An EFE model on skin-sleeve interactions during arm rotation

Skin and garment constitute a dynamic contact system for human body comfort and protection. Although dermatological injuries due to fabric actions during human body movement are common, there is still no general guidance or standard for measuring or evaluating skin/garment contact interactions, especially, during intense sports. A three-dimensional explicit finite element (EFE) model combined with Augmented Lagrange algorithm (ALA) is developed to simulate interactions between skin and fabric during rotation of the arm. Normalized effective shear stresses at the interface between skin and the sleeve during the arm rotation are provided to reflect the severity of the interactions. The effects due to changes in fabric properties, fabric-skin gap, and arm rotation rate are also illustrated. It has been demonstrated from our predictions that factors such as elastic modulus, friction coefficients, density of fabric, and the initial gap between skin and fabric influence significantly the shear stress and thus the discomfort and even injury potential to skin during intensive body movement such as sports and military. Thus this study for the first time confirms quantitatively that poorly chosen fabric with inappropriate garment design renders adverse actions on human skin.     

Development of a pressure-measuring device to optimize compression treatment of lymphedema and evaluation of change in garment pressure with simulated wear and tear

The use of compression garments in treating lymphedema following treatment of genital (penis, testes, uterus, cervical) and breast cancer treatment is a well-established practice. Although compression garments are classified in compression classes, little is known about the actual subgarment pressure exerted along the extremity. The aims of this study were to establish an in vitro method for measuring subgarment pressure along the extremity and to analyze initial and over time subgarment pressure of compression garments from three manufacturers. The measurements were performed with I-scan(?) (Tekscan Inc.) pressure measuring equipment once a week during a period of 4 weeks. Wear and tear was simulated by washing and putting on the garments on plastic legs every day. There was a statistically significant difference between the garments of some of manufacturers. There was no difference between garments from the same manufacturer. No significant decrease of subgarment pressure was observed during the trial period. The study demonstrated that Tekscan pressure-measuring equipment could measure subgarment pressure in vitro. The results may indicate that there was a difference in subgarment pressure exerted by garments from different manufacturers and that there was no clear decrease in subgarment pressure during the first four weeks of usage.     

A piece-wise non-linear elastic stress expression of human and pig coronary arteries tested in vitro.

Eight human and nineteen pig unembalmed proximal left anterior descending and circumflex coronary arteries were subjected to linear volume changes (2 s ramp time) at three fixed axial extensions while immersed in a physiological saline bath at body temperature. Measured parameters included: lumen pressure, outside diameter, axial force, and axial extension. The deformations were measured using a video dimensional analyzer. The arteries were inflated to pressures well above the physiological range at each axial extension. A latex inner tube was placed inside of each specimen to prevent leakage, and its effects upon the measured stresses were corrected analytically. With this method, the average circumferential and axial stresses could be computed directly from the experimental data. In both directions the average stresses measured displayed two distinct regions: stresses occurring for small diameter changes (physiological pressures) and stresses occurring for large diameter changes (high pressures). The resulting average small strain and large strain stress components were curve-fit separately and, when reassembled, provided a piece-wise model of the stress response of coronary arteries over a wide range of inflation pressures and axial extensions.     

Residual stress and strain in aortic segments

In the study of stresses and strains in vascular segments, it is generally assumed that the traction-free configuration assumed by a segment when there is no axial force and there are no intravascular and extravascular pressures is stress-free. To investigate the degree of validity of this assumption, 286 oval shaped rings were excised from three bovine and six porcine aortas and photographed. Radial cuts were made in these rings which opened up into horseshoe shapes and were also photographed. Smoothed boundary lengths at intimal and adventitial levels in the rings and their cut open configurations were measured from the photographs and the residual strains in the annular configuration relative to the open configuration were computed. It was found that: the average maximum residual intimal engineering strain in the uncut configuration was -0.082 for all nine aortas and -0.096 and -0.077 for the bovine and porcine aortas alone, respectively; the average maximum residual adventitial strain was 0.085 for all aortas, and 0.102 and 0.078 for the bovine and porcine aortas alone, respectively; an estimated average beneficial compressive stress of -0.188 X 10(5) Pa (corresponding to a strain level of -0.082) is available at the intimal level to counteract the in vivo tensile stress due to the intravascular pressure; an estimated average initial tensile stress of 0.195 X 10(5) Pa (corresponding to a strain level of 0.085) exists at the adventitial level which adds to the in vivo tensile stress due to the intravascular pressure. Although these stress levels are not large in comparison with the in vivo stress in the arterial wall, a detailed stress analysis must take into account these initial stresses.     

Effects of an improved biomechanical backpack strap design on load transfer to the shoulder soft tissues

The aim of the present study was to characterize shoulder strap structure and mechanical properties that may alleviate strains and stresses in the soft tissues of the shoulder. Utilizing a finite element model of the shoulder constructed from a single subject, we have quantified skin stresses exerted by backpack straps and the strains at the subclavian artery (SCA). For this end, standard shape straps with stiffness of 0.5, 1.2, and 5 MPa, were compared to the effects of optimized straps; a double-layered (soft outer layer and reinforced internal supporting layer) and newly-designed anatomically-shaped strap. Compared to the standard 0.5 MPa strap, the 5 MPa strap resulted in 4-times lower SCA strains and 2-times lower Trapezius stresses. The double-layered strap resulted in 40% and 50% reduction in SCA strains and skin stresses, respectively, with respect to the softer strap. The newly-designed anatomical strap exerted 4-times lower SCA strains and 50% lower skin stresses compared to the standard strap. This demonstrates a substantial improvement to the load carriage ergonomics when using a composite anatomical strap.     

Method for characterizing viscoelasticity of human gluteal tissue

Characterizing compressive transient large deformation properties of biological tissue is becoming increasingly important in impact biomechanics and rehabilitation engineering, which includes devices interfacing with the human body and virtual surgical guidance simulation. Individual mechanical in vivo behaviour, specifically of human gluteal adipose and passive skeletal muscle tissue compressed with finite strain, has, however, been sparsely characterised. Employing a combined experimental and numerical approach, a method is presented to investigate the time-dependent properties of in vivo gluteal adipose and passive skeletal muscle tissue. Specifically, displacement-controlled ramp-and-hold indentation relaxation tests were performed and documented with magnetic resonance imaging. A time domain quasi-linear viscoelasticity (QLV) formulation with Prony series valid for finite strains was used in conjunction with a hyperelastic model formulation for soft tissue constitutive model parameter identification and calibration of the relaxation test data. A finite element model of the indentation region was employed. Strong non-linear elastic but linear viscoelastic tissue material behaviour at finite strains was apparent for both adipose and passive skeletal muscle mechanical properties with orthogonal skin and transversal muscle fibre loading. Using a force-equilibrium assumption, the employed material model was well suited to fit the experimental data and derive viscoelastic model parameters by inverse finite element parameter estimation. An individual characterisation of in vivo gluteal adipose and muscle tissue could thus be established. Initial shear moduli were calculated from the long-term parameters for human gluteal skin/fat: G(∞,S/F)=1850 Pa and for cross-fibre gluteal muscle tissue: G(∞,M)=881 Pa. Instantaneous shear moduli were found at the employed ramp speed: G(0,S/F)=1920 Pa and G(0,M)=1032 Pa.     

Assessment of mechanical conditions in sub-dermal tissues during sitting: a combined experimental-MRI and finite element approach

A common but potentially severe malady afflicting permanent wheelchair users is pressure sores caused by elevated soft tissue strains and stresses over a critical prolonged period of time. Presently, there is paucity of information regarding deep soft tissue strains and stresses in the buttocks of humans during sitting. Strain and stress distributions in deep muscle and fat tissues were therefore calculated in six healthy subjects during sitting, in a double-donut Open-MR system, using a "reverse engineering" approach. Specifically, finite element (FE) models of the undeformed buttock were built for each subject using MR images taken at the coronal plane in a non-weight-bearing sitting posture. Using a second MR image taken from each subject during weight-bearing sitting we characterized the ischial tuberosity sagging toward the sitting surface in weight-bearing, and used these data as displacement boundary conditions for the FE models. These subject-specific FE analyses showed that maximal tissue strains and stresses occur in the gluteal muscles, not in fat or at the skin near the body-seat interface. Peak principal compressive strain and stress in the gluteus muscle were 74+/-7% and 32+/-9 kPa (mean+/-standard deviation), respectively. Peak principal compressive strain and stress in enveloping fat tissue were 46+/-7% and 18+/-4 kPa, respectively. Models were validated by comparing measured peak interface pressures under the ischial tuberosities (17+/-4 kPa) with those calculated by means of FE (18+/-3 kPa), for each subject. This is the first study to quantify sub-dermal tissue strain and stress distributions in sitting humans, in vivo. These data are essential for understanding the aetiology of pressure sores, particularly those that were recently termed "deep tissue injury" at the US National Pressure Ulcer Advisory Panel (NPUAP) 2005 Consensus Conference.     

Biomechanical modeling to prevent ischial pressure ulcers

With 300,000 paraplegic persons only in France, ischial pressure ulcers represent a major public health issue. They result from the buttocks? soft tissues compression by the bony prominences. Unfortunately, the current clinical techniques, with – in the best case – embedded pressure sensor mats, are insufficient to prevent them because most are due to high internal strains which can occur even with low pressures at the skin surface. Therefore, improving prevention requires using a biomechanical model to estimate internal strains from skin surface pressures. However, the buttocks? soft tissues? stiffness is still unknown. This paper provides a stiffness sensitivity analysis using a finite element model. Different layers with distinct Neo Hookean materials simulate the skin, fat and muscles. With Young moduli in the range [100–500 kPa], [25–35 kPa], and [80–140 kPa] for the skin, fat, and muscles, respectively, maximum internal strains reach realistic 50 to 60% values. The fat and muscle stiffnesses have an important influence on the strain variations, while skin stiffness is less influent. Simulating different sitting postures and changing the muscle thickness also result in a variation in the internal strains.     

Effect of skin pressure by clothing on small bowel transit time

We examined the effect of increased skin pressure from tight clothing on small bowel transit time by means of the breath hydrogen test, using milk that contained lactulose as an additional indigestible disaccharide, which is used as a test meal after overnight fasting. In this experiment, we measured the small bowel transit time from 9 healthy and non-constipated female subjects with two different skin pressures that were applied by loose-fitting experimental garment or an additional tight-fitting girdle on two consecutive days. The skin pressure of the latter condition was 8-9 mmHg higher than that of the former one on the participants' waist, abdomen and hip region. The experimental order of the two skin pressure conditions was counterbalanced. As a result, the small bowel transit time obtained with and without girdle did not differ significantly (165.0 +/- 26.0 minutes for less skin pressure condition and 173.3 +/- 26.8 minutes for more skin pressure condition, n = 9, p = 0.43). This result indicated that the skin pressure from clothing has no effect on the passage rate of food through the small intestine.     

Is obesity a risk factor for deep tissue injury in patients with spinal cord injury?

Deep tissue injury (DTI) is a severe form of pressure ulcers that occur in subcutaneous tissue under intact skin by the prolonged compression of soft tissues overlying bony prominences. Pressure ulcers and DTI in particular are common in patients with impaired motosensory capacities, such as those with a spinal cord injury (SCI). Obesity is also common among subjects with SCI, yet there are contradicting indications regarding its potential influence as a risk factor for DTI in conditions where these patients sit in a wheelchair without changing posture for prolonged times. It has been argued that high body mass may lead to a greater risk for DTI due to increase in compressive forces from the bones on overlying deep soft tissues, whereas conversely, it has been argued that the extra body fat associated with obesity may reduce the risk by providing enhanced subcutaneous cushioning that redistributes high interface pressures. No biomechanical evaluation of this situation has been reported to date. In order to elucidate whether obesity can be considered a risk factor for DTI, we developed computational finite element (FE) models of the seated buttocks with 4° of obesity, quantified by body mass index (BMI) values of 25.5, 30, 35 and 40 kg/m². We found that peak principal strains, strain energy densities (SED) and von Mises stresses in internal soft tissues (muscle, fat) overlying the ischial tuberosities (ITs) all increased with BMI. With a rise in BMI from 25.5 to 40 kg/m², values of these parameters increased 1.5 times on average. Moreover, the FE simulations indicated that the bodyweight load transferred through the ITs has a greater effect in increasing internal tissue strains/stresses than the counteracting effect of thickening of the adipose layer which is concurrently associated with obesity. We saw that inducing some muscle atrophy (30% reduction in muscle volume, applied to the BMI=40 kg/m² model) which is also characteristic of chronic SCI resulted in further substantial increase in all biomechanical measures reflecting geometrical distortion of muscle tissue, that is, SED, tensile stress, shear stress and von Mises stress. This result highlights that obesity and muscle atrophy, which are both typical of the chronic phase of SCI, contribute together to the state of elevated tissue loads, which consequently increases the likelihood of DTI in this population.     

Effect of shape and size of lung and chest wall on stresses in the lung.

Conflicting results have been reported on the changes in the distribution of pleural pressures caused by alterations of chest shape. To understand better the effect of shape and size of lung and chest wall on the distribution of stresses, strains, and surface pressures, we analyzed a theoretical model using the technique of finite elements. The study was in two parts. First we investigated the effects of changing the chest wall shape during expansion, and second we studied lungs of a variety of inherent shapes and sizes. We found that, in general, the distributions of alveolar size, mechanical stresses, and surface pressures in the lungs were dominated by the weight of the lung and that changing the shape of the lung or chest wall had relatively little effect. Only at high states of expansion where the lung was very stiff did changing the shape of the chest wall cause substantial changes. Altering the inherent shape of the lung generally had little effect but the topographical differences in stresses and surface pressures were approximately proportional to lung height. The results are generally consistent with those found in dog by Hoppin et al. (J. Appl. Physiol. 27: 863-873, 1969).     

A computational model of blast loading on the human eye

Ocular injuries from blast have increased in recent wars, but the injury mechanism associated with the primary blast wave is unknown. We employ a three-dimensional fluid–structure interaction computational model to understand the stresses and deformations incurred by the globe due to blast overpressure. Our numerical results demonstrate that the blast wave reflections off the facial features around the eye increase the pressure loading on and around the eye. The blast wave produces asymmetric loading on the eye, which causes globe distortion. The deformation response of the globe under blast loading was evaluated, and regions of high stresses and strains inside the globe were identified. Our numerical results show that the blast loading results in globe distortion and large deviatoric stresses in the sclera. These large deviatoric stresses may be indicator for the risk of interfacial failure between the tissues of the sclera and the orbit.     

Morphogenetic interactions between rotated skin cuffs and underlying stump tissues in regenerating axolotl forelimbs

Rotation of skin cuffs 180° around the longitudinal axis of the underlying tissues in the axolotl forelimb results in a high percentage of multiple regenerates after amputation through the rotated skin. Similar results occur after rotation of only the anteroposterior (A-P) axis of the skin. Rotation of only the proximodistal (Pr-Ds) axis of the skin results in normal regenerates whereas dorsoventral (D-V) axial skin rotation results in single regenerates with some disturbances in symmetry. Rotation of anterior or posterior half cuffs of skin produces results similar to those obtained after A-P rotation of full skin cuffs, and rotation of dorsal or ventral skin halves duplicates the results obtained by rotating full skin cuffs about the D-V axis. Skin cuffs rotated for periods from 6 months to over 2 years before amputation are also capable of causing multiple regenerates to form. No significant difference in the percentage of multiple regenerates was seen after skin rotation and limb amputation through shoulder, upper arm, and forearm levels. X-Radiation (4000 r) of either the skin or underlying tissues before skin rotation resulted in single regenerates after amputation. If a strip of normal skin was turned perpendicularly to the long axis of the irradiated underlying stump tissues, the regenerative response was blocked. In some of the above experiments, regenerates with longitudinally duplicated upper arm and forearm segments appeared. It is postulated that normally both the skin and the underlying limb tissues can influence morphogenesis during regeneration and that they work in harmony. In contrast, rotated skin and the underlying tissues each exert a morphogenetic influence upon the regenerating limb, and the regenerate is not able to integrate these disharmonious influences. This is reflected in the highly abnormal morphology of the regenerates. The nature of the morphogenetic influence disrupted by skin rotation is not yet known.     

Measurement of subcutaneous tissue fluid pressure using a skin-cup method

We developed a new method for measuring tissue fluid pressure in subcutaneous tissue. Porous Teflon cylinders were permanently implanted subcutaneously into the inguinal area of 10 dogs, and after several weeks a skin concavity formed in the center of each of the cylinders. A small needle attached to a recording system was inserted into the free tissue fluid lining the concavity, and the tissue fluid pressure averaged -8.8 +/- 2.7 (SD) mmHg. Next, a hollow Plexiglas cup was placed over the concavity and glued to the skin. The air pressure in the skin cup was continually adjusted (using an electromechanical servo-control system) to pull the skin upward and to hold it perfectly flat across the upper ridge of the Teflon cylinder. The simultaneously recorded needle and cup pressures averaged -9.1 +/- 2.4 and -8.6 +/- 2.6 mmHg, respectively, during steady-state conditions with the skin in a flat position. Both pressures also responded appropriately to dynamic changes in tissue fluid pressure caused by increasing and decreasing the volume of the free tissue fluid. Because the skin was flat, the equivalences of pressures above and below the skin is consistent with the hypothesis that the skin was not tethered significantly to the underlying tissues and that cup pressure accurately estimates the tissue free fluid pressure.     

Mechanotransduction in adipocytes

Obesity is widely recognized as a major public health problem due to its strong association with a number of serious chronic diseases including hyperlipidemia, hypertension, type II diabetes and coronary atherosclerotic heart disease. During the development of obesity, the positive energy balance involves recruitment of new adipocytes from preadipocytes in adipose tissue, which have proliferated and differentiated. Given that cells in adipose tissues are physiologically exposed to compound mechanical loading: tensile, compressive and shear strains/stresses, which are caused by bodyweight loads as well as by weight-bearing, it is important to determine whether the adipose conversion process is influenced by mechanical stimulations. In this article we provide a comprehensive review of the experimental studies addressing mechanotransduction in adipocytes, as well as of mathematical and computational models that are useful for studying mechanotransduction in adipocytes or for quantifying the responsiveness of adipocytes to different types of mechanical loading. The new understanding that adipogenesis is influenced by mechanical stimulations has the potential to open new and important research paths, driven by mechanotransduction, to explore mechanisms as well as treatment approaches in obesity and related conditions.     

Measuring skin dose in CT examinations under complex geometries: Instruments,methods and considerations

ObjectiveTo investigate skin dose in Computed Tomography (CT) and its dependence on scanning geometry.Materials and methodsMeasurements of entrance surface air kerma (ESAK) in free air and entrance skin dose (ESD) on an anthropomorphic phantom were performed in a 64-slice CT scanner, using two different instruments: the Dose Profiler (DP) and the QED skin diode (QEDSD). Using DP and QEDSD, the ESAK rate profiles at the isocenter and at different distances from it, were measured using axial scans. Using DP and helical scans the ESAK rate profile in the Z-axis was acquired. The same profile was acquired with the QEDSD also, using many axial scans and manual table translation. ESD measurements were performed with the DP and QEDSD, in axial and helical scan mode.ResultsESAK measurements with DP and QEDSD were in good agreement, for both point dose and profile measurements. The agreement was also good for ESD measurements but not for helical scans, due to variable X-ray beam overlapping and different tube angular positions at each scan start. It was observed that the ESD values at different Y-axis offsets were comparable to the respective ESAK values recorded at the same Y-axis offset distances without the phantom.ConclusionsBoth DP and QEDSD were proven suitable for performing point ESD measurements. However, calculating the skin dose distribution in CT examinations is a very challenging task. A practical approach would be for CT scanners to provide a conservative estimate of the peak skin dose using the isocenter ESAK value.     

Strains and stresses in sub-dermal tissues of the buttocks are greater in paraplegics than in healthy during sitting

A pressure-related deep tissue injury (DTI) is a severe pressure ulcer, which initiates in muscle tissue overlying a bony prominence (e.g. the ischial tuberosities, IT) and progresses outwards through fat and skin, unnoticed by the paralyzed patient. We recently showed that internal strains and stresses in muscle and fat of individuals at anatomical sites susceptible to DTI can be evaluated by integrating Open-MRI scans with subject-specific finite element (FE) analyzes (Linder-Ganz et al., Journal of Biomechanics, 2007); however, sub-dermal soft tissue strains/stresses from paraplegics are still missing in literature. We hypothesize that the pathoanatomy of the buttocks in paraplegia increases the internal soft tissue loads under the IT, making these patients inherently susceptible to DTI. We hence compared the strain and stress peaks in the gluteus muscle and fat tissues under the IT of six healthy and six paraplegic patients, using the coupled MRI-FE method. Peak principal compression, principal tension, von Mises and shear strains in the gluteus were 1.2-, 3.1-, 1.4- and 1.4-fold higher in paraplegics than in healthy, respectively (p<0.02). Likewise, peak principal compression, principal tension, von Mises and shear stresses in the gluteus were 1.9-, 2.5-, 2.1- and 1.7-fold higher for the paraplegics (p<0.05). Peak gluteal compression and shear stresses decreased by as much as 70% when the paraplegic patients moved from a sitting to a lying posture, indicating on the effectiveness of recommending such patients to lie down after prolonged periods of sitting. This is the first attempt to compare internal soft tissue loads between paraplegic and healthy subjects, using an objective standardized bioengineering method of analysis. The findings support our hypothesis that internal tissue loads are significantly higher in paraplegics, and that postural changes significantly affect these loads. The method of analysis is useful for quantifying the effectiveness of various interventions to alleviate sub-dermal tissue loads at sites susceptible to pressure ulcers and DTI, including cushions, mattresses, recommendations for posture and postural changes, etc.     

Dynamic measurement of the viscoelastic properties of skin

A wave propagation technique was used to measure the dynamic viscoelastic properties of excised skin when subjected to a low incremental strain. The propagation velocity, attenuation, and storage and loss moduli were determined from measured characteristics of a pulse propagating along a strip of skin. Experiments were conducted with the skin subjected to static stresses of 1500 Pa and 20,000 Pa. At low static stresses the skin response was viscoelastic with a loss tangent of approximately 0.6. In the frequency range of 0-1000 Hz, the wave velocity was relatively constant while the attenuation increased roughly linearly with frequency. However, results depended on the static stress. At the higher stress level the velocity was greater and the attenuation less than at the lower stress. At low stresses both the storage and loss moduli were relatively constant over the frequency range tested. The strong viscoelastic behavior of the tissue at higher frequencies is not predicted from models of the tissue determined from quasi-static test methods. In selecting a model to describe the behavior of skin, the test methods used for establishing the model must be consistent with its intended application.     

Mechanics of the human femoral adventitia including the high-pressure response

Adventitial mechanics were studied on the basis of adventitial tube tests and associated stress analyses utilizing a thin-walled model. Inflation tests of 11 nonstenotic human femoral arteries (79.3 +/- 8.2 yr, means +/- SD) were performed during autopsy. Adventitial tubes were separated anatomically and underwent cyclic, quasistatic extension-inflation tests using physiological pressures and high pressures up to 100 kPa. Associated circumferential and axial stretches were typically <20%, indicating "adventitiosclerosis." Adventitias behaved nearly elastically for both loading domains, demonstrating high tensile strengths (>1 MPa). The anisotropic and strongly nonlinear mechanical responses were represented appropriately by two-dimensional Fung-type stored-energy functions. At physiological pressure (13.3 kPa), adventitias carry ~25% of the pressure load in situ, whereas their circumferential and axial stresses were similar to the total wall stresses (~50 kPa in both directions), supporting a "uniform stress hypothesis." At higher pressures, they became the mechanically predominant layer, carrying >50% of the pressure load. These significant load-carrying capabilities depended strongly on circumferential and axial in-vessel prestretches (mean values: 0.95 and 1.08). On the basis of these results, the mechanical role of the adventitia at physiological and hypertensive states and during balloon angioplasty was characterized.     

Effect of superficial collagen patterns and fibrillation of femoral articular cartilage on knee joint mechanics-a 3D finite element analysis

Collagen fibrils of articular cartilage have specific depth-dependent orientations and the fibrils bend in the cartilage surface to exhibit split-lines. Fibrillation of superficial collagen takes place in osteoarthritis. We aimed to investigate the effect of superficial collagen fibril patterns and collagen fibrillation of cartilage on stresses and strains within a knee joint. A 3D finite element model of a knee joint with cartilage and menisci was constructed based on magnetic resonance imaging. The fibril-reinforced poroviscoelastic material properties with depth-dependent collagen orientations and split-line patterns were included in the model. The effects of joint loading on stresses and strains in cartilage with various split-line patterns and medial collagen fibrillation were simulated under axial impact loading of 1000 N. In the model, the collagen fibrils resisted strains along the split-line directions. This increased also stresses along the split-lines. On the contrary, contact and pore pressures were not affected by split-line patterns. Simulated medial osteoarthritis increased tissue strains in both medial and lateral femoral condyles, and contact and pore pressures in the lateral femoral condyle. This study highlights the importance of the collagen fibril organization, especially that indicated by split-line patterns, for the weight-bearing properties of articular cartilage. Osteoarthritic changes of cartilage in the medial femoral condyle created a possible failure point in the lateral femoral condyle. This study provides further evidence on the importance of the collagen fibril organization for the optimal function of articular cartilage.