Mechanical stress is the most important underlying mechanism in osteoarthritis of the knees, while systemic processes may contribute most to hand osteoarthritis, Dutch researchers have found.
"How obesity results in osteoarthritis [OA] is not quite clear, but several mechanisms are thought to play a role, such as increased mechanical stress and systemic processes that are associated with adipose tissue," said senior study author Dr. Margreet Kloppenburg, professor of rheumatology at Leiden (the Netherlands) University Medical Center.
Dr. Margreet Kloppenburg
"Adipose tissue is known to be a source of active mediators, proinflammatory proteins and hormones, influencing inflammation, lipids, glucose metabolism, and insulin resistance," she said. "These systemic processes also could result in the development of OA. Our aim was to understand more about the link between obesity and OA because this insight could help us reach our ultimate goal: to improve treatment for OA patients."
Dr. Kloppenburg and her colleagues reviewed records from 6,628 participants in the Netherlands Epidemiology of Obesity (NEO) study, a population-based cohort of adults aged 45-65 years that is designed to investigate pathways leading to common diseases and conditions in overweight and obese individuals. Participants had a mean age of 56 years and a body mass index of 26 kg/m2; 56% were women. The estimated prevalence of OA was 10% in the knee, 8% in the hand, and 4% in both.
Researchers measured weight and fat mass and calculated fat-free mass. They also calculated odds ratios (ORs) to test for associations between surrogates for mechanical stress (weight and fat-free mass) and systemic processes (metabolic syndrome) with OA in knees alone, hands alone, or both knees and hands. Adjusted ORs were calculated for each OA type in three weight categories: less than 75 kg, 75-90 kg, and more than 90 kg.
After adjustment for metabolic factors, knee OA was significantly associated with weight (OR, 1.49) and fat-free mass (OR, 2.05). Similar results were observed for OA in both the knees and hands. In hand OA, however, investigators found the opposite: Hand OA was significantly associated with metabolic syndrome, independent of weight (OR, 1.46), and had no associations with weight and fat-free mass, Dr. Kloppenburg reported at the annual European Congress of Rheumatology.
"As we hypothesized, knee OA was predominantly associated with surrogates for mechanical stress, whereas hand OA was predominantly associated with surrogates for systemic processes," she said. "But what we had not expected was that surrogates for mechanical stress were predominantly associated with OA in both the knees and hands. This suggests that the co-occurrence of knee and hand OA may not be based on a common underlying pathogenic mechanism, but may represent the presence of two different types of OA."
Adjusted ORs for knee OA and for OA of both the knees and hands were greater in the higher weight categories, but, in hand OA, ORs did not increase with weight.
"Our study supports findings from clinical trials in obese patients with knee OA demonstrating that weight loss, together with exercise, which can potentially modify mechanical stress, is beneficial," she said. "It would be worthwhile to investigate whether weight loss also is beneficial in hand OA."
The NEO study is supported by the Dutch Arthritis Association, Leiden University Medical Center, and Leiden University. The investigators had no conflicts of interest to declare.