Why Does My Knee Crack?

Knee Crack - physical therapy home service

One of the most common questions asked by knee patients is, “Why does my knee Crack?” There are several distinctively annoying sounds that can come from the knee: some of them are not worth worrying about, and others are more problematic. Here is a list of some of the more common knee noises and what the typical causes are.

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  • Loud and sudden snapping noises that occur with initiating movements such as standing up, ascending stairs, and bending / straightening the knee

These clicking noises may or may not be accompanied by pain and are high in pitch. The cause of this type of clicking tends to be tied in to how the kneecap, or patella, sits on top of the underlying trough that the femur bone makes underneath it.This X-ray view of two knees (above) gives us a visualization of how the kneecap should ideally rest. The kneecap can at times slightly move to the side and make uneven contact with the femur bone underneath it. When correction of this slight misalignment occurs, a cracking noise is heard as the patella snaps back into a better alignment. These slight misalignments are often the result of muscle imbalances and weaknesses in the legs. If these clicking noises are not accompanied with pain, I will typically tell patients not to worry about them. If you look closely at the X-ray, the outside (lateral) portion of the “trough” that the kneecap rests in is a bit higher, so it is not at all uncommon for the kneecap to momentarily get stuck when it tracks slightly to the side.

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  • Grinding noises that last for several seconds while an individual is squatting and returning from squatting.

Many people will liken this sound to slowly moving sandpaper over a surface. This sound also tends to be high in pitch.This sound is produced by unevenness in the cartilage that coats the underside of the patella as it makes contact with the underlying tissue and bone. With squatting motions, the at times “ridged” underlying cartilage of the kneecap grinds against the underlying bone, even though the kneecap may not be misaligned and tracking off to the side as in the first example. Think of this type of noise as the result of the kneecap being pressed downwards rather than off to the side.This phenomena can be the result of having tight quads and hip flexors which tether the patella downwards, or it can simply be a function of how “soft” the cartilage is under the kneecap. If this type of sound persists over months or years, it wouldn’t hurt to see a doctor.

  • Deep pitched grinding sounds that come from deep in the knee joint and are associated with bearing weight through the legs / sit to stand etc.

This type of deep sound tends to be reflective of joint arthritis in the femur and patella and is usually the result of age and years of repetitive stress. When X-rayed, there is less space noted between the bones because there is little or no cartilage present. The noise is created by “bone on bone” contact without the normal cartilage in place to provide shock absorption and lubrication. This type of noise is often associated with pain and should not be taken lightly. Go and see your doctor!


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