The name of this cracking or popping sensation is crepitus. It can affect different parts of the body, but it is common in the knee.
It usually happens when air bubbles develop in body tissues, but it can also happen when the tendons or ligaments snap over the bony structures in the knee, or as a result of patellofemoral pain syndrome (PFS), torn cartilage, or osteoarthritis (OA).
Other people may or may not be able to hear the sound.
The person may hear it when they extend their knee. They may be able to feel a crunching or cracking if they place their hand over the knee and bend or straighten it.
Words that people often use to describe the sound or feeling are "popping, snapping, catching, clicking, crunching, cracking, crackling, creaking, grinding, grating, and clunking."
Knee crepitus can happen at any age, but it is more common as people get older. It can affect one or both knees.
Crepitus is often harmless, but if it happens after a trauma or if there is pain and swelling, it may need medical attention.
Read on to find out more about why crepitus happens and what to do about it.
Structure of the knee
Air bubbles or changes to the structure of the knee can lead to crepitus.
To understand how crepitus affects the knee, let's look at the structure of the knee joint.
The knee is the largest joint in the body.
The three bones in the knee joint are:
- the thighbone (femur)
- the shinbone (tibia)
- the kneecap (patella)
The kneecap rests in a groove of the thighbone, called the trochlea. When a person bends or straightens their knee, the patella moves back and forth inside this groove.
Soft tissue provides padding and protection.
Two wedge-shaped or C-shaped pieces of cartilage between the thighbone and the shinbone are called the meniscus. These enable the bones to glide smoothly against each other.
The cartilage is tough and rubbery, and it helps to cushion the joint and keep it stable.
A thin layer of tissue — the synovial membrane — covers the joints and produces a small amount of synovial fluid. This helps to lubricate the cartilage.
The underside of the kneecap has a lining of cartilage. This cartilage "rubs" against the end of the femur in the trochlear area. With abnormal wear, it can cause grinding and crepitus.
Causes of crepitus
There are various causes of crepitus.
The popping sound usually comes from air seeping into the soft tissue, finding its way into the area around the joint and causing tiny bubbles in the synovial fluid.
When a person bends or stretches their knees, the bubbles can burst with a popping or cracking sound.
This may sound alarming, but it is usually harmless.
Damage to the knee joint
Sometimes, however, there is an underlying problem, for example, tissue damage or lesions. In this case, treatment may be necessary.
If there is pain as the knee snaps or catches, it can be because scar tissue, a meniscus tear, or a tendon is moving over a protruding bone within the knee joint.
Pain or swelling can be a sign of a more serious problem, such as patellofemoral pain syndrome (PFS), a tear in the cartilage or other soft tissue, or osteoarthritis (OA).
These issues may need medical attention. Let's look at them now in more detail.
Patellofemoral pain syndrome
Crepitus of the knee refers to a cracking or popping sound or sensation in the knee joint.
When the pressure between the kneecap and the femur is greater than usual, the cartilage in the joint can start to soften and wear away.
As it loses its smoothness, it can lead to a condition called patellofemoral pain syndrome (PFS), or "runner's knee."
PFS can result from trauma or overuse. It can also result if a part of the person's knee is badly aligned. It is a common source of knee pain in young people and athletes.
Rigorous exercise — such as jogging on an inclined surface, squatting, and climbing stairs — can put strain on the area between the femur and the kneecap joint.
A sudden increase in physical activity, such as exercising more frequently, or running further or on rougher terrain than usual, can also cause it.
Another risk factor for crepitus related to PFS is trauma to the knee. This could be due to a fall or hitting the knee on the dashboard of a car in a road traffic accident.
The individual may experience crepitus when climbing stairs or after sitting for a long time with the knees bent, as well as pain, swelling, puffiness, and stiffness.
Treatment for PFS
The first line of treatment for this condition includes rest, ice, compression, and elevation, or "RICE."
Anti-inflammatory medication and physical therapy exercises can also relieve it.
If these do not help, splinting, surgery, or both may be necessary. They may help to realign part of the knee.
To prevent this problem, anyone who is exercising or participating in sports should make sure they always use appropriate techniques, footwear, and equipment, and be sure to warm up before starting.
Crepitus can also be a sign of a torn meniscus. A meniscus can tear during sports activities, such as when a person twists their knee. It can also happen as people get older and the meniscus wears thin.
- difficulty extending the knee
The American Academy of Orthopaedic Surgeons (AAOS) explain that, when the meniscus tears, the individual may experience a "popping" sensation.
Normally, the person can still use the knee, but stiffness and swelling may appear over the next 2 to 3 days.
As with PFS, the first line of treatment is RICE and anti-inflammatory medication. Sometimes surgical repair is necessary.
Osteoarthritis of the knee
If crepitus occurs with pain, this can be an early sign of osteoarthritis (OA) of the knee. OA is normally a result of wear and tear, and it tends to develop and worsen with age.
In OA, the cartilage that covers the ends of bones in the joints gradually wears away. Bones rub on this increasingly rough surface, resulting in pain and mobility issues. It is more likely among people with obesity or those who have had an injury in the past.
A study published in the journal Osteoarthritis and Cartilage found that women aged 45 to 60 years who had both crepitus and patellofemoral pain had a 72 percent chance of developing OA, although they did not yet have a diagnosis of OA.
Tips and treatment
If a person has an early diagnosis of OA, the Osteoarthritis Foundation suggest using nonsurgical options to slow the progression, maximize mobility, and improve strength.
- lifestyle modifications, such as weight loss and exercise
- physical therapy
As OA progresses, treatment through medication or even knee replacement surgery may be necessary.
Crepitus following surgery or trauma
Research published in Clinics in Orthopedic Surgery shows that up to 18 percent of people who have a total knee arthroplasty (TKA), or knee replacement, will experience crepitus. This may due to the design and fit of the new knee.
This type of crepitus usually resolves without intervention.
However, if problems persist, a doctor may recommend debridement, a minor surgical procedure to remove debris from around the joint.
Another reason for crepitus after surgery is arthofibrosis, or the development of scar tissue. This can lead to pain and stiffness in the joint. It can also happen after a traumatic injury.
If the person experiences pain and stiffness after an injury or surgery, they should see a doctor. The doctor may recommend monitoring the knee, and it may need treatment.
Often, however, crepitus that follows an injury or surgery is not serious. Doctors suggest that, for some people, the crepitus may have been there before, but an increased awareness how the joint is reacting makes it more noticeable now.
Often, say the researchers, reassurance and rehabilitation are enough.
Keeping physically active and warming up before exercise can help protect the knees.
Treatment may not be necessary. If it is, the options will depend on the cause, as outlined above.
If crepitus occurs with exercise, the person should not stop exercising but modify the exercise.
Precautionary measures include:
- avoiding inclines or hills if running
- when using a bicycle, keep the tension on the pedals low
- when lifting weights, focus on the quadriceps or hamstring muscle groups, use lighter weights and do more repetitions
When exercising, people should always listen to their body. If there is pain, they should stop. Always exercise in moderation and stretch before exercising.
Protecting the knees
To help protect the knees, the American Association of Orthopedic Surgeons (AAOS) suggest exercises to strengthen the quadriceps. These are muscles in the front of the thigh.
Stronger quadriceps can decrease the load on the patellofemoral joint, reducing the risk of cartilage wearing away.
Exercises can help, but people who are concerned about their knees should consult a physician before starting a new exercise regime.
Other ways to protect the knees include:
- wearing suitable shoes
- warming up before exercise and stretching afterward
- maintaining a healthy body weight to reduce stress on the knees
Walking and swimming are also good activities for strengthening the leg muscles. In turn, this will contribute to better knee health.
Is there any supplement that will help with crepitus of the knee, for example, glucosamate or vitamin D?
There is no known supplement that will help with crepitus of the knee.
There are a few studies that claim that glucosamine has helped with pain and stiffness but high quality studies have shown no benefit over placebo.
Vitamin D supplements have no effect on the outcome of osteoarthritis of the knee.Answers represent the opinions of our medical experts. All content is strictly informational and should not be considered medical advice.