Episode 93 | Is Numbness Normal after ACL Surgery? Part 1

What is up team? We are back this week in full force. My voice is almost back to a hundred percent. And for those of you who listen to showing up in your ACL rehab, bless your soul, and thanks for sticking it out with me. And I’m excited to dive into this two-part series where we are going to answer the question: Is numbness normal after ACL surgery? And today, we are diving into part one where we are going to talk about numbness.

And a little bit of the details, diving into it and giving you guys a little bit more background and why it happens. And this is a super common question I get from almost every athlete we work with. And I get this from social media all the time—is numbness normal? How much is normal? When can I expect things to be normal? All of these different pieces of understanding what’s going on. And we’re hoping that this two-part series is really going to help answer that. And I’m excited to geek out on this, so I hope you guys are ready for a little bit of some anatomy lessons. But more so getting to the root cause of what is going on, why does it happen? And so let’s jump right in.

I’m going to go ahead and answer the very straightforward question: Is numbness normal after ACL? The short answer is yes. It is very common. Let’s dive into why it’s so common and what exactly is going on. But first, let’s define what numbness is. The technical term for numbness is paresthesia. And that is something that you’ll hear maybe medical doctors use or in the literature. But we’re going to really focus on numbness because that’s what most ACLers feel after surgery. And numbness is really a change, and especially a loss of sensation in a certain area. Sometimes it can come with other symptoms like tingling or changes in temperature. Sometimes it can be that prickly type sensation, the pins and needles type feeling. This is typically a sign of something neurogenic, or what we say is coming from a nerve.

Now, everyone has experienced this in one way or another. You’ve probably fallen asleep on your arm in an awkward position. You might have sat in your seat for a certain position for too long and your foot falls asleep, or maybe you feel those pins and needles in the bottom of your foot. Now, this is a little different than ACL surgery itself, but this will help to explain what exactly is going on. When this happens to you, this is usually because a nerve is being compressed or maybe stretched, leading to compression on those arteries that provide blood to the nerve. This limits oxygen and glucose to the nerve causing it to fall asleep. Once the position is changed or the compression is moved, usually it bounces back and wakes up. We all know this. But it’s different when we’re talking about ACL surgery to some degree, and it’ll make more sense as we continue on now.

For a brief anatomy lesson. Let’s talk about how the anatomy plays into this numbness that you feel at your knee. So what I want you to visualize is basically your nerves kind of like a tree. Visualize that tree. You have the top parts of the tree, and then you have basically the roots and the trunk. All the small ones off of those little roots. This is how our nerves work. You got your brain at the top, you’ve got your spinal cord, and then you have these nerve roots that are coming out. From there, you have smaller ones and even smaller ones that branch off of each or every one of those. Now, to keep things super simple here, we’re going to break these down into two different types of nerves that come out. 

One is sensory and one is motor. The sensory is the input; the motor is the output. Sensory nerves provide senses for touch and pain, temperature, vibrations, etc. And it gives our brain info about the environment around us. When you close your eyes, but you can still touch your elbow, you know what’s happening. And it’s due to sensory info going in and the nerves providing that to our brain. Motor nerves create the output, the function, or typically the action or the movement. Bending the knee, engaging the quads, and whatever movement happens within your body is all motor output. We’re going to skip ahead here for just a second. But what’s impacted in your ACL surgery is a specific sensory nerve called the infrapatellar branch of the saphenous nerve. Luckily, this does not impact function in most cases, since it is not a motor nerve, it is a sensory nerve. So it does affect sensation, mainly that numbness that most of you ACLers feel. 

Let’s keep rolling with this anatomy lesson here. The anatomy of the infrapatellar branch of the saphenous nerve. And one thing I do want to point out before we dive into this, is that remember that everybody’s body, like your actual human body, is a little different. But this is going to be a general anatomy overlook for the general population and for most people. The origin of this infrapatellar branch of the saphenous nerve actually starts up at the spinal cord. The spinal cord creates these nerve roots that come out of our lower back and they form to create the femoral nerve, sciatic nerve, and some other nerve branches. But these are the main ones that are going into our lower body and innervate our lower extremities. Now, the main focus here is the femoral nerve which runs to the front part of the hip and the front side of the body, and then it goes down this path through muscles along our groin called our adductors. And then it comes out and then it starts to split once it gets near the inside medial part of the knee and down the lower leg. 

When it gets to that inside part of the knee, near the sartorius and gracilis tendons. These are your inner hamstring muscles, so just think about that inner side. It branches into the saphenous nerve and the infrapatellar branch of the saphenous nerve. To give you a solid visual here, just imagine there’s a nerve that goes through the front part of the hip then towards the inner part of the groin, and then to the inner side of the knee. And that’s where we’re at right now. The saphenous nerve continues down the leg, and it is responsible for allowing people to feel sensation from the inner side of the knee and down towards the ankle on that inside area. One of the things with the infrapatellar branch is where the inside of the knee and more towards the front of the knee is where it starts to provide a sensation. If you were to take basically the palm of your hand, and if you were to cover the inside to the front side of your knee, that’s basically where that branch will help innervate and provide sensory feedback. And it crosses over basically the front of that knee joint and even beyond that. And I’m sure you know where I’m going here.

When you think about the incisions made in your ACL surgery, there’s typically incisions made around this area. And one of the things before we move forward I want to mention some other nerves that might play a role, but is not nearly as common: the medial sural cutaneous nerve, the lateral sural cutaneous nerve, and the lateral femoral cutaneous nerve. I want you guys to really ignore all of these names for the most part, just know that there are different nerves and branches. And the main player here is the infrapatellar branch of the saphenous nerve. And that is the one that by far is the most common and it makes the most sense based on the anatomy and based on the incisions that are made in the ACL reconstruction surgery. 

Now, one cool bonus about this episode is that I’m going to plug in some pictures in the podcast notes. If you click the links, I promise they will take you to some pretty cool pictures that can help you get a visual of what’s going on. And you guys know I’m like super big on making things practical and so you can understand. And I really feel like if you feel informed about what exactly is going on, man, then this can put your mind at ease and make it understanding to know, okay, why am I dealing with this? What is going on? And if you can visualize this, this will be a home run. And this makes so much sense. And even going through this for myself and digging a little deeper, I was like, wow, this makes so much sense. And it was really cool to be able to help present this to you guys as well. 

But when you look at this first picture, it’s basically showing you a network of the nerves of the lower extremities; starting from the hip all the way down to the foot, and it’s on the front side. And what’s really cool about this specific image is that it’s actually highlighting what gets blocked when you get a femoral nerve block. For those of you who don’t know, a femoral nerve block is one of the regional anesthetics that you can get whenever you are having ACL surgery. And that can help to block the pain temporarily for 24 to 48 hours or so. And this picture actually shows the pathway of those specific nerves. And if you look at it, you can see basically on the front side you have your anterior femoral cutaneous nerve that’s blocked with the femoral artery block. 

There is the saphenous nerve that gets blocked with the femoral nerve block, and there is the infrapatellar branch of the saphenous nerve that gets blocked with the femoral nerve block. But this goes to show you basically why it is that you don’t feel nearly as much pain and what is getting blocked because those sensory nerves are having analgesia put into it to essentially block it for a little bit. So this all makes sense. And what I want you to key in on, if you do look at it, is where that infrapatellar branch of the saphenous nerve goes. You’ll see a very light green color and that is basically at the front of the knee where the patellar tendon is. But if you look at that little branch that it’s connected to, that’s it. And so that makes so much sense of why people feel that numbness in that area. 

And how does it happen? With surgical techniques in ACL reconstructive surgery, it’s all going to really depend on the surgeon and the process, as well as the graft types, the approach that they take, and the incisions. But in general, ACL reconstructive surgery, it’s an arthroscopy, so that means it’s minimally invasive. And they have these tiny little incisions where they stick scopes in and where they’re going to operate out of. And with this, one of the drawbacks is essentially that they’re going to make that small hole which is going to help with not having a big scar or a big incision to heal. But the counter side of that is that they can’t always see exactly what they’re about to cut into and can’t necessarily visualize every single structure that they’re going to make the incision for. 

After an ACL reconstruction, there is numbness or tingling in those specific areas of the knee or even at the shin, and it is most likely due to damage to the infrapatellar branch of the saphenous nerve. This small nerve is easily missed by the surgeons and it’s almost hard to work around, especially with the specific types of surgeries. One that we’ll talk about with specific graft types like the hamstring tendon. And so that’s going to be a key factor here. But especially, if this is going to be performed via arthroscopy, it’s going to be tough to get around cutting through this nerve or even some parts of it. And numbness can come when that nerve is accidentally cut or stretched as they’re getting into the knee itself. 

This leads to the second picture that you’ll be able to look at, which basically shows this highlight of the front of the knee and almost like these little tiny hairs of the branches of that inferior branch of the saphenous nerve. And it shows that it runs towards the front and the inside part of the knee. And then when this gets cut, you can almost imagine why people feel that palm size type of numbness more to that front, inside part of the knee. And almost like a good area to think about is where that button on the inside of the knee and where that screw goes. And that’s typically an area that people will feel where there is that numbness or sensation after the surgery. 

If you take a look at that picture, it shows a risk zone and it talks about just the different little branches and some of the incisions. It will help to depict what exactly they’re trying to get with a safe zone. But sometimes what happens, and especially with the way that nerves in our bodies work, is that it’s not going to be perfect, but they’re hoping to be accurate with most people. But even based on that image, it is going to be nearly impossible for you to be able to dodge any of that nerve. Some of it is likely to get impacted, whether it is cut or stretched in the surgical process. 

And so how common is it to have this numbness after ACL surgery? When you read most of the research, it can range anywhere from 40% to almost 80% to 90% of people. Most studies, I would say, have a referencing point of around actually 80%. There was a study by Inderhaug in 2014, where they looked at the impact of sensory deficits after harvesting hamstring autografts for ACL reconstruction, 85% of the examined patients had sensory deficits. And in another study by Sanders in 2007. This was a research that found 74% of people who had numbness or tingling still felt this after six months after surgery. Twenty percent of those saw improvements after. The improvements in these symptoms had a decrease mostly in the size of the area that has been affected within that year of ACL reconstruction. 

And this is going to bring part one to an end. And we’re teeing up part two to understand, okay, what are the graft types that play a role? What’s normal versus not? Some of the anatomical variations, the nerve healing and regeneration. And what about the recovery of your numbness? All this is coming in part two. I wanted to set the stage here and help you gain an understanding of, especially the anatomy and understanding what exactly is going on initially in the process. So then that way you can gain clarity on, okay, this is what’s happening. Now, what can I do about this? Or maybe not do right? And most importantly, feel informed. So you know exactly, all right, I’m feeling numbness, is this normal? And also, what is the likelihood of me getting that pack? 

Tune in next week for part two. And before I hop off here, if you guys have a second to spare, please leave the podcast a five-star review. It helps us a ton, it helps ACLers get the word, and that way they can know and be informed in this process just like you. It’s so appreciated. Love you guys. I’ll catch you next week. This is your host, Ravi Patel, signing off.