Higher baseline pain scores among individuals with knee osteoarthritis (OA) were associated with worse structural damage over time, an analysis of data from the Osteoarthritis Initiative showed.
Among patients who had no radiographic evidence of OA at baseline, higher scores on the Western Ontario and McMaster Universities (WOMAC) OA pain index were associated with an increased incidence of radiographic disease over 4 years (OR 1.07, 95% CI 1.01-1.13, P=0.02), according to Yuanyuan Wang, PhD, of Monash University in Melbourne, Australia, and colleagues.
And for those who already had radiographic OA at baseline, higher baseline WOMAC pain scores were associated with increased progression of the radiographic changes (OR 1.07, 95% CI 1.03-1.10, P<0.001), the researchers reported online in Arthritis Research & Therapy.
Evidence has been accumulating supporting the concept that joint health depends on an interplay between structures including cartilage, muscle, and bone, and that pain can have an adverse effect on these structures through inflammation and interference with mobility.
“Thus, it is plausible that knee pain not only is a consequence of structural deterioration in OA but also contributes to structural progression. Clarifying this is important because if this is the case, targeting the factors related to knee pain may offer a potential strategy for slowing disease progression of OA,” Wang and colleagues wrote.
Previous studies examining the potential influence of pain on OA progression have had mixed and inconclusive results, possibly because of differences in study populations, definitions, and assessment of symptoms, and duration of follow-up.
The Osteoarthritis Initiative, which is sponsored by the National Institutes of Health, is a large observational cohort that includes almost 5,000 individuals with knee OA or at risk for the disorder. This database offered a useful resource for analyzing the effects of pain on structural progression, the researchers noted.
The primary structural changes associated with OA are cartilage volume loss, which is assessed with magnetic resonance imaging, and the incidence and progression of radiographic knee changes on the Kellgren-Lawrence grading system.
Symptomatic OA was defined as a WOMAC pain score of 5 or higher. Patients with scores below 5 at both baseline and at 1 year were classified as having no pain, those who had scores above 5 at either baseline or at 1 year were classified as having fluctuating pain, and those with scores above 5 at both time points were classified as having persistent pain.
The analysis included 2,120 individuals classified as having non-radiographic OA, in that their baseline Kellgren-Lawrence grade was 0 or 1, or 2,249 with radiographic OA with grades 2 to 4. Mean ages were 60 in the non-radiographic group and 63 in the radiographic group, and 58% of both groups were women.
In the non-radiographic group, higher baseline pain scores were associated with a greater loss in cartilage volume in the medial compartment (regression coefficient 0.04%, 95% CI 0.02-0.06) and lateral compartment (0.04%, 95% CI 0.02-0.06) after adjustment for age, sex, body mass index, and Kellgren-Lawrence grade.
Similarly, in the radiographic group, a higher baseline pain score was associated with worse cartilage loss in the medial (regression coefficient 0.04%, 95% CI 0.02-0.07) and lateral (0.05%, 95% CI 0.03-0.07) compartments.
In the non-radiographic group, the annual rate of cartilage loss after adjustment for age, sex, body mass index, and Kellgren-Lawrence grade was 0.63% through 4 years of follow-up for those with no knee pain, 0.81% for those with fluctuating pain, and 0.93% for those with persistent pain (P for trend = 0.003). Fluctuating knee pain also was associated with the development of radiographic OA (OR 1.62, 95% CI 1.04-2.54, P for trend = 0.03).
For the radiographic group, the annual rates of cartilage loss were 1.26%, 1,47%, and 1.60% in those with no pain, fluctuating pain, and persistent pain, respectively (P for trend = 0.01). Persistent knee pain was associated with greater progression of radiographic damage (OR 1.82, 95% CI 1.28-2.60, P for trend = 0.001).
“These data suggest that knee pain is an important predictive factor for the deterioration of knee structural outcomes and highlight the significant adverse impact of persistent knee pain on knee structures,” Wang and colleagues stated.
“This study suggests that controlling knee pain early in the disease course as well as over time by targeting the underlying mechanisms may be important for preserving knee structure and reducing the burden of knee OA,” they concluded.
Among the mechanisms contributing to pain and structural changes are inflammatory hyperalgesia, genetic factors, and central mechanisms in the brain influencing fear and aversive conditioning, the researchers noted.
A limitation of the study, they said, was the lack of adjustment for medications.
The Osteoarthritis Initiative is a public-private partnership funded by the National Institutes of Health, Merck, Novartis, GlaxoSmithKline, and Pfizer.
Three of the co-authors reported financial ties with ArthroLab.
Primary Source
Arthritis Research & Therapy
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