Its value is continually changing during the thrust as the stylus encounters increasing tissue resistance. Stylus force becomes therefore a function of stylus excursion, i.e., location. The greater the excursion, the greater the force. For this reason, we have opted to control excursion in this experiment while monitoring the stylus force. Most adjusting techniques, both hand and instrument, use rapid thrusts such as this with comparable durations.
Participation is contingent upon passage of the clinic physical and signing an informed consent.
The experiment itself basically involves assessing each subject by x-ray, leg check, and palpation, adjusting and then reassessing. A flowchart of this process is shown in figure 1. Upon acceptance, each subject is assigned randomly to one of four possible study groups. The subject is blinded to his group assignment but is aware that group differences exist. Note that in the Zero preload groups, the stylus is moved back far enough that it never contacts the skin.