Materials Testing System Machine Research Articles

Experimental study and modeling of rubber joints for railway vehicles using magnetorheological shear stiffening elastomers

With the rapid development of transportation industry, advanced rail vehicle technology receives more attention than ever. The stiffness of the train’s rubber joint at the primary suspension system has a crucial influence on the operation stability and curve-passing performance. When the train is running on straight track at high speed, a high primary longitudinal stiffness in bogie design is required, whereas running on the curve track calls for a soft primary longitudinal stiffness. To solve this critical problem, a new rubber joint based on magnetorheological shear stiffening elastomer (MSSE) was proposed. Its stiffness can be adjusted by not only external magnetic field but also its inherent frequency-dependent property, ensuring the functionality of the rubber joint even when the controller fails. The prototype of the MSSE joint was fabricated and assembled. Stiffness controllability of the MSSE joint was evaluated using an material testing system (MTS) machine, with MTS testing performed under varying displacement amplitude at fixed frequency to investigate the influence of the varying displacement amplitude on the effective stiffness. The results revealed that the stiffness of this MSSE joint can be controlled effectively credited to the rate-dependent SSE and adjustable electromagnetics, exhibiting exceptional fail-safe characteristics. Lastly, a dynamic model was established to describe the dynamic performance of the rubber joint. All the above studies demonstrate the feasibility of the joint to satisfy the conflicting stiffness requirements to achieve high speed stability and curve trafficability simultaneously.

Effect of Fibular Malrotation on Tibiotalar Joint Contact Mechanics in a Weber B Ankle Fracture Model.

In minimally displaced Weber B ankle fractures, the distal fibular fracture fragment can be externally rotated. This malrotation is difficult to detect on radiographs and, when left malreduced through nonoperative treatment, may contribute to altered joint mechanics, predisposing to posttraumatic osteoarthritis. This study evaluates the effects of fibular malrotation on tibiotalar joint contact mechanics. Six cadaveric ankles were tested using a materials testing system (MTS) machine. A tibiotalar joint sensor recorded contact area and pressure. Samples were tested in the intact, neutrally rotated, and malrotated state. Each trial applied a 686N axial load and a 147N Achilles tendon load in neutral position, 15° dorsiflexion, and 15° plantarflexion. In the comparison of malrotated to intact ankles, peak contact pressure was found to be significantly greater at neutral flexion (intact 5.56 MPa ± 1.39, malrotated 7.21 MPa ± 1.07, P = .03), not significantly different in dorsiflexion, and significantly decreased in plantarflexion (intact 11.2 MPa ± 3.04, malrotated 9.01 MPa ± 1.84, P = .01). Significant differences in contact area were not found between conditions. The findings suggest that fibular malrotation contributes to significant alterations in tibiotalar joint contact pressures, which may contribute to the development of posttraumatic osteoarthritis. When malrotation of the fibula is suspected on plain radiographs, a computer tomography (CT) scan should be obtained to evaluate its extent and further consideration should be given to surgical treatment. Level V: Bench testing.

Does the Effectiveness and Mechanical Strength of Kanamycin-Loaded Bone Cement in Musculoskeletal Tuberculosis Compare to Vancomycin-Loaded Bone Cement

BackgroundAntibiotic-loaded bone cement (ALBC) is used to deliver antimycobacterial agents into the focal lesion of musculoskeletal tuberculosis. Although kanamycin is currently used as an antimycobacterial agent for the treatment of multidrug-resistant tuberculosis, there is no information about its suitability in ALBC. MethodsAn in vitro experiment was conducted with cylindrical shape of 40 g of bone cement with 1, 2, and 3 g of kanamycin. Eluate (1 mL) was extracted from each specimen to measure the level of elution and antimycobacterial activity on days 1, 4, 7, 14, and 30. The quantity of kanamycin in eluates was evaluated by a liquid chromatography-mass spectrometry system, and the antimycobacterial activity of eluates against Mycobacterium tuberculosis H37Rv was calculated by comparing the minimal inhibitory concentration. The ultimate compression strength was conducted using a material testing system machine (Instron 3366; Instron, Norwood, MA) before and after elution. ResultsEluates from ALBC containing 2 and 3 g of kanamycin had effective antimycobacterial activity for 30 days, whereas eluates from ALBC containing 1 g of kanamycin were partially active until day 30. The pre-eluted compression strength of kanamycin-loaded cement and vancomycin-loaded cement was weaker as they contained a larger amount of antibiotics. There was no statistical difference between the strength of all kanamycin regimens and 1 g of vancomycin in the ultimate compression test. After 30 days of elution, the strength of all kanamycin-loaded cement and vancomycin-loaded cement cylinders was significantly lower than that of initial specimens (P < .05). ConclusionThe antimycobacterial activity of ALBC containing more than 2 g of kanamycin was effective during a 30-day period. The ultimate compression strength of bone cement loaded with 1-3 g of kanamycin was comparable with 1 g of vancomycin while maintaining effective elution until day 30.

Anisotropic influence of fracture toughness on loading rate dependency for granitic rocks

Granite is a significantly anisotropic rock that is affected by the pre-existing microcrack distribution. In rock engineering applications in a variety of fields, it is crucial to understand the influence of the internal microcrack distribution on the mechanical properties of the rock. In this paper, static and dynamic fracture toughness tests were conducted with straight notched disc bend (SNDB) specimens of Youngju granite to investigate the relationship between the microcrack-induced fracture toughness anisotropy and the loading rate dependency. Three groups of specimens were manufactured with three different orthogonal directions, which were determined by the P-wave velocity measurement. In order to conduct the static and dynamic fracture toughness tests, a servo-controlled Material Testing System (MTS) machine and a split Hopkinson pressure bar (SHPB) apparatus were respectively used. In the dynamic test, to achieve the stress equilibrium state in the measurement, a careful pulse shaping technique with a copper and rubber pulse shaper was used. The results of the entire range of tests in this study revealed that the fracture toughness of Youngju granite has a clear loading rate dependency. Further, we found that the preferred orientation of pre-existing microcracks causing strong anisotropy of fracture toughness under static loading rates became significantly weaker in the dynamic loading state. Finally, a possible reason for this relationship between the fracture toughness anisotropy and the loading rate dependency is discussed with different fracturing processes of rock under the static and the dynamic loading states using image analysis for generated cracks.

A locking compression plate versus the gold-standard non-locking plate with lag screw for first metatarsophalangeal fusion: A biomechanical comparison

IntroductionThe treatment of end-stage first metatarso-phalangeal joint (MTP) arthritis has been arthrodesis. A dorsal non-locking plate with a lag screw has been the standard traditional fixation method. This study compares the biomechanical strength of a locking compression plate (LCP) with and without internal compression versus this known gold standard. MethodsIn group 1, six matched pairs of cadaver great toes were used to compare the standard non-locking dorsal plate and 3.5mm lag screw to an anatomic locking compression plate in which a lag screw was utilized rather than the internal compression features of the plate. In group 2, another six matched pairs of cadaver great toes were used to compare the gold standard to the locking compression plate, utilizing the plate’s internal compression feature instead of a lag screw. A material testing system (MTS) machine applied loads to the MTP joints and measured displacement and stiffness of the constructs. The stiffness of the constructs (Young’s modulus) was calculated from the force-displacement curves, and the displacement was measured. ResultsThe locking compression plate group that used the compression features of the plate, without the lag screw, had less joint displacement and higher stiffness than control (p<0.05). The same plating construct in which a lag screw was used rather than internal compression of the plate was found to be stiffer than the control (p<0.05), but displacement was not statistically significant. DiscussionThe results suggest that a locking compression plate alone provides the stiffest construct for a first MTP joint fusion.

A Comparative Biomechanical Analysis of 2 Double-Row, Distal Triceps Tendon Repairs.

Background:Triceps tendon ruptures are rare orthopaedic injuries that almost always require surgical repair. This study tests the biomechanical properties of an original anchorless double-row triceps repair against a previously reported knotless double-row repair.Hypothesis:The anchorless double-row triceps repair technique will yield similar biomechanical properties when compared with the knotless double-row repair technique.Study Design:Controlled laboratory study.Methods:Eighteen cadaver arms were randomized into 2 groups. One group received the anchorless repair and the other received the knotless anchor repair. A materials testing system (MTS) machine was used to cycle the repaired arms from 0° to 90° with a 2.5-pound weight for 1500 cycles at 0.25 Hz. Real-time displacement of the tendon was measured during cycling using a probe. Load to failure was performed after completion of cyclic loading.Results:The mean displacement with the anchorless technique was 0.77 mm (SD, 0.25 mm) at 0° (full elbow extension) and 0.76 mm (SD, 0.38 mm) at 90° (elbow flexion). The mean displacement with the anchored technique was 0.83 mm (SD, 0.57 mm) at 0° and 1.01 mm (SD, 0.62 mm) at 90°. There was no statistically significant difference for tendon displacement at 0º (P = .75) or 90º (P = .31). The mean load to failure with the anchorless technique was 618.9 N (SD, 185.6 N), while it was 560.5 N (SD, 154.1 N) with the anchored technique, again with no statistically significant difference (P = .28).Conclusion:Our anchorless double-row triceps repair technique yields comparable biomechanical properties to previously described double-row triceps tendon repair techniques, with the added benefit of avoiding the cost of suture anchors.Clinical Relevance:This anchorless double-row triceps tendon repair can be considered as an acceptable alternative to a knotless anchor repair for triceps tendon ruptures.

The influence of water, snow and granular ice on ice failure processes, ice load magnitude and process pressure

This paper describes the outcomes of a series of laboratory ice crushing experiments that was performed (Sopper, 2016) to investigate the effects of external boundary condition and indenter contact geometry on ice load magnitude under crushing conditions. Four boundary conditions were considered: dry cases, submerged cases, and cases with the presence of snow and granular ice material on the indenter surface. Indenter geometries were a flat plate, wedge shaped indenter, (reverse) conical indenter, and a hemispherical indenter. These were impacted with artificially produced ice specimens of conical shape with 20° and 30° cone angles. All indenter – ice combinations were tested in dry and submerged environments at 1mm/s and 100mm/s indentation rates. Additional tests with the flat indentation plate were conducted at 10mm/s impact velocity and a subset of scenarios with snow and granular ice material was evaluated.The tests were performed using a material testing system (MTS) machine located inside a cold room at an ambient temperature of –7°C. Data acquisition comprised time, vertical force, and displacement. In several tests with the flat plate and wedge shaped indenter, supplementary information on local pressure patterns and contact area were obtained using tactile pressure sensors. All tests were recorded with a high speed video camera and still photos were taken before and after each test. Thin sections were taken of some specimens as well.Ice loads were found to strongly depend on contact condition, interrelated with pre-existing confinement and indentation rate. Submergence yielded higher forces, especially at the high indentation rate. This was very evident for the flat indentation plate and spherical indenter, and with restrictions for the wedge shaped indenter. No indication was found for the conical indenter. The presence of snow and granular ice significantly increased the forces at the low indentation rate (with the flat indentation plate) that were higher compared to submerged cases and far above the dry contact condition.Contact area measurements revealed a correlation of higher forces with a concurrent increase in actual contact area that depended on the respective boundary condition. In submergence, ice debris constitution, ice extrusion, as well as crack development and propagation were impeded. Snow and granular ice provided additional material sources for establishing larger contact areas. The dry contact condition generally had the smallest real contact area, as well as the lowest forces. The comparison of nominal and measured contact areas revealed distinct deviations which were dependent on the boundary conditions. The incorporation of those differences in contact process pressures-area relationships indicated that the overall process pressure was not substantially affected by changes in true contact area.

A biomechanical investigation of different screw head designs for vertebral derotation in scoliosis surgery

Background ContextThe posterior pedicle screw-rod system, which is widely used to correct spinal deformities, achieves a good correction rate in the frontal and coronal planes but not in the axial plane. Direct vertebral derotation (DVD) was developed to correct axial plane deformities. However, the design of screw head and body connection, in terms of monoaxial, polyaxial, and uniplanar screw, may influence the efficiency of DVD. PurposeThis study compared the efficiency of a newly designed uniplanar screw with that of monoaxial and polyaxial screws in the DVD maneuver. Study DesignA porcine spine model and monoaxial, polyaxial, and uniplanar screws were used to examine the biomechanics of the DVD maneuver. MethodsSix T7–T13 porcine thoracic spine segments were used as test specimens in this study. Pedicle screws were inserted in the left pedicles of the T9–T11 spinal segments and then connected with a rod. Three types of pedicle screws with different screw head designs (monoaxial, polyaxial, and uniplanar) were employed in this study. The material testing system (MTS) machine generated a rotational moment through the derotational tube on the T10 (apical body) pedicle screw, which simulated the motion applied during the surgical vertebral derotational procedure. The pedicle strain and the kinematics of the vertebral body and derotational tube were recorded to evaluate the derotational efficiency of different pedicle screw head designs. ResultsThe variances of the derotation for the monoaxial, polyaxial, and uniplanar screws were 2.22°±1.43°, 32.23°±2.26°, and 4.75°±1.60°, respectively; the derotation efficiency was 0.65, 0.51, and 0.12, respectively, when the torques of the spinal constructs reached 3 Nm. The rotational variance of the polyaxial screw was statistically greater than that of the monoaxial and uniplanar screws (p<.05). The maximum micro-strains of the pedicles for the monoaxial, polyaxial, and uniplanar screws were 1,067.45±550.35, 747.68±393.56, and 663.55±271.04, respectively, with no statistically significant differences (p>.05). ConclusionsThe screw head design played an important role in the efficiency and variance of the derotation during the DVD maneuver. The derotational efficiency of the newly designed uniplanar screw was closer to that of the monoaxial screw group than to that of the polyaxial screw group. The polyaxial screw was inferior to DVD owing to a derotational variance between the derotational tube and the apical body that was correlated with the range of motion of the screw head. In the present study, the pedicle strain was similar in all groups. However, the pedicle strain of the uniplanar screw group was lower than that of the monoaxial screw group and was similar to that of the polyaxial screw group when the angle of rotation of the apical body increased.

Biomechanical Comparison of Superior Versus Anterior Plate Position for Fixation of Distal Clavicular Fractures: A New Model.

Although most clavicular fractures are amenable to nonoperative management, metadiaphyseal fractures are considerably more complex, with rates of suboptimal healing as high as 75% when treated nonoperatively. The poor results are ascribed to the deforming forces on the distal clavicle from the surrounding muscles and the weight of the arm. It recently has been noted that some operative fixations of these fractures are also failing when a standard superiorly placed plate is used. We hypothesized that anterior plating, when compared with superior plating, improves the strength and durability of the construct by redirecting the axis of the major deforming force across rather than in line with the screws of the construct. Six pairs of fresh-frozen human cadaveric clavicles with the scapula attached by the coracoclavicular ligaments were osteotomized just medial to the ligaments and plated with a standard 3.5-mm limited-contact dynamic compression plate. Specimens were potted and mounted on a materials testing system machine, preserving the anatomic relationship of the clavicle and scapula. They were then loaded through the coracoclavicular ligaments to mimic the weight of the arm pulling inferiorly. Each specimen was loaded with 375 N at 1 Hz for 2000 cycles. Sequential loading was then applied at 25-N intervals until failure. Statistical analysis was performed using a Wilcoxon signed-rank test. The superiorly plated specimens failed after fewer cycles and with lower force than the anteriorly plated specimens. The median number of cycles to failure was 2082 for anterior plated specimens and 50 for superiorly plated (P = 0.028). The median load to failure was 587.5 N in the anterior group and 375 N in the superior group (P = 0.035). The median stiffness was 46.13 N/mm for anterior and 40.45 N/mm for superior (P = 0.375) plates. Anteriorly plated distal third clavicular fractures have superior strength and durability compared with fractures plated superiorly when using a physician-contoured, 3.5-mm, limited-contact, dynamic compression plate in this cadaver model.

Does Proximal-Distal Tibial Tunnel Placement for PCL Reconstruction Matter?

The purpose of this study was to investigate the biomechanical effects of proximal-distal tibial tunnel placement on posterior laxity in PCL reconstruction. Eighteen human cadaveric knees were studied, consisting of nine matched pairs. Transtibial PCL reconstruction was performed using a simulated arthroscopic technique. The native PCL was resected, and Achilles tendon autografts were used for PCL reconstruction. The specimens were divided into two groups based on tibial tunnel placement: 1) anatomic tunnel and 2) non-anatomic tunnel. The anatomic tibial tunnel was placed at the footprint of the PCL, 1 cm distal to the joint line, while the non-anatomic tibial tunnel was placed more proximal to this, at the joint line. A 150-N cyclic posterior tibial load was applied using a Materials Testing System (MTS) machine at 0⁰, 30⁰, 60⁰, and 90⁰ of knee flexion. In 10 specimens, a static 250-N posterior tibial load was applied at 90⁰ of knee flexion. Posterior tibial translation in the sagittal plane was recorded. A Mann-Whitney U test was used to compare posterior tibial translation between the two groups. Statistical significance was set defined as p <0.05. With application of a 150-N posteriorly directed cyclic force, the anatomic tunnel group demonstrated significantly less posterior tibial translation than the non-anatomic tunnel group at 0⁰, 30⁰, 60⁰, and 90⁰ of knee flexion (p <0.05). The anatomic tunnel group also demonstrated significantly less posterior tibial translation than the non-anatomic tunnel group at 90⁰ with a static 250-N posteriorly directed force applied (p <0.05). Anatomic distal tibial tunnel placement recreating the tibial origin of the PCL provided significantly greater restraint to posterior tibial translation than proximal non-anatomic tunnel placement. We recommend careful placement of an anatomic distal tibial tunnel during PCL reconstruction for avoidance of posterior laxity.

Nonanatomic Tibial Tunnel Placement for Single-Bundle Posterior Cruciate Ligament Reconstruction Leads to Greater Posterior Tibial Translation in a Biomechanical Model

To determine the effect of varying proximal-distal tibial tunnel placement on posterior cruciate ligament (PCL) laxity. Nine matched pairs (18 total) of cadaveric knees (mean age 79.3 years, range 60 to 89), were studied. The specimens from each pair were randomly divided into 2 groups based on tibial tunnel placement: (1) anatomic tunnel and (2) proximal nonanatomic tunnel. A 150-N cyclic posterior tibial load was applied using a Materials Testing System machine at 0°, 30°, 60°, and 90° of knee flexion. Each specimen completed 50 cycles at a rate of 0.2 Hz at each knee flexion angle. In 10 specimens, a static 250-N posterior tibial load was applied at 90° of knee flexion. Posterior tibial translation was recorded. Load to failure for all specimens was recorded. With application of a 150-N posteriorly directed cyclic force, the anatomic tunnel group had significantly less posterior tibial translation (millimeters, mean [standard deviation (SD)]) than the proximal nonanatomic tunnel group at 0°, 30°, 60°, and 90° of knee flexion: 1.1 (0.3) v 1.5 (0.4), P= .031; 1.1 (0.6) v 2.2 (0.9), P= .019; 0.9 (0.4) v 2.0 (0.6), P= .001; 0.9 (0.6) v 2.9 (0.7), P < .001, respectively. The anatomic tunnel group also demonstrated significantly less posterior tibial translation (millimeters, mean [SD]) than the nonanatomic tunnel group at 90° with a static 250-N posteriorly directed force applied (P <.05): 2.3 (1.3) v 6.1 (2.3), P= .016. Four pairs were excluded from the 250-N results because of prior load to failure testing. Anatomic tibial tunnel placement re-creating the tibial origin of the PCL results in significantly less posterior tibial translation than proximal nonanatomic tibial tunnel placement. Correct placement of the tibial tunnel during PCL reconstruction is essential for avoidance of posterior laxity. Anatomic tibial tunnel placement during PCL reconstruction may ensure a more stable reconstruction.

Development of Asian hip stem 4 – Experimental validation for stress distribution and micromotion

s / Osteoarthritis and Cartilage 23 (2015) A82eA416 A118 measure representing the knee function, and be used for follow-up of OA patients, to understand how OA affects the knee kinematics. 162 DEVELOPMENT OF ASIAN HIP STEM 4 e EXPERIMENTAL VALIDATION FOR STRESS DISTRIBUTION AND MICROMOTION M. Baharuddin yz, S.-H. Salleh x, M. Lee x, A. Mohd Noor x. yCyberjaya Univ. Coll. of Med. Sci., Cyberjaya, Malaysia; zUniv. of Malaya, Kuala Lumpur, Malaysia; xUniversiti Teknologi Malaysia, Skudai, Malaysia Purpose: Stress shielding and micromotion are two major issues which determine the success of newly designed cementless femoral stems. The correlation of experimental validation with finite element analysis (FEA) is essential to evaluate the stress distribution and fixation stability of the stem within the femoral canal. Methods: The experiment was performed to validate the finite element analysis of stress distribution and micromotion. A small left fourth generation composite femur was used because it mimicked an actual human femorawith Asian hipmorphology. The femur was loaded at the center of the femoral stem ball using an advanced material testing systemmachine at the rate of 1 kN/min, and constrained distally using a custom designed jig positioned at the base of the machine. The cyclic axial loading was set from 0 to 2000 N using a 5 kN load cell for 50 cycles. Micromotion was measured using two linear variable direct transducer (LVDT) proximally and distally, while strain distributionwas measured using four tri-axial rosettes medially and laterally at the metaphyseal region. Two holes of 4 mm diameter were drilled 10 mm below the osteotomy level for the proximal, and 10 mm above the femoral stem tip for the distal. The LVDT were fixed firmly at the extra cortical femora with the spring tip touching the steel pin. Elastic micromotion was computed using the difference between the peak and trough for each cycle. The rosette used in this study had three grid orientations 0 (e1), 90 (e2) and 45 (e3). The result for FEAwill focused on the equivalent von Mises stress and micromotion with similar loading condition and material properties as experimental testing. Figure 1. Experimental validation (a) Loading condition, (b) micromotion, (c) strain, (d) strain gauge orientation. Results:Micromotionwas found to be higher during the first load cycle compared to later cycles. The experimental and FEA results demonstrated abrupt changes between the first cycle and subsequent cycles. Elastic micromotion initially decreased for both locations before it stabilized during Cycles 7 and 8. Distal micromotion was initially 17.9 mm before it stabilized somewhere between 10 and 11.5 mm. On the other hand, proximal micromotion started at 4 mm before it stabilized in the range of 1.5 to 1.8 mm. The finite element analysis (FEA) discovered that themicromotion of proximal regionwas between 20 and 30 mm,while at the distal region ranged from 30 to 40 mm. These FEA results correlated well with the experimental results although the predicted micromotion value from FEA was slightly higher (z 10 20 mm). Although, the experimental testing was well correlated with FEA, the result from FEA were slightly higher due several limitations such as the friction coefficient (m 1⁄4 0.4) used in FEA for the implant bone interface, simplified boundary conditions, loading configurations, and materials properties (inhomogeneous). On the other hand, the maximum equivalent von Misses stress value was determined using FEA at locations similar to those used in experimental testing and was 15-20 MPa (A), 20-30 MPa (B), 5-10 MPa (C), and 15-20 MPa (D). The mean value for experimental testing was 14.26 ± 12.00 MPa (A), 11.68 ± 9.74 MPa (B), 6.14 ± 4.95 MPa (C), and 12.22 ± 9.81MPa (D). The femoral stem in this study distributed stress normally in both medially and laterally, which would prevent stress shielding from occurring and prolong the lifespan of the implant. Figure 2. Elastic Micromotion. Figure 3. FEA for stem micromotion. Figure 4. Strain distribution.Ă Table 1. Outcome measures for operated (OP) and non-operated (NOP) leg in ACL-patients during maximal unilateral counter movement jump testing. ACL patients (n 1⁄4 24) OP-limb NOP-limb Limb-to-limb asymmetry (%) P-value

Effect of Temperature on Mechanical Properties of Nanoclay-Reinforced Polymeric Nanocomposites. I: Experimental Results

In this paper, the effect of temperature and nanoclay reinforcement percentage on nanoclay-reinforced polymeric nanocomposites is studied. First, polypropylene (PP 3371) resin reinforced with various nanoclay percentages is tested at room, elevated, and low temperatures. The tests are conducted on ASTM Type I specimens instrumented with strain gauges in a material testing system machine equipped with an environmental chamber. Next, to ascertain the effect of various PP resins, nanoclay-reinforced Borealis and total petrochemical (TP 3868) tensile specimens are tested from low to elevated temperatures. In addition, nanoclay-reinforced epoxy specimens are tested at room temperature. The test results are plotted as stress-strain curves and the mechanical properties of the nanocomposites including the Young’s modulus, Poisson’s ratio, ultimate stress, and failure strain are determined. The tensile test results indicate that the Young’s modulus of the nanocomposite increases with increasing nanoclay reinforcement percentage. The temperature has even a more significant effect. It was observed that as the temperature decreases the material becomes brittle, has higher stiffness, and fails at lower strains. High temperatures have the opposite effect. As the temperature increases the material loses stiffness and becomes more ductile. Temperature and nanoclay reinforcement also affect the Poisson’s ratio but this effect is less significant. In general, as the temperature increases the Poisson’s ratio also increases. However, an increase in nanoclay reinforcement generally reduces the Poisson’s ratio. It is also noted that the type of resin used may have a significant effect on the mechanical properties of the nanocomposite.

The Effect on External Rotation of an Anchor Placed Anterior to the Biceps in Type 2 SLAP Repairs in a Cadaveric Throwing Model

This study examined whether there is a difference in external rotation (ER) between type 2 SLAP repairs consisting of anchors placed only posterior to the biceps insertion compared with repairs with an additional anchor placed anterior to the biceps. Seven cadaveric shoulders from donors with a mean age of 39.4 years were tested. Type 2 SLAP lesions were created, followed by a 3-anchor repair: a standard repair with 2 anchors posterior to the biceps plus an additional anchor anterior to the biceps. The specimens were placed on a material testing system machine and rotation was measured under a constant torque. The sutures were then removed sequentially from anterior to posterior during testing. The average ER of the intact shoulder was 115.7° ± 2.6°. After SLAP tear creation and cyclic loading, the ER was 118.5° ± 2.6°, which decreased to 116.5° ± 2.6° after repair. This corresponds to a reduction of 2.0° of ER (P < .0001) with the repair. After release of the anterior anchor, the ER increased to 117.9° ± 2.6°, which corresponds to an increase in shoulder motion of 1.4° of ER (P = .0011). Additional release of the middle anchor, leaving only the posterior anchor intact, resulted in 118.0° ± 2.7° of ER, which corresponds to an increase of only 0.1° of ER (P = .7667). Following type 2 SLAP repair in the cadaveric shoulder, removing the effect of the anchor anterior to the biceps resulted in a small but statistically significant increase in ER. The anterior anchor had the greatest effect on ER. The presence of 1 or 2 anchors posterior to the biceps did not have a significant effect on rotation. When performing SLAP repairs on those in whom even a small loss of ER would be detrimental, such as baseball pitchers, avoidance of the use of an anchor anterior to the biceps should be considered.

Experimental study of percutaneous vertebroplasty with a novel bone void filling container system

To investigate vertebral augmentation with a novel reticulate bone filling container system by polymethyl methacrylate (PMMA) injection in cadaveric simulated vertebral compressive fracture and explore the effect of reticulate bone filling container on cement distribution controlling within vertebral body and the restoration of biomechanical properties after augmentation. A total of 28 freshly frozen human vertebrae specimens were randomly divided into 4 groups. After the measurements of bone mineral density (BMD) and vertebral height, each vertebra received an axle load by a MTS (material testing system) machine to test the initial strength and stiffness. Subsequently a simultaneous compressive fracture model was created to measure the stiffness and height of fractured vertebrae. Then the augmentation procedure was performed. Afterward the biomechanical properties and the vertebral height were similarly measured as pre-operatively. The expansion of bone filling container and the distribution of cement within vertebral body were morphologically observed by crossing the specimens in sagittal midline and also integrated with the radiographic results. Stiffness was significantly restored comparing with that of fractured level (P < 0.05). And the bipedicular groups had better restoration results than the unipedicular groups. The strength and height of specimens significantly increased after the augmentation procedure but without difference among groups. In axial radiographic view, the distribution of cement in vertebral body was oval or long oval-shaped in double-layer bone filling container groups while it was irregular in single-layer groups. After crossing, the double-layer version expanded well in vertebral body and could enwrap most of injected cement. There was only a little leakage near the vessel layer. But the single-layer version had a poor expansion and a large amount of cement leakage. This novel reticulate bone void filling container system with different layers may restore both the biomechanical properties and the height of fractured vertebrae. But, with the benefit of reducing cement leakage, a double-layer design can enwrap most of injected PMMA and has a brighter prospect of clinical application.

Biomechanical similarities among subscapularis repairs after shoulder arthroplasty

Many authors suggest that subscapularis deficiency after shoulder arthroplasty has a negative effect on long-term outcomes. Thus, increasing emphasis has been placed on the technique for repair of the tendon. This study evaluated the biomechanical strength of 3 different repairs: osteotomy, tendon to bone, and a combined method. Twenty-four paired shoulders from deceased donors were prepared for shoulder arthroplasty. The subscapularis tendon was removed/repaired with the lesser tuberosity in the osteotomy group, was removed periosteally in the bone-to-tendon group, and was tenotomized in the combined group. The tendon-to-bone repair used bone tunnels, and the combined construct added tendon-to-tendon fixation. A materials testing system machine was used for cycling. A digital motion analysis system with spatial markers was used for analysis. There were no significant differences (P > .05) in age, bone mineral density, or construct thickness. No statistically significant differences (P > .05) in elongation amplitude (P = .67) or cyclic elongation (P = .58) were detected within the constructs or between repair techniques. Failure testing revealed no differences in maximum load, stiffness, or mode of failure. There remains no consensus about the optimal method of repairing the subscapularis tendon during shoulder arthroplasty. Furthermore, the results of the current study do not support one technique over another with regard to initial fixation properties. All constructs investigated exhibited comparably robust biomechanical performance. Durability may, therefore, be more a result of healing potential than the specific construct chosen.

Reconstruction interlocking nails for ipsilateral femoral neck and shaft fractures: Biomechanical analysis of effect of supplementary cannulated screw on intracapsular femoral neck fracture

Background To stabilize the femoral head in ipsilateral femoral neck and shaft fractures, one cannulated screw was supplemented in front of the reconstruction interlocking nail (recon nail). Methods Twenty-eight left sawbone femurs were divided into two groups. The 14 femurs in each group were osteotomized with subcapital or transcervical fractures. The shafts of all femurs were also osteotomized, and 1 cm of the distal segmental cortex was excised. Next, all the fractures were treated with static recon nails to concomitantly stabilize both femoral neck and shaft fractures. Additionally, seven subcapital fractures and seven transcervical fractures were supplemented with one cannulated screw in front of the recon nails. All specimens were tested with a Material Testing System machine to investigate the relative stability during uniaxial cyclic compression. Findings The subcapital and transcervical fractures supplemented with one cannulated screw could bear more loads than those without screw supplementation ( P < 0.01 and P < 0.01, respectively at any testing interval). Moreover, in the case of the subcapital fractures, the single supplemented cannulated screw could reduce the displacement at 500 N by 24% ( P < 0.001). On the other hand, in the case of the transcervical fractures, one supplemented cannulated screw could reduce the displacement at 500 N by 4% ( P = 0.003). Interpretation From the biomechanical viewpoint, the subcapital fractures in combined fractures are recommended to supplement with one cannulated screw in front of the recon nails to eliminate complications associated with stabilization.

Ex vivo calibration and validation of in vivo equine bone strain measures

Data are required to confirm that strain gauges recording high bone strains in Thoroughbred racehorses provide an accurate record of bone strain. To test the accuracy and reliability of very high in vivo strain recordings made during fast exercise in Thoroughbred racehorses. Strains were recorded during exercise from rosette gauges implanted onto the mid-shaft dorsal cortex of each third metacarpal bone (MC3) in 6 yearling and 6 mature Thoroughbreds in a previous experiment. Bulk elastic modulus (E(US)) was calculated from ultrasound speed and single photon absorptiometry measures. Each cleaned MC3 with the original gauge in situ and new gauges placed in a region of strain similarity (as shown by photoelastic coating) was loaded in a materials testing system (MTS) and strains recorded during loading. Elastic moduli were calculated from strain measures from new rosette gauges on the medial, dorsal, lateral and palmar surfaces (E(m); E(d); E(El); E(p), and bulk moduli calculated from the displacement of the MTS machine heads during loading (Ebt). Peak loads were increased incrementally to failure. Of 14 original gauges tested against new gauges, 11 recorded strains from 80-115% of the new gauges and 3 showed reduced function (31-40%). Ebt were similar to E(m), and E(US) were similar to E(l) and not significantly different from Ed. Maximum strains at yield were recorded by the medial gauges and ranged from -7500 to -16,000 microepsilon. Similarities between recordings from gauges used in vivo and new gauges confirmed the reliability and likely accuracy (or possible underestimate) of very high strains (exceeding -6000 microepsilon) recorded in exercising Thoroughbred racehorses. The similarity between E(bt) and E(m) confirms that the gauges measured the true distortion of the bone in the MTS. These results confirm that mammalian bone may withstand much greater compressive loads than -4000 microepsilon under some conditions at least.

A Method for the Consistent Creation and Quantitative Testing of Postoperative Pelvic Adhesions in a Porcine Model

Introduction: The assessment of methods for the prevention of postoperative pelvic adhesions is hampered by the lack of a quantifiable adhesion measurement technique. Currently available methods for adhesion model assessment rely on qualitative grading scales; a quantitative method would have many attendant benefits, including standardized reporting. Methods: A technique was developed to generate consistent and significant adhesions in a swine model that are suitable for quantitative assessment using a Material Testing System (MTS) machine platform. In this method, the uterine horns are cannulated and then attached to the pelvic sidewall using loose silk sutures. The underlying sidewall and adjacent uterine serosa are injured with electrocautery. Following a two-week survival the entire complex of uterine horn and sidewall are excised en bloc and prepared for MTS testing. Results: Extrication of the adhesion, as measured by the MTS platform, generates a quantitative assessment of adhesion strength that can be scaled and analyzed to produce several continuous variable descriptions. Discussion: This technique represents a novel quantitative method for adhesion assessment in an animal model. This quantitative technique may then be applied to accurately assess a range of adhesion prevention techniques, producing results which can be standardized for comparison.

A Biomechanical Comparison of All-Inside Meniscus Repair Techniques

The aim of this study was to assess the biomechanical characteristics of six all-inside meniscal single suture repair techniques using a porcine model. Peripheral longitudinal tears were created in freshly isolated porcine menisci. Tears were repaired using the single vertical technique with six different repair complexes including those involving sutures (#2 FiberWire, #2 Ethibone, flexible anchors (Fast-Fix, RapidLoc), and rigid anchors (Meniscal-Dart, BioStinger). Displacement, ultimate failure strength, stiffness, and site of failure were measured using a Materials Testing System machine. An initial 2 N preload was applied, followed by loading between 5 and 20 N for 300 cycles. Failure strength was determined lastly by increasing tension at a rate of 5 mm/min until failure. Failure strength was highest in the #2 FiberWire group (175.6 N). This was significantly higher than in all other groups (P < 0.05). The second highest failure load was evident in the #2 Ethibone group (113.8 N). This was significantly higher than in all other groups bar the #2 FiberWire group (P < 0.05). Stiffness was also significantly higher in the #2 FiberWire group compared with all other groups (8.5 N/mm, P < 0.05). There were no between-group differences in displacement. When grouped by repair technique, failure load was significantly higher, and displacement was significantly lower, in suture compared with both flexible and rigid anchor repaired menisci (P < 0.01 for all comparisons). Although stiffness was also higher in the suture group, there were no significant between-group differences detected. Suture techniques exhibited biomechanical superiority over biodegradable flexible and rigid anchor devices for meniscus repair.