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

School of Physiotherapy, Faculty of Health Sciences, The University of Sydney, Lidcombe, New South Wales, Australia.

BACKGROUND AND PURPOSE: This study determined the test-retest reliability of measurements of responses to posteroanterior (PA) forces made using a recently developed instrument. SUBJECT: 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.

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