Accuracy of piezoelectric accelerometers measuring displacement of a spinal adjusting instrument.

The accuracy and reproducibility of an electronic system to measure the displacement of a spring-loaded chiropractic adjusting instrument was examined. The electronic system included a piezoelectric force transducer, piezoelectric accelerometer transducers and a digital oscilloscope. Accuracy was studied by comparing electronic measurements with the expansion allowed by the mechanically limiting expansion-control knob of the instrument. The results suggested improvements for future accuracy verification checks and detected accuracy within about 10% of the expansion of the commonly used expansion-control-knob revolutions. Preliminary experiments are presented to show application of the system to studies on thrusts into the spine. The impedance-head-equipped spring-loaded Activator chiropractic adjusting instrument had a low velocity when used on the patient and appeared to cause bone movement and a measurable EMG response.