The reliability and validity of an instrumented staple system for in vivo measurement of local bone deformation

We recently presented a pilot study using an instrumented staple system for measuring in vivo local deformation on tibia. Methodological development has now proceeded in vitro. Consecutively, we performed 1. a sheep bone micrometer study, 2. a sheep bone four-point bending test and 3. a pig bone four-point and three-point bending test. This was done in order to secure a standardized application of the staple, to analyze the interaction of the bone and the staple and to secure calibration and the reliability of the system to be used in vivo. With reference to the above studies: 1. There was a linear relationship (r = 0.998) between the applied deformation of the bone and the measured deformation of the staple. ICC values ranged from 0.866 to 0.997. 2. An excellent intra-test reliability as well as linearity between staple measures and surface strain on the bone was observed (r = 0.998). 3. The slope of regression lines (k) was min 7.2 and max 9.4. The results from this test are used for calibration of the instrumented staple. Great variations were found between tension and compression measurements. However, within each test the SD was negligible. We suggest that the instrumented staple system may be calibrated in vitro and validly used for in vivo measurement of local bone deformation.