Why does my knee crack when I lunge down or squat?

Why does my knee crack when I lunge down or squat? I get this question a lot in my clinic. Or is it normal that my knee cracks and pops during activity? The short answer…NO! That is definitely not normal. But I usually tell them exactly why this happens and what can be done to stop it. This symptom ranges from those that have had surgery, had an injury, have arthritis and everywhere in between. So why is it that people have this happen? Let’s take a look at the anatomy of the knee and look further into the symptoms.

The knee is made of up 2 bones, your Femur which is your thigh bone and your Tibia which is your shin bone. They come together to form the Tibiofemoral joint. It is a hinge joint because it is able to bend and straighten with the help of muscle activation. Sitting on top of the knee is a small bone called the Patella or knee cap. The knee cap’s job is to give the quadriceps tendon a lever to sit on and pull so that the knee can straighten. It also slides in a groove on the femur as the knee moves. All of these 3 bones have Hyaline cartilage on them. This is a smooth surface that prevents bones rubbing together. Healthy Hyaline cartilage looks pearly white. As we get older this cartilage tends to break down like tread on a tire. This in turn causes Arthritis. The knee also has some stabilizing ligaments comprised of the ACL/PCL/MCL/LCL. Each ligament prevents the knee from going in a certain direction. ACL prevents the shin bone from going forwards, the PCL prevents the shin from going backwards and the MCL/LCL prevents the knee from going side to side. So…why do some people complain that their knee is cracking?

There can be multiple reasons why your knee cracks or clicks. Let’s go over a few to try and understand why:

Your knee cap is not tracking properly

As stated above the Patella or knee cap is a small bone that sits in a groove on your knee. It tracks in this groove as the knee goes from straight to bent. If the knee cap is not tracking correctly in the groove it will make a cracking or clicking sound. This sound is made when the knee cap gets pushed back in the groove itself. In turn if the knee cap continues on this path it will start to wear down the Hyaline cartilage and cause Arthritis. Some causes of the knee cap not tracking properly are injury to the knee and weakness of your quad muscles. One muscle in particular is the Vastus Medialis Oblique or VMO. This muscle is the tear drop muscle that sits towards the middle of your knee and is part of your quad. It helps to pull the knee cap medically as you straighten your knee. If this muscle is weak it can cause the knee cap to track incorrectly and that is when you hear a cracking sound as you squat down or lung.

You have Arthritis

If you are already unfortunate enough to have Arthritis then the sounds you hear in your knee are most likely coming from that. As we age our joints break down and the more wear and tear we put on them the faster Arthritis tends to come. When this happens you lose the pearly white cartilage in places and bone starts to rub together causing inflammation and pain. As your bones rub they can cause sounds and one is a click or a crack.

You have a meniscus tear

Your meniscus sit in between your femur and your tibia. They are cartilage that look like circular cups that provide a shock absorption as well as a surface for your knee to move freely on. Having a meniscus tear is a fairly common injury. When this happens it is usually from a twisting or pivoting injury. As your knee moves the bones slide on top of the meniscus. If they are healthy no sounds can be heard. If there is a tear sometimes a flap can be formed and every time you move your knee the flap gets caught and then releases causing a crack to be heard. Sometimes the flap does not relocate and you can get a feeling of being stuck and the knee does not want to straighten or bend all the way.

I do want to say that sometimes a crack in the knee can happen and not be caused by anything. An occasional crack that is not associated with pain is nothing to be concerned about. But a knee that cracks consistently should not go unnoticed. So if you ever experience a crack or a pop in your knee consistently, don’t hesitate to seek out your Physical Therapist to take a look at it.


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