by Kathleen A. Hogan, MD
The holidays are a time when many people eat and drink a bit too much and then resolve to lose that weight in the new year. Unfortunately, once weight is gained, it is often difficult to lose. Many people notice that gaining weight seems to affect their joints, causing knee pain. Does excessive body weight cause knee arthritis or just make the symptoms worse?
Relationship Between Body Weight and Knee Arthritis
Symptomatic knee arthritis affects approximately 13% of women and 10% of men over the age of 60 in the United States. There are many causes of knee arthritis including age, injury, mechanical mal-alignment, and genetic factors. Multiple studies have shown a relationship between body weight and the development of knee arthritis. For example, a person with a body mass index (BMI) of over 30 (obese) has an almost 7 times increases in the incidence of knee arthritis compared to someone with a BMI of less than 25 (normal weight). A BMI increase of 5 points is associated with an over 30% increase in the prevalence of knee arthritis.
Impact of Increased Body Weight
How does this increased weight cause knee arthritis? Elevated body weight increases the mechanical stresses on the knee joint. Every 1 pound of weight gained increases the forces on the knee by a factor of 4. Decreased activity many lead to decreased muscle strength which also increases joint reactive forces. Gait analysis studies have shown that the compressive and sheer forces on the tibia-femoral joint are much higher in patients with elevated body mass compared to normal weight individuals. In a study of identical twins, every 1 kg weight gain (2.2 lbs) was found to increase the likelihood of X-ray findings of arthritis in the knee and hands by 9-13%. It is also thought that there may be metabolic and inflammatory factors in patients who are overweight which also contribute to cartilage damage, even in non weight bearing joints such as the hand. Inflammatory cytokines such as TNF alpha and interleukin -1 and adipokines such as leptin and adionectin are elevated in patients with obesity. The role of these factors in the development of arthritis is currently being studied.
Benefits of Losing Weight
Does losing weight help with knee pain even if you have arthritis? Yes, multiple studies show that weight loss does have beneficial effects, even in patients with x-ray findings of arthritis. Women in the Framingham Knee Osteoarthritis Study who lost weight (BMI decrease of 2 points) significantly decreased their probability of developing knee arthritis. Other studies have shown that when obese patients were able to lose 10% of their body weight, there was a significant improvement in knee pain, physical function, and decreased knee compressive forces with walking. MRIs can also show improvement in knee cartilage with weight loss. The American Academy of Orthopedic Surgeons (AAOS) recommends weight loss through diet and exercise for patients with knee arthritis and a BMI of > 25. Multiple studies have shown the benefit of low impact aerobic exercise and strengthening to improve the symptoms of knee arthritis.
Recommendations for the New Year
Gaining weight can certainly increase the likelihood of developing joint pain and arthritis. If you find yourself putting on a few pounds over the holiday, make sure you stick to your New Years resolution to shed those pounds, as they tend to accumulate if not gotten rid of quickly! While knee arthritis can not always be prevented, low impact exercise, strength training, and maintaining a healthy body weight can help decrease your chance of needing joint replacement in the future.