Self-motion trajectories can facilitate orientation-based figure-ground segregation.

Segregation of objects from the background is a basic and essential property of the visual system. We studied the neural detection of objects defined by orientation difference from background in barn owls (Tyto alba). We presented wide-field displays of densely packed stripes with a dominant orientation. Visual objects were created by orienting a circular patch differently from the background. In head-fixed conditions, neurons in both tecto- and thalamofugal visual pathways (optic tectum and visual Wulst) were weakly responsive to these objects in their receptive fields. However, notably, in freely viewing conditions, barn owls occasionally perform peculiar side-to-side head motions (peering) when scanning the environment. In the second part of the study we thus recorded the neural response from head-fixed owls while the visual displays replicated the peering conditions; i.e., the displays (objects and backgrounds) were shifted along trajectories that induced a retinal motion identical to sampled peering motions during viewing of a static object. These conditions induced dramatic neural responses to the objects, in the very same neurons that where unresponsive to the objects in static displays. By reverting to circular motions of the display, we show that the pattern of the neural response is mostly shaped by the orientation of the background relative to motion and not the orientation of the object. Thus our findings provide evidence that peering and/or other self-motions can facilitate orientation-based figure-ground segregation through interaction with inhibition from the surround.NEW & NOTEWORTHY Animals frequently move their sensory organs and thereby create motion cues that can enhance object segregation from background. We address a special example of such active sensing, in barn owls. When scanning the environment, barn owls occasionally perform small-amplitude side-to-side head movements called peering. We show that the visual outcome of such peering movements elicit neural detection of objects that are rotated from the dominant orientation of the background scene and which are otherwise mostly undetected. These results suggest a novel role for self-motions in sensing objects that break the regular orientation of elements in the scene.

A Biomechanical Foot-Worn Device Improves Total Knee Arthroplasty Outcomes.

BACKGROUND: Biomechanics after total knee arthroplasty (TKA) often remain abnormal and may lead to prolonged postoperative recovery. The purpose of this study is to assess a biomechanical therapy after TKA. METHODS: This is a randomized controlled trial of 50 patients after unilateral TKA. One group underwent a biomechanical therapy in which participants followed a walking protocol while wearing a foot-worn biomechanical device that modifies knee biomechanics and the control group followed a similar walking protocol while wearing a foot-worn sham device. All patients had standard physical therapy postoperatively as well. Patients were evaluated throughout the first postoperative year with clinical measures and gait analysis. RESULTS: Improved outcomes were seen in the biomechanical therapy group compared to the control group in pain scores (88% vs 38%, P = .011), function (86% vs 21%, P = .001), knee scores (83% vs 38%, P = .001), and walking distance (109% vs 47%, P = .001) at 1 year. The therapy group showed healthier biomechanical gait patterns in both the sagittal and coronal planes at 1 year. CONCLUSION: A postoperative biomechanical therapy improves outcomes following TKA and should be considered as an additional therapy postoperatively.

Force transmission through the wrist during performance of push-ups on a hyperextended and a neutral wrist.

STUDY DESIGN: Cross-sectional cohort. INTRODUCTION: Push-ups are used ubiquitously to evaluate and strengthen the upper body. They are usually performed in 1 of 2 main ways: with the wrist in hyperextension and with the wrist in a neutral position. PURPOSE OF THE STUDY: The purpose of our study was to compare the dynamic forces in the wrist during the 2 push-up styles. METHODS: Fourteen volunteers performed push-ups in 2 different patterns: on a hyperextended wrist and a neutral wrist (NW). Two force plates and a motion capture system were used to measure the ground reaction forces (GRFs) and the kinematics of the upper extremity during push-ups. Kinematic and kinetic analyses were performed using Matlab software (Mathworks, Natick, MA). RESULTS: The GRF vector was distributed differently during the different types of push-ups. For both methods, the total GRF carried by the upper dominant extremity was larger than those of the nondominant extremity. In the NW configuration, the GRF vector was more uniform throughout the push-up in the vertical direction. The horizontal distance between the capitate bone location and the GRF origin was smaller in hyperextension. The forces traveled more dorsally over a wider area and more ulnarly in the hyperextended wrist. DISCUSSION: Forces are transmitted differently through the wrist in the 2 methods. Push-ups on an NW are likely safer because ligaments may be preferentially loaded in hyperextension. Further study may delineate the differences in the anatomic location of force transmission and the long-term clinical effect on the wrist. CONCLUSIONS: This study supports the performance of push-ups on a wrist in neutral flexion extension; both to enable patients after surgery or injury to strengthen the upper body and prevent injury and long-term wear in the wrist. The knowledge gained from this study may assist in outlining guidelines for push-up performance. LEVEL OF EVIDENCE: Diagnostic level 2a.

Instantaneous screws of weight-bearing knee: what can the screws tell us about the knee motion.

There are several ways to represent a given object's motion in a 3D space having 6DOF i.e., three translations and three rotations. Some of the methods that are used are mathematical and do not provide any geometrical insight into the nature of the motion. Screw theory is a mathematical, while at the same time, geometrical method in which the 6DOF motion of an object can be represented. We describe the 6DOF motion of a weight-bearing knee by its screw parameters, that are extracted from 3D Optical Reflective motion capture data. The screw parameters which describe the transformation of the shank with respect to the thigh in each two successive frames, is represented as the instantaneous screw axis of the motion given in its Plücker line coordinate, along with its corresponding pitch and intensity values. Moreover, the Striction curve associated with the motion provides geometrical insight into the nature of the motion and its repeatability. We describe the theoretical background and demonstrate what the screw can tell us about the motion of healthy subjects' knee.

Foot center of pressure trajectory alteration by biomechanical manipulation of shoe design.

BACKGROUND: Footwear-generated biomechanical manipulations have been shown to alter lower limb kinetics. It has been suggested that this is due to altered trajectory of the foot's center of pressure (COP), conveying a shift in location of the ground reaction force and modifying moments and forces acting on proximal body segments. However, past studies have focused on qualitative association between footwear design and the COP locus. Moreover, this association was calculated via indirect analysis. The purpose of the present study was to directly examine and quantify the correlation between measured footwear biomechanical manipulation and the location of the COP trajectory during gait. METHODS: A novel biomechanical device allowing flexible positioning of 2 convex-shaped elements attached to its sole was utilized. A total of 20 healthy male adults underwent direct in-shoe pressure measurements while walking with the device set at 7 mediolateral configurations. COP data were collected during gait and analyzed with respect to different stance subphases. RESULTS: COP location significantly correlated with a shift of the elements medially or laterally. The linear model describing this correlation was found to be statistically significant. CONCLUSION: There was significant correlation between the plantar orientation of the shoe device configuration and the COP. CLINICAL RELEVANCE: Changes in COP trajectory may be valuable in patients suffering from multiple foot disorders elevating pressure on the foot. Accurate COP control could aid in the manipulation of the forces acting on the proximal joints during gait. In addition, these findings may have implications in the field of biomechanical apparatus design and practice.

Graded stiffness offloading insoles better redistribute heel plantar pressure to protect the diabetic neuropathic foot.

BACKGROUND: Diabetic heel ulceration is a common, detrimental, and costly complication of diabetes. This study investigates a novel "graded-stiffness" offloading method, which consists of a heel support with increasing levels of stiffness materials to better redistribute plantar pressure for heel ulcer prevention and treatment. RESEARCH QUESTION: Is the novel "graded-stiffness" solution better able to redistribute heel pressure and reduce focal stress concentration areas of the heel? METHODS: Twenty healthy young men walked with four, 3D-printed, insole configurations. The configurations included the "graded-stiffness" insoles with and without an offloading hole under the heel tissue at risk for ulcerations and two conventional offloading supports of flat insoles with no offloading and simple holed offloading insoles. In-shoe plantar pressure was measured using the Pedar-X system. Peak pressure and pressure dose were measured at three heel regions: offloaded region, perimeter of offloaded region, and periphery region. RESULTS: The simple offloading configuration reduced pressure at the offloaded region; however, pressure at the perimeter of the offloading region significantly increased. With respect to ANOVA, the "graded-stiffness" offloading configurations were more effective than existing tested solutions in reducing and redistributing heel peak pressure and pressure dose, considering all heel regions. SIGNIFICANCE: The "graded-stiffness" offloading solution demonstrated a novel flexible and customized solution that can be manufactured on-demand through a precise selection of the graded-stiffness offloading location and material properties to fit the shape and size of the ulcer. This study is a follow-up in-vivo pilot study, in a healthy population group, to our previous computation modeling work that reported the efficiency of the "graded-stiffness" configuration, and which emphasizes its potential for streamlining and optimizing the prevention and treatment of diabetic heel ulcers.

3D surface topographic measurements for idiopathic scoliosis are highly correlative to patient self-image questionnaires.

PURPOSE: Adolescent idiopathic scoliosis (AIS) is a deformity of the spine that results in external asymmetry of the torso in the shoulder, waist, and rib hump. Several patient reported outcome measures (PROMS) including the Trunk Appearance Perception Scale (TAPS) and SRS-22r self-image domain are used to measure the patient's self-perception. The purpose of this study is to investigate the relationship between objective surface topographic measurements of the torso to subjective patient self-perception. METHODS: 131 AIS subjects and 37 controls participated in this study. All subjects completed TAPS and SRS-22r PROMS followed by whole body 3d surface topographic scanning. An automated analysis pipeline was used to compute 57 measurements. Multivariate linear models were developed to predict TAPS and SRS-22r self-image using each unique combination of 3 parameters and leave one out validation where the best combinations were selected. RESULTS: Back surface rotation, waist crease vertical asymmetry and rib prominence volume were most predictive of TAPS. The final predicted TAPS values from leave one out cross validation was correlated to ground truth TAPS scores with an R value of 0.65. Back surface rotation, silhouette centroid deviation, and shoulder normal asymmetry were most predictive of SRS-22r self-image with a correlation of R = 0.48. CONCLUSION: Surface topographic measurements of the torso are correlated to TAPS and SRS-22r self-image scores in AIS patients and controls, with TAPS exhibiting a stronger relationship, better reflecting the patient's external asymmetries.

Effects of dual-channel functional electrical stimulation on gait performance in patients with hemiparesis.

The study objective was to assess the effect of functional electrical stimulation (FES) applied to the peroneal nerve and thigh muscles on gait performance in subjects with hemiparesis. Participants were 45 subjects (age 57.8 ± 14.8 years) with hemiparesis (5.37 ± 5.43 years since diagnosis) demonstrating a foot-drop and impaired knee control. Thigh stimulation was applied either to the quadriceps or hamstrings muscles, depending on the dysfunction most affecting gait. Gait was assessed during a two-minute walk test with/without stimulation and with peroneal stimulation alone. A second assessment was conducted after six weeks of daily use. The addition of thigh muscles stimulation to peroneal stimulation significantly enhanced gait velocity measures at the initial and second evaluation. Gait symmetry was enhanced by the dual-channel stimulation only at the initial evaluation, and single-limb stance percentage only at the second assessment. For example, after six weeks, the two-minute gait speed with peroneal stimulation and with the dual channel was 0.66 ± 0.30 m/sec and 0.70 ± 0.31 m/sec, respectively (P < 0.0001). In conclusion, dual-channel FES may enhance gait performance in subjects with hemiparesis more than peroneal FES alone.

A novel graded-stiffness footwear device for heel ulcer prevention and treatment: a finite element-based study.

Diabetic heel ulceration is a serious, destructive, and costly complication of diabetes. In this study, a novel "graded-stiffness" offloading method was proposed. This method consists of heel support with multi-increasing levels of stiffness materials, to prevent and treat heel ulcers. A three-dimensional finite element model of the heel was used to evaluate the novel "graded-stiffness" orthotic device compared to two existing solutions: (1) an insole with a hole under the active ulcer and (2) an insole with a hole filled with a soft material (elastic modulus of 15 kPa). Volumetric exposure evaluation of internal tissues to stress was performed at two volume-of-interests: (1) the area of the heel soft tissues typically at high risk for ulceration, and (2) the soft tissues surrounding the high-risk area. The models predict that the "graded-stiffness" offloading solution is more effective than existing solutions in distributing and reducing heel internal loads, considering both volume-of-interests. Comparing different material gradient combinations for the offloading support reveals considerable variation of the heel stress distribution. In clinical practice, the "graded-stiffness" technological solution enables to form an adaptable and flexible system that can be customized to a specific patient, through adequate selection of the offloading materials, to fit the shape and size of the ulcer. This solution can be made as an off-the-shelf product or alternatively, be manufactured by-demand using 3D printing tools. The proposed novel practical offloading solution has the potential for streamlining and optimizing the prevention and treatment of diabetic heel ulcers.

Plantar pressure modifications in experienced runners following an exhaustive run.

Running-induced fatigue alters foot strike pattern. The purpose of this study was to assess plantar pressure and centre of pressure (CoP) trajectory alterations after a 30-minute run at sub-maximal speed in experienced long-distance runners. Plantar pressure data from 9 experienced heel-to-toe male runners was collected before and after a 30-minute run on a treadmill at a speed 5% above the respiratory compensation point (RCP) of each participant. Significant changes in the plantar-pressure map were found post-run, including increased impulses in the first metatarsal head (9.92%, p < 0.001) and hallux areas (16.19%, p < 0.001), and decreased impulses in the fourth and fifth metatarsal heads (4.95%, p < 0.05). The CoP curve showed a medial shift (p < 0.01). The plantar-pressure map and CoP trajectory were altered following a 30-minute exhausting run. These changes may indicate an increase in stress on joints and tissues when individuals are fatigued and may promote overload injuries.

Reliability of automated topographic measurements for spine deformity.

PURPOSE: This study introduces a novel surface-topographic scanning system capable of automatically generating a suite of objective measurements to characterize torso shape. RESEARCH QUESTION: what is the reliability of the proposed system for measurement of trunk alignment parameters in patients with adolescent idiopathic scoliosis (AIS) and controls? METHODS: Forty-six adolescents (26 with AIS and 20 controls) were recruited for a prospective reliability study. A series of angular, volumetric, and area measures were computed from topographic scans in each of three clinically relevant poses using a fully automated processing pipeline. Intraclass correlation coefficients (ICC(2,1)) were computed within (intra-) and between (inter-) raters. Measurements were also performed on a torso phantom. RESULTS: Topographic measurements computed on a phantom were highly accurate (mean RMS error 1.7%) compared with CT. For human subjects, intra- and inter-rater reliability were both high (average ICC > 0.90) with intrinsic (pose-independent) measurements having near-perfect reliability (average ICC > 0.98). CONCLUSION: The proposed system is a suitable tool for topographic analysis of AIS; topographic measurements offer an objective description of torso shape that may complement other imaging modalities. Further research is needed to compare topographic findings with gold standard imaging of spinal alignment, e.g., standing radiography. CONCLUSION: clinical parameters can be reliably measured in a fully automated system, paving the way for objective analysis of symmetry, body shape pre/post-surgery, and tracking of pathology without ionizing radiation.

Finite element-based method for determining an optimal offloading design for treating and preventing heel ulcers.

Diabetic heel ulceration, a serious, destructive, and costly complication of diabetes, is often treated by custom-made offloading footwear. One common offloading device is a custom-made insole designed with a hole under the damaged site that is intended to reduce local mechanical loads on the ulcer. However, current devices do not take into account the increasing loads at the wound peripheries, and quantitative assessments and scientific guidelines for the optimal design of the offloading hole are lacking. Here, we develop a novel method to determine the volumetric exposure to mechanical loading of a human heel, at two volume of interests (VOIs) during walking in 150 different finite-element footwear configurations. We defined the two VOIs as (1) the area of the heel soft tissues typically at high risk of ulceration, and (2) the soft tissues surrounding the high risk area. For all model variants, three hole-geometry parameters were defined: (1) radius, (2) radius of curvature (ROC) and (3) depth. We found two combinations of the offloading parameters which minimize heel loads in both VOIs. The first is with a large offloading radius, large ROC and large depth, whereas the second is with a large offloading radius, large depth but relatively small ROC. Our novel practical scientific analysis method, that takes into account the ulcer site as well as the peripheral area, has the potential to optimize development of offloading solutions by streamlining the examination of their biomechanical efficiency, and thus may revolutionize prevention and treatment of diabetic ulcers at any foot location.

Analysis of subject specific grasping patterns.

Existing haptic feedback devices are limited in their capabilities and are often cumbersome and heavy. In addition, these devices are generic and do not adapt to the users' grasping behavior. Potentially, a human-oriented design process could generate an improved design. While current research done on human grasping was aimed at finding common properties within the research population, we investigated the dynamic patterns that make human grasping behavior distinct rather than generalized, i.e. subject specific. Experiments were conducted on 31 subjects who performed grasping tasks on five different objects. The kinematics and kinetics parameters were measured using a motion capture system and force sensors. The collected data was processed through a pipeline of dimensionality reduction and clustering algorithms. Using finger joint angles and reaction forces as our features, we were able to classify these tasks with over 95% success. In addition, we examined the effects of the objects' mechanical properties on those patterns and the significance of the different features for the differentiation. Our results suggest that grasping patterns are, indeed, subject-specific; this, in turn, could suggest that a device capable of providing personalized feedback can improve the user experience and, in turn, increase the usability in different applications. This paper explores an undiscussed aspect of human dynamic patterns. Furthermore, the collected data offer a valuable dataset of human grasping behavior, containing 1083 grasp instances with both kinetics and kinematics data.

Mechanism of reducing knee adduction moment by shortening of the knee lever arm via medio-lateral manipulation of foot center of pressure: A pilot study.

Prominent conservative treatment options for medial-compartment knee osteoarthritis include footwear that reduces knee adduction moment (KAM) correlated with detrimental loads in the medial compartment of the knee, thus providing clinical benefit. The proposed mechanism by which they reduce KAM is a lateral shift in foot center of pressure (COP) and a consequent shortening of the knee lever arm (KLA), thereby reducing KAM, which can be simply calculated as KLA multiplied by the frontal plane ground reaction force (FP-GRF). The present study investigated this mechanism for a unique biomechanical device capable of shifting COP by means of moveable convex elements attached to the shoe. Fourteen healthy young male subjects underwent gait analysis in two COP configurations of the device for comparison: (1) laterally and (2) medially deviated. Average midstance KLA and KAM were decreased by 8.2% and 8.7%, respectively, in the lateral COP compared to medial. Ground reaction force parameters, frontal plane knee angle (FP-KA), and spine lateral flexion angle (SLF) did not differ between COP configurations. No study parameters differed for terminal stance. Linear mixed effects models showed that COP and FP-GRF components, but not FP-KA and SLF, were significant predictors of KLA. In addition, KLA and FP-GRF were significant predictors of KAM; although, FP-GRF did not change significantly with medio-lateral COP shift, while KLA did. This suggests that the mechanism by which the study device reduces KAM is primarily through shortening of KLA brought on by a lateral shift in COP.

The effect of unstable shoe designs on the variability of gait measures.

BACKGROUND: Unstable footwear designs are popular as training devices to strengthen human neuromuscular control, and many studies have evaluated their effect on gait parameters in comparison to conventional footwear designs. However, there is minimal research on variability of gait measures during walking with unstable shoes. Therefore, the study objective was to compare variability of gait measures between stable and unstable shoe configurations, in conjunction with kinematic and kinetic changes. METHODS: Fifteen healthy male subjects walked in both a stable and unstable footwear device configuration while full-body gait kinematic and kinetic data was collected. Averages and standard deviations of gait trials were compared between the two configurations at different stages of each step. RESULTS: Comparison of gait variability between both footwear configurations revealed that variability of frontal-plane foot center of pressure offset, transverse-plane ankle moment, and frontal-plane shoulder angle decreased significantly while walking in the unstable configuration, while transverse-plane spine angle variability increased. No changes in variability of gait measures at the knee, hip, or pelvis were observed. Kinematic and kinetic changes were observed throughout the whole body with the unstable shoe. CONCLUSION: Our findings suggest that the unstable device used in the study may reduce gait variability at the two extremes of the kinematic chain (i.e., foot, ankle, and shoulders), but increase variability of spine rotation angle. This may suggest a compensatory mechanism to maintain both stability and adaptability, and may have potential clinical implications for gait retraining and enhancing dynamic gait stability and joint stability, pending further investigation.

Anatomical Wrist Patterns on Plain Radiographs.

BACKGROUND: Interpreting the structure in the wrist is complicated by the existence of multiple joints as well as variability in bone shapes and anatomical patterns. Previous studies have evaluated lunate and capitate shape in an attempt to understand functional anatomical patterns. OBJECTIVE: The purpose of this study was to describe anatomical shapes and wrist patterns in normal wrist radiographs. We hypothesized that there is a significant relationship in the midcarpal joint with at least one consistent pattern of wrist anatomy. METHODS: Seventy plain posteroanterior (PA) and lateral wrist radiographs were evaluated. These radiographs were part of a previously established normal database, had all been read by a radiologist as normal, and had undergone further examination by 2 hand surgeons for quality. Evaluation included: lunate and capitate shape (type 1 and 2 lunate shape according to the classification system by Viegas et al.), ulnar variance, radial inclination and height, and volar tilt. RESULTS: A significant association was found between lunate and capitate shape using a dichotomal classification system for both lunate and capitate shapes (p=0.003). Type 1 wrists were defined as lunate type1and a spherical distal capitate. Type 2 wrists had a lunate type 2 and a flat distal capitate. No statistically significant associations were detected between these wrist types and measurements of the radiocarpal joint. CONCLUSION: There was a significant relationship between the bone shapes within the midcarpal joint. These were not related to radiocarpal anatomical shape. Further study is necessary to better describe the two types of wrist patterns that were defined and to understand their influence on wrist biomechanics and pathology.

Trunk kinematic, kinetic, and neuro-muscular response to foot center of pressure translation along the medio-lateral foot axis during gait.

Footwear devices that shift foot center of pressure (COP), thereby impacting lower-limb biomechanics to produce clinical benefit, have been studied regarding degenerative diseases of knee and hip joints, exhibiting evidence of clinical success. Ability to purposefully affect trunk biomechanics has not been investigated for this type of footwear. Fifteen healthy young male subjects underwent gait and electromyography analysis using a biomechanical device that shifts COP via moveable convex elements attached to the shoe sole. Analyses were performed in three COP configurations for pairwise comparison: (1) neutral (control) (2) laterally deviated, and (3) medially deviated. Sagittal and frontal-plane pelvis and spine kinematics, external oblique activity, and frontal and transverse-plane lumbar moments were affected by medio-lateral COP shift. Transverse-plane trunk kinematics, activity of the lumbar longissimus, latissimus dorsi, rectus abdominus, and quadratus lumborum, and sagittal-plane lumbar moment, were not significantly impacted. Two linear mixed effects models assessed predictive impact of (I) COP location, and (II) trunk kinematics and neuromuscular activity, on the significant lumbar moment parameters. The COP was a significant predictor of all modeled frontal and transverse-plane lumbar moment parameters, while pelvic and spine rotation, and lumbar longissimus activity were significant predictors of one frontal-plane lumbar moment parameter. Model results suggest that, although trunk biomechanics and muscle activity were altered by COP shift, COP offset influences lumbar kinetics directly, or via lower-limb changes not assessed in this study, but not by means of alteration of trunk kinematics or muscle activity. Further study may reveal implications in treatment of low back pain.

Control of knee coronal plane moment via modulation of center of pressure: a prospective gait analysis study.

OBJECTIVES: Footwear-generated biomechanical manipulations (e.g., wedge insoles) have been shown to reduce the magnitude of adduction moment about the knee. The theory behind wedged insoles is that a more laterally shifted location of the center of pressure reduces the distance between the ground reaction force and the center of the knee joint, thereby reducing adduction moment during gait. However, the relationship between the center of pressure and the knee adduction moment has not been studied previously. The aim of this study was to examine the association between the location of the center of pressure and the relative magnitude of the knee adduction moment during gait in healthy men. METHODS: A novel foot-worn biomechanical device which allows controlled manipulation of the center of pressure location was utilized. Twelve healthy men underwent successive gait analysis testing in a controlled setting and with the device set to convey three different para-sagittal locations of the center of pressure: neutral, medial offset and lateral offset. RESULTS: The knee adduction moment during the stance phase significantly correlated with the shift of the center of pressure from the functional neutral sagittal axis in the coronal plane (i.e., from medial to lateral). The moment was reduced with the lateral sagittal axis configuration and augmented with the medial sagittal axis configuration. CONCLUSIONS: The study results confirm the hypothesis of a direct correlation between the coronal location of the center of pressure and the magnitude of the knee adduction moment.

Fully automated computer algorithm for calculating articular contact points with application to knee biomechanics.

A fully automated computer algorithm for calculating the articular contact points between two bone surface models is presented. The algorithm requires the bone surface models and their relative positions as inputs in order to resolve the articular contact path. In the case of surface model overlap due to measurement errors or as a solution of an optimization procedure, the result is a volumetric estimation of the space confined between the two surfaces. The algorithm is based on attaching a grid of lines to one bone surface model and calculating the intersecting points of each of the lines in the grid with both bone surface models. The contact points are then determined as the closest points between the surfaces along the lines in the grid. The same contact points are used to evaluate any volume that is confined between two overlapping surface models. The algorithm is ideal for use in biomechanical studies, simulations of joint motion, and optimizations that require an iterative process to determine contact path and relative bone position. The algorithm is applied to a Sawbones knee model that is moved from flexion to extension while being tracked by an optical tracking system. The contact path of the two bones is generated and an example of calculating bone impingement is provided.

The effects of body weight unloading on kinetics and muscle activity of overweight males during Overground walking.

BACKGROUND: Excess body weight has become a major worldwide health and social epidemic. Training with body weight unloading, is a common method for gait corrections for various neuromuscular impairments. In the present study we assessed the effects of body weight unloading on knee and ankle kinetics and muscle activation of overweight subjects walking overground under various levels of body weight unloading. METHODS: Ten overweight subjects (25 ≤ BMI < 29.9 kg/m2) walked overground under a control and three (0%, 15%, 30%) body weight unloading experimental conditions. Gait parameters assessed under these conditions included knee and ankle flexion moments and the Electromygraphic activity of the Tibialis Anterior, Lateral Gastrocnemius and Vastus Lateralis. FINDINGS: Increasing body weight unloading levels from 0% to 30% was found to significantly reduce the peak knee flexion and ankle plantarflexion moments. Also observed was a significant reduction in muscle activity of the Tibialis Anterior, Lateral Gastrocnemius and Vastus Lateralis under the three body-weight unloading conditions. INTERPRETATION: Our results demonstrate that a reduction of up to 30% overweight subjects' body weight during gait is conducive to a reduction in the knee and ankle flexion moments and in the balancing net quadriceps moment and ankle flexors moment. The newly devised body weight unloading device is therefore an effective method for reducing joint loads allowing overweight people who require controlled weight bearing scenarios to retrain their gait while engaging in sustained walking exercise.