Comparison of Various Prosthetic Foot-Ankle Mechanisms

Subject Selection and Consent:

Subjects will be selected based on the following priority. Subjects who have previously participated in similar studies with the Biomechatronics lab and who have already been screened for health and mobility level will be contacted first. If additional subjects are needed, a recruitment flyer and screening questionnaire will be sent to potential candidates. Copies of both the flyer and questionnaire are included in the attachments section. Prior to the experimental sessions, subjects will be asked to read and sign a informed consent form and will explain the project to them and answer any questions that they may have. They will also be given time to become familiar with the equipment being used before beginning any trials. If needed, subjects will be aligned and fitted by a professional prosthetist at A Step Ahead Prosthetics in Burlington, MA. No personnel at A Step Ahead Prosthetics will conduct research or have any vested interest in research outcomes or publication.

Attire:

Subjects will be asked to wear tight-fitting clothes, such as a skin-tight shirt, running shorts and low-profile shoes. If this is not possible, clothes will be provided according to subject needs. The investigators will provide and may require subjects to wear a skin-tight Velcro outfit that allows us to place reflective balls for video camera capture.

Location(s) and Timeline:

Experimental sessions will be conducted in the MIT Biomechatronics Laboratory (E14-274), 75 Amherst St., Cambridge, MA 02139 and the basement connecting MIT Building 66, 68, and E19 (31 Ames St., Cambridge, MA 02139). The basement is a publicly accessible area, and visible signage will be posted to alert passerby. Any alignment and fitting of prosthetic devices will take place at either the aforementioned location or at A Step Ahead Prosthetics, 21 A. St., Burlington, MA 01803 by a trained prosthetist.

Total study duration is expected to be 8 hours per subject, likely over two 4-hour sessions. These sessions can be completed either in a single day or over two days.

Powered Prosthesis:

Subjects will be given three or four computer-controlled quasi-passive (QP) ankle-foot prostheses to attach in place of their customary prosthesis during a session, depending on the arm. These include the Blatchford Elan, Ossur Proprio, a variable-stiffness prosthesis (VSA), and a variable-angle prosthesis (VAA). These QP prostheses have the capability of providing active assistance or changing mechanical properties during walking. Controls will be adjusted either through a wireless link or hardwire connection depending on the device. Subjects will be given as much time as necessary to practice using the prostheses before the experiments begin.

Passive Prosthesis:

Subjects will be given 1-3 passive prostheses to attach in place of their customary prosthesis during a session. These include the Ossur Pro-Flex XC and a passive sliding-beam prosthesis based on the Variable Stiffness prosthesis above with the electronics and actuator removed. In the first arm, a passive prosthesis that can change ankle equilibrium angle manually will be used. Subjects will be given as much time as necessary to practice using the prosthesis before the experiments begin.

Data Collection:

Data collection is expected to take place in two segments. In the first segment, each subject will walk on a treadmill at three speeds between 0.5-1.5m/s (slow to fast walking), chosen based on their comfort. At each speed, all five prostheses will be tested, randomly selected, for 2mins each. Motion will be captured with a VICON motion capture system, and ground reaction forces will be measured using a Bertec force-sensitive treadmill. For each speed, once all prostheses have been tested, each subject will be given a questionnaire to ascertain how each prosthesis performed at heel strike (early stance), roll over (mid stance), and powered plantar flexion (late stance). In addition, each subject will be asked how each prosthesis generally performed, and their personal preference. This testing will occur across the three walking speeds, resulting in three completed questionnaires.

In addition, subjects will walk in a figure-8 pattern at a preferred gait speed around two cones placed on the level-ground walking surface and separated by up to 30 feet. Handrails and a harness will be available to the subject as needed. Subjects will perform the walking figure-8 for a minimum of 5 times for each randomly-selected prosthesis. Once all prostheses have been tested, each subject will be given a questionnaire to ascertain how each prosthesis generally performed, and their personal preference.

Each subject will ascend and descend stairs and a ramp inclined between 4°-8° from horizontal at their preferred speed, in a randomly selected order. This incline is akin to between an ADA-compliant wheelchair ramp and a moderately inclined hill. Motion will be captured with a VICON motion capture system, and ground reaction forces will be measured using a Bertec force-sensitive treadmill for slope ambulation, and a force-sensitive staircase for stair ambulation. All five prostheses will be tested, randomly selected. Subjects will perform each of stair ascent and stair descent for a minimum of 5 times per prosthesis. For slopes and stairs, subjects will be asked to test different stiffnesses and angles and pick a preferred setting for the VSA and VAA, respectively. Data will be collected for a total of 2mins for slope ascent and 2mins for slope descent with each prosthesis. If necessary, subjects will test up to 5 ankles on an ADA-compliant over-ground ramp for additional slope ascent and slope descent evaluation. This will provide additional evaluation of differences between treadmill and over-ground slope walking for both subject and researcher. Subjects will walk up and down the ramp a minimum of 5 times per prosthesis. Handrails are available along the entire ramp, and a researcher will be beside the subject for assistance. For each slope and stair ascent/descent, once all prostheses have been tested, each subject will be given a questionnaire to ascertain how each prosthesis generally performed, and their personal preference. This testing will occur across the slope terrain types, as well as after the stair ascent/descent trial, resulting in three completed questionnaires for each subject. If time allows, subjects may also be asked to test test up to 5 ankles a 30 ft. over-ground course consisting of level-ground, stairs, and slopes in order to evaluate transitions between terrains. Subjects will perform the course a minimum of 3 times. This will not be evaluated via questionnaire and is meant to provide information to the researcher on future prosthetic design. Handrails are available for all elements except an adjustable ramp, for which a researcher will be beside the subject for assistance.