Total Contact Area Research Articles

Foot Function In Extinct Bipeds: Does The Laetoli G1 Individual Exhibit A Modern Footprint Shape?

PURPOSE: Because the foot serves as the critical interface between the body and its support, the foot has long been assumed to be optimized for an animal's activities of daily living. Primate quadrupeds, on the one hand, have abducted great toes and mobile feet that bend at the tarso-metatarsal junction, potentially to conform to cylindrical substrates. On the other hand, humans are characterized as having feet with an arch that is rigid at toe-off but more flexible during stance. The human arch creates a footprint shape that is classically depicted as having midfoot contact area only along the lateral border. The G1 footprints from the Laetolil Formation, Tanzania dated at 3.6 million years ago are said to exhibit this modern appearance, supporting the notion that foot shape has remained relatively unchanged since the origins of bipedalism. Recent evidence based on fossilized foot bones calls this assumption into question. Modern human feet, however, do not all exhibit the classic shape so we undertook a study to determine if the shape of the Laetoli footprints fall within the modern human distribution. METHODS: In order to assess quantitatively the variation in modern footprint shape, the footprints of 160 walking adults (115 women and 45 men) with no history of foot and ankle pain were collected using a pressure sensitive mat (RSScan, RSScan International, Olen, Belgium). Nine prints from the Laetoli G1 trail (right G1-26, -34, and -36; left: G1-25, -27, -33, -35, -37 and -39) were digitized using a single topographic line to represent the footprint outline from drawings available in the literature. Footprint shape was assessed using the arch index, the ratio of midfoot to total foot contact area, and the Laetoli prints were compared to the modern distribution. RESULTS: The G1 individual's prints are planus (AI= 0.36 (right) and=0.34 (left)), but they fall within the modern human range (AI range: 0 - 0.38), albeit at the flat-footed margin. CONCLUSIONS: The individual which made the Laetoli G1 trail likely engaged in normal activities similar to modern humans, including habitual bipedal walking.

Plantar Pressure Differences Between Genders When Comparing Racing Flats and Traditional Training Shoes

With the increasing popularity of running around the world available shoe types have been increasing. Racing flats have begun to be used not only as a racing shoe, but also for daily training. It has been suggested that decreased cushioning in racing flats could lead to increased plantar loading, which has been linked to an increased risk of lower leg injuries. Previous reports have indicated that lower leg injury risk is gender dependent. PURPOSE: To determine differences in plantar pressure distributions between men and women when running in training shoes and racing flats. METHODS: Each subject was asked to run over-ground at a self-selected speed 7 times in each shoe while in-shoe plantar pressure data were collected at 50 Hz. Contact area (CA), maximum force (MF), and contact time under the entire foot as well as beneath the medial midfoot (MMF), lateral midfoot (LMF), medial forefoot (MFF), middle forefoot (MiFF), and lateral forefoot (LFF) were obtained. CA was normalized to total insole contact area and MF was normalized to body weight. Shoe testing order was randomized to avoid fatigue effects. No significant running speed differences existed, therefore, each variable was analyzed using a 2×2 (shoe x gender) repeated measures ANOVA (a=0.05). RESULTS: In men, MF was increased in the racing flats (p=0.016) in the MMF, yet was increased at the MFF in the training shoe (p=0.018). Independent of gender, CA was decreased in the racing flats beneath the entire foot (p=0.029) and in the MMF (p=0.013) and MFF (p=0.030), and increased in the LFF (p=0.023). In the racing flats MF was increased beneath the entire foot (p<0.001) and the LFF (p<0.001). Independent of the shoe, CA was decreased in men beneath the MFF (p=0.007) and MiFF (p<0.001), while MF was increased in the LFF (p=0.002). CONCLUSIONS: These results indicate that racing flats increase loading beneath the total foot and in the LFF. The LFF is an area of increased stress fracture risk specifically in men, who also demonstrated an increase in MF in this region. Based on the gender differences in loading, it appears that running shoe design and cushioning should be gender specific in an attempt to prevent injuries. It is possible that wearing racing flats for high mileage running coupled with the observed increases in loading could be a factor in lower limb injuries.

Establishing safety limits for transcranial direct current stimulation

Establishing safety limits for transcranial direct current stimulation

An increase in thermodynamic efficiency and compactness of contact apparatuses via spatially organized structure of the active material bed

The possibility of filling the hollow input (diffuser) and output (confuser) sections of contact apparatuses by an active material is analyzed. The equation determining the distribution function of the sizes of material particles along the axis of a conelike apparatus, which provides the minimum volume of the bed of particles at the specified values of the total surface area of the interfacial contact in the bed and total flow resistance of the bed, is derived. It is shown that the change in the conventional shape of the apparatus to a construction in the form of a junction of two truncated cones filled with the active material allows one to decrease the total volume of the apparatus by 30%. The dependence of the thermodynamic efficiency and compactness of the regenerative facility on the particle size of the active material bed is numerically analyzed. The existence of a critical particle size which determines the minimum necessary volume of the bed providing high thermodynamic efficiency of the process is shown.

Effect of injury to plantar ligaments on plantar pressure distribution

Objective To explore the changes in plantar pressure distribution and contact area after injury to the plantar ligaments in a normal adult cadaveric model. Methods Seven fresh adult cadaverie feet were used in the test. F-scan insoles were put under the plantar aspect of the feet when the specimens were loaded to 700 N vertieally. The plantar pressure data in the specimens were collected and stored before and after the plantar fascia, spring ligament, short plantar ligament and long plantar ligament were sectioned. Results were statistically analyzed. Results The peak pressure was always observed at the hindfoot area in all conditions. The peak plantar pressure on the forefoot was observed at the third metatarsal area and in-creased when the plantar ligaments were sectioned, while the total contact area of the foot was constant in both intact and pathological situations. Conclusion After the plantar ligaments are injured, the plantar pressure of the foot changes significantly and the pressure concentration occurs at the lateral foot, which may lead to clinical symptoms. Key words: Foot injury; Ligaments; Plantar pressure; Biomechanies

Can foot anthropometric measurements predict dynamic plantar surface contact area?

BackgroundPrevious studies have suggested that increased plantar surface area, associated with pes planus, is a risk factor for the development of lower extremity overuse injuries. The intent of this study was to determine if a single or combination of foot anthropometric measures could be used to predict plantar surface area.MethodsSix foot measurements were collected on 155 subjects (97 females, 58 males, mean age 24.5 ± 3.5 years). The measurements as well as one ratio were entered into a stepwise regression analysis to determine the optimal set of measurements associated with total plantar contact area either including or excluding the toe region. The predicted values were used to calculate plantar surface area and were compared to the actual values obtained dynamically using a pressure sensor platform.ResultsA three variable model was found to describe the relationship between the foot measures/ratio and total plantar contact area (R2 = 0.77, p < 0.0001)). A three variable model was also found to describe the relationship between the foot measures/ratio and plantar contact area minus the toe region (R2 = 0.76, p < 0.0001).ConclusionThe results of this study indicate that the clinician can use a combination of simple, reliable, and time efficient foot anthropometric measurements to explain over 75% of the plantar surface contact area, either including or excluding the toe region.

FMF-06 CONTACT CHARACTERISTICS OF A RUBBER ROLLER AND A FLEXIBLE MEDIUM(Flexible Media Feeding and Handling Machines II,Technical Program of Oral Presentations)

A method for of numerically calculating the asperity contact mechanics between a rubber roller and a smooth sheet was developed by considering the van der Waals force at the contacting asperities. As the rms asperity height decreased, adhesion and a jump-in contact phenomenon were observed. When the friction force was assumed to be proportional to either the total contact area or the real contact force, the obtained friction coefficient was decreased with an increase in the applied load.

The biomechanical implications of wearing ill-fitting shoes

No research has ever been performed to investigate the effects that ill-fitting shoegear have on the biomechanics of the feet. This project investigated changes in peak pressures and total contact area of the foot during walking as based on the rearfoot, midfoot, and forefoot in different shoegear conditions. Subjects were fitted with appropriately sized shoes, and either shoes that were one size too small or shoes that were one size too large. Data was collected using the Pedar © system. Our results cannot be analyzed by statistical means because of the small enrollment in our study. But, shoes are beneficial to the feet regardless of what size shoe worn, because peak pressure is decreased over all areas of the foot. However, properly fitted shoes are superior to those that are one full size smaller or larger because they have the lowest peak pressures throughout the foot. Contact area is decreased in the proper shoe size as compared to the smaller shoe size. This was determined to be beneficial because of less shoe irritation, which can lead to ulceration or deformity. In the larger shoe, contact area remained the same, determined by the constant size of the foot, whereas the size of the shoe increased. Overall, a properly fitted shoe provides the greatest advantage over ill fitting shoes.

Poster 50: Evaluation of Ankle-Foot Orthoses on Plantar Contact Area and Loading at Footstrike in Cerebrovascular Accident

Objective: To assess the effect of an ankle-foot orthoses (AFO) on plantar contact area and loading during footstrike on the entire hemiplegic foot. Design: With and without design. Setting: Rehabilitation research center. Participants: 19 participants (age, 52.95±10.55y) with hemiplegia secondary to cerebrovascular accident (CVA). Interventions: Walking at a self-selected pace, with and without the AFO. Main Outcome Measures: Contact area as a percentage of total plantar contact area (in cm2) and loading force (in newtons) on the plantar surface of the affected limb during footstrike.

COMPUTER-BASED IDENTIFICATION OF PLANTAR PRESSURE IN TYPE 2 DIABETES SUBJECTS WITH AND WITHOUT NEUROPATHY

Diabetes mellitus is a medical disorder characterized by varying or persistent hyperglycemia (elevated blood sugar levels), especially after eating. People with diabetes have problems converting food to energy. The most common form of diabetes is type 2 diabetes. Foot disease is a common complication of diabetes that can have tragic consequences. Abnormal plantar pressures are considered to play a major role in the pathologies of neuropathic ulcers in the diabetic foot. The purpose of this study was to classify the plantar pressure distribution in normal and type 2 diabetes subjects with and without neuropathy. Foot scans were obtained using the F-Scan (Tekscan, USA) in-shoe pressure measurement system. Various pedobarographic parameters such as the total plantar force, total contact area, peak pressures, and percentage medial impulse (PMI) were evaluated. These parameters were subjected to analysis of variance (ANOVA) test with a &gt;95% confidence interval, giving excellent p-values in all of the categories. When these extracted parameters were presented to the artificial neural network (ANN) for classification, the neural network classifier was seen to be correct in more than 90% of the test cases.

Bone Cells Grown on Micropatterned Surfaces are More Sensitive to Fluid Shear Stress

Bone has the ability to adapt its structure to meet its mechanical environment. In spite of great efforts to understand the mechanisms underlying this phenomenon, little is known about bone mechanotransduction at the cellular level. In this work, we propose that there is an interaction between the architecture of the cell and mechanosensitivity. Specifically, we hypothesized that cell spreading plays an important role in bone cell mechanotransduction. To test our hypothesis, we utilized micropatterned surfaces that allowed us to control the degree of cell spreading. Focal adhesion area is also known to depend on cell spreading. Thus patterns were utilized that maintained a constant total adhesive contact area, but permitted differing degrees of spreading. MC3T3-E1 osteoblasts cultured on these patterned surfaces were exposed to dynamic fluid shear stress. The fluid flow-induced changes in intracellular calcium [Ca2+]i were determined as a function of the degree of spreading. Cells grown on micropatterned surfaces were more responsive in general than those grown on traditional unpatterned surfaces. Interestingly, however, we found that cells with a higher degree of spreading were less responsive to mechanical loading. This work provides new insights into the interplay of cellular structure and mechanotransduction.

Coordination measurements in compacted NaCl irregular powders using X-ray microtomography

X-ray microtomography and three-dimensional (3D) image analysis are used to quantify the structural evolution during cold isostatic compaction of two irregularly shaped NaCl powders having different mean particle sizes (75 and 400 μm) and somewhat different aspect ratios. Varying the compaction pressure to vary the powder packing density, the structure of the different packings is quantified in terms of the mean coordination number and of the mean contact area between contacting particles. These parameters are extracted using a 3D image analysis algorithm that is tested beforehand for consistency with compacted monosized sphere packings generated numerically. It is found that the mean area of contact between the irregular particles, which have been studied here, varies, as a function of relative density, according to the same relationship as that derived for spherical particles. The number of contacts, and hence the total contact area, per particle are on the other hand roughly 50% higher than for compacted monomodal spheres.

PSPMT/APD Hybrid DOI Detectors for the PET Component of a Dedicated Breast PET/CT System—A Feasibility Study

We explore two depth of interaction (DOI) capable detectors with a high effective packing fraction to be used for the PET portion of a next generation cylindrical pendant breast PET/CT scanner. The proposed dual-readout detectors consist of an unpolished (14 14) array of LSO crystals coupled to a position sensitive-PMT (PSPMT) at the back end for position sensing and either (A) a (2 2) matrix of avalanche photodiodes (APDs) or (B) a single large APD at the front end for measuring DOI. Increased effective packing fraction is achieved by choosing the APDs such that the total front surface contact area of the APD matrix or the single large APD approximately matches both the contact area of the crystal array and the active area of the PSPMT. This results in reduced dead space between adjacent detectors when placed in a cylindrical scanner geometry. We propose to recover DOI for the crystals that are partially occluded due to the inactive area of the APD by using the optical crosstalk from neighboring crystals. We conducted preliminary studies utilizing five prototype modules: two of which used a (9 9) array of LSO crystals, and three that used a (14 14) LSO array of crystals. The readout was performed either by a , or a position sensitive-APD (PSAPD) at the front end and a PSPMT at the rear end. At room temperature, the average energy and DOI resolutions degraded only by 2% and 0.3 mm respectively for edge crystals compared to the center crystals for all PSAPDs. The energy resolution and the DOI resolution for the detector design with readout (A) was estimated to be 14.2% and 4.0 mm, and that for the design with readout (B) was estimated at 14.7% and 4.4 mm. After cooling to 10, the performance of the second design was close to that of the first design. We conclude that a dedicated cylindrical breast PET/CT scanner could be operated with either of the proposed DOI detector schemes, thus improving packing fraction, and hence, sensitivity and NEC. The two designs have different advantages and drawbacks: the first design performs well at room temperature, however, the readout is complex, while the second design has a simpler readout scheme but requires a cooling system for it to achieve optimal performance.

Effect of Different Flooring Systems on Weight and Pressure Distribution on Claws of Dairy Cows

Weight and pressure distribution on the claw were studied in Swedish Holsteins housed in different flooring systems. A total of 127 cows housed in different sections of the experimental barn were used. Each section had different flooring in the walking and standing areas. There were rubber mats or abrasive mastic asphalt flooring on the alleys or a low-abrasive slatted concrete floor. Some sections had feed-stalls equipped with rubber mats; other sections did not. The vertical ground reaction force, contact area, and average contact pressure were determined on the left hind foot using the I-Scan system and analyzed with the F-scan system. These determinations were made in each of the following 3 zones of the claw: bulb, wall, and sole. Most of the weight on claws exposed to concrete floors was carried by the bulb (37.4±3.5 and 18.3±2.9% of weight exerted on the foot in the lateral and medial claw, respectively) and the wall zone (20.0±2.6 and 13.4±2.4% on lateral and medial claw, respectively). The weight and pressure distribution in cows kept on sections with rubber covered alleys but passing daily over the asphalt floor on their way to the milking parlor did not differ in any zones, except for lateral bulbs, compared with those exposed to slatted concrete alone. Still, the weight bearing of the sole zone in cows kept on rubber mats without access to asphalt was less than that of cows kept on concrete slatted floors (5.1±0.7 vs. 12.7±1.1% and 1.1±0.5 vs. 8.7±0.7% in lateral and medial claws, respectively). In cows kept on asphalt flooring without feed-stalls, most weight was exerted to the sole zone (36.2±2.9 and 22.2±1.8% in lateral and medial claws, respectively). Feed-stalls in combination with asphalt flooring yielded a decreased total contact area (30.1±1.2cm2) compared with asphalt floors without feed-stalls (35.7±1.2cm2). The largest total contact area was obtained on the asphalt floor without feed-stalls, resulting in a lower contact pressure (39.8±2.3 N/cm2) than in claws exposed to concrete (66.0±2.7N/cm2) or rubber mats (56.7±1.7N/cm2). In conclusion, housing with abrasive floors resulted in claws with increased contact area at the sole surface and therefore, decreased contact pressure, but reduced the weight-bearing role of the strongest part of the claw capsule, the claw wall.

The effect of foot type on in-shoe plantar pressure during walking and running

The purpose of this study was to determine if low arch feet have altered plantar loading patterns when compared to normal feet during both walking and running. Fifty healthy subjects (34 normal feet, 16 flat feet) walked and ran five trials each at standard speeds. In-shoe pressure data were collected at 50 Hz. Contact area, peak pressure, maximum force, and force-time integral were analyzed in eight different regions of the foot. Foot type was determined by examining navicular height, arch angle, rearfoot angle, and a clinical score. A series of 2 × 2 repeated measures ANOVAs were used to determine statistical differences ( α < 0.05). A significant interaction existed between foot type and movement type for the maximum force in the medial midfoot. Total foot contact area, maximum force and peak pressure were significantly increased during running. Contact area in each insole area, except for the rearfoot, was significantly increased during running. Peak pressure and maximum force were significantly increased during running in each of the foot regions. However, the force-time integral was significantly decreased during running in the rearfoot, lateral midfoot, middle forefoot, and lateral forefoot. Significant differences between foot types existed for contact area in the medial midfoot and maximum force and peak pressure in the lateral forefoot. The maximum force and peak pressures were significantly decreased for the flat foot type. Therefore, individuals with a flat foot could be at a lower risk for lateral column metatarsal stress fractures, indicating that foot type should be assessed when determining an individual's risk for metatarsal stress fractures.

Humidity control of particle emissions in aeolian systems

Humidity is an important control of the wind speed required to entrain particles into an air flow and is well known to vary on a global scale, as do dust emissions. This paper reports on wind tunnel experiments which quantify this control through placing a polymer capacitance sensor immediately at the bed surface. The sensor measured changes in the humidity (RH) of the pore air in real time. RH was varied between 15% and 80% and the critical wind speed determined for the release of particles to the air stream. The results strongly support earlier suggestions that fine particles are most affected in relatively dry atmospheres, particularly those which are tightly packed. An analytical model is proposed to describe this relationship which depends on determination of the matric potential from the Kelvin equation. The total contact area between particle asperities adjoined by pendular rings is represented as a power function of the number of layers of adsorbed water. The value of the exponent appears to be governed by the surface roughness of the particles and their packing arrangement. Parallel developments in colloid interface science and atomic force microscopy, relevant to industrial and pharmaceutical applications, support these conclusions in principle and will likely have an important bearing on future progress in parameterization of the proposed model.

Finite element analysis of rough surfaces based on ultimate‐stress asperity concept

AbstractAn improved mathematical elastic–plastic model for the contact of rough surfaces that is based on an accurate finite element solution of a deformable single asperity and a rigid flat surface is developed to provide dimensionless expressions for the contact area and contact load. This model differs from the existing models, in that it accounts for the level of interference beyond expected failure. The finite element solution is used to define the limits at which failure occurs. A fictitious ultimate‐stress asperity is introduced to facilitate the derivation of the contact model. This model considers a realistic picture of elastic–plastic deformation where elastic, plastic and failure behaviors can occur simultaneously for an asperity. Subsequent comparison of the results for estimating contact area and load using the present model and the earlier methods shows identical results for pure elastic contacts with plasticity index values at about 0.5 but substantial difference for the net elastic–plastic contacts having plasticity index values above 0.8. When plasticity index reaches 6 and beyond, the three models predict similar total contact area and load values and that the contact is purely plastic. Copyright © 2008 John Wiley &amp; Sons, Ltd.

Correlation between periodontal status and biting force in patients with chronic periodontitis during the maintenance phase of therapy

The association between periodontal status and biting force is unclear. The aim of this study was to investigate the relation between periodontal status and biting force in patients with chronic periodontitis during the maintenance phase of periodontal treatment. A total of 198 patients, who had entered a periodontal maintenance programme, were examined for the presence of restorations on the occlusal surface, probing pocket depth, clinical attachment loss (CAL), bleeding on probing, and mobility of teeth. Quantitative analysis of total biting force, occlusal contact area and biting pressure (defined by biting force per 1 mm(2) of occlusal contact area) was performed using microcapsular pressure-sensitive sheets. A multiple stepwise regression analysis showed that total biting force and occlusal contact area were positively associated with the number of present teeth and negatively associated with female gender, mean CAL and mean probing pocket depth. Biting pressure was positively associated with CAL. Reduced periodontal support was found to be associated with decreased total biting force and with increased biting pressure (defined as force per 1 mm(2) of occlusal contact area).

Elastic-Plastic Microcontact Analysis of a Sphere and a Flat Plate

ABSTRACTThe elastic-plastic microcontact model of a sphere in contact with a flat plate is developed in the present study to investigate the effect of surface roughness on the total contact area and contact load. From the study done by the finite element method, the dimensionless asperity contact area, average contact pressure, and contact load in the elastoplastic regime are assumed to be a power form as a function of dimensionless interference (δ/δec). The coefficients and exponents of the power form expressions can be determined by the boundary conditions set at the two ends of the elastoplastic deformation regime. The contact pressures evaluated by the present model are compared with those predicted by the Hertz theory, without considering the surface roughness and the reported model, including the roughness effect, but only manipulating in the elastic regime. The area of non-zero contact pressure is enlarged if the surface roughness is considered in the microcontact behavior. The maximum contact pressure is lowered by the presence of surface roughness if the contact load is fixed. Under a normal load, both the contact pressure and the contact area are elevated by raising the plasticity index for the surface of the same surface roughness.

Bearing Surface Design Changes Affect Contact Patterns in Total Knee Arthroplasty

The impact of design changes intended to improve wear of knee replacements can be assessed from analysis of retrieved implants. We hypothesized changes in bearing surface conformity from the Insall-Burstein II knee to a successor, the Optetrak, intended to improve contact stresses would be apparent in wear patterns observed on retrieved tibial inserts. From 151 Insall-Burstein II and 54 Optetrak retrieved components, 35 pairs (Insall-Burstein II and Optetrak) were matched on length of implantation, body mass index, and age. Digital images of the bearing surfaces were used to identify and measure wear modes, which were then converted to a percentage of the total possible contact area. Burnishing was the most prevalent mode for both designs followed by scratching and then pitting. The percentage of involved area was greater for the Optetrak for 23 pairs. Interestingly, for the nine matched pairs with length of implantation longer than 2 years, six of the Insall-Burstein II inserts had considerably greater scratching and pitting and five exhibited abrasion and creep absent from Optetrak implants. Bearing surface design is a major factor that can affect kinematics and contact patterns. Our observations confirm the considerable impact of small changes in conformity and suggest models predicting contact stresses adequately reflect in vivo performance.