Extracellular matrix-coating pedicle screws conduct and induce osteogenesis

Advances in implants and bone graft types for lumbar spinal fusion surgery

The increasing prevalence of spinal disorders worldwide necessitates advanced treatments, particularly interbody fusion for severe cases that are unresponsive to non-surgical interventions. This procedure, especially 360° lumbar interbody fusion, employs an interbody cage, pedicle screw-and-rod instrumentation, and autologous bone graft (ABG) to enhance spinal stability and promote fusion. Despite significant advancements, a persistent 10% incidence of non-union continues to result in compromised patient outcomes and escalated healthcare costs. Innovations in lumbar stabilisation seek to mimic the properties of natural bone, with evolving implant materials like titanium (Ti) and polyetheretherketone (PEEK) and their composites offering new prospects. Additionally, biomimetic cages featuring precisely engineered porosities and interconnectivity have gained traction, as they enhance osteogenic differentiation, support osteogenesis, and alleviate stress-shielding. However, the limitations of ABG, such as harvesting morbidities and limited fusion capacity, have spurred the exploration of sophisticated solutions involving advanced bone graft substitutes. Currently, demineralised bone matrix and ceramics are in clinical use, forming the basis for future investigations into novel bone graft substitutes. Bioglass, a promising newcomer, is under investigation despite its observed rapid absorption and the potential for foreign body reactions in preclinical studies. Its clinical applicability remains under scrutiny, with ongoing research addressing challenges related to burst release and appropriate dosing. Conversely, the well-documented favourable osteogenic potential of growth factors remains encouraging, with current efforts focused on modulating their release dynamics to minimise complications. In this evidence-based narrative review, we provide a comprehensive overview of the evolving landscape of non-degradable spinal implants and bone graft substitutes, emphasising their applications in lumbar spinal fusion surgery. We highlight the necessity for continued research to improve clinical outcomes and enhance patient well-being.

Surface hardening of Ti-Al-V superalloy spinal implant by using the boronization method

BACKGROUND

We compared the raw Ti-Al-V super alloy transpedicular implant screws with boronized and surface-hardened transpedicular implant screws.

OBJECTIVE

To improve patients' postoperative prognosis with the production of harder and less fragile screws.

METHODS

Surface hardening was achieved by applying green-body encapsulation of the specimen with elemental boron paste which is sintered at elevated temperatures to ensure the boron-metal diffusion. Boron transported into the Ti-Al-V super alloy matrix gradually while suppressing aluminum and a homogeneously boronized surface with a thickness of ∼15 microns was obtained. The uniform external shell was enriched with TiB2, which is one of the hardest ceramics. The Ti-Al-V core material, where boron penetration diminishes, shows cohesive transition and ensures intact core-surface structure.

RESULTS

Scanning electron microscope images confirmed a complete homogeneous, uniform and non-laminating surface formation. Energy-dispersive X-ray monitored the elemental structural mapping and proved the replacement of the aluminum sites on the surface with boron ending up the TiB2. The procedure was 8.6 fold improved the hardness and the mechanical resistance of the tools.

CONCLUSIONS

Surface-hardened, boronized pedicular screws can positively affect the prognosis. In vivo studies are needed to prove the safety of use.

Postfusion effect on pullout strength of pedicle screws with expandablepeek shell and conventional screws

The pullout performance of various pedicle screws after artificial fusion process was investigated in this study. Normal, cannulated (cemented), novel expandable and normal (cemented) pedicle screws were tested. Polyurethane foams (Grade 10 and Grade 40) produced by casting method were used as test materials. The instrumentation of pedicle screws has been carried out with production of foams, simultaneously. For cemented pedicle screws, 3D models were prepared with respect to the anteriosuperior and oblique radiographs by using PMMA before casting procedure. Pullout tests were performed in an Instron 3369 testing device. Load versus displacement graph was recorded and the ultimate force was defined as the pullout strength sustained before failure of screw. As expected, the pullout strengths of pedicle screws in postfusion are higher than before fusion. Pullout strengths increased significantly by artificial fusion in Grade 10 foams compared to Grade 40 foams. Additionally, while the pullout strengths of normal, cannulated and novel expandable pedicle screws increased by artificial fusion, cemented normal pedicle screws had lower pullout values than before fusion in Grade 40 foams. When the cemented normal pedicle screws are excluded, other screws have almost similar pullout strength level. On the other hand, the pedicle screws have different increasing behaviour also, there is no correlation between each other. As a result, the novel expandable pedicle screws can be used instead of normal and cannulated ones due to their performances in non-cemented usage.

Metallic Implants Used in Lumbar Interbody Fusion

Over the last decade, pedicle fixation systems have evolved and modifications in spinal fusion techniques have been developed to increase fusion rates and improve clinical outcomes after lumbar interbody fusion (LIF). Regarding materials used for screw and rod manufacturing, metals, especially titanium alloys, are the most popular resources. In the case of pedicle screws, that biomaterial can be also doped with hydroxyapatite, CaP, ECM, or tantalum. Other materials used for rod fabrication include cobalt-chromium alloys and nitinol (nickel-titanium alloy). In terms of mechanical properties, the ideal implant used in LIF should have high tensile and fatigue strength, Young's modulus similar to that of the bone, and should be 100% resistant to corrosion to avoid mechanical failures. On the other hand, a comprehensive understanding of cellular and molecular pathways is essential to identify preferable characteristics of implanted biomaterial to obtain fusion and avoid implant loosening. Implanted material elicits a biological response driven by immune cells at the site of insertion. These reactions are subdivided into innate (primary cellular response with no previous exposure) and adaptive (a specific type of reaction induced after earlier exposure to the antigen) and are responsible for wound healing, fusion, and also adverse reactions, i.e., hypersensitivity. The main purposes of this literature review are to summarize the physical and mechanical properties of metal alloys used for spinal instrumentation in LIF which include fatigue strength, Young's modulus, and corrosion resistance. Moreover, we also focused on describing biological response after their implantation into the human body. Our review paper is mainly focused on titanium, cobalt-chromium, nickel-titanium (nitinol), and stainless steel alloys.

Hydroxyapatite Use in Spine Surgery—Molecular and Clinical Aspect

Hydroxyapatite possesses desirable properties as a scaffold in tissue engineering: it is biocompatible at a site of implantation, and it is degradable to non-toxic products. Moreover, its porosity enables infiltration of cells, nutrients and waste products. The outcome of hydroxyapatite implantation highly depends on the extent of the host immune response. Authors emphasise major roles of the chemical, morphological and physical properties of the surface of biomaterial used. A number of techniques have been applied to transform the theoretical osteoconductive features of HAp into spinal fusion systems—from integration of HAp with autograft to synthetic intervertebral implants. The most popular uses of HAp in spine surgery include implants (ACDF), bone grafts in posterolateral lumbar fusion and transpedicular screws coating. In the past, autologous bone graft has been used as an intervertebral cage in ACDF. Due to the morbidity related to autograft harvesting from the iliac bone, a synthetic cage with osteoconductive material such as hydroxyapatite seems to be a good alternative. Regarding posterolateral lumbar fusion, it requires the graft to induce new bone growth and reinforce fusion between the vertebrae. Hydroxyapatite formulations have shown good results in that field. Moreover, the HAp coating has proven to be an efficient method of increasing screw fixation strength. It can decrease the risk of complications such as screw loosening after pedicle screw fixation in osteoporotic patients. The purpose of this literature review is to describe in vivo reaction to HAp implants and to summarise its current application in spine surgery.

Collagen-based biocomposites inspired by bone hierarchical structures for advanced bone regeneration: ongoing research and perspectives

Bone is a hard-connective tissue composed of matrix, cells and bioactive factors with a hierarchical structure, where the matrix is mainly composed of type I collagen and hydroxyapatite. Collagen fibers assembled by collagen are the template for mineralization and make an important contribution to bone formation and the bone remodeling process. Therefore, collagen has been widely clinically used for bone/cartilage defect regeneration. However, pure collagen implants, such as collagen scaffolds or sponges, have limitations in the bone/cartilage regeneration process due to their poor mechanical properties and osteoinductivity. Different forms of collagen-based composites prepared by incorporating natural/artificial polymers or bioactive inorganic substances are characterized by their interconnected porous structure and promoting cell adhesion, while they improve the mechanical strength, structural stability and osteogenic activities of the collagen matrix. In this review, various forms of collagen-based biocomposites, such as scaffolds, sponges, microspheres/nanoparticles, films and microfibers/nanofibers prepared by natural/synthetic polymers, bioactive ceramics and carbon-based materials compounded with collagen are reviewed. In addition, the application of collagen-based biocomposites as cytokine, cell or drug (genes, proteins, peptides and chemosynthetic) delivery platforms for proangiogenesis and bone/cartilage tissue regeneration is also discussed. Finally, the potential application, research and development direction of collagen-based biocomposites in future bone/cartilage tissue regeneration are discussed.

Biomaterials in Spinal Implants: A Review

The aim to find the perfect biomaterial for spinal implant has been the focus of spinal research since the 1800s. Spinal surgery and the devices used therein have undergone a constant evolution in order to meet the needs of surgeons who have continued to further understand the biomechanical principles of spinal stability and have improved as new technologies and materials are available for production use. The perfect biomaterial would be one that is biologically inert/compatible, has a Young’s modulus similar to that of the bone where it is implanted, high tensile strength, stiffness, fatigue strength, and low artifacts on imaging. Today, the materials that have been most commonly used include stainless steel, titanium, cobalt chrome, nitinol (a nickel titanium alloy), tantalum, and polyetheretherketone in rods, screws, cages, and plates. Current advancements such as 3-dimensional printing, the ProDisc-L and ProDisc-C, the ApiFix, and the Mobi-C which all aim to improve range of motion, reduce pain, and improve patient satisfaction. Spine surgeons should remain vigilant regarding the current literature and technological advancements in spinal materials and procedures. The progression of spinal implant materials for cages, rods, screws, and plates with advantages and disadvantages for each material will be discussed.

Does incorporating collagen and chondroitin sulfate matrix in implant surfaces enhance osseointegration? A systematic review and meta-analysis

Implant surface modification has been used to improve osseointegration. However, evidence regarding improved new bone formation (NBF) and osseointegration with the use of collagen-chondroitin sulfate (CS) matrix coated implants remains unclear. The aim of this study was to assess the efficacy of collagen-CS matrix coating on the osseointegration of implants. The focused question was "Does the incorporation of collagen-CS matrix in implant surfaces influence osseointegration?" To answer the question, indexed databases were searched up to July 2017 using various combinations of the key words "collagen", "chondroitin sulfate", "osseointegration", and "implants". The initial literature search identified 497 articles, of which 18 reporting experimental studies fulfilled the inclusion criteria. Thirteen of the studies included (72%) reported that implants coated with a collagen-CS matrix presented higher NBF, bone-to-implant contact, and/or bone volume density. The strength of this observation was supported by meta-analysis results. Nevertheless, the results should be interpreted with caution due to the lack of standardization regarding the dosage formulation of collagen-CS, short-term follow-up, and lack of assessment of confounders. On experimental grounds, the incorporation of collagen-CS matrix into implant surfaces appears to promote osseointegration. From a clinical perspective, the results from animal models support phase I studies in healthy humans.

Recent coating developments for combination devices in orthopedic and dental applications: A literature review

Orthopedic and dental implants have been used successfully for decades to replace or repair missing or damaged bones, joints, and teeth, thereby restoring patient function subsequent to disease or injury. However, although device success rates are generally high, patient outcomes are sometimes compromised due to device-related problems such as insufficient integration, local tissue inflammation, and infection. Many different types of surface coatings have been developed to address these shortcomings, including those that incorporate therapeutic agents to provide localized delivery to the surgical site. While these coatings hold enormous potential for improving device function, the list of requirements that an ideal combination coating must fulfill is extensive, and no single coating system today simultaneously addresses all of the criteria. Some of the primary challenges related to current coatings are non-optimal release kinetics, which most often are too rapid, the potential for inducing antibiotic resistance in target organisms, high susceptibility to mechanical abrasion and delamination, toxicity, difficult and expensive regulatory approval pathways, and high manufacturing costs. This review provides a survey of the most recent developments in the field, i.e., those published in the last 2-3years, with a particular focus on technologies that have potential for overcoming the most significant challenges facing therapeutically-loaded coatings. It is concluded that the ideal coating remains an unrealized target, but that advances in the field and emerging technologies are bringing it closer to reality. The significant amount of research currently being conducted in the field provides a level of optimism that many functional combination coatings will ultimately transition into clinical practice, significantly improving patient outcomes.

Study of bone-screw surface fixation in lumbar dynamic stabilization

BACKGROUND

We aimed to use the animal model of dynamic fixation to examine the interaction of the pedicle screw surface with surrounding bone, and determine whether pedicle screws achieve good mechanical stability in the vertebrae.

METHODS

Twenty-four goats aged 2-3 years had Cosmic ® pedicle screws implanted into both sides of the L2-L5 pedicles. Twelve goats in the bilateral dynamic fixation group had fixation rods implanted in L2-L3 and L4-L5. Twelve goats in the unilateral dynamic fixation group had fixation rods randomly fixed on one side of the lumbar spine. The side that was not implanted with fixation rods was used as a static control group.

RESULTS

In the static control group, new bone was formed around the pedicle screw and on the screw surface. In the unilateral and bilateral dynamic fixation groups, large amounts of connective tissue formed between and around the screw threads, with no new bone formation on the screw surface; the pedicle screws were loose after the fixed rods were removed. The bone mineral density and morphological parameters of the region of interest (ROI) in the unilateral and bilateral dynamic fixation group were not significantly different (P > 0.05), but were lower in the fixed groups than the static control group (P < 0.05). This showed the description bone of the ROI in the static control group was greater than in the fixation groups. Under loading conditions, the pedicle screw maximum pull force was not significantly different between the bilateral and unilateral dynamic fixation groups (P > 0.05); however the maximum pull force of the fixation groups was significantly less than the static control group (P < 0.01).

CONCLUSIONS

Fibrous connective tissue formed at the bone-screw interface under unilateral and bilateral pedicle dynamic fixation, and the pedicle screws lost mechanical stability in the vertebrae.