Mean Contact Pressure Research Articles

Strain gradient effects in periodic flat punch indenting at small scales

Experiments on soft polycrystalline aluminum have yielded evidence that, besides the required punch load, both the size and shape of imprinted features are affected by the scale of the set-up, e.g. substantial details are lost when the characteristic length is on the order of 10μm. The objective of this work is to clarify the role played by strain gradients on this issue, and to shed light on the underlying mechanisms. For this, indentation by a periodic array of flat punch indenters is considered, and a gradient enhanced material model that allows for a numerical investigation of the fundamentals are employed. During a largely non-homogeneous deformation, the material is forced up in between the indenters so that an array of identical imprinted features is formed once the tool is retreated. It is confirmed that the additional hardening owing to plastic strain gradients severely affects both the size and shape of these imprinted features. In particular, this is tied to a large increase in the mean contact pressure underneath the punch, which gives rise to significant elastic spring-back effects during unloading.

Effect of surface parameters on finite element method based deterministic Gaussian rough surface contact model

Three-dimensional rough surface contact models enrich the understanding of the influence of surface texture in rough surface contacts. Most of the existing contact models did not consider the effect of elasto-plastic deformation and neighboring asperity interactions for the rough surface contact analysis, or only to a limited extent. In the present work, three-dimensional contact analyses of Gaussian rough surfaces are carried out using finite element method. By fast Fourier transform approach, Gaussian rough surfaces having auto-correlation lengths of 0.5, 2.0, 5.0, and 10 µm and surface roughness of 0.001, 0.01, and 0.1 µm are generated. The generated rough surfaces are transferred to finite element method based ANSYS package for micro-contact analysis. The continuity of elastic, elasto-plastic, and plastic deformations of near realistic feature-based asperities and effects of asperity interactions are inherently included in the present analysis. Each rough surface contact analysis is carried out in such a manner to cover the entire asperity distribution with incremental displacements. The contact load, real area of contact, and contact pressure are extracted from each analysis. The results showed that the surface having low surface roughness, the asperities deform mostly elastically whereas in medium and high surface roughness surfaces, the elasto-plastic and plastic deformation of asperities are significant and also in low auto-correlation length surface, the intensification of sub surface stresses cause the mean contact pressure ratio to reach peak value whereas in high auto correlation length surface, the larger size of asperities and the neighboring asperity interaction keep the mean contact pressure ratio at low level.

Glenohumeral Contact Pressure With Simulated Anterior Labral and Osseous Defects in Cadaveric Shoulders Before and After Soft Tissue Repair

Background: Glenoid rim fractures and erosion can result from traumatic and repeated shoulder dislocations, leading to glenoid bone loss. Traditional instability surgery includes Bankart repair to restore soft tissue anatomy, although a recent trend is to address glenoid bone deficiency when appropriate with a bone block procedure. Hypothesis/Purpose: The purpose of this study was to quantify glenohumeral joint contact pressures as a function of anterior labral detachment, progressive anterior glenoid bone loss, and labral repair. The hypothesis was that a critical glenoid defect size exists whereby labral repair alone cannot restore joint contact pressures, therefore favoring bone block augmentation over soft tissue repair. Study Design: Controlled laboratory study. Methods: Eight fresh-frozen cadaveric shoulders were tested under a 440-N compressive load simulating glenohumeral abduction positions of 30° and 60° in neutral rotation and 60° with 90° of external rotation. Glenohumeral joint contact pressures were recorded with a Tekscan pressure sensor system in these configurations: (1) intact specimen, (2) Bankart lesion, (3) 10% anterior rim bone defect, (4) 10% bone defect with labral repair, (5) 20% bone defect, (6) 20% bone defect with labral repair, (7) 30% bone defect, and (8) 30% bone defect with labral repair. The joint contact pressures were compared at all configurations. Results: The Bankart lesion and 10%, 20%, and 30% glenoid defects showed significant (P < .05) increases in mean contact pressures over baseline values. Labral repair at 10% bone loss reduced mean contact pressures to below the intact state, and labral repair of 20% defects demonstrated normalized mean contact pressures. However, mean contact pressures remained statistically elevated compared with baseline values after labral repair of 30% glenoid defects. Conclusion: Glenohumeral joint contact pressures were restored to baseline values after labral repair of 10% and 20% anterior glenoid bone defects. Conversely, labral repair at 30% glenoid bone loss did not restore glenohumeral contact mechanics, yielding elevated contact pressures despite repair. Further study is warranted to investigate the stability (resistance to dislocations) of the glenohumeral joint after labral repair and bone block augmentation. Clinical Relevance: A critical glenoid defect size exists in which labral repair alone does not restore normal glenohumeral contact pressures. Surgeons should carefully evaluate glenoid bone loss before selecting a surgical treatment for shoulder instability.

Computationally Efficient Magnetic Resonance Imaging Based Surface Contact Modeling as a Tool to Evaluate Joint Injuries and Outcomes of Surgical Interventions Compared to Finite Element Modeling

Joint injuries and the resulting posttraumatic osteoarthritis (OA) are a significant problem. There is still a need for tools to evaluate joint injuries, their effect on joint mechanics, and the relationship between altered mechanics and OA. Better understanding of injuries and their relationship to OA may aid in the development or refinement of treatment methods. This may be partially achieved by monitoring changes in joint mechanics that are a direct consequence of injury. Techniques such as image-based finite element modeling can provide in vivo joint mechanics data but can also be laborious and computationally expensive. Alternate modeling techniques that can provide similar results in a computationally efficient manner are an attractive prospect. It is likely possible to estimate risk of OA due to injury from surface contact mechanics data alone. The objective of this study was to compare joint contact mechanics from image-based surface contact modeling (SCM) and finite element modeling (FEM) in normal, injured (scapholunate ligament tear), and surgically repaired radiocarpal joints. Since FEM is accepted as the gold standard to evaluate joint contact stresses, our assumption was that results obtained using this method would accurately represent the true value. Magnetic resonance images (MRI) of the normal, injured, and postoperative wrists of three subjects were acquired when relaxed and during functional grasp. Surface and volumetric models of the radiolunate and radioscaphoid articulations were constructed from the relaxed images for SCM and FEM analyses, respectively. Kinematic boundary conditions were acquired from image registration between the relaxed and grasp images. For the SCM technique, a linear contact relationship was used to estimate contact outcomes based on interactions of the rigid articular surfaces in contact. For FEM, a pressure-overclosure relationship was used to estimate outcomes based on deformable body contact interactions. The SCM technique was able to evaluate variations in contact outcomes arising from scapholunate ligament injury and also the effects of surgical repair, with similar accuracy to the FEM gold standard. At least 80% of contact forces, peak contact pressures, mean contact pressures and contact areas from SCM were within 10 N, 0.5 MPa, 0.2 MPa, and 15 mm2, respectively, of the results from FEM, regardless of the state of the wrist. Depending on the application, the MRI-based SCM technique has the potential to provide clinically relevant subject-specific results in a computationally efficient manner compared to FEM.

Altered Tibiofemoral Contact Mechanics Due to Lateral Meniscus Posterior Horn Root Avulsions and Radial Tears Can Be Restored with in Situ Pull-Out Suture Repairs

An avulsion of the posterior root attachment of the lateral meniscus or a radial tear close to the root attachment can lead to degenerative knee arthritis. Although the biomechanical effects of comparable injuries involving the medial meniscus have been studied, we are aware of no such study involving the lateral meniscus. We hypothesized that in situ pull-out suture repair of lateral meniscus root avulsions and of complete radial tears 3 and 6 mm from the root attachment would increase the contact area and decrease mean and peak tibiofemoral contact pressures, at all knee flexion angles, relative to the corresponding avulsion or tear condition. Eight human cadaveric knees underwent biomechanical testing. Eight lateral meniscus conditions (intact, footprint tear, root avulsion, root avulsion repair, radial tears at 3 and 6 mm from the posterior root, and repairs of the 3 and 6-mm tears) were tested at five different flexion angles (0°, 30°, 45°, 60°, and 90°) under a compressive 1000-N load. Avulsion of the posterior root of the lateral meniscus or an adjacent radial tear resulted in significantly decreased contact area and increased mean and peak contact pressures in the lateral compartment, relative to the intact condition, in all cases except the root avulsion condition at 0° of flexion. In situ pull-out suture repair of the root avulsion or radial tear significantly reduced mean contact pressures, relative to the corresponding avulsion or tear condition, when the results for each condition were pooled across all flexion angles. Posterior horn root avulsions and radial tears adjacent to the root attachment of the lateral meniscus significantly increased contact pressures in the lateral compartment. In situ pull-out suture repairs of these tears significantly improved lateral compartment joint contact pressures. In situ repair may be an effective treatment to improve tibiofemoral contact profiles after an avulsion of the posterior root of the lateral meniscus or a complete radial tear adjacent to the root. In situ repairs should be further investigated clinically as an alternative to partial lateral meniscectomy.

Influence of radial head prosthetic design on radiocapitellar joint contact mechanics

Our aim was to test whether anatomically designed metallic radial head implants could better reproduce native radiocapitellar contact pressure and areas than nonanatomic implants. The distal humerus and proximal radius from 6 cadaveric upper extremities were serially tested in supination with 100 N of compression force at 4 angles of flexion (0°, 30°, 60°, and 90°). By use of a thin flexible pressure transducer, contact pressures and areas were measured for the native radial head, an anatomic implant, a nonanatomic circular monopolar implant, and a bipolar nonanatomic implant. The data (mean contact pressure and mean contact area) were modeled using a 2-factor repeated-measures analysis of variance with P ≤ .05 considered to be significant. The mean contact areas for the prosthetic radial heads were significantly less than those seen with the intact radial heads at every angle tested (P < .01). The mean contact pressures increased significantly with all prosthetic radial head types as compared with the native head. The mean contact pressures increased by 29% with the anatomic prosthesis, 230% with the monopolar prosthesis, and 220% with the bipolar prosthesis. Peak pressures of more than 5 MPa were more commonly observed with both the monopolar and bipolar prostheses than with the anatomic or native radial heads. The geometry of radial head implants strongly influences their contact characteristics. In a direct radius-to-capitellum axial loading experiment, an anatomically designed radial head prosthesis had lower and more evenly distributed contact pressures than the nonanatomic implants that were tested.

Biomechanical Consequences of a Complete Radial Tear Adjacent to the Medial Meniscus Posterior Root Attachment Site

Objectives:Complete radial tears near the medial meniscus posterior root attachment site disrupt the circumferential integrity of the meniscus (similar to a posterior root avulsion). These tears can compromise the circumferential integrity and have been reported in biomechanical studies to simulate the meniscectomized state. The purpose of the study was to quantify the tibiofemoral contact load and contact area changes that occur in cadaveric knees from complete posterior horn radial tears and subsequent repairs of the medial meniscus adjacent to the posterior root attachment site.Methods:Six non-paired fresh-frozen human cadaveric knees each underwent 45 different testing conditions: 9 medial meniscus conditions (intact, root avulsion, root repair, serial radial tear and in-situ repair at 3, 6, and 9 mm from the root attachment site) at 5 flexion angles (0°, 30°, 45°, 60° and 90°); under a 1000-N axial load. Tekscan sensors were used to measure contact area and pressure in the medial and lateral compartments.Results:The medial meniscus root avulsion and all radial tear conditions resulted in significantly decreased contact area and increased mean contact pressure compared with the intact state for knee flexion angles beyond 0° (P < .05). Medial Compartment Contact Area Individual comparisons of meniscus conditions for results at 30°, 45°, 60° and 90° of flexion demonstrated the following. At each angle, the root avulsion and 3, 6 and 9 mm radial tears resulted in a significant reduction (range 33%-45% decrease) in medial compartment contact area. Medial Compartment Contact PressureIndividual comparisons of meniscus conditions were performed at 30°, 45°, 60° and 90° of flexion. At each angle, the root avulsion and all radial tears resulted in a significant increase in average contact pressure (range 46%-110%) when compared to the intact meniscus. Root Repair and In-situ Repairs The root repair and in-situ repairs restored contact area and pressure to levels statistically indistinguishable from the intact meniscus, and increased contact area and decreased contact pressure when compared to the corresponding tear conditions (Figure).Conclusion:Posterior horn radial tears adjacent to the medial meniscus root that extend to the meniscocapsular junction can lead to derangement of the loading profiles of the medial compartment that are similar to a root avulsion. Repair of these radial tears with an in-situ pullout technique restored joint mechanics to the intact state. Clinical Relevance Complete radial tears of the posterior horn of the medial meniscus, are biomechanically equivalent to root avulsions and could potentially lead to medial compartment arthrosis. An in-situ repair offers an alternative treatment to meniscectomy and can reestablish the posterior anchor point, thus improving load distribution in the medial compartment.

Biomechanical Consequences of a Complete Radial Tear Adjacent to the Medial Meniscus Posterior Root Attachment Site

Background: Complete radial tears near the medial meniscus posterior root attachment site disrupt the circumferential integrity of the meniscus (similar to a posterior root avulsion). These tears can compromise the circumferential integrity, and they have been reported in biomechanical studies to be comparable with the meniscectomized state. Purpose: To quantify the tibiofemoral contact pressure and contact area changes that occur in cadaveric knees from complete posterior horn radial tears and subsequent repairs of the medial meniscus adjacent to the posterior root attachment site. Study Design: Controlled laboratory study. Methods: Six nonpaired fresh-frozen human cadaveric knees each underwent 45 different testing conditions: 9 medial meniscus conditions (intact, root avulsion, root repair, serial radial tear at 3, 6, and 9 mm from the root attachment site, and in situ repair at the same 3 distances from the root attachment site) at 5 flexion angles (0°, 30°, 45°, 60°, and 90°), under a 1000-N axial load. Tekscan sensors were used to measure contact area and pressure in the medial and lateral compartments. Results: The medial meniscus root avulsion and all radial tear conditions resulted in significantly decreased contact area and increased mean contact pressure compared with the intact state for knee flexion angles beyond 0° (P < .05). The root repair and in situ repairs restored contact area and pressure to levels statistically indistinguishable from those of the intact meniscus and increased contact area and decreased contact pressure compared with the corresponding tear conditions. Conclusion: Posterior horn radial tears adjacent to the medial meniscus root that extend to the meniscocapsular junction can lead to derangement of the loading profiles of the medial compartment that are similar to a root avulsion. Repair of these radial tears with an in situ pull-out technique restored joint mechanics to the intact state. Clinical Relevance: Complete radial tears of the posterior horn of the medial meniscus, which occur relatively frequently, are biomechanically equivalent to root avulsions and could potentially lead to medial compartment arthrosis. An in situ repair offers an alternative treatment to meniscectomy and can reestablish the posterior anchor point, thus improving load distribution in the medial compartment. Future clinical studies of these repairs are recommended.

Effect of Ulnar Ostectomy on Intra‐Articular Pressure Mapping and Contact Mechanics of the Congruent and Incongruent Canine Elbow Ex Vivo

To determine (1) the effect of elbow incongruity on contact mechanics and (2) the effect of treatment of this incongruity with 1 of 2 ulnar ostectomies in the canine elbow. Ex vivo biomechanical study. Unpaired cadaveric canine forelimbs (n = 17). In a servohydraulic testing frame, thin-film pressure sensors were placed into the lateral and medial compartments of the elbow. Specimens were tested in 135° of elbow joint flexion at 200 N of cyclic axial force, followed by a 20 seconds hold. Intra-articular contact area (CA), mean contact pressure (mCP) and peak contact pressure (pCP) were measured in each compartment. After radial shortening, testing was repeated and limbs randomized into proximal ulnar ostectomy with IM pin (PUO) or sequential distal ulnar ostectomy (DUO), interosseous ligament release (DUO-L), and ulnar attachment of the abductor pollicis longus muscle and interosseous membrane release (DUO-ML). Paired t-tests were used to compare each treatment to baseline values. Differences between treatment groups were evaluated with a mixed model with random effect to adjust for the clustering of limbs within dog. P < .05 was considered significant. Radial shortening resulted in shift of mCP and pCP from the lateral to the medial compartment. The PUO group resulted in normalization of medial compartment mCP and decrease of pCP, whereas in the DUO group return to baseline was achieved only after DUO-ML. PUO is effective in unloading medial compartment pCP in an incongruent joint.

Tire rating based on soil compaction capacity

Compaction Capacity (CC) rating of tires presents a unique numerical CC index evaluating soil compaction risk of loaded tires. The CC rating presented here is a final product of experimental research and analysis of relations between external load and soil compaction, avoiding the intermediary role of soil stress. The research included laboratory model measurements of soil compaction by rigid round pressure plates in a cylindrical soil container. Equation for the CC index reads: CC=1000 [(soil dry density/1420)−1], where the number 1420 indicates the dry density of loam in kg/m3, critical for plant growth. The CC rating takes into account the area of tire−ground contact patch and tire load, which depends on inflation pressure. If the average dry density is 10% higher than the critical dry density, the CC index equals 100. This is considered as a practical limit to ecological tire operation on cultivated crop-producing land. Agricultural tires with mean contact pressures less than 70kPa have zero CC index. Their qualities are classified by Low Compaction Capacity (LCC) index based on 1290kg/m3 soil dry density. Both the CC and LCC indices do not distinguish between towed and driven wheels. The tables in this paper show how these simple indices can complement load data published by tire manufacturers.

Evaluation of contact characteristics of a patient-specific artificial dysplastic hip joint.

This study addresses the results of the experimental measurements for the contact surface areas and contact pressure distributions of a dysplastic hip joint. The hip joint consists of pelvis, proximal femur and artificial cartilages for both acetabulum and femoral head. The dysplastic hip joint is modeled in three dimensional (3D) form using the computerized tomography (CT) images obtained in vivo of an adult female patient. The modeled hip joint components are manufactured as a non-natural dysplastic hip joint using different materials and manufacturing processes. The dysplastic hip joint produced is subjected to compression forces experimentally to measure the contact surface area and contact pressure distributions between the femoral head and acetabulum using the pressure sensitive Fuji film. Different types of specific fixtures and molds are designed and manufactured to produce the dysplastic hip joint components and perform the experimental studies. The measured results using a non-natural dysplastic hip joint are compared with relevant results reported in current literature considering the peak and mean contact pressure values. Therefore, the obtained results showed that the non-natural dysplastic hip models can be generated and replaced to determine the contact characteristics for an elusive cadaveric model. In conclusion, the artificial models might be useful to understand the contact pressure distributions and potential changes in surface pressure contours and their effects on the stress distributions.

What’s New in Shoulder and Elbow Surgery

This annual update on shoulder and elbow surgery is based on a review of presentations at meetings of the Arthroscopy Association of North America (Specialty Day, March 25, 2006, Chicago, Illinois; Twenty-fifth Annual Meeting, May 18 to 21, 2006, Hollywood, Florida), the American Shoulder and Elbow Surgeons (Twenty-second Open Meeting, Specialty Day, March 25, 2006, Chicago, Illinois; Twenty-third Closed Meeting, September 13 to 15, 2006, Chicago, Illinois), The American Orthopaedic Society for Sports Medicine (Specialty Day, March 25, 2006, Chicago, Illinois), the American Academy of Orthopaedic Surgeons (Seventy-third Annual Meeting, March 22 to 25, 2006, Chicago, Illinois), and the Orthopaedic Research Society (Fifty-second Annual Meeting, March 19 to 22, 2006, Chicago, Illinois). ### Rotator Cuff #### Basic Science Park proposed a transosseous equivalent rotator cuff repair technique and performed a biomechanical study to evaluate footprint contact pressure in a variety of repair configurations. A “suture-bridging” technique utilizing medial anchors with suture limbs traversing over the cuff to a lateral interference screw attachment was compared with a double-row anchor repair. A four-limb suture bridge (two medial anchors with four limbs over the cuff laterally) established a significantly higher mean contact pressure area (72.3%) compared with a two-limb suture bridge (57.3%) and a double-row repair (35.1%) (p < 0.05). The authors concluded that increasing footprint contact pressure may aid in rotator cuff healing. #### Impingement Milano investigated the influence of acromioplasty on outcome following arthroscopic rotator cuff repair. Eighty patients were prospectively randomized into two groups, with half undergoing rotator cuff repair with acromioplasty and half undergoing rotator cuff repair without acromioplasty. The outcome measures that were evaluated were the Constant score and the Quick-DASH and Work-DASH self-administered questionnaires. Comparison between the two groups failed to demonstrate a significant difference at two years of follow-up. The authors concluded that acromioplasty does not affect the outcome of arthroscopic rotator cuff repair. …

Influence of microstructure on nano-mechanical properties of single planar solid oxide fuel cell in pre- and post-reduced conditions

The present work investigates, both the macro- and nano-mechanical properties of all the three component layers e.g., anode, cathode and electrolyte of a planar single solid oxide fuel cell (SOFC). The flexural fracture strength experiments in three point bending mode are employed in both pre- and post-reduced conditions to study the macro-mechanical failure behavior of the single cell. Further, the nanoindentation technique is utilized in both pre- and post-reduced conditions to evaluate the nanomechanical properties e.g. nanohardness, Young’s modulus, mean contact pressure, relative stiffness and relative spring back at scale in both pre- and post-reduced conditions. The nanohardness and Young’s modulus of the pre-reduced anode are considerably degraded after reduction as NiO gets converted to Ni. However, as expected; those of the pre-reduced electrolyte and cathode are only slightly decreased after reduction because there are no chemical conversions involved. Further, the experimentally obtained data of nanomechanical properties, is explained with the application of the well established Weibull statistics as the microstructures with characteristically present pores and defects are highly heterogeneous in nature. The characteristic values of the various nanomechanical properties are analyzed using Weibull distribution for the anode, electrolyte and cathode layers of the SOFC in both pre- and post-reduced conditions.

A Variable-Impedance Prosthetic Socket for a Transtibial Amputee Designed from Magnetic Resonance Imaging Data

ABSTRACTThis article evaluates the design of a variable impedance prosthetic (VIPr) socket for a transtibial amputee using computer-aided design and manufacturing (CAD/CAM) processes. Compliant features are seamlessly integrated into a three-dimensional printed socket to achieve lower interface peak

Effectiveness of surgical reconstruction to restore radiocarpal joint mechanics after scapholunate ligament injury: An in vivo modeling study

Disruption of the scapholunate ligament can cause a loss of normal scapholunate mechanics and eventually lead to osteoarthritis. Surgical reconstruction attempts to restore scapholunate relationship show improvement in functional outcomes, but postoperative effectiveness in restoring normal radiocarpal mechanics still remains a question. The objective of this study was to investigate the benefits of surgical repair by observing changes in contact mechanics on the cartilage surface before and after surgical treatment. Six patients with unilateral scapholunate dissociation were enrolled in the study, and displacement driven magnetic resonance image-based surface contact modeling was used to investigate normal, injured and postoperative radiocarpal mechanics. Model geometry was acquired from images of wrists taken in a relaxed position. Kinematics were acquired from image registration between the relaxed images, and images taken during functional loading. Results showed a trend for increase in radiocarpal contact parameters with injury. Peak and mean contact pressures significantly decreased after surgery in the radiolunate articulation and there were no significant differences between normal and postoperative wrists. Results indicated that surgical repair improves contact mechanics after injury and that contact mechanics can be surgically restored to be similar to normal. This study provides novel contact mechanics data on the effects of surgical repair after scapholunate ligament injury. With further work, it may be possible to more effectively differentiate between treatments and degenerative changes based on in vivo contact mechanics data.

Scapholunate ligament injury adversely alters in vivo wrist joint mechanics: An MRI‐based modeling study

We investigated the effects of scapholunate ligament injury on in vivo radiocarpal joint mechanics using image-based surface contact modeling. Magnetic resonance images of 10 injured and contralateral normal wrists were acquired at high resolution (hand relaxed) and during functional grasp. Three-dimensional surface models of the radioscaphoid and radiolunate articulations were constructed from the relaxed images, and image registration between the relaxed and grasp images provided kinematics. The displacement driven models were implemented in contact modeling software. Contact parameters were determined from interpenetration of interacting bodies and a linear contact rule. Peak and mean contact pressures, contact forces and contact areas were compared between the normal and injured wrists. Also measured were effective (direct) contact areas and intercentroid distances from the grasp images. Means of the model contact areas were within 10 mm(2) of the direct contact areas for both articulations. With injury, all contact parameters significantly increased in the radioscaphoid articulation, while only peak contact pressure and contact force significantly increased in the radiolunate articulation. Intercentroid distances also increased significantly with injury. This study provides novel in vivo contact mechanics data from scapholunate ligament injury and confirms detrimental alterations as a result of injury.

Biomechanical consequences of a posterior root tear of the lateral meniscus: stabilizing effect of the meniscofemoral ligament

The purpose of this study was to evaluate the effects of different types of lateral meniscus root tears in terms of tibiofemoral contact stress. Ten porcine knees each underwent five different testing conditions with the menisci intact, a simulated lateral posterior root tear with and without cutting the meniscofemoral ligament and with an artificial tear of the posterior root of the medial meniscus. Biomechanical testing was performed at 30° of flexion with an axial load of 100N. A pressure sensor (st Sensor Type S2042, Novel, Munich) was used to measure the tibiofemoral contact area and the tibiofemoral contact pressure. Data were analyzed to assess the differences in contact area and tibiofemoral peak contact pressure among the five meniscal conditions. There was no significant difference in mean contact pressure between the state with the menisci intact and an isolated posterior root tear of the lateral meniscus. In case of a root tear and a tear of the meniscofemoral ligament, the contact area decreased in comparison with the intact state of the menisci. After additional cutting of the meniscofemoral ligament, the tibiofemoral contact pressure was significantly higher in comparison with the intact state and the avulsion injury. In the medial compartment, joint compression forces were significantly increased in comparison with the intact state after cutting the posterior root of the medial meniscus (P<0.05). The consequence of a medial meniscus root tear is well known and was verified by this analysis. The results of the present study show that the biomechanical consequences of a lateral meniscus root tear depend on the state of the meniscofemoral ligament. An increase in tibiofemoral contact pressure is only to be expected in combined injuries of the meniscus root and the meniscofemoral ligaments. Posterior lateral meniscus root tear might have a better prognosis in terms of the development of osteoarthritis when the meniscofemoral ligament is intact.

Effect of lateral meniscectomy and osteochondral grafting of a lateral femoral condylar defect on contact mechanics: a cadaveric study in dogs

BackgroundOsteochondral autograft transfer (OAT) aims at restoring normal articular cartilage surface geometry and articular contact mechanics. To date, no studies have evaluated the contact mechanics of the canine stifle following OAT. Additionally, there are no studies that evaluated the role of the meniscus in contact mechanics following OAT in human or canine femorotibial joints. The objective of this study was to measure the changes in femorotibial contact areas (CA), mean contact pressure (MCP) and peak contact pressure (PCP) before and after osteochondral autograft transplantation (OAT) of a simulated lateral femoral condylar cartilage defect with an intact lateral meniscus and following lateral meniscectomy.ResultsWith an intact lateral meniscus, creation of an osteochondral defect caused a decrease in MCP and PCP by 11% and 30%, respectively, compared to the intact stifle (p < 0.01). With an intact meniscus, implanting an osteochondral graft restored MCP and PCP to 96% (p = 0.56) and 92% (p = 0.41) of the control values. Lateral meniscectomy with grafting decreased CA by 54% and increased PCP by 79% compared to the intact stifle (p < 0.01).ConclusionsOAT restored contact pressures in stifles with a simulated lateral condylar defect when the meniscus was intact. The lateral meniscus has a significant role in maintaining normal contact pressures in both stifles with a defect or following OAT. Meniscectomy should be avoided when a femoral condylar defect is present and when performing OAT.

Analysis of the effect of nano-roughness on the friction of a vitreous polymer

The rheological behavior at the interface between a polymer surface and a rigid indenter during dry friction is linked to the local pressure and the roughness of the surface of the indenter. This study analyzed experimental results for the friction coefficient μ versus the mean contact pressure pmean obtained at ambient temperature on polycarbonate. The rigid indenters consisted of spherical glass tips of several radii having surfaces of two types: polished to tight tolerance (optical lenses) or nano-roughened (chemical etching). Below the yield stress (pmean<100MPa), the intrinsic friction coefficient followed a master curve for smooth indenters whereas nano-roughnesses reduced the friction (from 5.5 to 140nm Rrms). To explain these experimental results an original model based on the classical laws of contact mechanics was developed and provides a basis to study the rheology of confined polymer layers.

On the Appropriate Use of Representative Stress Quantities at Correlation of Spherical Contact Problems

Correlation of contact problems is discussed in a detailed manner with focus on spherical contact. The finite element method is used to determine appropriate stress quantities, representative stresses, aiming at a general description of contact quantities such as mean contact pressure, and the size of the contact area. It is shown that the mean contact pressure can be well described by a single master curve, while this is not so for the size of the contact area. The latter feature is explained partly by a pronounced effect from elastic deformation, but is also shown that large deformation effects can have a substantial influence on correlation attempts. The analysis is restricted to classical Mises elastoplasticity, but the results can also serve as a guideline for similar attempts when using more advanced constitutive modeling. An obvious application of the present results concerns material characterization by indentation testing.