Contact Force Data Research Articles

Improved Rotator Cuff Footprint Contact Characteristics With an Augmented Repair Construct Using Lateral Edge Fixation

Background: The transosseous-equivalent (TOE) rotator cuff repair construct has become the gold standard for the repair of medium and large rotator cuff tears. Repair failure, however, continues to be a problem. One contributing factor may be the inability of the TOE repair to replicate the native footprint contact characteristics during shoulder movement, especially in rotation. This results in higher strain across the repair, which leads to gapping and predisposes the construct to failure. In an effort to better reproduce the native compression forces throughout the footprint, an augmented TOE construct supplemented with lateral edge fixation is proposed, and the contact characteristics were compared with those of the gold standard TOE construct. Hypothesis: The augmented TOE repair will demonstrate improved footprint contact characteristics when compared with the classic TOE repair. Study Design: Controlled laboratory study. Methods: Ten fresh-frozen cadaveric shoulders underwent supraspinatus repair using both the classic TOE double-row construct and the augmented TOE repair. For the augmented repair, 2 luggage tag sutures were used to secure the lateral edge and incorporated into the lateral row anchors. A Tekscan pressure sensor (Tekscan Inc) placed under the repaired tendon was used to collect footprint contact area, force, peak pressure, and contact pressure data for each construct. Results: The augmented construct demonstrated significantly greater contact forces (average difference, 4.9 N) and significantly greater contact pressures (average difference, 23.1 kPa) at all degrees of abduction and all degrees of rotation. At 30° of internal and 30° of external rotation at both 0° and 30° of shoulder abduction, the augmented construct demonstrated significantly greater peak contact pressures. Conclusion: The augmented construct showed superior contact characteristics when compared with the classic TOE technique. The addition of lateral edge fixation to the classic TOE repair significantly improves bone-tendon contact characteristics with minimal additional surgical effort. Clinical Relevance: The results of this study indicate that lateral augmentation of the classic TOE repair produces a biomechanically superior construct that may optimize tendon healing.

Evaluation of finite element human body models for use in a standardized protocol for pedestrian safety assessment

Objective: Finite element human body models (HBMs) must be certified for use within the EuroNCAP pedestrian safety assessment protocol. We demonstrate that the Global Human Body Model Consortium (GHBMC) simplified pedestrian series of HBMs meet all criteria set forth in Technical Bulletin (TB) 024 (v 1.1 Jan. 2019) for model certification. We further explore variation in head contact time (HIT) and location by HBM size and impact speed across 48 full body impact simulations.Methods: The EuroNCAP Pedestrian Protocol (v. 8.5, Oct. 2018) assesses the overall safety of adult and child pedestrians by outlining a variety of physical tests and finite element simulations using HBMs. These tests are designed to assess the efficacy of vehicle safety technology such as active bonnets. The 50th percentile male simplified pedestrian model (M50-PS, H:175 cm, W:74.5 kg), six-year-old (6YO-PS, H:117 cm, W:23.4 kg), 5th percentile female (F05-PS, H:150 cm, W:50.7 kg), and 95th percentile male (M95-PS, H:190 cm, W:102 kg) were simulated through the suite of cases totaling 48 simulations (12 each). The process gathers three kinematic trajectories and contact force data from designated anatomical locations. The impacting vehicles include a family car (FCR), multi-purpose vehicle (MPV), roadster (RDS), and sports utility vehicle (SUV), all provided by TU Graz, Vehicle Safety Institute as part of the Coherent Project, each simulated at 30 kph, 40 kph, and 50 kph. Each simulation underwent a 23-point pre-simulation check and post-simulation model response comparison. The posture of all HBMs met criteria consisting of 15 measures. All simulations were conducted in LS-Dyna R. 7.1.2.Results and Conclusions: All simulations normal terminated. For each of the simulations, sagittal plane coordinate histories of the center of the head, 12th thoracic vertebrae, and center of acetabulum were compared with standard corridors and did not exceed the tolerance of 50 mm deviation. Head contact time was also compared with the reference values and did not exceed the tolerance interval of +3.5% and -7%. Comparison of contact forces was required for monitoring purposes only. The head contact time of the models for each simulation was recorded and compared by model size, impact speed, and vehicle geometry. Head contact times varied by roughly 3-fold, were lowest for the child model, and showed the greatest sensitivity for the tallest stature model (M95-PS). As stated in the certification process, other body sizes within a model family qualify for certification if the 50th percentile male model passes, provided that model sizes meet the required posture.

Pacing Mediated Heart Rate Acceleration Improves Catheter Stability and Enhances Markers for Lesion Delivery in Human Atria During Atrial Fibrillation Ablation.

This study sought to investigate the effect of pacing mediated heart rate modulation on catheter-tissue contact and impedance reduction during radiofrequency ablation in human atria during atrial fibrillation (AF) ablation. In AF ablation, improved catheter-tissue contact enhances lesion quality and acute pulmonary vein isolation rates. Previous studies demonstrate that catheter-tissue contact varies with ventricular contraction. The authors investigated the impact of modulating heart rate on the consistency of catheter-tissue contact and its effect on lesion quality. Twenty patients undergoing paroxysmal AF ablation received ablation lesions at 15 pre-specified locations (12 left atria, 3 right atria). Patients were assigned randomly to undergo rapid atrial pacing for either the first half or the second half of each lesion. Contact force and ablation data with and without pacing were compared for each of the 300ablation lesions. Compared with lesion delivery without pacing, pacing resulted in reduced contact force variability, as measured by contact force SD, range, maximum, minimum, and time within the pre-specified goal contact force range (p< 0.05). There was no difference in the mean contact force or force-time integral. Reduced contact force variability was associated with a 30% greater decrease in tissue impedance during ablation (p< 0.001). Pacing induced heart rate acceleration reduces catheter-tissue contact variability, increases the probability of achieving pre-specified catheter-tissue contact endpoints, and enhances impedance reduction during ablation. Modulating heart rate to improve catheter-tissue contact offers a new approach to optimize lesion quality in AFablation. (The Physiological Effects of Pacing on Catheter Ablation Procedures to Treat Atrial Fibrillation [PEP AF]; NCT02766712).

Arterial blood pressure estimation using ultrasound: Clinical results on healthy volunteers and a medicated hypertensive volunteer.

This study presents a non-occlusive and non-invasive ultrasound-based technique to measure blood pressure. Most popular clinically-used arterial blood pressure measurement techniques suffer from important weaknesses including being inaccurate, invasive, or occlusive. In the proposed technique, an ultrasound probe is placed on the patient's carotid artery and the contact force between the probe and the tissue is slowly increased while ultrasound images and contact force data are recorded. From this data, the artery is segmented and the segmentation data is sent into an optimization procedure; after post-processing, blood pressure is displayed to the user. This technique was applied to 24 healthy single-visit volunteers, one multi-visit healthy volunteer, and one multi-visit medicated hypertensive volunteer. Compared to the oscillometric cuff, the accuracy and precision of the algorithm-reported systolic pressure is -2.4 ± 10.2 mmHg, and for diastolic pressure is -0.3 ± 8.2 mmHg. This method has the potential to occupy a clinical middle-ground between the arterial catheter and the oscillometric cuff.

Noninvasive Blood Pressure Estimation Using Ultrasound and Simple Finite Element Models.

Many commercially available arterial blood pressure measurement devices suffer from a range of weaknesses. For example, common weaknesses include being inaccurate, invasive, and ad hoc; many also require explicit user calibration or cut off blood flow to a limb. A novel algorithmic approach is presented to accurately estimate systolic and diastolic blood pressure in a way that does not require any explicit user calibration, is noninvasive, and does not cut off blood flow. The approach uses ultrasound images of the arterial wall and corresponding contact force data to obtain blood pressure estimates. To acquire data, an ultrasound probe was placed on the patient's carotid artery and the contact force was increased from 1.5 to 12N. The artery was then algorithmically segmented from the recorded DICOM B-Mode data. The segmentation data and the contact force were used as input into the Levenberg-Marquardt optimization method to solve for the parameters, including blood pressure, of a simple finite element model of the carotid artery. The algorithm was validated on 24 healthy volunteers. Algorithm arterial blood pressure predictions were compared to oscillometric blood pressure cuff readings. Regression and Bland-Altman analyses were performed on the data. Both systolic pressure and diastolic pressure can be estimated using this novel noninvasive ultrasound-based method (systolic accuracy/precision: $-$ 2.36mmHg/10.21mmHg; diastolic accuracy/precision: $-$ 0.32/8.23mmHg). The method occupies a clinical middle ground between the arterial catheter and cuff-based techniques. It has the potential to give accurate results for patients with hypertension and atherosclerosis.

Randomized trial comparing pulmonary vein isolation using the SmartTouch catheter with or without real-time contact force data

Contact force (CF) information may improve the safety and efficacy ofablation for paroxysmal atrial fibrillation (PAF). The purpose of this study was to assess the impact of CF data on ablation for PAF. Patients undergoing first-time PAF ablation were randomized at 7 UK centers toablation with (CF-on) or without (CF-off) CF data available to the operator, using the same ablation catheter and mapping system. An ablation CF of 5-40g was targeted. Pulmonary vein (PV) reconnection was assessed with adenosine at 60 minutes. Follow-up for arrhythmia recurrence was for 1 year with 7-day Holter recordings at 6 and 12 months. One hundred seventeen patients were studied (59 CF-on, 58 CF-off). In the CF-on group, a reduction in acute PV reconnection rates (22% vs 32%, P = .03) but no significant difference in 1-year success rates off antiarrhythmic drugs (49% vs 52%, P = .9) was observed. There was no difference in major complication rates: 2 of 59 (3%) CF-on, 3 of 58 (5%) CF-off (P = .7). Procedural and fluoroscopy times were not significantly different (P>.5). Overall mean CFs per ablation were not different between groups (13.4 [9.1-19.6]g CF-on, 13.4 [7.4-22.4]g CF-off, P = .5), but a greater proportion of readings in the CF-on group were in the target range (80% vs 68%, P<.001). This randomized multicenter study demonstrated that CF data availability was associated with reduced acute PV reconnection but not improved 1-year success rates, procedural and fluoroscopy times, or complication rates. There was a reduction in extremes of CF, above and below the study target range, suggesting greater CF control during ablation.

Impact of Catheter Contact Force on Human Left Atrial Electrogram Characteristics in Sinus Rhythm and Atrial Fibrillation.

During left atrial mapping, optimal contact parameters minimizing variation secondary to catheter contact are not established. Across 30 patients undergoing first-time atrial fibrillation ablation, 1965 stable mapping points (1409 atrial fibrillation, 556 sinus rhythm), comprising 8-s contact force (CF) and bipolar electrogram data were analyzed. Points were taken in groups at locations with CF or catheter orientation actively changed between acquisitions. Complexes were less positive at higher CF (Spearman ρ, -0.2; P<0.005, both rhythms). Increasing CF at a location significantly increased complex size, but only where initial CF was <10 g, and if the change was ≥4.5 g in sinus rhythm and ≥8 g in atrial fibrillation (P<0.0005, both rhythms): if initial CF was ≥10 g, no change was observed, regardless of CF change (P>0.05, both). Atrial ectopics during sinus rhythm were observed more frequently when CF was ≥10 g (P<0.0005). Increasing CF at a location was associated with an increase in the complex fractionated atrial electrogram interval confidence level score, but only if initial CF was <10 g and CF increased ≥8 g (P=0.003). The dominant frequency and organization index were unaffected by CF (P>0.1 for both). Changing catheter orientation from perpendicular to parallel in atrial fibrillation was associated with smaller, more positive complexes (P=0.001 for both), but no changes in complex fractionated atrial electrogram scores, dominant frequency or organization index (P>0.08 for each). During left atrial electrogram mapping, including complex fractionated atrial electrogram but not spectral parameter mapping, CF and catheter orientation influence results: consequently, mapping CFs should be ≥10 g to negate the influence of CF. URL: http://clinicaltrials.gov/. Unique identifier: NCT01587404.

51 Contact Force Data Availability Reduces Acute Pulmonary Vein Reconnection: Early Results from the Smart AF Trial: Abstract 51 Table 1

<h3>Introduction</h3> Contact force (CF) sensing data may facilitate wide area circumferential ablation (WACA). We present data from an interim analysis of the first multicentre randomised controlled trial studying the impact of this data on the ablation of paroxysmal atrial fibrillation (PAF). <h3>Methods</h3> At 7 UK centres, patients undergoing first-time PAF ablation were randomised to ablation with (CF-on) or without CF data (CF-off) available to the operator. Planned recruitment is 120 patients with 1 year follow-up. Using a 3D mapping system and the SmartTouch CF-sensing catheter (Biosense Webster), all patients underwent WACA. Subsequently a 1 h waiting time was observed before assessing acute pulmonary vein (PV) reconnection; if the PV remained isolated, 18 mg adenosine was administered intravenously. The primary end point was acute PV reconnection (spontaneous/adenosine induced). PVs were assessed separately, but cases of a common trunk were taken as one vein. PVs that appeared isolated but were assessed without completing the waiting period were excluded from the acute reconnection analysis. Follow-up is ongoing and 3 month outcomes are reported. <h3>Results</h3> 116 patients have been recruited: age 59 ± 11 years, 57% male, EHRA score 2.7 ± 0.6, AF duration 37 [16–70] months (no significant baseline characteristic differences between groups). There were no differences in procedural parameters (Table 1). There was a significant, 40%, reduction in acute PV reconnection in the CF-on group (Table 1). There were two tamponades and one minor pericardial effusion in the CF-on group, and 1 minor haematoma in the CF-off group. 90 patients (43 CF-off, 47 CF-on) have completed 3 month follow-up: at this point there is no difference in EHRA scores (CF-off 1.6 ± 0.6, CF-on 1.5 ± 0.6, p = 0.8). <h3>Conclusions</h3> Addition of CF sensing data had no impact on procedure, fluoroscopy or ablation times, but did reduce acute PV reconnection rates, suggesting more effective ablation application, and consequently more durable PV isolation. Whether this translates to improved long-term success will be assessed on study completion.

Thermal expansion imaging for monitoring lesion depth using M-mode ultrasound during cardiac RF ablation: in vitro study.

We demonstrate a novel method for automatic direct lesion depth (LD) tracking during coagulation from time series of a single A-mode ultrasound (US) transducer custom fit at the tip of a RFA catheter. This method is named thermal expansion imaging (TEI). A total of 35 porcine myocardium samples were ablated (LD 0.5-5 mm) while acquiring US, electrical impedance (EI) and contact force (CF) data. US images are generated in real time in terms of echo intensity (M-mode) and phase (TEI). For TEI, displacements between US time series are estimated with time-domain cross-correlation. A modified least squares strain estimation with temporal and depth smoothing reveals a thermal expansion boundary (TEB)--negative zero-crossing of temporal strain--which is associated to the coagulated tissue front. M-mode does not reliably delineate RFA lesions. TEI images reveal a traceable TEB with RMSE = 0.50 mm and R2 = 0.85 with respect to visual observations. The conventional technique, EI, shows lower R2 = 0.7 and > 200 % variations with CF. The discontinuous time progression of the TEB is qualitatively associated to tissue heterogeneity and CF variations, which are directly traceable with TEI. The speed of sound, measured in function of tissue temperature, increases up to a plateau at 55°C , which does not explain the observed strain bands in the TEB. TEI successfully tracks LD in in vitro experiments based on a single US transducer and is robust to catheter/tissue contact, ablation time and even tissue heterogeneity. The presence of a TEB suggests thermal expansion as the main strain mechanism during coagulation, accompanied by compression of the adjacent non-ablated tissue. The isolation of thermally induced displacements from in vivo motion is a matter of future research. TEI is potentially applicable to other treatments such as percutaneous RFA of liver and high-intensity focused ultrasound.

Robust Automated Step Extraction From Time-Series Contact Force Data Using the PDShoe.

This paper presents a method of stride identification, extraction, and analysis of data sets of time-series contact force data for ambulating subjects both with and without Parkinson's disease (PD). This method has been made robust with the use of seeded K-Means clustering, fast Fourier transformation (FFT) spectral analysis, and minimum window size rejection. These methods combine to produce well selected strides of active walking data. We are able to calculate quality of walking measures of stride duration, stance duration (as percent of gait cycle - %GC), swing duration (%GC), time to maximum heel force (%GC), time to maximum toe force (%GC), time spent in heel contact (%GC), and time spent in toe contact (%GC).

68 * Catheter contact force and human left atrial electrogram parameters in sinus rhythm and atrial fibrillation

Background: Mechanical stretch is known to affect atrial electrical properties. Within the left atrium (LA) the mapping catheter delivers a stretch stimulus which may also affect the tissue's electrical properties. Methods and Results: Across 22 patients (16 in atrial fibillation (AF), 6 in sinus rhythm (SR)), undergoing first-time AF ablation, 1,774 stable LA mapping points comprising 8 second contact force (CF) and electrogram data were acquired. CF data was collected using a SmartTouch catheter with the Carto3 electroanatomic navigation system (Biosense Webster Inc, USA). Electrogram data was collected using LabSystem Pro (Bard Electrophysiology Division, USA). The electrogram data was analysed using custom-written automated scripts and the Carto3 automated complex fractionated electrogram (CFE) analysis tools. Points were taken in groups of 3 to 4 eight second recordings at the same location with CF or catheter orientation actively changed between acquisitions. There was no correlation between bipolar electrogram size and baseline CF in AF or SR, with a significant variation in electrogram size by atrial location (p 0.2). Changing catheter orientation from perpendicular to parallel did not affect bipolar electrogram size, DF or CFE measurements, but did result in a more negative electrogram (p=0.003). An increasing CF correlated with an increase in atrial ectopic incidence during SR (Point-Biserial Correlation 0.12, p=0.03). On sub-analysis by location, the correlation at the infero-posterior LA was strongest (Point-Biserial correlation 0.38, p=0.01). Conclusions: CF changes weakly correlate with changes in the SR and AF electrogram. CFE and DF measurements are not significantly affected by changes in CF or catheter orientation but higher CF is associated with increased atrial ectopics in sinus rhythm. These results suggest that electrograms observed in mapping studies are only minimally affected by changes in contact force and confirm the sensitivity of the left atrium to mechanical stretch. ![Graphic][1] [1]: /embed/inline-graphic-1.gif

Novel Contact Force Catheters are Effective and Safe for Paroxysmal AF Ablation

This article discusses the 12-month findings from the Comparison of Pulmonary Vein Isolation Using SmartTouch Catheter With or Without Real-Time Contact Force Data trial [SMART; NCT01730924]. The study met its safety and effectiveness endpoints with no unanticipated device-related adverse events, and with 72% of the ablated patients free from atrial fibrillation recurrence. Furthermore, increased freedom from arrhythmia was correlated with increased percentage of time within physician-targeted contact force range.

1A1-D05 床反力の特徴値を用いた動作認識(リハビリテーションロボティクス・メカトロニクス(1))

Optical motion capture systems, which are used in broad fields of research, are costly; they need large installation space and calibrations. We find difficulty in applying it in typical homes and care centers. Therefore we propose to use low cost contact force measurement systems to develop rehabilitation and healthcare monitoring tools. Here, we propose a novel algorithm for motion recognition using the feature vector from force data solely obtained during a daily exercise program. We recognized 7 types of movement of 2 candidates. The results show that the recognition rate of each motion has high score. The results also confirm that there is a clustering of each movement in personal exercise data, and a similarity of the clustering even for different candidates thus that motion recognition is possible using contact force data.

Development of a Measurement System for Contact Force Analysis of Trolley Line

A measurement system of contact force between overhead contact line and pantograph of train is developed which measures the contact force by using four sets of full-bridge strain gauges instead of load cells and accelerometers. The sensors are installed on the pan head of pantograph and the measured data from the sensors are transmitted to a server system in the train by way of wireless Lan. This configuration of the measuring system makes it easy to install on the trains without any alteration of train system. The measurement system is applied to KTX on the Kyungbu high speed line, and the measured contact force data shows good agreement with those measured by load cell and accelerometers. The waveform of the contact force between overhead contact line and pantograph contains essential information about their conditions. The proposed measurement system can probe any defects on overhead contact lines with train running at high speed, which will be a powerful solution for the maintenance of long-distance overhead contact lines.

Simultaneous prediction of muscle and contact forces in the knee during gait

Musculoskeletal models are currently the primary means for estimating in vivo muscle and contact forces in the knee during gait. These models typically couple a dynamic skeletal model with individual muscle models but rarely include articular contact models due to their high computational cost. This study evaluates a novel method for predicting muscle and contact forces simultaneously in the knee during gait. The method utilizes a 12 degree-of-freedom knee model (femur, tibia, and patella) combining muscle, articular contact, and dynamic skeletal models. Eight static optimization problems were formulated using two cost functions (one based on muscle activations and one based on contact forces) and four constraints sets (each composed of different combinations of inverse dynamic loads). The estimated muscle and contact forces were evaluated using in vivo tibial contact force data collected from a patient with a force-measuring knee implant. When the eight optimization problems were solved with added constraints to match the in vivo contact force measurements, root-mean-square errors in predicted contact forces were less than 10 N. Furthermore, muscle and patellar contact forces predicted by the two cost functions became more similar as more inverse dynamic loads were used as constraints. When the contact force constraints were removed, estimated medial contact forces were similar and lateral contact forces lower in magnitude compared to measured contact forces, with estimated muscle forces being sensitive and estimated patellar contact forces relatively insensitive to the choice of cost function and constraint set. These results suggest that optimization problem formulation coupled with knee model complexity can significantly affect predicted muscle and contact forces in the knee during gait. Further research using a complete lower limb model is needed to assess the importance of this finding to the muscle and contact force estimation process.

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.

Effective gait patterns for offloading the medial compartment of the knee

Gait modification offers a noninvasive option for offloading the medial compartment of the knee in patients with knee osteoarthritis. While gait modifications have been proposed based on their ability to reduce the external knee adduction moment, no gait pattern has been proven to reduce medial compartment contact force directly. This study used in vivo contact force data collected from a single subject with a force-measuring knee replacement to evaluate the effectiveness of two gait patterns at achieving this goal. The first was a "medial thrust" gait pattern that involved medializing the knee during stance phase, while the second was a "walking pole" gait pattern that involved using bilateral walking poles commonly used for hiking. Compared to the subject's normal gait pattern, medial thrust gait produced a 16% reduction and walking pole gait a 27% reduction in medial contact force over stance phase, both of which were statistically significant based on a two-tailed Mann-Whitney U-test. While medial thrust gait produced little change in lateral and total contact force over the stance phase, walking pole gait produced significant 11% and 21% reductions, respectively. Medial thrust gait may allow patients with knee osteoarthritis to reduce medial contact force using a normal-looking walking motion requiring no external equipment, while walking pole gait may allow patients with knee osteoarthritis or a knee replacement to reduce medial, lateral, and total contact force in situations where the use of walking poles is possible.

Estimation of Wear and Strain of Contact Wire Using Contact Force of Pantograph

The contact force of pantograph is one of the most important indexes in evaluating current-collection performance. Quality of contact wires maintenance will be more improved by use of observed contact force. However, specific methods for applying the contact force have yet to be proposed. This paper discusses possibility of estimation of wear and strain of contact wire using the contact force data. For this purpose, the learning capability of an artificial neural network is used. A complex number version of a backpropagation algorithm is used for a learning weight. As the result of this study, the author verified that estimation of the wear and the strain of contact wire using the contact force is valid.

Three-dimensional dynamic hip contact area and pressure distribution during activities of daily living

Estimation of the hip joint contact area and pressure distribution during activities of daily living is important in predicting joint degeneration mechanism, prosthetic implant wear, providing biomechanical rationales for preoperative planning and postoperative rehabilitation. These biomechanical data were estimated utilizing a generic hip model, the Discrete Element Analysis technique, and the in vivo hip joint contact force data. The three-dimensional joint potential contact area was obtained from the anteroposterior radiograph of a subject and the actual joint contact area and pressure distribution in eight activities of daily living were calculated. During fast, normal, and slow walking, the peak pressure of moderate magnitude was located at the lateral roof of the acetabulum during mid-stance. In standing up and sitting down, and during knee bending, the peak pressures were located at the edge of the posterior horn and the magnitude of the peak pressure during sitting down was 2.8 times that of normal walking. The peak pressure was found at the lateral roof in climbing up stairs which was higher than that in going down stairs. These results can be used to rationalize rehabilitation protocols, functional restrictions after complex acetabular reconstructions, and prosthetic component wear and fatigue test set up. The same model and analysis can provide further insight to soft tissue loading and pathology such as labral injury. When the pressure distribution on the acetabulum is inverted onto the femoral head, prediction of subchondral bone collapse associated with avascular necrosis can be achieved with improved accuracy.

Measurement of Stiffness and Damping Characteristics of Computer Keyboard Keys

To determine the stiffness and damping of computer keyboard keys, a computer-controlled test rig that can measure computer key displacement, velocity, and contact force has been designed. The test rig, consisting of a single-axis stage carrying a probe for contacting keys, has been used to collect contact force and motion data as computer keys are depressed and released at constant velocities up to 80mm∕s. Keys that employ a rubber-dome under their caps to achieve the necessary compliance and toggling action were tested. The results demonstrate a nonlinear stiffness force versus displacement characteristic at a given speed and the presence of damping-type forces that increase with key depression speed at a given displacement. In particular, the results indicate that the peak force at the 80mm∕s rate of depression increases relative to the quasistatic (0.5mm∕s) force level by over 12% for the “Enter,” “K,” and “Spacebar” keys. This paper describes the hardware and software configuration, and presents sample results of the stiffness and damping characteristics of keys during depression-return stroke tests.