Subject: The Activator® Adjusting Instrument – Biomechanical

Title: Skin Accelerometer Displacement and Relative Bone Movement of Adjacent Vertebrae in Response to Chiropractic Percussion Thrusts.

Reference: Smith DB, Fuhr AW, Davis BP. Skin accelerometer displacement and relative bone movement of adjacent vertebrae in response to chiropractic percussion thrusts. J Manipulative Physiol Ther 1989; 12(2):26-37.

Abstract: The authors studied relative bone movements in response to manipulative light taps to the spine. Piezoelectric accelerometers attached to bone of an anesthetized dog measured transverse, X-Z plane, movements of L2-L3 adjacent vertebrae while percussion thrusts of an instrument used for manipulation made inputs three vertebrae above and five vertebrae below the L2-L3 joint interface. Small, relative 1-mm translations and 0.5 rotations occurred during the first 19 msec. When one set of accelerometers were stabilized on the skin surface, half of the skin-bone translation maxima erred less than 2%. However, skin translations averaged 77% (SD=2%) of bone translations and skin rotations averaged 95% (SD=26%) of bone rotations. The results suggest the possibility that, with further development, piezoelectric accelerometers can be a noninvasive tool to study dynamic, relative, bone movement. (J Manipulative Physiol Ther 1989; 12:( 2):26-37.

Key Words: Manipulation, Chiropractic