title: The reciprocal effects of pain intensity and activity limitations: implications for outcomes assessment in clinical trials.
abstract: OBJECTIVE
  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.
  
  
  CONCLUSIONS
  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.
authors: Department of Rehabilitation Medicine, University of Washington, Seattle, WA.
authors: Mark P
authors: MP
authors: Jensen
authors: Ivan R
authors: IR
authors: Molton
mesh_terms: D000203:Activities of Daily Living / Q000523:psychology*; D000328:Adult; D000700:Analgesics / Q000627:therapeutic use; D018771:Arthralgia / Q000175:diagnosis* / Q000188:drug therapy / Q000503:physiopathology* / Q000523:psychology*; D002986:Clinical Trials as Topic / Q000379:methods; D004008:Diclofenac / Q000627:therapeutic use; D005260:Female; D006801:Humans; D008297:Male; D009864:Ontario; D020370:Osteoarthritis, Knee / Q000175:diagnosis / Q000188:drug therapy / Q000503:physiopathology* / Q000523:psychology*; D017063:Outcome Assessment, Health Care / Q000379:methods*; D010147:Pain Measurement / Q000187:drug effects / Q000379:methods; D020127:Recovery of Function; D016896:Treatment Outcome
chemical_list: D000700:Analgesics; D004008:Diclofenac