Background/Purpose:

The pain experienced by osteoarthritis (OA) patients is neither constant nor stable and most patients experience episodes of pain exacerbations or flares. A number of factors have been hypothesized that could increase the risk of pain exacerbations in people with knee OA.  Using a web based case-crossover study design, we evaluated whether intermittent use of analgesics is a risk factor for pain exacerbations in people with knee OA.

Methods:

Participants with a diagnosis of symptomatic knee OA were recruited and followed for 3 months at 10-day intervals (control periods).  Participants were also instructed to log on to the study website if they experienced a knee pain exacerbation during the follow-up period (case periods). Via the internet, we collected data on triggers occurring during “control periods” as well as “case periods”. Pain exacerbation was defined as an increase of 20 mm in a participant’s VAS knee pain score (VAS 0-100) over the follow-up period from his/her mildest pain score reported at the baseline visit. We collected data on analgesic use type and pattern during 7 days prior to the exacerbation dates. We asked participants whether they have taken analgesic over a specific time span (1 day, 2 days, 3-7 days prior). We assessed the effect of intermittent analgesic use on the risk of pain exacerbation compared with regular use using the conditional logistic regression model. Intermittent use was defined as taking analgesic in one of the three time spans only. Regular use was defined as taking analgesic daily over the prior 7 days.

Results:

Of 268 participants (women: 61%, mean age: 62 years, mean BMI: 29.4 kg/m²) recruited in the study, 153 participants experienced at least one episode of knee pain exacerbation. Intermittent use of any analgesic during the prior 7 days was associated with an increased risk of flares with OR of 1.57 (95% CI 0.92, 2.67) (Table). This odds ratio differed greatly amongst different categories of analgesics; intermittent use of Meloxicam (COX 2-Selective) had the highest effect on pain exacerbation with OR of 7.02 (95% CI 1.70, 29.1).

Conclusion:

This study suggests that intermittent use of analgesics (compared with regular use) is associated with an increased risk of pain exacerbation in persons with symptomatic knee OA. The relationship was strongest for Meloxicam.  Further work to better elucidate this connection will be important, as this may represent an important target for efforts designed to prevent and treat OA pain exacerbations.

* Note: n =number of assessments