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Quantification of a Meaningful Change in Low Back Functional Impairment

Ferguson, Sue A., PhD*; Marras, William S., PhD*; Burr, Deborah L., PhD; Woods, Stephen, MD; Mendel, Ehud, MD§; Gupta, Purnendu, MD

doi: 10.1097/BRS.0b013e3181b34764
Clinical Case Series
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Study Design. Repeated measures study design.

Objective. Determine a meaningful change in low back functional impairment as measured with the lumbar motion monitor.

Summary of Background Data. A quantitative functional performance probability (P(n)) measure has been developed and is scored from 0.00 to 1.00. Previous research has shown that a 0.5 cut-off provides excellent sensitivity and specificity for identifying impaired and healthy low back function. However, a meaningful change in the P(n) measure has not been defined.

Methods. The lumbar motion monitor was used to repeatedly measure P(n) in 3 groups of subjects including (1) asymptomatic, (2) recovering low back pain (LBP) and, (3) nonrecovering LBP. The asymptomatic group had 20 subjects. The recovering and nonrecovering LBP had 18 and 8 subjects, respectively. The asymptomatic group was tested 5 times at 1-week intervals. The 2 LBP groups were tested every 2 weeks for 3 months (6 evaluations).

Results. The P(n) in the asymptomatic group did not significantly change over the observed period. On the basis of the variability in the asymptomatic group it was hypothesized that a meaningful change in P(n) was 0.14. The defined meaningful change was evaluated in 2 patient with LBP populations. The P(n) in the recovered LBP group significantly improved during the 3 month observation period and there was a corresponding reduction of symptoms. In the recovering LBP group the within subject standard deviation was 0.14 and all patients had at least 1 visit to visit change greater than 0.14. Furthermore, 11 of the 18 recovering patients with LBP had a meaningful change between the first 2 visits. In contrast, none of the nonrecovering LBP group had a meaningful change between the first 2 visits.

Conclusion. A meaningful change in P(n) was defined as 0.14.

A probability of normal (P(n)) low back functional performance has been developed. Based on the variability in an asymptomatic group a meaningful change in P(n) has been defined as 0.14. In group of recovering patients with low back pain, all had at least 1 visit to visit change greater than 0.14.

From the *Department of Integrated Systems Engineering, Biodynamics Laboratory, The Ohio State University, Columbus, OH; †College of Public Health and Health Professions, University of Florida, Gainesville, FL; ‡Department of Physical Medicine and Rehabilitation, The Ohio State University, Columbus, OH; §Department of Neurosurgery, The Ohio State University, Columbus, OH; and ¶Section of Orthopeadic Surgery and Rehabilitation Medicine, University of Chicago, Chicago, IL.

Acknowledgment date: November 16, 2008. Revision date: March 9, 2009. Acceptance date: March 12, 2009.

The device(s)/drug(s) that is/are the subject of this manuscript is/are exempt from FDA or corresponding national regulations.

No funds were received in support of this work. No benefits in any form have been or will be received from a commercial party related directly or indirectly to the subject of this manuscript.

Address correspondence and reprint requests to Sue A. Ferguson, PhD, Department of Integrated Systems Engineering, Biodynamics Laboratory, The Ohio State University, 210 Baker Systems, 1971 Neil Avenue, Columbus, OH 43210; E-mail: ferguson.4@osu.edu

© 2009 Lippincott Williams & Wilkins, Inc.