One of the most important steps is to keep a healthy body weight. People should maintain a healthy weight for many reasons, but the protection of the knee joints is one of the most important.
Overweight and obesity is a major risk factor for knee osteoarthritis (OA). Being overweight increases the risk of OA developing and makes the symptoms of OA worse.
How does obesity affect osteoarthritis?
OA is characterized by the breakdown of cartilage, the tissue that covers the ends of bones where they form a joint.
Excess body weight directly increases the pressure on the knee joints.
There are two main ways for OA to develop. The first is through forces acting upon the joints.
The second path is through an increase in inflammation. This increase can affect how muscles work and how sensitive nerve endings are. Inflammation leads to an increase in pain.
Fat is active tissue. It creates and releases chemicals within the body that can promote inflammation. These chemicals can further influence the development of OA.
Body weight directly influences both pathways. Obesity not only raises the risk of developing arthritis, but it makes arthritis worse.
Being overweight increases the load placed on the knee joints which can help to speed up the breakdown of cartilage.
The Arthritis Foundation state that 1 pound of excess weight exerts about 4 pounds of extra pressure on the knees. If someone is overweight by 10 pounds, they have an extra 40 pounds of pressure on their knees.
Being overweight also puts extra stress on the joints. Extra stress makes the joints more likely to wear down and become damaged. The stress and damage are especially apparent in weight-bearing joints such as the knees and the hips.
Losing weight to help with knee pain
According to the CDC, 70.7 percent of U.S. adults are overweight or obese.
The risk of OA makes it important to keep BMI under control. Some people with OA have difficulty exercising because they are in so much pain. If this is the case, a doctor can help with finding exercise options.
People with OA should speak with a doctor before starting any type of exercise program. A nutritionist can help with improving diet.
Simple lifestyle changes can lead to weight loss which can help reduce overall pain and improve mobility.
Understanding body mass index
Over the years, the way doctors have determined what people should weigh has changed many times. The approach that is widely used today takes into account the health risks of being overweight.
The body mass index (BMI) is used to describe a person's weight. Having a higher BMI increases the risk of developing weight-related health problems.
BMI takes into account both weight and height in order to work out total body content. BMI is a person's weight in kilograms divided by the square of their height in meters.
Doctors can provide patients with a BMI score, or it can be worked out with a BMI calculator.
The Centers for Disease Control and Prevention (CDC) use the following ranges for BMI in adults.
- Underweight: a BMI of less than 18.5
- Normal or healthy weight range: a BMI of 18.5 to 24.9
- Overweight: a BMI of 25.0 to 29.9
- Obese: a BMI of 30.0 or higher
A BMI over 40 is typically considered morbidly or extremely obese.
In people who are very athletic or have a muscular build, a BMI score may overestimate body fat. A BMI score can also underestimate body fat in older people and people who have lost a lot of muscle.
The Obesity Action Coalition provide a few important facts concerning the relationship between OA, weight, and obesity.
- A person with obesity is 60 percent more likely to develop arthritis than someone of a normal body weight.
- Joint pain symptoms and severity increase with BMI scores. For every 11 pounds of weight gain, there is a 36 percent increased risk of developing OA.
- Women with obesity have nearly four times the risk of OA of the knee, and men with obesity have five times the risk of OA of the knee compared with leaner individuals.
Studies and research on weight loss and knee pain
A Framingham study notes that among women with a baseline body mass index (BMI) greater than or equal to 25, weight loss was associated with a significantly lower risk of knee OA.
Research suggests that losing weight reduces the risk of knee OA.
For a woman of normal height, for every 11 pounds of weight lost (approximately 2 BMI units), the risk of OA of the knee dropped by more than 50 percent. A comparable weight gain was associated with an increased risk of developing OA of the knee.
The researchers concluded that among older adults, if obese men lost enough weight to fall into the overweight category and men in the overweight category lost enough weight to move into the normal weight category, OA of the knee would decrease by 21.5 percent.
Similar changes in weight category by women would result in a 33 percent decrease in knee OA.
Weight loss should be combined with a healthy diet to ease knee pain caused by OA. Wake Forest University conducted a study showing the importance of diet and exercise in helping OA of the knee.
A total of 454 obese adults aged 55 and older with OA took part in an 18-month study. The study examined three different treatment plans: a diet and exercise plan, a diet-only plan, and an exercise-only plan.
Results showed that the diet and exercise group lost more pounds, had less knee pain, walked fast and felt better while performing their daily activities than the other participants.
They reported a 51 percent reduction in pain. Those who just followed a special diet had a 25 percent reduction and those who just exercised had a 28 percent reduction.
The study helped to showcase how a combination of diet and exercise can help to alleviate OA symptoms. Even a 10 percent decrease in weight can make a noticeable difference.
Treatments for obesity and osteoarthritis
OA treatments are negatively affected by obesity. Patients may not get any relief and still have extensive joint problems if they are obese, even after successful knee surgery.
Joint replacement surgery is sometimes recommended in severe cases of OA. Being obese raises the risk for complications.
- Infection - obese patients seem to have double the rate of infection following total knee replacement compared with non-obese patients. Infection rates at the incision site and inside the joint near the plastic or metal parts are also higher.
- Heart problems - surgery puts stress on heart function. Obese patients typically have a higher rate of heart problems including heart attacks.
- Blood clots - obese patients have a higher risk of developing blood clots during or after surgery than non-obese patients.
- Further surgery - in obese patients, the metal or plastic parts can become infected or damaged. If this happens, the patient will need more surgery.
- Less successful results - obese individuals have less successful results than people with healthy BMI. They also often experience less reduction in pain and a smaller increase in the range of motion after surgery.
Patients who have joint replacement surgery can reduce the risk of complications by losing weight and reducing their BMI. Losing weight could even reduce pain to the point where surgery may not be needed.
Artificial joints often need to be revised, so the longer that surgery can be delayed, the better. Those that are obese will wear out or break the polyethylene (plastic) component of their artificial knee faster and thus require it to be reoperated on sooner than those of normal body weight.