While there's little doubt that being overweight can be detrimental to the body, a new study published online May 2 in Radiology adds to the evidence. MRI scans showed significantly less knee cartilage deterioration in obese people who lost more than 10% of their weight over four years.
Even subjects who only lost 5% of their weight experienced lower rates of cartilage degeneration than their peers who maintained their size. The findings add weight to the idea that slimming down could benefit people with mild to moderate osteoarthritis, as well as those at risk for the condition.
"Our findings suggest that weight loss may have a protective effect on knee cartilage and menisci and that greater weight loss may be even more beneficial for knee joint health in obese and overweight individuals," wrote a group led by Dr. Alexandra Gersing from the University of California, San Francisco (UCSF) (Radiology, May 2, 2017).
Osteoarthritis prevalence
Osteoarthritis affects more than 50% of U.S. adults 75 years and older and is the most common joint disease in the country. Compared with those at normal weight, obese men have approximately five times the risk of knee osteoarthritis, while obese women have approximately four times the risk.
Body mass index (BMI) is calculated by taking a person's weight and dividing the number by his or her height. For BMI values, 18.5 through 24.9 is considered normal, 25 through 29.9 is deemed overweight, and 30 or more is considered obese.
"Being overweight or obese can place extra pressure on joints and cartilage, causing them to wear away," the authors noted. "In addition, people with more body fat may have higher blood levels of substances that cause inflammation in the joints, raising the risk for osteoarthritis."
To determine the extent of the association between weight, weight loss, knee cartilage degeneration, and cartilage preservation, the researchers retrospectively compiled complete BMI data for 640 participants (mean age, 62.9 years ± 9.1 years). The subjects had a minimum BMI of 25 and took part in the Osteoarthritis Initiative, a nationwide research study focused on preventing and treating knee osteoarthritis.
The subjects had risk factors for osteoarthritis or evidence of mild to moderate osteoarthritis and had undergone 3-tesla MRI scans (Magnetom Trio, Siemens Healthineers) of their right knees. Results were available for baseline scans and follow-up at 12, 24, and 48 months. After the last images, the cohort was divided into three groups based on percentage of weight loss over the four-year study period:
- Stable weight: BMI change of less than 3% (320 subjects)
- Moderate weight loss: BMI decrease of 5% to 10% (238 subjects)
- Substantial weight loss: BMI decrease of more than 10% (82 subjects)
Two radiologists randomly interpreted the MR images at baseline and at 48 months. They were blinded to patient information and did not know when the right knee scans were acquired. Their task was to assess cartilage and meniscus defects using the modified Whole-Organ Magnetic Resonance Imaging Score (WORMS). Meniscal defects were rated from 0 for intact to 4 for severe or macerated; cartilage degeneration was rated from 0 for normal to 6 for severe.
Knee degeneration
Over 48 months, the percentage of weight change was significantly associated with an increase in cartilage WORMS, the researchers found. Individuals who lost more than 10% achieved the best results in preserving their right knee cartilage, as indicated in the table below.
| Adjusted mean change in WORMS (lower is better) |
||
| Weight loss group | Right knee cartilage degeneration | Menisci degeneration |
| > 10% | 1.0 | 0.7 |
| 5%-10% | 1.6 | 0.6 |
| Stable | 2.3 | 0.9 |
MRI scans of right knee at baseline (A and C) and after 48 months (B and D). Top-row images are of an obese 65-year-old woman with stable weight and mild knee pain; bottom-row images are of an obese 64-year-old woman with weight loss (11% less BMI) over 48 months. The woman with stable weight developed a full-thickness focal cartilage defect at the medial tibia (arrow). In contrast, no cartilage defects were seen in the woman with weight loss. Images courtesy of Radiology."These findings suggest that a larger amount of weight loss is more beneficial for cartilage than is moderate or no weight loss," the authors wrote. "Both weight loss groups showed reduced cartilage degeneration in the medial tibia, which supports the hypothesis that weight loss is most protective for the weight-bearing regions."
The researchers also recommended light to moderate exercise as one way to protect against cartilage degeneration in the knee.
"Our study emphasizes the importance of individualized therapy strategies and lifestyle interventions in order to prevent structural knee joint degeneration as early as possible in obese and overweight patients at risk for osteoarthritis or with symptomatic osteoarthritis," Gersing said in a statement.
