Tyagi Ramakrishnan

Combined gait asymmetry metric

People with physical impairments often have asymmetric gait. To evaluate if their overall symmetry is improving during intervention, there needs to be a simple metric that can help classify gait patterns that includes multiple measures of gait asymmetry. The Combined Gait Asymmetry Metric presented here is based on the Mahalanobis distance of multiple step parameters. We tested able-bodied subjects with perturbations that involve a change in leg length, the addition of ankle weights, and a combination of both perturbations. The Mahalanobis distances are calculated from perfect symmetry to all points in the data to analyze the effects of the different perturbations. The metric demonstrates how an overall view of symmetry can give a better perspective of asymmetry than only looking at a few individual parameters. This metric is straightforward and can be extended to include large numbers of spatiotemporal, kinematic, and kinetic parameters that more completely evaluate a change in gait symmetry.

Combined effects of leg length discrepancy and the addition of distal mass on gait asymmetry

Asymmetries in gait often arise due to some form of physical impairment. For example, a leg length discrepancy (LLD) or the change of limb mass can result in asymmetric gait patterns. Although adding mass and LLD have been studied separately, this research studies how gait patterns change as a result of asymmetrically altering both leg length and mass at a legs distal end. Spatio-temporal and kinetic gait measures are used to study the combined asymmetric effects of placing LLD and mass on the opposite and same side. There were statistically significant differences for the amount of mass and leg length added for all five parameters. Contrary to our hypothesis, there was no significant interaction between the amount of mass and leg length added. There were cases in all perturbations where a combination of mass and LLD make a gait parameter more symmetric than a single effect. These cases exhibit the potential for configurations with lower overall asymmetries even though each parameter has a slight asymmetry as opposed to driving one parameter to symmetry and other parameters to a larger asymmetry.

Knee orthosis with variable stiffness and damping that simulates hemiparetic gait

Individuals with unilateral stroke have neuromuscular weakness or paralysis on one side of the body caused by some muscles disengaging and others overexciting. Hyperextension of the knee joint and complete lack of plantar flexion of the ankle joint are common symptoms of stroke. This paper focuses on the creation and implementation of a small, lightweight, and adjustable orthotic device to be positioned around the knee of an able-bodied person to simulate hemiparetic gait. Force and range of motion data from able-bodied subjects fitted with the orthosis, inducing hemiparetic gait, was collected using the Computer Assisted Rehabilitation ENvironment (CAREN) system. The four parameters that the design focused on are damping, catch, hysteresis, and stiffness. The main goal of the project was to discern whether this device could be utilized as a viable research instrument to simulate hemiparetic gait. It was hypothesized that the device has the potential to be utilized in the future as a rehabilitation device for people with stroke since it has been designed to induce larger knee flexion as an after effect. A comparison between how the dominant leg was affected by the orthosis and how the non-dominant leg was affected was investigated as well. The results show that the device affected the velocities, knee angles, and force profiles of the subjects gait.

Comparing Gait with Multiple Physical Asymmetries Using Consolidated Metrics

Physical changes such as leg length discrepancy, the addition of a mass at the distal end of the leg, the use of a prosthetic, and stroke frequently result in an asymmetric gait. This paper presents a metric that can potentially serve as a benchmark to categorize and differentiate between multiple asymmetric bipedal gaits. The combined gait asymmetry metric (CGAM) is based on modified Mahalanobis distances, and it utilizes the asymmetries of gait parameters obtained from motion capture and force data recorded during human walking. The gait parameters that were used in this analysis represent spatio-temporal, kinematic, and kinetic parameters. This form of a consolidated metric will help researchers identify overall gait asymmetry by showing them if the overall gait symmetry is improving and avoid the case where one parameters symmetry is improving while another is getting worse. The CGAM metric successfully served as a measure for overall symmetry with eleven different gait parameters and successfully showed differences among gait with multiple physical asymmetries. The results showed that mass at the distal end had a larger magnitude on overall gait asymmetry compared to leg length discrepancy. It also showed that the combined effects are varied based on the cancelation effect between gait parameters. The metric was also successful in delineating the differences of prosthetic gait and able-bodied gait at three different walking velocities.

Evaluation of 3D printed anatomically scalable transfemoral prosthetic knee

This case study compares a transfemoral amputees gait while using the existing Ossur Total Knee 2000 and our novel 3D printed anatomically scalable transfemoral prosthetic knee. The anatomically scalable transfemoral prosthetic knee is 3D printed out of a carbon-fiber and nylon composite that has a gear-mesh coupling with a hard-stop weight-actuated locking mechanism aided by a cross-linked four-bar spring mechanism. This design can be scaled using anatomical dimensions of a human femur and tibia to have a unique fit for each user. The transfemoral amputee who was tested is high functioning and walked on the Computer Assisted Rehabilitation Environment (CAREN) at a self-selected pace. The motion capture and force data that was collected showed that there were distinct differences in the gait dynamics. The data was used to perform the Combined Gait Asymmetry Metric (CGAM), where the scores revealed that the overall asymmetry of the gait on the Ossur Total Knee was more asymmetric than the anatomically scalable transfemoral prosthetic knee. The anatomically scalable transfemoral prosthetic knee had higher peak knee flexion that caused a large step time asymmetry. This made walking on the anatomically scalable transfemoral prosthetic knee more strenuous due to the compensatory movements in adapting to the different dynamics. This can be overcome by tuning the cross-linked spring mechanism to emulate the dynamics of the subject better. The subject stated that the knee would be good for daily use and has the potential to be adapted as a running knee.

Evaluating the Gait of Lower Limb Prosthesis Users

Outcome assessments are vital in facilitating periodic, episodic and ongoing evaluation of persons with limb loss. There are many outcome measures used to quantify prosthetic fit, alignment, comfort, functionality and usability of lower limb prostheses. However, many measures are subjective, difficult to implement in a clinical setting and lack psychometric evaluation. This study used an immersive Computer Assisted Rehabilitation Environment (CAREN) virtual reality system with an instrumented spilt-belt treadmill and real time motion capture system as a research tool to evaluate and compare the gait of lower limb prosthesis users and non-amputees as a preliminary study to determine the effectiveness and appropriate use of outcome measures. The use of the CAREN system providing more real world scenarios such as ramps, inclines and unexpected inclines helped evaluate the hill assessment index (HAI) and the combined gait asymmetry metric (CGAM).

3D Printed Passive Compliant and Articulating Prosthetic Ankle Foot

The human ankle is crucial to mobility as it counteracts the forces and moments created during walking. Around 85% of the 1.7 million people in the United States living with limb loss are transtibial (below knee) and transfemoral (above knee) amputees who are missing their ankle and require a prosthetic. This paper presents the Compliant and Articulating Prosthetic Ankle (CAPA) foot, a solution that uses torsional springs to store and release energy at three different locations on the mechanism, assisting in forward motion. The CAPA foot utilizes 3D printing and allows for the full ankle range of motion in the sagittal plane. Testing was performed with the CAPA foot on the Computer Assisted Rehabilitation Environment on an able-bodied person wearing a prosthetic simulator. Compared to the conventional non-articulating Solid Ankle Cushioned Heel foot, the CAPA foot is shown to better mimic the ground reaction forces and ankle angles of a healthy gait.Copyright

POSITION AND WEIGHT ACTIVATED PASSIVE PROSTHETIC KNEE MECHANISM

The human knee is a complex and robust system. It is the most important joint for human gait because of its immense load bearing ability. The loss of such an important joint often makes it difficult for a person to ambulate. Because of this and the resulting unnatural application of forces, many trans-femoral amputees develop an asymmetric gait that leads to future complications. Prosthetic knees are required to be well-designed to cope with all variabilities. There have been many prosthetic knee designs, some more complex than others. This paper describes the design and preliminary testing of a novel passive position and weight activated knee locking mechanism for use in lower limb prosthetics. This knee mechanism is designed to be a simple and economical alternative to existing knee mechanisms. The mechanism utilizes the dynamics of the user to lock the knee during stance and unlock during the swing phase. The presence of one moving component and a simple assembly makes this design a good base for customization. Results from testing the knee mechanism shows trends that are different from a normal human knee, which is to be expected. The prosthetic knee is designed to have low friction during swing of the shank and, hence, the flexion and extension angles and angular velocities are larger compared to a normal knee. The kinematics show a cyclic trend that is highly repeatable. Further refinement and testing can make this mechanism more efficient in mimicking a normal knee.Copyright