Osteoarthritis (OA) of the knee is a leading cause of disability in people over the age of 65. Most cases of OA are the result of aging, wear and tear, and excess stress on a joint caused by obesity, overuse, or injury. In OA, moist cartilage wears down and becomes thin and rough. When enough cartilage wears away, the unprotected bones rub together, causing severe pain and reducing joint movement. As the bone tries to repair itself, bone spurs form, which makes the joints look knobby.
Our joints consist of two compartments: the “medial and the “lateral.” Under normal gait condition, generally the greatest forces imposed upon the lower extremity are across the medial knee joint space during walking. Weight contributes to the total knee compressive load, which is about four to six times the body weight. For each 1lb of additional weight, the compressive forces across the medial compartment increase by 4-6lbs. The lateral compartment is less affected. Essentially, excess weight causes excess stress on cartilage and exerts a major impact on the progression of knee osteoarthritis, especially in the medial compartments.
An adult who has body mass index (BMI) of 30 or higher is considered obese. The National Health Assessment and Nutrition Examination Survey for 2009 through 2010 found that about one third of American adults were obese. Furthermore, 35.3 percent of men and 35.8 percent of women were obese. It is estimated that persons in the highest quintile of body weight have up to ten times the risk of knee OA than those in the lowest quintile. The impact is also compounded in patients with deformed legs such as knock knee. Most obese people often have weak quadriceps muscles due to their sedentary life style. The weakness of the front of the thigh (quadriceps muscle) makes one further prone to developing knee osteoarthritis.
Some obese patients may eventually need knee surgery such as joint replacement. Although there is no absolute weight restriction for total knee replacement, some surgeons are reluctant to do total or partial knee arthroplasty on very obese patients because of concerns about increased complications of the surgery. Therefore, most surgeons encourage patients to lose weight before the procedure.
The adverse effects of being overweight on the knees are similar to those on the hips. Weight loss is the crucial step in preventing and treating knee and hip osteoarthritis. Weight loss can make a substantial difference in stopping the progression of arthritis and joint pain. If you are overweight or obese, it is never too late to lose weight through proper diet, exercise, drug therapy, or even gastric bypass surgery, if necessary, in order to reduce the risk of arthritis and other medical problems.