The researchers at Imperial College London, United Kingdom, tested the system’s ability to measure in-socket loading of the transtibial prosthesis users during walking. The low-cost prototype was evaluated with four people at various age and activity levels who had unilateral transtibial amputations. The pressure sensors were embedded in each participant’s socket and an inertial measurement unit was attached to the posterior side of the socket. Measurements were taken during level walking at self-selected speeds in a gait lab.
The device has 12 strips of 12 piezoresistive sensors (144 sensors in total) covering the inner surface. The sensors were produced using a low-cost piezoresistive material known as Velostat, chemical-etched copper electrodes, and an acetate backing.
Pressure profiles were generated using normalized sensor data for each participant during standing, walking stance-phase, and walking swing-phase. During the walking task, both central steps and turning steps were extracted when the participant was at the center
of the walkway and at the edge of the walkway, respectively, to allow observation of unperturbed walking and directional change. Pressure maps were generated using data averaged across the duration of the standing task and across five central gait cycles and five turning gait cycles.
The sensors were able to dynamically collect data, informing loading profiles within the socket, which were in line with expected distributions for patellar-tendon-bearing and total-surface-bearing sockets, the study’s authors wrote. The participant who used a patellar-tendon-bearing socket displayed loading predominately at the patellar tendon, tibial, and lateral gastrocnemius regions. The other subjects, who used total-surface-bearing sockets, indicated even load distribution throughout the socket except one participant who presented with a large socket-foot misalignment.
The research team concluded that the sensors provided objective data showing the pressure distributions inside the socket. The sensors were able to measure the pressure in the socket with sufficient accuracy to distinguish pressure regions that matched expected loading patterns.
The system was not able to produce accurate measures of absolute pressure due to the limitations of the transducer, according to the authors; however, the measurement of the socket’s relative pressure distribution will allow clinicians to determine if the socket design and prosthesis set up is as intended relative to the socket types. The locus of maximum pressure gives an indication of the residual limb movement within the socket, which, the researchers say, may not always be reported or noticed, particularly if it is not vertical, such as with pistoning.
Prosthetists may find potential clinical utility with the system when fitting sockets as it could provide a clearer and less skill-dependent indication of the loading profile than traditional techniques, such as clear check sockets and skin blanching, by providing quantitative information to complement their skills.
Work is ongoing with prosthetists and physiotherapists to further develop the hardware and understand how they would like to use the information via appropriate visualization methods.
The open-access study, “Mapping lower-limb prosthesis load distributions using a low-cost pressure measurement system,” was published in Frontiers in Medical Technology.
