Causes of Clicking Knees (Grating, Popping & Cracking Sounds)

Popping, cracking or clicking of the joints is not usually a cause for concern, provided that it does not occur all the time and it is not accompanied by symptoms like pain and swelling. However, it still maybe a sign of a problem that is not as yet clearly apparent. In these instances, clicking of a joint may be an early symptom. Although any joint can be affected, many people find that the jaw joints (temporomandibular joints), finger joints and knee joints are particularly prone to clicking, popping and cracking sounds.

Structures of the Knee Joint

In order to understand why knee clicking and popping may occur, it is important to know some of the basic concepts about knee anatomy and movement. The knee is one of the largest joints in the body and among the hardest. It bears most of the body weight when standing and significantly more force from the impact of walking and running. There are four bones involved in the knee joint thereby making it one of the most complex joints in the body.

Joint Anatomy

Bones and Cartilage

The knee is where the single large thigh bone (femur), two smaller leg bones (tibia and fibula) and the kneecap (patella) meet. Articular cartilage caps the end of the bones which move against each other. Special C-shaped bands of cartilage known as menisci provide added benefit for reducing friction. The knee is surrounded by a joint lining (synovium) which secretes lubricant (synovial fluid) to reduce friction when the bones move.

Muscles, Tendons and Ligaments

Several muscles attach to the surrounding bones by the way of tendons. The muscles and tendons also provide stability to the knee joint. However, the main structures for knee support, strength and stability are the ligaments. There are many groups of ligaments of the knee joint, including the cruciate and collateral ligament. Not only do the muscles and ligaments provide movement and stability of the joint when walking, but it is equally important for joint stability when standing.

knee joint

Does the knee make a sound?

Many people are surprised to find that the knee is not entirely silent. In fact sound emanates from many parts of the body particularly where movement is involved. These noises of the joint are referred to as a crepitus. However, the sound of articulation of a healthy knee is usually not audible to humans. There may be the odd incident when the knee may be heard, usually when it is under strain despite the lack of any disease. This may include a popping, clicking, cracking and grating sound.

Some people do experience clicking more often than others, especially when squatting. The exact cause of this knee clicking or cracking without any knee disease is not always clear. It is believed the gas dissolved in the joint fluid may suddenly “pop” when under pressure. This is known as a cavitation and is similar to cracking the knuckles and finger joints. Another cause for joint noises may actually arise from the ligaments around the joints. It can cause a snapping sound.

Causes of Knee Clicking and Cracking

There are several different types of knee problems that can cause unusual knee sounds like cracking, clicking and popping. Grating is a very specific noise associated with arthritis, and particularly osteoarthritis. The type of sound can be useful in identifying the problem to some extent but the abnormal sound alone it is an unreliable indicator. Instead other symptoms need to be considered and diagnostic investigations should also be done to confirm a diagnosis. Here are some of the more common and likely causes of abnormal knee sounds.


Arthritis is any inflammatory joint condition involving the capsule, lining, cartilage or ends of the bone of the joint. Osteoarthritis is not primarily an inflammatory joint condition despite its name. It is discussed in detail below. Rheumatoid arthritis is one of the more commonly known types of arthritis that occurs when the body’s immune system attacks the joint lining. Other types include septic arthritis from an infection, post-traumatic arthritis from an acute injury to the knee and gout from accumulation of uric acid crystals in the joint.


  • Pain in the joint
  • Swelling of the joint
  • Redness and heat over the joint
  • Stiffness (difficulty moving the joint and reduced range of motion)
  • Nodules and deformities in rheumatoid arthritis

Meniscus Tear

The menisci (singular ~ meniscus) are two C-shaped bands of cartilage that lie between the bones of the knee joint. Its purpose is to reduce friction between the structures during movement of the knee and to bear force. Although strong it can still be torn. A tear of the meniscus may occur during sporting activities or as a result of a road traffic accident. Apart from the tear there is also significant inflammation of the structures around it.


  • Popping sensation although a sound may not always be audible.
  • Pain and stiffness when attempting to straighten the leg,
  • Swollen knee joint.
  • Knee may lock with larger tears.

Cartilage Problems

The articular cartilages cap the ends of the bones involved in the joint. It protects the bones, reduces friction and functions as a shock absorber. The cartilage is constantly replenishing itself throughout life to counteract everyday wear and tear. However, there are times where the articular cartilage becomes worn out or damaged. Wearing down of the cartilage is seen in osteoarthritis which mostly affects older adults. Eventually the cartilage cracks and pieces break off. Torn knee cartilage may occur with a severe injury to the knee joint which can happen at any age.


  • Pain during and after physical activity.
  • Grating feeling and at times even a grating sound.
  • Stiffness and diminished flexibility.
  • Hard bumps in and around the joint (bone spurs).

Ligament Problems

The ligaments are thick bands of tissue that provide stability to the joint. There are several different groups of ligaments in the knee, including the patella ligament, collateral ligaments and cruciate ligaments (anterior, posterior and medial). These ligaments can become strain or even torn. When these ligaments are affected, the knee no longer has the same degree of stability. It can lead to the bones abnormally rubbing together and even lead to dislocations if several joints are torn simultaneously.


  • Knee pain
  • Swelling of the knee
  • Knee “gives in” when standing or walking


The knee has various support structures including muscles, tendons, a capsule and ligaments. Dislocation is where the bones in the knee joint slip out of position. It is rare unless most of the ligaments are torn simultaneously. The kneecap (patella) can become dislocated on its own even though the other bones are held in place within the joint. The most common causes of dislocations are related to trauma. Sporting injuries, falls and car crashes are the more likely causes of knee and kneecap dislocation.


  • Severe pain in the knee
  • Slight deformity (knee may look “crooked”)
  • Cannot stand on knee
  • Popping sensation and sound during dislocation and if the knee relocates into the normal position.
  • Loss of sensation, lack of pulse on lower leg and inability to move the lower leg and foot are rare but serious symptoms.

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