Load Frame Research Articles

Biomechanical Comparison of Two Surgical Repair Techniques of the Distal Biceps Tendon

This study aimed to characterize the relationship between the distal biceps tendon force and the supination and flexion rotations during the initiation phase and to compare the functional efficiency of anatomic versus nonanatomic repairs. Seven matched pairs of fresh-frozen cadaver arms were dissected to expose the humerus and elbow while preserving the biceps brachii, elbow joint capsule, and distal radioulnar soft tissue complex. For each pair, the distal biceps tendon was severed with a scalpel and then repaired with bone tunnels placed at either the anterior (anatomic) or the posterior (nonanatomic) aspect of the bicipital tuberosity on the proximal radius. A supination test with 90° of elbow flexion and an unconstrained flexion test were conducted on a customized loading frame. The biceps tension was applied incrementally at 200 g per step, whereas the radius rotation was tracked with a 3-dimensional motion analysis system. The tendon force needed to produce a degree of supination or flexion was derived as the regression slope of the tendon force-radial rotation plots. A two-tailed paired t test was performed to compare the difference between the anatomic repair and the nonanatomic repair cadavers. Significantly greater tendon force was required to initiate the first 10° of supination with the elbow in flexion for the nonanatomic group compared with the anatomic group (1.04 ± 0.44 N/degree vs 0.68 ± 0.17 N/degree, P= .02). The average nonanatomic to anatomic ratio was 149% ± 38%. No difference existed between the two groups in the mean tendon force needed to produce the degree of flexion. Our results show that anatomic repair is more efficient in producing supination than nonanatomic repair, but only when the elbow is in 90° of flexion. When the elbow joint is not constrained, the nonanatomic supination efficiency improved, and the difference between the techniques was not significant. The present study added to the body of evidence in comparing anatomic versus nonanatomic repair of the distal biceps tendon and serves as a foundation for future biomechanical and clinical studies in this topic. Given no difference when the elbow joint was not constrained, one could argue that surgeon comfort and preference could guide which technique to use when addressing the distal biceps tendon tears. More studies will be needed to clearly define whether there will be a clinical difference between the two techniques.

Preload and friction in an implant–abutment–screw complex including a carbon-coated titanium alloy abutment screw: an in vitro study

PurposeAn experimental approach was designed to measure the preload force, the coefficient of friction and the component of the tightening torque that is needed to surmount the thread-friction in an implant–abutment–screw complex that includes a carbon-coated screw. With the determined preload values the coefficient of friction was calculated.Methods25 unused complexes, containing an implant, an abutment and a carbon-coated titanium alloy abutment screw, were tested. A custom load frame with two load cells and associated electronics was used. The threads were not lubricated. All abutment screws were torqued ten times to 25 Ncm. The produced preload values and a force that was proportional to the thread-friction component of the tightening torque were recorded.ResultsMean preload values decreased significantly with the number of repetitions (p < 0.0001) from initially 329.9 N ± 33.3 (range 255.7 to 383.9) to 253.7 N ± 36.8 (range 200.1 to 332.5) for the last tightening procedure. The corresponding change in the calculated coefficient of friction was 0.33 ± 0.04 (range 0.28 to 0.43) to 0.44 ± 0.07 (range 0.32 to 0.56). For the thread-friction no corresponding trend for consecutive tightening repetitions could be noticed.ConclusionsIn the investigated implant–abutment units, repeated use of a coated abutment screw appears to increase the friction of the screw head and thereby decrease the preload. These results indicate that a pre-used coated implant–abutment–screw will fail reaching optimal screw preload.Graphical abstract

Elastic–Plastic Properties of Mesoscale Electrodeposited LIGA Nickel Alloy Films: Analysis of Measurement Uncertainties

Abstract It is well documented that the microstructure and properties of electrodeposited films, such as lithographie, galvanoformung, abformung (LIGA) Ni and its alloys, are highly sensitive to processing conditions hence the literature shows large discrepancies in mechanical properties, even for similar alloys. Given this expected material variability as well as the experimental challenges with small-scale mechanical testing, measurement uncertainties are needed for property values to be applied appropriately, and yet are uncommon in micro- and mesoscale tensile testing studies. In a separate paper, we reported the elastic–plastic properties of 200 μm-thick freestanding films of LIGA-fabricated nanocrystalline Ni-10%Fe and microcrystalline Ni-10%Co, with specimen gauge widths ranging from 75 μm to 700 μm, and tensile tested at strain rates 0.001 s−1 and 1 s−1. The loads were applied by commercial miniature and benchtop load frames, and strain was measured by digital image correlation. In this paper, we examine the measurement uncertainties in the ultimate tensile strength, apparent Young's modulus, 0.2% offset yield strength, and strain hardening parameters, and compare them to the standard deviations. For several of these properties, the standard deviation cannot be interpreted as the statistical scatter because the measurement uncertainty was larger. Microplasticity affects the measurement of the Young's modulus, thus we recommended measuring the modulus after specimens have been cyclically loaded. These measurement uncertainty issues might be relevant to similar works on small-scale tensile testing and might help the reader to interpret the discrepancies in literature values of mechanical properties for LIGA and electrodeposited films.

Redundant Parallel Beam Multiaxis Force Sensor—Stress Correlation Coefficient

The stress nonuniformity on the loading neck is an important factor that leads to the local force error of an individual multiaxis force sensor (MAFS) in a distributed multiaxis force sensing system (DMAFSS). The stress correlation coefficient is used to characterize the stress nonuniformity. The stress correlation coefficient decreases with the increase of the loading offset. A full-constrained high-relative-stiffness-ratio structure is important for an MAFS to obtain a good stress correlation coefficient on its loading neck under various external loads. An individual MAFS with two loading necks is employed in the sensing system to increase the relative stiffness ratio. A thin loading neck, a long loading neck distance, and a high stiffness loading frame are important for the high-relative-stiffness-ratio structure. A local high-relative-stiffness-ratio structure is valuable for a large-scale DMAFSS. The mechanical hinge on the loading neck is useful to realize a large-scale lightweight DMAFSS. The extreme load including the load outside the reference loading zone and the concentrated torque affects the stress correlation coefficient apparently which should be specified in future standards.

An experimental investigation on strength properties and flexural behaviour of ternary blended concrete

Depletion of natural resource materials has resulted from an increase in the consumption of component materials in the manufacturing of concrete. Recycling is the most effective method for dealing with the effective management of waste for preservation of the environment. Recently researchers are being conducted to utilize industrial waste by product as an admixture in the concrete production. In this study silica flour which is a waste from silica industry and waste glass powder from glass industry used for the replacement of cement. The concrete mixes were cast with replacement level such as 20%, 30% for OPC in this study. The target compressive strength of 40 MPa for the grade of M40 Concrete and specimens were casted such as cubes and beams and tested after the completion of curing to find the characteristic compressive strength and flexural behavior of beams. The compressive strength at the age of 7,14 and 28 days of curing were determined in the Compressive Testing Machine of 2000kN capacity and the results were compared and also discussions are presented on the trend of strength gain for such Ternary Blend Concrete (TBC) mixes. The RC Beams were tested in the loading frame of 500 kN Capacity and the results obtained from the testing of beam, the load versus deflection pattern were drawn and compared for various beams cast with different TBC mixes. The ductility index of the beam was calculated from load versus deflection curve. The results obtained from the investigation compared with the test specimens cast with normal concrete tested in the laboratory. From the result it is found that the TBC shall be an alternative to the conventional cement concrete and found well suitable for structural applications.

Shear wave elastography ultrasound does not quantify mechanical properties of the ulnar collateral ligament of the elbow.

To validate shear wave elastography (SWE) stiffness measurements for the ulnar collateral ligament (UCL) of the elbow compared to mechanical measurements. Eleven fresh frozen human cadaveric upper extremities were evaluated by a musculoskeletal-specialized radiologist to provide SWE measurements used to calculate stiffness at 4 points along the anterior band of the UCL at various load states and flexion angles. Specimens were then dissected and optical markers were placed on the UCL to track displacement during applied force by a load frame, thereby providing measurements to calculate the mechanical stiffness. These two stiffness values were compared by ANOVA for all load states and flexion angles. Measurements of stiffness by SWE for the UCL were three orders of magnitude smaller than the true mechanical testing stiffness and no correlations between SWE and mechanical measurements of stiffness were found at 30, 60 or 90 degrees of elbow flexion (R2 = 0.004, p = 0.85; R2 = 0.001, p = 0.92; R2 = 0.15, p = 0.24 respectively). SWE stiffness was greatest near the insertion of the ligament and lowest in the mid-substance of the ligament (p = 0.0002). SWE stiffness did not correlate with mechanical measurements. Clinical utility of musculoskeletal SWE may be better defined when biomechanical properties or clinical outcomes can be correlated with SWE measurements. The ultimate clinical utility of SWE in musculoskeletal tissues may be qualitative, as demonstrated by differences throughout the length of the UCL in this study.

Pengembangan Model Perbaikan dan Peningkatan Kekuatan Struktur Sambungan Balok-Kolom pada Bangunan Pasca Gempa

This paper presents an experimental study on repairing damaged beam-column reinforced concrete joints using carbon fiber reinforced polymer (CFRP). The test objects were in the shape of the letter T which represented the beam-column connection. The test object came from the previous research which had been failure. The retrofitted action includes strengthening the column position, injection with concrete glue and adding CFRP. Two kinds of CFRP were use, CFRP sheets (EB) and CFRP strips (NSM). The integrity of concrete after injection were tested with Ultrasonic Pulse Velocity (UPV). The retrofitted specimens were tested in loading frame to occurred strength, stiffness and ductility for each kind of retrofitted action. Three kind of tested were held, bending in one direction, shearing in one direction, and quasi cyclic bending. The selection test adjusted to the damage history of specimen.

Shear bond strength between denture teeth and denture base using different bonding resins and tooth surface treatments

Aim of studyThe aim of the present study was to evaluate the influence of surface treatments of the ridge lap area of PMMA acrylic denture teeth on their shear bond strength with different bonding resins to denture base milled from prefabricated PMMA block, in a two-way factorial experiment. The traditional heat-curing method was included as a reference method to compare to the proposed new method that employs digital technology. Materials and methodsFifty-four cylindrical rods were prepared from two different types of PMMA based denture resin; one specially designed for the computer-aided design and computer-aided manufacturing (CAD/CAM) milling method (groups A, n = 18 and B, n = 18) and a conventional heat-curing resin (group C, n = 18). A central maxillary incisor was selected as the experimental tooth. The specimens of each group A, B, and C were divided equally into three subgroups (a, b, c; n = 6 for every subgroup) according to three surface conditionings (no treatment, sandblasting, sandblasting plus methyl-methacrylate application, respectively). A specially designed bonding resin for digital dentures was used in group A, and a common self-curing resin for repairs in group B, while in group C the specimens were prepared by the conventional heat-curing method. Shear bond strength was determined using an electro-mechanic loading frame (MTS Insight) with a cross-head speed to 1 mm/min. ResultsThere was a statistically significant interaction between the construction method (A, B, C) and tooth surface treatment (a, b, c) (p = 0.026). After eliminating one subgroup, the effect of tooth surface treatment was not significant (p = 0.42). ConclusionsSurface treatment seems not to affect the teeth-base bond. Denture teeth bonded to a CAD/CAM denture base using PMMA self-curing resin for repairs (group B) showed the highest bond strength compared to groups A and C. Clinical significanceIn terms of bond strength, the digital denture construction method can be successfully used in everyday clinical and laboratory practice and replace effectively the conventional heat curing method.

Biomechanical evaluation of the impact of collared cementless total hip arthroplasty stems on implant subsidence: a cadaveric study in German Shepherd.

With the increasing use of cementless total hip arthroplasty (THA), stem subsidence has emerged as one of the primary complications. Although electron beam melting (EBM)-manufactured stems have been demonstrated to prevent subsidence, there has been limited investigation into the comparative biomechanical impact of collarless and collared EBM cementless stems on stem subsidence in veterinary medicine. This study aimed to compare the stem implant resistance and failure mechanical properties between collarless and collared EBM-manufactured stems. Seven pairs of femurs were harvested from canine cadavers. In each pair of femurs, the left femur was implanted with a collarless, and the right femur with a same-sized collared cementless stem. Specimen constructs were mounted to the loading frame of a testing machine and load was transferred to the femoral stem parallel to the longitudinal axis of the femur until the stem subsided 5 mm. Load and stem displacement data acquired during the tests were used to generate load-displacement curves and obtain stiffness, yield, and failure data for each specimen construct. Yield and failure energies were calculated as the areas under the load-displacement curves to the respective points. The effects of implant type and load during subsidence were analyzed using paired t-tests. The yield and failure loads for the collared stems were approximately 40% greater than for the collarless stems (156.39 ± 43.63 kgf vs. 112.01 ± 59.83 kgf, P<0.05). This study supported the advantages of collared EBM stems, including subsidence prevention and better initial stability for early osteointegration.

Application of predetermined motion and time system in sewing automat to enhance the productivity and operator utilisation

Purpose Automation and the new buzzword, “Industry 4.0”, have dominated the media headlines in recent months. In this scenario, apparel manufacturers should not only install automatic machines but also standardise them based on specific industry requirements, and precise measures are required for daily target demands. Design/methodology/approach This study demonstrates the application of Predetermined Motion and Time System (PMTS) tools in various automatic and semiautomatic machines to obtain higher productivity and the highest utilisation percentage of operator and automats between the 1:1 and 1:2 man vs machine configuration models. In this study, timeSSD® was used to calculate the micro motions of humans. In addition, a video annotation and modelling software Tracker was used to calculate high-speed machine movements with loading frames of 30 FPS. Findings After the implementation of PMTS tools, it was found that for a 1:1 man vs machine configuration, the operator utilisation is 75% per shift and the operator idle time is 50% per cycle time, and the operator is sitting idle for 2 h per 8 h of shift. So, there is scope to improve the utilisation and idle time of operator. Research limitations/implications With the PMTS software, an industrial engineer professional with knowledge of the micromotion economy can only calculate micromotion. Originality/value Exploring the first time in the world to establish standard allowed minute (SAM) of a partly automated single-unit sewing machine with partial human intervention and a semiautomatic machine. Theoretical underpinnings indicate that manufacturers use the experience to determine the SAM of any operation over time, necessitating this work to calculate standard minutes automatically.

An Experimental Study on the Socketed Pile in Soft Rock

Pile foundation systems are used in India in many projects such as metro and railways, flyovers, and multi-story buildings. The pile transfers superstructure load to the substructure, i.e. to rock layers by means of skin resistance and end-bearing resistance. In this study, an attempt is made to observe the performance of socketed piles in soft rock. A series of socketed small-scale model pile load laboratory studies have been conducted using the loading frame. Load tests were performed on a model steel pile to calculate its axial load-bearing capability at various socket depths. An unconfined compression test was performed on pseudo-rock variations to find out the properties of the soft rock used. The results showed the ability of the drilled pile to enhance the strength of the pseudo rock. An attempt was also made to calculate the optimum depth for the socketed pile in soft rock.

A new combined penetrometer-dielectric-low frequency acoustic-electrical conductivity sensor for measuring the soil physical characteristics

Development of simple and economical sensors to measure the soil physical properties is of great importance in precision agriculture. Building on a previous study with a fusion of penetrometer, dielectric and high-frequency acoustic sensors, the present work was aimed to develop a combined penetrometer-dielectric-microphone-apparent electrical conductivity (ECa) sensor to present a cost-effective instrument for measuring the soil physical properties. The multi-sensor probe consists of a cone connected to a load cell, an integrated dielectric-ECa sensor and a microphone inside the cone to record the passive sound produced at the soil-cone interface. To evaluate the multi-sensor probe, soils with different textural compositions (clay content from 142 to 537 g kg-1) were remoulded at three levels of water content and three levels of bulk density. The probe was tested in vertical penetration tests using a hydraulic loading frame. The results of acoustic signal processing using principal component analysis showed satisfactory differentiation between coarse and fine-grained texture classes. The output of the dielectric sensor was related to soil volumetric water content with R2 = 0.81 with some texture dependency. With fusion of penetrometer, dielectric and microphone sensors, R2 increased to 0.9 with RMSE= 0.031 m3 m-3. The soil relative density was predicted from data fusion of penetrometer, dielectric and microphone sensors with a regression model with R2 = 0.86 and RMSE= 3.11%. The ECa sensor showed rational responses to the concentration of NaCl solution as well as decreased the RMSE of soil water content and relative density prediction when fused with the other sensors. The multi-sensor probe developed is an economical instrument for simultaneously measuring the soil physical properties. Field evaluations are needed to further evaluate the sensor in wider range of soil texture and soil characteristics as well as in on-the-go measurement to be applied in precision agriculture.

Small Chondral Defects Affect Tibiofemoral Contact Area and Stress: Should a Lower Threshold Be Used for Intervention?

Chondral defects in the knee have biomechanical differences because of defect size and location. Prior literature only compares the maximum stress experienced with large defects. It was hypothesized that pressure surrounding the chondral defect would increase with size and vary in location, such that a size cutoff exists that suggests surgical intervention. Controlled laboratory study. Isolated chondral defects from 0.09 to 1.0 cm2 were created on the medial and lateral femoral condyles of 6 human cadaveric knees. The knees were fixed to a uniaxial load frame and loaded from 0 to 600 N at full extension. Another defect was created at the point of tibiofemoral contact at 30° of flexion. Tibiofemoral contact pressures were measured. Peak contact pressure was the highest value in the area delimited within a 3-mm rim around the defect. The location of the peak contact pressure was determined. At full extension, the mean maximum pressures on the medial femoral condyle ranged from 4.30 to 6.91 MPa at 0.09 and 1.0 cm2, respectively (P < .01). The location of the peak pressure was found posteromedial in defects between 0.09 and 0.25 cm2, shifting anterolaterally at sizes 0.49 and 1.0 cm2 (P < .01). The maximum pressures on the lateral femoral condyle ranged from 3.63 to 5.81 MPa at 0.09 and 1.0 cm2, respectively (P = .02). The location of the peak contact pressure point was anterolateral in defects between 0.09 and 0.25 cm2, shifting posterolaterally at 0.49 and 1.0 cm2 (P < .01). No differences in contact pressure between full extension and 30° of flexion were found for either the lateral or medial condyles. Full-thickness chondral defects bilaterally had a significant increase in contact pressure between defect sizes of 0.49 and 1.0 cm2. The location of the maximum contact pressures surrounding the lesion also varied with larger defects. Contact area redistribution and cartilage stress change may affect adjacent cartilage integrity. Size cutoffs may exist earlier in the natural history of chondral defects than previously realized, suggesting a lower threshold for intervention.

Relationship between vitamin D deficiency and thrombus load in patients with ST-elevation myocardial infarction.

Clinical studies detecting the increase in thrombotic events with vitamin D deficiency note the relationship between vitamin D and thrombosis. This study aims at evaluating the relationship between serum vitamin D levels and coronary thrombus burden. We retrospectively evaluated 77 patients with ST-elevated myocardial infarction (STEMI). Serum vitamin D levels, degree of coronary thrombus, Thrombolysis in Myocardial Infarction (TIMI) frame count and the extent and severity of atherosclerosis in coronary arteries were also measured in all cases. Patients were divided into 2 groups, according to thrombus load. The rate of vitamin D deficiency in the study population was 79.22% (< 20 ng/mL). Vitamin D levels were significantly higher in patients with a mild thrombus load than in patients with a severe thrombus load (16 vs. 13.95 p = 0.018). Gensini scores were significantly higher in patients with a severe thrombus burden than in patients with a mild thrombus burden (42 vs. 54.5 p = 0.014). There was a low negative correlation between vitamin D levels and thrombus burden classification grades (r = -0.304, p = 0.007), Cx TIMI frame counts (r = -0.402, p < 0.001), and RCA TIMI frame counts (r = -0.479, p < 0.001). There was a moderate negative correlation between serum vitamin D levels and LAD TIMI frame count (r = -0.507, p < 0.001). The results of our study showed that low 25(OH)D3 levels are an independent predictor of high coronary artery thrombus load and post-procedural TIMI frame count increase in patients with STEMI undergoing primary percutaneous coronary intervention.

Numerical Analysis of RCC Beam Using ABAQUS

Experimental investigation of RCC beam provide an important understanding on its flexural properties. The stages involved from the design to casting, curing, testing and interpretation of results is time consuming and involves economy and labour. To reduce the above said challenges, numerical investigation seems to be an alternate without involvement of money and labour. Preliminary design stages involves design equation which are provided by the basic experiments conducted and they also give the basic information to develop the finite element model. This paper presents the numerical investigation of RCC beam to study the flexural properties using an effective finite element analysis tool ABAQUS. RCC beam prototypes were casted and their flexural properties were experimentally investigated. The results were validated through the finite element model by providing suitable properties for the material that are actually used for the prototype with the desired loading and support conditions. Beam of size 3000 x 230 x 300 mm of M20 grade concrete was casted and tested in the loading frame for flexure and deflection. The study focussed for under reinforced, balanced and over reinforced sections. Numerical analysis was performed using ABAQUS for model geometry and the results were compared with the experimental results. The results agreed with both the experimental and numerical values. Numerical results helps in developing reliable models which can reduce the number of required test specimens for conducting experiments and the model can be used for various study. Also from the finite element results the propagation of cracks can be well understood for the actual specimen.

Dynamic Split Tensile Strength of Basalt, Granite, Marble and Sandstone: Strain Rate Dependency and Fragmentation

The aim of this study is to understand the strength behaviour and fragment size of rocks during indirect, quasi-static and dynamic tensile tests. Four rocks with different lithological characteristics, namely: basalt, granite, sandstone, and marble were selected for this study. Brazilian disc experiments were performed over a range of strain rates from ~ 10–5 /s to 2.7 × 101 /s using a hydraulic loading frame and a split Hopkinson bar. Over the range of strain rates, our measurements of dynamic strength increase are in good agreement with the universal theoretical scaling relationship of (Kimberley et al., Acta Mater 61:3509–3521, 2013). Dynamic fragmentation during split tension mode failure has received little attention, and in the present study, we determine the fragment size distribution based on the experimentally fragmented specimens. The fragments fall into two distinct groups based on the nature of failure: coarser primary fragments, and finer secondary fragments. The degree of fragmentation is assessed in terms of characteristic strain rate and is compared with existing theoretical tensile fragmentation models. The average size of the secondary fragments has a strong strain rate dependency over the entire testing range, while the primary fragment size is less sensitive at lower strain rates. Marble and sandstone are found to generate more pulverised secondary debris when compared to basalt and granite. Furthermore, the mean fragment sizes of primary and secondary fragments are well described by a power-law function of strain rate.

Muscle Engagement Monitoring Using Self-Adhesive Elastic Nanocomposite Fabrics.

Insight into, and measurements of, muscle contraction during movement may help improve the assessment of muscle function, quantification of athletic performance, and understanding of muscle behavior, prior to and during rehabilitation following neuromusculoskeletal injury. A self-adhesive, elastic fabric, nanocomposite, skin-strain sensor was developed and validated for human movement monitoring. We hypothesized that skin-strain measurements from these wearables would reveal different degrees of muscle engagement during functional movements. To test this hypothesis, the strain sensing properties of the elastic fabric sensors, especially their linearity, stability, repeatability, and sensitivity, were first verified using load frame tests. Human subject tests conducted in parallel with optical motion capture confirmed that they can reliably measure tensile and compressive skin-strains across the calf and tibialis anterior. Then, a pilot study was conducted to assess the correlation of skin-strain measurements with surface electromyography (sEMG) signals. Subjects did biceps curls with different weights, and the responses of the elastic fabric sensors worn over the biceps brachii and flexor carpi radialis (i.e., forearm) were well-correlated with sEMG muscle engagement measures. These nanocomposite fabric sensors were validated for monitoring muscle engagement during functional activities and did not suffer from the motion artifacts typically observed when using sEMGs in free-living community settings.

Biomechanical comparison of tuberosity-based proximal humeral locking plate compared to standard proximal humeral locking plate in varus cantilever bending

PurposeIn a prior biomechanical study using a tuberosity-based proximal humeral locking plate (TBP) an improvement in greater tuberosity (GT) fixation strength with the TBP compared to a standard proximal humeral locking plate (PHLP) was demonstrated. The purpose of this study is to compare the TBP to the PHLP with a simulated calcar gap fracture under cyclic varus cantilever forces. MethodsSeven matched pairs of cadaveric humeri were studied and 11A2.3 proximal humerus fractures were created by a 1 cm gap osteotomy at the surgical neck. Matched pairs were randomized for fixation using either a PHLP or a TBP. The proximal articular aspect of the humerus was potted and secured to the base of a load frame. The shaft was subjected to cyclic varus cantilever loading with a roller positioned 8 cm from the osteotomy. Change in vertical displacement of the diaphyseal fragment was monitored and digital images were obtained. Failure was defined as vertical displacement greater than 20 mm. Specimens not exhibiting failure over the course of 10,000 cycles were then loaded to 20 mm of vertical displacement. Reactant forces of the specimens at these displacements were recorded. ResultsFour/seven TBP specimens and four/seven PHLP specimens survived 10,000 cycles. The average cycles to failure for TBP specimens was 7325 cycles and 5715 cycles for PHLP specimens (p = 0.525). For the specimens that survived 10,000 cycles, the decrease in calcar gap was superior in the TBP specimens (p = 0.018). A similar trend was seen when these specimens were loaded to failure where the percent calcar gap recovery was higher for the TBP at 74.71 ± 10.07% versus 53.22 ± 30.35% for the PHLP (p = 0.072). In specimens that were loaded to failure after survival of 10,000 cycles the average stiffness of the TBP construct was 20.51 N/mm, and 11.74 N/mm for the PHLP construct (p = 0.024). ConclusionIn addition to superior GT fixation shown in a prior study, the TBP construct demonstrates significantly greater stiffness at the neck fracture compared to the PHLP, when loaded to failure. In addition, there was a trend towards less collapse in this calcar gap model.

30. Influence of toggling on pullout force and screw diameter increase in spine fixation

<h3>BACKGROUND CONTEXT</h3> Pedicle screw fixation provides spinal stabilization and maintains normal vertebral motions in degenerative spondylolisthesis and scoliosis. Pedicle screw fixation requires several parameters to be optimized at the screw-bone interface to minimize clinical and biomechanical failure, including screw trajectory, bone density and screw sizing. Although prior studies have demonstrated screw loosening as an effect of toggling, they ultimately focus on the magnitude of the pullout force after cyclic loading rather than screw-bone interface throughout cycling. <h3>PURPOSE</h3> A stiffness decay model may help to better predict stability and investigate the effects of pedicle screw diameter to pedicle width ratio on overall screw stability following cyclic loading in the thoracolumbar spine. <h3>OUTCOME MEASURES</h3> Pullout force, toggling forces, decay functions. <h3>METHODS</h3> Thoracolumbar vertebrae (T1-L5) were harvested from two cadaveric spines. Pedicle screws were placed using a standard surgical technique. Five-hundred cycles toggle testing was conducted with a uniaxial load frame followed by axial pullout tests. Exponential decay models with a stiffness coefficient were computed to examine toggling force over the number of toggle cycles for each screw. Linear regression modeling and Pearson's correlation tests were used to compare the decay coefficient with the ratio of the screw diameter to the pedicle diameter, the pullout strength, and pedicle loosening. Subgroup analysis was performed between under-sized (70% pedicle diameter) screws. <h3>RESULTS</h3> Sixty-eight pedicles were harvested. Of the 44 viable pedicles, 33 (75%) were from the thoracic spine and 11 (25%) were from the lumbar spine. There were 23 pedicle screws in the undersized group and 21 pedicle screws in the normal-sized group. The average screw diameter was 53% (SD 5%) of the pedicle diameter in the undersized group and 77% (SD 8%) of the pedicle diameter in the normal-sized group (p < 0.001). A significant association was found between the screw to pedicle diameter ratio and the natural log of the stiffness decay coefficient (p = 0.035). The average pullout force was 170 N (SD 75) in the under-sized pedicle group and 194 N (SD 109) in the normal-sized group (p=0.40). Higher pullout force was associated with a lower stiffness decay coefficient (p = 0.005). Both pullout force and the natural log of the stiffness decay coefficients were associated with the drop in maximum toggling force after 500 cycles (p = 0.026 and p < 0.001, respectively). Utilizing the stiffness decay coefficient provided a better fit model for the predicted drop in maximum toggling force with a lower Akaike information criterion. <h3>CONCLUSIONS</h3> Pedicle screws with a high stiffness decay coefficient during toggle testing had lower pullout strengths. While higher pedicle screw to bone diameter ratios were associated with increased stiffness decay coefficient, there was no relationship between pedicle screw size and pullout strength. In subgroup analysis, however, increasing pedicle screw to bone diameter ratios were associated with lower pullout strength in the normal-sized group. Clinically, selecting a screw size that maximizes the pedicle diameter-screw ratio may not always lead to better fixation in all spine levels or regions. <h3>FDA DEVICE/DRUG STATUS</h3> This abstract does not discuss or include any applicable devices or drugs.

Development of a controlled-atmosphere, rapid-cooling cryogenic chamber for tribological and mechanical testing.

Mechanical testing of seals, bearing materials, and mechanisms in cryogenic environments is a rapidly growing field of research, as it promises improvements in equipment performance and reliability for applications such as space exploration, liquid hydrocarbon storage, and superconducting devices. Cooling of test equipment is usually performed within a well-insulated test chamber, via direct or indirect evaporation of liquid cryogen. State-of-the-art equipment is frequently insufficient for rigorous testing, being expensive and cumbersome, cooling slowly, struggling to replicate relevant environmental conditions, and/or failing to reach the temperature of the cryogen. Herein, we employ a rapid prototyping approach using polymer 3D printing to iteratively refine cryogen-based cooling of a tribometer. The final design greatly exceeds the minimum temperature of state-of-the-art equipment, cooling a chamber to liquid nitrogen temperatures (-196 °C) while maintaining dry test conditions. When modified for use on a cryogenic tensile tester, the design cools to -150 °C in 149s, significantly improving upon state-of-the-art performance. By utilizing this 3D-printed equipment, we find that components produced via Fused Deposition Modeling with unmodified, commodity polylactic acid have favorable mechanical properties in a cryogenic environment: tensile strength of 110 MPa, elongation at break of 10%, and specific wear of 5.6 × 10-5mm3/Nm against stainless steel. By leveraging 3D printing for rapid manufacture of production-quality parts, highly refined cooling chamber designs have been experimentally developed for both a tribometer and a load frame in rapid succession, enabling significant improvements in cryogenic test capabilities.