Have you ever looked at a body mass index (BMI) chart, often found in physician offices, and thought, “That seems unrealistic or even inaccurate?”  At quick glance the charts often seem pretty rigid and show ideal weights in ranges that seem difficult to attain if one is overweight. In this article, the BMI chart will be broken down and explained in better detail so the next time you see one you might look at it a little differently. Hopefully providing a better understanding of it and allowing it to motivate you towards a healthier lifestyle. Once there is a better understanding of the chart itself, I would like to go a step further and explain why the BMI chart is so important in orthopedics. Also, I would like to discuss how it plays a major role in one of the leading causes of disability in this country, osteoarthritis (OA).

Body mass index (BMI) is a measure of body fat based on the relationship between ones height versus ones weight. It is a quick and easy screening tool that places individuals into categories of underweight, healthy weight, overweight and obese in relation to their height. The BMI chart does not account for things like age, sex, ethnicity, and muscle mass. It is also not a direct measure of body fat. However, it is a useful tool for looking at whether your weight is increasing your risk of disease. Major diseases that can be associated with obesity include:  high blood pressure, coronary artery disease, stroke, type 2 diabetes, and as previously mentioned, osteoarthritis.

OA has become one of the leading causes of disability in the United States, with obesity being the greatest modifiable risk factor for osteoarthritis. OA is a condition of joint degeneration, pain and dysfunction secondary in part to mechanical forces exerted across the joints involved. OA is characterized by a breakdown of cartilage and loss of joint space. As increased weight translates to increased force on weight-bearing joints, it is clear why a healthy weight and healthy joints commonly go hand-in-hand.

The following statistics are somewhat eye-opening as they show how big of an effect gravity has on our joints:

While walking, during the portion of gait where one is on a single leg, a force of 3-6 times that of the body weight is transmitted across the knee joint and forces 3 times that of the body weight are transmitted across the hip joint!  So, imagine if a person is 180 lbs. During every step of the day, there are forces upwards of 550lbs stressing the major weight-bearing joints of the body!  On the contrary, for each pound of weight lost there is a 4-fold reduction in load per step during daily activities. This makes weight loss important for both the prevention and management of osteoarthritis. One study showed that the risk of developing knee OA increases 36% for every 2 units of BMI increase or weight gain of about 11 lbs.

Patients who are overweight often find themselves in a “catch 22.”  People will get to a point where their knee or hip OA is so bad that it severely limits their ability to exercise and be active which often goes together with a healthy diet to effectively achieve weight loss. Patients will often say, “If only I could get the knee replacement, then I would be pain free and able to be active.”   A predicament then occurs because there are many issues associated with total joint replacements and increased complications when performed on obese patients. The plastic component in total joint replacements can wear down quicker in the face of increased forces transmitted across them with each step. There is also an increased risk of components loosening in overweight individuals as higher stresses are placed on the prostheses. Other risk factors that increase particularly in the obese population are infection, blood clots, stroke, wound healing issues, and need for revision surgery.

Another national epidemic that we face is childhood obesity. As obesity affects younger individuals, things like OA will start to affect the population at a younger age as well. This is not ideal for joint replacements due to the finite lifespan of each component. The problem this brings is increased need for revision surgeries at younger ages.

The goal of this article is to help bring awareness and understanding towards individuals who suffer from osteoarthritis and may be overweight or obese. Of all the treatment options for OA, the only one that can treat and somewhat prevent worsening OA is weight loss.  Please follow along for upcoming posts about diet, exercise and weight loss. Provided below is a link to a website that offers free information on weight reduction and plant-based diet plans.


Stevie Crisci, PA-C