Crepitus: Why Does My Knee Pop?

What is Joint Crepitus?

If you’ve ever heard distinct popping or cracking noises from your knees or other joints when moving around, you’ve experienced the symptom known as crepitus. Crepitus (or crepitation) is the term used by doctors to describe these popping sounds and sensations that originate from under the skin. Because of how common crepitus is, most people will have some kind of experience with it at some point in life, but it tends to occur more frequently as people get older.

Since the term crepitus specifically refers to the cracking or crunching noise, it can technically be used to describe any source of such a noise. This includes, for example, the crackling sounds that can sometimes accompany a respiratory illness or the grating sounds and sensations that can occur after a bone is fractured. The most common location where crepitus is experienced, however, is in the knee joints.

Structure of the Knee Joint

The knee is the largest joint in the body, and it is the location where three leg bones come together: femur (thighbone), tibia (shinbone), and patella (kneecap). The ends of all three bones are covered in cartilage, an elastic-like soft tissue that protects the bones from friction and impact. Between the femur and tibia, two pads of cartilage called the lateral and medial meniscus are located on the outside and inside of the knee, respectively.

The knee joint is a type of synovial joint that is held together by a joint capsule, a two-layered envelope that surrounds the joint. The inner layer is called the synovium and contains synovial fluid that keeps the joint lubricated. The outer layer of the joint capsule is composed of dense fibrous connective tissue and is connected to various tendons and ligaments attached to the bones of the leg. These ligaments and tendons are further connected to the hamstrings and quadriceps.

Every time you bend your knee, the patella moves back and forth across a part of the femur known as the patellar groove. The cartilage all around the knee protects the actual bones and facilitates smooth motion as the knee bends. The actual bending happens as muscles in the thigh tighten and relax based on signals from the brain.

What Are Possible Causes of Crepitus?

As primarily a symptom, the presence of crepitus doesn’t necessarily point to a specific underlying condition or cause. The location of the noise, however, along with the type of sensation and the circumstances surrounding it, can be useful for doctors in diagnosing the cause. Below are some common causes:

• Air Bubbles: In the course of normal daily movements, the joint is sometimes forced apart; pressure changes from the temporary widening of the joint capsule can then create small pockets of gas in the synovium. It has been traditionally understood that joint cracking noises were due to the bursting of these gas bubbles, but recent research suggests that it’s actually the formation of the bubbles that causes the noise.
• Snapping Tendons: Another possible explanation for crepitus is the sound of ligaments or tendons moving roughly over bony structures in the knee. They can get stretched out of place and then create a snapping sound as they snap back into place. This can also happen as a result of joint damage.
• Arthritis: All types of arthritis, but especially osteoarthritis and rheumatoid arthritis, cause joint cartilage to degenerate over time. As this happens, there is less and less padding to protect the bones from friction or absorb shock. In addition to joint pain and a variety of other symptoms, arthritis can lead to crepitus.
• Patellofemoral Pain Syndrome: Also known as “runner’s knee,” this condition comes about when consistent, long-term pressure on the patella causes the cartilage to wear away and lose its smoothness. This can be caused by trauma, overuse (as in distance running), or poor knee alignment. Symptoms include crepitus as well as knee pain, swelling, and stiffness in the joints.
• Meniscus Tear: Athletic activities and even simply twisting your knee can sometimes result in knee cartilage becoming torn. Any kind of damage to the cartilage of the meniscus can potentially lead to crepitus, usually as a result of the femur and tibia grinding against each other.
• Surgery: Studies have shown that many people who have joint replacement surgery experience crepitus afterwards. Most of the time this goes away on its own, but persistent issues with crepitus may indicate remaining debris in the joint that needs to be removed.

Crepitus Diagnosis and Treatment

Since it is so common to hear popping or cracking sounds in one’s joints, most people won’t even think to seek treatment for it. In some cases, though, the sounds are persistent and long-lived; in these cases medical attention may be necessary. In addition to a physical examination, the doctor may utilize imaging tests like a digital X-Ray or an ultrasound. In cases of potential arthritis, antibody tests and arthrocentesis may be necessary for a diagnosis.

Depending on the nature of the cause and the severity of condition, treatment may include management techniques and even possibly surgery. Below are some treatment options:

• Ice: while it won’t necessarily make the popping stop, ice can relieve inflammation and pain
• Pain relievers: over-the-counter non-steroidal anti-inflammatory drugs (NSAIDs) like ibuprofen can also provide pain relief
• Injections: steroid injections in the knee can be used to treat some of the possible underlying medical conditions (such as arthritis)
• Arthroscopy: this investigative “keyhole” surgery can be used to diagnose or repair damage to the joints
• Surgery: also known as knee arthroplasty, knee replacement surgery involves replacing elements of the knee with synthetic components in order to improve mobility or relieve pain

TrustCare Can Help

As noted above, most cases of crepitus are at worst a minor annoyance. Indeed, most people undoubtedly associate “creaky bones” with all the other normal parts of getting older. Still, persistent crepitus over a long period of time may be an indicator of damage to the knee joint or possibly even of arthritis. If you’ve noticed consistent cracking and popping noises from your knee or another joint, you should make an appointment to get checked out by a doctor.

At TrustCare Health, we are passionate about getting you excellent health care as quickly as possible. Whether you’re concerned about crepitus or any other ailment, our friendly staff is available to help. With numerous locations and convenient hours, we want to make it as easy as possible to find answers and medical advice when new health concerns pop up.