Triaxial force transducer for investigating stresses at the stump/socket interface

Although normal pressures at the stump socket interface of the lower-limb amputee have been investigated, little is known about the shear stresses that also occur. Studies suggest that the combination of both shear and normal stresses significantly exacerbates discomfort and vascular and tissue damage. A means of simultaneously measuring normal and shear stresses will aid in the investigation and improvement of prosthetic fit. A miniature triaxial force transducer (4.9 x 16 mm diameter) has been developed which can be recessed into the socket wall. The principle of operation, construction, performance and limitations of the device are described. Preliminary measurements of the interface stress variations over the gait cycle in a supra-condylar PTB socket are presented. These show clear differences in the stress patterns present when two different prosthetic feet are used.