Joint Inflammation Associated With Pain Sensitization in Knee Osteoarthritis

Inflammatory lesions of knee osteoarthritis (OA) may contribute to sensitization, which in turn, contributes to pain and its severity, according to a new study.

“This finding provides novel insights into mechanisms of pain in knee OA,” said lead author Tuhina Neogi, MD, PhD, of Boston University School of Medicine. “Another common lesion in knee OA, bone marrow lesions, did not appear to contribute to sensitization, though it is known to be associated with pain. This highlights the fact that there are likely many different mechanisms by which pain occurs in knee OA.”
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The study included 1111 subjects (mean age 67) in the Multicenter Osteoarthritis Study, a NIH-funded cohort of people with or at risk of knee OA, had knee radiographs and MRIs, and standardized quantitative sensory testing (QST) measures (temporal summation, pressure pain threshold (PPT)) at the wrist and patellae obtained at baseline and 2 years later.

The researchers found synovitis associated with a significant decrease in PPT at the patella (i.e., more sensitized) over 2 years (adjusted beta: -0.30, 95% CI -0.52 to -0.08). Effusion was similarly linked with a decrease in PPT at the wrist (-0.24, 95% CI -0.41 to -0.24) and with risk of incident temporal summation (adjusted OR 1.54, 95% CI 1.01-2.36). Bone marrow lesions weren’t associated with either QST measure.

These findings don’t have direct clinical implications presently, Neogi said. However, the study provides further rationale for developing and testing new treatments that target specific pathologic lesions in OA and pain mechanisms that can help to improve outcomes in patients with knee OA.

“This study can also be taken as an opportunity to educate primary care providers that OA is not a ‘non-inflammatory’ arthritis, contrary to what has traditionally been taught,” she said. “MRI studies have demonstrated evidence of inflammation in OA, though not as prominent as what is seen in other ‘inflammatory’ arthritis conditions. Nonetheless, PCPs are likely to see patients with knee OA who have or have had knee swelling; that is an indication of inflammation.”

Neogi plans to continue examining pain mechanisms in OA. One study will explore the role of systemic inflammation in driving pain sensitization, which is complementary to this current research.

-Mike Bederka

Reference:
Neogi T, Guermazi A, Roemer F, et al. Joint inflammation is associated with pain sensitization in knee osteoarthritis: The Multicenter Osteoarthritis Study. Arthritis Rheumatol. November 2015. [epub ahead of print] doi: 10.1002/art.39488.