In situ evaluation of lower limb prosthesis fit by spiral computed tomography

Spiral X-ray computed tomography (SXCT) volumetric imaging was applied to in situ goodness of fit evaluation for lower extremity (LE) prostheses with and without axial loading. SXCT data was obtained (Siemens Somatom PLUS-S) with and without the prosthesis in place. An algorithm was developed to map and measure the residuum bony and soft tissue structure and their relationship to the rigid prosthesis socket. A transform was applied along the main axis of the structure to estimate the local soft tissue thickness relative to bone and map it from a Cartesian coordinate voxel array into cylindrical and spherical (Lambert projection) maps. Interval changes in the soft tissue envelope relative to the underlying skeleton were measured by comparing maps obtained from serial examinations. The testretest repeatability and validity of SXCT methods was assessed using cadaver parts, phantom test objects, and human volunteers. The soft tissue envelope of lower limb residua were successfully determined, and the precision (repeatability) of SXCT was consistently better than 90%. Soft tissue SXCT mapping of a lower limb residuum is feasible with the prosthesis in situ and provides comprehensive information on the geometry and tissue characteristics for static evaluation of prosthesis fit.