A study presented at the American College of Rheumatology (ACR) Convergence 2021 investigated daily variability of pain among patients with knee osteoarthritis (OA), and the relationship between pain variability and physical activity.
For this longitudinal observational study, the researchers had participants with self-diagnosed knee OA utilize smartwatches to monitor their day-to-day pain variability. These data were analyzed to compare with standardized pain assessments. The study period lasted for three months.
In total, 25 participants were enrolled. The mean age was 65 years, and 13 participants were male. The median body mass index was 27 kg/m2. All participants received a consumer cellular smartwatch with a bespoke app to complete patient-reported outcome questionnaires about daily level of knee pain. Patients completed the questionnaire twice per day and completed the Knee Injury and Osteoarthritis Outcome Score (KOOS) assessment once per month. Daily step counts were also monitored to assess participants’ physical activity.
The study authors reported good feasibility outcomes for the use of the smartwatch app to record outcomes and continuously monitor patients. Based on the data, the investigators separated patients into three subgroups: patients who sustained high levels of pain, who sustained low levels of pain, and those with fluctuating pain. However, they noted “considerable day-to-day variation in pain levels within these categories.”
Regarding standardized pain assessments, the researchers noted that daily pain variability was still present in patients with stable monthly KOOS scores, which “[raises] doubt as to whether patients with stable monthly KOOS scores truly represent stable knee OA and whether this is an accurate method for monitoring OA,” they wrote.
Surprisingly, the team noted that the average step counts were similar between participants who reported both high and low levels of daily pain. However, those with fluctuating pain had markedly lower activity levels. “This may indicate that fluctuating pain (i.e., pain that is unpredictable/ always changing) may be more troublesome to knee OA patients than those with consistently high levels of pain,” the authors commented.
“This study provides important insights related to the day-to-day variability of pain in knee OA and its links to physical activity,” the researchers wrote. “The results from this can help us start to understand pain in people with knee OA. In the future, larger studies may inform the development of personalized physical activity recommendations for people with knee OA, based on their optimal level of physical activity in relation to their pain.”