Expanded Combined Loading Injury Criterion for the Human Lumbar Spine Under Dynamic Compression.

Contemporary injury tolerance of the lumbar spine for under-body blast references axial compression and bending moments in a limited range. Since injuries often occur in a wider range of flexion and extension with increased moment contribution, this study expands a previously proposed combined loading injury criterion for the lumbar spine. Fifteen cadaveric lumbar spine failure tests with greater magnitudes of eccentric loading were incorporated into an existing injury criterion to augment its applicability and a combined loading injury risk model was proposed by means of survival analysis. A loglogistic distribution was the most representative of injury risk, resulting in optimized critical values of Fr,crit = 6011 N, and My,crit = 904 Nm for the proposed combined loading metric. The 50% probability of injury resulted in a combined loading metric value of 1, with 0.59 and 1.7 corresponding to 5 and 95% injury risk, respectively. The inclusion of eccentric loaded specimens resulted in an increased contribution of the bending moment relative to the previously investigated flexion/extension range (previous My,crit = 1155 Nm), with the contribution of the resultant sagittal force reduced by nearly 200 N (previous Fr,crit = 5824 N). The new critical values reflect an expanded flexion/extension range of applicability of the previously proposed combined loading injury criterion for the human lumbar spine during dynamic compression.

Functional Outcome of Forearm Fractures Managed With Screw Nails vs. Dynamic Compression Plates: A Prospective Study.

Background Fractures of the forearm are very frequently encountered in day-to-day practice. These fractures have a bimodal age distribution. The forearm fractures are considered intra-articular and need absolute stability for adequate healing. The current treatment modalities include using intramedullary devices such as a square nail, locking intramedullary nail, or using a plate for fixation. In this study, we aim to determine the functional outcome of forearm fractures managed with a screw nail used as an intramedullary device as compared to a locking plate using the Grace-Eversmann criteria. Methodology Patients with forearm fractures were divided into two groups and treated with a screw nail and a dynamic compression plate. Patients were followed up at one month, three months, six months, and one year postoperatively and assessment was done using the Grace-Eversmann criteria. Results The study included a total of 30 subjects, ranging in age from 18 to 65. The majority of the patients had encountered a road traffic accident, following which they incurred a forearm fracture. Grace-Eversmann criteria was used for these patients at follow-up, and a total of 13 patients (86.6%) had good to excellent scores, which was similar when compared to the plate osteosynthesis group (86.6%). A significant difference in the amount of blood loss was noted in the screw nail osteosynthesis group as compared to the plate osteosynthesis group (p<0.05). Conclusions Though a dynamic compression plate is considered a standard method for fixation of the forearm fractures, the use of an intramedullary screw nail as a fixation device gives a similar result with excellent functional outcomes (Grace-Eversmann criteria). It also gives an added benefit of reduced blood loss and preservation of fracture biology.

Automated pipeline processing X-ray diffraction data from dynamic compression experiments on the Extreme Conditions Beamline of PETRA III.

Presented and discussed here is the implementation of a software solution that provides prompt X-ray diffraction data analysis during fast dynamic compression experiments conducted within the dynamic diamond anvil cell technique. It includes efficient data collection, streaming of data and metadata to a high-performance cluster (HPC), fast azimuthal data integration on the cluster, and tools for controlling the data processing steps and visualizing the data using the DIOPTAS software package. This data processing pipeline is invaluable for a great number of studies. The potential of the pipeline is illustrated with two examples of data collected on ammonia-water mixtures and multiphase mineral assemblies under high pressure. The pipeline is designed to be generic in nature and could be readily adapted to provide rapid feedback for many other X-ray diffraction techniques, e.g. large-volume press studies, in situ stress/strain studies, phase transformation studies, chemical reactions studied with high-resolution diffraction etc.

Comparison of dynamic compression system versus multiple cancellous screws in the treatment of femoral neck fractures in young adults.

INTRODUCTION: Femoral neck fractures have posed a significant global healthcare challenge and had notable impacts on the quality of life. Current treatment strategies for femoral neck fractures in young individuals have varied, emphasizing the need for optimal fixation methods. This study compared the clinical and radiological outcomes of the dynamic compression system (DCS) and multiple cancellous screws (MCS) methods. METHODS: This retrospective study included a total of 275 young adults with fresh femoral neck fractures treated with DCS and MCS. A matching analysis with a 1:1 ratio based on age, gender, fracture classification, and reduction quality was conducted. Demographic data were recorded, and comparisons were made according to follow-up time (FUT), hospitalization period, operation duration, femoral neck shortening, caput-collum-diaphysis (CCD) angle, Harris Hip Score (HHS), and post-operative complications. RESULTS: A total of 42 fractures were matched with a median age of 42 years (range, 22-48). In the DCS group, vertical neck shortening (median 1.92) was significantly lower than that in the MCS group (median 4.53) (P < 0.05). In the DCS group, horizontal femoral neck shortening, resultant femoral neck shortening, the amount of change in CCD angle, and HHS were 0.57 mm (0.43, 4.74 mm), 1.82 mm (0.40, 3.53 mm), 0.13° (-0.78°, 1.80°), and 91 (85-93), respectively. They were all non-significant than 1.00 mm (0.56, 6.23 mm), 2.74 mm (1.59, 6.71 mm), -0.18° (-1.11°,1.85°), and 91 (75, 93) in the MCS group, respectively (P > 0.05). There was no statistical difference in FUT, hospitalization period, operation time, and post-operative complications at the latest follow-up (P > 0.05). There were no complications such as pulmonary embolism, deep vein thrombosis, and incision infection reported. CONCLUSION: DCS and MCS demonstrated effectiveness in treating femoral neck fractures in young adults. The DCS implant provides additional stability in the vertical axis. A prospective randomized controlled study with a large sample size was needed to validate these findings.

Dynamic Response of Ti-6Al-2Zr-1Mo-1V Alloy Manufactured by Laser Powder-Bed Fusion.

Titanium parts fabricated by additive manufacturing, i.e., laser or electron beam-powder bed fusion (L- or EB-PBF), usually exhibit columnar grain structures along the build direction, resulting in both microstructural and mechanical anisotropy. Post-heat treatments are usually used to reduce or eliminate such anisotropy. In this work, Ti-6Al-2Zr-1Mo-1V (TA15) alloy samples were fabricated by L-PBF to investigate the effect of post-heat treatment and load direction on the dynamic response of the samples. Post-heat treatments included single-step annealing at 800 °C (HT) and a hot isotropic press (HIP). The as-built and heat-treated samples were dynamically compressed using a split Hopkinson pressure bar at a strain rate of 3000 s-1 along the horizontal and vertical directions paralleled to the load direction. The microstructural observation revealed that the as-built TA15 sample exhibited columnar grains with fine martensite inside. The HT sample exhibited a fine lamellar structure, whereas the HIP sample exhibited a coarse lamellar structure. The dynamic compression results showed that post-heat treatment at 800 °C led to reduced flow stress but enhanced uniform plastic strain and damage absorption work. However, the HIP samples exhibited both higher stress, uniform plastic strain, and damage absorption work owing to the microstructure coarsening. Additionally, the load direction had a subtle influence on the flow stress, indicating the negligible anisotropy of flow stress in the samples. However, there was more significant anisotropy of the uniform plastic strain and damage absorption. The samples had a higher load-bearing capacity when dynamically compressed perpendicular to the build direction.

Crashworthiness of 3D Lattice Topologies under Dynamic Loading: A Comprehensive Study.

Periodic truss-based lattice materials, a particular subset of cellular solids that generally have superior specific properties as compared to monolithic materials, offer regularity and predictability that irregular foams do not. Significant advancements in alternative technologies-such as additive manufacturing-have allowed for the fabrication of these uniquely complex materials, thus boosting their research and development within industries and scientific communities. However, there have been limitations in the comparison of results for these materials between different studies reported in the literature due to differences in analysis approaches, parent materials, and boundary and initial conditions considered. Further hindering the comparison ability was that the literature generally only focused on one or a select few topologies. With a particular focus on the crashworthiness of lattice topologies, this paper presents a comprehensive study of the impact performance of 24 topologies under dynamic impact loading. Using steel alloy parent material (manufactured using Selective Laser Melting), a numerical study of the impact performance was conducted with 16 different impact energy-speed pairs. It was possible to observe the overarching trends in crashworthiness parameters, including plateau stress, densification strain, impact efficiency, and absorbed energy for a wide range of 3D lattice topologies at three relative densities. While there was no observed distinct division between the results of bending and stretching topologies, the presence of struts aligned in the impact direction did have a significant effect on the energy absorption efficiency of the lattice; topologies with struts aligned in that direction had lower efficiencies as compared to topologies without.

Mechanics of dynamic compression plate application in fracture fixation.

BACKGROUND: Dynamic compression plating is a fundamental type of bone fracture fixation used to generate interfragmentary compression. The goal of this study was to investigate the mechanics of the surgical application of these plates, specifically how plate prebend, screw location, fracture gap, and applied torque influence the resulting compressive pressures. METHODS: Synthetic bones with transverse fractures were fixed with locking compression plates. One side of the fracture was fixed with locking screws. On the other side of the fracture, a nonlocking screw was inserted eccentrically to induce interfragmentary compression. A pressure mapping sensor within the fracture gap was used to record the resulting pressure distribution. Plate prebends of 0 mm, 1.5 mm, and 3 mm were tested. Three locations of the eccentric screw, four levels of screw torque, and two initial fracture gap conditions also were tested. FINDINGS: With increasing plate prebend, fracture compression pressures shifted significantly toward the far cortex; however, compression force decreased (P < 0.05). The 1.5 mm prebend plate resulted in the greatest contact area. Increasing screw torque generally resulted in greater fracture compression force. The introduction of a 1 mm fracture gap at the far cortex prior to dynamic compression resulted in little or no fracture compression. INTERPRETATION: The model showed that increasing plate prebend results in an increasing shift of fracture compression pressures toward the far cortex; however, this is accompanied by decreases in compressive force. Initial fracture gaps at the far cortex can result in little or no compression.

Dynamic Compression Plating Versus Antegrade Intramedullary Nailing for the Treatment of OTA/AO 12-A Fractures: A Retrospective Cohort Study.

BACKGROUND: Fractures of the humerus diaphysis are common and often result from motor vehicle accidents (MVAs). Treatment methods range from nonoperative approaches to various operative techniques, including antegrade intramedullary nailing (AIMN) and dynamic compression plate (DCP) fixation. This study aimed to compare the cost effectiveness and outcomes of plating and nailing for humerus diaphyseal fractures. METHODS:  A retrospective cohort study involving 59 cases of humerus diaphyseal OTA/AO 12-A fractures was conducted at King Saud Medical City (KSMC), a level I trauma center located in the center region in Riyadh, Saudi Arabia. Patients treated with AIMN, anterolateral plating, or posterior plating were included. Data on demographics, clinical parameters, radiographic healing, and costs were collected and analyzed. RESULTS: The average surgical duration was shorter in the AIMN group compared to the anterolateral and posterior plating groups but with no statistical significance (P > 0.05). The average length of stay (LOS) was shorter, and the change in hemoglobin levels was lower in the AIMN group when compared to other groups but without a statistically significant difference (P > 0.05). The average cost of AIMN was significantly higher than that of anterolateral and posterior plating groups (P < 0.0001). CONCLUSION:  While both nailing and plating procedures are options for treating OTA/AO 12-A fractures, AIMN carries a higher overall procedural cost. The practice of drain placement in our study population is likely the cause of the increased LOS in the plating groups. Relative additional analgesic requirements were associated with AIMN. Surgeons should consider meticulous hemostasis to avoid drain placement, which can decrease LOS, thus possibly decreasing unnecessary treatment costs of humerus shaft fractures.

A Retrospective Analysis of Dynamic Compression Plating Versus Intramedullary Nailing for the Management of Shaft of Humerus Fractures in an Urban Trauma Care Center.

Introduction There is constant debate regarding the best surgical technique for the fixation of shaft humerus fractures. Intramedullary nailing and dynamic compression plating are the most popular surgical options. Materials and methods In our study, we retrospectively analyze the results of 27 patients with shaft humerus fractures managed with intramedullary nailing (10) and dynamic compression plating (17) at our institute from September 2021 to October 2022. Preoperative clinical assessment sheets, postoperative follow-up sheets, operative notes, anesthesia sheets, and preoperative and follow-up radiographs were analyzed. Reamed antegrade nailing was done in all cases, while dynamic compression plating was done through a posterior approach. Results The operative time of the nailing group was 82.1 ± 7.61 mins, which was significantly lesser (P value <0.05) than that of the plating group, which was 119.59 ± 10.16 mins. The intraoperative blood loss of the patients who were managed with nailing was 71 ± 7.38 mL, which was significantly lesser (P value <0.05) than that of the plating group, which was 130.59 ± 11.44 mL. The patients in both groups had a statistically nonsignificant difference in terms of functional results, which were assessed using Rodriguez-Merchan criteria. Complications were similar in both groups with infection (17.65%), and postoperative radial nerve palsy (11.76%) was more common among the patients undergoing plating, and shoulder impingement(20%) was common among those undergoing nailing. Conclusion This study concluded that both surgical options are similar in the case of functional results. The selection of the surgical method should be as per the surgeon's surgical familiarity and personalized to individual patients.

Precontoured dynamic compression plate using patient-specific 3D-printed models in minimally invasive surgical technique for midshaft clavicle fractures.

INTRODUCTION: This study introduced a novel approach for the treatment of midshaft clavicle fractures, utilizing patient-specific 3D-printed models for accurate preoperative contouring of dynamic compression plates (DCPs) and an alternative minimally invasive plate osteosynthesis (MIPO) technique with precontoured DCPs through small vertical separated incisions. PATIENT AND METHODS: Mirror image 3D clavicular models were reproduced from 40 patients with acute displaced midshaft clavicle fractures who underwent MIPO using precontoured DCPs inserted through small, vertical separated incisions. Exclusion criteria included patients with open fractures, pathological fractures, ipsilateral limb injury, skeletal immature patients, and those who had previous clavicle fractures or surgery. Postoperative evaluation was conducted using clinical and radiographic review. The Constant-Murley and American Shoulder and Elbow Surgeons Shoulder Scores were used for clinical evaluations, and the Patient and Observer Scar Assessment Scale was used to assess surgical scars. RESULTS: The average time to union of all fractures was 12.88 weeks (range, 8-15) without loss of reduction. The patient-specific precontoured DCPs fitted well in all cases, with fracture consolidation and minimal three cortical sides connecting the fracture fragment. No hardware prominence and skin complications occurred, and clinical evaluation showed no existing difference compared with the contralateral sides. The average Constant-Murley and American Shoulder and Elbow Surgeons Shoulder Scores were 96.33 ± 3.66 and 93.26 ± 5.15, respectively. Two patients requested their implant removal, and scar qualities were satisfactory. CONCLUSIONS: Our study demonstrated that the use of a patient-specific precontoured DCP, in combination with 3D printing technology, provides accurate preoperative planning, effective fracture reduction, and improved postoperative outcomes in displaced midshaft clavicle fractures. The MIPO with a patient-specific precontoured DCP through separated vertical incisions along the Langer's lines appears to be a promising option, regarding appearance, avoiding associated complications, and obviating the need for reoperation. These results suggest that this technique has merit and can be a viable option for the treatment of midshaft clavicle fractures.

Outcomes From a Nurse Practitioner Led Dynamic Compression System Bracing Program for Pectus Carinatum.

BACKGROUND: Dynamic compression system (DCS) is often effective at treating pectus carinatum (PC). However, some patients will fail therapy. This study reports outcomes from a nurse-practitioner led bracing program, and evaluates what factors are predictive of successful therapy. METHODS: We performed a retrospective cohort study involving all patients treated with DCS bracing at our institution between February 2018 and February 2022. Patients with at least three visits were included. The primary outcome was achieving neutral chest. Factors considered potentially predictive included patient age, sex, initial pressure of correction (PIC), and the change in pressure of correction between the first two visits (deltaPC1). A Cox proportional hazards model was used for analysis, and Kaplan-Meier analyses estimated the median time to correction. RESULTS: 283 patients were evaluated. The median age was 14 (IQR 12-15), the majority were male (90.1 %) and white (92.6 %). The median PIC and deltaPC1was 4.13 PSI (IQR 3.17-5.3), and 1.34 PSI (IQR 0.54-2.25), respectively. 117 patients achieved correction. The median estimated time to correction was 7.5 months (95 % CI 5.9-10.1). In the final Cox model, greater deltaPC1 was associated with increased risk of correction (HR: 2.46; 95 % CI 2.03-2.98), and increased PIC was associated with decreased risk of correction up to one year of therapy (0-3 months HR 0.62, 95 % CI 0.50-0.78; 3-12 months HR 0.62; 95 % CI 0.45-0.85). CONCLUSIONS: DCS bracing administered by advanced care providers in collaboration with surgeons can effectively treat PC. The deltaPC1 and PIC are the factors most predictive of successful therapy. LEVEL OF EVIDENCE: Level III.

TRPV4 differentially controls inflammatory cytokine networks during static and dynamic compression of the intervertebral disc.

Background: The ion channel transient receptor potential vanilloid 4 (TRPV4) critically transduces mechanical forces in the IVD, and its inhibition can prevent IVD degeneration due to static overloading. However, it remains unknown whether different modes of loading signals through TRPV4 to regulate the expression of inflammatory cytokines. We hypothesized that TRPV4 signaling is essential during static and dynamic loading to mediate homeostasis and mechanotransduction. Methods: Mouse functional spine units were isolated and either cyclically compressed for 5 days (1 Hz, 1 h, 10% strain) or statically compressed (24 h, 0.2 MPa). Conditioned media were monitored at 6 h, 24 h, 2 days, and 5 days, with and without TRPV4 inhibition. Effects of TRPV4 activation was also evaluated without loading. The media was analyzed for a panel of 44 cytokines using a microbead array and then a correlative network was constructed to explore the regulatory relationships during loading and TRPV4 inhibition. After the loading regimen, the IVDs were evaluated histologically for degeneration. Results: Activation of TRPV4 led to an increase interleukin-6 (IL-6) family of cytokines (IL-6, IL-11, IL-16, and leukemia inhibitory factor [LIF]) and decreased the T-cell (CCL3, CCL4, CCL17, CCL20, CCL22, and CXCL10) and monocyte (CCL2 and CCL12) recruiting chemokines by the IVD. Dynamic and static loading each provoked unique chemokine correlation networks. The inhibition of TRPV4 during dynamic loading dysregulated the relationship between LIF and other cytokines, while the inhibition of TRPV4 during static loading disrupted the connectivity of IL-16 and VEGFA. Conclusions: We demonstrated that TRPV4 critically mediates the cytokine production following dynamic and static loading. The activation of TRPV4 upregulated a diverse set of cytokines that may suppress the chemotaxis of T-cells and monocytes, implicating the role of TRPV4 in maintaining the immune privilege of healthy IVD.

Dynamic intermittent compression cryotherapy with intravenous nefopam results in faster pain recovery than static compression cryotherapy with oral nefopam: post-anterior cruciate ligament reconstruction.

PURPOSE: To evaluate the effectiveness of dynamic intermittent compression cryotherapy (DICC) (CryoNov®) with an intravenous nefopam-based pain management protocol (DCIVNPP) in reducing post-operative pain following anterior cruciate ligament reconstruction (ACLR) compared to static compression cryotherapy (SCC) (Igloo®) and oral Nefopam. METHODS: This was a retrospective analysis of prospectively collected data including 676 patients who underwent primary ACLR in 2022. Patients were either in the DCIVNPP group or in the SCC (control group), and were matched for age, sex, and Lysholm and Tegner scores (338 per arm). The primary outcome was pain on the visual analogue scale (VAS), analyzed in relation to the minimal clinically important difference (MCID) and the Patient Acceptable Symptom State (PASS) thresholds for VAS. The secondary outcome was side effects. RESULTS: Postoperative pain in the DCIVNPP group was less severe on the VAS than in the control group (p < 0.05). The maximum difference in the VAS between groups was 0.57, which is less than the MCID threshold for VAS. The DCIVNPP group crossed the PASS threshold for VAS on Day 3, sooner than the control group. The side effect profiles were similar in both groups except for higher rates of dizziness and malaise in the DCIVNPP group, and higher rates of abdominal pain in the control group. Most of the side effects decreased over time in both groups, with no significant side effects after Day 3. CONCLUSION: DCIVNPP effectively allows for faster pain recovery than in the control group. The difference in side effects between the protocols may be due to mode of administration of nefopam. LEVEL OF EVIDENCE: III.

Dynamic Compression of the Ulnar Nerve Associated With the Anconeus Epitrochlearis Muscle: Do We Really Know Everything?

Ulnar nerve compression associated with the anconeus epitrochlearis muscle (AE) is an uncommon cause of peripheral nerve compression at the elbow. It is often seen in young women with a hypertrophied or severely edematous muscle. Its causes are unclear. Numerous observed features, such as a hypertrophic AE, a palpable mass on the medial side of the elbow, and the dynamic nature of symptoms, have sparked controversy in the literature. Its clinical presentation is often insidious, and occasionally symptoms only occur in prolonged positions (dynamic compression). EMG tests are usually negative, and a correct diagnosis relies on imaging. We present the case of a 21-year-old student and clarinet player who presented with dynamic compression of the ulnar nerve at the elbow associated with AE. Much remains to be elucidated about the incidence, pathophysiology, and contributing factors of this peripheral form of cubital compression. It may be time to revisit this condition.

A MHz X-ray diffraction set-up for dynamic compression experiments in the diamond anvil cell.

An experimental platform for dynamic diamond anvil cell (dDAC) research has been developed at the High Energy Density (HED) Instrument at the European X-ray Free Electron Laser (European XFEL). Advantage was taken of the high repetition rate of the European XFEL (up to 4.5 MHz) to collect pulse-resolved MHz X-ray diffraction data from samples as they are dynamically compressed at intermediate strain rates (≤103 s-1), where up to 352 diffraction images can be collected from a single pulse train. The set-up employs piezo-driven dDACs capable of compressing samples in ≥340 µs, compatible with the maximum length of the pulse train (550 µs). Results from rapid compression experiments on a wide range of sample systems with different X-ray scattering powers are presented. A maximum compression rate of 87 TPa s-1 was observed during the fast compression of Au, while a strain rate of ∼1100 s-1 was achieved during the rapid compression of N2 at 23 TPa s-1.

Non-hypertrophic chondrogenesis of mesenchymal stem cells through mechano-hypoxia programing.

Cartilage tissue engineering aims to generate functional replacements to treat cartilage defects from damage and osteoarthritis. Human bone marrow-derived mesenchymal stem cells (hBM-MSC) are a promising cell source for making cartilage, but current differentiation protocols require the supplementation of growth factors like TGF-ß1 or -ß3. This can lead to undesirable hypertrophic differentiation of hBM-MSC that progress to bone. We have found previously that exposing engineered human meniscus tissues to physiologically relevant conditions of the knee (mechanical loading and hypoxia; hence, mechano-hypoxia conditioning) increased the gene expression of hyaline cartilage markers, SOX9 and COL2A1, inhibited hypertrophic marker COL10A1, and promoted bulk mechanical property development. Adding further to this protocol, we hypothesize that combined mechano-hypoxia conditioning with TGF-ß3 growth factor withdrawal will promote stable, non-hypertrophic chondrogenesis of hBM-MSC embedded in an HA-hydrogel. We found that the combined treatment upregulated many cartilage matrix- and development-related markers while suppressing many hypertrophic- and bone development-related markers. Tissue level assessments with biochemical assays, immunofluorescence, and histochemical staining confirmed the gene expression data. Further, mechanical property development in the dynamic compression treatment shows promise toward generating functional engineered cartilage through more optimized and longer culture conditions. In summary, this study introduced a novel protocol to differentiate hBM-MSC into stable, cartilage-forming cells.

[Biomechanical analysis of miniplate fixation systems in restorative laminoplasty for spinal canal reconstruction].

OBJECTIVE: To investigate the biomechanical properties of H-shaped and L-shaped miniplate fixation systems (H-MFS and L-MFS, respectively) in restorative laminoplasty for spinal canal reconstruction (RL-SCR). METHODS: Laminectomy was performed in a 3D printed L4 vertebral model followed by RL-SCR using H-MFS or L-MFS, and the biomechanical properties of the reconstructed models were evaluated using static and dynamic compression tests. Biomechanical analyses of RL-SCR were also conducted in finite element models of the L3-L5 vertebrae with normal assignment (NA), laminectomy, or fixation with H-MFS or L-MFS, and the range of motion (ROM) of L3-L4 and L4-L5 was evaluated. RESULTS: In static compression test, the sustained yield load, compression stiffness, yield displacement and axial displacement- axial load were all significantly greater in H-MFS group (P < 0.05). Door closing, lamina collapse and plate breakage occurred in all the models in L-MFS group, and only some models in H-MFS group showed plate cracks and screw loosening. In dynamic compression tests, the peak load in H-MFS group reached 873 N (which was 95% of the average yield load in static compression), significantly greater than that in L-MFS group (P < 0.05). The ultimate load in L-MFS group was only 46.59% of that in H-MFS group (P>0.05). In finite element analysis, the ROM of the L3-L4 and L4- L5 segments were significantly smaller in NA, H-MFS and L-MFS groups than in laminectomy group. Compared with NA group, H-MFS group showed a greater ROM during extension, and L-MFS group showed greater ROM in flexion, extension, bending, and rotation; The overall ROM of the vertebral segments decreased in the order of laminectomy group, L-MFS group, H-MFS group, and NA group. CONCLUSION: Laminectomy causes structural destruction of the posterior column of the spine to affect its biomechanical stability. RL-SCR can effectively maintain the biomechanical stability of the spine, and H-MFS is superior to L-MFS in maintaining the integrity and biomechanical properties of the reconstructed spinal canal.

Effect of Arthrodesis Device Type and Trajectory on Subtalar Joint Compression.

The use of subtalar arthrodesis procedures has been widely implemented to relieve hindfoot issues after failure of conservative treatments; however, fusion failures persist in some patients with certain risk factors. Currently, surgeons utilize cannulated screws in these arthrodesis procedures to immobilize the subtalar joint. Recent clinical studies have demonstrated improved fusion outcomes in at-risk patients using sustained dynamic compression devices in the tibiotalocalcaneal complex. These devices utilize pseudoelastic nitinol which enables sustained dynamic compression when faced with postoperative bone resorption, joint settling, and bone relaxation. While the clinical success of these devices has been established in the tibiotalocalcaneal complex, the ability of sustained dynamic compression devices to apply joint compression in the subtalar joint has not been quantified. As such, the goals of this study were to (1) compare the ability of static compression devices and sustained dynamic compression devices to apply joint compression and (2) assess the impact of device trajectory on joint compression. A custom mechanical testing fixture was utilized to test the compression applied across the subtalar joint by one sustained dynamic compression device (in anterior and posterior trajectories) as compared to 2 cannulated screws (in both parallel and diverging trajectories). Testing revealed the sustained dynamic compression devices generated 53% greater compression as compared to the static compression devices, despite single versus dual device usage, respectively. Additionally, both types of devices applied joint compression forces in an insertion trajectory-independent manner. These data illustrate the ability of a single SDC device to maintain significantly improved joint compressive forces as compared to 2 static cannulated screws, regardless of insertion trajectory. These SDC devices may be of particular interest for at-risk patients or in revision cases.

Effects of different preservation on the mechanical properties of cortical bone under quasi-static and dynamic compression.

Introduction: Mechanical properties of biological tissue are important for numerical simulations. Preservative treatments are necessary for disinfection and long-term storage when conducting biomechanical experimentation on materials. However, few studies have been focused on the effect of preservation on the mechanical properties of bone in a wide strain rate. The purpose of this study was to evaluate the influence of formalin and dehydration on the intrinsic mechanical properties of cortical bone from quasi-static to dynamic compression. Methods: Cube specimens were prepared from pig femur and divided into three groups (fresh, formalin, and dehydration). All samples underwent static and dynamic compression at a strain rate from 10-3 s-1 to 103 s-1. The ultimate stress, ultimate strain, elastic modulus, and strain-rate sensitivity exponent were calculated. A one-way ANOVA test was performed to determine if the preservation method showed significant differences in mechanical properties under at different strain rates. The morphology of the macroscopic and microscopic structure of bones was observed. Results: The results show that ultimate stress and ultimate strain increased as the strain rate increased, while the elastic modulus decreased. Formalin fixation and dehydration did not affect elastic modulus significantly whereas significantly increased the ultimate strain and ultimate stress. The strain-rate sensitivity exponent was the highest in the fresh group, followed by the formalin group and dehydration group. Different fracture mechanisms were observed on the fractured surface, with fresh and preserved bone tending to fracture along the oblique direction, and dried bone tending to fracture along the axial direction. Discussion: In conclusion, preservation with both formalin and dehydration showed an influence on mechanical properties. The influence of the preservation method on material properties should be fully considered in developing a numerical simulation model, especially for high strain rate simulation.

A Study of Aluminum Honeycomb Structures under Dynamic Loading, with Consideration Given to the Effects of Air Leakage.

Aluminum honeycomb structures are used in the construction of protective materials due to the positive relationship between their mass and their energy-absorbing properties. Applying such materials in the construction of large machinery, such as military vehicles, requires the development of a new method of finite element modeling, one that considers conditions with high strain rates, because a material model is currently lacking in the available simulation software, including LS-DYNA. In the present study, we proposed and verified a method of numerically modeling honeycomb materials using a simplified Y element. Results with a good level of agreement between the full core model and the Y element were achieved. The obtained description of the material properties was used in the subsequent creation of a homogeneous model. In addition, we considered the influence of increases in pressure and the leakage of the air entrapped in the honeycomb cells. As a result, we were able to attain a high level of accuracy regarding the stress values across the entire range of progressive failure, from the loss of stability to full core densification, and across a wide range of strain rates.