Implant materials generate different peri-implant inflammatory factors: poly-ether-ether-ketone promotes fibrosis and microtextured titanium promotes osteogenic factors

Clinical and Radiographic Outcomes of Anterior Lumbar Interbody Fusions Using a Titanium Cage with a Biomimetic Surface

BACKGROUND

 We analyzed clinical and radiographic outcomes in patients undergoing anterior lumbar interbody fusions (ALIFs) using a new biomimetic titanium fusion cage (Titan nanoLOCK interbody, Medtronic, Minneapolis, Minnesota, United States). This specialized cage employs precise nanotechnology to stimulate inherent biochemical and cellular osteogenic reactions to the implant, aiming to amplify the rate of fusion. To our knowledge, this is the only study to assess early clinical and radiographic results in ALIFs.

METHODS

 We conducted a retrospective review of data for patients who underwent single or multilevel ALIF using this implant between October 2016 and April 2021. Indications for treatment were spondylolisthesis, postlaminectomy syndrome, or spinal deformity. Clinical and radiographic outcome data for these patients were collected and assessed.

RESULTS

 A total of 84 patients were included. The mean clinical follow-up was 36.6 ± 14 months. At 6 months, solid fusion was seen in 97.6% of patients. At 12 months, solid fusion was seen in 98.8% of patients. Significant improvements were seen in patient-reported outcome measures (PROMs; visual analog scale and Oswestry Disability Index) at 6 and 12 months compared with the preoperative scores (p < 0.001). One patient required reoperation for broken pedicle screws 2 days after the ALIF. None of the patients required readmission within 90 days of surgery. No patients experienced an infection.

CONCLUSIONS

 ALIF using a new titanium interbody fusion implant with a biomimetic surface technology demonstrated high fusion rates (97.6%) as early as 6 months. There was significant improvement in PROMs at 6 and 12 months.

The Effectiveness of Tritanium Cages in Preventing Osteolytic Vertebral Endplate Cysts After Lumbar Interbody Fusion

OBJECTIVE

Lumbar interbody fusion (LIF) is a common surgical procedure, but postoperative complications, such as osteolytic vertebral endplate cysts, can adversely affect patient outcomes. This study aims to investigate whether tritanium cages (Stryker, Mahwah, New Jersey, USA) are effective in preventing osteolytic vertebral endplate cysts after LIF.

METHODS

Clinical data from 8 years (2013-2020) of LIF procedures at our hospital were analyzed. Computed tomography was used to assess the formation of osteolytic vertebral endplate cysts 6 months after surgery. Clinical factors potentially associated with cyst formation were compared among 3 different interbody spacer materials: tritanium, titanium, and polyetheretherketone.

RESULTS

LIF was performed for 169 patients at 205 spinal levels, employing tritanium cages in 56 levels (48 patients), titanium in 103 levels (86 patients), and polyetheretherketone in 46 levels (35 patients). At 6 months after LIF, 27.3% of patients showed worsening of osteolytic vertebral endplate cysts. Multivariate logistic regression analysis showed that tritanium cages (odds ratio [OR], 3.86; 95% confidence interval [CI], 1.46-10.21) and titanium (OR, 2.55; 95% CI, 1.13-5.75), and posterior LIF (OR, 5.74; 95% CI, 2.24-14.74) were associated with a reduced risk of postoperative osteolytic vertebral endplate cysts.

CONCLUSIONS

Tritanium cages have shown promise in preventing postoperative osteolytic vertebral endplate cysts, suggesting their potential as a stable and effective choice in LIF procedures. These findings have significant implications for improving patient outcomes and warrant further investigation to optimize surgical techniques and materials.

An investigational time course study of titanium plasma spray on osseointegration of PEEK and titanium implants: an in vivo ovine model

BACKGROUND CONTEXT

Methods to improve osseointegration of orthopedic spinal implants remains a clinical challenge. Materials composed of poly-ether-ether-ketone (PEEK) and titanium are commonly used in orthopedic applications due to their inherent properties of biocompatibility. Titanium has a clinical reputation for durability and osseous affinity, and PEEK offers advantages of a modulus that approximates osseous structures and is radiolucent. The hypothesis for the current investigation was that a titanium plasma spray (TPS) coating may increase the rate and magnitude of circumferential and appositional trabecular osseointegration of PEEK and titanium implants versus uncoated controls.

PURPOSE

Using an in vivo ovine model, the current investigation compared titanium plasma-sprayed PEEK and titanium dowels versus nonplasma-sprayed dowels. Using a time course study of 6 and 12 weeks postoperatively, experimental assays to quantify osseointegration included micro-computed tomography (microCT), biomechanical testing, and histomorphometry.

STUDY DESIGN/SETTING

In-vivo ovine model.

METHODS

Twelve skeletally mature crossbred sheep were equally randomized into postoperative periods of 6 and 12 weeks. Four types of dowel implants-PEEK, titanium plasma-sprayed PEEK (TPS PEEK), titanium, and titanium plasma-sprayed titanium (TPS titanium) were implanted into cylindrical metaphyseal defects in the distal femurs and proximal humeri (one defect per limb, n=48 sites). Sixteen nonoperative specimens (eight femurs and eight humeri) served as zero time-point controls. Half of the specimens underwent destructive biomechanical pullout testing and the remaining half quantitative microCT to quantify circumferential bone volume within 1 mm and 2 mm of the implant surface and histomorphometry to compute direct trabecular apposition.

RESULTS

There were no intra- or perioperative complications. The TPS-coated implants demonstrated significantly higher peak loads at dowel pullout at 6 and 12 weeks compared with uncoated controls (p<.05). No differences were observed across dowel treatments at the zero time-point (p>.05). MicroCT results exhibited no significant differences in circumferential osseointegration between implants within 1 mm or 2 mm of the dowel surface (p>.05). Direct appositional osseointegration of trabecular bone based on histomorphometry was higher for TPS-coated groups, regardless of base material, compared with uncoated treatments at both time intervals (p<.05).

CONCLUSIONS

The current in vivo study demonstrated the biological and mechanical advantages of plasma spray coatings. TPS improved histological incorporation and peak force required for implant extraction.

CLINICAL SIGNIFICANCE

Plasma spray coatings may offer clinical benefit by improving biological fixation and osseointegration within the first 6 to 12 weeks postoperatively- the critical healing period for implant-based arthrodesis procedures.

Comparison of Lumbar Interbody Fusion with 3D-Printed Porous Titanium Cage Versus Polyetheretherketone Cage in Treating Lumbar Degenerative Disease: A Systematic Review and Meta-Analysis

OBJECTIVE

To compare the safety and radiological effectiveness of lumbar interbody fusion with a 3D-printed porous titanium (3D-PPT) cage versus a polyetheretherketone (PEEK) cage for the treatment of lumbar degenerative disease.

METHODS

This study was registered at PROSPERO (CRD42023461511). We systematically searched the PubMed, Embase, and Web of Science databases for related studies from inception to September 3, 2023. Review Manager 5.3 was used to conduct this meta-analysis. The reoperation rate, complication rate, fusion rate, and subsidence rate were assessed using relative risk and 95% confidence intervals.

RESULTS

Ten articles reporting 9 studies comparing lumbar interbody fusion with 3D-PPT cages versus PEEK cages for the treatment of lumbar degenerative disease were included. The subsidence rate at the 1-year follow-up in the 3D-PPT cage was significantly lower than that in the PEEK cage. The fusion rate in the 3D-PPT cage was significantly higher than that in the PEEK cage at the 6-month follow-up. No significant difference was identified between the 2 groups at the 12-month follow-up. No significant difference was identified between the 2 groups in terms of the complication rate and reoperation rate. There was a trend toward a lower complication rate and reoperation rate with the 3D-PPT cage.

CONCLUSIONS

Compared with the PEEK cage, the 3D-PPT cage may be a safer implant. The 3D-PPT cage was associated with a higher fusion rate and lower subsidence rate. The 3D-PPT cage may accelerate the intervertebral fusion process, improve the quality of fusion and prevent the occurrence of subsidence.

The Influence of Titanium-coated Poryetheretherketone Cages in Fusion Status after Posterior Lumbar Interbody Fusion with Cortical Bone Trajectory Screw Fixation

OBJECTIVE

Posterior lumbar interbody fusion (PLIF) with cortical bone trajectory (CBT) screw fixation (CBT-PLIF) shows potential for reducing adjacent segmental disease. Previously, our investigations revealed a relatively lower fusion rate with the use of carbon fiber-reinforced polyetheretherketone (CP) cages in CBT-PLIF compared with traditional pedicle screw fixation (PS-PLIF) using CP cages. This study aims to evaluate whether the implementation of titanium-coated polyetheretherketone (TP) cages can enhance fusion outcomes in CBT-PLIF.

METHODS

A retrospective analysis was conducted on 68 consecutive patients who underwent CBT-PLIF with TP cages (TP group) and 89 patients who underwent CBT-PLIF with CP cages (CP group). Fusion status was assessed using computed tomography at 1 year postoperatively and dynamic plain radiographs at 2 years postoperatively.

RESULTS

No statistically significant differences in fusion rates were observed at 1 and 2 years postoperatively between the TP group (86.8% and 89.7%, respectively) and the CP group (77.5% and 88.8%, respectively). Notably, the CP group exhibited a significant improvement in fusion rate from 1 to 2 years postoperatively (P = 0.002), while no significant improvement was observed in the TP group.

CONCLUSIONS

Examination of temporal changes in fusion rates reveals that only the TP group achieved a peak fusion rate 1 year postoperatively. This implies that TP cages may enhance the fusion process even after CBT-PLIF. Nevertheless, the definitive efficacy of TP cages for CBT-PLIF remains uncertain in the context of overall fusion rates.

Moderate sagittal plane deformity patients have similar radiographic and functional outcomes with either anterior or posterior surgery

PURPOSE

This study aimed to compare the functional and radiographic outcomes of two surgical interventions for adult spinal deformity (ASD): anterior lumbar interbody fusion with anterior column realignment (ALIF-ACR) and posterior approach using Smith-Peterson osteotomy with transforaminal lumbar interbody fusion and pedicle screw fixation (TLIF-Schwab2).

METHODS

A retrospective cohort study included 61 ASD patients treated surgically between 2019 and 2020 at a single tertiary orthopedic specialty hospital. Patients were divided into two groups: Group 1 (ALIF-ACR, 29 patients) and Group 2 (TLIF-Schwab2, 32 patients). Spinopelvic radiographic parameters and functional outcomes were evaluated at 3, 6, and 12 months postsurgery.

RESULTS

Perioperative outcomes favored the ALIF-ACR group, with significantly smaller blood loss, shorter hospital stay, and operative time. Radiographic and functional outcomes were similar for both groups; however, the ALIF-ACR group did have a greater degree of correction in lumbar lordosis at 12 months. Complication profiles varied, with the ALIF-ACR group experiencing mostly hardware-related complications, while the TLIF-Schwab2 group faced dural tears, wound dehiscence, and proximal junctional kyphosis. Both groups had similar revision rates.

CONCLUSION

Both ALIF-ACR and TLIF-Schwab2 achieved similar radiographic and functional outcomes in ASD patients with moderate sagittal plane deformity at 1-year follow-up. However, the safety profiles of the two techniques differed. Further research is required to optimize patient selection for each surgical approach, aiming to minimize perioperative complications and reoperation rates in this challenging patient population.

A Comprehensive Review of the Historical Description of Spine Surgery and Its Evolution

Major strides in the advancement of spine surgery came about in the 21st century. However, the extensive history of spine surgery can be traced back to long before this time. A clear description of the journey from a primitive yet accurate understanding of the human musculoskeletal system to today's modern aspects of spinal techniques is lacking. A narrative literature review was conducted to elucidate where spine surgery began and the techniques used that evolved over time. This review was conducted using PubMed and Google Scholar. Search terms used included "history of spine surgery," "evolution of spine surgery," "origins of spine surgery," "history of laminectomy," "history of spinal fusion," "history of lumbar interbody fusion," "minimally invasive spine surgery," and "navigation in spine surgery." We highlight the evolution of the basic understanding of anatomy and non-surgical and surgical techniques, including bracing, laminectomy, discectomy, and spinal fusion. The current evolution and integration of minimally invasive techniques, lumbar interbody fusion techniques, robotics, navigation, and motion preservation are discussed, as these are the major areas of focus for technological advancement. This review presents an overarching synopsis of the events that chronicle the progress made in spine surgery since its conception. The review uniquely contributes to the growing body of literature on the expansion of spine surgery and highlights major events in its history.

The "Sandwich" Extended Pedicle Subtraction Osteotomy for the Treatment of Fixed Sagittal Malalignment: Technical Description, Case Series, and Early Results With 2-Year Outcomes

BACKGROUND AND OBJECTIVES

Adult spinal deformity (ASD) with fixed sagittal malalignment (FSM) may require a pedicle subtraction osteotomy (PSO) for greater focal lordosis and restoration of global alignment. Despite growing trends in minimizing PSOs given their associated high risks, a considerable portion of patients with ASD still require a lumbar PSO most commonly because of iatrogenic flat back deformity. The purpose of this article is to describe a modified extended PSO technique with additional anterior column support coined the "sandwich" extended PSO (SE-PSO) to promote arthrodesis and report the outcomes in a consecutive case series.

METHODS

Patients with ASD treated with a lumbar SE-PSO at a single institution from 2015 to 2020 were analyzed. Complications, radiographic data, and patient-reported outcomes were compared preoperatively, at immediate postoperative follow-up, and at a 2-year postoperative follow-up (FU).

RESULTS

Fourteen patients who underwent revision operations for FSM were included. Improvements in segmental lordosis across the PSO site (14.8 ± 6.8 vs 39.9 ± 7.1, P < .0001), overall lumbar lordosis (14.6 ± 15.4 vs 44.6 ± 12.1, P < .0001), sacral slope (21.0 ± 10.5 31.1 ± 10.7, P = .0150), C7 sagittal vertical axis (140.1 ± 59.0 mm vs 35.9 ± 28.5, P < .0001), and spinopelvic mismatch (52.5 ± 21.3 vs 18.6 ± 14.1, P = .0001) were obtained in all patients. Eight patients experienced perioperative complications, with intraoperative durotomy being the most common (n = 7). Eight patients had a 2-year FU and demonstrated improvements in their segmental lordosis across the PSO site (14.3 ± 7.0 vs 41.3 ± 7.3, P = .0003), overall lumbar lordosis (8.7 ± 17.8 vs 46.1 ± 14.2, P = .0014), sacral slope (19.1 ± 12.8 vs 32.3 ± 12.5, P = .0479), C7 sagittal vertical axis (173.6 ± 54.4 mm vs 35.8 ± 30.0, P < .0001), and spinopelvic mismatch (63.0 ± 19.7 vs 21.1 ± 18.3, P < .0001), all of which were maintained at final FU (P > .05). At 2 years, a significant increase in Scoliosis Research Society-22r total score (2.5 ± 0.8 vs 3.6 ± 0.7, P = .0023 was reported. There were no reports of symptomatic pseudarthrosis or mechanical complications.

CONCLUSION

SE-PSO is an effective technique to correct FSM and is associated with low complications, improved patient-reported outcomes, and spinopelvic parameters that are maintained at 2 years.

Comparison between Three-Dimensional Printed Titanium and PEEK Cages for Cervical and Lumbar Interbody Fusion: A Prospective Controlled Trial

OBJECTIVES

The three-dimensional printing titanium (3DPT) cage with excellent biomechanical properties and osseointegration capabilities has been initially used in spinal fusion, while the polyetheretherketone (PEEK) cage, a bioinert material device, has been a widely used for decades with relatively excellent clinical outcomes. This study was performed to investigate the early radiographic and clinical outcomes of 3DPT cage versus PEEK cage in patients undergoing anterior cervical discectomy and fusion (ACDF) and transforaminal lumbar interbody fusion (TLIF).

METHODS

This prospective controlled trial, from December 2019 to June 2022, included patients undergoing ACDF and TLIF with 3DPT cages and compared them to patients using PEEK cages for treating spinal degenerative disorders. The outcome measures included radiographic parameters (intervertebral height [IH], subsidence, fusion status, and bone-cage interface contact) and clinical outcomes (Japanese Orthopaedic Association [JOA], Neck Disability Index [NDI], Oswestry Disability Index [ODI], Short Form 12-Item Survey [SF-12], Visual Analog Scale [VAS], and Odom's criteria). Student's independent samples t test and Pearson's chi-square test were used to compare the outcome measures between the two groups before surgery and at 1 week, 3 and 6 months after surgery.

RESULTS

For the patients undergoing ACDF, the 3DPT (18 patients/[26 segments]) and PEEK groups (18 patients/[26 segments]) had similar fusion rates at 3 months and 6 months follow-up (3 months: 96.2% vs. 83.3%, p = 0.182; 6 months: 100% vs. 91.7%, p = 0.225). The subsidence in the 3DPT group was significantly lower than that in the PEEK group (3 months: 0.4 ± 0.2 mm vs. 0.9 ± 0.7 mm p = 0.004; 6 months: 0.7 ± 0.3 mm vs. 1.5 ± 0.8 mm, p < 0.001). 3DPT and PEEK cage all achieved sufficient contact with the cervical endplates. For the patients undergoing TLIF, the 3DPT (20 patients/[26 segments]) and PEEK groups (20 patients/[24 segments]) had no statistical difference in fusion rate (3 months: 84.6% vs. 58.3%, p = 0.059; 6 months: 92.3% vs. 75%, p = 0.132). The subsidence was lower than that in the PEEK group without significantly difference (3 months: 0.9 ± 0.7 mm vs.1.2 ± 0.9 mm p = 0.136; 6 months: 1.6 ± 1.0 mm vs. 2.0 ± 1.0 mm, p = 0.200). At the 3-month follow-up, the bone-cage interface contact of the 3DPT cage was significantly better than that of the PEEK cage (poor contact: 15.4% vs. 75%, p < 0.001). The values of UAR were higher in the 3DPT group than in the PEEK group during the follow-up in cervical and lumbar fusion, there were more statistical differences in lumbar fusion. There were no significant differences in the clinical assessment between 3DPT or PEEK cage in spinal fusion.

CONCLUSION

The 3DPT cage and PEEK cage can achieve excellent clinical outcomes in cervical and lumbar fusion. The 3DPT cage has advantage in fusion quality, subsidence severity, and bone-cage interface contact than PEEK cage.

State-of-the-art polyetheretherketone three-dimensional printing and multifunctional modification for dental implants

Polyetheretherketone (PEEK) is a high-performance thermoplastic polymer with an elastic modulus close to that of the jawbone. PEEK has the potential to become a new dental implant material for special patients due to its radiolucency, chemical stability, color similarity to teeth, and low allergy rate. However, the aromatic main chain and lack of surface charge and chemical functional groups make PEEK hydrophobic and biologically inert, which hinders subsequent protein adsorption and osteoblast adhesion and differentiation. This will be detrimental to the deposition and mineralization of apatite on the surface of PEEK and limit its clinical application. Researchers have explored different modification methods to effectively improve the biomechanical, antibacterial, immunomodulatory, angiogenic, antioxidative, osteogenic and anti-osteoclastogenic, and soft tissue adhesion properties. This review comprehensively summarizes the latest research progress in material property advantages, three-dimensional printing synthesis, and functional modification of PEEK in the fields of implant dentistry and provides solutions for existing difficulties. We confirm the broad prospects of PEEK as a dental implant material to promote the clinical conversion of PEEK-based dental implants.

Surface Topography of PLA Implants Defines the Outcome of Foreign Body Reaction: An In Vivo Study

The formation of a dense fibrous capsule around the foreign body and its contracture is the most common complication of biomaterial implantation. The aim of our research is to find out how the surface of the implant influences the inflammatory and fibrotic reactions in the surrounding tissues. We made three types of implants with a remote surface topography formed of polylactide granules with different diameters: large (100-200 µm), medium (56-100 µm) and small (1-56 µm). We placed these implants in skin pockets in the ears of six chinchilla rabbits. We explanted the implants on the 7th, 14th, 30th and 60th days and performed optical coherence tomography, and histological, immunohistochemical and morphometric studies. We examined 72 samples and compared the composition of immune cell infiltration, vascularization, the thickness of the peri-implant tissues, the severity of fibrotic processes and α-SMA expression in myofibroblasts. We analyzed the scattering coefficient of tissue layers on OCT scans. We found that implants made from large granules induced a milder inflammatory process and slower formation of a connective tissue capsule around the foreign body. Our results prove the importance of assessing the surface texture in order to avoid the formation of capsular contracture after implantation.

The application of 3D-printed auto-stable artificial vertebral body in en bloc resection and reconstruction of thoracolumbar metastases

BACKGROUND

Nerve compression symptoms and spinal instability, resulting from spinal metastases, significantly impact the quality of life for patients. A 3D-printed vertebral body is considered an effective approach to reconstruct bone defects following en bloc resection of spinal tumors. The advantage of this method lies in its customized shape and innermost porous structure, which promotes bone ingrowth and leads to reduced postoperative complications.

OBJECTIVE

The purpose of this study is to assess the effectiveness of 3D-printed auto-stable artificial vertebrae in the en bloc resection and reconstruction of thoracolumbar metastases.

METHODS

This study included patients who underwent en bloc resection of thoracolumbar metastases based on the Weinstein-Boriani-Biagini surgical staging system, between January 2019 and April 2021. The patients were divided into two groups: the observation group, which was reconstructed using 3D-printed auto-stable vertebral bodies, and the control group, treated with titanium cages and allograft bone. Evaluation criteria for the patients included assessment of implant subsidence, instrumentation-related complications, VAS score, and Frankel grading of spinal cord injury.

RESULTS

The median follow-up period was 21.8 months (range 12-38 months). Among the patients, 10 received a customized 3D-printed artificial vertebral body, while the remaining 10 received a titanium cage. The observation group showed significantly lower operation time, intraoperative blood loss, and postoperative drainage compared to the control group (P < 0.05). At the final follow-up, the average implant subsidence was 1.8 ± 2.1 mm for the observation group and 5.2 ± 5.1 mm for the control group (P < 0.05). The visual analog scale (VAS) scores were not statistically different between the two groups at preoperative, 24 h, 3 months, and 1 year after the operation (P < 0.05). There were no statistically significant differences in the improvements of spinal cord functions between the two groups.

CONCLUSION

The utilization of a 3D-printed auto-stable artificial vertebra for reconstruction following en bloc resection of thoracolumbar metastases appears to be a viable and dependable choice. The low occurrence of prosthesis subsidence with 3D-printed prostheses can offer immediate and robust stability.

Human Whole Blood Interactions with Craniomaxillofacial Reconstruction Materials: Exploring In Vitro the Role of Blood Cascades and Leukocytes in Early Healing Events

The present study investigated early interactions between three alloplastic materials (calcium phosphate (CaP), titanium alloy (Ti), and polyetheretherketone (PEEK) with human whole blood using an established in vitro slide chamber model. After 60 min of contact with blood, coagulation (thrombin-antithrombin complexes, TAT) was initiated on all test materials (Ti > PEEK > CaP), with a significant increase only for Ti. All materials showed increased contact activation, with the KK-AT complex significantly increasing for CaP (p < 0.001), Ti (p < 0.01), and PEEK (p < 0.01) while only CaP demonstrated a notable rise in KK-C1INH production (p < 0.01). The complement system had significant activation across all materials, with CaP (p < 0.0001, p < 0.0001) generating the most pronounced levels of C3a and sC5b-9, followed by Ti (p < 0.001, p < 0.001) and lastly, PEEK (p < 0.001, p < 0.01). This activation correlated with leukocyte stimulation, particularly myeloperoxidase release. Consequently, the complement system may assume a more significant role in the early stages post implantation in response to CaP materials than previously recognized. Activation of the complement system and the inevitable activation of leukocytes might provide a more favorable environment for tissue remodeling and repair than has been traditionally acknowledged. While these findings are limited to the early blood response, complement and leukocyte activation suggest improved healing outcomes, which may impact long-term clinical outcomes.

Titanium‑coated polyetheretherketone cages vs. polyetheretherketone cages in lumbar interbody fusion: A systematic review and meta‑analysis

Fusion material is one of the key factors in the success of lumbar interbody fusion surgery. The present meta-analysis compared the safety and efficacy of titanium-coated (Ti) polyetheretherketone (PEEK) and PEEK cages. Published literature on the use of Ti-PEEK and PEEK cages in lumbar interbody fusion was systematically searched on Embase, PubMed, Central, Cochrane Library, China National Knowledge Infrastructure and Wanfang databases. A total of 84 studies were retrieved and seven were included in the present meta-analysis. Literature quality was assessed using the Cochrane systematic review methodology. After data extraction, meta-analysis was performed using the ReviewManager 5.4 software. Meta-analysis showed that, compared with that in the PEEK cage group, the Ti-PEEK cage group showed a higher interbody fusion rate at 6 months postoperatively (95% CI, 1.09-5.60; P=0.03) and improved Oswestry Disability Index (ODI) scores at 3 months postoperatively [95% CI, -7.80-(-0.62); P=0.02] and visual analog scale (VAS) scores of back pain at 6 months postoperatively [95% CI, -0.8-(-0.23); P=0.0008]. However, there were no significant differences in intervertebral bone fusion rate (12 months after surgery), cage subsidence rate, ODI score (6 and 12 months after surgery) or VAS score (3 and 12 months after surgery) between the two groups. The results of the meta-analysis showed that the Ti-PEEK group had an improved interbody fusion rate and higher postoperative ODI score in the early postoperative period (≤6 months).

Malignant melanoma resection and reconstruction with the first manifestation of lumbar metastasis: A case report

BACKGROUND

Malignant melanoma (MM) has shown an increasing incidence worldwide, and a potential to metastasize to almost any part of the body. Clinically, MM with bone metastasis as the initial manifestation is extremely rare. Spinal metastatic MM can cause spinal cord or nerve root compression, resulting in severe pain and paralysis. Currently, the primary clinical treatments for MM are surgical resection in conjunction with chemotherapy, radiotherapy, and immunotherapy.

CASE SUMMARY

Here, we report the case of a 52-year-old male who presented to the clinic with progressive low back pain and limited nerve function. No primary lesion or spinal cord compression was detected from computed tomography and magnetic resonance imaging of the lumbar vertebrae and positron emission tomography scan. A lumbar puncture biopsy confirmed the diagnosis of lumbar spine metastatic MM. Following surgical resection, the patient’s quality of life improved, symptoms were relieved, and comprehensive treatment was initiated, which prevented recurrence.

CONCLUSION

Spinal metastatic MM is clinically rare, and may cause neurological symptoms, including paraplegia. Currently, the clinical treatment plan consists of surgical resection in combination with chemotherapy, radiotherapy, and immunotherapy.

Immune cell response to orthopedic and craniofacial biomaterials depends on biomaterial composition

Materials for craniofacial and orthopedic implants are commonly selected based on mechanical properties and corrosion resistance. The biocompatibility of these materials is typically assessed in vitro using cell lines, but little is known about the response of immune cells to these materials. This study aimed to evaluate the inflammatory and immune cell response to four common orthopedic materials [pure titanium (Ti), titanium alloy (TiAlV), 316L stainless steel (SS), polyetheretherketone (PEEK)]. Following implantation into mice, we found high recruitment of neutrophils, pro-inflammatory macrophages, and CD4+ T cells in response to PEEK and SS implants. Neutrophils produced higher levels of neutrophil elastase, myeloperoxidase, and neutrophil extracellular traps in vitro in response to PEEK and SS than neutrophils on Ti or TiAlV. Macrophages co-cultured on PEEK, SS, or TiAlV increased polarization of T cells towards Th1/Th17 subsets and decreased Th2/Treg polarization compared to Ti substrates. Although SS and PEEK are considered biocompatible materials, both induce a more robust inflammatory response than Ti or Ti alloy characterized by high infiltration of neutrophils and T cells, which may cause fibrous encapsulation of these materials. STATEMENT OF SIGNIFICANCE: Materials for craniofacial and orthopedic implants are commonly selected based on their mechanical properties and corrosion resistance. This study aimed to evaluate the immune cell response to four common orthopedic and craniofacial biomaterials: pure titanium, titanium-aluminum-vanadium alloy, 316L stainless steel, and PEEK. Our results demonstrate that while the biomaterials tested have been shown to be biocompatible and clinically successful, the inflammatory response is largely driven by chemical composition of the biomaterials.

Fabrication of bFGF/polydopamine-loaded PEEK implants for improving soft tissue integration by upregulating Wnt/β-catenin signaling

The difficulties associated with polyetheretherketone (PEEK) implants and soft tissue integration for craniomaxillofacial bone repair have led to a series of complications that limit the clinical benefits. In this study, 3D printed multi-stage microporous PEEK implants coated with bFGF via polydopamine were fabricated to enhance PEEK implant-soft tissue integration. Multistage microporous PEEK scaffolds prepared by sulfonation of concentrated sulfuric acid were coated with polydopamine, and then used as templates for electrophoretic deposition of bFGF bioactive factors. Achieving polydopamine and bFGF sustained release, the composite PEEK scaffolds possessed good mechanical properties, hydrophilicity, protein adhesion properties. The in vitro results indicated that bFGF/polydopamine-loaded PEEK exhibited good biocompatibility to rabbit embryonic fibroblasts (REF) by promoting cell proliferation, adhesion, and migration. Ribonucleic acid sequencing (RNA-seq) revealed that bFGF/polydopamine-loaded PEEK implants significantly upregulated the expression of genes and proteins associated with soft tissue integration and activated Wnt/β-catenin signaling in biological processes, but related expression of genes and proteins was significantly downregulated when the Wnt/β-catenin signaling was inhibited. Furthermore, in vivo bFGF/polydopamine-loaded PEEK implants exhibited excellent performance in improving the growth and adhesion of the surrounding soft tissue. In summary, bFGF/polydopamine-loaded PEEK implants possess soft tissue integration properties by activating the Wnt/β-catenin signaling, which have a potential translational clinical application in the future.

Bone marrow stromal cells generate an osteoinductive microenvironment when cultured on titanium-aluminum-vanadium substrates with biomimetic multiscale surface roughness

Osseointegration of titanium-based implants possessing complex macroscale/microscale/mesoscale/nanoscale (multiscale) topographies support a direct and functional connection with native bone tissue by promoting recruitment, attachment and osteoblastic differentiation of bone marrow stromal cells (MSCs). Recent studies show that the MSCs on these surfaces produce factors, including bone morphogenetic protein 2 (BMP2) that can cause MSCs not on the surface to undergo osteoblast differentiation, suggesting they may produce an osteogenic environmentin vivo. This study examined if soluble factors produced by MSCs in contact with titanium-aluminum-vanadium (Ti6Al4V) implants possessing a complex multiscale biomimetic topography are able to induce osteogenesis ectopically. Ti6Al4V disks were grit-blasted and acid-etched to create surfaces possessing macroscale and microscale roughness (MM), micro/meso/nanoscale topography (MN), and macro/micro/meso/nanoscale topography (MMN^TM). Polyether-ether-ketone (PEEK) disks were also fabricated by machining to medical-grade specifications. Surface properties were assessed by scanning electron microscopy, contact angle, optical profilometry, and x-ray photoelectron spectroscopy. MSCs were cultured in growth media (GM). Proteins and local factors in their conditioned media (CM) were measured on days 4, 8, 10 and 14: osteocalcin, osteopontin, osteoprotegerin, BMP2, BMP4, and cytokines interleukins 6, 4 and 10 (IL6, IL4, and IL10). CM was collected from D14 MSCs on MMN^TMand tissue culture polystyrene (TCPS) and lyophilized. Gel capsules containing active demineralized bone matrix (DBM), heat-inactivated DBM (iDBM), and iDBM + MMN-GM were implanted bilaterally in the gastrocnemius of athymic nude mice (N= 8 capsules/group). Controls included iDBM + GM; iDBM + TCPS-CM from D5 to D10 MSCs; iDBM + MMN-CM from D5 to D10; and iDBM + rhBMP2 (R&D Systems) at a concentration similar to D5-D10 production of MSCs on MMN^TMsurfaces. Legs were harvested at 35D. Bone formation was assessed by micro computed tomography and histomorphometry (hematoxylin and eosin staining) with the histology scored according to ASTM 2529-13. DNA was greatest on PEEK at all time points; DNA was lowest on MN at early time points, but increased with time. Cells on PEEK exhibited small changes in differentiation with reduced production of BMP2. Osteoblast differentiation was greatest on the MN and MMN^TM, reflecting increased production of BMP2 and BMP4. Pro-regenerative cytokines IL4 and IL10 were increased on Ti-based surfaces; IL6 was reduced compared to PEEK. None of the media from TCPS cultures was osteoinductive. However, MMN-CM exhibited increased bone formation compared to iDBM and iDBM + rhBMP2. Furthermore, exogenous rhBMP2 alone, at the concentration found in MMN-CM collected from D5 to D10 cultures, failed to induce new bone, indicating that other factors in the CM play a critical role in that osteoinductive microenvironment. MSCs cultured on MMN^TMTi6Al4V surfaces differentiate and produce an increase in local factors, including BMP2, and the CM from these cultures can induce ectopic bone formation compared to control groups, indicating that the increased bone formation arises from the local response by MSCs to a biomimetic, multiscale surface topography.

Surface Treatments of PEEK for Osseointegration to Bone

Polymers, in general, and Poly (Ether-Ether-Ketone) (PEEK) have emerged as potential alternatives to conventional osseous implant biomaterials. Due to its distinct advantages over metallic implants, PEEK has been gaining increasing attention as a prime candidate for orthopaedic and dental implants. However, PEEK has a highly hydrophobic and bioinert surface that attenuates the differentiation and proliferation of osteoblasts and leads to implant failure. Several improvements have been made to the osseointegration potential of PEEK, which can be classified into three main categories: (1) surface functionalization with bioactive agents by physical or chemical means; (2) incorporation of bioactive materials either as surface coatings or as composites; and (3) construction of three-dimensionally porous structures on its surfaces. The physical treatments, such as plasma treatments of various elements, accelerated neutron beams, or conventional techniques like sandblasting and laser or ultraviolet radiation, change the micro-geometry of the implant surface. The chemical treatments change the surface composition of PEEK and should be titrated at the time of exposure. The implant surface can be incorporated with a bioactive material that should be selected following the desired use, loading condition, and antimicrobial load around the implant. For optimal results, a combination of the methods above is utilized to compensate for the limitations of individual methods. This review summarizes these methods and their combinations for optimizing the surface of PEEK for utilization as an implanted biomaterial.

Outcome of Ti/PEEK Versus PEEK Cages in Minimally Invasive Transforaminal Lumbar Interbody Fusion

STUDY DESIGN

Retrospective case-control study.

OBJECTIVES

This study aims to present the clinical and radiographical outcomes of the titanium-polyetheretherketone (Ti/PEEK) composite cage compared to those of the standard PEEK cage in patients receiving minimally invasive transforaminal lumbar interbody fusion (MI-TLIF).

METHODS

Patients receiving 1 level MI-TLIF between October 2015 and October 2017 were included with a minimum of 2-year follow-up. The patients were segregated into 2 groups; Ti/PEEK group and PEEK group. Each patient was propensity-matched using preoperative age, sex, and body mass index. Early fusion rate was evaluated by computed tomography at postoperative 6 months. Clinical outcomes were assessed using the visual analog scale (VAS) and Oswestry Disability Index (ODI) scores.

RESULTS

After matching, there were 27 patients included in each group. The demographics, diagnosis, and surgical details were not significantly different between the 2 groups. The 6-month rate was 88.9% in Ti/PEEK group. The fusion rate and cage subsidence rate had no difference between the 2 groups. The complication rate in the Ti/PEEK group was comparable to that in the PEEK group. There was no difference in VAS and ODI scores during a 2-year follow-up period.

CONCLUSIONS

The use of Ti/PEEK composite cage was as safe and effective as the use of PEEK cage in MI-TLIF. The 6-month fusion rate was 88.9%. Our finding revealed comparable clinical results for surgeons using Ti/PEEK composite cages in MI-TLIF compared to those using the PEEK cage.

Subsidence Rates Associated With Porous 3D-Printed Versus Solid Titanium Cages in Transforaminal Lumbar Interbody Fusion

STUDY DESIGN

Retrospective Cohort Study.

OBJECTIVE

To determine whether 3D-printed porous titanium (3DPT) interbody cages offer any clinical or radiographic advantage over standard solid titanium (ST) interbody cages in transforaminal lumbar interbody fusions (TLIF).

METHODS

A consecutive series of adult patients undergoing one- or two-level TLIF with either 3DPT or ST "banana" cages were analyzed for patient reported outcome measures (PROMs), radiographic complications, and clinical complications. Exclusion criteria included clinical or radiographic follow-up less than 1 year.

RESULTS

The final cohort included 90 ST interbody levels from 74 patients, and 73 3DPT interbody levels from 50 patients for a total of 124 patients. Baseline demographic variables and comorbidity rates were similar between groups (P > .05). Subsidence of any grade occurred more frequently in the ST group compared with the 3DPT group (24.4% vs 5.5%, respectively, P = .001). Further, the ST group was more likely to have higher grades of subsidence than the 3DPT group (P = .009). All PROMs improved similarly after surgery and revision rates did not differ between groups (both P > .05). On multivariate analysis, significant positive correlators with increasing subsidence grade included greater age (P = .015), greater body mass index (P = .043), osteoporosis/osteopenia (P < .027), and ST cage type (P = .019).

CONCLUSIONS

When considering interbody material for TLIF, both ST and 3DPT cages performed well; however, 3DPT cages were associated with lower rates of subsidence. The clinical relevance of these findings deserves further randomized, prospective investigation.

Impact of surface roughness and bulk porosity on spinal interbody implants

Spinal fusion surgeries are performed to treat a multitude of cervical and lumbar diseases that lead to pain and disability. Spinal interbody fusion involves inserting a cage between the spinal vertebrae, and is often utilized for indirect neurologic decompression, correction of spinal alignment, anterior column stability, and increased fusion rate. The long-term success of interbody fusion relies on complete osseointegration between the implant surface and vertebral end plates. Titanium (Ti)-based alloys and polyetheretherketone (PEEK) interbody cages represent the most commonly utilized materials and provide sufficient mechanics and biocompatibility to assist in fusion. However, modification to the surface and bulk characteristics of these materials has been shown to maximize osseointegration and long-term stability. Specifically, the introduction of intrinsic porosity and surface roughness has been shown to affect spinal interbody mechanics, vascularization, osteoblast attachment, and ingrowth potential. This narrative review synthesizes the mechanical, in vitro, in vivo, and clinical effects on fusion efficacy associated with introduction of porosity in Ti (neat and alloy) and PEEK intervertebral implants.

Poly (Ether-Ether-Ketone) for Biomedical Applications: From Enhancing Bioactivity to Reinforced-Bioactive Composites-An Overview

The global orthopedic market is forecasted to reach US$79.5 billion by the end of this decade. Factors driving the increase in this market are population aging, sports injury, road traffic accidents, and overweight, which justify a growing demand for orthopedic implants. Therefore, it is of utmost importance to develop bone implants with superior mechanical and biological properties to face the demand and improve patients' quality of life. Today, metallic implants still hold a dominant position in the global orthopedic implant market, mainly due to their superior mechanical resistance. However, their performance might be jeopardized due to the possible release of metallic debris, leading to cytotoxic effects and inflammatory responses in the body. Poly (ether-ether-ketone) (PEEK) is a biocompatible, high-performance polymer and one of the most prominent candidates to be used in manufacturing bone implants due to its similarity to the mechanical properties of bone. Unfortunately, the bioinert nature of PEEK culminates in its diminished osseointegration. Notwithstanding, PEEK's bioactivity can be improved through surface modification techniques and by the development of bioactive composites. This paper overviews the advantages of using PEEK for manufacturing implants and addresses the most common strategies to improve the bioactivity of PEEK in order to promote enhanced biomechanical performance.

The progress in titanium alloys used as biomedical implants: From the view of reactive oxygen species

Titanium and Titanium alloys are widely used as biomedical implants in oral and maxillofacial surgery, due to superior mechanical properties and biocompatibility. In specific clinical populations such as the elderly, diabetics and patients with metabolic diseases, the failure rate of medical metal implants is increased significantly, putting them at increased risk of revision surgery. Many studies show that the content of reactive oxygen species (ROS) in the microenvironment of bone tissue surrounding implant materials is increased in patients undergoing revision surgery. In addition, the size and shape of materials, the morphology, wettability, mechanical properties, and other properties play significant roles in the production of ROS. The accumulated ROS break the original balance of oxidation and anti-oxidation, resulting in host oxidative stress. It may accelerate implant degradation mainly by activating inflammatory cells. Peri-implantitis usually leads to a loss of bone mass around the implant, which tends to affect the long-term stability and longevity of implant. Therefore, a great deal of research is urgently needed to focus on developing antibacterial technologies. The addition of active elements to biomedical titanium and titanium alloys greatly reduce the risk of postoperative infection in patients. Besides, innovative technologies are developing new biomaterials surfaces conferring anti-infective properties that rely on the production of ROS. It can be considered that ROS may act as a messenger substance for the communication between the host and the implanted material, which run through the entire wound repair process and play a role that cannot be ignored. It is necessary to understand the interaction between oxidative stress and materials, the effects of oxidative stress products on osseointegration and implant life as well as ROS-induced bactericidal activity. This helps to facilitate the development of a new generation of well-biocompatible implant materials with ROS responsiveness, and ultimately prolong the lifespan of implants.

Surface Modifications of High-Performance Polymer Polyetheretherketone (PEEK) to Improve Its Biological Performance in Dentistry

This comprehensive review focuses on polyetheretherketone (PEEK), a synthetic thermoplastic polymer, for applications in dentistry. As a high-performance polymer, PEEK is intrinsically robust yet biocompatible, making it an ideal substitute for titanium-the current gold standard in dentistry. PEEK, however, is also inert due to its low surface energy and brings challenges when employed in dentistry. Inert PEEK often falls short of achieving a few critical requirements of clinical dental materials, such as adhesiveness, osseoconductivity, antibacterial properties, and resistance to tribocorrosion. This study aims to review these properties and explore the various surface modification strategies that enhance the performance of PEEK. Literatures searches were conducted on Google Scholar, Research Gate, and PubMed databases using PEEK, polyetheretherketone, osseointegration of PEEK, PEEK in dentistry, tribology of PEEK, surface modifications, dental applications, bonding strength, surface topography, adhesive in dentistry, and dental implant as keywords. Literature on the topics of surface modification to increase adhesiveness, tribology, and osseointegration of PEEK were included in the review. The unavailability of full texts was considered when excluding literature. Surface modifications via chemical strategies (such as sulfonation, plasma treatment, UV treatment, surface coating, surface polymerization, etc.) and/or physical approaches (such as sandblasting, laser treatment, accelerated neutral atom beam, layer-by-layer assembly, particle leaching, etc.) discussed in the literature are summarized and compared. Further, approaches such as the incorporation of bioactive materials, e.g., osteogenic agents, antibacterial agents, etc., to enhance the abovementioned desired properties are explored. This review presents surface modification as a critical and essential approach to enhance the biological performance of PEEK in dentistry by retaining its mechanical robustness.

Strontium-modified porous polyetheretherketone with the triple function of osteogenesis, angiogenesis, and anti-inflammatory for bone grafting

Polyetheretherketone (PEEK) is a potential bone repair material because of its stable chemical and good mechanical properties. However, the biological inertness of PEEK limits its clinical application. Sr²⁺ has multi biological functions, including promoting bone formation and blood vessel regeneration and inhibiting inflammation. In this paper, PEEK was modified with Sr²⁺ with the purpose to construct PEEK bone graft material with triple functions of osteogenesis, angiogenesis, and anti-inflammatory. The results showed that Sr-modified PEEK could stably release Sr²⁺ for a long time in the PBS solution, and indeed could promote the proliferation and differentiation of osteoblasts, promote angiogenesis, and inhibit inflammation. Therefore, it is believed that this multifunctional PEEK with Sr²⁺ should show great promise for clinical applications in bone repair.

An update of interbody cages for spine fusion surgeries: from shape design to materials

INTRODUCTION

Discectomy and interbody fusion are widely used in the treatment of intervertebral disc-related diseases. Among them, the interbody cage plays a significant role. However, the complications related to the interbody cage, such as nonunion or pseudoarthrosis, subsidence, loosening, and prolapse of the cage, cannot be ignored. By changing the design and material of the interbody fusion cage, a better fusion effect can be obtained, the incidence of appeal complications can be reduced, and the quality of life of patients after interbody fusion can be improved.

AREAS COVERED

This study reviewed the research progress of cage design and material and discussed the methods of cage design and material to promote intervertebral fusion.

EXPERT OPINION

Current treatment of cervical and lumbar degenerative disease requires interbody fusion to maintain decompression and to promote fusion and reduce the incidence of fusion failure through improvements in implant material, design, internal structure, and function. However, interbody fusion is not an optimal solution for treating vertebral instability.Abbreviations: ACDF, Anterior cervical discectomy and fusion; ALIF, anterior lumbar interbody fusion; Axi-aLIF, axial lumbar interbody fusion; BAK fusion cage, Bagby and Kuslich fusion cage; CADR, cervical artificial disc replacement; DBM, decalcified bone matrix; HA, hydroxyapatite; LLIF/XLIF, lateral or extreme lateral interbody fusion; MIS-TLIF, minimally invasive transforaminal lumbar interbody fusion; OLIF/ATP, oblique lumbar interbody fusion/anterior to psoas; PEEK, Poly-ether-ether-ketone; PLIF, posterior lumbar interbody fusion; ROI-C, Zero-profile Anchored Spacer; ROM, range of motion; SLM, selective melting forming; TLIF, transforaminal lumbar interbody fusion or.

Can a bioactive interbody device reduce the cost burden of achieving lateral lumbar fusion?

OBJECTIVE

Intervertebral devices are increasingly utilized for fusion in the lumbar spine, along with a variety of bone graft materials. These various grafting materials often have substantial cost burdens for the surgical procedure, although they are necessary to overcome the limitations in healing capacity for many traditional interbody devices. The use of bioactive interbody fusion devices, which have demonstrable stimulatory capacity for the surrounding osteoblasts and osteoprogenitor cells and allow for osseointegration, may reduce this heavy reliance on osteobiologics for achieving interbody fusion. The objective of this study was to evaluate the rate of successful interbody fusion with a bioactive lateral lumbar interbody titanium implant with limited volume and low-cost graft material.

METHODS

The authors conducted a retrospective study (May 2017 to October 2018) of consecutively performed lateral lumbar interbody fusions with a bioactive 3D-printed porous titanium interbody device. Each interbody device was filled with 2-3 cm3/cage of a commercially available ceramic bone extender (β-tricalcium phosphate-hydroxyapatite) and combined with posterior pedicle screw fixation. No other biological agents or grafts were utilized. Demographic, clinical, and radiographic variables were captured. Fusion success was the primary endpoint of the study, with graft subsidence, fixation failure, and patient-reported outcomes (Oswestry Disability Index [ODI] and visual analog scale [VAS]-back and -leg pain scores) collected as secondary endpoints. The authors utilized a CT-based fusion classification system that accounted for both intervertebral through-growth (bone bridging) and ingrowth (integration of bone at the endplate-implant interface).

RESULTS

In total, 136 lumbar levels were treated in 90 patients. The mean age was 69 years, and 63% of the included patients were female. Half (50.0%) had undergone previous spinal surgery, and a third (33.7%) had undergone prior lumbar fusion. A third (33.7%) were treated at multiple levels (mean levels per patient 1.51). One year after surgery, the mean improvements in patient-reported outcomes (vs preoperative scores) were -17.8 for ODI (p < 0.0001), -3.1 for VAS-back pain (p < 0.0001), and -2.9 for VAS-leg pain (p < 0.0001). Bone bridging and/or appositional integrity was achieved in 99.3% of patients, including 97.8% who had complete bone bridging. No fixation loosening or implant failure was observed at any segment. Low-grade graft subsidence (Marchi grade ≤ I) occurred in 3 levels (2.2%), and intraoperative endplate violation occurred twice (1.5%). High-grade subsidence was not found. No implant failure or revision surgery for pseudarthrosis/subsidence was necessary.

CONCLUSIONS

The use of bioactive titanium interbody devices with a large surface footprint appears to result in a very high rate of effective fusion, despite the use of a small volume of low-cost biological material. This potential change in the osteobiologics required to achieve high fusion rates may have a substantially beneficial impact on the economic burden inherent to spinal fusion.

Comparison Between 3-Dimensional-Printed Titanium and Polyetheretherketone Cages: 1-Year Outcome After Minimally Invasive Transforaminal Interbody Fusion

OBJECTIVE

Three-dimensional (3D)-printed titanium implants have been developed recently, but the utility is not yet proven. The aim of this study was to compare 3D-printed titanium and polyetheretherketone (PEEK) implants after minimally invasive transforaminal lumbar interbody fusion (MIS-TLIF).

METHODS

Between October 2018 and September 2021, we retrospectively analyzed 83 patients who underwent single-level MIS-TLIF (3D-printed titanium, 40; PEEK, 43). Radiologic parameters were assessed with x-ray and computed tomography (CT) at postoperative 1 week, 6 months, and 1 year. Clinical status was evaluated using Oswestry Disability Index, visual analogue scale score, and Bridwell fusion grading was assessed on 6-month and 1-year postoperative CT.

RESULTS

There were no differences between the 2 groups in demographics and clinical outcomes. At 1-year of follow-up, the reported 3D-printed titanium fusion grades were grade I: 77.5% (31 patients), grade II: 17.5% (7 patients), and grade III: 5% (2 patients). The PEEK fusion grades were grade I: 51.2% (22 patients), grade II: 41.9% (18 patients), and grade III: 7.0% (3 patients). For overall fusion rate (grade I + II), there was no difference between the 2 cages (95.0% vs. 93.0%, p = 0.705), but grade I was reported at a higher incidence in 3D-printed titanium than PEEK (77.5% vs. 51.2%, p = 0.013). There was no difference between cages based on subsidence and complications.

CONCLUSION

There were no significant differences in the overall fusion rate for MIS-TLIF surgery between 3D-printed titanium and PEEK, but the fusion grade was better in 3D-printed titanium than in PEEK. Long-term follow-up is required to verify the effectiveness.

Prospective, Randomized, Blinded Clinical Trial Comparing PEEK and Allograft Spacers in Patients Undergoing Anterior Cervical Discectomy and Fusion Surgeries

STUDY DESIGN

Prospective, randomized, blinded clinical trial.

OBJECTIVE

To examine clinical and radiological outcomes in patients undergoing anterior cervical discectomy and fusion (ACDF) surgeries randomized to receive either polyether-ether-ketone (PEEK) or structural bone allografts.

SUMMARY OF BACKGROUND DATA

The biomechanical qualities as well as osteoconductive, osteogenic, and osteoinductive properties of various graft materials have been previously evaluated. There remain questions, however, as to whether there are any clinical and/or radiographic outcome differences in the selection of interbody graft types for ACDF.

METHODS

Patients undergoing one- to three-level ACDF with single anterior plate fixation were randomized (1:1 ratio) to receive either cortical allograft or PEEK interbody spacers. Radiographic and clinical outcomes were assessed at 3, 6, 12, and 24 months with an additional postoperative radiographic assessment.

RESULTS

A total of 120 patients were enrolled and randomized. Comparing clinical outcomes, no differences in arm or neck pain scores were noted; however, there was a statistically significant (≤0.041) improvement in SF-36 PCS scores for the allograft group at all follow-up time points and a tendency toward lower disability scores. Overall, evidence of radiographic fusion was achieved in 87 (91.6%) patients: five (10.2%) and three (6.5%) patients had pseudoarthrosis (P = 0.72) in the PEEK and allograft groups, respectively. At 24 months' follow-up time, any cervical or segmental alignment restoration achieved with surgery was lost and no statistically significant changes were detected when all levels of surgery were included. Likewise, there were no statistically significant differences between the groups for anterior or posterior body height measurements at the 24 months' follow-up. Approximately 20% of patients had anterior and posterior subsidence, all grade 0 regardless of the group assignment.

CONCLUSION

Comparable radiographic outcomes were observed for patients undergoing one- to three-level PEEK versus allograft-assisted ACDF surgeries. Although MCID comparisons suggest that allograft and PEEK-treated patients have similar clinical outcomes, testing that incorporates the magnitude of the change suggests that there may be a statistically significant greater magnitude of improvement for the allograft group patients, but further studies with a larger sample size would be helpful to determine if a true effect exists.

Well-orchestrated physico-chemical and biological factors for enhanced secretion of osteogenic and angiogenic extracellular vesicles by mesenchymal stem cells in a 3D culture format

The secretome of mesenchymal stem cells (MSCs) is being studied for its regenerative potential for the treatment of various disorders, including bone diseases. However, mimicking the physiological parameters of native bone could further improve MSCs' secretory profile. The proteomic analysis revealed that MSCs have a diverse secretory profile depending on the cell formats used to grow them, such as two-dimensional (2D) or three-dimensional (3D) microenvironments. Stem cells are given biochemical and biophysical stimuli in a 3D milieu that mimics in vivo situations. Compared to the gold standard monolayer culture, extracellular vesicles (EVs) released under 3D conditions improved the EV cargo numerically and qualitatively. The higher requirements of EVs in clinical trials with consistent therapeutic potential are challenging. This review discusses the impact of cell culture formats on the regenerative potential of MSCs, specifically in bone regeneration. The poor yield and heterogeneity issues have hampered the therapeutic usage of EVs. Therefore, this review further explores various engineering approaches that could enhance EVs' scalability from MSCs and their therapeutic effectiveness beyond their native utility in bone tissue regeneration. This review also highlights some of the upcoming 3D approaches/models that might be useful for the enhanced secretion of therapeutic EVs from stem cells. Finally, we discuss possible future directions and conclusions in this domain.

Evolution of polyetheretherketone (PEEK) and titanium interbody devices for spinal procedures: a comprehensive review of the literature

INTRODUCTION

Interbody fusion is commonly utilized for arthrodesis and stability among patients undergoing spine surgery. Over the last few decades, interbody device materials, such as titanium and polyetheretherketone (PEEK), have been replacing traditional autografts and allografts for interbody fusion. As such, with the exponential growth of bioengineering, a large variety cage surface technologies exist. Different combinations of cage component materials and surface modifications have been created to optimize interbody constructs for surgical use. This review aims to provide a comprehensive overview of common surface technologies, their performance in the clinical setting, and recent modifications and material combinations.

MATERIALS AND METHODS

We performed a comprehensive review of the literature on titanium and PEEK as medical devices between 1964 and 2021. We searched five major databases, resulting in 4974 records. Articles were screened for inclusion manually by two independent reviewers, resulting in 237 articles included for review.

CONCLUSION

Interbody devices have rapidly evolved over the last few decades. Biomaterial and biomechanical modifications have allowed for continued design optimization. While titanium has a high osseointegrative capacity, it also has a high elastic modulus and is radio-opaque. PEEK, on the other hand, has a lower elastic modulus and is radiolucent, though PEEK has poor osseointegrative capacity. Surface modifications, material development advancements, and hybrid material devices have been utilized in search of an optimal spinal implant which maximizes the advantages and minimizes the disadvantages of each interbody material.

The response of soft tissue cells to Ti implants is modulated by blood-implant interactions

Titanium-based dental implants have been highly optimized to enhance osseointegration, but little attention has been given to the soft tissue-implant interface, despite being a major contributor to long term implant stability. This is strongly linked to a lack of model systems that enable the reliable evaluation of soft tissue-implant interactions. Current in vitro platforms to assess these interactions are very simplistic, thus suffering from limited biological relevance and sensitivity to varying implant surface properties. The aim of this study was to investigate how blood-implant interactions affect downstream responses of different soft tissue cells to implants in vitro, thus taking into account not only the early events of blood coagulation upon implantation, but also the multicellular nature of soft tissue. For this, three surfaces (smooth and hydrophobic; rough and hydrophobic; rough and hydrophilic with nanostructures), which reflect a wide range of implant surface properties, were used to study blood-material interactions as well as cell-material interactions in the presence and absence of blood. Rough surfaces stimulated denser fibrin network formation compared to smooth surfaces and hydrophilicity accelerated the rate of blood coagulation compared to hydrophobic surfaces. In the absence of blood, smooth surfaces supported enhanced attachment of human gingival fibroblasts and keratinocytes, but limited changes in gene expression and cytokine production were observed between surfaces. In the presence of blood, rough surfaces supported enhanced fibroblast attachment and stimulated a stronger anti-inflammatory response from macrophage-like cells than smooth surfaces, but only smooth surfaces were capable of supporting long-term keratinocyte attachment and formation of a layer of epithelial cells. These findings indicate that surface properties not only govern blood-implant interactions, but that this can in turn also significantly modulate subsequent soft tissue cell-implant interactions.

Comparison of Short-Term Radiographical and Clinical Outcomes After Posterior Lumbar Interbody Fusion With a 3D Porous Titanium Alloy Cage and a Titanium-Coated PEEK Cage

STUDY DESIGN

Clinical case series.

OBJECTIVES

To compare the short-term (≤1 year) radiographical and clinical outcomes between posterior lumbar interbody fusion (PLIF) with a titanium-coated poly-ether-ether-ketone (TCP) cage and PLIF with a three-dimensional porous titanium alloy (PTA) cage.

METHODS

Overall, 63 patients who had undergone 1- or 2-level PLIF since March 2015 were enrolled (median age, 71 years). The first 34 patients underwent PLIF with TCP cages (until June 2017) and the next 29 patients with PTA cages. Fusion status, vertebral endplate cyst formation (cyst sign: grade 0, none; grade 1, focal; and grade 2, diffuse), cage subsidence (grade 0, <1 mm; grade 1, 1-3 mm; and grade 2, >3 mm), and patient-reported quality of life (QOL) outcomes based on the Japanese Orthopaedic Association Back Pain Evaluation Questionnaire (JOABPEQ) were compared at 6 months and 1 year postoperatively between the 2 cage groups.

RESULTS

Cyst sign and cage subsidence grades were significantly lower in the PTA cage group than in the TCP cage group at 6 months postoperatively (cyst sign, p = 0.044; cage subsidence, p = 0.043). In contrast, the fusion rate and surgery effectiveness based on JOABPEQ at both 6 months and 1 year postoperatively were not different between the 2 groups.

CONCLUSIONS

Patient-reported QOL outcomes were similar between the TCP and PTA cage groups until 1 year postoperatively. However, a higher incidence and severity of postoperative vertebral endplate cyst formation in patients with the TCP cage was a noteworthy radiographical finding.

Tailoring the biologic responses of 3D printed PEEK medical implants by plasma functionalization

OBJECTIVE

The objective of this study was to determine the effect of two plasma surface treatments on the biologic responses of PEEK medical implants manufactured by fused filament fabrication (FFF) 3D printing technology.

METHODS

This study created standard PEEK samples using an FFF 3D printer. After fabrication, half of the samples were polished to simulate a smooth PEEK surface. Then, argon (Ar) or oxygen (O₂) plasma was used to modify the bioactivity of FFF 3D printed and polished PEEK samples. Scanning electron microscopy (SEM) and a profilometer were used to determine the microstructure and roughness of the sample surfaces. The wettability of the sample surface was assessed using a drop shape analyzer (DSA) after plasma treatment and at various time points following storage in a closed environment. Cell adhesion, metabolic activity, proliferation, and osteogenic differentiation of SAOS-2 osteoblasts were evaluated to determine the in vitro osteogenic activity.

RESULTS

SEM analysis revealed that several spherical nanoscale particles and humps appeared on sample surfaces following plasma treatment. The wettability measurement demonstrated that plasma surface treatment significantly increased the surface hydrophilicity of PEEK samples, with only a slight aging effect found after 21 days. Cell adhesion, spreading, proliferation, and differentiation of SAOS-2 osteoblasts were also up-regulated after plasma treatment. Additionally, PEEK samples treated with O₂ plasma demonstrated a higher degree of bioactivation than those treated with Ar.

SIGNIFICANCE

Plasma-modified PEEK based on FFF 3D printing technology was a feasible and prospective bone grafting material for bone/dental implants.

Radiological and Clinical Outcomes after Anterior Cervical Discectomy and Fusion (ACDF) with an Innovative 3D Printed Cellular Titanium Cage Filled with Vertebral Bone Marrow

Objectives

To assess the clinical and radiological outcomes after ACDF with 3D printed cellular titanium cages filled with bone marrow and to compare the clinical and radiological results with the current scientific literature.

Methods

ACDF was performed monosegmentally under standardized conditions. X-rays were analyzed to determine the range of motion, fusion rates, and subsidence preoperatively and 3 and 12 months postoperatively. Clinical outcome measurements included neck disability index (NDI), visual analogue scale (VAS) for brachialgia and cervicalgia, and patient satisfaction.

Results

18 patients were included in the study. The mean RoM decreased from 7.7° ± 2.6 preoperatively to 1.7° ± 1.1° after 3 months and 1.8° ± 1.2° 12 months after surgery. The fusion rates were at 94.4% after 3 and 12 months. The mean subsidence was 0.9 mm ± 0.5 mm 3 months postoperatively and 1.1 mm ± 0.5 mm 12 months after surgery. The mean NDI improved significantly from preoperatively to 12 months postoperatively (34.6 ± 6.2 and 3.4 ± 4.1, respectively). The VAS-neck also showed a large improvement from 5.8 ± 2.2 before and 1.3 ± 1.4 12 months after surgery, as did the VAS-arm (6.4 ± 1.5 and 0.9 ± 1.6, respectively). Patient satisfaction was high throughout the follow-up period.

Conclusion

ACDF with a 3D printed titanium cage resulted in fast fusion without pathological subsidence. In comparison to other cage materials such as PEEK, the 3D printed titanium cage was noninferior in regard to its fusion rate and clinical results.

A Review of Biomimetic Topographies and Their Role in Promoting Bone Formation and Osseointegration: Implications for Clinical Use

The use of metallic and polymeric materials for implants has been increasing over the past decade. This trend can be attributed to a variety of factors including a significant increase in basic science research focused on implant material characteristics and how various surface modifications may stimulate osseointegration and, ultimately, fusion. There are many interbody fusion devices and dental implants commercially available; however, detailed information about their surface properties, and the effects that various materials and surface modifications may have on osteogenesis, is lacking in the literature. While the concept of bone-implant osseointegration is a relatively recent addition to the spine fusion literature, there is a comparatively large body of literature related to dental implants. The purpose of this article is to summarize the science of surface modified bone-facing implants, focusing on biomimetic material chemistry and topography of titanium implants, to promote a better understanding of how these characteristics may impact bone formation and osseointegration. This manuscript has the following aspects: highlights the role of titanium and its alloys as potent osteoconductive bioactive materials; explores the importance of biomimetic surface topography at the macro-, micro- and nano-scale; summarizes how material surface design can influence osteogenesis and immune responses in vitro; focuses on the kinds of surface modifications that play a role in the process. Biomimetic surface modifications can be varied across many clinically available biomaterials, and the literature supports the hypothesis that those biomaterial surfaces that exhibit physical properties of bone resorption pits, such as roughness and complex hierarchical structures at the submicron and nanoscale, are more effective in supporting osteoblast differentiation in vitro and osteogenesis in vivo.

Clinical and Cost-Effectiveness of Lumbar Interbody Fusion Using Tritanium Posterolateral Cage (vs. Propensity-Matched Cohort of PEEK Cage)

Introduction

Surgical management of degenerative lumbar spine disorders is effective at improving patient pain, disability, and quality of life; however, obtaining a durable posterolateral fusion after decompression remains a challenge. Interbody fusion technologies are viable means of improving fusion rates in the lumbar spine, specifically various graft materials including autograft, structural allograft, titanium, and polyether ether ketone. This study assesses the effectiveness of Tritanium posterolateral cage in the treatment of degenerative disk disease.

Methods

Nearest-neighbor 1:1 matched control transforaminal lumbar interbody fusion with PEEK vs. Tritanium posterior lumbar (PL) cage interbody fusion patients were identified using propensity scoring from patients that underwent elective surgery for degenerative disk diseases. Line graphs were generated to compare the trajectories of improvement in patient-reported outcomes (PROs) from baseline to 3 and 12 months postoperatively. The nominal data were compared via the χ² test, while the continuous data were compared via Student's t-test.

Results

The two groups had no difference regarding either the 3- or 12-month Euro-Qol-5D (EQ-5D), numeric rating scale (NRS) leg pain, and NRS back pain; however, the Tritanium interbody cage group had better Oswestry Disability Index (ODI) scores compared to the control group of the PEEK interbody cage at both 3 and 12 months (p=0.013 and 0.048).

Conclusions

Our results indicate the Tritanium cage is an effective alternative to the previously used PEEK cage in terms of PROs, surgical safety, and radiological parameters of surgical success. The Tritanium cohort showed better ODI scores, higher fusion rates, lower subsidence, and lower indirect costs associated with surgical management, when compared to the propensity-matched PEEK cohort.

The Role of Surface Chemistry in the Osseointegration of PEEK Implants

Poly(etheretherketone) (PEEK) implants suffer from poor osseointegration because of chronic inflammation. In this study, we hypothesized that adding NH₂ and COOH groups to the surface of PEEK could modulate macrophage responses by altering protein adsorption and improve its osseointegration. NH₂ and COOH-functionalized PEEK surfaces induced pro- and anti-inflammatory macrophage responses, respectively, and differences in protein adsorption patterns on these surfaces were related to the varied inflammatory responses. The macrophage responses to NH₂ surfaces significantly reduced the osteogenic differentiation of mesenchymal stem cells (MSCs). MSCs cultured on NH₂ surfaces differentiated less than those on COOH surfaces even though NH₂ surfaces promoted the most mineralization in simulated body fluid solutions. After 14 days in rat tibia unicortical defects, the bone around NH₂ surfaces had thinner trabeculae and higher specific bone surface than the bone around unmodified implants; surprisingly, the NH₂ implants significantly increased bone-binding over the unmodified implants, while COOH implants only showed a trend for increasing bone-binding. Taken together, these results suggest that both mineral-binding and immune responses play a role in osseointegration, and PEEK implant integration may be improved with mixtures of these two functional groups to harness the ability to reduce inflammation and bind bone strongly.

Bone Mineralization and Spinal Fusion Evaluation of a Truss-based Interbody Fusion Device: Ovine Finite Element Analysis with Confirmatory In Vivo Outcomes

STUDY DESIGN

Finite element analysis (FEA) and in vivo ovine spinal interbody fusion study.

OBJECTIVE

To determine comparative load-induced strain amplitudes, bone mineralization and fusion outcomes associated with different diameter struts in a truss-based interbody fusion device.

SUMMARY OF BACKGROUND DATA

Additive manufacturing technology has been employed to develop implants that actively participate in the fusion process. The truss device enables the optimal transfer of compressive and tensile stresses via the struts. Mechanobiologic principles postulate that strut diameter can be regulated to allow different magnitudes of strain distribution within the struts which may affect fusion rates.

METHODS

Modeling of strain distributions as a function of strut diameter (0.75, 1.0, 1.25, and 1.5 mm) employed FEA that simulated physiologic loading conditions. A confirmatory in vivo ovine lumbar spinal interbody fusion study compared fusion scores and bone histomorphometric variables for cages with 0.75 and 1.5 mm strut diameters. Outcomes were compared at 3-, 6-, and 12-month follow-up intervals.

RESULTS

FEA showed an inverse association between strut diameter and peak strain amplitude. Cages with 1.0, 1.25, and 1.5 mm struts had peak strain values that were 36%, 60%, and 73% lower than the 0.75 mm strut strain value. In vivo results showed the mean fusion score for the 0.75 mm diameter strut cage was significantly greater by 3-months versus the 1.5 mm strut cage, and remained significantly higher at each subsequent interval (P < 0.001 for all comparisons). Fusion rates were 95%, 100%, and 100% (0.75 mm) and 72.7%, 86.4%, and 95.8% (1.5 mm) at 3, 6, and 12 months. Thinner struts had greater mineralized bone tissue and less fibrous/chondral tissue than the thicker struts at each follow-up.

CONCLUSION

Validating FEA estimates, cages with smaller diameter struts exhibited more rapid fusion consolidation and more aggressive osseointegration compared with cages with larger diameters struts.Level of Evidence: 4.

Metal failure and nonunion at L5-S1 after long instrumented fusion distal to pelvis for adult spinal deformity: Anterior versus transforaminal interbody fusion

PURPOSE

Pseudoarthrosis and metal failure at L5-S1 following long fusion surgery for adult spinal deformity (ASD) remain major issues. Few studies report on which anterior column support technique is better in terms of achieving fusion and avoiding metal failures. Our study aimed to evaluate the fusion status and metal failure rate at L5-S1 after anterior lumbar interbody fusion (ALIF) versus transforaminal lumbar interbody fusion (TLIF).

METHODS

The study population included patients aged >50 years who underwent surgery for ASD. Anterior column supports at L5-S1 using ALIF and TLIF were compared with ≥ 2-year follow-up. Fusion status on 2-year computed tomography (CT) scan, metal failure, visual analog scale (VAS), and Oswestry disability index (ODI) were evaluated.

RESULTS

98 patients were included in this study (53 ALIF group and 45 TLIF group). We achieved solid fusion on 2-year CT scans in 88.9% and 69.8% patients in the TLIF and ALIF group, respectively. Metal failure developed in nine (17.0%) and six (13.3%) patients in the ALIF and TLIF group, respectively. The most common failure type was unilateral L5-S1 rod fracture (7 and five patients in the ALIF and TLIF group, respectively). Only one patient with bilateral rod fractures in the ALIF group required revision surgery. There were no differences in the VAS and ODI scores at the last follow-up.

CONCLUSIONS

TLIF showed a better fusion rate than ALIF at L5-S1 after long instrumented fusion for ASD. However, the capacity to restore sagittal parameters was greater in the ALIF group. There were no differences between the groups regarding metal failure rate, revision surgery, or clinical outcomes.

Spinal Implant Osseointegration and the Role of 3D Printing: An Analysis and Review of the Literature

The use of interbody implants for spinal fusion has been steadily increasing to avoid the risks of complications and donor site morbidity when using autologous bone. Understanding the pros and cons of various implant designs can assist the surgeon in choosing the ideal interbody for each individual patient. The goal of these interbody cages is to promote a surface area for bony ingrowth while having the biomechanical properties to support the axial skeleton. Currently, the majority of interbody implants consists of metal or polyether ether ketone (PEEK) cages with bone graft incorporated inside. Titanium alloy implants have been commonly used, however, the large difference in modulus of elasticity from bone has inherent issues. PEEK implants have a desirable surface area with the benefit of a modulus of elasticity closer to that of bone. Unfortunately, clinically, these devices have had increased risk of subsidence. More recently, 3D printed implants have come into the market, providing mechanical stability with increased surface design for bony ingrowth. While clinical outcomes studies are limited, early results have demonstrated more reliable and quicker fusion rates using 3D custom interbody devices. In this review, we discuss the biology of osseointegration, the use of surface coated implants, as well as the potential benefits of using 3D printed interbodies.

Prospective, randomized, double-blinded clinical trial comparing PEEK and allograft spacers in patients undergoing transforaminal lumbar interbody fusion surgeries

BACKGROUND CONTEXT

Allograft and polyether-ether-ketone (PEEK) radiographic, biomechanical, histological properties have been extensively studied and both spacers have their advantages and shortcomings. There are no comparative randomized or double-blinded spinal fusion clinical trials reported to date.

PURPOSE

The study's primary objective was to prospectively investigate clinical and radiological outcomes in patients undergoing lumbar interbody fusions and randomized to receive either PEEK or structural bone allografts.

STUDY DESIGN/ SETTING

A prospective, randomized, double-blinded clinical trial was initiated at a single center.

PATIENT SAMPLE

A total of 138 patients were enrolled, randomized and 121 patients completed the study.

OUTCOME MEASURES

The primary clinical outcome parameters were scored from standardized patient-reported questionnaires. The severity of lower back and leg pain was evaluated using the 11-point Visual Analog Scale (VAS). The Oswestry Disability Questionnaire was used to evaluate chronic disability and activities of daily living. Health-related quality of life and functional outcomes were assessed using Health-related Quality of Life Questionnaire (SF-36 v2). Two scores within the scoring algorithm were analyzed: Physical Component (PCS) and Mental Component Summary (MCS). The primary radiological outcomes included restoration and maintenance of vertebral body height, lumbar sagittal and segmental alignment, and fusion status.

METHODS

All patients were followed for 2 years ± 2 months; radiographic and clinical outcomes were assessed at 3, 6, 12 and 24 months with an additional follow-up at 3 weeks for radiographic assessment.

RESULTS

A total of 138 patients undergoing transforaminal lumbar interbody fusions (TLIF) were randomized (1:1) to receive either cortical allograft or PEEK interbody lordotic spacers. Although no differences were detected between the allograft and PEEK patient groups at any of the follow-up time points, there was a highly significant (p<.0001) improvement in all clinical outcome measures. Overall, evidence of radiographic fusion was achieved in 118 (97.5%) patients at the 24 months follow-up. Three patients, all in the allograft group, had pseudoarthrosis and underwent revision surgeries. Postoperative improvement of sagittal alignment, anterior (ABH) or posterior body height (PBH) was initially achieved, but it was mainly lost or reduced at the final follow-up and there were no statistically significant differences between the groups. At the end of the study, improvement and maintenance of lumbar lordosis were achieved in 43.3% and 49.2% patients and segmental alignment in 38.3% and 36.1% for the allograft and PEEK patient groups, respectively. Similarly, ABH was improved and maintained in 28.3% and 36.1% patients and PBH in 28.3% and 44.3% for the allograft and PEEK groups, respectively.

CONCLUSIONS

Although allograft-assisted surgeries may have reduced fusion rates, the study findings demonstrated that TLIF surgery with two different types of cages and in conjunction with rhBMP-2 resulted in similar radiological or clinical outcomes and a highly statistically significant improvement in all clinical outcome measures at the end of the study regardless of the randomization group.

Comparison of 3D-printed titanium-alloy, standard titanium-alloy, and PEEK interbody spacers in an ovine model

BACKGROUND CONTEXT

Osseointegration is a pivotal process in achieving a rigid fusion and ultimately a successful clinical outcome following interbody fusion surgery. Advancements in 3D printing technology permit commonly used titanium interbody spacers to be designed with unique architectures, such as a highly interconnected and specific porous structure that mimics the architecture of trabecular bone. Interbody implants with a microscale surface roughness and biomimetic porosity may improve bony ongrowth and ingrowth compared to traditional materials.

PURPOSE

The purpose of this study was to compare the osseointegration of lumbar interbody fusion devices composed of surgical-grade polyetheretherketone (PEEK), titanium-alloy (TAV), and 3D-printed porous, biomimetic TAV (3DP) using an in vivo ovine model.

STUDY DESIGN

In Vivo Preclinical Animal Study METHODS: Eighteen sheep underwent two-level lateral lumbar interbody fusion randomized with either 3DP, PEEK, or TAV interbody spacers (n=6 levels for each spacer per time point). Postoperative time points were 6 and 12 weeks. Microcomputed tomography and histomorphometry were used to quantify bone volume (BV) within the spacers (ingrowth) and the surface bone apposition ratio (BAR) (ongrowth), respectively.

RESULTS

The 3DP-treatment group demonstrated significantly higher BV than the PEEK and TAV groups at 6 weeks (77.3±44.1 mm³, 116.9±43.0 mm³, and 108.7±15.2 mm³, respectively) (p<.05). At 12 weeks, there were no BV differences between groups (p>.05). BV increased in all groups from the 6- to 12-week time points (p<.05). At both time points, the 3DP-treated group (6w: 23.6±10.9%; 12w: 36.5±10.9%) had significantly greater BAR than the PEEK (6w: 8.6±2.1%; 12w: 14.0±5.0%) and TAV (6w: 6.0±5.7%; 12w: 4.1±3.3%) groups (p<.05).

CONCLUSIONS

3DP interbody spacers facilitated greater total bony ingrowth at 6 weeks, and greater bony ongrowth postoperatively at both 6 and 12 weeks, in comparison to solid PEEK and TAV implants.

CLINICAL SIGNIFICANCE

Based on these findings, the 3DP spacers may be a reasonable alternative to traditional PEEK and TAV spacers in various clinical applications of interbody fusion.

Calcium silicate enhances immunosuppressive function of MSCs to indirectly modulate the polarization of macrophages

Bioactive silicate ceramics (BSCs) have been widely reported to be able to induce bone tissue regeneration, but the underlying mechanisms have not been fully elucidated. Previous studies have reported that ionic products of BSCs can promote bone regeneration by directly simulating osteogenic differentiation of mesenchymal stem cells (MSCs) and modulating the polarization of macrophages to create a favorable inflammation microenvironment for initiating bone regeneration cascades. However, the immunomodulatory ability of MSCs also plays a critical role in bone regeneration but the effects of BSCs on the immunomodulatory ability of MSCs have been rarely investigated. This study aims to investigate the effects of ionic products of BSCs on the immunoregulatory ability of MSCs to further understand the mechanism of BSCs enhancing bone regeneration. Results showed that ionic products of calcium silicate (CS), one of the representative BSCs, could enhance the immunosuppressive function of human bone marrow mesenchymal stem cells (HBMSCs) by up-regulating the expression of immunosuppressive factors in HBMSCs via NF-κB pathway. In addition, CS-activated HBMSCs showed stronger stimulatory effects on M2 polarization of macrophages than CS ionic products. Furthermore, the macrophages educated by CS-activated HBMSCs showed stronger stimulatory effects on the early osteogenic differentiation of HBMSCs than the ones regulated by CS ionic products. These results not only provide further understanding on the mechanism of BSCs enhancing bone regeneration but also suggest that it is critical to consider the effects of biomaterials on the immunomodulatory function of the tissue forming cells when the immunomodulatory function of biomaterials is investigated.

Strategies to address mesenchymal stem/stromal cell heterogeneity in immunomodulatory profiles to improve cell-based therapies

Mesenchymal stromal cells (MSCs) have gained immense attention over the past two decades due to their multipotent differentiation potential and pro-regenerative and immunomodulatory cytokine secretory profiles. Their ability to modulate the host immune system and promote tolerance has prompted several allogeneic and autologous hMSC-based clinical trials for the treatment of graft-versus-host disease and several other immune-induced disorders. However, clinical success beyond safety is still controversial and highly variable, with inconclusive therapeutic benefits and little mechanistic explanation. This clinical variability has been broadly attributed to inconsistent MSC sourcing, phenotypic characterization, variable potency, and non-standard isolation protocols, leading to functional heterogeneity among administered MSCs. Homogeneous MSC populations are proposed to yield more predictable, reliable biological responses and clinically meaningful properties relevant to cell-based therapies. Limited comparisons of heterogeneous MSCs with homogenous MSCs are reported. This review addresses this gap in the literature with a critical analysis of strategies aimed at decreasing MSC heterogeneity concerning their reported immunomodulatory profiles. STATEMENT OF SIGNIFICANCE: This review collates, summarizes, and critically analyzes published strategies that seek to improve homogeneity in immunomodulatory functioning MSC populations intended as cell therapies to treat immune-based disorders, such as graft-vs-host-disease. No such review for MSC therapies, immunomodulatory profiles and cell heterogeneity analysis is published. Since MSCs represent the most clinically studied experimental cell therapy platform globally for which there remains no US domestic marketing approval, insights into MSC challenges in therapeutic product development are imperative to providing solutions for immunomodulatory variabilities.