• Kawchuk GN
• Perle SM

• Association of Chiropractic Colleges / congresses

METHODS: A porcine thoracic spine was mounted to bookend supports by stripping the pedicles, ribs and all soft tissues from the terminal vertebrae to leave the remaining vertebrae suspended horizontally. A triaxial accelerometer was affixed to the middle vertebrae with the X axis oriented superior/inferior, the Y axis medial/lateral and the Z axis posterior/anterior. An Air Activator™ fitted with an in-series load cell was then used to apply ten thrusts of increasing force to the skin over the spinous process of interest. Sampling rate was 50,000Hz. From these data, a reference plot of input force vs. resulting Z axis acceleration was created. Ten maximum force applications were then applied to the same spinous at 23.5°, 45°, -23.5° and -45° in the X axis. For each different line of drive application, the theoretical Z-axis force was computed by multiplying the cosine of the angle by the recorded force. The experimental Z-Axis force was determined by taking the Z-axis acceleration resulting from each angulated force application and then computing the Z-axis input force from the reference plot.

RESULTS: For the lines of drive of 23.5°, 45°, -23.5° and -45°, the Z-axis and X-axis vertebral accelerations were always less than those obtained from a line of drive of 0°. For lines of drive of 23.5°, 45°, -23.5° and -45°, the mean percentage difference between the theoretical and experimental forces was -9% , -3%, -4% and -6% respectively.

DISCUSSION: Errors of less than 10% between the theoretical and observed forces support the hypothesis under consideration. Additional support comes from the observation that as the angle of applied force increased from the vertical, the acceleration of the vertebra in the Z and X-axes never increased beyond acceleration values obtained at 0°. Therefore, at angles other than 0°, there is no continuation of force along the line of drive when a frictionless system is interposed between the point of force application and the vertebral target.

CONCLUSION: When a frictionless tissue system underlies a point of force application, any change in the line of drive from one that is perpendicular to the skin results in a predictable decrease of force acting to accelerate the vertebra. The force lost in the Z-axis is not recovered in the direction of the line of drive. In other words, when there is soft tissue between the point of contact and the target vertebra, line of drive in a manipulation greater than 0° is irrelevant to vertebral motion and serves only to decrease the force applied by the practitioner.

This abstract is reproduced with the permission of the publisher.