Obesity and sarcopenic obesity—but not sarcopenia alone—appear to be associated with a higher risk of knee osteoarthritis (OA) in women, according to a recent study. Increasing the emphasis on weight loss strategies is critical for optimizing outcomes for patients with knee OA.
Obesity has been identified as a major risk factor for knee osteoarthritis (OA), but previous studies investigating this link have defined obesity using anthropometric measures, such as body weight or BMI. “Physical measurements reflect aggregate measures of fat, muscle, and bone mass,” explains Devyani Misra, MD, MSc. “As a result, it’s unclear if the risk of knee OA by obesity is through aggregate body weight or amount of fat mass.”
Furthermore, in some older adults, increases in fat mass are not accompanied by increases in muscle mass, leading to a state of high fat but low muscle mass. This condition is known as sarcopenic obesity. Several risk factors for the development of sarcopenic obesity have been identified in clinical research, including low physical activity, inflammation, and malnutrition, among others. On its own, sarcopenia has been associated with several adverse outcomes, including functional limitations, but it is unknown whether inappropriately low muscle mass, as reflected by sarcopenia, adversely impacts the risk of developing knee OA.
A New Analysis
By studying body composition, the additional risks posed by high fat mass and low muscle mass over that of obesity without sarcopenia can be evaluated. “To examine this association more closely, my colleague and I undertook a study in which we defined obesity by fat mass measured by whole body dual energy x-ray and examined the role of sarcopenia, as defined by low muscle mass,” says Dr. Misra. “Our thinking was that if obesity increases risk of OA, then sarcopenia—which is generally associated with low body weight—should be associated with a lower risk of knee OA.”
In a study published in Arthritis & Rheumatology, Dr. Misra and her team examined the longitudinal association of body composition as defined by the relative presence of adiposity and sarcopenia with the risk of incident radiographic knee OA. They studied participants from a large cohort of older adults who either had knee OA or were at risk for it. Subjects included those who had who had dual energy x-ray at baseline, which provided fat and muscle mass data. Knee x-rays were performed and read for OA status at baseline and follow-up and information on other covariates was available. Subjects were divided into four exposure categories: 1) obese, 2) sarcopenic obese, 3) sarcopenia, and 4) non-obese non-sarcopenic.
Among 1,653 subjects without radiographic knee OA at baseline, the investigators found higher risks for radiographic knee OA among obese women and men over 60 months. “Increased risk of knee OA was found in sarcopenic obese women and men, but the results did not reach statistical significance in men,” says Dr. Misra (Table). “Sarcopenia was not associated with knee OA in women or men.” The longitudinal analysis adds a new dimension to care in that it demonstrated an increased risk of knee OA with body composition-based obesity.
Assessing the Implications
According to Dr. Misra, findings from the study have important implications for management of knee OA. “Considering our results suggest that the risk of knee OA in both women and men is primarily linked to adiposity, greater efforts are needed to emphasize the importance of losing weight through diet and exercise when managing this patient population,” she says. A key take home message for clinicians is to utilize weight loss interventions that target both high fat mass and low muscle mass. Preventive efforts may need to expand the focus from simply reducing obesity to also ameliorating sarcopenic obesity in efforts to reduce the growing incidence and prevalence of knee OA.
Dr. Misra adds that the study team intends to build on these results to further investigate fat tissue derived inflammatory markers as mediators for knee OA risk. Although the study did not provide direct evidence for a metabolic or mechanical pathway for knee OA in obesity, it did indicate there is an important role of adiposity (ie, fat mass over muscle mass). Ultimately, body composition assessments may provide important new insights into the association of obesity with knee OA, especially regarding sarcopenic obesity.