Increase In Contact Pressure Research Articles

INFLUENCE OF ELECTRON IRRADIATION ON STRUCTURAL PHASE TRANSFORMATIONS DURING MICROINDENTATION OF n-Si

   Influence of electron irradiation on structural changes in the process of microindentation by the Vickers method in (111) oriented n-Si has been studied.  It is shown, that electron irradiation with 1.1013 cm-2 fluence causes weak increase of elastic modulus and average contact pressure  causing plastic deformation. In the area of unloading of the functional dependences of the indenter load-displacement, a plateau and a gradual change in the slope are simultaneously revealed.  The mentioned changes are characteristic of partial amorphization and structural transformations in the metastable phases of silicon. Electron irradiation reveales a tendency to increase the critical pressures of phase transformations in the range of 4-5.5 GPa of average contact pressure.

Pressure-Assisted Lubrication of DC01 Steel Sheets to Reduce Friction in Sheet-Metal-Forming Processes

Friction in sheet-metal-forming processes not only affects the values of the force parameters of the process but also determines the quality of the surface of the drawpieces. This paper presents an approach to reducing the coefficient of friction by directly applying pressurized oil to the contact zone. For this purpose, a special test stand was built to carry out the strip draw test, commonly used to model the phenomenon of friction in the deep-drawing process. This test consisted of pulling a strip between flat countersamples made of 145Cr6 cold-work tool steel covered with an abrasion-resistant Mtec (AlTiN) coating. During the pilot tests, various contact pressures, lubricants with different viscosities, and different lubricant pressures were used. The influence of friction conditions on the surface roughness of the samples and the relationship between the friction conditions and the value of the coefficient of friction were determined. The supply of the lubricant under pressure into the contact zone has a beneficial effect on reducing friction. The coefficient of friction decreases with increasing lubricant pressure for contact pressures of 2–6 MPa. For a contact pressure of 8 MPa, the lubricant pressure is the least favorable for reducing the coefficient of friction. At higher lubricant pressures (12 and 18 bar), the lubrication efficiency depends on the viscosity of the lubricant and decreases with increasing contact pressure.

Biomechanical impact of elbow motion in elbow stiffness.

A mechanical block in the elbow due to osteophytes in the olecranon fossa is a common clinical symptom for elbow stiffness. This study aims to understand the biomechanical characteristics or changes in the stiff elbow in the resting (or neutral) and swing position of the arm using a cadaveric model. The hypotheses included the following: (1) a difference exists in the articular contact pressure of the elbow by comparing the non-stiff and stiff models in in vivo studies; (2) the degree of stiffness would affect the increase of the joint loading of the elbow. Controlled laboratory study, cadaveric study. Eight fresh-frozen specimens from individuals of both sexes were included in the biomechanical study. The specimen was mounted on a custom-designed jig system with gravity-assisted muscle contracture to mimic the elbow in a standing position. The elbow was tested in two conditions (the resting and passive swing). Contact pressure was recorded for three seconds in the resting position, which was the neutral position of the humerus. By dropping the forearm from 90° of the elbow flexion, the passive swing was performed. The specimens were tested sequentially in three stages of stiffness (stage 0, no stiffness; stage 1, 30° of extension limitation; and stage 2, 60° of extension limitation). After data collection was completed in stage 0, a stiff model was sequentially created for each stage. The stiff model of the elbow was created by blocking the olecranon by inserting a 2.0K-wire into the olecranon fossa horizontally with the intercondylar axis. The mean contact pressures were 279 ± 23, 302 ± 6, and 349 ± 23kPa in stages 0, 1, and 2, respectively. The increases in the mean contact pressure in stages 2 versus 0 were significant (P < 0.0001). The mean contact pressures were 297 ± 19, 310 ± 14, and 326 ± 13kPa in stages 0, 1, and 2, respectively. The peak contact pressures were 420 ± 54, 448 ± 84, and 500 ± 67kPa in stages 0, 1, and 2, respectively. The increases in mean contact pressure in stage 2 versus 0 were significant (P = 0.039). The increases in peak contact pressure in stages 0 versus 2 were significant (P = 0.007). The elbow bears the load created by gravity and muscle contracture in the resting and swing motion. Moreover, extension limitation of stiff elbow increases the load bearing in the resting position and swing motion. Careful surgical management should be considered for meticulous clearance of bony spur around olecranon fossa to resolve the extension limitation of the elbow.

Contact Electrification Characteristics of Polytetrafluoroethylene and Metal

In industrial production, the contact electrification phenomenon between materials will cause equipment damage and bring potential safety hazards to personnel, so it is necessary to study the contact electrification mechanism of materials. In order to explore the contact electrification characteristic mechanism between polytetrafluoroethylene and brass, aluminum alloy, a contact separation electrification test platform was built to pay attention to the change rule of surface potential of composite materials under contact pressure, environmental relative humidity, temperature and material temperature difference. The test results show that the surface potential first increases and then decreases slightly with the increase of contact pressure, and the surface potential is stable when the contact pressure is greater than 7 KN; The contact electrification of materials decreases with the increase of relative humidity; At 15°C ~35°C, the material surface potential is proportional to the temperature; With the temperature difference between the two test materials becoming larger, the contact potential shows a law of first increasing and then decreasing. Through the analysis of the contact electrification characteristics of materials under different conditions, it can provide a direction for further research on the contact electrification mechanism and industrial electrostatic protection.

Posterior Root Tears of the Lateral Meniscus Only Affect Tibiofemoral Contact Forces when the Meniscofemoral Ligament Is Involved: A Cadaveric Study

The objective of this study was to examine the impact of progressive radial tears in the lateral meniscal root on the lateral compartment contact forces and joint surface area through a range of motion of knee and evaluate the role of the meniscofemoral ligament (MFL) in preventing adverse tibiofemoral joint forces. Ten fresh frozen cadaveric knees were tested using 6 experimental conditions (0% lateral meniscal posterior root tear, 25% tear, 50% tear, 75% tear, 100% tear, 100% tear and resection of MFL) at five flexion angles (0°, 30°, 45°, 60°, and 90°) under 100-1,000-N axial load. Contact joint pressure and lateral compartment surface area were measured using Tekscan sensors. Statistical analysis, including descriptive, ANOVA, and post hoc Tukey analysis, was performed. Progressive radial tears of the lateral meniscal root were not associated with an increase in tibiofemoral contact pressure or decrease in lateral compartment surface area. Complete lateral root tear and resection of MFL were associated with increased joint contact pressure (P < .001) at knee flexion angles of 30, 45, 60, and 90° and decreased lateral compartment surface (P < .001) at all knee flexion angles area compared to complete lateral meniscectomy alone. Isolated complete tears of lateral meniscus root and progressive radial tears of the lateral meniscus posterior root were not associated with any change to tibiofemoral contact forces. However, additional resection of the MFL increased contact pressure and decreased lateral compartment surface area.

Friction Behaviour of 6082-T6 Aluminium Alloy Sheets in a Strip Draw Tribological Test.

Aluminium alloy sheets cause many problems in sheet metal forming processes owing to their tendency to gall the surface of the tool. The paper presents a method for the determination of the kinematic friction coefficient of friction pairs. The determination of coefficient of friction (COF) in sheet metal forming requires specialised devices that 'simulate' friction conditions in specific areas of the formed sheet. In this article, the friction behaviour of aluminium alloy sheets was determined using the strip drawing test. The 1-mm-thick 6082 aluminium alloy sheets in T6 temper were used as test material. Different values for nominal pressures (4.38, 6.53, 8.13, 9.47, 10.63, and 11.69 MPa) and different sliding speeds (10 and 20 mm/min.) were considered. The change of friction conditions was also realised with several typical oils (hydraulic oil LHL 32, machine oil LAN 46 and engine oil SAE 5W-40 C3) commonly used in sheet metal forming operations. Friction tests were conducted at room temperature (24 °C). The main tribological mechanisms accompanying friction (adhesion, flattening, ploughing) were identified using a scanning electron microscope (SEM). The influence of the parameters of the friction process on the value of the COF was determined using artificial neural networks. The lowest value of the COF was recorded when lubricating the sheet metal surface with SAE 5W40 C3 engine oil, which is characterised as the most viscous of all tested lubricants. In dry friction conditions, a decreasing trend of the COF with increasing contact pressure was observed. In the whole range of applied contact pressures (4.38-11.69 MPa), the value of the COF during lubrication with SAE 5W40 C3 engine oil was between 0.14 and 0.17 for a sliding speed of 10 mm/min and between 0.13 and 0.16 for a sliding speed of 20 mm/min. The value of the COF during dry friction was between 0.23 and 0.28 for a sliding speed of 10 mm/min and between 0.22 and 0.26 for a sliding speed of 20 mm/min. SEM micrographs revealed that the main friction mechanism of 6082-T6 aluminium alloys sheet in contact with cold-work tool steel flattens surface asperities. The sensitivity analysis of the input parameters on the value of COF revealed that oil viscosity has the greatest impact on the value of the COF, followed by contact pressure and sliding speed.

Impact of Radiocapitellar Interposition Arthroplasty on Ulnohumeral Joint Biomechanics.

Radial head excision has been shown to increase contact pressures within the ulnohumeral joint. Radiocapitellar interposition arthroplasty with the use of a soft tissue graft is an alternative for the treatment of isolated radiocapitellar arthritis or with failure of radial head replacement. We investigated contact pressures and contact area within the ulnohumeral joint after radial head excision (RHE) compared to radiocapitellar interposition arthroplasty with dermal autograft (RCIA). Six fresh-frozen cadaver elbows were tested on a custom dynamic elbow frame. A pressure sensor was inserted into the intact elbow joint, and mean contact pressure, peak contact pressure, contact area, and force within the ulnohumeral joint were recorded at 0°, 30°, 60°, 90°, and 120° of flexion as a valgus load was applied to the elbow. The radial head was then excised and specimens were retested. Finally, a dermal graft matched to the size of the resected radial head was inserted in the radiocapitellar space and the specimens were tested a third time. At 90° of flexion, contact pressure within the ulnohumeral joint was significantly lower with RCIA compared with RHE (110.8 kPa vs. 216.8 kPa.; P = 0.013). Mean peak contact pressure was also significantly lower with RCIA compared with RHE at 90° (279.4 vs. 626.7 kPa; P =0.025). No statistically significant differences were seen in mean contact area or force between the three testing conditions at any flexion position. RCIA with a dermal graft reduced contact pressures within the ulnohumeral joint compared to radial head excision at 90° of flexion without a significant change in contact area or contact force.

Analysis of Contact Characteristics of Rough Surface/Microporous For Flat Friction Pair

The rough surface has serious friction, wear and thermal damage during the sliding friction process in engineering applications, which leads to the failure of the friction pair. The rough surface contact is simplified into a rough surface with fractal properties and an ideal plane. The interaction between the asperities of the contacting body and the coupling effect of frictional heat flow at the frictional interface is considered. The impact of contact pressure and temperature rise between microporous model and non porous model on rough surface was compared, as well as the impact of Sa on the area, contact pressure and temperature rise of the friction pair. The results show that in the process of uniform sliding friction, when the asperities pass through the micropores, the asperities are embedded in the edge of the micropores so that the peak contact pressure increases, cutting occurs, and the deformation is affected by the interaction between the micropores and the asperities. The position of the highest pressure point is not fixed due to the deformation of the asperity, which improves the force of the asperity, and the micro-hole reduces the contact zone, thereby reducing the contact of the asperity and the pressure extreme point and reducing the pressure.Micropores reduce the temperature and enhance the wear condition of the end face. Small surface roughness can decrease the risk of end face wear.

Enhanced Interfacial Adhesion and Increased Isotropy of 3D Printed Parts with Microcellular Structure Fabricated via a Micro‐Extrusion CO2‐Foaming Process

Compared with the cumbersome traditional manufacturing processes, the fused filament fabrication (FFF) 3D printing technology can freely fabricate complex porous parts, but cannot produce microcellular structures, and suffers from inherent poor interfacial adhesion and anisotropy due to periodic heating. Herein, a novel micro‐extrusion CO2‐foaming process is applied in the FFF process, and foamed 3D printed polyetherimide (PEI) parts with internal microcellular structure are fabricated. The tensile strength of the foamed part with a density of 0.85 g cm−3 is 42.8 MPa, which was significantly higher than 22.6 MPa for the unfoamed counterpart. Moreover, the side length of periodic triangular voids between raster is reduced from 207 to 105 μm, and the degree of anisotropy is reduced from 79.5% to 13.8%. CO2 plasticization leads to a reduction in glass‐transition temperature and viscosity of polymer systems, and the diffusion and entanglement of interfacial molecular chains are facilitated by the increase in contact area and pressure caused by foaming and expansion. The micro‐extrusion CO2 foaming endows the 3D printed parts with lightweight, internal microcellular structure, enhanced interface bonding, and isotropic mechanical properties, which will broaden the application scopes of FFF‐3D printing technology.

Experimental Analysis of Frictional Performance of EN AW-2024-T3 Alclad Aluminium Alloy Sheet Metals in Sheet Metal Forming

Friction occurring in the area of contact between the sheet metal and the tool in sheet metal forming is one of the factors determining the quality of the surface of the drawpiece and the formability of the workpiece. Knowledge of the friction conditions allows the optimal forming conditions to be determined in terms of lubrication and applied pressures. The article presents the results of experimental studies of friction in EN AW-2024-T3 Alclad sheets using a special device simulating the sheet–tool contact in the blank-holder area during SMF. The friction tests were carried out at various pressures, under dry friction, and with the use of typical oils with a wide range of viscosity. The effect of the friction process parameters on the COF and surface roughness parameters Rsk and Rku was analysed using analysis of variance. The model F-values imply that the regression models for all the output parameters were significant. A monotonic decrease in the COF with an increase in the mean contact pressure and lubricant viscosity was observed for both dry and lubricated conditions. DELVAC 1340 engine oil with the highest viscosity significantly lowered the COF. The lubrication efficiency with LAN46 machine oil and LVH22 hydraulic oil showed an upward trend with an increasing mean contact pressure. In general, friction reduces the value of average roughness, Ra, and skewness, Rsk. Meanwhile, friction under contact pressures in the analysed range (4.4–11.7 MPa) causes an increase in kurtosis, Rku.

Biomechanical outcomes of superior capsular reconstruction for irreparable rotator cuff tears by different graft materials-a systematic review and meta-analysis.

Irreparable rotator cuff tears (IRCT) are defined as defects that cannot be repaired due to tendon retraction, fat infiltration, or muscle atrophy. One surgical remedy for IRCT is superior capsular reconstruction (SCR), which fixes graft materials between the larger tuberosity and the superior glenoid. The Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) criteria were followed for conducting the systematic review and meta-analysis. From their inception until February 25, 2022, Pubmed, Embase, and Cochrane Library's electronic databases were searched. Studies using cadavers on SCR for IRCT were also included. The humeral head's superior translation and subacromial peak contact pressure were the primary outcomes. The humeral head's anteroposterior translation, the kind of graft material used, its size, and the deltoid load were the secondary outcomes. After eliminating duplicates from the search results, 1,443 unique articles remained, and 20 papers were finally included in the quantitative research. In 14 investigations, the enhanced superior translation of the humeral head was documented in IRCTs. In 13 studies, a considerable improvement following SCR was found, especially when using fascia lata (FL), which could achieve more translation restraints than human dermal allograft (HDA) and long head of bicep tendon (LHBT). Six investigations reported a subacromial peak contact pressure increase in IRCTs, which could be rectified by SCR, and these studies found a substantial increase in this pressure. The results of the reduction in subacromial peak contact pressure remained consistent regardless of the graft material utilized for SCR. While there was a statistically significant difference in the change of graft material length between FL and HDA, the change in graft material thickness between FL and HDA was not significant. The humeral head's anterior-posterior translation was rising in IRCTs and could be returned to its original state with SCR. In five investigations, IRCTs caused a significant increase in deltoid force. Furthermore, only one study showed that SCR significantly decreased deltoid force. With IRCT, SCR might significantly decrease the glenohumeral joint's superior and anterior-posterior stability. Despite the risks for donor-site morbidity and the longer recovery time, FL is still the best current option for SCR.

Femoral-tibial contact stresses on fixed rotational femur models.

This study aims to quantitatively evaluate the femoral-tibial contact pressure on the knee under certain malrotaional degrees. Femoral-tibial contact pressure was carried out on 14 fixed rotational knee models under 200/400/600 N vertical load using ultra-low-pressure sensitive film technology, rotation angles including neutral position (0°, anatomically reduced), 5°, 10°, and 15° internally and externally. Data were collected and analyzed with SPSS software. There are significant statistical differences between the medial contact pressure among rotational deformities (including neutral position) (P < 0.01), the increase in the degree of fixed internal malrotation of the femur resulted in a linear increase in the medial femoral-tibial contact pressures (P < 0.05) under 200/400/600 N vertical load, while increase in the degree of fixed external malrotation resulted in a linear decrease (P < 0.05). Except the 200 N compression, we can't find significant differences in lateral contact pressures (P > 0.05). In the comparison of medial to lateral contact pressures, no statistically significant differences were found in neutral and 5° internal rotation under 200/400 N, neutral, 5° internal rotation, and 15° external rotation under 600 N. In contrast, medial contact pressures were higher than lateral at other angles (P < 0.05). Obvious contact pressure changes were observed in rotatory femur. Doctors should detect rotational deformity as much as possible during operation and perform anatomical reduction. For patients with residual rotational deformities, indication of osteotomy should not be too broad.

Assessment of the Tribological Performance of Bio-Based Lubricants Using Analysis of Variance

The purpose of this article is to determine the coefficient of friction of a DC04 steel sheet using a specially designed flat-die strip drawing test. Four different bio-based lubricants, edible (sunflower and rape-seed) and non-edible (karanja and moringa) were used in the study. The experiments were carried out for different contact pressure values. The as‐received specimens were pre‐strained with strains of 7, 14, and 21%. The values of the coefficient of friction as a ratio of the friction force to the normal force were determined. The influence of the viscosity of the lubricant and the contact pressure on the value of the coefficient of friction has been investigated using ANOVA. A tendency to a decrease in the coefficient of friction with increasing contact pressure was observed. Significance results obtained after the ANOVA analysis confirmed the influence of normal pressure and oil viscosity on the value of the coefficient of friction. At the same time, the hypothesis about the influence of the sheet pre-straining on the value of the coefficient of friction was not confirmed by the significant interactions.

The role of the lateral part of the distal triceps and the anconeus in varus stability of the elbow: A biomechanical study: The role of the lateral triceps tendon and anconeus under gravity varus.

The role of the lateral part of the distal triceps as a stabilizer in the lateral collateral ligament (LCL) deficient elbow and whether its effect in improving the stability is independent of that of the anconeus is unclear. Seven cadaveric elbows were tested under gravity varus stress using a custom-made machine designed to simulate muscle loads while allowing passive flexion of the elbow. An injury model was created by sectioning the LCL and sparing the common extensor origin. The lateral part of the distal triceps tendon was loaded sequentially with 0 N, 10 N, 25 N and 40 N. Each stage of the lateral part of the distal triceps loading was tested with the anconeus unloaded (inactive) or with a 25 N load applied (active). Articular contact pressure on the coronoid, the medial facet, and the lateral facet were collected and processed using TekScan sensors and software. A significant decrease in the mean coronoid contact pressure was seen with sequential loading of the lateral part of the distal triceps (p < 0.001). The ratio of medial to lateral facet contact pressures (M/L ratio) significantly decreased with sequential loading of the lateral part of the distal triceps (p < 0.001), indicating a better distribution of the contact pressure between the medial and lateral facets as the lateral part of the distal triceps was loaded. These effects were statistically significant, both with and without anconeus loading. There was no significant modification of the effect of the lateral part of the distal triceps loading on the contact pressure by the anconeus loading (p = 0.47). However, with active anconeus loading, the contact pressure and the M/L ratio were significantly lower for any stage of lateral triceps loading (p < 0.001), indicating a synergistic effect of the anconeus. In an LCL-deficient elbow, the lateral part of the distal triceps loading prevents the increased contact pressure on the coronoid under varus stress and improves the distribution of contact pressures on the coronoid. Anconeus loading further decreases and improves the distribution of the contact pressures; however, its effect is independent of that of the lateral part of the distal triceps. These results substantiate a role of the lateral part of the distal triceps as a dynamic constraint against elbow varus and have clinical implications for prevention and rehabilitation of elbow instability.

Influence of Graft Positioning during the Latarjet Procedure on Shoulder Stability and Articular Contact Pressure: Computational Analysis of the Bone Block Effect.

The Latarjet procedure is the most popular surgical procedure to treat anterior glenohumeral (GH) instability in the presence of large anterior glenoid bone defects. Even though the placement of the bone graft has a considerable influence on its efficacy, no clear indications exist for the best graft position. The aim of this study was to investigate the influence of the medial-lateral positioning of the bone graft on the contact mechanics and GH stability due to the bone block effect. Four finite element (FE) models of a GH joint, with a 20% glenoid bone defect, treated by the Latarjet procedure were developed. The FE models differed in the medial-lateral positioning of the bone graft, ranging from a flush position to a 4.5 mm lateral position with respect to the flush position. All graft placement options were evaluated for two separate shoulder positions. Anterior GH instability was simulated by translating the humeral head in the anterior direction, under a permanent compressive force, until the peak translation force was reached. Joint stability was computed as the ratio between the shear and the compressive components of the force. The lateralization of the bone graft increased GH stability due to the bone block effect after a 3 mm lateralization with respect to the flush position. The increase in GH stability was associated with a concerning increase in peak contact pressure due to the incongruous contact between the articulating surfaces. The sensitivity of the contact pressures to the medial-lateral positioning of the bone graft suggests a trade-off between GH stability due to the bone block effect and the risk of osteoarthritis, especially considering that an accurate and consistent placement of the bone graft is difficult in vivo.

Analysis of brain signal change response in amygdala evoked by skin pressure stimulus.

It was well known that the human body would produce an uncomfortable sensation when the fabric exerted a certain amount of pressure irritation on the skin. The amygdala had long been thought to be the source of negative emotion perception. However, up to now, the brain signal changes in the amygdala evoked by skin exposure pressure had not been known. In this work, a series of gradually increasing contact pressure stimulus from boneless corsets was repeatedly applied to the body's waist and abdomen, and the technology of functional magnetic resonance imaging (fMRI) was adopted to detect the brain response synchronously. The results shown that both subjective comfort score and percent signal changes (PSCs) of amygdala decreased with the increase of skin contact pressure. When the skin pressure applied to the waist and abdomen of the human body exceeded about 1kPa, blood oxygen level dependent signal in the amygdala was negatively activated. Besides, the degree of response of PSCs was intense than subjective evaluation, and the standard deviations of PSCs between individuals were much smaller than subjective evaluations. It was suggested that skin contact pressure stimulus caused the attention of the amygdala brain area. The greater the stimulus, the higher the attention, but such attention was caused by negative activation of the amygdala induced by skin discomfort. In addition, skin comfort representation based on brain perception was superior to subjective representation due to its higher response sensitivity and antipsychological interference ability.

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.

Transtibial Repair of Lateral Meniscus Posterior Root Tears Improves Contact Biomechanics in Pediatric Cadavers

A paucity of data exists on the treatment of pediatric lateral meniscus root tears (LMPRTs). This study aims to characterize the biomechanics of the lateral knee joint in pediatric cadavers following LMPRT and root repair. Our hypotheses were: (1) compared with the intact state, LMPRT would be associated with decreased contact area; (2) compared with the intact state, LMPRT would be associated with increased contact pressures; and (3) compared with LMPRT, root repair would restore contact area and pressures toward intact meniscus values. Eight cadaver knees (ages 8-12 years) underwent contact area and pressure testing of the lateral compartment. Tekscan pressure mapping sensors covering the tibial plateau were inserted underneath the lateral meniscus. Appropriate pressure load equivalents were applied by a robot at degrees of flexion: 0, 30, 60. Three meniscus conditions were tested: (1) intact, (2) complete root tear, and (3) repaired root tear. Root repairs were performed with transtibial pullout sutures. Statistical analysis was performed. Root tear significantly decreased mean contact area at 30° (P= .0279) and 60° (P= .0397). Root repair increased mean contact area and did not significantly differ from intact states. Differences in contact pressures between meniscus states were not statistically significant. Relative to the intact state. the greatest increase in contact pressures occurred between 0° and 30°. Root repair decreased mean contact pressures at 0° and 30°. At 60°, mean contact pressures of the repair state were closer in magnitude to the tear state than the intact state. Conclusions: LMPRT decreases contact area and increases contact pressures in the lateral knee compartment. Repair of LMPRT improves tibiofemoral contact area at high (>30°) degrees of flexion and contact pressures at low (<30°) degrees of flexion. Transosseous pullout repair is a clinically validated treatment for LMPRT. This study provides baseline biomechanics data of transtibial pullout repair of pediatric LMPRTs.

Biomechanical Changes in the Ankle Joint after Syndesmosis and Deltoid Injury and Subsequent Repair in a Cadaveric Model

Category: Ankle; Trauma Introduction/Purpose: 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 to both. The purpose of this study was to measure differences in tibiotalar joint contact pressures and tibiotalar contact area in the presence of deltoid ligament injury, syndesmotic injury, and after their respective repairs using a cadaveric model. Our hypotheses were 1) injury to the syndesmosis and deltoid would increase contact pressures and decrease contact area, 2) repaired injuries would restore biomechanics to near native state, and 3) that there would be similar tibiotalar contact pressures and contact area with syndesmosis repair alone compared to syndesmosis and deltoid ligament repair. Methods: Twelve human cadaveric lower extremities were randomized and tested under a series of conditions: 1) native, 2) sectioning of syndesmosis or deltoid, 3) sectioning of both the syndesmosis and deltoid, 4) repair of syndesmosis or deltoid, 5) repair of both. 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 and deltoid ligament repairs were performed with a single suture anchor. Specimens were tested under each condition with an axial compressive and torsional load. Contact pressures and area within the ankle were measured with a digitized pressure sensor (Tekscan, Boston MA). Changes in contact pressure and area were compared with two-way repeated measure analysis of variance and significant findings were tested with post-hoc pairwise comparisons of estimated marginal means with Bonferroni-adjusted p-values for multiple comparisons (α = 0.05). Results: The highest mean contact pressure was seen when the deltoid was injured, but the syndesmosis was still intact (4.43 +/- 1.328 mPa) compared to mean contact pressure of 3.142 +/-0.511 mPa in the native condition. The lowest mean contact pressure was seen when the deltoid was repaired, but the syndesmosis was still disrupted (3.068 +/- 0.477). However, these differences in mean contact pressures did not differ significantly with pairwise comparison. Total contact area was significantly less following syndesmosis repair in isolation when compared to the native condition (609.55+-312.37mm2 vs 903.854mm2 p=0.0183). When the syndesmosis was repaired, irrespective of the state of the deltoid, the distribution of contact pressures shifted from the medial half of the joint to the lateral half of the joint in all but one specimen. Conversely, after deltoid ligament repair the distribution of pressure remain concentrated in the medial half of the joint, like the native state. Conclusion: We did not find a significant difference in overall mean ankle contact pressures between the various tested conditions. However, there can be a significant decrease in the joint contact area and a shift in the distribution of contact pressures within the joint after syndesmosis repair that was not seen after deltoid repair. In fact, with a deltoid repair alone, the distribution of contact pressures and the joint contact area did not differ significantly from the native state. These changes in contact area and distribution of pressures may affect long-term clinical and radiographic outcomes.

Analytical Model of the Frictional Heating in a Railway Brake Disc at Single Braking with Experimental Verification.

A one-dimensional thermal problem of friction was formulated, taking into account the contact pressure increase at the beginning of the process. The obtained solution to this problem allows for the quick calculation of the transient temperature distribution in a railway brake disc during single braking application. In order to validate the developed model, the experimental tests were performed for two friction pairs consisting of the cast iron brake disc and pads comprising two composite materials. Theoretical results were compared with the data measured by thermocouples embedded in the brake disc during the full-size dynamometer tests. The maximum temperature values found based on the analytical solution are convergent with the corresponding empirical data. The consistency of the results obtained for two friction couples demonstrates the usefulness of the proposed computational model.