Interfacial pressure and shear sensor systems for lower limb prosthetic applications

Abstract

Lower limb prosthetic socket provides the interface for the transfer of loads between the ground and the stump. During daily physical activities, the stump has to endure mechanical stresses in normal (pressure) and tangential (shear) directions to the stump/socket interface, both of which may cause discomfort, pain, and a host of stump health problems. Despite the importance of the issues, there is currently no clinically-friendly sensor technology available to monitor both pressure and shear at the stump/socket interface.In this thesis, two sensor systems were developed - both capable of simultaneously measuring dynamic pressure and shear at the lower limb stump/socket interface. In particular, two thin, capacitive sensors based on flexible elastomers (3D-printed and silicone) were designed and fabricated. To acquire sensor signals, appropriate data acquisition circuitries and PC software were produced. A viscoelastic model for real-time processing of the sensor signals was developed, to improve their dynamic response. The sensor systems were characterised in research lab settings, and their performance was verified against comprehensive design requirements.The characterised sensor systems were validated at the stump/socket interface in a series of amputee walking tests, and a range of clinical factors were investigated. Pressure and shear were measured at up to three discrete locations of a trans-femoral stump. Their temporal profiles when walking on level and inclined surfaces were obtained. The results suggest that ankle flexion resistance may have an effect on both the magnitudes and the temporal profiles of pressure and shear at the stump/socket interface.The thesis delivers a tool for measuring pressure and shear at the stump/socket interface in a clinically-friendly manner. What is more, it contributes to the prosthetic field by bringing an insight into the pressure and shear at the trans-femoral stump/socket interface, thus enhancing the understanding of its biomechanics. In the future such a sensor technology could potentially aid daily monitoring of socket fit, assist prosthetists with socket fitting, support research on the stump/socket interface biomechanics, etc.<br/