Aims

Limb salvage surgery (LSS) is the primary treatment option for primary bone malignancy. It involves the removal of bone and tissue, followed by reconstruction with endoprosthetic replacements (EPRs) to prevent amputation. Trabecular metal (TM) collars have been developed to encourage bone ingrowth (osseointegration (OI)) into EPRs. The primary aim of this study was to assess whether OI occurs when TM collars are used in EPRs for tumour.

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The efficacy of saline irrigation for treatment of implant-associated infections is limited in the presence of porous metallic implants. This study evaluated the therapeutic efficacy of antibiotic doped bioceramic (vancomycin/tobramycin-doped polyvinyl alcohol composite (PVA-VAN/TOB-P)) after saline wash in a mouse infection model implanted with titanium cylinders.

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The aims of this study were to determine the success of a reconstruction algorithm used in major acetabular bone loss, and to further define the indications for custom-made implants in major acetabular bone loss.

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The mean age of patients undergoing total knee arthroplasty (TKA) has reduced with time. Younger patients have increased expectations following TKA. Aseptic loosening of the tibial component is the most common cause of failure of TKA in the UK. Interest in cementless TKA has re-emerged due to its encouraging results in the younger patient population. We review a large series of tantalum trabecular metal cementless implants in patients who are at the highest risk of revision surgery.

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Dislocation remains a leading cause of failure following revision total hip arthroplasty (THA). While dual-mobility (DM) bearings have been shown to mitigate this risk, options are limited when retaining or implanting an uncemented shell without modular DM options. In these circumstances, a monoblock DM cup, designed for cementing, can be cemented into an uncemented acetabular shell. The goal of this study was to describe the implant survival, complications, and radiological outcomes of this construct.

Although 3D-printed porous dental implants may possess improved osseointegration potential, they must exhibit appropriate fatigue strength. Finite element analysis (FEA) has the potential to predict the fatigue life of implants and accelerate their development. This work aimed at developing and validating an FEA-based tool to predict the fatigue behavior of porous dental implants. Test samples mimicking dental implants were designed as 4.5 mm-diameter cylinders with a fully porous section around bone level. Three porosity levels (50%, 60% and 70%) and two unit cell types (Schwarz Primitive (SP) and Schwarz W (SW)) were combined to generate six designs that were split between calibration (60SP, 70SP, 60SW, 70SW) and validation (50SP, 50SW) sets. Twenty-eight samples per design were additively manufactured from titanium powder (Ti6Al4V). The samples were tested under bending compression loading (ISO 14801) monotonically (N=4/design) to determine ultimate load (F. ult. ) (Instron 5866) and cyclically at six load levels between 50% and 10% of F. ult. (N=4/design/load level) (DYNA5dent). Failure force results were fitted to F/F. ult. = a(N. f. ). b. (Eq1) with N. f. being the number of cycles to failure, to identify parameters a and b. The endurance limit (F. e. ) was evaluated at N. f. = 5M cycles. Finite element models were built to predict the yield load (F. yield. ) of each design. Combining a linear correlation between FEA-based F. yield. and experimental F. ult. with equation Eq1 enabled FEA-based prediction of F. e. . For all designs, F. e. was comprised between 10% (all four samples surviving) and 15% (at least one failure) of F. ult. The FEA-based tool predicted F. e. values of 11.7% and 12.0% of F. ult. for the validation sets of 50SP and 50SW, respectively. Thus, the developed FEA-based workflow could accurately predict endurance limit for different implant designs and therefore could be used in future to aid the development of novel porous implants. Acknowledgements: This study was funded by EU's Horizon 2020 grant No. 953128 (I-SMarD). We gratefully acknowledge the expert advice of Prof. Philippe Zysset

Abstract. Objectives. Young patients receiving metallic bone implants after surgical resection of bone cancer require implants that last into adulthood, and ideally life-long. Porous implants with similar stiffness to bone can promote bone ingrowth and thus beneficial clinical outcomes. A mechanical remodelling stimulus, strain energy density (SED), is thought to be the primary control variable of the process of bone growth into porous implants. The sequential process of bone growth needs to be taken into account to develop an accurate and validated bone remodelling algorithm, which can be employed to improve porous implant design and achieve better clinical outcomes. Methods. A bone remodelling algorithm was developed, incorporating the concept of bone connectivity (sequential growth of bone from existing bone) to make the algorithm more physiologically relevant. The algorithm includes adaptive elastic modulus based on apparent bone density, using a node-based model to simulate local remodelling variations while alleviating numerical checkerboard problems. Strain energy density (SED) incorporating stress and strain effects in all directions was used as the primary stimulus for bone remodelling. The simulations were developed to run in MATLAB interfacing with the commercial FEA software ABAQUS and Python. The algorithm was applied to predict bone ingrowth into a porous implant for comparison against data from a sheep model. Results. The accuracy of the predicted bone remodelling was verified for standard loading cases (bending, torsion) against analytical calculations. Good convergence was achieved. The algorithm predicted good bone remodelling and growth into the investigated porous implant. Using the standard algorithm without connectivity, bone started to remodel at locations unconnected to any bone, which is physiologically implausible. The implementation of bone connectivity ensures the gradual process of bone growth into the implant pores from the sides. The bone connectivity algorithm predicted that the full remodelling required more time (approximately 50% longer), which should be considered when developing post-surgical rehabilitation strategies for patients. Both algorithms with and without bone connectivity implementation converged to same final stiffness (less than 0.01% difference). Almost all nodes reached the same density value, with only a limited number of nodes (less than 1%) in transition areas with a strong density gradient having noticeable differences. Conclusions. An improved bone remodelling algorithm based on strain energy density that modelled the sequential process of bone growth has been developed and tested. For a porous metallic bone implant the same final bone density distribution as for the original adaptive elasticity theory was predicted, with a slower and more fidelic process of growth from existing surrounding bone into the porous implant. Declaration of Interest. (b) declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research reported:I declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project

3D printing acetabular cups offers the theoretical advantage of enhanced bony fixation due to greater design control of the porous implant surfaces. Analysing retrieved 3D printed implants can help determine whether this design intent has been achieved. We sectioned 14 off-the-shelf retrieved acetabular cups for histological analysis; 7 cups had been 3D printed and 7 had been conventionally manufactured. Some of the most commonly used contemporary designs were represented in both groups, which were removed due to either aseptic loosening, unexplained pain, infection or dislocation. Clinical data was collected for all implants, including their age, gender, and time to revision. Bone ingrowth was evaluated using microscopic assessment and two primary outcome measures: 1) bone area fraction and 2) extent of bone ingrowth. The additively manufactured cups were revised after a median (IQR) time of 24.9 months (20.5 to 45.6) from patients with a median (IQR) age of 61.1 years (48.4 to 71.9), while the conventional cups had a median (IQR) time to revision of 46.3 months (34.7 to 49.1, p = 0.366) and had been retrieved from patients with a median age of 66.0 years (56.9 to 68.9, p = 0.999). The additively and conventionally manufactured implants had a median (IQR) bone area fraction of 65.7% (36.4 to 90.6) and 33.9% (21.9 to 50.0), respectively (p < 0.001). A significantly greater amount of bone ingrowth was measured into the backside of the additively manufactured acetabular cups, compared to their conventional counterparts (p < 0.001). Bone occupied a median of 60.0% and 5.7% of the porous depth in the additively manufactured and conventional cups, respectively. 3D printed components were found to achieve a greater amount of bone ingrowth than their conventionally manufactured counterparts, suggesting that the complex porous structures generated through this manufacturing technique may encourage greater osteointegration

The success of cementless orthopaedic implants relies on bony ingrowth and active bone remodelling. Much research effort is invested to develop implants with controllable surface roughness and internal porous architectures that encourage these biological processes. Evaluation of these implants requires long-term and costly animal studies, which do not always yield the desired outcome requiring iteration. The aim of our study is to develop a cost-effective method to prescreen design parameters prior to animal trials to streamline implant development and reduce live animal testing burden. Ex vivo porcine cancellous bone cylinders (n=6, Ø20×12mm) were extracted from porcine knee joints with a computer-numerically-controlled milling machine under sterile conditions within 4 hours of animal sacrifice. The bone discs were implanted with Ø6×12mm additive manufactured porous titanium implants and were then cultured for 21days. Half underwent static culture in medium (DMEM, 10% FBS, 1% antibiotics) at 37°C and 5% CO. 2. The rest were cultured in novel high-throughput stacked configuration in a bioreactor that simulated physiological conditions after surgery: the fluid flow and cyclic compression force were set at 10ml/min and 10–150 N (1Hz,5000 cycles/day) respectively. Stains were administered at days 7 and 14. Samples were evaluated with widefield microscopy, scanning electron microscopy (SEM) and with histology. More bone remodelling was observed on the samples cultured within the bioreactor: widefield imaging showed more remodelling at the boundaries between the implant-bone interface, while SEM revealed immature bone tissue integration within the pores of the implant. Histological analysis confirmed these results, with many more trabecular struts with new osteoid formation on the samples cultured dynamically compared to static ones. Ex vivo bone can be used to analyse new implant technologies with lower cost and ethical impact than animal trial. Physiological conditions (load and fluid flow) promoted bone ingrowth and remodelling

Revision surgeries for orthopaedic infections are done in two stages – one surgery to implant an antibiotic spacer to clear the infection and another to install a permanent implant. A permanent porous implant, that can be loaded with antibiotics and allow for single-stage revision surgery, will benefit patients and save healthcare resources. Gyroid structures can be constructed with high porosity, without stress concentrations that can develop in other period porous structures [1] [2]. The purpose of this research is to compare the resulting bone and prosthesis stress distributions when porous versus solid stems are implanted into three proximal humeri with varying bone densities, using finite element models (FEM). Porous humeral stems were constructed in a gyroid structure at porosities of 60%, 70%, and 80% using computer-aided design (CAD) software. These CAD models were analyzed using FEM (Abaqus) to look at the stress distributions within the proximal humerus and the stem components with loads and boundary conditions representing the arm actively maintained at 120˚ of flexion. The stem was assumed to be made of titanium (Ti6Al4V). Three different bone densities were investigated, representing a healthy, an osteopenic, and an osteoporotic humerus, with an average bone shape created using a statistical shape and density model (SSDM) based on 75 cadaveric shoulders (57 males and 18 females, 73 12 years) [3]. The Young's moduli (E) of the cortical and trabecular bones were defined on an element-by-element basis, with a minimum allowable E of 15 MPa. The Von Mises stress distributions in the bone and the stems were compared between different stem scenarios for each bone density model. A preliminary analysis shows an increase in stress values at the proximal-lateral region of the humerus when using the porous stems compared to the solid stem, which becomes more prominent as bone density decreases. With the exception of a few mesh dependent singularities, all three porous stems show stress distributions below the fatigue strength of Ti-6Al-4V (410 MPa) for this loading scenario when employed in the osteopenic and osteoporotic humeri [4]. The 80% porosity stem had a single strut exceeding the fatigue strength when employed in the healthy bone. The results of this study indicate that the more compliant nature of the porous stem geometries may allow for better load transmission through the proximal humeral bone, better matching the stress distributions of the intact bone and possibly mitigating stress-shielding effects. Importantly, this study also indicates that these porous stems have adequate strength for long-term use, as none were predicted to have catastrophic failure under the physiologically-relevant loads. Although these results are limited to a single boney geometry, it is based on the average shape of 75 shoulders and different bone densities are considered. Future work could leverage the shape model for probabilistic models that could explore the effect of stem porosity across a broader population. The development of these models are instrumental in determining if these structures are a viable solution to combatting orthopaedic implant infections

Aims

The aim of this study was to assess the clinical and radiological outcomes of an antiprotrusio acetabular cage (APC) when used in the surgical treatment of periacetabular bone metastases.

Aims

Unicompartmental and total knee arthroplasty (UKA and TKA) are successful treatments for osteoarthritis, but the solid metal implants disrupt the natural distribution of stress and strain which can lead to bone loss over time. This generates problems if the implant needs to be revised. This study investigates whether titanium lattice UKA and TKA implants can maintain natural load transfer in the proximal tibia.

Abstract. Objectives. Currently, total hip replacement surgery is an effective treatment for osteoarthritis, where the damaged hip joint is replaced with an artificial joint. Stress shielding is a mechanical phenomenon that refers to the reduction of bone density as a result of altered stresses acting on the host bone. Due to solid metallic nature and high stiffness of the current orthopaedic prostheses, surrounding bones undergo too much bone resorption secondary to stress shielding. With the use of 3D printing technology such as selective laser melting (SLM), it is now possible to produce porous graded microstructure hip stems to mimics the surrounding bone tissue properties. Method. In this study we have compared the physical and mechanical properties of two triply periodic minimal surface (TPMS) lattice structure namely gyroid and diamond TPMS. Based on initial investigations, it was decided to design, and 3D print the gyroid and diamond scaffolds having pore size of 800 and 1100 um respectively. Scaffold of each type of structure were manufactured and were tested mechanically in compression (n=8), tension (n=5) and bending (n=1). Results. Upon FEA validation of the scaffold in Abaqus, the desired scaffold for hip implant application was evaluated to have a young's modules of 12.15 GPa, yield strength of 242 MPa and porosity of 55%. Topology and lattice optimization were performed using nTopology to design an optimised graded porous hip implant based on stress shielding reduction. It was understood that the designed optimised hip implant can reduce the stress shielding effect by more than 65% when compared to the conventional generic implant. Conclusions. The designed hip implant presented in this work shows clinical promise in reducing bone loss while having enhanced osseointegration with the surrounding cortical bones. Hence, this will help reduce the risk of periprosthetic fracture and the probability of revision surgery

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We wanted to evaluate the effects of a bone anabolic agent (bone morphogenetic protein 2 (BMP-2)) on an anti-catabolic background (systemic or local zoledronate) on fixation of allografted revision implants.

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The main advantage of 3D-printed, off-the-shelf acetabular implants is the potential to promote enhanced bony fixation due to their controllable porous structure. In this study we investigated the extent of osseointegration in retrieved 3D-printed acetabular implants.

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Aseptic loosening is a leading cause of uncemented arthroplasty failure, often accompanied by fibrotic tissue at the bone-implant interface. A biological target, neutrophil extracellular traps (NETs), was investigated as a crucial connection between the innate immune system’s response to injury, fibrotic tissue development, and proper bone healing. Prevalence of NETs in peri-implant fibrotic tissue from aseptic loosening patients was assessed. A murine model of osseointegration failure was used to test the hypothesis that inhibition (through Pad4^-/- mice that display defects in peptidyl arginine deiminase 4 (PAD4), an essential protein required for NETs) or resolution (via DNase 1 treatment, an enzyme that degrades the cytotoxic DNA matrix) of NETs can prevent osseointegration failure and formation of peri-implant fibrotic tissue.

OSSTEC is a pre-spin-out venture at Imperial College London seeking industry feedback on our orthopaedic implants which maintain bone quality in the long term. Existing orthopaedic implants provide successful treatment for knee osteoarthritis, however, they cause loss of bone quality over time, leading to more dangerous and expensive revision surgeries and high implant failure rates in young patients. OSSTEC tibial implants stimulate healthy bone growth allowing simple primary revision surgery which will provide value for all stakeholders. This could allow existing orthopaedics manufacturers to capture high growth in existing and emerging markets while offering hospitals and surgeons a safer revision treatment for patients and a 35% annual saving on lifetime costs. For patients, our implant technology could mean additional years of quality life by revising patients to a primary TKA before full revision surgery. Our implants use patent-filed additive manufacturing technology to restore a healthy mechanical environment in the proximal tibia; stimulating long term bone growth. Proven benefits of this technology include increased bone formation and osseointegration, shown in an animal model, and restoration of native load transfer, shown in a human cadaveric model. This technology could help capture the large annual growth (24%) currently seen in the cementless knee reconstruction market, worth $1.2B. Furthermore, analysis suggests an additional market of currently untreated younger patients exists, worth £0.8B and growing by 18% annually. Making revision surgery and therefore treatment of younger patients easier would enable access to this market. We aim to offer improved patient treatment via B2B sales of implants to existing orthopaedic manufacturer partners, who would then provide them with instrumentation to hospitals and surgeons. Existing implant materials provide good options for patient treatments, however OSSTEC's porous titanium structures offer unique competitive advantages; combining options for modular design, cementless fixation, initial bone fixation and crucially long term bone maintenance. Speaking to surgeons across global markets shows that many surgeons are keen to pursue bone preserving surgeries and the use of porous implants. Furthermore, there is a growing demand to treat young patients (with 25% growth in patients younger than 65 over the past 10 years) and to use cementless knee treatments, where patient volume has doubled in the past 4 years and is following trends in hip treatments. Our team includes engineers and consultant surgeons who have experience developing multiple orthopaedic implants which have treated over 200,000 patients. To date we have raised £175,000 for the research and development of these implants and we hope to gain insight from industry professionals before further development towards our aim to begin trials for regulatory approval in 2026. OSSTEC implants provide a way to stimulate bone growth after surgery to reduce revision risk. We hope this could allow orthopaedic manufactures to explore high growth markets while meaning surgeons can treat younger patients in a cost effective way and add quality years to patients' lives

As compared to magnesium (Mg) and iron (Fe), solid zinc (Zn)-based absorbable implants show better degradation rates. An ideal bone substitute should provide sufficient mechanical support, but pure Zn itself is not strong enough for load-bearing medical applications. Modern processing techniques, like additive manufacturing (AM), can improve mechanical strength of Zn. To better mimic the in vivo situation in the human body, we evaluated the degradation behavior of porous Zn implants in vitro under dynamic conditions. Our study applied selective laser melting (SLM) to build topographically ordered absorbable Zn implants with superior mechanical properties. Specimens were fabricated from pure Zn powder using SLM and diamond unit cell topological design. In vitro degradation was performed under both static and dynamic conditions in a custom-built set-up under cell culture conditions (37 °C, 20% O2 and 5% CO2) for up to 28 days. Mechanical properties of the porous structures were determined according to ISO 13314: 2011 at different immersion time points. Modified ISO 10993 standards were used to evaluate biocompatibility through direct cell seeding and indirect extract-based cytotoxicity tests (MTS assay, Promega) against identically designed porous titanium (Ti-6Al-4V) specimens as reference material. Twenty-four hours after cell seeding, its efficacy was evaluated by Live-Dead staining (Abcam) and further analyzed using dual channel fluorescent optical imaging (FOI) and subsequent flow cytometric quantification. Porous Zn implants were successfully produced by means of SLM with a yield strength and Young's modulus in the range of 3.9–9.6 MPa and 265–570 MPa, respectively. Dynamic flow significantly increased the degradation rate of AM porous Zn after 28 days. Results from Zn extracts were similar to Ti-6Al-4V with >95% of cellular activity at all tested time points, confirming level 0 cytotoxicity (i.e., This study clearly shows the great potential of AM porous Zn as a bone substituting material. Moreover, we demonstrate that complex topological design permits control of mechanical properties and degradation behavior

Abstract. Introduction. The long-term biological success of cementless orthopaedic prostheses is highly dependent on osteointegration. Pre-clinical testing of new cementless implant technology however, requires live animal testing, which has anatomical, loading, ethical and cost challenges. This proof-of-concept study aimed to develop an in vitro model to examine implant osteointegration under known loading/micromotion conditions. Methods. Fresh cancellous bone cylinders (n=8) were harvested from porcine femur and implanted with additive manufactured porous titanium implants (Ø4 × 15 mm). To simulate physiological conditions, n=3 bone cylinders were tested in a bioreactor system with a cyclic 30 µm displacement at 1Hz for 300 cycles every day for 15 days in a total of 21 days culture. The chamber was also perfused with culture medium using a peristaltic pump. Control bone cylinders were cultured under static conditions (n=5). Samples were calcein stained at day 7. Post-testing, bone cylinders were formalin fixed and bony ingrowth was measured via microscopy. Results. Viability of the freshly harvested ex vivo bone cylinders was maintained for up to 28 days. Two samples remain unanalysed due to COVID lockdown, one in each group. Similar to osteointegration seen in live animal models, evidence of bony ingrowth was seen more markedly at the bone-implant interface under dynamic conditions. This was evident by a greater intensity of calcein staining, confirming the deposition of new bone, at the bone-implant interface. In comparison, under static conditions, calcein staining was observed randomly all over the cylinder. Conclusion. This proof-of-concept study demonstrates that implant bony adaptation and ingrowth can be measured in vitro under known cyclic micromotion/loading conditions. This comparatively low cost, low ethical impact, controlled loading laboratory method has potential to accelerate the rate of implant development whilst conforming with the principles of NC3Rs. Declaration of Interest. (b) declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research reported:I declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project