We’ll be using the following study,
What we’re looking at here is does excessively bending your knee while you walk increase the likelihood of having arthritis around your knee cap?
More specifically, this study looked at the latter half of a step.
First half = bringing your leg forward and foot hits the ground. (Primarily flexing your hip.)
Second half = have your foot on the ground and push off for the leg swing. (Primarily extending your hip.)
The orange is what we’re concerned with. Particularly the latter phase.
What was found was those with a greater knee flexion moment impulse at ankle push-off, had a greater amount of arthritis progression in the patellofemoral joint (PFJ).
When this group went to push their foot off the ground, their knee bent more, and it stayed there longer, than those who didn’t progress in PFJ arthritis.
Many years ago a client of mine brought her husband in to see me. He had been having some knee issues with running. The first thing I noticed was the leg of the knee bothering him had a very atrophied calf.
I had him do a heel raise on that leg. This is what happened:
Instead of going straight up and down,
his knee shot forward. He couldn’t generate the movement from his ankle, so he tried to do it from his knee.
If you’re upright, and you push your knee forward enough, the heel will elevate. From there, you can straighten your knee.
Voila! Your heel is off the ground and your leg is straight. You end up doing a roundabout way of getting your heel off the ground. A roundabout way where the knee is doing more -moving more- than it typically would.
It made sense to me at the time “We should probably fix this.” That doing this every time he ran -bending his knee more than he needed to- could beat the knee up over time. A couple months later he wrote this,
I had never heard anything about this at the time, but felt confident I was on to something. This study reaffirms that pattern and what can happen from it.
No, that doesn’t mean you’ll have pain
The authors make the point those who progressed their patellofemoral joint arthritis didn’t necessarily have more pain, although PFJ osteoarthritis has been implicated with pain. This is something we’ve known for a very long time. Your joints looking a certain way doesn’t mean you’ll be in pain.
That said, most of us don’t want arthritis. (Sometimes you might.) Particularly in a case like we’re talking about here.
“Arthritis is a normal response to an abnormal stimulus”
I wrote about this last year. That one way to prevent excessive movement, or to handle excessive movement, was to put some bone around that area. (“Arthritis.”) This is exactly what we’re seeing in this study. A knee which moves more, a knee which bends more, adapts. In this case, it adapts by acquiring extra bone around the exact area which is loaded more -the patella and femur.
“The observed difference in the magnitude of knee flexion moment and impulse during the second half of stance was relatively small, which is consistent with the difference previously observed between individuals with and without PFJ OA. [21,55] Given the highly repetitive nature of walking during daily activities, even a small increase in knee flexion moment over each step may result in a large increase in the cumulative loading on the PFJ over time.”
I loved this quote because this is a largely overlooked area in the exercise / pain management / physical therapy worlds. That small movements, done what can be thousands of times per day, over years and years, add up.
The progression happened over only one year!
For many chronic ailments, only looking at things for a year may be a limitation. What if the arthritis progressors didn’t have more pain after a year, but would after two years? There is some strength in this here though. It illustrates how quickly arthritis can progress, given the right environment.
Another potential factor with all the above is if the people who bent their knees more did so because they are lacking knee extension range of motion. When they lay down with their legs straight, one knee might look something like this,
If you can’t straighten your knee fully, you’ll bend it excessively while walking. Such as when you are going to push off from the foot.
(This can be a cause of a limp.)
It’s important to regain knee extension range of motion, but also to not go too long without it. You’re asking for extra bone formation everyday you move on a knee which can’t fully straighten. And once you have extra bone, it’s not always easy to get rid of it!
For more on how to regain knee extension range of motion, check this out.