Background/Purpose: For inclusion in osteoarthritis clinical trials, participants often need to have a pain ‘flare’, usually defined as a pain increase over a period of time prior to study entry. Outside of clinical trial settings, there is no consensus regarding what constitutes a pain flare. The purpose of this study was to examine how individuals with knee osteoarthritis experience pain flares and their impact on daily living.

Methods: 45 participants (64 + 10 years; 55% female) with knee osteoarthritis underwent a baseline clinic visit as part of a larger pharmaceutical trial. At this visit, symptom measures were collected and participants were trained in procedures to collect data using a wrist-worn accelerometer in a 7-day home monitoring period. Participants wore the Actiwatch-Score and entered ratings of pain severity (0-10 scale) eight times per day. They were also asked to provide information at the end of each day in a logbook. Participants were asked to provide a definition of a pain flare and used that definition to indicate in the logbook if they experienced a pain flare that day and what they were doing when it occurred. Pain variability was calculated as the standard deviation of the pain ratings over the 7 day period. We hypothesized that pain flares and pain variability would be strongly related.

Results: When asked to define ‘pain flare’, descriptors of ‘sharp’ and ‘increase in pain’ were used by 30% and 21% of the sample respectively. Other descriptors included ‘intense/severe’, ‘electrical’ and various descriptors (e.g., twinge, stabbing, pulsation). Pain flares were most often described to be of short duration. During the home monitoring period, 77% of the sample experienced at least one pain flare and the mean was 2.2 + 2.0. Pain flares were most strongly associated with their worst daily pain (r = .51), followed by weekly average pain severity (r = .42), pain interference on the Brief Pain Inventory (r= .39), and WOMAC pain scale (r= .37). When asked to describe what they were doing when a pain flare occurred, participants most frequently mentioned activity-related causes (stair climbing, walking, shopping), while very few mentioned stiffness due to inactivity or being awakened by night pain. Pain flares were not significantly associated with pain variability (r = .12) or with neuropathic pain as measured by the PainDetect (r= .09); however PainDetect was most strongly correlated with WOMAC Pain (r=0.60), WOMAC Physical Function (r=0.57), and BPI severity (r=0.60).   

Conclusion: Pain flares occurred frequently over a week for people with osteoarthritis, were of short duration, and were most often experienced during activities. Interestingly, pain flares were not associated with pain variability. Although pain flares and pain variability may be activity-related, WOMAC subscales, which asked about pain or function during activities, were most strongly associated with a neuropathic component to pain. These findings provide further insight into the pain experience for people with knee osteoarthritis. Pain flares appear to be characterized by researchers and individuals with knee osteoarthritis in a variety of ways suggesting the need for additional research in this area.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/characteristics-of-pain-flares-in-knee-osteoarthritis/