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The Reciprocal Effects of Pain Intensity and Activity Limitations: Implications for Outcomes Assessment in Clinical Trials

Jensen, Mark P. PhD; Molton, Ivan R. PhD

doi: 10.1097/AJP.0b013e318287a27d
Original Articles

Objectives: To examine the reciprocal effects of pain intensity and limitations in physical functioning over time.

Methods: This study presents findings from a reanalysis of a 7-center trial conducted in Ontario, Canada, included 209 adults with chronic knee pain secondary to osteoarthritis. Patients were randomized to receive 28 days of therapy with an active solution (1.5% w/w diclofenac sodium in dimethyl sulfoxide) or 1 of 2 control solutions containing no diclofenac. The key outcome measures used in the current analyses were administered throughout the study period and assessed pain intensity, perceived activity limitations, and a composite score measuring both domains. A structural cross-lagged regression approach was used to determine the reciprocal effects of pain and activity limitations over time.

Results: In both study groups, participants (N=209) experienced significant reductions in mean pain intensity and activity limitations from baseline to weeks 1, 2, 3, and 4 (P<0.001 for both variables). Similarly, there were significant reductions in the activity limitations outcome at weeks 1 and 4 for the active versus control group (P<0.05 for both). Higher levels of perceived activity limitations predicted more future pain at all time points. Cross-lagged associations in which pain predicted subsequent perceived activity limitations were not significant at any time point. All 3 outcome measures evidenced similar responsiveness to the treatment.

Conclusion: These analyses showed that a decrease in activity limitations results in a decrease in pain intensity. However, changes in pain intensity had no effect on subsequent activity limitations in the study sample. None of the 3 outcome variables emerged as being more responsive to treatment than the others.

Department of Rehabilitation Medicine, University of Washington, Seattle, WA

Funding for this support was provided independently by the authors. The current analyses were funded by Covidien, Mansfield, MA. Mark P. Jensen has received consulting fees or research support from RTI Health Solutions, Research Triangle Park, NC, Covidien, Mansfield, MA, Bristol-Myers Squibb, New York, NW, Schwarz Biosciences, Raleigh, NC, Analgesic Research, Needham, MA, Depomed, Newark, CA, Eli Lilly, Indianapolis, CA, Pfizer, New York, NY, Merck, Whitehouse Station, NJ, Medtronic, Minneapolis, MN, and Smith & Nephew, Andover, MA within the past 36 months. Ivan R. Molton received consulting fees from Jensen Consulting for performing the analyses for this study.

Reprints: Mark P. Jensen, PhD, Department of Rehabilitation Medicine, University of Washington, Box 359612, Harborview Medical Center, 325 Ninth Avenue, Seattle, WA 98104 (e-mail: mjensen@uw.edu).

Received July 12, 2012

Accepted January 12, 2013

© 2014 by Lippincott Williams & Wilkins