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06-04-2014 | Pain medicine | Article

Knee OA pain chronic rather than progressive

Abstract

Free abstract

medwireNews: Researchers suggest that patients with knee osteoarthritis (OA) typically experience persistent rather than worsening symptoms.

They looked at the trajectory of OA-related pain over the course of 6 years and identified five distinct pain trajectories: no pain, mild pain, low moderate pain, high moderate pain and severe pain.

Importantly, the team found that none of the trajectories demonstrated marked improvement or worsening of pain symptoms over time, except for a slight initial improvement for all trajectories.

“While pain fluctuated over time, our observation that subject pain did not tend to change over 6 years of follow-up is more consistent with the characterization of OA as a disease of chronic rather than progressive symptoms”, say lead author Jamie Collins (Brigham and Women’s Hospital, Boston, Massachusetts, USA) and colleagues.

The researchers analysed data on 1753 patients with symptomatic knee OA participating in the Osteoarthritis Initiative. They all had a baseline Kellgren-Lawrence (KL) score of 2 or above and Western Ontario and McMaster osteoarthritis index (WOMAC) scores above 0.

Group-based trajectory modelling over 6 years of follow-up identified the five distinct pain trajectories that were based on pain measured at baseline.

Analysis restricted to months 12 through 72 (thereby omitting the initial improvement at baseline) showed that 10% of patients were in the no pain trajectory (WOMAC score averaging below 5, approximately), 34% the mild pain trajectory (WOMAC score between 9 and 11), 34% the low moderate pain trajectory (WOMAC score between 19 and 21), 16% the high moderate pain trajectory (WOMAC score between 38 and 45) and 5% the severe pain trajectory (WOMAC score between 55 and 71).

Patients tended to stay within these trajectories throughout the 6 years, so participants with moderate pain tended to stay in the moderate pain trajectory, while participants with more severe pain tended to say in the severe pain trajectory.

KL grade, along with other factors such as age, body mass index and comorbidities, was associated with worse pain, but investigating pain trajectories according to baseline KL and function did not change the results.

Knee OA as a chronic rather than a progressive disease brings with it the challenge of recognising when pain is inadvertently being hidden through pain-avoiding behaviours, the researchers note.

“What may appear as a stable pattern of pain may actually reflect increasing pain-related activity limitation and greater reliance upon analgesics in order to maintain a bearable level of pain”, they remark in Osteoarthritis and Cartilage.

medwireNews (www.medwirenews.com) is an independent clinical news service provided by Springer Healthcare Limited. © Springer Healthcare Ltd; 2014

By Lucy Piper, Senior medwireNews Reporter