The Friction-Reduced Table (FR-Table) was developed as a "smart table" optimized for measuring evoked changes in leg length inequality with various clinical provocations, such as turning the head. The first prototype was constructed in 1993. In 1995 Spinalight, Inc. of Woodstock, Georgia fabricated a more sophisticated version of the table, which never proved commercially successful. A patent application failed. The FR-Table afforded quasi-independent movements to the legs, by placing left/right leg pieces mounted on file drawer slides on the caudal end. The pelvic, thoracic, and upper thoracic parts of the table were allowed universal frontal plane movements through ball transfers placed at each of their corners. All table sections could be immobilized by electromagnets that could contact their ferrous undersides, as controlled by a switching system that could cut the energy to any of the table sections individually or to all of them at once. Individual leg movements were measured 11 times/second in real time, with submillimetric accuracy. The first measuring system constructed was optoelectric, the second potentiometric. Both were reliable and sensitive. As the leg pieces moved, the voltage passed to an analog-to-digital card changed, which was transformed to millimeters of leg movement. Of 8 studies conducted on the FR-Table, only 1 was a peer-reviewed article. The single-most important research finding was that functional LLI can be directly measured and is a stable clinical entity, conserved and visible across a variety of test conditions when the measuring apparatus permits semi-independent movement of the legs.
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