Theory of small vertebral motions: an analytical model compared to data

Object. Develop an analytical theory describing the dynamics of small impulses applied to vertebrae, such as in chiropractic adjustments or spinal manipulative therapy. Design. Data were compared with damped harmonic oscillator models of vertebrae. Background. Evidence accumulates that chiropractic adjustments are effective in addressing a variety of health problems. However, the biomechanics characterizing spinal manipulation is largely unknown. Recently, relative separations of the L2–L3 vertebrae subsequent to activator adjusting instrument thrusts were measured in vivo at 2048 Hz. Results. Nine-parameter models for axial, shear and angular motions were fit to sets of 350 data points. They required frequencies of 5, 8 and 11 Hz, corresponding to well-known spinal resonances. The fits are excellent, with 0.75