Indian researchers have designed a trans-femoral prothesis with plantar insole sensors that they found allow users to achieve near able-bodied gait kinematics. The passive prosthesis uses a magneto-rheological (MR) damping system with electronic control based on plantar insole feedback. While plantar insoles typically provide information only for the stance phase, the researchers developed a novel sensing method that would allow control during both the stance and swing phases of the gait cycle. Their design employs 24 sensors in 4 groups located in strategic positions on the heel, mid-foot, metatarsal, and toe (see figure). Positioning of the sensors aligns with dominant plantar pressure points identified in previous walking experiments.
The mechanical design includes an MR damper, a hinge-type knee joint, and leg assembly brace supports. Information from the sensors provides enough information to control the current in the MR damper to allow for normal gait throughout the entire gait cycle.
The researchers’ goal was to develop an affordable prosthesis for manufacture and use in developing countries in accordance with the recommendations of the ISPO Consensus Conference on Appropriate Prosthetic Technology in Developing Countries. As such, the prosthesis was tested on a 24-year-old amputee, also from India, who walked 80 feet in each of 10 trials to test the design. The knee joint flexed up to 15° ± 5° in early stance; swing phase flexion only reached 45 ± 7°, which is below the biologically acceptable limit of 70°. However, the knee-angle trajectory provided by this prosthesis allowed the user to achieve near able-bodied gait kinematics with stability while achieving knee flexion-extension during heel strike and mid-stance. It also achieved controlled swing phase knee flexion-extension.
Designed for use in low-income and low resource countries, the researchers believe their prototype has commercialization potential in developing countries as well.
Pandit S, Godiyal AK, Vimal AK, et al. An affordable insole-sensor-based trans-femoral prosthesis for normal gait. Sensors. 2018;18:706; doi:10.3390/s18030706.