Mean Contact Pressure Research Articles

The role of fibular for supramalleolar osteotomy in treatment of varus ankle arthritis: a biomechanical and clinical study.

BackgroundSupramalleolar osteotomy (SMOT) is a well-accepted treatment method for mid-stage varus ankle osteoarthritis (OA). However, few studies have examined the role of fibular osteotomy in SMOT. The objective of the current study was to compare the biomechanical and clinical outcomes of SMOT with and without fibular osteotomy.MethodsEight cadaveric lower legs with 10° varus/valgus SMOT models were tested using a Tekscan ankle sensor. Tibiotalar joint contact with and without fibular osteotomy conditions were compared. Forty-one varus ankle OA patients treated with SMOT were included; 22 underwent fibular osteotomy, and 19 did not. The Maryland foot score and radiological angles were used for clinical evaluation.ResultsThe mean contact area and pressure did not differ significantly between normal and varus/valgus conditions with the fibula preserved. After fibular osteotomy, the mean contact area decreased and the mean contact pressure increased significantly in varus and valgus conditions (P < 0.01). The loading center moved to the opposite direction with and without fibular osteotomy in varus/valgus conditions. After a mean follow-up of 36.6 months (range 17–61), there was no significant difference in the Maryland scores of the two groups. However, in the fibular osteotomy group, the talar tilt angle decreased (P < 0.05), and the tibiocrural angle improved significantly (P < 0.01).ConclusionsFibular osteotomy facilitates the translation of tibiotalar contact pressure and is helpful for varus ankle realignment in patients with large talar tilts and small tibiocrural angles.

Comparison of the efficiency of an extra-articular absorber system and high tibial osteotomy for unloading the medial knee compartment: an in vitro study.

The unloading effect of an extra-articular absorber system on the knee joint medial compartment was compared with high tibial osteotomy (HTO) under physiological conditions in vitro. Seven fresh-frozen cadaveric knees were used to test isokinetic flexion-extension motions under physiological loading using a biomechanical knee simulator. Tibiofemoral area contact and peak contact pressures were measured using pressure-sensitive film in the untreated medial compartment. Pressures were measured after KineSpring System implantation and HTO (5° and 10° correction angles) performed with an angular-stable internal fixator (Tomofix). Implantation of the unloading device resulted in significantly decreased medial compartment area contact pressure (Δ0.02±0.01MPa, p=0.001) and peak contact pressure (Δ0.3±0.1MPa, p=0.001) compared with the first test cycle results in the untreated knee. HTO significantly decreased the pressure (p=0.001). Compared with the first test cycle, HTO (5° correction angle) decreased the mean contact pressure by Δ0.03±0.01MPa and peak contact pressure by Δ0.3±0.01MPa. With a 10° correction angle, HTO decreased contact pressure by Δ0.04±0.02MPa and peak contact pressure by Δ0.4±0.1MPa compared with that at the 5° correction angle. Implantation of an extra-capsular unloading device resulted in a significant unloading effect on the medial compartment comparable to that achieved with HTO at 5° and 10° correction angles. Thus, implantation of an extra-articular, extra-capsular absorber could become the method of choice when treating patients with unicompartmental osteoarthritis that cannot be adequately treated by HTO because of their straight-leg axis.

The cross-sectional shape of the fourfold semitendinosus tendon is oval, not round.

BackgroundThe looped side of the semitendinosus tendon (ST) graft (i.e., the side inserted into the femoral tunnel during anterior cruciate ligament reconstruction) appears to be oval rather than round. The purpose of this study was to investigate the cross section of the fourfold semitendinosus tendon graft and, more specifically, the differences in pressure exerted by a rounded rectangular tunnel versus a round femoral tunnel.MethodsSeven STs were harvested from cadaveric knees and a fourfold ST graft was made. Aluminum cubes with round or rectangular tunnels containing four-way pressure-sensitive conductive sensors (vertically and bilaterally) were used. The area of both cubes was the same. The graft was inserted into the tunnels 15 mm from the looped edge. After measuring pressure, the graft was fixed using ultraviolet-curing acrylic resin and was cut at 7.5 mm and 15 mm from the lapel edge. The area, axes for the best fitting ellipse of the cross-section, and ellipticity of the axes were measured.ResultsIn the round tunnel, the mean contact pressure was 287.0 ± 136.7 gf at the bilateral sensor; there was no contact pressure detected by the vertical sensor. In the rounded rectangular tunnel, the mean contact pressure was 260.9 ± 186.4 gf at the bilateral sensor and 352.9 ± 49.5 gf at the vertical sensor. Ellipticity was 1.25 ± 0.13 at 7.5 mm, and 1.17 ± 0.07 at 15 mm from the lapel edge of the graft.ConclusionsThe cross-sectional shape of the fourfold ST graft was not round, but oval. Moreover, the rounded rectangular tunnel was more fitted to the graft than the round tunnel.

Radiocapitellar contact characteristics during prosthetic radial head subluxation

Metallic radial head prostheses are often used in the management of comminuted radial head fractures and elbow instability. We hypothesized that during radiocapitellar subluxation, the contact pressure characteristics of an anatomic radial head prosthesis will more closely mimic those of the native radial head compared with a monopolar circular or a bipolar circular radial head design. With use of 6 fresh frozen cadaver elbows, mean radiocapitellar contact pressures, contact areas, and peak pressures of the native radial head were assessed at 0, 2, 4, and 6 mm of posterior subluxation. These assessments were repeated after the native radial head was replaced with anatomic, monopolar circular and bipolar circular prostheses. The joint contact pressures increased with the native and the prosthetic radial head subluxation. The mean contact pressures for the native radial head and anatomic prosthesis increased progressively and significantly from 0 to 6 mm of subluxation (native, 0.6 ± 0.0 MPa to 1.9 ± 0.2 MPa; anatomic, 0.7 ± 0.0 MPa to 2.1 ± 0.3 MPa; P < .0001). The contact pressures with the monopolar and bipolar prostheses were significantly higher at baseline and did not change significantly further with subluxation (monopolar, 2.0 ± 0.1 MPa to 2.2 ± 0.2 MPa [P = .31]; bipolar, 1.7 ± 0.1 MPa to 1.9 ± 0.1 MPa [P = .12]). The pattern of increase in contact pressures with the anatomic prosthesis mimicked that of the native radial head. Conversely, the circular prostheses started out with higher contact pressures that stayed elevated. The articular surface design of a radial head prosthesis is an important determinant of joint contact pressures.

Improved core model of indentation and its application to measure diamond hardness

A model of the indentation using conical and pyramidal indenters has been proposed, in which not only a sample but the indenter as well are elastoplastically deformed and their materials obey the Mises yield condition. These conditions are characteristic of the measuring of diamond hardness through a diamond indenter. The model that has been proposed generalizes and refines the known simplified Johnson’s model, which uses an elastically deformed indenter. The proposed model makes it possible to determine approximately the sizes of elastoplastic zones in the indenter and sample, the effective apex angle of the loaded indenter and effective angles of the indenter and imprint after unloading. Based on this model a procedure of the determination of the sample and indenter yield strengths (Ys and Yi, respectively) has been developed, in which the relations that use the experimental values of the effective angle of the sample imprint and measured values of the Meyer hardness, HM (mean contact pressure) are added to theoretical relations of the indentation model. The developed computational procedure was applied in indentation experiments on synthetic diamond at the temperature 900°C (at which diamond exhibits a noticeable plastic properties) using natural diamond pyramidal indenters having different apex angles. According to the proposed model, the stress-strain states of samples and indenters have been investigated and their yield strengths and plasticity characteristics were defined. The stress–strain curve of the diamond in the stress-total strain coordinates has been constructed. The strain hardening of diamond was also studied.

Finite element analysis of contact deformation regimes of an elastic-power plastic hardening sinusoidal asperity

A series of finite element simulations of frictionless contact deformation between an elastic-power plastic sinusoidal asperity and a rigid flat are carried out to explore the influence of the ratio of yield stress to elastic modulus on the evolution of contact deformation regime. The deformation behavior comprises five regimes with four transitional states corresponding to four critical events determined by curve-fitting of simulation results. The transitional boundaries between neighboring deformation regimes are: (1) initiation of plastic deformation; (2) plastic deformation just reaches the top surface; (3) the whole contact surface just experiences plastic deformation; (4) the attainment of maximum mean contact pressure. It is found the mean contact pressures at transitional events are closely associated with yield stress and characteristic stress, which can be used as normalization parameters.

Nanoindentation Studies of the Effects of Ion Irradiation on the Near Surface Mechanical Response of Annealed Ti40Cu32Pd14Zr10Sn2Si2 Metallic Glass Ribbons

Nanoindentation experiments with a Berkovich indenter and a spherical indenter were performed to study the effects of annealing at temperatures below the glass transition temperature and room temperature ion irradiation on the near surface mechanical response of Ti40Cu32Pd14Zr10Sn2Si2 metallic glass (MG) ribbons. The specimens were isothermally annealed in vacuum at 573 K and 673 K for 4 hrs. Annealing was seen to increase the hardness of the specimens and decrease their ductility. The annealed specimens were subsequently irradiated by 3.5 MeV Cu2+ ions at room temperature using a fluence of 1 × 1012 ions/cm2 or 1 × 1016 ions/cm2. Nanoindentation experiments on the annealed and irradiated specimens showed a reduction in hardness and an increase in ductility for the specimens irradiated at a fluence of 1 × 1012 ions/cm2. Although the values of the mean contact pressure and critical shear stress under the spherical indenter showed an easier formation of shear bands after irradiation, increasing the irradiation fluence to 1 × 1016 ions/cm2 was seen to increase the hardness value and decrease the ductility of the specimens.

Strain gradient plasticity analysis of elasto-plastic contact between rough surfaces

From a microscopic point of view, the real contact area between two rough surfaces is the sum of the areas of contact between facing asperities. Since the real contact area is a fraction of the nominal contact area, the real contact pressure is much higher than the nominal contact pressure, which results in plastic deformation of asperities. As plasticity is size dependent at size scales below tens of micrometers, with the general trend of smaller being harder, macroscopic plasticity is not suitable to describe plastic deformation of small asperities and thus fails to capture the real contact area and pressure accurately. Here we adopt conventional mechanism-based strain gradient plasticity (CMSGP) to analyze the contact between a rigid platen and an elasto-plastic solid with a rough surface. Flattening of a single sinusoidal asperity is analyzed first to highlight the difference between CMSGP and J2 isotropic plasticity. For the rough surface contact, besides CMSGP, pure elastic and J2 isotropic plasticity analysis is also carried out for comparison. In all cases, the contact area A rises linearly with the applied load, but with a different slope which implies that the mean contact pressures are different. CMSGP produces qualitative changes in the distributions of local contact pressures compared with pure elastic and J2 isotropic plasticity analysis, furthermore, bounded by the two.

Static metal sealing mechanism of a subsea pipeline mechanical connector

The static metal sealing mechanism is essential for the structural design of subsea pipeline mechanical connector. By analyzing the sealing mechanism and contact pressure on sealing face, the critical condition of the seal is obtained. Based on the superposition theorem of elasticity, the formula of critical mean contact pressure ensuring seal is deduced. The finite element analysis result of critical mean contact pressure agrees with the analysis result very well and the critical mean contact pressure decreases with the increase in pipeline wall thickness and sealing width; however, the radius of pipeline has less influence on it. The critical mean contact pressure of 8-in subsea pipeline mechanical connector is 223.34 MPa and subsea pipeline mechanical connector is designed with ANSYS. The internal pressure experiments indicate that the sealing performance of final designed subsea pipeline mechanical connectors is higher than the design pressure of 4.5 MPa and all the initial designed ones cannot seal up to 4.5 MPa. By observing the sealing indentation on pipeline surface, when the mean contact pressure is higher than the critical mean contact pressure and the contact pressure variance is smaller, a full contact is seen to form a seal. Finally, the vibration experiments prove that the number of vibration is more than 107 and final designed subsea pipeline mechanical connector meets the experiment specification.

Biomechanical Consequences of Excessive Patellar Distalization

Iatrogenic patellar baja can be a result of excessive tibial tubercle distalization or overtightented patellar tendon repair. Tubercle distalization is increasing in popularity for the treatment of recurrent patella instability. Clinically, patellar baja can present as a debilitating problem with motion loss, increased pain, and arthrosis progression. However, previous biomechanical studies have not shown an increase in patellofemoral joint contact pressures. The purpose of this study is to examine the patellofemoral contact pressure after a tibial tubercle distalization osteotomy. Ten matched pair fresh-frozen cadaveric knees were studied. Average Blackburne-Peel ratio of the native knees was 0.91. The knees were placed on a testing rig, with a fixed femur and tibia mobile through 90° of flexion. Individual quadriceps heads and the iliotibial band were separated and loaded with 205 N in anatomic directions using a weighted pulley system. A straight tubercle distalization osteotomy of 1 cm was performed and fixed with screws, with and without a lateral release. Patellofemoral contact pressures were measured at 0°, 10°, 20°, 30°, 45°, 60°, and 90° of flexion using pressure-sensitive films on the medial and lateral trochlea. The contact force, area and pressure were measured at the following states: (1) native knee, (2) with distalization and (3) distalization with lateral release. Average Blackburne-Peel ratio after distalization was 0.64. Tibial tubercle distalization resulted in a six fold increase in mean contact pressures at 0° (0.15 versus 0.90 MPa, p<0.001), and a 55% increase at 10° of flexion (0.70 versus 1.09 MPa, p=0.02). After distalization, total contact area was significantly higher at 0° of flexion (17.7 mm2 versus 58.4 mm2, p=0.02). Lateral release after distalization did not significantly change contact pressure (p>0.21). Our results suggest that patellar baja, as a result of excessive patellar distalization, can cause increased patellofemoral contact pressures during early flexion.

Glenohumeral kinematics after soft tissue interposition graft and glenoid reaming: A cadaveric study.

Background:The management of young patients with glenohumeral arthritis is controversial. Resurfacing of the glenoid with biologic interposition and reaming of the glenoid have been suggested as potential treatment options. The goal of this study was to determine the change in glenohumeral contact pressures in interposition arthroplasty, as well as glenoid reaming in an arthritis model. We hypothesized that interposition with meniscal allograft will lead to the best normalization of contact pressure throughout the glenohumeral range of motion.Materials and Methods:Eight fresh-frozen cadaveric shoulders were tested in static positions of humeral abduction with a compressive load. Glenohumeral contact area, contact pressure, and peak force were determined sequentially for (1) intact glenoid (2) glenoid with cartilage removed (arthritis model) (3) placement of lateral meniscus allograft (4) placement of Achilles allograft (5) arthritis model with reamed glenoid.Results:The arthritis model demonstrated statistically higher peak pressures than intact glenoid and glenoid with interpositional allograft. Meniscal and Achilles allograft lowered mean contact pressure and increased contact area to a level equal to or more favorable than the control state. In contrast, the reamed glenoid did not show any statistical difference from the arthritis model for any of the recorded measures.Conclusion:Glenohumeral contact pressure is significantly improved with interposition of allograft at time zero compared to an arthritic state. Our findings suggest that concentric reaming did not differ from the arthritic model when compared to normal. These findings favor the use of allograft for interposition as a potential treatment option in patients with glenoid wear.

Effect of the Proximal Abducting Ulnar Osteotomy on Intra-Articular Pressure Distribution and Contact Mechanics of Congruent and Incongruent Canine Elbows Ex Vivo.

To determine the effects of the Proximal Abducting Ulnar Osteotomy (PAUL) on contact pressures of congruent and incongruent (short radius) canine elbows. Ex vivo biomechanical study. Unpaired normal cadaveric canine forelimbs (n=16). A servohydraulic testing frame and thin-film sensors were utilized to measure intra-articular contact area (CA), mean contact pressure (mCP), and peak contact pressure (pCP) for medial and lateral elbow compartments. Percent contribution of the medial compartment relative to the whole (%Med) was also examined. Baseline data were collected in 9 congruent elbows and 7 incongruent elbows where the radius was shortened. Both sets of elbows were tested following ulnar osteotomy and sequential placement of 2 and 3 mm PAUL plates and paw repositioning (to account for any medial to lateral shift of transarticular forces). Paired t-tests compared sequential procedural steps. P<.05 was significant. For congruent elbows, the 2 mm PAUL plate decreased CA in both compartments compared to baseline; lateral pCP increased with subsequent paw repositioning. Induction of radio-ulnar incongruity decreased CA and increased mCP medially, decreased pCP laterally, and increased %MedCA and %MedmCP compared to baseline. Both PAUL plates decreased mCP and pCP medially, with no effect laterally. Paw repositioning had no effect. The PAUL procedure had no effect on medial compartment pressure in the congruent elbow. It may ameliorate increased medial compartment pressure in the incongruent elbow. This change does not result from a medial to lateral compartmental shift and deserves further investigation.

Biomechanical response of lumbar facet joints under follower preload: a finite element study.

BackgroundFacet joints play a significant role in providing stability to the spine and they have been associated with low back pain symptoms and other spinal disorders. The influence of a follower load on biomechanics of facet joints is unknown. A comprehensive research on the biomechanical role of facets may provide insight into facet joint instability and degeneration.MethodA nonlinear finite element (FE) model of lumbar spine (L1-S1) was developed and validated to study the biomechanical response of facets, with different values of follower preload (0 N,500 N,800 N,1200 N), under loadings in the three anatomic planes. In this model, special attention was paid to the modeling of facet joints, including cartilage layer. The asymmetry in the biomechanical response of facets was also discussed. A rate of change (ROC) and an average asymmetry factor (AAF) were introduced to explore and evaluate the preload effect on these facet contact parameters and on the asymmetry under different loading conditions.ResultsThe biomechanical response of facets changed according to the loading condition. The preload amplified the facet force, contact area and contact pressure in flexion-extension; the same effect was observed on the ipsilateral facet while an opposite effect could be seen on the contralateral facet during lateral bending. For torsion loading, the preload increased contact area, decreased the mean contact pressure, but had almost no effect on facet force. However, all the effects of follower load on facet response became weaker with the increase of preload. The greatest asymmetry of facet response could be found on the ipsilateral side during lateral bending, followed by flexion, bending (contralateral side), extension and torsion. This asymmetry could be amplified by preload in the bending (ipsilateral), torsion loading group, while being reduced in the flexion group.ConclusionsAn analysis combining patterns of contact pressure distribution, facet load, contact area and contact pressure can provide more insight into the biomechanical role of facets under various moment loadings and follower loads. The effect of asymmetry on facet joint response should be fully considered in biomechanical studies of lumbar spine, especially in post structures subjected to physiological loadings.Electronic supplementary materialThe online version of this article (doi:10.1186/s12891-016-0980-4) contains supplementary material, which is available to authorized users.

Plasticity evolution in a coated sphere compressed by a rigid flat

A finite element analysis is used to study the plasticity evolution in a coated sphere compressed by a rigid flat. This is done for hard coatings with moderate to large thicknesses and a wide range of material properties. Empirical expressions are provided for critical interferences of the first and second yield inceptions, in the coating and on the substrate side of the interface, respectively. A new criterion for substrate plasticity level (SPL) is suggested, which seems to control the plasticity evolution within the coating. Plasticity boundaries are presented, showing that a third yield inception may occur as the interference increases. Also, some complex behavior of elastic core formation below the contact area that causes reduction in the mean contact pressure is shown as the SPL increases.

Safety and Effectiveness of SAF-R, a Novel Patient Positioning Device for Robot-Assisted Pelvic Surgery in Trendelenburg Position

We found current robotic positioning devices to be inadequate and cumbersome. Furthermore, we realized there were no premarket well-designed studies to prove their safety and efficacy. In this prospective pilot study, we aimed to investigate the safety and effectiveness of a novel patient-positioning device (SAF-R) to secure the patient in Trendelenburg (T-burg) position for robot-assisted pelvic surgery. Sixteen patients undergoing robot-assisted pelvic operation in T-burg position were enrolled. Patients were positioned using SAF-R board. Pressure sensor mats were used for real-time monitoring of the contact pressures and contact area on the shoulders and calves throughout the surgery. Data collection included patients' body mass index (BMI), time needed for positioning, total time in the T-burg position, contact pressure and contact area readings from the sensor mats, and the patient shifting distance on the table. Patients were also followed for 1-month postoperatively for any position-related adverse event. The median age of the patients was 56.5 years with median BMI of 27.3. The median positioning time was 6 minutes, duration of T-burg position was 3.5 hours, and patient shift on the table was 1 cm. The contact pressure over the shoulders was in the safe range (< 80 mm Hg) before and at the end of the surgery in all cases (right: 13.12 ± 1.12 vs 20.25 ± 1.56 mm Hg, left: 12.84 ± 1.05 vs 19.60 ± 1.09 mm Hg, p = 0.001). The changes in the mean contact pressure over the calves and the mean contact area for the shoulders and calves during the T-burg position were not significantly different. No significant position-related complication was detected during follow-up. SAF-R surgical board is a safe, reliable, and timesaving positioning device for patients undergoing robotic pelvic surgery in the T-burg position.

Self‐Assembly of Graphene Oxide on Silicon Substrate via Covalent Interaction: Low Friction and Remarkable Wear‐Resistivity

Few‐layer graphene oxide (GO) is assembled on the silicon surface by a self‐assembly approach via covalent interaction using 3‐aminopropyltrimethoxysilane (APTMS) as a bifunctional chemical linker. X‐ray photoelectron spectroscopy results suggest chemical interactions between oxygen functionalities of GO and amino group of APTMS thin film. The oxygen functionalities of GO thin film are eliminated by vacuum ultraviolet (VUV) photon exposure. Topographic images reveal efficient grafting of GO on the silicon and suggest the presence of few layers in the GO thin film along with wrinkles and folds. Microtribological properties of VUV‐reduced GO (rGO) thin film are probed under the mean contact pressure of 0.3–0.6 GPa. The rGO thin film exhibits low and steady friction (0.12–0.15) compared to that of bare silicon (0.6). The rGO thin film could survive for ≈37 000 laps at 100 mN load, revealing its remarkable wear‐resistivity. Microscopic images and carbon mapping reveal the deposition of delaminated graphene lamellae on the counter steel ball surface. The low friction and excellent wear‐resistivity of rGO thin film are collectively attributed to low‐resistance to shear between the neighboring lamellae of rGO, full coverage and strong interaction of rGO thin film with silicon, and deposition of delaminated graphene lamellae on the counter steel surface.

Edge indentation of ice with a displacement-controlled oscillating cylindrical structure

Indentation tests were performed with a cylindrical structure subject to a controlled harmonic oscillation. The aim of the experiments is to study ice behaviour when loaded at a varying rate of indentation closely resembling that during frequency lock-in. Focus of the experiments is on the development of the global load, local pressure and contact area during indentation. To this end, a tactile sensor is installed at the ice–structure interface which allows for detailed measurement of these quantities. During the experiment the frequency and amplitude of structural oscillation were varied, as well as the indentation velocity. Results show that ice behaviour changes from brittle to transitional, and ultimately to ductile, as the relative velocity between ice and structure decreases during a cycle of oscillation. Both transitional and ductile behaviour result in an increase of the maximum global ice load upon fracture. The obtained increase in maximum global load depends on the duration of ductile behaviour of the ice. The longer the duration, the greater the increase in maximum global load compared to peak loads in the brittle regime. Tactile sensor measurements indicate that the increase in global load occurs as a result of a combined increase in contact area and mean contact pressure. The obtained results provide insight into the parameters influencing the occurrence of frequency lock-in of structures interacting with level ice.

Adhesive contact of the Weierstrass profile

The Weierstrass series was considered in Ciavarellaet al.(Ciavarellaet al.2000Proc. R. Soc. Lond. A456, 387–405. (doi:10.1098/rspa.2000.0522)) to describe a linear contact problem between a rigid fractally rough surface and an elastic half-plane. In such cases, no applied mean pressure is sufficiently large to ensure full contact, and specifically there are not even any contact areas of finite dimension. Later, Gao &amp; Bower (Gao &amp; Bower 2006Proc. R. Soc. A462, 319–348. (doi:10.1098/rspa.2005.1563)) introduced plasticity in the Weierstrass model, but concluded that the fractal limit continued to lead to what they considered unphysical predictions of the true contact size and number of contact spots, similar to the elastic case. In this paper, we deal with the contact problem between rough surfaces in the presence of adhesion with the assumption of a Johnson, Kendall and Roberts (JKR) regime. We find that, for fractal dimensionD&gt;1.5, the presence of adhesion does not qualitatively modify the contact behaviour. However, for fractal dimensionD&lt;1.5, a regularization of the contact area can be observed at a large magnification where the contact area consists of segments of finite size. Moreover, full contact can occur at all scales forD&lt;1.5 provided the mean contact pressure is larger than a certain value. We discuss, however, the implication of our assumption of a JKR regime.

Plane Contact and Partial Slip Behaviors of Elastic Layers With Randomly Rough Surfaces

A plane contact and partial slip model of an elastic layer with randomly rough surface were established by combining the Greenwood–Williamson (GW) rough contact model and the Cattaneo–Mindlin partial slip model. The rough surface of the elastic layer bonded to a rigid base is modeled as an ensemble of noninteracting asperities with identical radius of curvature and Gaussian-distributed heights. By employing the Hertzian solution and the Cattaneo–Mindlin solution to each individual asperity of the rough surface, we derive the total normal force, the real contact area, and the total tangential force for the rough surface, respectively, and then examine the normal contact and partial slip behaviors of the layer. An effective Coulomb coefficient is defined to account for interfacial friction properties. Furthermore, a typical stick–slip transition for the rough surface was also captured by distinguishing the stick and slip contacting asperities according to their respective indentation depths. Our analysis results show that an increasing layer thickness may result in a larger real contact area, a lower mean contact pressure, and a higher effective Coulomb coefficient.

Influence of lateral meniscal posterior root avulsions and the meniscofemoral ligaments on tibiofemoral contact mechanics.

The purpose of this study was to investigate the effect of lateral meniscal posterior root avulsions combined with intact meniscofemoral ligaments (MFLs), deficient MFLs, anterior cruciate ligament (ACL) tears and reconstructions, and root repairs using an established tibiofemoral contact mechanics testing protocol. Ten fresh-frozen cadaveric knees were tested with six knee conditions (1: intact; 2: lateral meniscal posterior root avulsion; 3: root avulsion and deficient MFLs; 4: condition3 with ACL tear; 5: condition4 with ACL reconstruction; 6: ACL reconstruction with root repair) at five flexion angles (0°, 30°, 45°, 60°, and 90°), under a 1000-N axial load. Contact area and pressure were measured with Tekscan sensors. Compared to the intact state, condition2 did not significantly change lateral compartment contact area or pressure. Changes in contact mechanics were greater at increased flexion angles; for condition3 at 0° and 90°, contact area decreased 37 and 52% [95% CI (21-53) and (39-66), respectively] and mean contact pressure increased 55 and 87% [95% CI (33-76) and (59-114), respectively]. Root repair with ACL reconstruction was not significantly different from the intact state. The MFLs protect the lateral compartment from changes in contact mechanics in the setting of a lateral meniscal posterior root avulsion, whereas a combination of lateral meniscal root avulsion and deficient MFLs leads to significant changes. Concurrent ACL reconstruction and lateral meniscal root repair restore mean contact pressure and area to the intact state and are recommended in this combined injury to prevent or slow the development of lateral compartment arthritis.