I was standing in the gym the other day when a CrossFit buddy saw my un-braced leg for the first time. The extent of atrophy shocked her. How could I have lost ALL my muscle? I was at least partially weight bearing from day 1 post surgery. I started PT within 3 days of surgery. I had been working out.

I knew atrophy happened and was “normal” post surgery, but I realized then that I didn’t know exactly why. It happens so quickly (within days) that there is no way it is solely from lack of use.

Her incredulity – and my inability to explain how this could happen to my leg – prompted me to try to understand more.

So here is the Cary explanation. It wouldn’t pass muster in a scientific journal, but hopefully it will provide a little insight.

When an injury (or even swelling or pain) occurs to the knee joint, the knee sends out a distress signal to the brain. The brain responds by inhibiting the muscles surrounding the joint: Specifically the quadriceps muscle (big muscle that is the front of your thigh). Even after the joint is mended, this (wait for it: big scientific term) Arthrogenic Muscle Inhibition continues and prohibits the nervous system from activating the quadriceps muscle. Once burned…

Arthrogenic Muscle Inhibition (AMI) appears to be the main factor in immediate and ongoing atrophy of the quadriceps and other muscles surrounding the knee; more importantly it can inhibit the ability to reverse the atrophy.

What this means is that recovery does not just mean strength training to rebuild muscle and strength; it means teaching your brain to activate your muscles again. Tricky tricky.

Add on top of this the lack of real use of the leg muscles for 6 weeks and voila!: One wimpy, weak, muscle-less leg.


Let’s look at my case study:


Day 0: I fall, with assist from Puck. Quadriceps tendon detaches from knee. Knee sends holy sh** signal to brain. Brain immediately turns off quadriceps and other surrounding muscles. Given that the quadriceps was no longer attached, this seems redundant, but the brain is just doing what it is trained to do.

Day 3: Surgery. Quadriceps tendon is deftly sewn back on to knee by wonderful surgeon.

Day 7: First PT appointment. I attempt to flex quadriceps muscle. Nothing happens. I have no control of my leg. I stare at it, willing it to move. It ignores me.

Day 8-Day 42: I diligently do my PT. This involves trying to flex my quadriceps muscle a lot. And trying to activate my gluteus (butt) muscles. After 3 weeks, I succeed in lifting my straight leg an inch off the ground. I am ecstatic. This is proof that I am regaining control. It is also immensely frustrating. I’m not doing anything that will reverse or really even slow the atrophy; but at least I am convincing my brain that it’s ok to use the muscles.

Day 43: Brace comes off! Reality sets in. I have a long road back. The surgeon stresses to me the importance of reversing the atrophy as rapidly as I can.

Day 44 – today: It’s been less than a week, but I see progress. I’m able to activate my muscles more effectively. I’m gaining control and stability. I am able to bend my knee enough to complete a full pedal stroke on the bike. I’m starting to chip away at the atrophy. Slowly.

The evidence suggests that AMI can linger and cause ongoing strength deficiencies.

Not an acceptable outcome.

Awareness is the first step.