Total Contact Force Research Articles

AN ORTHOSIS HAS ONLY A MINOR EFFECT ON THE LOADS ACTING ON A SPINAL IMPLANT

Until recently the contact loads acting in the glenohumeral joint have been calculated using musculoskeletal models or measured in vitro. Now, contact forces and moments are measured in vivo using telemeterized shoulder implants. Mean total contact forces from four patients during eight activities of daily living are reported here.Lifting a coffee pot (1.5 kg) with straight arm caused an average force of 105.0%BW (%body weight) (range: 90–124.6%BW), while setting down the coffee pot in the same position led to higher forces of 122.9%BW on the average (105.3–153.4%BW). The highest joint contact forces were measured when the straight arm was abducted or elevated by 90° or more, with a weight in the hand. Lifting up 2 kg from a board up to head height caused a contact force of 98.3%BW (93–103.6%BW); again, setting it down on the board led to higher forces of 131.5%BW (118.8–144.1%BW). In contrast to previously calculated high loads, the contact force during passive holding of a 10 kg weight laterally was only 12.3%BW (9.2–17.9%BW), but when lifting it up to belt height it increased to 91.5%BW (87–95%BW).The moments transferred inside the joint at our patients varied much more than did the forces both inter and intra-individually.Our data suggest that patients with shoulder problems or during the first post-operative weeks after shoulder fractures or joint replacements should avoid certain activities encountered during daily living e.g. lifting or holding a weight with an outstretched arm. Some energy-related optimization criteria used in the literature for analytical musculoskeletal shoulder models must now be reconsidered.

Influence of Limb Alignment on Mediolateral Loading in Total Knee Replacement

Malalignment after total knee replacement could cause overloading of the implant bearing as well as of the bone itself, leading to osteolysis and early loosening. To quantify the stresses the implant has to withstand and to define a safe zone of limb alignment, the total contact forces as well as their mediolateral distribution have to be determined. Analytical gait data and mathematical models have been used for this purpose. We performed this study to determine in vivo loads of five patients after implantation of an instrumented tibial baseplate. Five patients with osteoarthritis of the knee received total knee replacement. The tibial component was instrumented with strain gauges for the measurement of three forces and three moments. The signals from the gauges were transferred telemetrically to an external receiver. At twelve months after surgery, postoperative measurements were obtained with the patients walking at a self-selected comfortable speed across a level walkway. Peak axial and medial forces of fifteen to twenty gait cycles were averaged and reported as a percent of individual body weight. During the stance phase of the gait cycle, two maxima of the axial force occurred. Typical values were 215% of body weight at the first peak and 266% of body weight at the second peak. The medial load share was typically 73% at the first axial force peak and 65% at the second axial force peak. Analysis of inter-individual variations revealed a linear correlation with limb alignment. A deviation of 1° varus from neutral alignment increased the medial load share by 5%. Consistent with the results of previous studies, we found that the force transferred by the medial compartment was usually greater than that transferred by the lateral compartment. Concerning the design of total knee replacements, an asymmetric tibial component with a larger medial contact area could possibly reduce peak contact stress on the bone and improve fixation of the implant. Mediolateral load distribution was quantified and correlated with limb alignment, thereby permitting the effects of malalignment after total knee replacement to be estimated.

A Novel Force Modeling Scheme for Needle Insertion Using Multiple Kalman Filters

In this paper, the interaction force between a surgical needle and soft tissue is studied. The force is modeled using a novel nonlinear dynamic model. Encouraged by the LuGre model for representing friction forces, the proposed model captures all stages of needle-tissue interaction, including puncture, cutting, and friction forces. An estimation algorithm for identifying the parameters of the model is presented. This online approach, which is based on sequential extended Kalman filtering, enables us to characterize the total contact force using an efficient mathematical model. The algorithm compares the axial force measured at the needle base with its expected value and then adapts the model parameters to represent the actual interaction force. While the nature of this problem is very complex, the use of multiple Kalman filters makes the system highly adaptable for capturing the force evolution during an interventional procedure in standard operating conditions. To evaluate the performance of our model, experiments were performed on artificial phantoms.

Contact force–controlled zero-fluoroscopy catheter ablation of right-sided and left atrial arrhythmia substrates

Conventional catheter ablation of cardiac arrhythmias is associated with radiation risks for patients and laboratory personnel. However, nonfluoroscopic catheter guidance may increase the risk for inadvertent cardiac injury. A novel radiofrequency ablation catheter capable of real-time tissue-tip contact force measurements may compensate for nonfluoroscopic safety issues. To investigate the feasibility of contact force-controlled zero-fluoroscopy catheter ablation. In 30 patients (including 12 pediatric patients), zero-fluoroscopy catheter ablation of right-sided (right atrium, n = 20; right ventricle, n = 2) and left atrial (n = 8) arrhythmias was attempted. Inclusion criteria were symptomatic suspected atrioventricular nodal reentrant tachycardia, atrioventricular reentrant tachycardia, focal right atrial and ventricular arrhythmias, and lone atrial fibrillation. A novel irrigated-tip catheter with an integrated contact force sensor was used for nonfluoroscopic 3-dimensional electroanatomical mapping and radiofrequency ablation. Transseptal access was gained under transesophageal guidance for ablation of left-sided arrhythmias. Procedural success without fluoroscopy was achieved in 29 of the 30 patients (97%). In 1 patient, endocardial nonfluoroscopic ablation failed because of an epicardial accessory pathway within a coronary sinus aneurysm. Mean total contact force and amplitude of force undulations were kept below 50 g during mapping and below 40 g during ablation to prevent contact force peaks (>100 g). Apart from a transient second-degree type I atrioventricular block, no complications occurred. The mean procedure time was 2.8 ± 0.9 hours. There were no arrhythmia recurrences during a mean follow-up of 6.2 ± 4.2 months. Contact force-controlled zero-fluoroscopy catheter ablation is generally feasible in right-sided and left atrial cardiac arrhythmias.

Study on Contact Force of Tooth Profile Modification

Linear, conic, cubic, and sine relief curve are compiled and established in MATLAB, on which gear models are built in UG and a new method of establishing relief gear models is proposed in this paper. Based on the theory of elastic, contact method is used on the proposed finite element models of gears by software LS-DYNA. Total contact force of teeth face, contact force of single tooth and equivalent stress on relief gears in different cases are obtained. The results show that contact impact existing in meshing between teeth of gears is ameliorated, contact force of tooth face and equivalent stress is reduced. The effect of cubic and sine relief curve is the best. So dynamic simulation on relief gears has great significance for reducing contact force between teeth faces of gears.

A tri-axial touch sensor with direct silicon to PC-board packaging

Touch sensors are receiving increasing attention nowadays in both research and products. In this work, we present a novel tri-axial touch sensor that measures contact force in three mutually perpendicular directions simultaneously. As a discrete touch sensing device, this sensor will be useful for capturing the three dimensional profile of the total contact force, such as the force of fingertip–object interaction during a robotic manipulation task. The primary distinctive feature of this sensor is the direct silicon to PCB (Printed Circuit Board) assembly scheme, effectively decomposing the incoming force vector into three independent components while eliminating the needs for complex micro fabrication and chip packaging. The design, fabrication process and testing results of this sensor are presented. Static loading tests for both single axial devices and tri-axial sensors in both normal and shear directions are presented. Data regarding sensitivities and cross-sensitivities are obtained. A linear compensation scheme is proposed using calibration matrix to correct the output data for linear errors caused by cross-talk. As a preliminary application, the sensor is also characterized as a force-proportional pointing device. Real time data are recorded during fingertip–sensor interaction through circular biaxial motions and are compared with bench mark data obtained from vision tracking method in both time and frequency domains.

Finite Element Lumbar Spine Facet Contact Parameter Predictions are Affected by the Cartilage Thickness Distribution and Initial Joint Gap Size

Current finite element modeling techniques utilize geometrically inaccurate cartilage distribution representations in the lumbar spine. We hypothesize that this shortcoming severely limits the predictive fidelity of these simulations. Specifically, it is unclear how these anatomically inaccurate cartilage representations alter range of motion and facet contact predictions. In the current study, cadaveric vertebrae were serially sectioned, and images were taken of each slice in order to identify the osteochondral interface and the articulating surface. A series of custom-written algorithms were utilized in order to quantify each facet joint's three-dimensional cartilage distribution using a previously developed methodology. These vertebrae-dependent thickness cartilage distributions were implemented on an L1 through L5 lumbar spine finite element model. Moments were applied in three principal planes of motion, and range of motion and facet contact predictions from the variable thickness and constant thickness distribution models were determined. Initial facet gap thickness dimensions were also parameterized. The data indicate that the mean and maximum cartilage thickness increased inferiorly from L1 to L5, with an overall mean thickness value of 0.57 mm. Cartilage distribution and initial facet joint gap thickness had little influence on the lumbar range of motion in any direction, whereas the mean contact pressure, total contact force, and total contact area predictions were altered considerably. The data indicate that range of motion predictions alone are insufficient to establish model validation intended to predict mechanical contact parameters. These data also emphasize the need for the careful consideration of the initial facet joint gap thickness with respect to the spinal condition being studied.

Hamstrings loading contributes to lateral patellofemoral malalignment and elevated cartilage pressures: An in vitro study

BackgroundHamstrings loading has previously been shown to increase tibiofemoral posterior translation and external rotation, which could contribute to patellofemoral malalignment and elevated patellofemoral pressures. The current study characterizes the influence of forces applied by the hamstrings on patellofemoral kinematics and the pressure applied to patellofemoral cartilage. MethodsTen knees were positioned at 40°, 60° and 80° of flexion in vitro, and loaded with 586N applied through the quadriceps, with and without an additional 200N applied through the hamstrings. Patellofemoral kinematics were characterized with magnetic sensors fixed to the patella and the femur, while the pressure applied to lateral and medial patellofemoral cartilage was measured with pressure sensors. A repeated measures ANOVA with three levels, combined with paired t-tests at each flexion angle, determined if loading the hamstrings significantly (P<0.05) influenced the output. FindingsLoading the hamstrings increased the average patellar flexion, lateral tilt and lateral shift by approximately 1°, 0.5° and 0.2mm, respectively. Each increase was significant for at least two flexion angles. Loading the hamstrings increased the percentage of the total contact force applied to lateral cartilage by approximately 5%, which was significant at each flexion angle, and the maximum lateral pressure by approximately 0.3MPa, which was significant at 40° and 60°. InterpretationThe increased lateral shift and tilt of the patella caused by loading the hamstrings can contribute to lateral malalignment and shifts pressure toward the lateral facet of the patella, which could contribute to overloading of lateral cartilage.

RF MEMS Metal-Contact Switches With mN-Contact and Restoring Forces and Low Process Sensitivity

This paper presents an electrostatic RF microelectromechanical systems (MEMS) metal contact switch based on a tethered cantilever topology. The use of tethers results in a design that has low sensitivity to stress gradients, biaxial stresses, and temperature. A switch with a footprint of 160 × 190 μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and based on a 8-μm-thick gold cantilever with an Au/Ru contact is implemented on a high-resistivity silicon substrate and results in a total contact force of 0.8-1.2 mN at 80-90 V, a restoring force of 0.5 mN, a pull-in voltage of 61 V, an up-state capacitance of 24 fF, and an actuation time of 6.4 μ s. The device achieves a switch resistance of 2.4±1.4 Ω to 1.8±0.6 Ω at 90-100 V in open laboratory environments (nonpackaged). This design has the potential to replace conventional electromagnetic relays in application areas such as automated testing equipment and high-performance switching networks.

A Finite Element‐Based Elastic‐Plastic Model for the Contact of Rough Surfaces

Three‐dimensional elastic‐plastic contact of two nominally flat rough surfaces is considered. Equations governing the shoulder‐shoulder contact of asperities are derived based on the asperity constitutive relations from a finite element model of the elastic‐plastic interaction proposed by Kogut and Etsion (2002), in which asperity scale constitutive relations are derived using piecewise approximate functions. An analytical fusion technique is developed to combine the piecewise asperity level constitutive relations. Shoulder‐shoulder asperity contact yields a slanted contact force consisting of two components, one in the normal direction and a half‐plane tangential component. Statistical summation of the asperity level contact force components and asperity level contact area results in the total contact force and total contact area formulae between two rough surfaces. Approximate equations are developed in closed form for contact force components and contact area.

The Effects of Embedded Optical Fiber Density on the Impact Response and Lifetime of Laminated Composites

Graphite fiber/epoxy, two-dimensional woven composite laminates were fabricated with various densities of embedded optical fibers at the midplane. The specimens were subjected to multiple low-velocity impacts until failure, as the energy dissipated by the laminate and the maximum contact force were measured for each impact event. Cumulative probability distributions were calculated for each embedded optical fiber density, from which probability distribution functions in terms of embedded optical fiber density were extrapolated. At low fiber densities, the total energy dissipated by the specimen and the total maximum contact force over the lifetime of the specimen decreased rapidly with increasing optical fiber density. After a threshold embedded optical fiber density, the optical fibers dominated the failure mode of the laminate and the laminate lifetime, and the overall stiffness was not affected by the embedded optical fiber density. The obtained probability distribution functions could be applied for future optimization of embedded sensor placement for smart composite structures.

Analysis on the fundamental deformation effect of a robot soft finger and its contact width during power grasping

This paper attempts to develop a simple contact model of a robot soft finger which is applied for power grasping. The geometrical relationship between contact parameters such as the deformation, contact width, and touch angle are derived for the developed cylindrical finger of soft material. The proposed nonlinear model of the soft finger deforms on the application of load and contact surface grows correspondingly with an angle. The deformation and contact width are related with contact touch angle, which changes as load varies. The force relationship between contact parameters and geometrical data is then derived. The developed analytical model enables to determine the total contact force at the contact surface during the manipulation. An experiment is conducted with three different hyper elastic materials and the deformations and contact width for various loads are determined. The material properties of finger materials are computed using measured deformation. The suitable soft material for developing robot soft fingers is then selected based on the deformation of the finger and frictional coefficients between finger material and the selected target materials. The numerical simulation is also done for the developed model, and it well matches with the experimental results. The developed soft finger model and its force function can be usefully applied to soft-fingered object manipulations in future.

Effects of gloves on the total grip strength applied to cylindrical handles

The major objectives of this study were to establish an alternative method for measuring the effects of gloves on the grip strength applied to cylindrical handles and to quantify the strength reduction due to the use of typical anti-vibration (AV) gloves. Different from previous studies that measure the grip force in a specific plane, the alternative method measures the total contact force normal to a cylindrical handle; the total grip strength is defined as the total contact force measured when a subject applies a power grip to the handle with his/her maximum voluntary contraction (MVC) effort. Two instrumented cylindrical handles (30 and 40 mm) were used in this study. Ten subjects participated in the experiment. Four types of AV gloves and two types of non-AV gloves were used in the experiment. Compared with bare-handed trials, each of the four anti-vibration gloves reduced the grip strength by more than 29%, regardless of handle size. One of the non-AV gloves also largely reduced the grip strength (≥25%) whereas the grip strength reduction of the other one was less than 10%. The gloves also influenced the grip force distribution pattern around the circumference of the cylindrical handles. The results suggest that the thickness of a glove is one of the major factors associated with these effects. Relevance to industry Glove use is generally recommended to keep the hands warm and dry and to protect them from many other hazards, provided this is consistent with safe and effective tool operation. However, a user of thicker, stiffer gloves, such as some AV gloves, could be trading one health risk for another. Knowledge of the effects of gloves on grip strength can help workers, managers, and safety professionals make informed decisions about glove selection and use in the workplace. This knowledge may also lead to work glove improvements.

Contributions of individual muscles to hip joint contact force in normal walking

The human hip joint withstands high contact forces during daily activity and is therefore susceptible to injury and structural deterioration over time. Knowledge of muscle-force contributions to hip joint loading may assist in the development of strategies to prevent and manage conditions such as osteoarthritis, femoro-acetabular impingement and fracture. The main aim of this study was to determine the contributions of individual muscles to hip contact force in normal walking. Muscle contributions to hip contact force were calculated based on a previously published dynamic optimization solution for normal walking, which provided the time histories of joint motion, ground reaction forces, and muscle forces during the stance and swing phases of gait. The force developed by each muscle plus its contribution to the ground reaction force were used to determine the muscle’s contribution to hip contact force. Muscles were the major contributors to hip contact force, with gravitational and centrifugal forces combined contributing less than 5% of the total contact force. Four muscles that span the hip – gluteus medius, gluteus maximus, iliopsoas, and hamstrings – contributed most significantly to the three components of the hip contact force and hip contact impulse (integral of hip contact force over time). Three muscles that do not span the hip – vasti, soleus, and gastrocnemius – also contributed substantially to hip joint loading. These results provide additional insight into lower-limb muscle function during walking and may also be relevant to studies of cartilage degeneration and bone remodelling at the hip.

A Contact Model of Nominally Flat Rough Surfaces Based on a Visco-Elasto-Adhesive Interaction

Approximate closed-form equations are derived for normal contact force between nominally flat rough surfaces in dry contact. The formulation is based on the asperity-level interaction in which adhesive forces between two asperities and elastic and rate-dependent forces are included. The elastic and time rate-dependent portion of force is derived using a viscoelastic interaction of the two asperities. Statistical consideration of rough surfaces then furnishes the mathematical formulation of total normal force due to adhesion, elastic, and rate-dependent properties of the solids in contact. The probabilistic formulation of contact force leads to integral equations. From these are derived approximate closed-form expressions that relate the microscale properties of the surfaces to the macroscale behavior in the form of the total normal contact force between the surfaces. The approximate equations for visco-elasto-adhesive contact of rough surfaces illustrate the dependence of the contact force on the time rate of approach based on a combination of 1/6, 1/3, and 1 power laws.

In vivo measurement of shoulder joint loads during activities of daily living

Until recently the contact loads acting in the glenohumeral joint have been calculated using musculoskeletal models or measured in vitro. Now, contact forces and moments are measured in vivo using telemeterized shoulder implants. Mean total contact forces from four patients during eight activities of daily living are reported here. Lifting a coffee pot (1.5 kg) with straight arm caused an average force of 105.0%BW (%body weight) (range: 90–124.6%BW), while setting down the coffee pot in the same position led to higher forces of 122.9%BW on the average (105.3–153.4%BW). The highest joint contact forces were measured when the straight arm was abducted or elevated by 90° or more, with a weight in the hand. Lifting up 2 kg from a board up to head height caused a contact force of 98.3%BW (93–103.6%BW); again, setting it down on the board led to higher forces of 131.5%BW (118.8–144.1%BW). In contrast to previously calculated high loads, the contact force during passive holding of a 10 kg weight laterally was only 12.3%BW (9.2–17.9%BW), but when lifting it up to belt height it increased to 91.5%BW (87–95%BW). The moments transferred inside the joint at our patients varied much more than did the forces both inter and intra-individually. Our data suggest that patients with shoulder problems or during the first post-operative weeks after shoulder fractures or joint replacements should avoid certain activities encountered during daily living e.g. lifting or holding a weight with an outstretched arm. Some energy-related optimization criteria used in the literature for analytical musculoskeletal shoulder models must now be reconsidered.

Aberrant pelvis and hip kinematics impair hip loading before and after total hip replacement

Musculoskeletal loading is an important factor affecting the development of osteoarthritis, bone remodelling and primary fixation of total hip replacement (THR). In this study, we analyzed the relation between muscular force, gait kinematics and kinetics and hip loading in 20 patients before and six weeks after THR. Hip contact forces were calculated from gait analysis data using musculoskeletal modelling, inverse dynamics and static optimization. We found aberrant pelvis and hip kinematics and kinetics before and six weeks after surgery, confirming previous findings in literature. Furthermore, we found a decrease in the total contact force and its vertical component. These changes result in a decrease of the associated inclination angles of the total hip contact force in the sagittal and transverse planes, changing the orientation towards more vertical implant loading after THR. These changes in hip loading were related to observed gait kinematics and kinetics. Most importantly, excessive pelvic obliquity and associated hip adduction related to impaired implant loading. We concluded, therefore, that physical therapy in the early post-operative phase should primarily focus on stretching of anterior and medial structures and strengthening of hip flexors and abductors to achieve normalization of the hip and pelvis kinematics and consequently normalize hip loading.

Subject-specific hip geometry and hip joint centre location affects calculated contact forces at the hip during gait

Hip loading affects the development of hip osteoarthritis, bone remodelling and osseointegration of implants. In this study, we analyzed the effect of subject-specific modelling of hip geometry and hip joint centre (HJC) location on the quantification of hip joint moments, muscle moments and hip contact forces during gait, using musculoskeletal modelling, inverse dynamic analysis and static optimization. For 10 subjects, hip joint moments, muscle moments and hip loading in terms of magnitude and orientation were quantified using three different model types, each including a different amount of subject-specific detail: (1) a generic scaled musculoskeletal model, (2) a generic scaled musculoskeletal model with subject-specific hip geometry (femoral anteversion, neck-length and neck-shaft angle) and (3) a generic scaled musculoskeletal model with subject-specific hip geometry including HJC location. Subject-specific geometry and HJC location were derived from CT. Significant differences were found between the three model types in HJC location, hip flexion–extension moment and inclination angle of the total contact force in the frontal plane. No model agreement was found between the three model types for the calculation of contact forces in terms of magnitude and orientations, and muscle moments. Therefore, we suggest that personalized models with individualized hip joint geometry and HJC location should be used for the quantification of hip loading. For biomechanical analyses aiming to understand modified hip joint loading, and planning hip surgery in patients with osteoarthritis, the amount of subject-specific detail, related to bone geometry and joint centre location in the musculoskeletal models used, needs to be considered.

Evaluation of predicted knee‐joint muscle forces during gait using an instrumented knee implant

Musculoskeletal modeling and optimization theory are often used to determine muscle forces in vivo. However, convincing quantitative evaluation of these predictions has been limited to date. The present study evaluated model predictions of knee muscle forces during walking using in vivo measurements of joint contact loading acquired from an instrumented implant. Joint motion, ground reaction force, and tibial contact force data were recorded simultaneously from a single subject walking at slow, normal, and fast speeds. The body was modeled as an 8-segment, 21-degree-of-freedom articulated linkage, actuated by 58 muscles. Joint moments obtained from inverse dynamics were decomposed into leg-muscle forces by solving an optimization problem that minimized the sum of the squares of the muscle activations. The predicted knee muscle forces were input into a 3D knee implant contact model to calculate tibial contact forces. Calculated and measured tibial contact forces were in good agreement for all three walking speeds. The average RMS errors for the medial, lateral, and total contact forces over the entire gait cycle and across all trials were 140 +/- 40 N, 115 +/- 32 N, and 183 +/- 45 N, respectively. Muscle coordination predicted by the model was also consistent with EMG measurements reported for normal walking. The combined experimental and modeling approach used in this study provides a quantitative framework for evaluating model predictions of muscle forces in human movement.

A Microcontact Model Developed for Asperity Heights with a Variable Profile Fractal Dimension, A Surface Fractal Dimension, Topothesy, and Non-Gaussian Distribution

AbstractThe cross sections formed by the contact asperities of two rough surfaces at an interference are islandshaped, rather than having the commonly assumed circular contour. These island-shaped contact surface contours show fractal behavior with a profile fractal dimension Ds. The surface fractal dimension for the asperity heights is defined as D and the topothesy is defined as G. In the study of Mandelbrot, the relationship between D and Ds was given as D = Ds + 1 if these two fractal dimensions are obtained before contact deformation. In the present study, D, G, and Ds are considered to be varying with the mean separation (or the interference at the rough surface) between two contact surfaces. The D-Ds relationships for the contacts at the elastic, elastoplastic, and fully plastic deformations are derived and the inceptions of the elastoplastic deformation regime and the fully plastic deformation regime are redefined using the equality of two expressions established in two different ways for the number of contact spots (N). The contact parameters, including the total contact force and the real contact area, were evaluated when the size distribution functions (n) for the three deformation regimes were available. The results indicate that both the D and Ds parameters in these deformation regimes increased with increasing the mean separation (d*). The initial plasticity index before contact deformation (ψ)0 is also a factor of importance to the predictions of the contact load (F*t) and contact area (At*) between the model of variable D and G, non-Gaussian asperity heights and circular contact area and the present model of variable D and G, non-Gaussian asperity heights and fractal contact area.