Ultrasonic quantification of osseous displacements resulting from skin surface indentation loading of bovine para-spinal tissue

Objective. To validate an ultrasound-based technique which quantifies uni-planar subcutaneous displacement of an osseous object resulting from an externally applied load. Background. Many spinal conditions are thought to be characterized by aberrant vertebral displacements yet the invasive nature of many investigative techniques has left the clinical significance of this relation incompletely understood. Method. Six bovine bone/paravertebral tissue preparations were indented by one of two ultrasonic transducers (5 and 7 MHz) fitted to an electromechanical actuator. The resulting osseous displacement along the principal indentation axis was calculated by subtracting the change in transducer/bone distance between ultrasonic images collected at tissue contact and maximal load from the change in actuator displacement. A dial gauge contacting the bone was used as a displacement criterion measure. Results. Using the 7 MHz transducer, the mean error of the technique was 6.74% (SD=3.98) while the mean error associated with the 5 MHz transducer was 12.73% (SD=7.49). Conclusions. This non-invasive technique is capable of quantifying subcutaneous uni-planar bone displacement with an accuracy comparable to similar invasive techniques over a comparable displacement range.