What Causes Knee Pain When Bending & How To Fix It

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We put a lot of wear-and-tear on our knees — there’s about 1.5x our bodyweight on each knee while walking, and that force becomes 7-8x our body weight when we squat!

Obviously, with that much weight going through our knees, there’s a good chance that we’ll develop some type of pain. 

Today, we’ll specifically look at why you’re getting knee pain when bending

Knee pain when bending has many different causes, ranging from bursitis, strains/sprains, tendinopathy, arthritis, and more. 

Luckily, we can pinpoint what’s causing you the pain by understanding where these structures in your knee are and how they become irritated.

Also, if you’re serious about getting into a proper squat without pain, check out our guide on how to improve your squat mobility!

Anatomy 101

As I mentioned, there’s a ton of stuff going on in your knee…which can make this a bit tricky.

But that’s life! Things can’t be too simple for us — where’s the fun in that!

We’re going to break it down into 4 sections, looking at:

  • bursae
  • muscles and tendons
  • ligaments
  • meniscus/cartilage

Each section provides a unique set of clues that can help us zero-in on what’s causing us pain when we bend our knees.

Bursae In The Knee

Bursae are little fluid-filled sacs located all around the body, sitting between bones and tendons. 

They act to reduce friction between a tendon and the bone beneath it, preventing constant rubbing of tendon on bone (it’s as uncomfortable as it sounds).

There are 5 bursae around the knee that we need to take a look at:

  • Suprapatellar Bursa — This bursa sits above the kneecap underneath the quadriceps tendon, helping the tendon glide up and down when you bend and straighten your knee.
  • Prepatellar Bursa — The prepatellar bursa sits right underneath your skin on top of the kneecap, acting as a cushion for it. 
  • Infrapatellar Bursa — There are actually two infrapatellar bursae: the deep and superficial bursae. They sit underneath the patellar tendon (which connects your quad muscles to your shin), protecting the tendon from the tibia.
  • Pes Anserine Bursa (AKA subsatorial bursa) — This bursa is found about 2 inches under the inside knee joint line, cushioning the tibia from the semitendinosus, gracilis, and sartorius tendons. 
  • Semimembranosus Bursa — The semimembranosus bursa is where the name implies: underneath the semimembranosus tendon! It sits on the backside of the knee. 

The locations of these are important — we’ll get to that later!

Muscles & Tendons

If you take a look at any anatomy picture of the lower body, it’s easy to get overwhelmed by the sheer amount of stuff that seems to be going on.

I’m going to simplify all that for you — trust me, wading through all that stuff could give you a headache that rivals your knee pain. 

Muscles act to move a joint (in this case, the knee) and are connected to bones by tendons.

Both muscles and tendons play a massive role in movement function and pain

Let’s dive into the 4 muscle/tendon combos we want to be aware of:

  • Hamstrings — The hamstrings are a triplet of 3 muscles at the back of your leg, consisting of the biceps femoris (which attaches to the outside shin), semitendinosus, and semimembranosus (which both attach to the inside shin). They mainly work to bend your knee.
  • Quadriceps — These are your 4 big thigh muscles, consisting of the rectus femoris, vastus medialis, vastus lateralis, and vastus intermedius. They all attach to the kneecap through the quadriceps tendon, and then attach to the shin through the patellar tendon. They act to straighten your knee.
  • Gastrocnemius — This is the outer one of your two calf muscles. It attaches from your Achilles tendon to above the knee joint into the inside and outside of your femur (thigh bone). It helps with knee bending. 
  • Iliotibial Band — Also called the IT Band, it’s a long piece of fascia extending from some hip muscles and connects to just below the outside of the knee joint. It mainly acts to provide stability to the outside of your knee.

After organizing the seemingly chaotic mess that is our lower body, we can see that there are a handful of potential muscular/tendon culprits that give us knee pain when bending.


Ligaments are similar to tendons, except they connect bone to bone and don’t contract.

There are 4 main ligaments we want to be aware of:

  • Medial Collateral Ligament — The MCL connects on the inside of your knee from your femur to your tibia, helping prevent your knee from bending inwards and twisting too far.
  • Lateral Collateral Ligament — The LCL connects on the outside of your knee from your femur to your fibula, and prevents excessive outward knee bending and twisting. 
  • Anterior Cruciate Ligament — The ACL starts at the front of the top surface of the tibia, and moves up and back to connect to your femur. It helps stop your shin bone from sliding too far forwards on your femur. 
  • Posterior Cruciate Ligament — The PCL creates an “X” shape with your ACL, running and connecting the opposite way of it. It supports your shin from sliding too far backwards on your femur. 

The main function of all these ligaments is to provide stability and prevent excessive movement in your knee.

Meniscus & Cartilage

The menisci are 2 crescent-shaped pieces of cartilage that sit at the top of your tibia.

They act as shock absorbers when you walk, run, jump, etc., to keep your femur and your tibia from smashing into each other.

Your bone-ends (femur and tibia) are surrounded by cartilage, which also acts to absorb shock and prevent your bones from rubbing together whenever you move or put weight on your legs.

Causes of Knee Pain When Bending

Now that we’ve got a better understanding of what’s going on in our knee, we can dive into what the causes of pain may be.

Let’s divide this into 4 different sections of knee pain when bending: pain above our kneecap, pain in front of our knee, pain on the inside or outside of our knee, or pain behind the knee.

Pain Above Our Knee When Bending

Pain above the kneecap usually indicates 1 of 3 things: bursitis, quadriceps tendinopathy, or osteoarthritis.

1. Knee Bursitis

Bursitis is when a bursa becomes inflamed or irritated due to repetitive friction, direct force, infection, or overuse.

This can cause swelling and pain in the bursa, especially when compressed — like when bending the knee!
Since we’re looking at pain above the knee when bending, the suprapatellar bursa is the most likely culprit.

2. Quadriceps Tendinopathy

Tendinopathy is a fancy word that describes issues or injuries in a tendon.

This usually happens with overuse and repetitive motions or strains — often indicating that you should strengthen your legs with an exercise program — and presents with soreness that often gets worse with activity or weight-bearing. 

The quadriceps tendon starts above the knee before attaching to the kneecap, so this may be the cause of your knee pain when bending.

3. Osteoarthritis

Osteoarthritis is known as the “wear-and-tear” form of arthritis.

This usually hits after 50-60 years old, causing pain and swelling in our knee due to a decrease in cartilage around the area, allowing our femur and tibia to rub together to cause inflammation.

This type of pain can be above or inside our knee, and often makes your knee feel stiff in the mornings when you wake up.

Pain In Front Of Our Knee When Bending

Moving down a bit, there are four main causes of pain in the front of your knee when bending.

1. Patellar Tendinopathy

Also called Jumper’s Knee, this type of tendinopathy affects your patellar tendon.

When we bend our knees, our patellar tendon stretches — which isn’t a bad thing — but if the tendon is irritated, this may cause pain or discomfort in the area.

2. Bursitis

Bursitis at the front of the knee usually affects the prepatellar bursa and/or the infrapatellar bursae.

In prepatellar bursitis, also called carpenter’s knee or housemaid’s knee, there may be swelling right over the kneecap, with pain increasing when you put pressure on your knees or bend your leg.

Infrapatellar bursitis is similar, but usually gives off pain a little bit under the knee cap with swelling staying around that area as well.


PFPS, which stands for “patello-femoral pain-syndrome,” is an umbrella term for pain in the knee.

It’s usually caused by several factors, including weaknesses in the muscles around the knee, overloading the joint, or abnormal tracking of the kneecap.

When the kneecap isn’t aligned properly and glides outside of its normal path during bending and straightening of our knees, it’s easy for our knee joint to become overloaded because the forces surrounding our kneecap have changed. 

Having weaknesses in different muscles will allow other muscles to pull harder and put forces on our knee that it doesn’t like — think of our muscles playing tug-of-war with each other. They should be equally balanced, but if one is stronger than the other, we have an unequal force acting on our knees… 

…which it doesn’t like.

4. ACL Irritation

If the pain feels a bit deeper in your knee, it could be your ACL that’s irritated.

Twisting or running may aggravate the ACL and cause a bit of pain — unless there’s been an incident where you felt a pop or immediate sharp pain, it’s probably just the ligament that’s not happy with some extra strain that was put on it.

Pain Inside Or Outside Our Knee When Bending

Looking at pain on either side of the knee, we have four things we want to know about — check out our article on inside knee pain for a closer look.

1. Meniscus Injury

Any strong twists or change in directions can bug those menisci.

If you have swelling and pain in your outer or inner knee, along with having your knee feel like it wants to lock up on you, there may be a tear in either of the menisci — this usually happens with a specific incident such as twisting the knee really hard.

2. MCL/LCL Injury

This can happen if you bend your knee outwardly or inwardly pretty hard.

You can sprain the MCL or LCL doing this because of the strong force, and it usually results in localized pain and swelling at the injury site.

3. Bursitis

This time we’re looking at the pes anserine bursa, located on the inside of your knee close to your MCL.

Pes anserine bursitis is very common in runners, swimmers, and basketball players, and presents with pain and swelling on the inside of your knee.

4. Hamstring Tendinopathy

In this case, we could be looking at the semimembranosus and semitendinosus tendons if the pain is on the inside of the knee, and the biceps femoris tendon if the pain is on the outside of the knee. 

Since the hamstrings run behind the knee as well, this pain can spread from the back of the knee to the sides at the tendons’ insertion points in the tibia and fibula. 

This is more common with runners/sprinters or people who jump a lot.

Pain Behind Our Knee When Bending

Let’s flip the leg around and check the back of our knee.

1. Bursitis

We want to be aware of the semimembranosus bursa here.

When we bend our knee, semimembranosus bursitis can cause high levels of irritation because we squish that bursa every time we bend the leg, causing further irritation.

2. Baker’s Cyst

Also known as a popliteal cyst, a Baker’s Cyst typically happens because the knee has swelling that pushes into either a bursa at the back of your knee or gets trapped, causing an outward “growth.”

This can feel like a marble in the soft spot behind your knee, and typically gets angry when we keep bending our knee and putting pressure on it.

3. Hamstring/Gastrocnemius Tendinopathy

Since our hamstrings and gastrocnemius tendons also run behind our knees, tendinopathy in this area can be a cause as well.

This typically happens if you’re a runner or strained either muscle during stretching or exercise.

How To Fix Knee Pain When Bending

Now that we have a better idea of what’s causing our pain, how do we fix it?

See, that’s an interesting question here.

Depending what the problem is, there can be several solutions — there’s no one-size-fits-all fix for knee pain when bending, and it’s best to double-check with your doctor or physiotherapist. 

Regardless, let’s check out a couple options.


One thing that can help control your pain for nearly all of these is the RICE protocol:

  • R — Rest. You don’t need to go on bed rest, but try to minimize the aggravating activities
  • I — Ice. Some light icing can help decrease the swelling and pain.
  • C — Compression. Using a brace or wrapping up the painful spot can help decrease the swelling and provide support, especially if you sprained a ligament. 
  • E — Elevation. When you’re relaxing, pop your leg up on something to elevate your knee and help flush the swelling out.

Exercises For Knee Pain When Bending

Another thing that may help is stretching and strengthening. 

This might require a bit more guidance, but doing exercises like our at-home leg workout in a pain-free range can help strengthen your muscles and help your knee.

You want to begin with low-intensity exercises and ease-off the ones that worsen your symptoms — sometimes a light stretching program is the thing to start with!

The key is to slowly build up your tolerance to different exercises and activity levels, without further irritating things — like going for a 5 minute walk rather than a 20 minute run!


This is very specific to certain cases, and only considered when you’ve injured yourself pretty badly. 

Your doctor will discuss these options in more detail, but could include:

  • ligament reconstruction 
  • tendon repair
  • meniscus repair


Knee pain when bending can happen for many different reasons — with the amount of stuff going on in and around the knee, it’s no surprise something could go wrong. 

Pain usually comes from the bursae, muscles/tendons, ligaments, or meniscus, and is often taken care by avoiding the aggravating movements, exercising, and rest.

Now, it’s easy to feel lost with all this, especially in what kind of exercises to do. That’s why we want to offer you a free consultation call with a Certified Coach to help you set-up a program that you can do from anywhere, and take back control of your pain and body!


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