Three-dimensional lower-extremity residua measurement systems error analysis

Accurate and reproducible geometric measurement of lower-extremity residua is required for custom prosthetic socket design. The authors compared three-dimensional electromagnetic point digitizer, spiral X-ray computed tomography (SXCT) and three-dimensional optical surface scanning (OSS) with caliper measurements and evaluated the precision and accuracy of each system. Digitizer, SXCT and OSS were used to measure lower-limb residuum geometry of 13 transtibial adult amputees. Six markers were placed on each subject's residuum and corresponding positive plaster models, and distance measurements were taken to determine precision and accuracy for each system. The digitizer, SXCT and OSS measurements were precise within 1 percent in vivo and 0.5 percent on positive plaster models. When compared with caliper measures, these measures were within 2 percent in vivo and 1 percent on positive plaster models. SXCT and three-dimensional optical surface-imaging systems, which are feasible for capturing the comprehensive three-dimensional surface geometry of transtibial residua, provide distance measurements statistically equivalent to calipers. In addition, SXCT can readily distinguish internal soft tissue and bony structure of the residuum.