Treatment of lumbar discitis using silicon nitride spinal spacers: A case series and literature review

Silicon-containing nanomedicine and biomaterials: materials chemistry, multi-dimensional design, and biomedical application

The invention of silica-based bioactive glass in the late 1960s has sparked significant interest in exploring a wide range of silicon-containing biomaterials from the macroscale to the nanoscale. Over the past few decades, these biomaterials have been extensively explored for their potential in diverse biomedical applications, considering their remarkable bioactivity, excellent biocompatibility, facile surface functionalization, controllable synthesis, etc. However, to expedite the clinical translation and the unexpected utilization of silicon-composed nanomedicine and biomaterials, it is highly desirable to achieve a thorough comprehension of their characteristics and biological effects from an overall perspective. In this review, we provide a comprehensive discussion on the state-of-the-art progress of silicon-composed biomaterials, including their classification, characteristics, fabrication methods, and versatile biomedical applications. Additionally, we highlight the multi-dimensional design of both pure and hybrid silicon-composed nanomedicine and biomaterials and their intrinsic biological effects and interactions with biological systems. Their extensive biomedical applications span from drug delivery and bioimaging to therapeutic interventions and regenerative medicine, showcasing the significance of their rational design and fabrication to meet specific requirements and optimize their theranostic performance. Additionally, we offer insights into the future prospects and potential challenges regarding silicon-composed nanomedicine and biomaterials. By shedding light on these exciting research advances, we aspire to foster further progress in the biomedical field and drive the development of innovative silicon-composed nanomedicine and biomaterials with transformative applications in biomedicine.

Candida spondylodiscitis: a systematic review and meta-analysis of seventy two studies

OBJECTIVES

Knowledge of Candida spondylodiscitis is limited to case reports and smaller case series. Controversy remains on the most effective diagnostical and therapeutical steps once Candida is suspected. This systematic review summarized all cases of Candida spondylodiscitis reported to date concerning baseline demographics, symptoms, treatment, and prognostic factors.

METHODS

A PRISMA-based search of PubMed, Web of Science, Embase, Scopus, and OVID Medline was performed from database inception to November 30, 2022. Reported cases of Candida spondylodiscitis were included regardless of Candida strain or spinal levels involved. Based on these criteria, 656 studies were analyzed and 72 included for analysis. Kaplan-Meier curves, Fisher's exact, and Wilcoxon's rank sum tests were performed.

RESULTS

In total, 89 patients (67% males) treated for Candida spondylodiscitis were included. Median age was 61 years, 23% were immunocompromised, and 15% IV drug users. Median length of antifungal treatment was six months, and fluconazole (68%) most commonly used. Thirteen percent underwent debridement, 34% discectomy with and 21% without additional instrumentation. Median follow-up was 12 months. The two year survivorship free of death was 80%. The two year survivorship free of revision was 94%. Younger age (p = 0.042) and longer length of antifungal treatment (p = 0.061) were predictive of survival.

CONCLUSION

Most patients affected by Candida spondylodiscitis were males in their sixties, with one in four being immunocompromised. While one in five patients died within two years of diagnosis, younger age and prolonged antifungal treatment might play a protective role.

Metastatic spondylodiscitis in central venous catheter related bloodstream infections in hemodialysis patients: Risk factors and prognosis

BACKGROUND

Infection is one of the most common causes of death in hemodialysis patients. Catheter infections are among the most common infections in this patient group. Spondylodiscitis which has a high incidence in ESRD is more commonly encountered in patients with CVCs compared to AVF. In this study, we aimed to evaluate the frequency and risk factors of spondylodiscitis in catheter-related bloodstream infections in hemodialysis patients.

METHODS

In total, 1620 patients were screened and 42 male and 35 female patients with central catheter infection with a mean age of 65.8 ± 14.9 years were included in this study. Patients with metastatic infections secondary to CVC related bloodstream infections were determined. The diagnosis of spondylodiscitis was based on clinical information, computed tomography (CT) and magnetic resonance imaging (MRI), and vertebral cultures.

RESULTS

Metastatic infection due to catheter infection was observed in 15 patients (19.5%). In the regression analysis, CRP level and RRT time were found to be significantly correlated with the development of metastatic infection. Spondylodiscitis was the most common subtype of metastatic infections (8/15). The presence of lumbar hernia was associated with increased risk of metastatic spondylodiscitis in case of catheter infection in hemodialysis patients. The only factor associated with resistance to medical treatment was the time from admission to diagnosis.

CONCLUSION

Patients with long RRT time and high blood CRP levels on admission should be closely monitored for metastatic infection in patients with CVC related bloodstream infections. Screening for spondylodiscitis with CT or MRI should be performed in patients with symptoms, since early diagnosis may prevent the development of possible neurological deficits and treatment resistance.

Recent advances in the application and biological mechanism of silicon nitride osteogenic properties: a review

Silicon nitride, an emerging bioceramic material, is highly sought after in the biomedical industry due to its osteogenesis-promoting properties, which are a result of its unique surface chemistry and excellent mechanical properties. Currently, it is used in clinics as an orthopedic implant material. The osteogenesis-promoting properties of silicon nitride are manifested in its contribution to the formation of a local osteogenic microenvironment, wherein silicon nitride and its hydrolysis products influence osteogenesis by modulating the biological behaviors of the constituents of the osteogenic microenvironment. In particular, silicon nitride regulates redox signaling, cellular autophagy, glycolysis, and bone mineralization in cells involved in bone formation via several mechanisms. Moreover, it may also promote osteogenesis by influencing immune regulation and angiogenesis. In addition, the wettability, surface morphology, and charge of silicon nitride play crucial roles in regulating its osteogenesis-promoting properties. However, as a bioceramic material, the molding process of silicon nitride needs to be optimized, and its osteogenic mechanism must be further investigated. Herein, we summarize the impact of the molding process of silicon nitride on its osteogenic properties and clinical applications. In addition, the mechanisms of silicon nitride in promoting osteogenesis are discussed, followed by a summary of the current gaps in silicon nitride mechanism research. This review, therefore, aims to provide novel ideas for the future development and applications of silicon nitride.

Vertebral Candidiasis, the State of the Art: A Systematic Literature Review

OBJECTIVE

In recent years, Candida spondylodiscitis has represented an increasingly emerging disease in clinical practice. This condition requires long-term antibiotic therapy and sometimes surgical treatments. The main purpose of this study is to investigate the epidemiology, clinical and radiological aspects, treatment protocols, and outcomes of Candida-mediated vertebral osteomyelitis.

METHODS

A systematic review of the English literature was performed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines.The research was conducted on Medline, Cochrane library, PubMed, and Scopus using as search terms "vertebral"; "spinal"; "infection"; "spondylodiscitis"; "discitis"; "osteomyelitis"; "Candida"; and "Candidosis." A case of vertebral candidiasis that was surgically managed was also reported.

RESULTS

In total, 88 articles were included in our systematic review. Including the reported case, our analysis covered 113 cases of vertebral candidiasis. Candida albicans was isolated in 64 cases (56.1%), Candida tropicalis in 21 (18.4%), Candida glabrata in 14 (12.3%), and Candida parapsilosis in five (4.4%). The mean duration of the follow-up was 395 days. Finally, 87 (82%) patients completely recovered, ten (9.4%) died, and nine (8.5%) reported sequelae.

CONCLUSION

This systematic review summarized the state of the art on vertebral candidiasis, describing data on its clinical features, diagnostic criteria and current limitations, and treatment alternatives and their outcomes.

Use of antibiotic-impregnated beads in the treatment of lumbosacral surgical site infection: A retrospective case series

Background

Different adjuvant local-antibiotic techniques are described in management of surgical-site infections (SSIs). Antibiotic-laden polymethyl methacrylate (PMMA) spacers have been used in peri-prosthetic infections. However, their role in treatment of spinal SSIs is not well-recognised.

Methods

After approval from Institutional Review Board, we retrospectively evaluated the data of patients aged≥18 years, who were treated for SSIs of lumbo-sacral region (2010-2019). Among them, those who underwent treatment with the placement of cement beads (temporarily/permanently) were identified. This approach was utilised for post-surgical spondylodiscitis patients with significant, associated infection or abscess involving the paraspinal musculature. Only those with≥2 years' follow-up, were included.Patient demographic details, site of infection, details regarding laboratory/radiological investigations, management-protocol followed, pathogen grown, antibiotics used (their dosage and duration of use), complications encountered and outcome were recorded.

Results

13 patients [4 males, age:57.3 ± 12.4 years] were included. Seven had co-morbidities. One had upper-lumbar involvement, one sacral and others had lower-lumbar (L4/distally) disease. While 7 had recent-onset infection (≤2 months since primary surgery), 6 had chronic infection. In 2, 8, 2, and 1 patients, primary surgery was microdiscectomy, TLIF, PLF, and adult-deformity surgery, respectively.Nine underwent two-staged intervention and 4 underwent single procedure. Eleven had PMMA beads, while 2 underwent calcium sulphate bead insertion. Culture grew E coli in 3, Pseudomonas in 2; and E fecalis, K pneumoniae, MSSA and MRSA in one patient each. In 4 patients, beads were not removed. All patients underwent 2 weeks of parenteral antibiotics, followed by 8-12 weeks of oral medications. There was complete remission in all patients, except one who required additional VAC therapy.

Conclusion

Local antibiotic-laden bead application is an effective adjuvant strategy (along with debridement and systemic antibiotics) for the treatment of spinal SSI, where there is substantial infection involving the paraspinal musculature. It is cost-effective and often necessitates second procedure for bead removal.

A Novel Antipathogenic Agent for Nonwoven Fabric

Medical-grade masks and N95 respirators containing non-woven fibers are designed to prevent the spread of airborne diseases. While they effectively trap respiratory droplets and aerosols, they cannot lyse entrapped pathogens. Embedded antimicrobial agents such as silver, copper, zinc, iodine, peptides, quaternary ammonium salts, or nanoparticles have been used to overcome this limitation. However, their effectiveness remains debatable because these materials can be toxins, allergens, irritants, and environmental hazards. Recently, silicon nitride (Si3N4) was found to be a potent antipathogenic compound, and it may be an ideal agent for masks. In powder or solid form, it is highly effective in inactivating bacteria, fungi, and viruses while leaving mammalian tissue unaffected. The purpose of this study was to serially assess the antiviral efficacy of Si3N4 against SARS-CoV-2 using powders, solids, and embedded nonwoven fabrics. Si3N4 powders and solids were prepared using conventional ceramic processing. The “pad-dry-cure” method was used to embed Si3N4 particles into polypropylene fibers. Fabric testing was subsequently conducted using industrial standards—ISO 18184 for antiviral effectiveness, ASTM F2299 and EN 13274-7 for filtration efficiency, EN 14683 for differential pressure drop, and ISO 18562-2 for particle shedding. A modification of ISO 18562-3 was also employed to detect ammonia release from the fabric. Antiviral effectiveness for Si3N4 powders, solids, and embedded fabrics were 99.99% at ≤ 5 min, ~ 93% in 24 h, and 87% to 92% in 120 min, respectively. Results of the standard mask tests were generally within prescribed safety limits. Further process optimization may lead to commercial Si3N4-based masks that not only “catch” but also “kill” pathogenic microbes.

Silicon Nitride as a Biomedical Material: An Overview

Silicon nitride possesses a variety of excellent properties that can be specifically designed and manufactured for different medical applications. On the one hand, silicon nitride is known to have good mechanical properties, such as high strength and fracture toughness. On the other hand, the uniqueness of the osteogenic/antibacterial dualism of silicon nitride makes it a favorable bioceramic for implants. The surface of silicon nitride can simultaneously inhibit the proliferation of bacteria while supporting the physiological activities of eukaryotic cells and promoting the healing of bone tissue. There are hardly any biomaterials that possess all these properties concurrently. Although silicon nitride has been intensively studied as a biomedical material for years, there is a paucity of comprehensive data on its properties and medical applications. To provide a comprehensive understanding of this potential cornerstone material of the medical field, this review presents scientific and technical data on silicon nitride, including its mechanical properties, osteogenic behavior, and antibacterial capabilities. In addition, this paper highlights the current and potential medical use of silicon nitride and explains the bottlenecks that need to be addressed, as well as possible solutions.

Silicon Nitride, a Bioceramic for Bone Tissue Engineering: A Reinforced Cryogel System With Antibiofilm and Osteogenic Effects

Silicon nitride (SiN [Si3N4]) is a promising bioceramic for use in a wide variety of orthopedic applications. Over the past decades, it has been mainly used in industrial applications, such as space shuttle engines, but not in the medical field due to scarce data on the biological effects of SiN. More recently, it has been increasingly identified as an emerging material for dental and orthopedic implant applications. Although a few reports about the antibacterial properties and osteoconductivity of SiN have been published to date, there have been limited studies of SiN-based scaffolds for bone tissue engineering. Here, we developed a silicon nitride reinforced gelatin/chitosan cryogel system (SiN-GC) by loading silicon nitride microparticles into a gelatin/chitosan cryogel (GC), with the aim of producing a biomimetic scaffold with antibiofilm and osteogenic properties. In this scaffold system, the GC component provides a hydrophilic and macroporous environment for cells, while the SiN component not only provides antibacterial properties and osteoconductivity but also increases the mechanical stiffness of the scaffold. This provides enhanced mechanical support for the defect area and a better osteogenic environment. First, we analyzed the scaffold characteristics of SiN-GC with different SiN concentrations, followed by evaluation of its apatite-forming capacity in simulated body fluid and protein adsorption capacity. We further confirmed an antibiofilm effect of SiN-GC against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) as well as enhanced cell proliferation, mineralization, and osteogenic gene upregulation for MC3T3-E1 pre-osteoblast cells. Finally, we developed a bioreactor to culture cell-laden scaffolds under cyclic compressive loading to mimic physiological conditions and were able to demonstrate improved mineralization and osteogenesis from SiN-GC. Overall, we confirmed the antibiofilm and osteogenic effect of a silicon nitride reinforced cryogel system, and the results indicate that silicon nitride as a biomaterial system component has a promising potential to be developed further for bone tissue engineering applications.

Comprehensive in vitro comparison of cellular and osteogenic response to alternative biomaterials for spinal implants

A variety of novel biomaterials are emerging as alternatives to conventional metals and alloys, for use in spinal implants. These promise potential advantages with respect to e.g. elastic modulus compatibility with the host bone, improved radiological imaging or enhanced cellular response to facilitate osseointegration. However, to date there is scarce comparative data on the biological response to many of these biomaterials that would give insights into the relative level of bone formation, resorption inhibition and inflammation. Thus, in this study, we aimed to evaluate and compare the in vitro biological response to standard discs of four alternative biomaterials: polyether ether ketone (PEEK), zirconia toughened alumina (ZTA), silicon nitride (SN) and surface-textured silicon nitride (ST-SN), and the reference titanium alloy Ti6Al4V (TI). Material-specific characteristics of these biomaterials were evaluated, such as surface roughness, wettability, protein adsorption (BSA) and apatite forming capacity in simulated body fluid. The activity of pre-osteoblasts seeded on the discs was characterized, by measuring viability, proliferation, attachment and morphology. Then, the osteogenic differentiation of pre-osteoblasts was compared in vitro from early to late stage by Alizarin Red S staining and real-time PCR analysis. Finally, osteoclast activity and inflammatory response were assessed by real-time PCR analysis. Compared to TI, all other materials generally demonstrated a lower osteoclastic activity and inflammatory response. ZTA and SN showed generally an enhanced osteogenic differentiation and actin length. Overall, we could show that SN and ST-SN showed a higher osteogenic effect than the other reference groups, an inhibitive effect against bone resorption and low inflammation, and the results indicate that silicon nitride has a promising potential to be developed further for spinal implants that require enhanced osseointegration.

Two-year results of a double-blind multicenter randomized controlled non-inferiority trial of polyetheretherketone (PEEK) versus silicon nitride spinal fusion cages in patients with symptomatic degenerative lumbar disc disorders

Background

During lumbar spinal fusion, spacer cages are implanted to provide vertebral stability, restore sagittal alignment, and maintain disc and foraminal height. Polyetheretherketone (PEEK) is commonly used by most spine surgeons. Silicon nitride (Si₃N₄) is a less well-known alternative although it was first used as a spacer in lumbar fusion over 30 years ago. The present study was designed to see if Si₃N₄ cages would perform similarly to PEEK in a randomized controlled trial.

Methods

A non-inferiority multicenter 100-patient study was designed where both the observer and patient were blinded. Single- or double-level transforaminal lumbar interbody fusion with pedicle screw fixation using an oblique PEEK or Si₃N₄ cage was performed. The primary non-inferiority outcome was the Roland-Morris Disability Questionnaire (RMDQ). Secondary measures included the Oswestry Disability Questionnaire, Visual Analogue Scales (VAS) for back and leg pain, SF-36 Physical and Mental Function indices, patient and surgeon Likert scores on perceived recovery, and X-ray and CT radiological evaluations for subsidence, segmental motion, and fusion. Follow-up evaluations occurred at 3, 6, 12, and 24 months.

Results

After exclusions for protocol violations and canceled surgeries, 92 patients were randomized (i.e., 48 for PEEK and 44 for Si₃N₄). There were no differences in baseline demographics, pre-operative disabilities, or pain scores between the groups. Both treatment arms showed significant improvements in disability, pain, and recovery scores. No significant differences were observed for subsidence, segmental motion, or fusion. For the primary outcome (i.e., RMDQ scores), the non-inferiority of Si₃N₄ compared to PEEK could not be established using the original protocol criteria. However, the comparison was undermined by larger than anticipated patient fallout coupled with higher than expected RMDQ score standard deviations. A post hoc analysis coupled with a more extensive review of the literature was conducted which resulted in the selection of a revised clinically justified non-inferiority margin; and using this method, the non-inferiority of Si₃N₄ was affirmed.

Conclusions

This study demonstrated that the use of either PEEK or Si₃N₄ cages is safe and effective for patients undergoing lumbar spine fusion for chronic degenerative disc disease.

Fretting corrosion of Si3 N4 vs CoCrMo femoral heads on Ti-6Al-V trunnions

Fretting corrosion at the head-neck taper junction was compared between silicon nitride (Si₃ N₄ ) and commercially available cobalt chrome (CoCrMo) femoral heads on titanium (Ti-6Al-4V) trunnions. An electrochemical setup was used to capture the fretting currents (characterized by oxide abrasion and repassivation) during cyclic loading. Onset load, pull-off force (disassembly load), short term and long term (1 million cycles) fretting currents were used to compare the fretting corrosion performance between the test group (Si₃ N₄ /Ti-6Al-4V) and the control group (CoCrMo/Ti-6Al-4V). Incremental cyclic fretting corrosion tests showed that the Si₃ N₄ /Ti-6Al-4V combination had statistically lower (P < .05) average fretting current of 0.189 µA (SD = 0.114 µA) compared to 0.685 µA (SD = 0.630 µA) for CoCrMo/Ti-6Al-4V for cyclic load of 3200 N. Similarly, for the one million cycle fretting corrosion tests, the Si₃ N₄ /Ti-6Al-4V couples had statistically lower (P < .05) average current (0.048 µA, SD = 0.025 µA) vs CoCrMo/Ti-6Al-4V couples (0.366 µA, SD = 0.143 µA). The Si₃ N₄ heads also had higher onset loads (P < .05) for fretting (vs CoCrMo, 2200 N vs 1740 N) indicating a difference in surface contact mechanics between the two groups. Scanning electron microscopy with energy dispersive spectroscopy confirmed material transfer from the trunnions to the heads for both groups tested, and from head to trunnion for the CoCrMo heads. Minimal Si₃ N₄ transfer was noted. The electrochemical, mechanical, and microscopic inspection data supported the hypothesis that Si₃ N₄ /Ti-6Al-4Vcombination had better fretting corrosion performance compared to CoCrMo/Ti-6Al-4V.

Clinical outcomes for lumbar fusion using silicon nitride versus other biomaterials

BACKGROUND

In lumbar fusion surgery, intervertebral spacer cages made of silicon nitride (Si3N4) ceramic are an available option among other biomaterials. While the surface chemistry of Si3N4 is known to favor bone fusion, large-scale clinical studies attesting to its efficacy are lacking. This multicenter retrospective study compared lumbar fusion outcomes for Si3N4 cages to previously reported data for other cage materials.

METHODS

Pre-operative patient demographics, comorbidities, changes in visual analog scale (ΔVAS) pain scores, complications, adverse events, and secondary surgical interventions (SSI) were compiled from the records of 450 patients who underwent Si3N4 lumbar spinal fusion at four separate U.S. surgical centers. For comparison, MEDLINE/PubMed and Google Scholar searches identified studies reporting similar outcomes for other biomaterials. A total of 1,025 patients from 26 cohorts reported in 14 publications met inclusion criteria for this control group.

RESULTS

Overall, the mean last-follow-up for all patients was 341±293 days (11.4±9.8 months), with the longest follow-up being 6.4 years. Patients with Si3N4 implants were similar in gender and age distribution to the control group but had higher BMI values (30.9±6.1 vs. 25.8±4.1, P<0.01) and lower tobacco use (15.8% vs. 30.0%, P<0.01). Both the Si3N4 and control groups showed significant improvements in VAS pain scores from preoperative to last follow-up. For the Si3N4 group, ΔVAS was 36.8±35.4 points compared to 37.6±22.5 points (P=0.63) for the metadata group. Complications and reoperations for the Si3N4 and the control groups were similar (i.e., 9.8% and 3.1% versus 12.4% and 2.9%, P=0.16 and P=0.84, respectively).

CONCLUSIONS

Lumbar fusion with Si3N4 spacers compared favorably with the improvements reported with other commonly used biomaterial cages.

Surgical Management of L5-S1 Spondylodiscitis on Previously Documented Isthmic Spondylolisthesis: Case Report and Review of the Literature

Background

Although lumbar isthmic spondylolisthesis is frequent in the Caucasian population, its association with spondylodiscitis is extremely rare. Case Description. The authors reported the case of a 44-year-old patient affected by pyogenic spondylodiscitis on previously documented isthmic spondylolisthesis at the L5-S1 level. The patient was surgically treated by circumferential arthrodesis combining anterior lumbar interbody fusion (ALIF), followed by L4-S1 percutaneous osteosynthesis using the same anesthesia. Appropriate antibiotherapy to methicillin-susceptible Staphylococcus aureus, found on the intraoperative samplings, was then delivered for 3 months, allowing satisfactory evolution on the clinical, biological, and radiological levels. Discussion. This is the first case report of spondylodiscitis affecting an isthmic spondylolisthesis surgically treated by circumferential arthrodesis. In addition to providing large samplings for analysis, it confirms the observed evolution over the past 30 years in modern care history of spondylodiscitis, increasingly including surgical treatment with spinal instrumentation, thus avoiding the need of an external immobilization. Care must nonetheless be exercised in performing the ALIF because of the inflammatory tissue increasing the risk of vascular injury.

Conclusion

Spondylodiscitis occurring on an L5-S1 isthmic spondylolisthesis can be safely managed by circumferential arthrodesis combining ALIF then percutaneous osteosynthesis in the same anesthesia, obviously followed by appropriate antibiotherapy.

Clinical outcomes for anterior cervical discectomy and fusion with silicon nitride spine cages: a multicenter study

BACKGROUND

Intervertebral spacers made of silicon nitride (Si3N4) are currently used in cervical and thoracolumbar fusion. While basic science data demonstrate several advantages of Si3N4 over other biomaterials, large-scale clinical results on its safety and efficacy are lacking. This multicenter retrospective study examined outcomes for anterior cervical discectomy and fusion (ACDF) using Si3N4 cages. Results were compared to compiled metadata for other ACDF materials.

METHODS

Pre-operative patient demographics, comorbidities, changes in visual analog scale (VAS) pain scores, complications, adverse events, and secondary surgical interventions were collected from the medical records of 860 patients who underwent Si3N4 ACDF at four surgical centers. For comparison, MEDLINE/PubMed and Google Scholar searches were performed for ACDF using other cage or spacer materials. Nine studies with 13 cohorts and 736 patients met the inclusion criteria for this control group.

RESULTS

Overall, the mean last-follow-up for all patients was 319±325 days (10.6±10.8 months), with the longest follow-up being 6.5 years. In comparison to the metadata, patients from the Si3N4 groups were older (57.9±12.2 vs. 56.8±11.1 y, P=0.06) and had higher BMI values (30.0±6.3 vs. 28.1±6.5, P<0.01), but gender and smoking were not different. The Si3N4 patients reported significant improvements in VAS pain scores at last follow-up (i.e., pre-op of 71.0±22.1 vs. follow-up of 36.4±31.5, P<0.01). Although both preoperative and last-follow-up pain scores were higher for Si3N4 patients than the control, the overall change in scores (ΔVAS) was similar. From pre-op to last-follow up, ΔVAS values were 35.4±34.3 for patients receiving the Si3N4 implants versus 34.4±27.3 for patients from the meta-analysis (P=0.56). The complication and reoperation rate for the Si3N4 and the metadata were also comparable (i.e., 7.39% and 0.31% versus 9.79% and 0%, P=0.17 and 0.25, respectively).

CONCLUSIONS

ACDF outcomes using Si3N4 implants matched the clinical efficacy of other cage biomaterials.

3D-additive deposition of an antibacterial and osteogenic silicon nitride coating on orthopaedic titanium substrate

A 3D-additive manufacturing approach produced a dense Si₃N₄ ceramic coating on a biomedical grade commercially pure titanium (cp-Ti) substrate by an automatic laser-sintering procedure. Si₃N₄ coatings could be prepared with thicknesses from the single to the tens of microns. A coating thickness, t = 15 ± 5 μm, was selected for this study, based on projections of homogeneity and scratching resistance. The Si₃N₄ coating met the 20 N threshold required for biomaterial applications, according to the standard scratch testing (ASTM C1624-05). The Si₃N₄ coating imparted both the antibacterial and osteogenic properties of bulk Si₃N₄ to the cp-Ti substrate. Both properties were comparable to those previously described for bulk Si₃N₄ biomedical implants. The newly developed Si₃N₄-coating was applied to commercially available Ti-alloy acetabular shells for total hip arthroplasty. A "glowing" test based on luciferase gene transformation was applied to visualize the colonization of gram-negative Escherichia coli on Si₃N₄-coated and uncoated Ti-alloy acetabular shells. The results showed that the coating technology conferred resistance to Staphylococcus epidermidis and Escherichia coli adhesion onto the bulk acetabular sockets.

State of the union: a review of lumbar fusion indications and techniques for degenerative spine disease

Lumbar fusion is an accepted and effective technique for the treatment of lumbar degenerative disease. The practice has evolved continually since Albee and Hibbs independently reported the first cases in 1913, and advancements in both technique and patient selection continue through the present day. Clinical and radiological indications for surgery have been tested in trials, and other diagnostic modalities have developed and been studied. Fusion practices have also advanced; instrumentation, surgical approaches, biologics, and more recently, operative planning, have undergone stark changes at a seemingly increasing pace over the last decade. As the general population ages, treatment of degenerative lumbar disease will become a more prevalent-and costlier-issue for surgeons as well as the healthcare system overall. This review will cover the evolution of indications and techniques for fusion in degenerative lumbar disease, with emphasis on the evidence for current practices.

Spondylodiscitis in end-stage renal disease: a systematic review

OBJECTIVE

Discitis and osteomyelitis are seen in end-stage renal disease (ESRD) patients due to repeated vascular access for hemodialysis and urinary tract infections leading to recurrent bacteremia. Discitis and osteomyelitis are underdiagnosed due to the nonspecific initial presentation of back pain. In this article, we review the literature for better understanding of the problem and the importance of early diagnosis by primary care physicians and nephrologists. In addition, we discuss the decision-making, follow-up, management, and neurological outcomes.

METHODS

A detailed PubMed search was performed using the following terms: "end stage renal disease (ESRD)" and "chronic renal failure (CRF)," combined with "spine infections," "spondylodiscitis," "discitis," and "osteomyelitis." Search results were limited to articles written in English, case reports, and case series from 1973 to 2012. Editorials, reviews, and commentaries were excluded. Only studies involving human patients were included. The authors also included 4 patients from their own patient population.

RESULTS

A total of 30 articles met the inclusion criteria. Including the 4 patients from the authors' patient population, 212 patients with spine infections and maintenance dialysis were identified. The patients' ages ranged from 38 to 78 years. The duration of dialysis ranged from a few days to 16 years. The time from onset of back pain to diagnosis ranged from 3 days to 6 months. The most common causative organism was Staphylococcus aureus, followed by Staphylococcus epidermidis and gram-negative bacteria. Most of the patients were treated with antibiotics alone (76.8%), although surgery was indicated when patients presented with neurological deficits (p < 0.011). Approximately one-quarter of the patients developed neurological deficits, with devastating consequences. Fever and neurological deficits at presentation, culture positive for methicillin-resistant S. aureus, and age > 65 years were highly correlated with mortality in our analysis.

CONCLUSIONS

Several risk factors lead to failure of antibiotics and progression of disease in patients with ESRD. Challenges to diagnosis include vague presenting symptoms, co-existing destructive spondyloarthropathy, poor immune response, chronic elevations of inflammatory markers, and recurrent bacteremia. Infectious processes are more likely to cause permanent neurological deficits than transient deficits. The authors recommend close observation and serial imaging of these patients for early signs of neurological deficits. Any signs of disease progression will require aggressive surgical debridement.

A single center retrospective clinical evaluation of anterior cervical discectomy and fusion comparing allograft spacers to silicon nitride cages

BACKGROUND

Iliac crest autograft or allograft spacers have been traditionally utilized in anterior cervical discectomy and fusion (ACDF) to provide vertebral stabilization and enhanced osteogenesis. However, abiotic cages have largely replaced these allogenic sources due to host-site morbidities and disease transmission risks, respectively. Although devices made of polyetheretherketone (PEEK) or titanium-alloys (Ti) have gained wide popularity, they lack osteoinductive or conductive capabilities. In contrast, silicon nitride (Si3N4) is a relatively new implant material that also provides structural stability and yet purportedly offers osteopromotive and antimicrobial behavior. This study compared radiographic outcomes at ≥12 months of follow-up for osseous integration, fusion rate, time to fusion, and subsidence in ACDF patients with differing intervertebral spacers.

METHODS

Fifty-eight ACDF patients (108 segments) implanted with Si3N4 cages were compared to thirty-four similar ACDF patients (61 segments) implanted with fibular allograft spacers. Lateral radiographs (normal, flexion, and extension) were obtained at 3, 6, 12, and 24 months to assess osseous integration, the presence of bridging bone, the absence of peri-implant radiolucencies, subsidence, and fusion using both interspinous distance (ISD) and Cobb angle methods.

RESULTS

In patients with ≥12 months of follow-up, fusion for the allograft spacers and Si3N4 cages was 86.84% and 96.83%, respectively (ISD method, P=0.10), and 67.65% and 84.13%, respectively (Cobb angle method P=0.07), while osseointegration was 76.32% and 93.65%, respectively (P=0.02). The time to fusion significantly favored the Si3N4 cages (4.08 vs. 8.64 months (ISD method, P=0.01), and 6.76 vs. 11.74 months (Cobb angle method, P=0.04). The assessed time for full osseointegration was 7.83 and 19.24 months for Si3N4 and allograft, respectively (P=0.00). Average subsidence at 1-year follow-up was 0.51 and 2.71 mm for the Si3N4 and allograft cohorts, respectively (P=0.00).

CONCLUSIONS

In comparison to fibular allograft spacers, Si3N4 cages showed earlier osseointegration and fusion, higher fusion rates, and less subsidence.