Servohydraulic Testing System Research Articles

Glenoid component cyclical failure decreases with increasing baseplate contact: a biomechanical study

BackgroundGlenoid baseplate loosening remains a common mode of failure in reverse shoulder arthroplasty. One of the key factors to baseplate stability is theorized to be maximization of baseplate backside contact. The purpose of this biomechanical study is to investigate the role of varying degrees of backside bony glenoid support in component stability for reverse total shoulder arthroplasty. MethodsTwenty synthetic scapular models were divided into 3 test groups of 5 scapulae with glenoid baseplate contacts of 40%, 60%, and 75%, and one control group with glenoid baseplate contact of 100%. Standardized application of a commercially available glenoid baseplate and glenosphere was performed. The scapulae were mounted on a linear bearing with a humeral component and polyethylene liner which were affixed to a biaxial servohydraulic fatigue testing system. Each specimen was loaded for 10,000 cycles or to failure, about a 55° arc along the glenosphere at a rate of 1 Hz as a 750 N compression load was applied. Failure was defined as fracture of the scapula with implant fixation compromise. Before and after loading, stability of the baseplate was assessed by quantifying the total motion between the model and the baseplate with digital calipers as a ramp load between 0 and 150 N was applied. Two-sample unpaired t-tests were performed with significance set at P < .05. ResultsBaseplate contacts of 40% (1623 ± 227, P = .0001), 60% (3299 ± 1170, P = .0001), and 75% (5615 ± 1587, P = .0077) demonstrated statistically significant decrease in the average number of cycles to failure in all cohorts compared to our control (8641 ± 1070). Cycles taken for initial cracks to progress to failure showed no significant differences; 40% contact (862 ± 452, P = .4751), 60% contact (1651 ± 996, P = .4318), 75% contact (2882 ± 1347, P = .0620), and 100% control (1166 ± 657). Baseplate contacts of 40% (6150.4 ± 444.0, P = .0006), 60% (4647.1 ± 552.3, P = .0072), and 75% (2927.8 ± 918.5, P = .2573) demonstrated increasing micromotion (pre-post cyclical loading) in all cohorts compared to our control (2074.7 ± 1164.6) with statistical significance at 40% and 60%. ConclusionThese biomechanical tests demonstrate that decreasing glenoid baseplate backside contact leads to increased micromotion and fewer cycles to failure. This supports the surgical goal of achieving maximal glenoid baseplate backside contact, suggesting that decreased glenoid baseplate support could contribute to significant loosening.

The effect of orthodontic bracket base shape on shear bond strength to human enamel, an in vitro study.

The purpose of this study was to evaluate the in vitro effect of orthodontic bracket base shape on shear bond strength (SBS) to human enamel and assess the nature of debonding fractures using the Adhesive Remnant Index (ARI). Orthodontic brackets with different-shaped bases (flower, heart, rectangle) were bonded to 120 extracted human third molars. Shear bond strength was measured using a Servohydraulic Test System at 24 h and 2 months after bonding. Adhesive Remnant Index scores were evaluated under 10x magnification to assess the amount of resin left on the tooth. The control bracket (rectangular base shape) had the highest mean SBS (26.8 ± 8.2 megapascals [MPa]), and significantly differed from the flower (17.2 ± 4.4 MPa) and heart (18.9 ± 3.5 MPa) base shapes (p < 0.001). The mean SBS between debonding times at 24 h (21.5 ± 7.4 MPa) and 2 months (20.4 ± 6.7 MPa) were not statistically significant (p > 0.05). Analysis of ARI scores showed a significant difference between flower-24 h versus heart-2 months (p = 0.039), flower-24 h versus heart-24 h (p = 0.004), and control-2 months versus heart-24 h (p = 0.015). Bracket base shape influenced SBS, with the rectangular base shape having a higher mean SBS compared to flower and heart base shapes. Variations in ARI scores occurred based on bracket shape and were of a mixed adhesive-cohesive nature. All bracket shapes had bond strengths above the clinically acceptable range of 6-8 MPa, and may thus provide adequate SBS in a clinical situation.

Experimentally Dissociating the Acute Mechanisms of Endplate Fracture Lesions and Schmorl's Node Injuries Using a Porcine Cervical Spine Model.

This is an in vitro biomechanical study. This study evaluated the influence of localized trabecular bone strength deficits and loading rate as determinants of Schmorl's node and fracture lesion incidence. The failure load (ultimate compression tolerance [UCT]), loading stiffness, and failure morphology were assessed after acute compression loading and failure. The cartilaginous endplate is vulnerable to injuries such as Schmorl's nodes and fracture lesions. While both injuries are associated with acute compression traumas, the factors that distinguish their incidence are poorly understood. Forty-eight porcine spinal units (domestic hog, 5-10 mo, ~110kg) were assigned to one of eight experimental groups that differed by initial condition (control, sham, experimentally produced chemical fragility, and structural void) and loading rate (3 kN/s, 9kN/s). A servo-hydraulic materials testing system was used to perform acute compression testing until observed failure in the specimen. Post-loading dissection was performed to classify injury morphologies. Between group differences in UCT and loading stiffness were evaluated using a general linear model and injury distributions were evaluated using chi-squared statistics. Schmorl's nodes occurred exclusively in chemical fragility (63%) and structural void groups (37%) and were more prevalent with a 9kN/s (75%) loading rate compared with 3kN/s (25%). In contrast, fracture lesions occurred in all FSUs assigned to the control groups (100%) and the majority of those assigned to the sham groups (92%). No between-group differences were observed for UCT and loading stiffness. Pre-existing strength deficits of the subchondral trabecular bone can alter endplate injury morphology, particularly when coupled with high loading rates, but the localized strength deficits that were associated with Schmorl's nodes did not appreciably influence measured joint properties.

Damage assessment of concrete via acoustic emission and mesoscopic damage constitutive model

This paper experimentally investigated the acoustic emission (AE) behavior of concrete specimens. By using the MTS810 servo hydraulic testing system and the multi-channel AE system, a series of specimens graded C40, C50, and C60 were loaded under uniaxial compression. The spatial distribution of the AE events, AE events rate, and AE energy rate were recorded. Additionally, a theoretical mesoscopic damage constitutive (MDC) model, which defines the theoretical mesoscopic damage variable as the ratio of the fractured micro-elements to the total micro-elements, was introduced. The results indicated that the spatial distribution of AE events resembled the shape of failure modes. Moreover, the theoretical mesoscopic damage calculated by the MDC model matched well with the observed experimental damage, represented by the AE events. This association not only related the theoretical mesoscopic damage with experimental macroscopic damage, but also revealed that the macroscopic damage of concrete stemmed from mesoscopic fracture. Additionally, the AE energy was related both to the energy of fractured micro-elements and its derivative in the MDC model.

Wire arc additive manufactured AWS ER100S-G steel: Very high cycle fatigue characterization

This paper presents a comprehensive study on the very high cycle fatigue (VHCF) characterization of a wire arc additive manufactured (WAAM) AWS ER100S-G steel. The demand for high-performance materials with superior fatigue properties has grown exponentially. However, the VHCF behavior of large-format WAAM’d structures remains relatively unexplored. In this study, a series of VHCF tests were conducted under fully reversed cyclic loading conditions to investigate the extended fatigue life (performance) of the WAAM ER100S-G steel. The VHCF properties, relative to conventional fatigue employing a servohydraulic testing system, of the WAAM ER100S-G steel were evaluated by analyzing the stress-life (S-N) curves, fatigue crack initiation, and propagation behavior, in a statistical framework, and the fracture surfaces. The results revealed the controlling mechanisms of VHCF failure of the WAAM ER100S-G steel and the fatigue response of the material beyond the conventional fatigue limit of 107 cycles. The findings provide valuable insights into the influence of WAAM-induced defects/microstructure on the extended fatigue performance of WAAM ER100S-G steel, which can aid in optimizing fatigue and durability design guidelines for additive manufacturing applications in high-cycle and very high-cycle fatigue domains.

Vibro-acoustic modulation based measurements in CFRP laminates for damage detection in Open-Hole structures

The occurrence of matrix cracks, fibre failures and delaminations results in a critical degradation of the structural integrity of composites. A reliable early detection of these damages is mandatory for a safe operation. In this paper, the application of Vibro-Acoustic Modulation measurement in notched carbon fibre reinforced polymers (CFRP) for damage detection is demonstrated. A piezoceramic actuator introduces an ultrasonic signal into the specimen, which is modulated by a low-frequency vibration excited by a servo-hydraulic testing system. The specimens tested are open hole tensile specimens according to ASTM D5766, made from a quasi-isotropic CFRP layup. Degradation in the form of matrix cracks or delaminations localised along the drill hole significantly reduces the stiffness and can be detected as a modulation increase. Taking into account the extent of the crack size and the acoustic emission (AE), a magnitude estimate of the modulation increase is possible. In consequence, the presented method can be used for damage monitoring in CFRP.

Evaluation of Intramedullary Olecranon Screw Fixation for Simple Olecranon Fractures: A Biomechanical Study

The purpose of this study was to biomechanically evaluate the stability of the 6.5 mm intramedullary (IM) olecranon screw compared to locking compression plate fixation for Orthopedic Trauma Association/AO Foundation (OTA/AO) 2U1B1 olecranon fractures under cyclic range of motion of the elbow. Twenty paired elbows were randomized to either IM olecranon screw or locking compression plate fixation of a simulated OTA/AO 2U1B1 fracture. Pullout strength was tested by increasing force applied to the triceps and proximal fragment. Fracture gap displacement was measured using differential variable reluctance transducers as the elbow was cycled through a 135° arc of motion using a servohydraulic testing system. Analysis of variance revealed significant interaction between group and load on fracture distraction after the 500th cycle in three settings: between the plate at 5-pound load and screw at 35-pound load, the screw at 5-pound load and screw at 35-pound load, and between the plate at 15-pound load and screw at 35-pound load. The difference in the rate of failure between plate (2 of 80 samples) and screw (4 of 80 samples) was not statistically significant. For OTA/AO 2U1B1 olecranon fractures, a single 6.5 mm IM olecranon screw demonstrated similar stability when compared to the locking compression plates throughout range of motion testing. From a biomechanical perspective, 6.5 mm IM screws and locking compression plates have similar ability to maintain fracture reduction following simulated elbow range of motion exercises in OTA/AO 2U1B1 fractures, giving surgeons another option in the management of these fractures.

Biomechanical Evaluation of Transverse Patella Fracture Fixation using Headless Screws: A Comparison of Suture vs. Cable as a Tension Band.

To explore the performance of headless screws with FiberWire Suture as a tension band and headless screws with a mini-cable tension band in patella fixation. A transverse osteotomy was created in six matched pairs of fresh-frozen cadaver knee joints. One knee was randomly assigned to receive fixation with headless screws plus a cable tension band (Synthes 1.3 mm cable with crimp), while the other was fixed with headless screws plus a suture tension band (#5 FiberWire). Using a servo-hydraulic material testing system, the specimens were first tested non-destructively under 20% of the reported mean failure load with standard technique of cannulated screws with tension band wiring. The specimen was then loaded to 1000 N to test the construct's failure strength. All tests were run under displacement-control with loading threshold. A motion analysis system was used to track the interfragmentary motion to assess fixation stability. The correlation between fixation strength and score of bone density was also examined. In the non-destructive loading test, gap displacement under 150N was 0.10 mm or less for 11 of 12 specimens, and the difference between the two groups was not statistically significant. In the destructive test, 3 of 12 specimens maintained reduction (gap<2mm) at the maximum load of 1000 N. Of the failed specimens, the mean strength was 648±185 N for suture and 784±228 N for cable (p=0.24). Regression analysis shows bone density was associated with the failure load of the tendon (R2=0.43, p=0.02). There was no significant difference in fixation strength or sub-failure fragment displacement between the suture and cable tension band techniques when using headless screws, but suture on average was weaker.

Spatial-Time Inhomogeneity Due to the Portevin-Le Chatelier Effect Depending on Stiffness

This work is devoted to the study of the influence of the rigidity of the loading system on the kinetics of the initiation and propagation of the Portevin-Le Chatelier (PLC) strain bands due to the jerky flow in Al-Mg alloy. To estimate the influence of the loading system, the original loading attachment, which allows reducing the stiffness in a given range, was used. Registration of displacement and strain fields on the specimen surface was carried out with the Vic-3D non-contacting deformation measurement system based on the Digital Image Correlation (DIC) technique. The mechanical uniaxial tension tests were carried out using samples of Al-Mg alloy at the biaxial servo-hydraulic testing system Instron 8850. As a result of tensile tests, deformation diagrams were obtained for Al-Mg alloy samples tested at different values of stiffness of the loading system: 120 MN/m (nominal value), 50 MN/m, 18 MN/m, and 5 MN/m. All diagrams show discontinuous plastic deformations (the Portevin-Le Chatelier effect). It is noted that a decrease in the rigidity of the loading system leads to a change in the type of jerky flow. At constant parameters of the loading rate, temperature, and chemical composition of the material, the PLC effects of types A, B, and C are recorded in tests.

Mechanical behavior of steel fiber reinforced recycled aggregate concrete under dynamic triaxial compression

An experimental study of cylindrical steel fiber reinforced recycled aggregate concrete (SFRAC) specimens subjected to hydrostatic pressure and dynamic axial loading in a triaxial cell was performed. A confining stress range of 0–40 MPa and strain rate from 10−5 s−1 to 10−2 s−1 were employed using a servo-hydraulic testing system. In addition, two other control variables – volume fraction of steel fiber and replacement ratio of recycled coarse aggregate were also considered. A series of complete stress-strain curves were obtained, and the results were discussed in the aspects of the failure modes, peak triaxial strength, toughness, octahedral stress and failure criterion. The results indicated that an increase in the confining pressure resulted in a change in the failure modes, a significant increase in the peak strength and ductility. In particular, with an increase in confining pressure, the enhancement of strain rate on the peak strength decreased, indicating that there was a coupling effect between these two. The steel fibers had little influence on the failure modes of SFRAC, but significantly improved its ductility and toughness. The addition of recycled coarse aggregates markedly reduced the peak strength and the reduction reached nearly 20%, which was larger than other reports in uniaxial and true triaxial loading. Finally, a failure criterion for SFRAC specimens subjected to dynamic loading was used for validating the experimental results.

3D printed plates based on generative design biomechanically outperform manual digital fitting and conventional systems printed in photopolymers in bridging mandibular bone defects of critical size in dogs.

Conventional plate osteosynthesis of critical-sized bone defects in canine mandibles can fail to restore former functionality and stability due to adaption limits. Three-dimensional (3D) printed patient-specific implants are becoming increasingly popular as these can be customized to avoid critical structures, achieve perfect alignment to individual bone contours, and may provide better stability. Using a 3D surface model for the mandible, four plate designs were created and evaluated for their properties to stabilize a defined 30 mm critical-size bone defect. Design-1 was manually designed, and further shape optimized using Autodesk ® Fusion 360 (ADF360) and finite element analysis (FE) to generate Design-2. Design-4 was created with the generative design (GD) function from ADF360 using preplaced screw terminals and loading conditions as boundaries. A 12-hole reconstruction titanium locking plate (LP) (2.4/3.0 mm) was also tested, which was scanned, converted to a STL file and 3D printed (Design-3). Each design was 3D printed from a photopolymer resin (VPW) and a photopolymer resin in combination with a thermoplastic elastomer (VPWT) and loaded in cantilever bending using a customized servo-hydraulic mechanical testing system; n = 5 repetitions each. No material defects pre- or post-failure testing were found in the printed mandibles and screws. Plate fractures were most often observed in similar locations, depending on the design. Design-4 has 2.8-3.6 times ultimate strength compared to other plates, even though only 40% more volume was used. Maximum load capacities did not differ significantly from those of the other three designs. All plate types, except D3, were 35% stronger when made of VPW, compared to VPWT. VPWT D3 plates were only 6% stronger. Generative design is faster and easier to handle than optimizing manually designed plates using FE to create customized implants with maximum load-bearing capacity and minimum material requirements. Although guidelines for selecting appropriate outcomes and subsequent refinements to the optimized design are still needed, this may represent a straightforward approach to implementing additive manufacturing in individualized surgical care. The aim of this work is to analyze different design techniques, which can later be used for the development of implants made of biocompatible materials.

Nano-twinning and uncommon α´-martensite formation as a result of very high cycle fatigue of metastable austenitic stainless steel at 573 K

Microstructural changes were investigated regarding the existence of the true endurance limit of a cyclic loaded metastable austenitic stainless steel AISI 347 in the very high cycle regime at 573 K. The fatigue tests were performed in stress control with a stress load ration R = -1 using a servo-hydraulic testing system with a load frequency of 980 Hz. Local cyclic plastic deformation and slip bands formation were observed even in the specimens that achieved the endurance limit at 5 × 108 cycles. Moreover, in these specimens further microstructural effects like nano-twins and α´-martensite formation were detected by transmission electron microscopy. While nano-twin formation takes place in the bulk material, the α´-martensite nucleates at the specimen's surface. Therefore, the α´-martensitic transformation is not the main mechanism responsible for the true endurance limit observed in the investigated AISI 347 at 573 K.

Hooks Versus Pedicle Screws at the Upper Instrumented Level: An In Vitro Biomechanical Comparison.

Controlled laboratory study. The aim was to compare motions at the upper instrumented vertebra (UIV) and supra-adjacent level (UIV+1) between two fixation techniques in thoracic posterior spinal fusion constructs. We hypothesized there would be greater motion at UIV+1 after cyclic loading across all constructs and bilateral pedicle screws (BPSs) with posterior ligamentous compromise would demonstrate the greatest UIV+1 range of motion. Proximal junctional kyphosis is a well-recognized complication following long thoracolumbar posterior spinal fusion, however, its mechanism is poorly understood. Twenty-seven thoracic functional spine units were randomly divided into three UIV fixation groups (n=9): (1) BPS, (2) bilateral transverse process hooks (TPHs), and (3) BPS with compromise of the posterior elements between UIV and UIV+1 (BPS-C). Specimens were tested on a servohydraulic materials testing system in native state, following instrumentation, and after cyclic loading. functional spine units were loaded in flexion-extension (FE), lateral bending, and axial rotation. After cyclic testing, the TPH group had a mean 29.4% increase in FE range of motion at UIV+1 versus 76.6% in the BPS group ( P <0.05). The BPS-C group showed an increased FE of 49.9% and 62.19% with sectioning of the facet joints and interspinous ligament respectively prior to cyclic testing. BPSs at the UIV led to greater motion at UIV+1 compared to bilateral TPH after cyclic loading. This is likely due to the increased rigidity of BPS compared to TPH leading to a "softer" transition between the TPH construct and native anatomy at the supra-adjacent level. Facet capsule compromise led to a 49.9% increase in UIV+1 motion, underscoring the importance of preserving the posterior ligamentous complex. Clinical studies that account for fusion rates are warranted to determine if constructs with a "soft transition" result in less proximal junctional kyphosis in vivo .

Biomechanical evaluation of subscapularis peel repairs augmented with the long head of the biceps tendon for anatomic total shoulder arthroplasty.

Subscapularis failure is a troublesome complication following anatomic total shoulder arthroplasty (aTSA). Commonly discarded during aTSA, the long head of the biceps tendon (LHBT) may offer an efficient and cheap autograft for the augmentation of the subscapularis repair during aTSA. The purpose of this study was to biomechanically compare a standard subscapularis peel repair to 2 methods of subscapularis peel repair augmented with LHBT. 18 human cadaveric shoulders (61±9 years of age) were used in this study. Shoulders were randomly assigned to biomechanically compare subscapularis peel repair with (1) traditional single-row repair, (2) single row with horizontal LHBT augmentation, or (3) single row with V-shaped LHBT augmentation. Shoulders underwent biomechanical testing on a servohydraulic testing system to compare cyclic displacement, load to failure, and stiffness. There were no significant differences in the cyclic displacement between the 3 techniques in the superior, middle, or inferior portion of the subscapularis repair (P>.05). The horizontal (436.7±113.3 N; P=.011) and V-shape (563.3±101.0 N; P<.001) repair demonstrated significantly greater load to failure compared with traditional repair (344.4±82.4 N). The V-shape repair had significantly greater load to failure compared to the horizontal repair (P<.001). The horizontal (61.6±8.4 N/mm; P<.001) and the V-shape (62.8±6.1; P<.001) repairs demonstrated significantly greater stiffness compared to the traditional repair (47.6±6.2 N). There was no significant difference in the stiffness of the horizontal and V-shape repairs (P=.770). Subscapularis peel repair augmentation with LHBT autograft following aTSA confers greater time zero load to failure and stiffness when compared to a standard subscapularis peel repair.

EXPERIMENTAL STUDY OF IMPACT COMPRESSION MECHANICAL PROPERTIES OF THE CELLULAR CONCRETE WITH CORAL SAND FINE AGGREGATE

The compressive behavior of the cellular concrete with coral sand fine aggregate was experimentally investigated under quasi-static and high-strain-rate loadings. Quasi-static tests at strain rate of 10-5/s were conducted using a servo-hydraulic material test system. Impacting tests at strain rates ranging from 70/s to 140/s were performed using &amp;Phi;74 mm conic variable cross-sectional split Hopkinson pressure bar (SHPB) equipment. The strain rate effects on the compressive strength, elastic modulus, and peak toughness were studied. The results indicated that the compressive strength, elastic modulus, and peak toughness all increased with increasing strain rate and displayed clear strain-rate dependence. At high strain rates the compressive strength decreased with increasing the porosity, while the dynamic increase factor of compressive strength (DIF-f&lt;sub&gt;c&lt;/sub&gt;) due to the pure rate effect showed a reverse tendency, which may contribute to more significant path altering effect in specimens with higher porosity.

Experimental and Numerical Analysis of Chlorinated Polyethylene Honeycomb Mechanical Performance as Opposed to an Aluminum Alloy Design.

Manufacturing aircraft components through 3D printing has become a widespread concept with proven applicability for serial production of certain structural parts. The main objective of the research study is to determine whether a chlorinated polyethylene material reinforced with milled carbon fibers has the potential of replacing the current 5052 NIDA aluminum alloy core of the IAR330 helicopter tail rotor blade, under the form of a honeycomb structure with hexagonal cells. Achieving this purpose implied determining the tensile and compression mechanical properties of the material realized by fused deposition modeling. The tensile tests have been conducted on specimens manufactured on three printing directions, so that the orthotropic nature of the material may be taken into account. The bare compression tests were realized on specimens manufactured from both materials, with similar honeycomb characteristics. All the mechanical tests have been performed on the Instron 8872 servo hydraulic testing system and the results have been evaluated with the Dantec Q400 Digital Image Correlation system. The experimental tests have been reproduced as finite element analyses which have been validated by results comparison, in order to determine if the compression model is viable for more complex numerical analysis.

Experimental and theoretical studies on friction contact of bolted joint interfaces

This paper presents experimental and theoretical modeling studies on the tangential contact stiffness and friction hysteresis of bolted joint interfaces under transversal vibration. A new test rig was developed to measure the interface fretting response of bolted joints. This rig is based on a servo-hydraulic fatigue testing system in which the contact surfaces are arranged symmetrically to avoid bending of the specimen that could affect the friction measurement. Force-displacement curves were measured under different tangential loads and compared with those found in the literature. A multi-scale contact modeling method was proposed to calculate the tangential contact stiffness and reproduce the friction hysteresis of bolted joint interfaces. This method overcomes the complexity of identifying contact stiffness, which usually requires a model of the dynamic behavior of the joint and frequency responses measured with dedicated fretting test stands. Specifically, this method comprehensively considers the multi-scale features of randomly rough surfaces, the non-uniform contact pressure distribution, and the convenience of phenomenological contact models in simulating frictional hysteresis, relying on fractal contact theory and discretized Iwan model. The effectiveness of the proposed method was verified by comparing the simulation results with the experimental counterparts in different cases of tangential loading. The successful validation demonstrates the potential of the proposed modeling method for application to structures with bolted joint.

Biomechanical analysis of sacroiliac joint motion following oblique-pulling manipulation with or without pubic symphysis injury

Background: Oblique-pulling manipulation has been widely applied in treating sacroiliac joint (SIJ) dysfunction. However, little is known about the biomechanical mechanism of the manipulation. This study aims to analyze the SIJ motion under oblique-pulling manipulation, in comparison with compression and traction loads. Methods/Study Design: A total of six specimens of embalmed human pelvis cadavers were dissected to expose the SIJ and surrounding ligaments. Through a servo-hydraulic testing system, biomechanical tests were performed on the stable pelvis and the unstable pelvis with pubic symphysis injury (PSI). A three-dimensional (3D) photogrammetry system was employed to determine the separation and nutation in three tests: axial compression (test A), axial traction (test B), and oblique-pulling manipulation (test C). Results: After applying the testing loads, the range of nutation was no more than 0.3° (without PSI) and 0.5°(with PSI), separately. Except for test B, a greater nutation was found with PSI (p < 0.05). Under both conditions, nutation following test A was significantly greater than that of other tests (p < 0.05). SIJ narrowed in test A and separated in tests B and C, where the range of motion did not exceed 0.1 mm (without PSI) or 0.3 mm (with PSI) separately. Under both conditions, the separation of SIJ in test C was not as apparent as the narrowness of SIJ in test A (p < 0.05). Compared to SIJ, a more significant increasing displacement was found at the site of the iliolumbar ligament (p < 0.05). Nevertheless, when the force was withdrawn in all tests, the range of nutation and separation of SIJ nearly decreased to the origin. Conclusion: Pubic symphysis is essential to restrict SIJ motion, and the oblique-pulling manipulation could cause a weak nutation and separation of SIJ. However, the resulting SIJ motion might be neutralized by regular standing and weight-bearing load. Also, the effect on SIJ seems to disappear at the end of manipulation. Therefore, the stretching and loosening of surrounding ligaments need to be paid more attention to.

Mechanical Characteristics Evaluation of a Single Ply and Multi-Ply Carbon Fiber-Reinforced Plastic Subjected to Tensile and Bending Loads.

Carbon fiber-reinforced composites represent a broadly utilized class of materials in aeronautical applications, due to their high-performance capability. The studied CFRP is manufactured from a 3K carbon biaxial fabric 0°/90° with high tensile resistance, reinforced with high-performance thermoset molding epoxy vinyl ester resin. The macroscale experimental characterization has constituted the subject of various studies, with the scope of assessing overall structural performance. This study, on the other hand, aims at evaluating the mesoscopic mechanical behavior of a single-ply CFRP, by utilizing tensile test specimens with an average experimental study area of only 3 cm2. The single-ply tensile testing was accomplished using a small scale custom-made uniaxial testing device, powered by a stepper motor, with measurements recorded by two 5-megapixel cameras of the DIC Q400 system, mounted on a Leica M125 digital stereo microscope. The single-ply testing results illustrated the orthotropic nature of the CFRP and turned out to be in close correlation with the multi-ply CFRP tensile and bending tests, resulting in a comprehensive material characterization. The results obtained for the multi-ply tensile and flexural characteristics are adequate in terms of CFRP expectations, having a satisfactory precision. The results have been evaluated using a broad experimental approach, consisting of the Dantec Q400 standard digital image correlation system, facilitating the determination of Poisson’s ratio, correlated with the measurements obtained from the INSTRON 8801 servo hydraulic testing system’s load cell, for a segment of the tensile and flexural characteristics determination. Finite element analyses were realized to reproduce the tensile and flexural test conditions, based on the experimentally determined stress–strain evolution of the material. The FEA results match very well with the experimental results, and thus will constitute the basis for further FEA analyses of aeronautic structures.

Paper 93: Biomechanical Comparison of Tibiotalar Contact Pressures After Syndesmosis Injury With or Without Deltoid Ligament Repair

Objectives:Recent studies have stressed the important role of the deltoid ligament in maintaining global ankle stability. However, controversy remains around whether deltoid ligament repair is necessary in addition to syndesmotic repair when addressing injuries that disrupt both the syndesmosis and deltoid ligament. The purpose of this study was to measure differences in tibiotalar joint contact pressures and tibio-talar torsional stability in the presence of deltoid ligament injury, syndesmotic injury, and after their respective repairs using a cadaveric model. Our hypotheseis were 1) injury to the syndesmoosis and deltoid would increase contact pressures and decrease torsional stability, 2) repaired injuries would restore biomechanics to near native state, and 3)that there would be similar tibiotalar contact pressures and torsional stability with syndesmosis repair alone compared to syndesmosis and deltoid ligament repair.Methods:Twelve fresh-frozen human cadaveric lower extremity specimens with intact ankle joints were randomized and tested under a series of conditions: 1) intact syndesmosis and deltoid, 2) sectioning of syndesmosis or deltoid, 3) sectioning of both the syndesmosis and deltoid, 4) repair of syndesmosis or deltoid, 5) repair of both the syndesmosis and deltoid. In one group, the syndesmosis was sectioned and repaired first and in the other the deltoid was sectioned and repaired first. The syndesmosis was repaired with a single high-tensile strength suture mechanism (TightRope, Arthrex), and deltoid ligament repairs were performed with a single suture anchor (FiberTak, Arthrex). Specimens were tested under each condition with 800 N axial compression load, followed by cyclic torsional preconditioning of 5 Nm internal tibial torque (i.e., external foot rotation) at a rate of 2.5 Nm/s, and then a single rotation test of 7.5 Nm internal tibial torque at 1 Nm/s under 800 N axial compression load on a servohydraulic mechanical testing system. Contact pressures within the tibiotalar joint were measured with a digitized pressure sensor film (Tekscan, Boston MA), and coronal plane motion about the tibia was measured in angular displacement.Results:There was no significant difference in peak contact pressures between conditions except when the comparing an isolated deltoid ligament injury to a combined deltoid and syndesmosis injury (4.43±1.33MPa vs 2.67±0.45MPa, p=0.038). Total contact area was less following syndesmosis repair in isolation (609.55±312.37mm2) and combined syndesmosis and deltoid repair (598.28±181.47mm2) compared to all other conditions (p<0.001). There was also a decrease in total contact area compared to native state when the deltoid was repaired in isolation (951.51±72.79mm2 vs 888.72±105.74mm2, p=0.027). The mean external rotation angle was greater when the syndesmosis (15.67±5.39°), deltoid (13.21±3.28°), and both injuries combined (16.59±4.01°) compared to native state (8.55±2.02°), however these values did not achieve statistical significance. Additionally, There was no statistically significant difference in external rotation angle between isolated syndesmosis, isolated deltoid, or combined repairs.Conclusions:These findings demonstrate that ankle contact pressures and torsional stability do not differ significantly when a deltoid ligament repair is performed in conjunction with a syndesmosis repair for a purely ligamentous injury. However, the change in contact area following syndesmosis repair may play a role in the development of post-traumatic arthritis. This finding reinforces the importance of striving for an anatomic syndesmotic reduction, and care should be taken not to over-reduce the syndesmosis during repair.