An in vitro comparison of bone deformation measured with surface and staple mounted strain gauges

Chicken tibiae were chosen as a model for human second metatarsals. Local s urface bone deformation in a 4-point bending configuration was measured in vitro by both strain gauge instrumented staples and strain gauges bonded to the bone's cortical surface. A series of staple bridge dimensions (0.5, 0. 6, 0.8 and 1.0 mm) was compared to test for staple influence on bone charac teristics and greatest measurement validity and reliability. Thicker staple inhibition of bone deformation was the greatest but differences to thinner staples were not statistically significant (p > 0.05). All staples except 0.5 mm had maximum deviations from linearity less than 1%. The 1.0 mm stapl e had an R-2 value of 0.992 +/- 0.006 plotted against the 4-point bending i nput force and 0.994 +/- 0.002 plotted against the surface strain gauge sig nal. The mean intraclass correlation coefficients (ICC) calculated with fou r input forces (30, 60, 90 and 120 N) and for loading and unloading conditi ons for the 0.5, 0.6, 0.8 and 1.0 mm staples were 0.75, 0.83, 0.87 and 0.92 , respectively. Finally, the differences in slope of the staple strain gaug e signal plotted against surface strain gauge signal between input force lo ading and unloading conditions (0.32), and between input compression and te nsion conditions (0.79) was least for the 1.0 mm staple which also resulted in the lowest standard deviations. These results suggested the appropriate ness of the 1.0 mm staple for in vivo application. (C) 1999 Elsevier Scienc e Ltd. All rights reserved.