Doctor...Why do my knees “snap, crackle, and pop?

Often patients will come to the office complaining their knees crack, or pop or snap.  If your knees sound like a bowl of Rice Krispies, there are a number of possibilities.

Popping in the knees can occur at any age.  Even young people will sometimes describe a popping sound with certain movements.  Young women who present with this symptom along with some dull aching in the front of the knee usually have a condition called chondromalacia patella.  This is a condition where the cartilage behind the kneecap softens. Usually this problem responds to conservative measures such as exercises, medications, and physical therapy.

However if the abnormal sounds are accompanied by other symptoms such as stiffness, aching, or pain, and the patient is older, then further investigation is probably indicated.

When symptoms of pain and stiffness are present, it’s likely there is damage to cartilage.  Cartilage is the gristle at the end of long bones that cushions the joint.  The knee joint consists of the femur (upper leg bone), tibia (lower leg bone) and patella (knee cap).  Each of these bones has a cap of cartilage that allows the bones to glide against each other.  There is also a thin layer of lubricating material called synovial fluid.

Cartilage consists of cells called chondrocytes that sit inside a matrix composed of a mixture of proteoglycans and collagen.  With age, particularly if there is a history of trauma, the cartilage cells and the matrix undergo changes.  Water content initially increases, then decreases.  The ratio of proteoglycans to collagen changes.  Cartilage cells also undergo metabolic changes.  Destructive enzymes are produced and the cartilage begins to form small cracks, called fissures.  Another problem is the thin layer of synovial fluid no longer functions properly.

With further deterioration, cartilage begins to flake.  This leads to the creation of abnormal sounds called “crepitus.” 

This crepitus is very apparent if you place your hand against the knee cap and bend the knee.  Crepitus is due to irregularities occurring in the cartilage on the underside of the knee cap.

While crepitus by itself is not a major concern, it is something that bears watching.  That is because over time the likelihood of other symptoms occurring is increased.

Symptoms of aching and stiffness often signify the presence of osteoarthritis.  Further evaluation by a rheumatologist with history, physical examination, and x-rays are indicated.  X-rays, unfortunately, are not sufficiently sensitive to pick up early osteoarthritis. Sometimes more sensitive techniques like magnetic resonance imaging are called for. Laboratory tests might be needed to exclude other diagnostic possibilities.

If osteoarthritis is diagnosed, a program consisting of weight control, exercise, analgesics or anti-inflammatory drugs, injections of corticosteroids or viscosupplements (lubricants), braces, and physical therapy can provide needed relief.  The exact “mix” of treatments will be determined by the findings determined by the medical work-up.