Smart sockets for lower limb prostheses
Creators: name: Hopkins, Matthew Owen
Publisher: name: Imperial College London
Year: 2018

description: Major limb amputation affects up to five-thousand people a year in England alone, with recent conflicts in Afghanistan and Iraq often contributing individuals with complex amputations to the affected population. Despite considerable advances in technology of lower limb prosthetic legs, the socket interface between the residual limb and prostheses has remained largely unchanged. Amputees with poor fitting sockets can endure loading through pressure intolerant portions of their residual limb, introducing discomfort. Continued high pressures, shear stresses and the build-up of heat can lead to the development of numerous conditions such as pressure sores, stump oedema and skin carcinoma. The onset of such conditions can significantly impact use of the prosthetic limb and lead to reliance on a wheelchairs or crutches. Prosthetists aim to control issues such as excessive localised loading and shear stress through alteration of the socket design, however, there is limited information on suitable thresholds for prevention of tissue damage. Prosthetists must rely on their own judgement, experience and notoriously unreliable verbal feedback from prosthetic limb users. The focus of this thesis is the development of an in-socket pressure measurement system or ‘smart-socket’, to provide prosthetists with a mechanism for improved socket design and avoid the onset of conditions such as pressure sores. A secondary aim of the research was to deliver a portable and unobtrusive system to allow for data collection outside of laboratory or clinical environments, with the potential to provide a long-term monitoring solution. Device hardware consisted of low-cost, low-profile piezoresistive pressure sensors, developed in conjunction with printed circuit boards responsible for data sampling and transfer. A network of up to 144 piezoresistive pressure sensors is used to transduce local loads in combination with a 9 degree of freedom inertial measurement unit mounted on the socket. Readings may be transferred via Bluetooth for real-time measurement or stored on an SD-card. Accompanying software including phone and Windows applications were developed for the purposes of receiving, processing and logging data. System performance was explored using mechanical tests within the range of 0-400kPa. The sensors exhibit a non-linear output with an approximate resolution of 10kPa and a minimal drift of 0.026 Volts per minute. The proposed system’s suitability for application to a clinical environment was examined using an NHS cohort study in which participants had the sensors embedded within their prosthetic sockets. A series of tasks were undertaken to mimic common everyday activities such as ambulation and stair ascent whilst under optical motion-tracking. The results of the research demonstrated an ability to map the inner socket pressure profile in real time, with inertial measurement offering indications of gait phase. The results provide a case for the utility of such a system in clinical environments, to aid with the fitting of prosthetic sockets and the rehabilitation of amputees. The measurements may provide a useful comparative tool for prosthetists in identifying the positions of loads throughout the socket. The system may also be used to monitor significant shifts in loading resulting from socket misalignment or poor socket fit.