Based on simple physics, patients with a higher BMI put more physical stress on their knees. But what about knee replacements? Is it possible that BMI affects knee replacement outcome? How about Total Knee Replacement postoperative pain, and function? Depuy Orthopaedics, a knee replacement prosthesis manufacturer, funded a study that gives insight into those questions.
We all learned that Mass times Gravity equals Force, back in the day. But is it that simple, or is there something else going on affecting knee replacement outcome? Most recent studies show that it’s not only the mechanical impact of more weight on the knee which creates problems, but also the impact of the metabolic syndrome caused by that additional weight. Metabolic syndrome is the blood sugar instability that leads to type 2 diabetes. This blood sugar instability ultimately impacts the chemical environment of the joint – causing more bad chemicals that break it down.
The study looked at 1545 total knee replacement patients whose pain and functions scores were followed for 3 years after surgery. The results were that going into surgery with a higher BMI negatively affected pain and function scores. A post operative 10% increase in BMI also negatively affected the subjects pain and function scores, and interestingly, losing weight after surgery did not positively affect pain and function scores. Older patients were slowest to improve and men generally improved more than women. So, heavier patients or those who have more disability have less of a positive response to knee replacement, and those that again gain weight after surgery also do more poorly.
The upshot? These findings echo what we already know about high blood sugar being a risk factor for chronic pain after knee replacement, but provide clarity from the perspective of increased BMI without known high blood sugar affecting knee replacement outcome. Clearly, the chemical environment in the knee is the “what else is going on”. The important point, though, is that the same negative chemical environment in the joint which breaks down tissue leading to surgery, makes healing from the surgery significantly less successful. Interestingly, our registry data shows that our unique supercharged protocol of stem cell injections isn’t impacted by BMI meaning heavier patients with knee arthritis seem to do as well as lighter patients.