Biomechanical Testing Research Articles

Bone Allograft Pedicle Screw Augmentation: A Biomechanical Study.

We performed a comprehensive cadaveric biomechanical study to compare the fixation strength of primary screws, screws augmented with bone allograft, and screws augmented with polymethylmethacrylate cement. To evaluate a novel technique for screw augmentation using morselized cortico-cancellous bone allograft to fill the widened screw track of failed pedicle screws. To date, there are no known biological methods available for failed pedicle screw augmentation or fixation. Biomechanical tests were performed using 2 different testing modalities to quantify fixation strength including axial screw pullout and progressive cyclic displacement tests. Fifty vertebrae were instrumented with pedicle screws. Our study showed that bone allograft augmentation using the same diameter screw was noninferior to the fixation strength of the initial screw. In the axial pullout test, screws undergoing bone allograft repair failed at 25% lower loads compared with native screws, and screws augmented with cement showed approximately twice as much strength compared with native screws. In the cyclic displacement test, screws fixed with cement resisted loosening the best of all the groups tested. However, screws augmented with bone graft were found to have an equal strength to native screw purchase. our study did not find a correlation with bone mineral density as a predictor for failure in axial pullout or cyclic displacement tests. Bone allograft augmentation for pedicle screw fixation was noninferior to the initial screw purchase in this biomechanical study. This bone allograft technique is a viable option for screw fixation in the revision setting when there is significant bone loss in the screw track.

Ferroptosis Inhibition with Deferoxamine Alleviates Radiation-Induced Fibrosis.

Background Radiation-induced fibrosis (RIF) is a debilitating sequelae of radiation therapy that has been shown to improve with topical treatment with the iron chelator deferoxamine (DFO). We investigated whether DFO exerts this effect through attenuation of ferroptosis, a recently described iron-dependent pathway of cell death. Methods Adult C57BL/6J mice were treated with topical DFO or ferrostastin-1 (Fer-1) and irradiated with 30 Grays of ionizing radiation to the dorsal skin to promote development of chronic RIF. Immunofluorescent staining with 4-hydroxynonenal (4-HNE) antibody was carried out directly following irradiation to assess ferroptosis activity. Perfusion testing with laser Doppler was performed throughout the healing interval. Eight weeks following radiation, dorsal skin was harvested and analyzed histologically and biomechanically. Results Immunohistochemical staining demonstrated lower presence of 4-HNE in non-irradiated skin, DFO-treated skin, and Fer-1-treated skin compared to irradiated, untreated skin. DFO resulted in histological measurements (dermal thickness and collagen content) that resembled normal skin, while Fer-1 treatment yielded less significant improvements. These results were mirrored by analysis of extracellular matrix ultrastructure and biomechanical testing, which recapitulated the ability of topical DFO treatment to alleviate RIF across these parameters while Fer-1 resulted in less notable improvement. Finally, perfusion levels in DFO treated irradiated skin were similar to measurements in normal skin, while Fer-1 treatment did not impact this feature. Conclusions Ferroptosis contributes to the development of RIF and attenuation of this process leads to reduced skin injury. DFO further improves RIF through additional enhancement of perfusion not seen with Fer-1.

Metformin treatment prevents experimental metabolic syndrome-induced femoral bone marrow adiposity in rats.

Motivation for the study. Most research supports a negative association between metabolic syndrome and bone health, although there is an overall lack of consensus. Therefore, there is a need for research in this area to develop a better understanding. Main findings. Metabolic syndrome induced by a fructose-rich diet increases the adipogenic predisposition of bone marrow progenitor cells and femoral medullary adiposity in rats. Furthermore, this can be partially prevented by co-treatment with metformin. Implications. Experimental metabolic syndrome has negative effects on bone tissue and can be prevented by oral treatment with metformin as a normoglycemic drug. To determine the effect of metformin (MET) treatment on adipogenic predisposition of bone marrow progenitor cells (BMPC), bone marrow adiposity and bone biomechanical properties. 20 young adult male Wistar rats were sorted into four groups. Each of the groups received the following in drinking water: 100% water (C); 20% fructose (F); metformin 100 mg/kg wt/day (M); or fructose plus metformin (FM). After five weeks the animals were sacrificed. Both humeri were dissected to obtain BMPC, and both femurs were dissected to evaluate medullary adiposity (histomorphometry) and biomechanical properties (3-point bending). BMPC were cultured in vitro in adipogenic medium to evaluate RUNX2, PPAR-γ and RAGE expression by RT-PCR, lipase activity and triglyceride accumulation. The fructose-rich diet (group F) caused an increase in both triglycerides in vitro, and medullary adiposity in vivo; being partially or totally prevented by co-treatment with metformin (group FM). No differences were found in femoral biomechanical tests in vivo, nor in lipase activity and RUNX2/PPAR-γ ratio in vitro. DRF increased RAGE expression in BMPC, being prevented by co-treatment with MET. Metabolic syndrome induced by a fructose-rich diet increases femoral medullary adiposity and, in part, the adipogenic predisposition of BMPC. In turn, this can be totally or partially prevented by oral co-treatment with MET.

Impact of NaOH based perfusion-decellularization protocol on mechanical resistance of structural bone allografts

ABSTRACT Introduction To mitigate the post-operative complication rates associated with massive bone allografts, tissue engineering techniques have been employed to decellularize entire bones through perfusion with a sequence of solvents. Mechanical assessment was performed in order to compare conventional massive bone allografts and perfusion/decellularized massive bone allografts. Material and methods Ten porcine femurs were included. Five were decellularized by perfusion. The remaining 5 were left untreated as the “control” group. Biomechanical testing was conducted on each bone, encompassing five different assessments: screw pull-out, 3-points bending, torsion, compression and Vickers indentation. Results Under the experimental conditions of this study, all five destructive tested variables (maximum force until screw pull-out, maximum elongation until screw pull-out, energy to pull out the screw, fracture resistance in flexion and maximum constrain of compression) were statistically significantly superior in the control group. All seven nondestructive variables (Young’s modulus in flexion, Young’s modulus in shear stress, Young’s modulus in compression, Elastic conventional limit in compression, lengthening to rupture in compression, resilience in compression and Vickers Hardness) showed no significant difference. Discussion Descriptive statistical results suggest a tendency for the biomechanical characteristics of decellularized bone to decrease compared with the control group. However, statistical inferences demonstrated a slight significant superiority of the control group with destructive mechanical stresses. Nondestructive mechanical tests (within the elastic phase of Young’s modulus) were not significantly different.

A novel anatomical locked medial femoral condyle plate: a biomechanical study.

Fixation with a distal lateral femoral plate is a standard approach in treating osteoporotic or comminuted supracondylar femur fractures. However, in clinical practice, this method may prove inadequate, necessitating the application of a plate on the medial side of the distal femur. The aim of this study is to perform a biomechanical evaluation of the newly manufactured anatomically locked plate applied to the distal medial femoral condyle. The plate underwent 2 biomechanical tests by simulating an AO/OTA 33A3 type supracondylar fracture model on synthetic femur bones. The samples were divided into three groups. Fracture fixations were carried out on the medial side using the distal femur medial anatomical locking plate (DFMALP) in group A samples, on the lateral side using the distal femur lateral anatomical locking plate in group B samples, and on both sides in group C samples. In the axial compression test, stability was preserved 23% more in group C than in group B. During the cyclic axial compression test, total displacement was 21% less in group C than in group B. Group A was collapsed at early cycle degrees. In our study, it was observed that the application of DFMALP in conjunction with the lateral plate in AO/OTA 33A3 fragmented supracondylar femur fractures significantly enhanced biomechanical fracture stability. This is a Level 2 prospective, randomized controlled study.

Ex vivo biomechanical evaluation and comparison of lateral femoro-fabella ligament suture and lateral suture with bone anchor for cranial cruciate ligament repair in cats.

To compare the biomechanical properties of lateral femoro-fabella ligament suture (FFLS) and lateral suture with a bone anchor suture (BAS) for management of feline cranial cruciate ligament disease. 12 femurs from 6 mature cat cadavers. The samples were collected from April to June 2023. The specimens had an FFLS and, subsequently, BAS placed and were positioned into a biomechanical testing machine, preloaded from 5 N to 15 N for 100 cycles, and subsequently, a load to suture failure was applied. The displacement at 5 N and 15 N, the total precycle displacement (millimeters), the force at 3 mm displacement and at failure (newtons), the displacement at failure (millimeters), and the stiffness to failure (Newton:millimiter) were recorded. Nonparametric Wilcoxon signed-rank tests were used to compare data between the 2 groups. The displacement at 5 N and 15 N and the total precycle displacement were significantly higher in the FFLS group compared to the BAS group. Additionally, the FFLS group results showed less consistent displacement and marked variability. The force (newtons) at 3 mm displacement was higher in the BAS group. There was no significant difference in force and no significant difference in displacement at failure between the 2 groups. However, the stiffness to failure (N/mm) was significantly higher in the BAS group. BAS represented a more stable and reliable femur attachment for extracapsular suture in cats. To demonstrate the stability and reliability between BAS and FFLS and influence implant selection in the treatment of cranial cruciate ligament rupture in cats with evaluation of biomechanical properties.

Characteristics of the Gantzer muscle and implications for its use as a tendon-graft source in upper extremity reconstruction

BackgroundThe Gantzer muscle is an anatomical variant muscle that functions in flexion of the volar forearm. The prevalence and laterality of this muscle has been studied more recently in the literature. This study aimed to determine the prevalence and size of this muscle and tendon. MethodsThis was an observational study done from September 2021 to January 2022 at the University of North Texas Health Science Center in Fort Worth, Texas. Cadaveric dissection was conducted in the Department of Physiology and Anatomy. 50 pairs for a total of 100 forearms were dissected bilaterally in cadavers comprising 17 females (34 %) and 33 males (66 %) to identify the Gantzer muscle. The mean age at death was 68.8 years of age (range 40–91 years). When present, the dimensions of each Gantzer tendon were measured in millimeters using digital calipers. As a study of cadaveric specimens, this study was exempt from Institutional Review Board (IRB) approval. ResultsThe Gantzer muscle was present in 62 of the 100 forearms (62 %). All 62 Gantzer muscles originated from flexor digitorum superficialis (FDS) (100 %). Of the 62 Gantzer muscles, 42 inserted distally into flexor pollicus longus (FPL) (72.5 %), while the remaining 17 muscles inserted distally into flexor digitorum profundus (FDP) (27.5 %). The tendons inserting into FDP had an average length of 65.495 mm, while those inserting into FPL had an average length of 16.353 mm (p = 0.002). The Gantzer muscle was present in 24 of the 33 male specimens (72.7 %) and 13 of the 17 female specimens (76.4 %). Of the 62 Gantzer muscles, 50 were present bilaterally (80.6 %), and there was no significant difference in bilateral occurrence between sexes (p = 0.189). ConclusionsOur results suggest that the Gantzer muscle may be of sufficient size and present commonly enough in the general population to be considered as an alternative graft source for certain upper extremity reconstruction procedures in place of, or in addition to, palmaris longus, extensor toe tendons, and other commonly used tendon grafts. In this study, when palmaris longus was absent in a specimen, a Gantzer muscle was likely present, and may provide surgeons an alternative tendon graft source in the upper extremity without requiring additional incisions in the lower extremity for alternative tendon graft sources. Further biomechanical testing of the Gantzer tendon with comparisons to other common tendon graft sources is warranted.

Biomechanical analysis of a new cannulated screw for unstable femoral neck fractures.

The treatment of unstable femoral neck fractures (FNFs) remains a challenge. In this study, a new cannulated screw for unstable FNFs was designed to provide a new approach for the clinical treatment of these injuries, and its biomechanical stability was analyzed using finite element analysis and mechanical tests. An unstable FNF model was established. An internal fixation model with parallel inverted triangular cannulated screws (CSs) and a configuration with two superior cannulated screws and one inferior new cannulated screw (NCS) were used. The biomechanical properties of the two fixation methods were compared and analyzed by using finite element analysis and mechanical tests. The NCS model outperformed the CSs model in terms of strain and stress distribution in computer-simulated reconstruction of the inverted triangular cannulated screw fixation model for unstable FNFs. In the biomechanical test, the NCS group showed significantly smaller average femoral deformation (1.08 ± 0.15mm vs. 1.50 ± 0.37mm) and fracture line displacement (1.43 ± 0.30mm vs. 2.01 ± 0.47mm). In the NCS group, the mean stiffness was significantly higher than that in the CSs group (729.37 ± 82.20N/mm vs. 544.83 ± 116.07N/mm), and the mean compression distance was significantly lower than that in the CSs group (2.87 ± 0.30mm vs. 4.04 ± 1.09mm). The NCS combined with two ordinary cannulated screws in an inverted triangle structure to fix unstable FNFs can provide better biomechanical stability than CSs and exhibit a length- and angle-stable construct to prevent significant femoral neck shortening.

In Vitro Assessment of Knee Joint Biomechanics Using a Virtual Anterior Cruciate Ligament Reconstruction.

Understanding the biomechanical impact of injuries and reconstruction of the anterior cruciate ligament (ACL) is vital for improving surgical treatments that restore normal knee function. The purpose of this study was to develop a technique that enables parametric analysis of the effect of the ACL reconstruction (ACLR) in cadaver knees, by replacing its contributions with that of a specimen-specific virtual ACLR that can be enabled, disabled, or modified. Twelve ACLR reconstructed knees were mounted onto a motion simulator. In situ ACLR graft forces were measured using superposition, and these data were used to design specimen-specific virtual ACLRs that would yield the same ligament force-elongation behaviors. Tests were then repeated using the virtual ACLR in place of the real ACLR and following that in ACL deficient knee by disabling the virtual ACLR. In comparison to the ACL deficient state, the virtual ACLRs were able to restore knee stability to the same extent as real ACLRs. The average differences between the anterior tibial translation (ATT) of the virtual ACLR versus the real ACLR were +1.6 ± 0.9 mm (p = 0.4), +2.1 ± 0.4 mm (p = 0.4), and +1.0 ± 0.9 mm (p = 0.4) during Anterior drawer, Lachman and Pivot-shift tests, respectively, which is small in comparison to the full ATT range of motion (ROM) of these knees. Therefore, we conclude that a virtual ACLR can be used in place of real ACLR during biomechanical testing of cadaveric knees. This capability opens the door for future studies that can leverage parameterization of the ACLR for surgical design optimization.

Comparison of digital nerve repair techniques: a systematic review

Introduction: Digital nerves are the most injured upper limb peripheral nerves [1]. There are numerous different methods of repair, with no standardised treatment options or guidelines. This systematic review aims to evaluate literature that investigated thebiomechanical strength of digital nerve repairs through varying methods in cadaveric models.Aims/Hypothesis: The aim of the study is to evaluate the literature available for digital nerve repairs and directly compare which surgical method yields the best results. The primary outcome is maximum load to failure of the repaired digital nerve following biomechanical (tensile) strength testing. We postulate that out of all the repair methods, augmentation of repair with fibrin glue or additional conduit will increase the load to failure compared to suture only repair.Methodology: We utilised the PRISMA methodology to conduct the systematic review. The following databases were searched: Embase, Medline, Cochrane, and Web of Science. Studies were reviewed and screened by two researchers following an inclusion and exclusion strategy to retrieve relevant papers.Results: A total of seven papers were included in the final review; these papers reported biomechanical data on cadaveric digital nerve repairs. Due to heterogenicity of methods between papers, a combination of quantitative and qualitative analysis of the results was made.Conclusion: The use of minimal suturing with conduit or glue or both has the ability to increase the maximum load to failure of digital nerve repairs compared to suture only methods. This has additional benefits to decrease the number of sutures required for repair. This thereby reduces potential scarring and inflammation.

Biomechanical evaluation of a fixation technique with a modified hemicerclage for tibial tuberosity transposition: an ex vivo cadaveric study.

(1) To determine stiffness, load at failure, and mode of failure of a novel fixation method with a tension modified-hemicerclage (MH) for tibial tuberosity transposition, and (2) to compare the biomechanical properties of this novel fixation technique to 2 pins (2Pins) and 2 pins and tension band wire fixation (2Pins + TBW). Thirty cadaveric stifles from dogs between 5.2 and 13.1 kg were assigned to 3 treatment groups: Group 1: fixation technique with MH; Group 2: 2Pins; Group 3: 2Pins + TBW. Biomechanical testing was performed with the tibia positioned at an angle of 135° relative to vertical position. Tensile force was applied to the patellar ligament until catastrophic failure was observed. The mode of failure, the load at failure, and the stiffness were compared among treatment groups. The mean stiffness of the novel fixation (38.1 N/mm 7.1) and the 2Pins + TBW (40.2 N/mm 9.3) were greater than the 2Pins (26.7 N/mm 6.7). There was no significant difference between the novel fixation technique and 2Pins + TBW in stiffness and maximum load to failure. The 2Pins (284.3 N 70.5) failed at a significantly lower load than the tension modified-hemicerclage (555.7 N 225.9 N) and 2Pins + TBW (715.3 N 339.8 N). A fixation technique using a modified hemicerclage had the same strength and stiffness as the 2Pins + TBW and was stronger and stiffer than the 2 Pins technique in a cadaveric model.

Presoaking Grafts in Vancomycin Does Not Impair Graft-Bone Healing in a Rat Anterior Cruciate Ligament Reconstruction Model

Background: The vancomycin presoaking technique (wherein grafts are treated with a vancomycin solution [VS] for anterior cruciate ligament reconstruction [ACLR]) reduces the infection rate after ACLR. However, the effects of this technique on graft-bone healing have not been fully elucidated. Purpose: To investigate the effects of vancomycin presoaking on graft-bone healing in a rat ACLR model. Study Design: Controlled laboratory study. Methods: Long flexor digitorum longus tendons were obtained from 9 Wistar rats, and each was randomly allocated to the normal saline (NS) or VS groups. The grafts were immersed in sterile saline for 30 minutes in the NS group and in a 5-mg/mL VS in the VS group. The presence of time-zero graft bacterial contamination was confirmed, and the grafts were incubated in Fluidised Thioglycollate Broth for 2 weeks. ACLR was performed on the right knees of 65 male Wistar rats using the flexor digitorum longus tendons. Each graft was similarly treated. Biomechanical testing, micro–computed tomography, and histological evaluations were performed 4 and 12 weeks postoperatively. Results: The VS group showed significantly reduced graft contamination at time zero (P = .02). The mean maximum loads to failure were 13.7 ± 8.2 N and 11.6 ± 4.8 N in the NS and VS groups, respectively, at 4 weeks (P = .95); and 23.2 ± 13.2 N and 30.4 ± 18.0 N in the NS and VS groups, respectively, at 12 weeks (P = .35). Regarding micro–computed tomography, the mean bone tunnel volumes were 3.76 ± 0.48 mm3 and 4.40 ± 0.58 mm3 in the NS and VS groups, respectively, at 4 weeks (P = .41); and 3.51 ± 0.38 mm3 and 3.67 ± 0.35 mm3 in the NS and VS groups, respectively, at 12 weeks (P = .54). Histological semiquantitative examination revealed no clear between-group differences at any time point. Conclusion: Presoaking grafts in vancomycin in a rat ACLR model demonstrated no discernible adverse effects on short- and midterm biomechanical, radiological, and histological investigations. Clinical Relevance: The findings provide guidance for surgeons when considering this technique.

Biomechanical testing of ex vivo porcine tendons following high intensity focused ultrasound thermal ablation.

Magnetic resonance-guided focused ultrasound (MRgFUS) has been demonstrated to be able to thermally ablate tendons with the aim to non-invasively disrupt tendon contractures in the clinical setting. However, the biomechanical changes of tendons permitting this disrupting is poorly understood. We aim to obtain a dose-dependent biomechanical response of tendons following magnetic resonance-guided focused ultrasound (MRgFUS) thermal ablation. Ex vivo porcine tendons (n = 72) were embedded in an agar phantom and randomly assigned to 12 groups based on MRgFUS treatment. The treatment time was 10, 20, or 30s, and the applied acoustic power was 25, 50, 75, or 100W. Following each MRgFUS treatment, tendons underwent biomechanical tensile testing on an Instron machine, which calculated stress-strain curves during tendon elongation. Rupture rate, maximum treatment temperature, Young's modulus and ultimate strength were analyzed for each treatment energy. The study revealed a dose-dependent response, with tendons rupturing in over 50% of cases when energy delivery exceeded 1000J and 100% disruption at energy levels beyond 2000J. The achieved temperatures during MRgFUS were directly proportional to energy delivery. The highest recorded temperature was 56.8°C ± 9.34 (3000J), while the lowest recorded temperate was 18.6°C ± 0.6 (control). The Young's modulus was highest in the control group (47.3 MPa ± 6.5) and lowest in the 3000J group (13.2 MPa ± 5.9). There was no statistically significant difference in ultimate strength between treatment groups. This study establishes crucial thresholds for reliable and repeatable disruption of tendons, laying the groundwork for future in vivo optimization. The findings prompt further exploration of MRgFUS as a non-invasive modality for tendon disruption, offering hope for improved outcomes in patients with musculotendinous contractures.

Effect of Insertional Direction of Pedicle Screw on Screw Loosening: A Biomechanical Study on Synthetic Bone Vertebra under a Physiology-like Load.

It is now understood that pedicle screw loosening at the implant-bone interface can lead to poor screw-bone interface purchase and decreased fixation stability. Previous biomechanical tests used cadaveric vertebrae and pull-out or torque loads to assess the effect of the insertional direction of pedicle screws on screw loosening. However, these tests faced challenges in matching biomechanical differences among specimens and simulating in vivo loads applied on pedicle screws. This study aimed to evaluate the effect of the insertional direction of pedicle screws on screw loosening using tension-compression-bending loads and synthetic bone vertebrae. Polyaxial pedicle screws were inserted into nine synthetic bone vertebrae in three directions (three samples per group): cranial, parallel, and caudad (-10°, 0°, +10° of the pedicle screw rod to the upper plane of the vertebra, respectively). Pedicle screws in the vertebrae were loaded using a polyethylene block connected to a material testing machine. Tension-compression-bending loads (100N-250N) with 30,000 cycles were applied to the pedicle screws, and displacements were recorded and then cycle-displacement curve was drawn based on cycle number. Micro-CT scans were performed on the vertebrae after removing the pedicle screws to obtain images of the screw hole, and the screw hole volume was measured using imaging analysis software. Direct comparison of displacements was conducted via cycle-displacement curve. Screw hole volume was analyzed using analysis of variance. The correlation between the displacement, screw hole volume and the direction of pedicle screw was assessed by Spearman correlation analysis. The smallest displacements were observed in the caudad group, followed by the parallel and cranial groups. The caudad group had the smallest screw hole volume (p < 0.001 and p = 0.009 compared to the cranial and parallel groups, respectively), while the volume in the parallel group was greater than that in the cranial group (p = 0.003). Correlation analysis revealed that the insertional direction of the pedicle screw was associated with the displacement (p = -0.949, p < 0.001) and screw hole volume (p = -0.944, p < 0.001). Strong correlations were found between the insertional direction of the pedicle screw and relevant parameters, including displacement and screw hole volume. Pedicle screw insertion in the caudad direction resulted in the least pedicle screw loosening.

Brazil nut–enriched diet modulates bone mineral density and body composition in an experimental model of chronic kidney disease

ObjectiveThis study investigates the effects of a Brazil nut-enriched diet on body composition and bone parameters in CKD animal model. MethodsMale Wistar rats were assigned to the following groups: Sham (n=8), Nx (n=6), nephrectomized rats, and NxBN (n=6), nephrectomized rats and an enricheddiet with 5% Brazil nut. Body composition parameters were obtained by dual-energy X- ray absorptiometry (DXA). Bioclin kits determined plasmatic calcium. The femurs werecollected to determine absolute mass and length, bone mineral density, and biomechanical tests. ResultsThe NxBN group exhibited a higher total body bone mineral density (BMD) value than the Nx group (0.177±0.004g/cm2vs 0,169±0.003g/cm2; p=0.0397). No significant differences were observed regarding absolute mass, length, BMD, and biomechanical parameters in the femurs of the groups. Moreover, no significant differences were found in plasmatic calcium levels among the groups. ConclusionsBrazil-nut enriched diet modulated BMD in CKD experimental model, and further studies are demanded to understand the pathways involved in this finding.

Relationship between histomorphology and biomechanical properties of the ascending aortic wall in the aneurysm zone

Introduction. Thoracic aortic aneurysm (TAA) ranks 17th among all causes of a death. Over the past decade, the incidence rate of TAA increased several times and occurs in about 10 out of 100 thousand people per year. The search for the causes that lead to TAA is an urgent task. Local mechanical stress on the aortic wall leads to significant molecular and cellular changes in its tissue.Aim: To investigate the relationship between biomechanical properties and histological changes in the TAA tissue.Material and Methods. Thirty patients with TAA were included in the study. During surgery, fragments of the resected ascending aorta were obtained from each patient and subjected to uniaxial biomechanical testing to failure on an Instron 3343 testing machine (Instron, USA). Ultimate tensile stress at failure (σv, MPa), ultimate strain at failure (ε, mm/mm × %) and area under stress-strain curves (S, cm2) were calculated. In addition, the intraoperative material was fixed in formalin for histological examination of cellular and tissue changes in the aneurysm area. Inflammatory changes, the severity of aortic wall fibrosis and collagen/elastin ratio were assessed.Results. Atherosclerotic changes of the thoracic aortic wall were found in 43.3% (subgroup 1), aortitis – in 3.3%, connective tissue dysplasia – in 53.3% (subgroup 2) of the patients. Patient with inflammatory changes of the aortic wall was excluded. The biomechanical properties of the aorta were not statistically different between groups. A correlation was found between age with εcirc (r = –0.49) and Scirc (r = –0.54) and Slong (r = –0.5). A correlation was also found between εcirc and the degree of fibrosis in the medial layer of the aortic wall (r = –0.5) and collagen/elastin ratio (r = –0.61).Conclusions. Atherosclerotic changes in the aortic wall do not change the biomechanical properties of the TAA. However, structural changes in the medial layer of the aortic wall in the aneurysm zone result in reduced of its mechanical strength.

The effect of Ding’s screws and tension band wiring for treatment of olecranon fractures: a biomechanical study

Although tension band wiring (TBW) is popular and recommended by the AO group, the high rate of complications such as skin irritation and migration of the K-wires cannot be ignored. Ding’s screw tension band wiring (DSTBW) is a new TBW technique that has shown positive results in the treatment of other fracture types. The objective of this study was to evaluate the stability of DSTBW in the treatment of olecranon fractures by biomechanical testing. We conducted a Synbone biomechanical model by using three fixation methods: DSTBW, intramedullary screw and tension band wiring (IM-TBW), and K-wire TBW, were simulated to fix the olecranon fractures. We compared the mechanical stability of DSTBW, IM-TBW, and TBW in the Mayo Type IIA olecranon fracture Synbone model using a single cycle loading to failure protocol or pullout force. During biomechanical testing, the average fracture gap measurements were recorded at varying flexion angles in three different groups: TBW, IM-TBW, and DSTBW. The TBW group exhibited measurements of 0.982 mm, 0.380 mm, 0.613 mm, and 1.285 mm at flexion angles of 0°, 30°, 60°, and 90° respectively. The IM-TBW group displayed average fracture gap measurements of 0.953 mm, 0.366 mm, 0.588 mm, and 1.240 mm at each of the corresponding flexion angles. The DSTBW group showed average fracture gap measurements of 0.933 mm, 0.358 mm, 0.543 mm, and 1.106 mm at the same flexion angles. No specimen failed in each group during the cyclic loading phase. Compared with the IM-TBW and TBW groups, the DSTBW group showed significant differences in 60° and 90° flexion angles. The mean maximum failure load was 1229.1 ± 110.0 N in the DSTBW group, 990.3 ± 40.7 N in the IM-TBW group, and 833.1 ± 68.7 N in the TBW group. There was significant difference between each groups (p < 0.001).The average maximum pullout strength for TBW was measured at 57.6 ± 5.1 N, 480.3 ± 39.5 N for IM-TBW, and 1324.0 ± 43.8 N for DSTBW. The difference between maximum pullout strength of both methods was significant to p < 0.0001. DSTBW fixation provides more stability than IM-TBW and TBW fixation models for olecranon fractures.

Latarjet procedure: biomechanical evaluation of 2-screw coracoid fixation

Coracoid nonunion is a relevant complication following the Latarjet procedure and is influenced by multiple factors, including the method of graft fixation. The purpose of this study was to evaluate and characterize the biomechanical properties of various two-screw fixation constructs used for coracoid graft fixation in the Latarjet procedure. Forty model scapulae (Sawbones Inc., Vashon, WA, USA) were used for this study. A 15% anterior inferior glenoid bone defect was created. The coracoid was osteotomized at the juncture of the vertical and horizontal aspects, transferred to the anterior-inferior edge of the glenoid, and fixed with either two 3.5mm fully threaded cannulated cortical screws, two 3.5mm fully threaded solid cortical screws, two 3.5mm partially threaded cannulated screws, or two 4.5mm partially threaded malleolar screws (MS). Biomechanical testing was performed with an Instron material testing machine (Instron Corp., Norwood, MA, USA) by applying loads to the lateral aspect of the transferred coracoid graft. The constructs were preconditioned with nondestructive cyclical loading (0N-20N) to determine construct stiffness. After 100 cycles of dynamic loading, the construct was loaded to failure to determine ultimate failure load, yield displacement, and mode of failure. All failures were associated with plastic deformation of the screws and coracoid graft fracture. There was a significantly lower initial stiffness for partially threaded cannulated screws compared to MS (186±49.3N/mm vs. 280±65.5N/mm, P=.01) but no significant differences among the other constructs. There was no difference in ultimate failure load (P=.18) or yield displacement (P=.05) among constructs. Two screw coracoid fixation of the coracoid in a simulated classic Latarjet procedure with 3.5mm fully threaded cortical and cannulated screws is comparable to 4.5mm MS in strength, stiffness, and displacement at failure. On the other hand, partially threaded 3.5mm cannulated screws provide inferior fixation stiffness and could potentially affect clinical outcomes.

Isopsoralen Improves Glucocorticoid-induced Osteoporosis by Regulating Purine Metabolism and Promoting cGMP/PKG Pathway-mediated Osteoblast Differentiation.

The effects of Isopsoralen (ISO) in promoting osteoblast differentiation and inhibiting osteoclast formation are well-established, but the mechanism underlying ISO's improvement of Glucocorticoid- Induced Osteoporosis (GIOP) by regulating metabolism remains unclear. This study aims to elucidate the mechanism of ISO treatment for GIOP through non-targeted metabolomics based on ISO's efficacy in GIOP. Initially, we established a GIOP female mouse model and assessed ISO's therapeutic effects using micro-CT detection, biomechanical testing, serum calcium (Ca), and phosphorus (P) level detection, along with histological analyses using hematoxylin and eosin (HE), Masson, and tartrate-resistant acidic phosphatase (TRAP) staining. Subsequently, non-targeted metabolomics was employed to investigate ISO's impact on serum metabolites in GIOP mice. RT-qPCR and Western blot analyses were conducted to measure the levels of enzymes associated with these metabolites. Building on the metabolomic results, we explored the effects of ISO on the cyclic Guanosine Monophosphate (cGMP)/Protein Kinase G (PKG) pathway and its role in mediating osteoblast differentiation. Our findings demonstrate that ISO intervention effectively enhances the bone microarchitecture and strength of GIOP mice. It mitigates pathological damage, such as structural damage in bone trabeculae, reduced collagen fibers, and increased osteoclasts, while improving serum Ca and P levels in GIOP mice. Non-- targeted metabolomics revealed purine metabolism as a common pathway between the Control and GIOP groups, as well as between the ISO high-dose (ISOH) group and the GIOP group. ISO intervention upregulated inosine and adenosine levels, downregulated guanosine monophosphate levels, increased Adenosine Deaminase (ADA) expression, and decreased cGMP-specific 3',5'-cyclic phosphodiesterase (PDE5) expression. Additionally, ISO intervention elevated serum cGMP levels, upregulated PKGI and PKGII expression in bone tissues, as well as the expression of Runt-related transcription factor 2 (Runx2) and Osterix, and increased serum Alkaline Phosphatase (ALP) activity. In summary, ISO was able to enhance the bone microstructure and bone strength of GIOP mice and improve their Ca, P, and ALP levels, which may be related to ISO's regulation of purine metabolism and promotion of osteoblast differentiation mediated by the cGMP/PKG pathway. This suggests that ISO is a potential drug for treating GIOP. However, further research is still needed to explore the specific targets and clinical applications of ISO.

Calcium-fortified fresh milk ameliorates postmenopausal osteoporosis via regulation of bone metabolism and gut microbiota in ovariectomized rats

The aging of the global population has made postmenopausal osteoporosis prevention essential; however, pharmacological treatments are limited. Herein, we evaluate the effect of calcium-fortified fresh milk (FM) in ameliorating postmenopausal osteoporosis in a rat model established using bilateral ovariectomy. After 3 months of FM (containing vitamin D, and casein phosphopeptides, 1000 mg Ca/100 g) or control milk (110 mg Ca/100 g milk) supplementation, bone changes were assessed using dual-energy X-ray absorptiometry, microcomputed tomography, and bone biomechanical testing. The results revealed that FM can regulate bone metabolism and gut microbiota composition, which act on bone metabolism through pathways associated with steroid hormone biosynthesis, relaxin signaling, serotonergic synapse, and unsaturated fatty acid biosynthesis. Furthermore, FM administration significantly increased bone mineral content and density in the lumbar spine and femur, as well as femoral compressive strength, while improving femoral trabecular bone parameters and microarchitecture. Mechanistically, we found that the effects may be due to increased levels of estrogen, bone formation marker osteocalcin, and procollagen type I N-propeptide, and decreased expression of the bone resorption marker C-telopeptide and tartrate-resistant acid phosphatase 5b. Overall, the findings suggest that FM is a potential alternative therapeutic option for ameliorating postmenopausal osteoporosis.