Presented at: The 15th Annual Biomechanics of the Spine Conference. Seoul, Korea, October, 1984
Upper cervical specific adjusting techniques require a highly precise and controlled thrust. Such an adjustment may be very difficult to deliver in a repeatable fashion by hand and may take years to refine. The use of adjusting instruments enables precise and repeatable adjustments to be delivered with little physical effort and shifts the emphasis of training to the derivation of adjusting direction factors. Adjustments become more uniform from doctor to doctor as the variable of adjusting skill is minimized. Because machines support the adjusting apparatus itself, the strain placed on the doctor during the adjustment is eased with the result that much finer control of adjustment direction is achieved.
In addition to the advantages of instrument adjusting in the clinical setting, many chiropractic research designs can benefit from the repeatability inherent in adjustments delivered by means of an instrument. Such repeatability would be best documented and insured if the adjusting instrument were capable of monitoring the descriptive parameters of the adjustment.
For these purposes a flexible adjusting device, the Sid Williams Research Instrument, has been designed and built that insures repeatability through the use of a computer system which controls the adjustment and the electronically monitors the position, force and direction of the stylus (Fig. 1). The system further provides a new index of repeatability in that the stylus force can be measured during the set-up of the patient to allow repeatable preloading of the adjustment.
Structurally the instrument is composed of a steel frame supporting a padded platform and the adjusting apparatus. The platform has a hinged shoulder piece that can be tilted up or down 20 degrees from the horizontal. The headpiece has a special mastoid support and can be moved vertically 5 inches and horizontally 4 inches to accommodate mastoid or temporal support. The headpiece also tilts freely from side to side and from front to back with a range of 65 degrees. The stressbar, which is used for pre-stressing the cervical curve prior to adjustment, is fully adjustable and may be positioned on either side.
The adjusting instrument support is at the head of the table and has six degrees of freedom. The base is a carriage which rolls on tracks that allow 26 inches of travel from side to side. The carriage also pivots 25 degrees to the right and left and telescopes to give vertical movement of 10 inches. A geared cantilever supports the adjusting head itself and allows 24 inches of movement horizontally toward the foot of the table.
The adjusting head can be positioned to accommodate a Line of Drive (LOD) of up to Forty-five degrees, high or low. It can also accommodate a Rotational Couple (RC) of up to Forty-five degrees anterior or posterior. The adjusting thrust is provided by a motor driven cam. There is a mechanical control of thrust depth between zero and one half inch; the thrust time is electronically variable between 150 and 20 milliseconds, which translates to a thrust velocity of approximately 0.83 to 6.25 inches per second, respectively for a one eighth inch thrust.
The mechanical portion of the instrument is interfaced to an Apple II+ Computer through an analog to digital converter. The A/D converter gathers data from a group of transducers located at strategic positions on the instrument. Position information is collected for the vertical, lateral and longitudinal carriage motions as well as for the two rotations of the adjusting head. Positional accuracy is measured to with to within plus or minus 1mm, while the angles of the adjusting vector are measured to within one degree.
A special high resolution LVDT (Linear Velocity Displacement TRansformer) monitors the position and movement of the stylus during an adjustment. A strain gage force transducer, accurate to within .02%, is mounted on the stylus. It is set up to register overload at 5 pound force. Force transducers with the same accuracy are also located under the head support and on the cervical stress bar for measuring the force delivered to the patient during an adjustment and the reaction of the patient's head and neck. The headpiece transducer is set to register overload at 45 pounds; the stressbar transducer is not overload protected.
The actual adjustment is normally triggered by a foot switch, although it may be given by hand also. The stylus force transducer and a special circuit in the Apple prevents actuation of the stylus motor until a safe preload has been set. The computer can also be set to deliver a preset number of thrusts.
Data gathering and analysis is under the control of the computer system. Of particular interest are the time, direction and position characteristics of the adjusting force. The preload in preparation for the adjustment is calculated. The computer is currently set up to provide graphs of the stylus force and the stylus displacement (Fig.2). Head-piece and stress-bar force are normally plotted on the second graphics screen (Fig.3). The work done during an adjustment can be calculated from these curves.
Since the actual numeric values of parameters are also available, data may be stored on disk for later statistical analysis. These values are also available on the screen by command for purposes of monitoring, comparing or setting the instrument to perform a repeat adjustment. The form this information takes on the screen is show in figure 4.
The application of this instrument in a research setting is not limited to strictly giving and monitoring adjustments. It may also be used, for example, to provide profiles of force versus time for different adjusting techniques, such as hand versus actuator. We further anticipate using it for quantifying muscle palpation by monitoring force versus tissue depression. The potential of the Sid Williams Research Instrument as a research tool has barely been tapped; we anticipate using it in many future studies.