Use of a spinal model to quantify the forces and motion that occur during therapists' tests of spinal motion

School of Physical Therapy, Texas Woman's University, Houston 77030.

BACKGROUND AND PURPOSE. Despite the widespread use of spinal mobilization, little is known about the forces used or the accuracy of therapists in estimating the forces they use in administering the technique. The purposes of this study were to quantify the forces used and to determine the accuracy of therapists in applying forces on a mechanical model. SUBJECTS. Ten physical therapists participated. METHODS. A spinal model was used to measure applied force and displacement under different conditions of stiffness. The therapists applied oscillatory posteroanterior mobilizations to the model under three different conditions of stiffness. RESULTS. Mean peak forces across grades and stiffness levels ranged between 57.59 and 178.27 N. The forces were generally lower in the least stiff condition. Displacement varied with stiffness and mobilization grade. In the least stiff condition, the mean displacement varied between 2.25 and 3.45 mm for grades 1 to 4, respectively. CONCLUSION AND DISCUSSION. Inter-therapist variability was high, and there was a systematic bias in underestimating the magnitude of applied force and in overestimating motion. The variability in force application and the general overestimation of motion detection may explain the poor reliability of measurements obtained with clinical tests based on motion palpation.

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