and 7 days post‐infection and analyzed using the same assays. Results In vitro, UFG wires had significantly lower CFU counts than standard wires at 4 h (p = 0.0005), 1 day (p = 0.0001), and 3 days (p = 0.0314). In the subcutaneous pouch model, UFG wires showed significantly reduced bacterial load at Day 1 by CFU (p = 0.011). In the spinal implant model, CFU counts were significantly lower on UFG wires at Day 3 (p = 0.015). Conclusions UFG stainless steel implants demonstrated a significant reduction in early biofilm formation by Staphylococcus aureus in both in vitro and in vivo, suggesting a delay in the biofilm formation process. These findings support the potential of UFG materials as promising candidates for infection‐resistant spinal implants. This is the first in vivo study to demonstrate that ultrafine‐grained stainless steel possesses potential antibacterial properties capable of resisting the adhesion of bacteria and, subsequently, microcolony formation and biofilm maturation. Incorporating ultrafine‐grained materials in the manufacture of orthopedic implants or medical devices could uniquely balance antibacterial properties with biocompatibility, making them highly suitable for these applications.

Background Throughout the last years, carbon‐fibre‐reinforced PEEK (CFP) pedicle screw systems were introduced to replace standard titanium alloy (Ti) implants for spinal instrumentation, promising improved radiotherapy (RT) treatment planning accuracy. We compared the dosimetric impact of both implants for intensity modulated proton (IMPT) and volumetric arc photon therapy (VMAT), with the focus on uncertainties in Hounsfield unit assignment of titanium alloy. Methods Retrospective planning was performed on CT data of five patients with Ti and five with CFP implants. Carbon‐fibre‐reinforced PEEK systems comprised radiolucent pedicle screws with thin titanium‐coated regions and titanium tulips. For each patient, one IMPT and one VMAT plan were generated with a nominal relative stopping power (SP) (IMPT) and electron density (ρ) (VMAT) and recalculated onto the identical CT with increased and decreased SP or ρ by ±6% for the titanium components. Results Recalculated VMAT dose distributions hardly deviated from the nominal plans for both screw types. IMPT plans resulted in more heterogeneous target coverage, measured by the standard deviation σ inside the target, which increased on average by 7.6 ± 2.3% (Ti) vs 3.4 ± 1.2% (CFP). Larger SPs lead to lower target minimum doses, lower SPs to higher dose maxima, with a more pronounced effect for Ti screws. Conclusions While VMAT plans showed no relevant difference in dosimetric quality between both screw types, IMPT plans demonstrated the benefit of CFP screws through a smaller dosimetric impact of CT‐value uncertainties compared to Ti. Reducing metal components in implants will therefore improve dose calculation accuracy and lower the risk for tumor underdosage.

Radiation therapy, in conjunction with surgical implant fixation, is a common combined treatment in cases of bone metastases. However, metal implants generally used in orthopedic implants perturb radiation dose distributions. Carbon‐Fiber Reinforced Polyetheretherketone (CFR‐PEEK) material has been recently introduced for production of intramedullary nails and plates. The purpose of this work was to investigate the perturbation effects of the new CFR‐PEEK screws on radiotherapy dose distributions and to evaluate these effects in comparison with traditional titanium screws. The investigation was performed by means of Monte Carlo (MC) simulations for a 6 MV photon beam. The project consisted of two main stages. First, a comparison of measured and MC calculated doses was performed to verify the validity of the MC simulation results for different materials. For this purpose, stainless steel, titanium, and CFR‐PEEK plates of various thicknesses were used for attenuation and backscatter measurements in a solid water phantom. For the same setup, MC dose calculations were performed. Next, MC dose calculations for titanium, CFR‐PEEK screws, and CFR‐PEEK screws with ultrathin titanium coating were performed. For the plates, the results of our MC calculations for all materials were found to be in good agreement with the measurements. This indicates that the MC model can be used for calculation of dose perturbation effects caused by the screws. For the CFR‐PEEK screws, the maximum dose perturbation was less than 5%, compared to more than 30% perturbation for the titanium screws. Ultrathin titanium coating had a negligible effect on the dose distribution. CFR‐PEEK implants have good prospects for use in radiotherapy because of minimal dose alteration and the potential for more accurate treatment planning. This could favorably influence treatment efficiency and decrease possible over‐ and underdose of adjacent tissues. The use of such implants has potential clinical advantages in the treatment of bone metastases.

In order to meet the clinical requirements of spine surgery, this paper proposed the exploratory research of computer-aided design and selective laser melting (SLM) fabrication of a bionic porous titanium spine implant. The structural design of the spinal implant is based on CT scanning data to ensure correct matching, and the mechanical properties of the implant are verified by simulation analysis and laser selective melting experiment. The surface roughness of the spinal implant manufactured by SLM without post-processing is Ra 15 μm, and the implant is precisely jointed with the photosensitive resin model of the upper and lower spine. The surface micro-hardness of the implant is HV 373, tensile strength σb = 1238.7 MPa, yield strength σ0.2 = 1043.9 MPa, the elongation is 6.43%, and the compressive strength of porous structure under 84.60% porosity is 184.09 MPa, which can meet the requirements of the reconstruction of stable spines. Compared with the traditional implant and intervertebral fusion cage, the bionic porous spinal implant has the advantages of accuratefit, porous bionic structure and recovery of patients, and the ion release experiment proved that implants manufactured by SLM are more suitable for clinical application after certain treatments. The elastic modulus of the sample is improved after heat treatment, mainly because the microstructure of the sample changes from α' phase to α + β dual-phase after heat treatment. In addition, the design of high-quality bionic porous spinal implants still needs to be optimized for the actual needs of doctors.

Purpose of Review In this article, we review the most recent advancements in the approaches to EOS diagnosis and assessment, surgical indications and options, and basic science innovation in the space of early-onset scoliosis research. Recent Findings Early-onset scoliosis (EOS) covers a diverse, heterogeneous range of spinal and chest wall deformities that affect children under 10 years old. Recent efforts have sought to examine the validity and reliability of a recently developed classification system to better standardize the presentation of EOS. There has also been focused attention on developing safer, informative, and readily available imaging and clinical assessment tools, from reduced micro-dose radiographs, quantitative dynamic MRIs, and pulmonary function tests. Basic science innovation in EOS has centered on developing large animal models capable of replicating scoliotic deformity to better evaluate corrective technologies. And given the increased variety in approaches to managing EOS in recent years, there exist few clear guidelines around surgical indications across EOS etiologies. Despite this, over the past two decades, there has been a considerable shift in the spinal implant landscape toward growth-friendly instrumentation, particularly the utilization of MCGR implants. Summary With the advent of new biological and basic science treatments and therapies extending survivorship for disease etiologies associated with EOS, the treatment for EOS has steadily evolved in recent years. With this has come a rising volume and variation in management options for EOS, as well as the need for multidisciplinary and creative approaches to treating patients with these complex and heterogeneous disorders.

Study design Technical note and case series. Objectives 3D-printed implants (3DPI) for spinal surgery are a relatively recent development. We report on our experience with the rapid creation and regulatory approval of patient-specific 3DPI for use in complex spinal reconstruction, including a novel expedited turnaround time for implant creation. Methods Four patients underwent placement of 3DPI to replace osseous anatomy during complex spinal reconstructions. These implants were created and used to replace patient-specific anatomy created by either en bloc tumor resection or by severe neurogenic spinal arthropathy. The surgical planning, implant creation, and postoperative outcomes are outlined. Results All patients underwent successful implantation of 3DPI, which was confirmed on postoperative imaging at most recent follow-up. The time to plan, create, obtain regulatory approval, and use the first 3DPI was 28 days. Subsequent 3DPI could be planned, approved, and used in surgery in as little as 4-5 days, which is faster than previously-published reports. Thus, a 3DPI could be generated based on osseous defects created during stage 1 of a multistage surgical plan and implanted during a subsequent stage in an especially expedited manner. Conclusions 3DPI may be used to effectively replace patient-specific anatomy during complex spinal reconstructions, including for osseous defects that are generated after the initial surgical procedure. These 3DPI may be created, approved, and used in surgery over much faster timelines than have been previously reported. Additional cases utilizing these custom 3DPI will further elucidate their utility during complex reconstructions.

In recent years, the field of 3D printing technology has experienced rapid advancements, notably expanding its application within the medical sector. This study focuses on the custom design of 3D-printed spinal implants, specifically examining porous interbody fusion products. It integrates considerations of mechanical strength and bone ingrowth to establish a finite element model of porous interbody fusion, subsequently conducting topology optimization to design three distinct types of spinal interbody fusion implants. Analytical investigations were carried out on the stress and displacement responses of these three implant types under compressive loading. Furthermore, a detailed stress analysis was conducted on implants varying in porosity, length, and screw angle of the bone graft to assess the performance characteristics of the porous interbody fusion devices. Results indicated that the Type C implant exhibited superior performance, demonstrating a stress reduction to 89.21 MPa and a displacement change of 0.006 mm, optimally at a 60% porosity level. Adjustments in the lengths and screw clamp angles of the splint ensured that the maximal stress experienced by each vertebra remained below the yield limits of both cortical and cancellous bone, thus preventing vertebral damage. This paper presents a comparative analysis of three types of porous interbody fusion devices, providing substantial data support and a theoretical framework that can inform the future development of fusion products.

Bacterial biofilms on orthopedic implants are resistant to the host immune response and to traditional systemic antibiotics. Novel therapies are needed to improve patient outcomes. TRL1068 is a human monoclonal antibody (mAb) against a biofilm anchoring protein. For assessment of this agent in an orthopedic implant infection model, efficacy was measured by reduction in bacterial burden of Staphylococcus aureus, the most common pathogen for prosthetic joint infections (PJI). Systemic treatment with the biofilm disrupting mAb TRL1068 in conjunction with vancomycin eradicated S. aureus from steel pins implanted in the spine for 26 of 27 mice, significantly more than for vancomycin alone. The mechanism of action was elucidated by two microscopy studies. First, TRL1068 was localized to biofilm using a fluorescent antibody tag. Second, a qualitative effect on biofilm structure was observed using scanning electron microscopy (SEM) to examine steel pins that had been treated in vivo. SEM images of implants retrieved from control mice showed abundant three-dimensional biofilms, whereas those from mice treated with TRL1068 did not. Clinical Significance: TRL1068 binds at high affinity to S. aureus biofilms, thereby disrupting the three-dimensional structure and significantly reducing implant CFUs in a well-characterized orthopedic model for which prior tested agents have shown only partial efficacy. TRL1068 represents a promising systemic treatment for orthopedic implant infection.