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Does Silent Inflammation Explain Rise in "Non-OA" Knee Pain?

An Italian study detects a high prevalence of inflammatory abnormalities in the knee joints of older adults, usually absent clinical signs of osteoarthritis.

D'Agostino MA, Iagnocco A, Aegerter P, et al., Does subclinical inflammation contribute to impairment of function of knee joints in aged individuals? High prevalence of ultrasound inflammatory findings. Rheumatology (Oxford). 2015 Apr 13. pii: kev032. [Epub ahead of print]

Knee pain and physical impairment is more prevalent among people over age 60 and has been increasing in recent yearswithout an accompanying surge in osteoarthritis (OA) diagnoses.1 Now Italian researchers show reason to suspect a connection to inflammation.

Their analysis of data for about 500 men and women (ages 50 to 80) reveals ultrasound evidence of inflammation-related structural knee damage in 70%, but radiographic damage only in a small percentage.

The relationship between aging, joint damage, and inflammation is still unclear, they say. But their results suggest “a substantial contribution of inflammation in progressive impairment of joint function with age,” the authors state.

The cross-sectional clinical and ultrasound data come from a long-running prospective cohort study investigating the epidemiology and pathogenesis of atherosclerosis and joint disorders.

At baseline in 1990, and every 5 years since, men and women seen at Bruneck Hospital in Brunico, Italy, underwent clinical and laboratory exams. At a 2010 follow-up, 488 people were evaluated for joint swelling and knee pain (433 had ultrasound of both knees), as well as for levels of physical activity and daily function, comorbid diseases, and use of pain medications.

All but five of the group presented with inflammatory or structural abnormalities, most of them mild. Only around a third reported knee pain, and a mere 14% of this subset had signs of knee swelling on physical exam.

“The increase in degenerative joint abnormalities with age could have been expected; however, the observation of a high prevalence of inflammatory signs in the knee joint, even if mild in most cases, and the relative absence of clinical findings was astonishing,” the researchers comment.

Of those with knee pain, 82 had radiographic damage, but low Western Ontario and McMaster Universities Arthritis Index (WOMAC) clinical severity scores.

Although the study was not designed to look for clinical evidence of OA, subclinical inflammation-related joint damage may increase the risk of OA, they posit, either by creating an "inflammatory milieu" or due to accumulation of structural damage. (Physical activity did not correlate with structural damage in this study.)

The researchers note that comorbid diseases in the elderly, such as cardiovascular disease and diabetes, increase systemic inflammation. Earlier studies from the same cohort find diabetes an independent predictor for knee replacement.

In this study, those more likely to have knee symptoms and ultrasound signs of inflammation were older men with a higher body mass index and diabetes.

Two long-running US health studies first reported an unexplained rise in knee pain back in 2011. The ongoing National Health and Nutrition Examination Survey (NHANES) found the frequency of knee pain increased 65% in women and men in the 20 years after 1974.

Among participants in the Framingham Osteoarthritis Study, the frequency of knee pain doubled in women and tripled in men from 1983 to 2005. Although 24.7% of women and 16.5% of men report knee pain, x-rays demonstrated no change in the frequency of OA during that time.1



1. Uyen-Sa DT, Nguyen D, Zhang Y, et al., Increasing Prevalence of Knee Pain and Symptomatic Knee Osteoarthritis. Ann Intern Med. 2011; Dec 6; 155:725–732.