Virtual Poster Session

Welcome to the Virtual Poster Session, a new and powerful tool for networking and information exchange. Here you can share your work, search though the poster library, and start a dialogue with others in your field. Each uploaded poster that pertains to force measurement and testing can currently be used to apply for an academic travel scholarship; please see the Scholarships page for application details and deadlines.

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Name: tiffytiru

Background: Patellofemoral pain (PFP) is a common condition seen in orthopedic practice. A commonly cited hypothesis as to the cause of PFP is increased patellofemoral joint (PFJ) stress secondary to abnormal lower extremity kinematics (ie. excessive hip internal rotation and knee valgus). However, the influence of these motions on PFJ contact mechanics is unknown.

Purpose: To assess the influence of hip rotation and knee valgus on PFJ stress using finite element (FE) analysis.

Methods: Patella cartilage stress profiles for a healthy participant were quantified utilizing a subject-specific FE model. Input parameters included: joint geometry, quadriceps muscle forces, and weight-bearing PFJ kinematics. Using a nonlinear FE solver, quasi-static loading simulations were performed to quantify patella cartilage stress during a static squatting maneuver (45° knee flexion). To simulate hip rotation (0-8°) and knee valgus (0-12°), the femur and tibia were rotated in the transverse and frontal plane respectively in 2° increments.

Results: Increasing hip rotation resulted in a linear increase in patella cartilage stress. In contrast, increasing knee valgus resulted in a decrease in patella cartilage stress. The combination of hip rotation and knee valgus did not result in higher PFJ cartilage stress compared to isolated hip rotation.

Conclusions: Patella cartilage stress appears to be influenced to a greater degree by hip internal rotation as opposed to knee valgus. Surprisingly, higher degrees of knee valgus resulted in decreased cartilage stress (in the absence of hip rotation). Our finding supports the premise that persons exhibiting excessive hip internal rotation may be pre-disposed to elevated patella cartilage stress.

Name: hmculbertson

This work introduces the Penn Haptic Texture Toolkit (HaTT), a publicly available repository of haptic texture models for use by the research community. HaTT includes 100 haptic texture and friction models, the recorded data from which the models were made, images of the textures, and the code and methods necessary to render these textures using an impedance-type haptic interface such as a SensAble Phantom Omni. This work reviews our previously developed methods for modeling haptic virtual textures, describes our technique for modeling Coulomb friction between a tooltip and a surface, discusses the adaptation of our rendering methods for display using an impedance-type haptic device, and provides an overview of the information included in the toolkit. Each texture and friction model was based on a ten-second recording of the force, speed, and high-frequency acceleration experienced by a handheld tool moved by an experimenter against the surface in a natural manner. We modeled each texture’s recorded acceleration signal as a piecewise autoregressive (AR) process and stored the individual AR models in a Delaunay triangulation as a function of the force and speed used when recording the data. Measurements of the user’s instantaneous normal force and tangential speed are used to synthesize texture vibrations in real time. These vibrations are transformed into a texture force vector that is added to the friction and normal force vectors for display to the user.

Name: pranav-parikh@u...

Transcranial anodal stimulation (tDCS) improves manual dexterity in healthy old adults. The underlying changes in finger force behavior for this improved dexterity have not been reported. Here, we investigated the effects of tDCS (20-min) over primary motor cortex (M1) combined with repeated practice on the Grooved pegboard test (tDCS+MP) on the fingertip forces applied to an object during grasp and manipulation. Eight right-handed able-bodied individuals (60-85 years) participated in a sham-controlled, single-blinded study. Each participant received anodal and sham intervention in two sessions at least 5-day apart. Before and after intervention, they performed a ‘key-slot’ task that required inserting a slot on an object onto a stationary bar, an isometric force production task using a pinch grip, and the Grooved pegboard test. Anodal relative to sham tDCS+MP allowed participants to better retain the improved performance on the pegboard test. For the isometric task, anodal tDCS+MP significantly increased the variability of force compared to sham tDCS+MP. More importantly, the improved retention of performance post-anodal tDCS correlated with the reduction in force angle variability on the key-slot task, but not with the change in force variability on the isometric task. Our findings suggest that anodal tDCS+MP facilitated retention of learning on a skillful manual task in healthy old adults, consistent with the role of M1 in retention of learning versus skill acquisition. Furthermore, improved force steadiness is one of the potential mechanisms through which short-term anodal tDCS during motor training yields improved performance on a functional task.

Name: donyafrank

A comprehensive characterization of small-scale fluid-sediment interactions will improve understanding of large-scale ocean engineering phenomena, resulting in more accurate wave forecasting and improved ocean circulation models. The critical shear stress is typically used to determine the initiation of sediment motion in coastal applications. However, this shear stress criterion was primarily developed for steady flows and has been inconclusive in some wave environments where sediment motion may be induced by horizontal pressure gradients. Evidence suggests that the incipient motion formulation should account for the combined effects of the horizontal pressure gradients and bed shear stresses. Other researchers have made one-dimensional and two-dimensional measurements of near-bed velocities. However, previously available technologies could not resolve the three-dimensional velocities at the bed or directly measure sediment motion.
Accurate investigation of the hydrodynamic forces that initiate coastal sediment transport requires high resolution measurements at the fluid-sediment interface. We have made previously unavailable high spatial and temporal resolution laboratory measurements at the sediment bed with state-of-the-art instruments. Additionally, we have performed one of the first direct measurements of sediment motion in response to waves with newly-developed electronic grains. The MEMs sensors are 2.5 x 1.5 x 1.4 cm and measure three-dimensional accelerations, store the data onboard, and transmit them wirelessly after retrieval. The Smart Sediment Grains (SSGs) were developed by embedding MEMs sensors in gravel-sized Delrin plastic spheres. These spheres allow uninhibited movement in any direction, similar to a smooth sand grain. The SSGs are the first freely moving electronic grains that measure sediment dynamics which previous technologies could not, giving insight into the underlying wave forces driving sediment transport. The SSGs enhance our ability to measure the motion, transport, and settling of sediments in the nearshore by capturing translation and rotation of the sediment. This will improve our predictive capabilities of sediment transport phenomena such as beach erosion and seabed evolution in response to wave forces; as well as improve parameterizations of the bottom friction for ocean circulation and wave energy dissipation models.
The SSGs have been successfully deployed in small and field-scale wave flumes to measure the response of coarse gravel sediments to wave forcing. High resolution profiling Acoustic Doppler Velocimeters and a Particle Image Velocimetry system, comprising a laser and four high speed cameras, measured the three-dimensional fluid velocities at the bed. These measurements provide resolution high enough to fully examine the small-scale fluid forces exerted on each individual sediment grain. The SSGs accurately captured the sediment response to the waves at the onset of sediment transport. Additionally, broader incipient motion experiments were conducted with a variety of sediment grain diameters and densities for comparison. The results suggest evidence of pressure gradient influenced incipient motion; in contrast with the more commonly used threshold for sediment motion based on the bed shear stress. Calculated values of the Sleath parameter, used to quantify the effects of the pressure gradients, were comparable with field observations of pressure
gradient induced sediment transport. The data also suggest that vortex shedding could be a factor in triggering sediment transport.
We have directly measured incipient motion in waves by resolving the near-bed fluid velocities and collecting direct measurements of sediment motion with state-of-the-art instruments. The data are being used to validate theoretical and numerical models of the wave bottom boundary layer and bottom friction estimates. These results will be synthesized to propose a comprehensive incipient motion criterion comprising the effects of the shear stress and the pressure gradients, also taking into account a variety of flow and sediment characteristics.
The current configuration of the SSGs helps to identify the characteristics of incipient motion and determine orientation. These mobile nodes make a significant step towards resolving the Lagrangian dynamics of individual coarse gravel-sized particles within the mobile bed layer in the nearshore. On a larger scale, they will reduce the effects of beach erosion by improving beach nourishment design. With technological advancements, these SSGs can be minimized and made field-deployable with enclosures configured to other applications to provide transformative measurements in geotechnical engineering, hydrology, oceanography and human health monitoring.

Listed In: Other
Name: nesbitt.rj

Functional demands placed on the human knee’s anterior cruciate ligament (ACL) vary with activity but remain impossible to measure directly in-vivo. Our lab is characterizing these demands in the sheep model by recording in vivo knee kinematics and ACL transducer voltages during activities of daily living (ADLs), reproducing these motions using the instrumented limb, and measuring the 3D forces in the ligament. However, up to 13% of patients sustaining ACL injuries will also sustain dual medial meniscus (MM) injuries and up to 10% will sustain dual medial collateral ligament (MCL) injuries. These structures are frequently left unrepaired, which may alter the ACL’s functional demands, resulting in inadequate ACL reconstruction outcomes for patients with dual injuries. Although these structures have been shown to alter ACL loading in cadaveric studies, the extent to which they impact ACL functionality during in vivo ADLs remains unknown. Moreover, changes in ACL functionality over time due to joint healing and remodeling have yet to be investigated. In this study, we aimed to track stifle joint remodeling in response to surgically imposed MCL transections and medial meniscectomies through monitoring vertical ground reaction forces (VGRFs) for three ADLs over 12 weeks. Results of this study may then be used in conjunction with future robotic studies as a tool to estimate in vivo load requirements for ACL reconstructions in patients with dual injuries.

Name: bwannipa

Objective: To evaluate the effect of auditory cues toward postural control in patients with Parkinson's disease (PD).
Background: Auditory cues have been proved to be one of rehabilitation strategies for PD [1]. Most of Parkinson's Disease patients present postural instabilities regarding the severity of the disease [2, 3]. Rhythmic Auditory Stimulation (RAS) has been justified to be a standardized neurological motor therapy (NMTs) in PD, which cue-ing benefits may be associated with the activation of cerebellum-thalamic-cortical circuitry [4]. A potential method to stimulate the putamen that might help regulate PD brain's circuits could be providing music as a rhythmical cue [4]. A distinct manifestation in PD is also the arm swing reduction [5] which limits the capability of maintaining balance. It is rare to explore the static standing balance in Parkinson's Disease.
Methods: 5 idiopathic PD patients (5 female) aged 72.6 ± 2.51 years, duration of the disease 15 ± 1.22 years (mean ± SD), H&Y 2.5-3 participated in this study. They were recruited from Yawata Medical Center, Ishikawa, Japan in June and November, 2014. The subjects were instructed to stand on the balance platform (Nintendo Wii Fit) and swing arm; Alternation (Alt) and Synchronization (Syn) in 3 scenarios; with no auditory cues (AC), with AC 5% increased and with AC 5 % decreased. The data were analyzed by Wilcoxon Signed Ranks Test and the dimensional clustering method [6] on MATLAB.
Results: Tempo at 95% improved area, RMS and Min ML in Alternation, and decreased the path length in rest 2. Tempo at 105% decreased area and RMS in rest 2 statistically significant. A case with H&Y stage 3 showed poorer postural control in both Antero-Posterior (AP) and Medio-Lateral (ML) directions. Most cases presented the higher Center of Pressure (CoP) displacement in ML direction. AC with arm swing regulated the pattern of CoP trajectories.
Conclusions: Auditory cues with arm swing - Alternation improved postural control in the PD patients. This concept might be considered clinically to be a rehabilitation program for Parkinson's disease (PD) to improve standing balance. It is a need to enlarge the sample size and develop more rehabilitation programs for improving balance in PD.

Name: lsosdian

Background: Gait abnormalities can influence surgical outcomes in people with severe knee osteoarthritis (OA) and thus a thorough understanding of gait abnormalities in these people prior to arthroplasty is important. Varus-valgus thrust is a characteristic linked to OA disease progression that has not yet been investigated in a cohort with severe knee OA awaiting knee arthroplasty. The aims of this study were to determine i) prevalence of varus and valgus thrust in a cohort with severe knee OA compared to an asymptomatic group, ii) whether the thrust magnitude differed between these groups iii) differences between varus and valgus thrusters within the OA cohort and iv) whether certain measures could predict thrust in the OA cohort.

Methods: 40 patients with severe knee OA scheduled for primary TKR and 40 asymptomatic participants were recruited. Three-dimensional gait analysis was performed on all participants, with the primary biomechanical measures of interest being: varus and valgus thrust, knee adduction angle, peak KAM, and KAM impulse. Additionally, static knee alignment and quadriceps strength were assessed in the subgroup with knee OA.

Findings: No difference was found in the prevalence of varus and valgus thrust between the severe OA and control groups (Pearson chi-square = 3.735, p value = 0.151). The OA varus thrust group had a significantly higher peak KAM (p=0.000), KAM impulse (p=0.001), static alignment (p=0.021), and lower quadriceps strength (p=0.041) than the valgus thrust group. Peak KAM and quadriceps strength were found to explain 34.9% of the variation in maximum thrust, such that an increase in KAM and a decrease in quadriceps strength were associated with an increase in maximum (varus) thrust.

Interpretation: Few differences between the severe OA and control groups were seen, however dichotomizing the groups into varus and valgus cohorts revealed a number of biomechanical differences. Patients with severe OA are often treated as a homogenous cohort; however, by classifying which individuals have a varus or valgus thrust, we have identified a subset of patients with poorer biomechanics who could potentially be at a higher risk of a worse outcome after surgery.

Name: Valentina

Our previous study showed that exposure to Galvanic Vestibular Stimulation (GVS) induces temporary postural deficits similar to the ones experienced by astronauts after microgravity exposure. Preliminary evidence suggests that repeated exposures to GVS might induce adaptation of sway response. We studied whether repeated exposure to pseudorandom GVS over a 3 month period facilitates the adaptation response. Twenty healthy subjects were randomly assigned into 2 groups: suprathreshold (5mA) GVS, and subthreshold (1mA). The test battery included: Romberg, sensory organization test (posturography), dynamic visual acuity, and torsional eye movement. Each test was performed with no GVS, and then with 10 min of GVS per session for 12 consecutive weeks. Sensorimotor adaptation was also measured during two follow up sessions at weeks 18 and 36. Results showed that subthreshold GVS did not affect vestibular scores. Suprathreshold GVS significantly decreased vestibular scores during the first few weeks, with postural performance returning to baseline around the 6th week of exposure. This improvement was maintained during the follow up sessions. Our results suggest that 60 min of subthreshold GVS are sufficient to elicit adaptation to the stimulus. No significant changes were shown in low-level vestibulo-ocular reflexes during torsional eye movement, or vestibulo-spinal reflexes during Romberg; confirming that adaptation only occurs at the level of the CNS. NASA NCC 9-58; NNX09AL14G

Name: Florian Paternoster

When an active muscle is stretched, the resulting post-eccentric steady-state force is known to be greater than the isometric force at the corresponding muscle length. The aim of our research was to clarify if residual force enhancement (RFE) is relevant for voluntary human muscle action in everyday like scenarios. Therefore 13 healthy subjects participated in our study and had to perform bilateral leg extensions using a motor-driven leg press dynamometer, measuring external reaction forces (Fext) as well as activity of 9 lower extremity muscles. In addition, ankle (Ma) and knee (Mk) joint torque were calculated using inverse dynamics. Subjects performed isometric and isometric-eccentric-isometric contractions (20° stretch, ω=60°/s) at 30% of maximum voluntary activation. Visual feedback of VL muscle activation was given to control submaximal muscle action. We did not find differences in VL activation level between contraction conditions and time points. Mean VL activity ranged between 29.1 ± 2.2% and 29.8±2.5% MVA. We found significantly enhanced Fext (p < 0.002) as well as joint torques in knee (p < 0.002) and ankle joint (p < 0.033) for all instances in time. In summary RFE seems to be relevant in everyday like human motion.

Name: pienciak

We investigated whether stability affects the learning and/or transfer of human postural control strategies. Subjects learned novel postural control strategies in a more stable standing configuration and then transferred to a less stable configuration, or vice versa. Initial learning was not affected by stability. However, transfer of learned control from one context to another was affected by the change in stability between contexts. These results suggest that in rehabilitation it is important to consider the context in which task learning occurs, as well as the context in which the task will be performed in the future.