A Long-Term in Vivo Bone Strain Measurement Device

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Abstract
Bone remodeling resulting from implant insertion has been attributed to changes in the bone's strain state. Since remodeling takes several months, it was this study's purpose to develop a long-term in vivo strain sensor. Porous surfaced metal tabs were attached to a standard strain gauge. Two standard gauges and the porous tabbed gauge were attached to one femur and three standard gauges to the contralateral femur of a greyhound. Tissue ingrowth provided an attachment mechanism for the porous tabbed gauge in vivo. Gauge measurements were compared to those from the standard gauges. Post sacrifice testing allowed further comparisons. After histo-logical preparation the femoral section shapes as well as the gauge locations were examined and photographed. The porous tabbed gauge remained bonded and sensed strain throughout the 8-week implantation period, while the standard gauges debonded and were unable to detect strain after 3 weeks. During testing, the measurements from the porous tabbed gauge were lower than those from the standard gauges. This was consistent with the histology which indicated that fibrous tissue had invaded the gauge's porous surface. Although the use of tissue ingrowth as an attachment mechanism seems to be worthwhile, a means of insuring bone ingrowth is necessary.

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