Being overweight, particularly if you have a higher than average body mass index, may increase your risk for developing severe osteoarthritis in your hips and knees, according to research presented this week at the American College of Rheumatology Annual Scientific Meeting in San Francisco, Calif.

Osteoarthritis, or OA as it is commonly called, is the most common joint disease affecting middle-age and older people. It is characterized by progressive damage to the joint cartilage—the slippery material at the end of long bones—and causes changes in the structures around the joint. These changes can include fluid accumulation, bony overgrowth, and loosening and weakness of muscles and tendons, all of which may limit movement and cause pain and swelling.

Swedish researchers recently measured the body mass, waist, waist-to-hip ratio, weight and percentage of body fat of 11,026 male and 16,934 female members from the general population—who ranged in age from 45 to 73 years—and of that group, 1,022 OA patients who had undergone joint replacement surgery were identified 11 years later.

Researchers then compared 471 patients who had total knee replacement and 551 patients who had total hip replacement due to OA with those who did not to define the relationships between body mass and knee and hip OA leading to joint replacement. They also explored the relationships between C-reactive protein, metabolic syndrome and the incidence of severe knee and hip OA.

After adjusting for other important risk factors, including age, sex, smoking status, other illnesses, C-reactive protein, and physical activity level, researchers determined that being overweight by any measure identified was associated with knee OA leading to joint replacement. Of all measures, a higher body mass was the biggest risk factor associated with developing severe hip or knee OA for both men and women.

In this study, which is the largest and the first that compares the effect of different measures of body mass on the risk of severe OA over time in the knees and hips of both men and women in the same population, investigators also demonstrated that the risk increase of developing severe OA is more strongly related to increased joint loading due to being overweight than to the metabolic changes associated with being overweight or obese (such as, increased CRP and metabolic syndrome).

“[Being] overweight is one of the few factors leading to osteoarthritis that we can actually do something about,” explains Stefan Lohmander, MD, PhD; professor and senior consultant; Lund University, department of orthopaedics, clinical services, Lund, Sweden, and lead investigator in the study. “Understanding the connection between being overweight and getting osteoarthritis, and the size of the risk, is therefore important when considering disease prevention. We have shown that the risk increase starts already with being moderately overweight, and increases with each further increase in body mass. This is true for men and for women, and for knees and for hips.”

When considering the impact this may have on patients in the United States, Dr. Lohmander says, “This study was done in Sweden and started more than 10 years ago. The frequency of obesity and its severity was (and is) less severe in Sweden than in the U.S. Had this study been done in the U.S. today, I expect that we would have seen even more dramatic increases in [the] risk of osteoarthritis of the knee and hip due to [being] overweight and obesity. Osteoarthritis should be added to the already long list of diseases increasing steeply due to the obesity epidemic.”

The ACR is an organization of and for physicians, health professionals, and scientists that advances rheumatology through programs of education, research, advocacy and practice support that foster excellence in the care of people with or at risk for arthritis and rheumatic and musculoskeletal diseases. For more information on the ACR’s annual meeting, see http://www.rheumatology.org/annual.

Editor’s Notes: Dr. Lohmander will present this research during the ACR Annual Scientific Meeting at the Moscone Center from 9:00 – 11:00 AM on Sunday, October 26, in Hall A. Dr. Lohmander will be available for media questions and briefing at 8:30 AM on Tuesday, October 28 in the on-site press conference room, 114.

Presentation Number: 201

Incidence Of Severe Knee And Hip Osteoarthritis In Relation To Different Measures Of Body Mass, Metabolic Syndrome, And CRP. A Population-based Prospective Cohort Study

Stefan Lohmander1, Maria Gerhardsson2, Jan Rollof2, Peter M. Nilsson1, Gunnar Engström2. 1Lund University, Lund, Sweden; 2AstraZeneca R&D, Lund, Sweden

Purpose: To determine in a large prospective population-based cohort study the relationships in men and women between measures of body mass and incidence of severe knee and hip OA leading to arthroplasty. To explore the relationships between CRP, Metabolic syndrome (MetS) and incidence of severe knee or hip OA.

Methods: BMI, waist, waist-hip ratio (WHR), weight, and % body fat (BF%) was measured at baseline in 11026 men and 16934 women, 45 to 73 y old, from the general population. Incidence of severe OA was defined as arthroplasty due to knee or hip OA monitored over 11 years by linkage with Swedish hospital discharge register. Cox’ proportional hazards assessed incidence of surgery due to knee or hip OA in relation to risk factors with adjustments for confounders. A subset (n=5171, mean age 57.5+5.9 y) had data on overweight, blood pressure, HDL, triglycerides, glucose and hsCRP. MetS was defined as by ATPIII-NCEP.

Results: 471 individuals had TKR and 551 had THR for OA. After adjustment for age, sex, smoking and physical activity, the RR of knee OA (4th vs. 1st quartile) were 8.1 (95% CI 5.3-12.4) for BMI, 6.7 (4.5-9.9) for waist, 6.5 (4.6-9.43) for weight, 3.6 (2.6-5.0) for BF% and 2.2 (1.7-3.0) for WHR. The corresponding RR for hip OA were 2.6 (2.0-3.4) for BMI, 3.0 (2.3-4.0) for weight, 2.5 (1.9-3.3) for waist, 1.3 (0.99-1.6) for WHR and 1.5 (1.2-2.0) for BF%. Relationships persisted after adjustment for comorbidities. After adjustment for age, sex, smoking and CRP, presence of MetS in the subset was associated with an increased risk of knee OA (RR 2.1, CI 1.4-3.4), but not after adjustment for BMI (RR 1.12, CI 0.68-2.0). MetS was not associated with incidence of hip OA. In women, CRP was associated with hip and knee OA in unadjusted analysis, but not after risk factor adjustments.

Conclusions: All measures of overweight were associated with incidence of knee OA leading to arthroplasty; the strongest relative risk gradient observed for BMI. Incidence of hip OA showed smaller differences between normal weight and obesity, but BMI was a significant risk factor also for hip OA. The increased incidence of knee OA in subjects with MetS was largely explained by increased BMI. CRP was not associated with incidence of severe knee or hip OA leading to TKR or THR when possible confounding factors were taken into account.
Our results support a major link between overweight and biomechanics in increasing knee and hip OA risk in both men and women, but do not support a major role for systemic inflammation per se as a risk for incidence of OA, at least not in association with obesity. We cannot exclude a role for local inflammation associated with excess adipose tissue in the joint. Blood for hsCRP assay was sampled several years before OA surgery. It is possible that CRP better reflects occurrence and progression of OA in patients with established disease, than the risk of developing OA in a population-based setting.

Disclosure Block: S. Lohmander, None; M. Gerhardsson, AstraZeneca R&D, 3; J. Rollof, AstraZeneca R&D, 3; P.M. Nilsson, None; G. Engström, AstraZeneca R&D, 3.

Source: American College of Rheumatology (ACR)