Vibhor Agrawal

Symmetry in External Work (SEW): A novel method of quantifying gait differences between prosthetic feet

Unilateral transtibial amputees (TTAs) show subtle gait variations while using different prosthetic feet. These variations have not been detected consistently with previous experimental measures. We introduce a novel measure called Symmetry in External Work (SEW) for quantifying kinetic gait differences between prosthetic feet. External work is the result of changes in kinetic and potential energy of body center of mass (CoM). SEW is computed by integrating vertical ground reaction forces obtained using F-scan in-sole sensors. Since various prosthetic feet have different designs, we hypothesized that SEW will vary with the type of foot used. This hypothesis was tested with a single unilateral TTA using four prosthetic feet (Proprio, Trias+, Seattle Lite and SACH). The Proprio (mean symmetry 94.5% ± 1.1%) and the Trias+ (92.1% ± 2.5%) feet exhibited higher symmetry between the intact and prosthetic limbs, as compared to the Seattle (67.8% ± 19.3%) and SACH (35.7% ± 11.1%) feet. There was also a good agreement in vertical CoM excursion between the intact foot and prosthetic feet with heel-toe foot plate designs. Results indicate that SEW measure may be a viable method to detect kinetic differences between prosthetic feet and could have clinical applications because of relatively low cost instrumentation and minimal subject intervention.

Weight distribution symmetry during the sit-to-stand movement of unilateral transtibial amputees

This study characterises weight distribution symmetry between the intact and amputated limbs of unilateral transtibial amputees during a sit-to-stand movement. A total of 12 amputees and 12 age-matched, non-amputees performed the activity for two conditions – rising with and without chair arm-rest assistance. The sit-to-stand movement was divided into five events: Pre-Ascent; Ascent Initiation; Seat-Off; Deceleration; Standing. Symmetry in ground reaction forces between limbs was calculated at each event together with the rise time. Results indicate that during the course of the movement, amputees increased loading of the intact limb by approximately 27%, resulting in a significant asymmetry at seat-off and deceleration events. Non-amputees loaded the dominant limb more than the non-dominant limb throughout the activity but did not exhibit substantial weight shifts. Weight distribution symmetry was not significantly different between the two rising conditions in either population. Amputees had significantly longer rise times than non-amputees only while rising without arm-rest assistance. Statement of Relevance: Sit-to-stand movements are performed frequently every day. Incorrect movement biomechanics caused by musculoskeletal impairments can lead to reduced functional independence and secondary co-morbidities. This study defines five events of a sit-to-stand cycle and is the first to address asymmetries of transtibial amputees, providing ergonomic insights for clinical assessment and intervention.

Influence of gait training and prosthetic foot category on external work symmetry during unilateral transtibial amputee gait.

Background: Prosthetic foot prescription guidelines lack scientific evidence and are concurrent with an amputee’s concurrent with an amputee’s Medicare Functional Classification Level (K-Level) and categorization of prosthetic feet. Objective: To evaluate the influence of gait training and four categories of prosthetic feet (K1, K2, K3, and microprocessor ankle/foot) on Symmetry in External Work for K-Level-2 and K-Level-3 unilateral transtibial amputees. Design: Randomized repeated-measures trial. Methods: Five K-Level-2 and five K-Level-3 subjects were tested in their existing prosthesis during Session 1 and again in Session 2, following 2 weeks of standardized gait training. In Sessions 3–6, subjects were tested using a study socket and one of four randomized test feet. There was an accommodation period of 10–14 days with each foot. Symmetry in External Work for positive and negative work was calculated at each session to determine symmetry of gait dynamics between limbs at self-selected walking speeds. Results: K-Level-2 subjects had significantly higher negative work symmetry with the K3 foot, compared to K1/K2 feet. For both subject groups, gait training had a greater impact on positive work symmetry than test feet. Conclusion: Higher work symmetry is possible for K-Level-2 amputees who are trained to take advantage of K3 prosthetic feet designs. There exists a need for an objective determinant for categorizing and prescribing prosthetic feet. Clinical relevance Findings that gait training can influence symmetry of gait dynamics and that K-Level-2 amputees can achieve greater work symmetry with a K3 foot having a “J-shaped” ankle and heel-to-toe footplate could potentially impact prosthetic care and foot prescription by clinicians and reimbursement guidelines by third-party health-care payers.

Comparison of four different categories of prosthetic feet during ramp ambulation in unilateral transtibial amputees

Background: Comparative effectiveness of prosthetic feet during ramp ambulation in unilateral transtibial amputees, who function at different Medicare Functional Classification Levels, has not been published. Objective: To determine differences in symmetry in external work between four categories of prosthetic feet in K-Level-2 and K-Level-3 unilateral transtibial amputees during ramp ascent and descent. Study design: Randomized repeated-measures trial. Methods: Ten subjects completed six testing sessions during which symmetry in external work was calculated using F-scan in-sole sensors. Between testing sessions 1 and 2, subjects received standardized functional prosthetic training. In Sessions 3–6, subjects tested four feet—solid ankle cushion heel, stationary attachment flexible endoskeleton, Talux (categories K1, K2, and K3, respectively), and Proprio-Foot (microprocessor ankle)—using a study socket and had a 10- to 14-day accommodation period with each foot. Results: During ramp descent, K-Level-2 subjects demonstrated higher symmetry in external work values with Talux and Proprio-Foot compared to the solid ankle cushion heel foot. K-Level-3 subjects also had higher symmetry in external work values with the Talux foot than the solid ankle cushion heel foot. Ramp ascent symmetry in external work values were not significantly different between feet. Conclusions: Prosthetic foot category appears to influence symmetry in external work more during decline walking than incline walking. K-Level-2 unilateral transtibial amputees achieve greater symmetry from K3 dynamic response prosthetic feet with J-shaped ankle and microprocessor ankles while descending ramps. Clinical relevance The findings suggest that K-Level-2 unilateral transtibial amputees benefit from K3 dynamic response prosthetic feet with J-shaped ankle. These results support the prescription of K3 feet for K-Level-2 amputees who frequently negotiate ramps.

Missing Sample Recovery for Wireless Inertial Sensor-Based Human Movement Acquisition

This paper presents a novel, practical, and effective routine to reconstruct missing samples from a time-domain sequence of wirelessly transmitted IMU data during high-level mobility activities. Our work extends previous approaches involving empirical mode decomposition (EMD)-based and auto-regressive (AR) model-based interpolation algorithms in two aspects: 1) we utilized a modified sifting process for signal decomposition into a set of intrinsic mode functions with missing samples, and 2) we expand previous AR modeling for recovery of audio signals to exploit the quasi-periodic characteristics of lower-limb movement during the modified Edgren side step test. To verify the improvements provided by the proposed extensions, a comparison study of traditional interpolation methods, such as cubic spline interpolation, AR model-based interpolations, and EMD-based interpolation is also made via simulation with real inertial signals recorded during high-speed movement. The evaluation was based on two performance criteria: Euclidian distance and Pearson correlation coefficient between the original signal and the reconstructed signal. The experimental results show that the proposed method improves upon traditional interpolation methods used in recovering missing samples.

The development and concurrent validity of a real-time algorithm for temporal gait analysis using inertial measurement units

The use of inertial measurement units (IMUs) for gait analysis has emerged as a tool for clinical applications. Shank gyroscope signals have been utilized to identify heel-strike and toe-off, which serve as the foundation for calculating temporal parameters of gait such as single and double limb support time. Recent publications have shown that toe-off occurs later than predicted by the dual minima method (DMM), which has been adopted as an IMU-based gait event detection algorithm.In this study, a real-time algorithm, Noise-Zero Crossing (NZC), was developed to accurately compute temporal gait parameters. Our objective was to determine the concurrent validity of temporal gait parameters derived from the NZC algorithm against parameters measured by an instrumented walkway. The accuracy and precision of temporal gait parameters derived using NZC were compared to those derived using the DMM. The results from Bland-Altman Analysis showed that the NZC algorithm had excellent agreement with the instrumented walkway for identifying the temporal gait parameters of Gait Cycle Time (GCT), Single Limb Support (SLS) time, and Double Limb Support (DLS) time. By utilizing the moment of zero shank angular velocity to identify toe-off, the NZC algorithm performed better than the DMM algorithm in measuring SLS and DLS times. Utilizing the NZC algorithms gait event detection preserves DLS time, which has significant clinical implications for pathologic gait assessment.

Measurement of lower limb segmental excursion using inertial sensors during single limb stance

Advances in wearable technology have afforded health scientists and clinicians the ability to quantify clinically meaningful kinematic data with performance-based outcome measures in a variety of environments. However, no method for assessing segmental excursion of the lower limb during single limb stance (SLS) with wearable technology has been described in the literature nor has its clinical meaning been explored. This study introduces a clinically friendly measure to quantify lower limb segmental excursion during SLS with inertial measurement units (IMUs) which called the region of limb stability (ROLS). The purpose of this study was to determine the concurrent validity of an IMU-based system versus an optical motion capture system and to determine the effects of knee injury on the ROLS value. Excursion areas of five healthy adults were calculated with the IMU-based system and data were compared with an optical motion capture system. There were high correlations (0.82-0.93) and no significant difference (p > 0.05) in the tested parameters between the optical- and IMU-based systems. The IMU-based method was also implemented in five Division I athletes with knee injuries to determine changes in ROLS due to the injury. The ROLS Symmetry Index value offered a higher sensitivity and specificity to assess the presence of knee impairment than the sacral IMU. Quantified lower limb segmental excursion via IMUs can make better and more precise return-to-sport decisions that would decrease the risk of re-injury.

A practical step length algorithm using lower limb angular velocities

The use of Inertial Measurement Units (IMUs) for spatial gait analysis has opened the door to unconstrained measurements within the home and community. Bandwidth, cost limitations, and ease of use has historically restricted the number and location of sensors worn on the body. In this paper, we describe a four-sensor configuration of IMUs placed on the shanks and thighs that is sufficient to provide an accurate measure of temporal gait parameters, spatial gait parameters, and joint angle dynamics during ambulation. Estimating spatial gait parameters solely from gyroscope data is preferred because gyroscopes are less susceptible to sensor noise and a system comprised of only gyroscopes uses decreased bandwidth compared to a typical 9 degree-of-freedom IMU. The purpose of this study was to determine the validity of a novel method of step length estimation using gyroscopes attached to the shanks and thighs. An Inverted Pendulum Model algorithm (IPM) was proposed to calculate step length, stride length, and gait speed. The algorithm incorporates heel-strike events and average forward velocity per step to make these assessments. IMU algorithm accuracy was determined via concurrent validity with an instrumented walkway and results explained via the collision model of gait. The IPM produced accurate estimates of step length, stride length, and gait speed with a mean difference of 3 cm and an RMSE of 6.6 cm for step length, thus establishing a new approach for spatial gait parameter calculation. The lack of numerical integration in IPM makes it well suited for use in continuous monitoring applications where sensor sampling rates are restricted.

Analysis of weight distribution strategies in unilateral transtibial amputees during the stand-to-sit activity.

Current methods of quantifying the stand-to-sit activity (StTS) are resource intensive and have not been applied to unilateral transtibial amputees (TTAs). The purpose of this study is to define five phases of arm-rest assisted and unassisted StTS using simple instrumentation and implement this method for assessing TTA movement patterns. Twelve TTAs and 12 age-matched non-amputees performed StTS with and without arm-rest support. Symmetry of weight distribution between lower limbs was calculated for five StTS phases: Descent Initiation; Descent Deceleration; Seat-Contact; Stabilisation and Sitting. TTAs demonstrated an asymmetrical weight distribution pattern and a tendency to transfer weight to the intact limb during the course of the activity. Non-amputees had relatively higher symmetry and did not exhibit substantial weight shifts during the activity. Symmetry indices were similar for assisted and unassisted sitting in both subject groups. These results highlight a need for therapeutic interventions in TTAs for reducing loading asymmetries and associated co-morbidities. Practitioner Summary: This study defines a novel method for quantifying stand-to-sit movements using clinically friendly equipment and is the first to investigate the stand-to-sit activity of unilateral transtibial amputees. The observed differences in inter-limb weight distribution strategies between amputees and non-amputees could provide insights for clinical assessment and intervention.

Testing the assumption of normality in body sway area calculations during unipedal stance tests with an inertial sensor

The quantification of postural sway during the unipedal stance test is one of the essentials of posturography. A shift of center of pressure (CoP) is an indirect measure of postural sway and also a measure of a persons ability to maintain balance. A widely used method in laboratory settings to calculate the sway of body center of mass (CoM) is through an ellipse that encloses 95% of CoP trajectory. The 95% ellipse can be computed under the assumption that the spatial distribution of the CoP points recorded from force platforms is normal. However, to date, this assumption of normality has not been demonstrated for sway measurements recorded from a sacral inertial measurement unit (IMU). This work provides evidence for non-normality of sway trajectories calculated at a sacral IMU with injured subjects as well as healthy subjects.The quantification of postural sway during the unipedal stance test is one of the essentials of posturography. A shift of center of pressure (CoP) is an indirect measure of postural sway and also a measure of a persons ability to maintain balance. A widely used method in laboratory settings to calculate the sway of body center of mass (CoM) is through an ellipse that encloses 95% of CoP trajectory. The 95% ellipse can be computed under the assumption that the spatial distribution of the CoP points recorded from force platforms is normal. However, to date, this assumption of normality has not been demonstrated for sway measurements recorded from a sacral inertial measurement unit (IMU). This work provides evidence for non-normality of sway trajectories calculated at a sacral IMU with injured subjects as well as healthy subjects.