Aims

Highly cross-linked polyethylene (HXLPE) greatly reduces wear in total hip arthroplasty, compared to conventional polyethylene (CPE). Cross-linking is commonly achieved by irradiation. This study aimed to compare the degree of cross-linking and in vitro wear rates across a cohort of retrieved and unused polyethylene cups/liners from various brands.

Aim. Orthopedic implants play a tremendous role in fixing bone damages due to aging as well as fractures. However, these implants tend to get colonized by bacteria on the surface, leading to infections and subsequently prevention of healing and osteointegration. Recently, Roupie et al. showed that a nisin layer-by-layer based coating applied on biomaterials has both osteogenic and antibacterial properties. The Galleria mellonella larva is a well-known insect infection model that has been used to test the virulence of bacterial and fungal strains as well as for the high throughput screening of antimicrobial compounds against infections. Recently, we have developed an insect infection model with G. mellonella larvae to study implant-associated biofilm infections using Kirschner (K)-wires as implant material. Here, we would like to test the antibacterial capacity of nisin layer-by-layer based coatings on K-wires against Staphylococcus aureus in the G. mellonella larva implant infection model. Method. Prior to the implantation procedure, G. mellonella larvae are maintained at room temperature on wheat germ in an incubator. The larvae received bare titanium K-wires (uncoated), or either control-coated or nisin-coated K-wires. After one hour, the larvae were injected with 5×10. 5. S. aureus bacteria per larva (i.e., hematogenous implant infection model). Next, the larvae were incubated at 37. o. C in an incubator and the survival of the larvae was monitored for five days. Moreover, the number of bacteria on the implant surface and in the surrounding tissue was determined after 24h of incubation. Further, scanning electron microscopy (SEM) analyses were performed to study the effect of nisin on biofilm formation. Results. The larvae receiving the nisin-coated K-wires showed significantly higher survival rates compared to uncoated titanium K-wires, although not when compared to control-coated K-wires. A more than 1-log reduction in number of bacteria on the implant surface and in the surrounding tissue was observed in larvae receiving the nisin-coated K-wires, when compared to uncoated titanium K-wires SEM analysis showed reduced colonization of the bacteria nisin-coated K-wires compared to the controls. Conclusions. In conclusion, the antimicrobial nisin layer-by-layer based coating applied on titanium surfaces is able to prevent implant-related S. aureus biofilm infection in G. mellonella and is a promising antimicrobial strategy to prevent implant-related infections

Aim. Arthroscopic interventions have revolutionized the treatment of joint pathologies. The appropriate diagnostics and treatment are required for infections after ligament reconstructions using non-resorbable material such as tendon grafts, anchors, and sutures, prone to biofilm formation. The infection rate is around 1% for knee and shoulder, while up to 4% for Achilles tendon reconstructions. Despite high number of these procedures worldwide, there is limited evidence about the best treatment protocol. Our study aimed to provide a general protocol for the treatment of small implants for soft tissue reconstruction. Method. Between 2019 and 2023, we treated 48 infections of ligament, meniscus, and tendon reconstructions out of 7291 related procedures performed in the same time period. Early infection (<30 days) were treated with an arthroscopic debridement and implant retention (DAIR), except Achilles tendons had open DAIR, while those with delayed or chronic infection (>30 days) were treated with extensive debridement and lavage combined with one-stage exchange (OSE) or implant removal. During surgery, at least 5 microbiological s and samples for histopathology were obtained. The removed material was sonicated. After surgery, all patients were one week on iv. antibiotics, followed by oral antibiofilm antibiotics for 6 weeks including rifampicin and/or a quinolone. All patients were followed for at least 1 year. Failure was defined as the need for additional revision surgery after finished iv. antibiotic treatment. Results. Among 48 patients, 38 were early and 10 were late acute or chronic infections. The incidence of infection for our cohort was 0.7%. We observed 27 infections after ligament reconstruction of the knee, 15 of the shoulder, 5 of the ankle, and 1 infection of the elbow joint. 40 patients were treated with DAIR, 5 with OSE, and 3 with implant removal. We had 11 C. acnes, 10 S. aureus, 6 S. epidermidis, 2 P. aeruginosa, 2 S. lugdunensis, 10 mixed flora, and 3 culture-negative infections. 12 patients received antibiotics before surgery, and all culture-negative infections were related to this subgroup. We observed 2 failures, both in a combination of proximal tibial osteotomy and ligament reconstruction of the knee joint. The success rate of our protocol was 96%. Conclusions. Prompt surgical treatment followed by 6 weeks of antibiotic treatment cured 96% of infections of small implants after reconstruction procedures of knee, shoulder, and ankle joints. Our study is the first to provide a treatment protocol for infections of small implants after ligament reconstruction procedures

Introduction. Since the expanded war in Ukraine in 2022, explosives, mines, debris, blast waves, and other factors have predominantly caused injuries during artillery or rocket attacks. These injuries, such as those from shelling shrapnel, involve high-energy penetrating agents, resulting in extensive necrosis and notable characteristics like soft tissue defects and multiple fragmentary fractures with bone tissue defects and a high rate of infection complications caused by multi resistant gram-negative (MRGN) pathogens. Material and Methods. We conducted a prospective study at our center between March 2022 and December 2023. Out of the 56 patients from Ukraine, 21 met the inclusion criteria who had severe war injuries were included in the study. Each of these patients presented with multiple injuries to both bones and soft tissues, having initially undergone treatment in Ukraine involving multiple surgeries. The diagnosis of infection was established based on the EBJIS criteria. Prior to our treatment patients had undergone multiple revision surgeries, including debridement, biopsies, implant and fixator replacement. Additionally, soft tissue management required previously VAC therapy and flap reconstruction for successful treatment. Results. All 21 infections manifested as bone infections (11; 52%), followed by implant-associated infections (5; 24%), soft tissue infections (4; 19%), and septic arthritis (1; 5%). In all patients, the infection was polymicrobial, caused by 3- and 4-MRGN pathogens, as Klebsiella pneumonia 4MRGN, Proteus mirabilis 4MRGN, Enterobacter cloacae 4MRGN etc. Upon admission, all patients carried a diagnosis and exhibited signs indicative of chronic infection. 19 (90.5%) patients required complex antibiotic regimens combined with multiple wound revisions and debridements, changes of fixators and combination of systemic and local antibiotic therapy. In 6 patients (28%) high dosages of local antibiotics such as gentamycin, vancomycin and meropenem were incorporated into a carrier of bio-absorbable calcium sulfate, calcium sulfate/hydroxyapatite which were introduced into the hip joint, femoral canal or bone defect for dead space management during the surgery. When local antibiotics were administered at intervals, the microbiology results at implantation showed negative results. 2 (9%) patients had new infections (different site, different pathogens), 1 (4.8%) is still under the treatment. In 17 (81%) patients infection complications were treated successfully with no recurrence of infection. Conclusion. War injuries result in complex bone and soft-tissue infections caused by 3-, 4-MRGN pathogens. Addressing this challenge necessitates multidisciplinary approach with multiple, thorough surgical debridements, effective local, and systemic antimicrobial therapy. As for the outlook we can see potential in local antibiotic carriers

Aims. Bone and joint infections cause significant morbidity, often requiring combination medical and surgical treatment. The presence of foreign material reduces the number of organisms required to cause an infection. The aim of this study was to assess whether there was a difference in the species of organism identified on culture in osteomyelitis compared to prosthetic joint infection. Method. This was a retrospective observational cohort study of patients that had surgical intervention for prosthetic joint infection or osteomyelitis with positive microbial culture between 2019 and 2022. Data including patient demographics, site of injury, BACH score for osteomyelitis and JS-BACH score for prosthetic joint infection, organism classification and antibiotic resistance to vancomycin and gentamicin were extracted from the medical record. Logistic and multiple regressions were used to adjust for potential confounding variables. Results. A total of 445 patients were included in the study; 267 patients with osteomyelitis or fracture-related infection and 177 patients with prosthetic joint infection. The patients with prosthetic joint infection were older (Mean age 70 for PJI; IQR 60-77 vs 56 for OM/FRI; IQR 39-64), more likely to be female (55.6% vs 26.2%) and had a higher BMI and ASA compared to those with osteomyelitis. Symptom duration tended to be longer in osteomyelitis/FRI (p<0.001). Staphylococcus aureus was the most common pathogen isolated in both osteomyelitis (155/267 (58.1%)) and prosthetic joint infection (85/177 (48.9%), followed by other Gram negative pathogens with 77/267 (28.8%) in osteomyelitis and 48/177 (27.1%) in prosthetic joint infection. On multivariate analysis, there was no difference between the rate of Staphylococcus aureus infection between the two groups. The rate of polymicrobial infection was higher in patients with osteomyelitis (92/267 (34.5%)) compared to prosthetic joint infection (38/177 (23.7%), however after adjustment for confounders there was no difference, p = 0.842. There was no difference in the presence of gentamicin resistant organisms or vancomycin resistant Gram positive organisms in osteomyelitis compared to prosthetic joint infection. Conclusion. Causative pathogens are similar in these two common forms of bone and joint infection. There was no significant difference in the identification, presence of polymicrobial infection or gentamicin and vancomycin resistance in organisms isolated in osteomyelitis compared to prosthetic joint infection. This may have implications for empiric antibiotic choice and local antibiotic therapy in the management of bone and joint infection

Introduction. In specific conditions, infection may lead to bone loss and is difficult to treat. 1. Current clinical approaches rely on the introduction of antibiotics. While these may be effective, there are concerns regarding the rise of antimicrobial resistance. There is therefore interest in the development of antimicrobial bone graft substitutes for dental and trauma surgery. Aim & Objectives. The incorporation of zinc into biomaterials has been shown to confer broad spectrum antimicrobial activity, but this has not yet been applied to the development of a commercial bone graft substitute. The aim of this research was therefore to prepare and characterise a series of zinc-substituted nanoscale hydroxyapatite (nHA) materials, including evaluation of antimicrobial activity. Method. Zinc (Zn) substituted nHA materials were prepared (0, 5, 10, 15 & 20 mol.% Zn) using a wet chemical precipitation method with a rapid mixing. (2). The reaction was carried out using zinc hydroxide at pH 10. The suspension formed was washed and dried into both powder & paste forms. The resultant powders were characterized using transmission electron microscopy (TEM) and X-ray diffraction (XRD). The antimicrobial activity was evaluated against Staphylococcus aureus (S8650 strain - isolated from an osteomyelitis case), by two techniques. The Miles and Misra method was applied to determine the number of colony-forming units (CFUs) in bacterial suspensions incubated with pastes. Secondly, a biofilm initialization method was used to evaluate the capacity of the materials to prevent biofilm formation. One-way analysis of variance (ANOVA) was used for the statistical analysis and results with p-value < 0.05 were considered statistically significant. Results. XRD indicated the formation of pure hydroxyapatite with up to 10 mol.% Zn without any side products. However, when Zn was increased to 15 & 20 mol %, zinc oxide (ZnO) peaks were detected. The TEM showed nanoscale needle-like particles when Zn was increased compared to nHA particles. Regarding the antibacterial activity, ZnHA pastes at all concentrations caused a significant reduction in bacterial CFUs in a dose-dependent manner (50, 100 & 200 mg). Additionally, even the lowest zinc substitution (5 mol.%) significantly reduced biofilm formation. Conclusion. The results demonstrated a novel method to produce a Zn-substituted nHA that showed antimicrobial activity against a pathogen isolated from a bone infection

Aim. The osteolytic process of osteomyelitis is, according to textbooks, caused by increased osteoclast activity due to RANKL production by osteoblasts. However, recent findings contradict this theory. Therefore, the aim was to investigate, in a porcine osteomyelitis model, how osteolysis is affected by massive inflammation and RANKL blocking, respectively. In parallel, patients with chronic osteomyelitis, diabetes, foot osteomyelitis, and fracture related infections (FRI) were included for advanced histological analysis of osteolysis. Methods. In pigs, a tibial implant cavity was created and inoculated with 10. 4. CFU of Staphylococcus aureus: Group A (n=7). Group B (n=7); + 1cm. 3. spongostan into the cavity. Group C (n=4); + systemic Denosumab treatment. Spongostan was used as an avascular material to support bacterial growth and thus increase the inflammatory response. Denosumab treatment was administrated to suppress osteoclast activity by RANKL inhibition (as in osteoporotic patients). The volume of osteolysis was accessed by CT scans. Immunohistochemistry with antibodies towards Cathepsin K was used to identify osteoclasts within the bone lesions. Briefly, the number of Cathepsin K positive cells, i.e., both precursors and bone resorbing osteoclasts, respectively, were counted in 10 high power fields (400x). In total, 50 bone infection patients were included (Herlev Hospital). From each patient five parried samples were taken for histology and microbiology, respectively. Histopathology, CT osteolysis volume estimation, and molecular expression of osteoclasts and inflammatory markers are ongoing. One FRI patient was osteoporotic and treated with Denosumab for 6 years. Results. All pigs were confirmed infected in the implant cavity. The volume (2.41 ± 1.29cm. 3. ) of osteolysis was significantly increased in the spongostan group in comparison to Group A (1.24 ± 0.59 cm. 3. ) (p=0.04). Thereby, the spongostan group had bacteria deeper into the bone from the inoculation point. Sufficient Denosumab treatment, i.e. reduced serum Ca was seen in 3 pigs. None of the Denosumab treated pigs showed reduced osteolysis in comparison to Group A (1.42 ± 0.63 cm. 3. ). The Cathepsin K score of Group C was 17 (15-23 IQR) of precursor osteoclasts and 2 (0-2 IQR) of osteoclasts in Howship lacunae. The Denosumab treated patient showed substantial osteolysis and histological analysis confirmed acute inflammatory. Conclusions. Application of spongostan, i.e., bacterial host optimization and massive inflammation promotes osteolysis and local bacterial dissemination. Osteoclast blocking with Denosumab showed no impact on osteolysis. Elucidation of the pathophysiology causing bone loss in osteomyelitis is fundamental. However, the widely accepted osteoclast-based theory might not be the only relevant

Aim. Local antibiotics, delivered to the site of infection, achieve high tissue concentrations and are used as an adjunct to systemic therapy. Local gentamicin provides levels well above the minimum inhibitory concentration and may be sufficient on its own, however, the efficacy of single or combination local antibiotics has not been studied. This retrospective study evaluated the effect of combination aminoglycoside and vancomycin local antibiotic treatment compared to aminoglycoside alone in the surgical management of bone infection. Method. We studied patients with microbiologically confirmed osteomyelitis and fracture-related infection, who had implantation of antibiotic carriers as part of their surgical management. Data including patient demographics, type of surgery, microbiological characteristics, BACH score, duration of antibiotic treatment and clinical outcomes were collected. Failure of therapy was a composite of recurrence of infection, continued or new antimicrobial therapy, or reoperation with suspected or confirmed infection at one year after index surgery. Results. There were 266 patients who met the inclusion criteria. Nine patients died before the outcome endpoint at 12 months and five patients were lost to follow up so were excluded. 252 patients were included in the final analysis and were well matched with regard to demographics, BACH score and microbiology. 113 patients had treatment with aminoglycoside alone and 139 patients had combination aminoglycoside and vancomycin. There was no difference in the failure rate between groups; 10/113 (8.8%) in the aminoglycoside alone and 12/139 (8.6%) in the combination group, p = 0.934. There was no difference for reoperation, ongoing suppressive antibiotic use, or clinical suspicion of infection. Multivariate analysis showed that there was no added benefit of combination therapy (OR 1.54: 95%CI 0.59-4.04, p=0.38). BACH score and low BMI were associated with increased risk of failure (BACH OR 3.49: 95%CI 1.13-10.76, p=0.03; Low BMI OR 0.91: 95%CI 0.84-0.99, p-0.037). The form of the carrier material (pellets or injectable paste) had no effect on failure rate (p=0.434). Aminoglycoside resistance (confirmed and presumed) occurred in 39/113 (34.5%) of the aminoglycoside only group and 36/139 (25.9%) of the combination group (p=0.137). The presence of aminoglycoside resistance had no effect on failure rate (OR 0.39: 95%CI 0.05-3.01, p=0.37). Conclusions. Clinical outcome was not improved by the addition of vancomycin to aminoglycoside alone as local therapy for the management of osteomyelitis and FRI. Laboratory measured resistance, using currently accepted breakpoints, may not be relevant in local therapy

Introduction. In recent years, many studies demonstrated the efficacy of an early switch to oral antibiotics after surgical treatment in orthopaedic related infections. However, large analyses on periprosthetic joint infections (PJIs) are lacking. Material and Methods. We conducted a retrospective observational multicenter study in patients diagnosed with an early postoperative PJI (i.e less than 3 months after the index arthroplasty) treated with debridement, antibiotics and implant retention (DAIR). Patients from Europe and the USA were included. These two cohorts served as a quasi-randomised trial since an early oral antibiotic switch is routine practice in Europe versus a long duration of intravenous (IV) antibiotic treatment in the USA. Failure was defined as the clinical need for: i) a second DAIR, ii) implant removal, iii) suppressive antibiotic treatment or iv) infection related death. Results. A total of 668 patients were included. 277 received IV antibiotics for <14 days, 232 were given IV antibiotics between 14 - 27 days and 159 received IV antibiotics for >27 days. The overall 1-year failure rate within the 3 groups was 41.5%, 44.4% and 42.1%, respectively (P 0.80), and mainly comprised the need for a second DAIR. The results did not change when analyzing patients with or without obesity, the causative microorganism or the type of oral antibiotics. Conclusion. In early postoperative PJIs, a longer duration of IV antibiotic treatment is not associated with a lower failure rate of a DAIR procedure

Aims

The first metatarsal pronation deformity of hallux valgus feet is widely recognized. However, its assessment relies mostly on 3D standing CT scans. Two radiological signs, the first metatarsal round head (RH) and inferior tuberosity position (ITP), have been described, but are seldom used to aid in diagnosis. This study was undertaken to determine the reliability and validity of these two signs for a more convenient and affordable preoperative assessment and postoperative comparison.

Introduction. Promoting bone mass homeostasis keeps skeleton away from osteoporosis. a-Ketoglutarate (a-KG) is an indispensable intermediate of tricarboxylic acid cycle (TCA) process for cellular energy production. a-KG mitigates cellular senescence, tissue degeneration, and oxidative stress. We investigated whether a-KG affected osteoblast activity or osteoporosis development. Method. Serum and bone specimens were biopsied from 26 patients with osteoporosis or 24 patients without osteoporosis who required spinal surgery. Ovariectomized or aged mice were fed 0.25% or 0.75% a-KG in drinking water for 8 – 12 weeks ad libitum. Bone mineral density, trabecular/cortical bone microarchitecture, mechanical strength, bone formation, and osteoclastic erosion were investigated using mCT, material testing device, in vivo calcein labelling, and TRAP histochemical staining. Serum a-KG, osteocalcin, and TRAP5b levels were quantified using ELISA kits. Bone-marrow mesenchymal cells and macrophages were incubated osteogenic and osteoclastogenic media. Histone H3K27me3 levels and enrichment were investigated using immunoblotting and chromatin precipitation-PCR. Result. Serum a-KG levels in patients with osteoporosis were less than controls; and were correlated with T-scores of hips (R2 = 0.6471, P < 0.0001) and lumbar spine (R2 = 0.7235, P < 0.001) in osteoporosis (AUC = 0.9941, P < 0.001). a-KG supplement compromised a plethora of osteoporosis signs in ovariectomized or aged mice, including bone mass loss, trabecular bone microarchitecture deterioration, and mechanical strength loss. It elevated serum osteocalcin levels and decreased serum TRAP5b. a-KG preserved caclein-labelling bone formation and repressed osteoclast resorption. It reversed osteogenic differentiation of bone-marrow stromal cells and reduced osteoclast formation in ovariectomized mice. Mechanically, a-KG attenuated H3K27 hypermethylation and Runx2 transcription repression, improving mineralized matrix production in osteogenic cells. Conclusion. Decreased serum a-KG is correlated with human and murine osteoporosis. a-KG reverses bone loss by repressing histone methylation in osteoblasts. This study highlighted a-KG supplement as a new biochemical option for protecting osteoporosis

Introduction. Tendon ruptures are a common injury and often require surgical intervention to heal. A refixation is commonly performed with high-strength suture material. However, slipping of the thread is unavoidable even at 7 knots potentially leading to reduced compression of the sutured tendon at its footprint. This study aimed to evaluate the biomechanical properties and effectiveness of a novel dynamic high-strength suture, featuring self-tightening properties. Method. Distal biceps tendon rupture tenotomies and subsequent repairs were performed in sixteen paired human forearms using either conventional or the novel dynamic high-strength sutures in a paired design. Each tendon repair utilized an intramedullary biceps button for radial fixation. Biomechanical testing aimed to simulate an aggressive postoperative rehabilitation protocol stressing the repaired constructs. For that purpose, each specimen underwent in nine sequential days a daily mobilization over 300 cycles under 0-50 N loading, followed by a final destructive test. Result. After the ninth day of cyclic loading, specimens treated with the dynamic suture exhibited significantly less tendon elongation at both proximal and distal measurement sites (-0.569±2.734 mm and 0.681±1.871 mm) compared to the conventional suture group (4.506±2.169 mm and 3.575±1.716 mm), p=0.003/p<0.002. Gap formation at the bone-tendon interface was significantly lower following suturing using dynamic suture (2.0±1.6 mm) compared to conventional suture (4.5±2.2 mm), p=0.04. The maximum load at failure was similar in both treatment groups (dynamic suture: 374± 159 N; conventional suture: 379± 154 N), p=0.925. The predominant failure mechanism was breakout of the button from the bone (dynamic suture: 5/8; conventional suture: 6/8), followed by suture rupturing, suture unraveling and tendon cut-through. Conclusion. From a biomechanical perspective, the novel dynamic high-strength suture demonstrated higher resistance against gap formation at the bone tendon interface compared to the conventional suture, which may contribute to better postoperative tendon integrity and potentially quicker functional recovery in the clinical setting

Introduction

Experimental bone research often generates large amounts of histology and histomorphometry data, and the analysis of these data can be time-consuming and trivial. Machine learning offers a viable alternative to manual analysis for measuring e.g. bone volume versus total volume.

The objective was to develop a neural network for image segmentation, and to assess the accuracy of this network when applied to ectopic bone formation samples compared to a ground truth.

Introduction. To develop an international guideline (AOGO) about use of osteobiologics in Anterior Cervical Discectomy and Fusion (ACDF) for treating degenerative spine conditions. Method. The guideline development process was guided by AO Spine Knowledge Forum Degenerative (KF Degen) and followed the Guideline International Network McMaster Guideline Development Checklist. The process involved 73 participants with expertise in degenerative spine diseases and surgery from 22 countries. Fifteen systematic reviews were conducted addressing respective key topics and evidence were collected. The methodologist compiled the evidence into GRADE Evidence-to-Decision frameworks. Guideline panel members judged the outcomes and other criteria and made the final recommendations through consensus. Result. Five conditional recommendations were created. A conditional recommendation is about the use of allograft, autograft or a cage with an osteobiologic in primary ACDF surgery. Other conditional recommendations are about use of osteobiologic for single or multi-level ACDF, and for hybrid construct surgery. It is suggested that surgeons use other osteobiologics rather than human bone morphogenetic protein-2 in common clinical situations. Surgeons are recommended to choose one graft over another or one osteobiologic over another primarily based on clinical situation, and the costs and availability of the materials. Conclusion. This AOGO guideline is the first to provide recommendations for the use of osteobiologics in ACDF. Despite the comprehensive searches for evidence, there were few studies completed with small sample sizes and primarily as case series with inherent risks of bias. Therefore high quality clinical evidence is demanded to improve the guideline

Introduction. Achieving an appropriate primary stability after implantation is a prerequisite for the long-term viability of a dental implant. Virtual testing of the bone-implant construct can be performed with finite element (FE) simulation to predict primary stability prior to implantation. In order to be translated to clinical practice, such FE modeling must be based on clinically available imaging methods. The aim of this study was to validate an FE model of dental implant primary stability using cone beam computed tomography (CBCT) with ex vivo mechanical testing. Method. Three cadaveric mandibles (male donors, 87-97 years old) were scanned by CBCT. Twenty-three bone samples were extracted from the bones and conventional dental implants (Ø4.0mm, 9.5mm length) were inserted in each. The implanted specimens were tested under quasi-static bending-compression load (cf. ISO 14801). Sample-specific homogenized FE (hFE) models were created from the CBCT images and meshed with hexahedral elements. A non-linear constitutive model with element-wise density-based material properties was used to simulate bone and the implant was considered rigid. The experimental loading conditions were replicated in the FE model and the ultimate force was evaluated. Result. The experimental ultimate force ranged between 67 N and 789 N. The simulated ultimate force correlated better with the experimental ultimate force (R. 2. =0.71) than the peri-implant bone density (R. 2. =0.30). Conclusion. The developed hFE model was demonstrated to provide stronger prediction of primary stability than peri-implant bone density. Therefore, hFE Simulations based on this clinically available low-radiation imaging modality, is a promising technology that could be used in future as a surgery planning tool to assist the clinician in evaluating the load-bearing capacity of an implantation site. Acknowledgements. Funding: EU's Horizon 2020 grant No: 953128 (I-SMarD). Dental implants: THOMMEN Medical AG

Introduction. Pedicle screw loosening in posterior instrumentation of thoracolumbar spine occurs up to 60% in osteoporotic patients. These complications may be alleviated using more flexible implant materials and novel designs that could be optimized with reliable computational modeling. This study aimed to develop and validate non-linear homogenized finite element (hFE) simulations to predict pedicle screw toggling. Method. Ten cadaveric vertebral bodies (L1-L5) from two female and three male elderly donors were scanned with high-resolution peripheral quantitative computed tomography (HR-pQCT, Scanco Medical) and instrumented with pedicle screws made of carbon fiber-reinforced polyether-etherketone (CF/PEEK). Sample-specific 3D-printed guides ensured standardized instrumentation, embedding, and loading procedures. The samples were biomechanically tested to failure in a toggling setup using an electrodynamic testing machine (Acumen, MTS) applying a quasi-static cyclic testing protocol of three ramps with exponentially increasing peak (1, 2 and 4 mm) and constant valley displacements. Implant-bone kinematics were assessed with a stereographic 3D motion tracking camera system (Aramis SRX, GOM). hFE models with non-linear, homogenized bone material properties including a strain-based damage criterion were developed based on intact HR-pQCT and instrumented 3D C-arm scans. The experimental loading conditions were imposed, the maximum load per cycle was calculated and compared to the experimental results. HR-pQCT-based bone volume fraction (BV/TV) around the screws was correlated with the experimental peak forces at each displacement level. Result. The nonlinear hFE models accurately (slope = 1.07, intercept = 0.2 N) and precisely (R. 2. = 0.84) predicted the experimental peak forces at each displacement level. BV/TV alone was a weak predictor (R. 2. <0.31). Conclusion. The hFE models enable fast design iterations aiming to reduce the risk of screw loosening in low-density vertebrae. Improved flexible implant designs are expected to contribute to reduced complication rates in osteoporotic patients

Introduction. Patient-specific biomechanical modeling using Finite Element Analysis (FEA) is pivotal for understanding the structural health of bones, optimizing surgical procedures, assessing outcomes, and validating medical devices, aligning with guidance issued by standards and regulatory bodies. Accurate mapping of image-to-mesh-material is crucial given bone's heterogeneous composition. This study aims to rigorously assess mesh convergence and evaluate the sensitivity of material grouping strategies in quantifying bone strength. Method. Subject-specific geometry and nonlinear material properties were derived from computed tomography (CT) scan data of one cadaveric human vertebral body. Linear tetrahedral elements with varying edge lengths between 2mm and 0.9mm were then generated to study the mesh convergence. To compare the effectiveness of different grouping strategies, three approaches were used: Modulus Gaping (a user-defined absolute threshold of Young's modulus ranging from 500 MPa to 1 MPa), Percentual Thresholding (relative parameter thresholds ranging from 50% to 1%), and Adaptive clustering (unsupervised k-means-based clustering ranging from 10 to 200 clusters). Adaptive clustering enables a constant number of unique material properties in cross-specimen studies, improving the validity of results. Result. Mesh convergence was evaluated via fracture load and reached at a 1mm mesh size across grouping strategies. All strategies exhibit minimal deviation (within 5%) from individually assigned material parameters, except Modulus Gaping, with a 500 MPa threshold (32% difference). Computational efficiency, measured by runtime, significantly improved with grouping strategies, reducing computational cost by 82 to 94% and unique material count by up to 99%. Conclusion. Different grouping strategies offer comparable mesh convergence, highlighting their potential to reduce computational complexity while maintaining accuracy in the biomechanical modeling of bones and suggesting a more efficient approach than individual element materials. The higher efficiency of FEA may increase its applicability in clinical settings with limited computational resources. Further studies are needed to refine grouping parameters and assess their suitability across different subjects

Introduction. A long nail is often recommended for treatment of complex trochanteric fractures but requires longer surgical and fluoroscopy times. A possible solution could be a nail with an appropriate length which can be locked in a minimally invasive manner by the main aiming device. We aimed to determine if such a nail model* offers similar structural stability on biomechanical testing on artificial bone as a standard long nail when used to treat complex trochanteric fractures. Method. An artificial osteoporotic bone model was chosen. As osteosynthesis material two cephalomedullary nails (CMN) were chosen: a superior locking nail (SL-Nail) which can be implanted with a singular targeting device, and a long nail (long-nail) with distal locking using free-hand technique. AO31-A2.2 fractures were simulated in a standardized manner. The insertion of the nail was strictly in accordance with the IFU and surgical manual of the manufacturer. The nail was locked dynamically proximally and statically distally. Axial height of the construct, varus collapse, and rotational deformity directly after nail insertion were simulated. A Universal Testing Machine was used. Measurements were made with a stereo-optic tracking system. Reactive movements were recorded and evaluated in all six degrees of freedom. A comparative analysis provided information about the stability and deformation of the assemblies to be compared. Result. There was a detectable difference in the axial fracture movement resulting in narrowing of the fracture gap. The load displacement was 1.7mm higher for the SL-Nail. There was no difference in varus collapse or rotational deformity between the nail variants. Conclusion. We conclude that there are small differences which are clinically insignificant and that a superior locking nail can safely be used to manage complex trochanteric fractures. *DCN SL nail, SWEMAC, Linköping, Sweden. Funding: no funding

Introduction. Osteoporosis accounts for a major risk factor of fracture-associated disability or premature death in the elderly. Enhancement of bone anabolism for slowing osteoporosis is highly demanding. Exerkine fibronectin type III domain containing 5 (FNDC5) regulates energy metabolism, inflammation, and aging. This study was aimed to investigate whether Fndc5 signaling in osteoblasts changed estrogen deficiency-mediated bone loss or microarchitecture deterioration. Method. Female osteoblast-specific Fndc5 transgenic mice (Fndc5Tg), which overexpressed Fndc5 under the control of key osteoblast marker osteocalcin promoter, were given bilateral ovariectomy to induce estrogen deficiency-mediated osteoporosis. Bone mass, microstructures, and biomechanical properties were quantified using μCT imaging and material testing. Dynamic bone formation was traced using fluorescence calcein. Osteogenic differentiation and adipocyte formation of bone-marrow mesenchymal cells were investigated using von Kossa staining and Nile red staining, respectively. Serum osteocalcin, CTX-1 and TRAP5b levels were quantified using designated ELISA kits. Mitochondrial respiration was investigated using Seahorse Extracellular Flux Analyzer. Result. Fndc5Tg mice developed relatively higher bone mass and microarchitecture than wild-type mice. Fndc5 overexpression attenuated the losses of bone mineral density and trabecular network, including trabecular volume, thickness, and trabecular number, and improved cortical thickness and porosity in ovariectomized mice. Gain of Fndc5 function preserved biomechanical characteristics (maximum load, breaking force, and energy), serum bone formation marker osteocalcin levels, and bone formation rate, whereas it reduced serum bone resorption makers CTX-1 and TRAP5b levels, osteoclast overburden, and marrow adiposis. In vitro, Fndc5 reversed the estrogen deficiency-mediated mineralized matrix underproduction and adipocyte formation of bone-marrow mesenchymal cells, and inhibited osteoclast formation in osteoporotic bone. Mechanistically, Fndc5 activated AMPK signaling, promoting mitochondrial respiration and ATP production to enhance osteoblastic activity. Conclusion. Fndc5 signaling exerted bone-protective actions delaying estrogen deficiency-mediated osteoporosis. This study highlighted a new molecular remedial option for osteoporosis development by manipulating Fndc5 functions

Introduction. Understanding knee joint biomechanics is crucial, but studying Anterior cruciate ligament (ACL) biomechanics in human adolescents is challenging due to limited availability cadaveric specimens. This study aims to validate the adolescent porcine stifle joint as a model for ACL studies by examining the ACL's behavior under axial and torsion loads and assessing its deformation rate, stiffness, and load-to-failure. Methods. Human knee load during high-intensity sports can reach 5-6 times body weight. Based on these benchmarks, the study applied a force equivalent to 5-times body weight of juvenile porcine samples (90 pounds), estimating a force of 520N. Experiments involved 30 fresh porcine stifle joints (Yorkshire breed, Avg 90 lbs, 2-4 months old) stored at -22°C, then thawed and prepared. Joints were divided into three groups: control (load-to-failure test), axially loaded, and 30-degree torsion loaded. Using a servo-hydraulic material testing machine, the tibia's longitudinal axis was aligned with the load sensor, and specimens underwent unidirectional tensile loading at 1 mm/sec until rupture. Data on load and displacement were captured at 100 Hz. Results. One-way ANOVA showed statistically significant differences in maximum failure force among loading conditions (p = 0.0039). Post hoc analysis indicated significant differences between the control and 500N (non-twisted) groups (p = 0.014) and between the control and 500N (twisted) groups (p = 0.003). However, no significant difference was found between 500N (non-twisted) and 500N (twisted) groups (p = 0.2645). Two samples broke from the distal femur growth plates, indicating potential growth plate vulnerability in adolescent porcines. Conclusions. The study validates the adolescent porcine stifle joint as a suitable model for ACL biomechanical research, demonstrating that torsional loads are as damaging to the ACL's integrity as equivalent axial loads. It also highlights the potential vulnerability of growth plates in younger populations, reflected in the porcine model