USE OF A SPINAL MODEL TO QUANTIFY THE FORCES AND MOTION THAT OCCUR DURING THERAPISTS TESTS OF SPINAL MOTION

Background and Purpose. Despite the widespread use of spinal mobilizat ion, little is known about the forces used or the accuracy of therapis ts in estimating the forces they use in administering the technique. T he purposes of this study were to quantify the forces used and to dete rmine the accuracy of therapists in applying forces on a mechanical mo del. Subjects. Ten physical therapists participated. Methods. A spinal model was used to measure applied force and displacement under differ ent conditions of stiffness. The therapists applied oscillatory poster oanterior mobilizations to the model under three different conditions of stiffness. Results. Mean peak forces across grades and stiffness le vels ranged between 57.59 and 178.27 N. The forces were generally lowe r in the least stiff condition. Displacement varied with stiffness and mobilization grade. In the least stiff condition, the mean displaceme nt varied between 2.25 and 3.45 mm for grades 1 to 4, respectively. Co nclusion and Discussion. Intertherapist variability was high, and ther e was a systematic bias in underestimating the magnitude of applied fo rce and in overestimating motion. The variability in force application and the general overestimation of motion detection may explain the po or reliability of measurements obtained with clinical tests based on m otion palpation.