TidBits – Knee Pain and Weight Loss

It has become a well established dogma that obesity relates to increased chances of osteoarthritis, but interestingly enough we don’t know until it’s too late.  Let me explain the theorized process. 

Let’s start by telling you that it has been shown that in healthy individuals the mJSW (or minimum joint space width) will remain constant without decrease throughout the lifespan of the individual.  For women and men, the average space is 4.8mm and 5.7mm respectively¹.  What this means is that when a person has healthy knees their entire life, they will not have cartilage breakdown.  This means that NOT EVERYONE WILL GET OSTEOARTHRITIS OF THE KNEE!

Cartilage is the cushion of the knee, is it is also used to cushion the knee against undue forces exerted on it from our weight.  The surprise is that cartilage doesn’t really have good blood flow.  Interesting right?  Our cartilage has poor blood flow.  So how does it heal?  Well, it gets fed by the fluid inside the knee joints.  When we take a step we compress the cartilage.  Think of a sponge being pressed flat for an analogy.  Our cartilage exchanges fluid and oxygen, and nutrients by being repeatedly compressed and released.  This happens when we walk! 

 Then we begin to gain weight.  This is where the problems set in. A higher BMI is directly correlated with the overall likelihood of damage of the knee cartilage.  We call these injuries cartilage defects.  This is really a very poor word choice.  The truth is that these “defects” are traumatic lesions in the cartilage.  One study rates them on a scale where a grade one is localized blistering without damage to the top or bottom of the lesion; a grade two is where the top or bottom of the cartilage is actually damaged and less than half of the thickness is gone; a grade three is where the injury leads to more than half of the thickness of the cartilage; and a grade four is where the injury is so great that the bone is now showing². 

So wait, doesn’t this sound really painful?  Well, here is the scary part.  Cartilage is aneural.  This means that there aren’t any pain sensing nerves that live inside the cartilage to tell us when it is injured.  That means we can’t feel when there is a blister, or a crater in our knee joint cartilage.  We don’t typically start to get much pain until the cartilage is so bad that it is actually already a grade 4 injury! 

This is why it is so important to understand exactly what is happening with your weight and how you begin your workout regiment at the gym, or the pool, or just your stretching program.  There are rules, and reasons as to why you start certain ways.  Walking into a gym, starting on the treadmill and jogging for 5 minutes may be the worst possible thing you can do if overweight or obese.    

The good news is that weight loss is a great predictor of reduced risk of knee pain.  The bad news is that knee pain doesn’t always disappear if we wait until it’s already started, because in many ways if it is severe, the damage is already done.  Keep that in mind when considering how you start your program.   You should seek the help of a professional to help you focus on your weight loss before you begin any type of training program that could damage your knees.  You may be injuring them more than you know. 

Please subscribe.  So much more to come.

Sincerely,

Dr. Rich

1.      BMC Musculoskelet Disord. 2008 Sep 8;9:119

2.      Rheumatology (2010) 49 (12):2362-2369