Evaluation of a new device for measuring responses to posteroanterior forces in a patient population .1. Reliability testing

Background and Purpose. This study determined the test-retest reliability of measurements of responses to posteroanterior (PA) forces made using a recently developed instrument. Subjects. Twenty-two subjects with nonspecific low back pain participated. Methods. The length of the low-stiffness or ''toe'' region and the slope of the linear portion of the force-displacement curve were measured on two occasions. Reliability of repeated measurements was evaluated by intraclass correlation coefficients and percentage-of-agreement scores. The presence of a systematic change in the response to PA forces was evaluated by a paired-samples t test. Results. High reliability coefficients were obtained for both indices of the response to PA forces. The t test revealed no systematic change with repeated testing. Conclusion and Discussion. The new device provides highly reliable measurement of the lumbar PA force-displacement relationship and may prove useful in evaluating theories that have suggested a relationship between spinal symptoms and abnormal PA stiffness.