Knee pain and clicking

Runner’s Knee

If you enjoy running, you’re probably familiar with the many benefits it can provide. It’s a great way to beat stress and stay in shape while being outdoors.

Unfortunately, if you run regularly, you also face a good chance of developing knee pain. Over recent decades, as more people have taken up running, including the greater numbers participating in marathons, running-related injuries have increased. In several studies examining injuries in marathon runners, knee injuries were by far the most common.

Knee Pain from Running: What Is Runner’s Knee?

Research has found that a condition called patellofemoral pain syndrome, also known as “runner’s knee,” accounts for up to 25 percent of all injuries that develop in runners. This problem typically causes pain around or just behind your kneecap. You’re likely to feel knee pain after you’ve been sitting down for awhile with your knees bent, or when you run, squat, or climb stairs. The knee pain may feel dull or sharp. You may also notice a popping or clicking feeling in your knee.

At the knee joint, your thigh bone (femur) and shin bone (tibia) come together. Your kneecap (the patella) is aligned in a groove at the bottom of your femur, and movement within this groove is referred to as patellar tracking. If your kneecap doesn’t move properly in this groove, as you bend and extend your leg while running, it may cause runner’s knee.

Runner’s Knee: Risk Factors

Specific factors that can contribute to runner’s knee include:

  • Weak thigh muscles
  • Poor flexibility — tight thigh muscles and ligaments
  • Overuse — running too much
  • Trauma or injury
  • Poor alignment of the kneecap, resulting in wear and tear of the cartilage of the kneecap

Other causes of knee pain in people who enjoy running include arthritis, damage to cartilage that normally allows the bones to glide freely in the joint, or irritation of tendons in the joint.

Runner’s Knee: Prevention

According to the American Academy of Orthopedic Surgeons, there are several ways to prevent runner’s knee, including shedding extra pounds to lessen the stress on your knees, increasing your running speed and distances gradually, and running on relatively soft surfaces when possible. Also be sure to stretch well before exercising and wear well-fitted, quality running shoes.

Runner’s Knee: Rest and Rehab

One of the most important steps you can take to treat runner’s knee is to simply take fewer steps. In other words, ease off the running. You may need to cut your mileage down or temporarily switch to another activity such as swimming or cycling. Elevating your leg and putting a cold pack on the joint for a short time after running may also reduce knee pain.

Rehabilitation is another large component of the treatment of runner’s knee. Studies have found that many people with runner’s knee eventually get relief from their symptoms simply by doing exercises to address the problem. Your physician or physical therapist can create a customized program of stretching and strengthening exercises specific to the cause of your runner’s knee.

Other common treatments include:

  • Wearing special inserts in your shoes
  • Wearing a brace or taping the kneecap for support during activity
  • Surgery to remove damaged cartilage or to realign the patella if other treatments don’t resolve the problem

By taking some steps to prevent knee pain caused by running, you’ll be able to continue your workouts without a problem. If you have symptoms of runner’s knee, paying attention to your knee pain and taking care of it swiftly to avoid further injury are key to continuing to do what you love — running.

Do your knees make noise? There’s probably no reason for concern. Popping and cracking sounds usually aren’t signs that something’s wrong.

“A lot of joints crack and the knees are a really common joint to crack,” says David McAllister, MD, director of the UCLA’s Sports Medicine Program. “Most people have knees that crack when they squat down or go through the full arc of motion. We generally don’t worry about cracking or popping when it isn’t associated with pain or swelling.”

Curious why your healthy knees might be making noises? As we age, the tissue that covers the bones, called cartilage, can develop uneven areas. When we squat or stand, sounds come from these rougher surfaces gliding across each other. It could also be the tissue that connects bones to other bones, called ligaments, tightening as you move, or the joint lining moving over bones.

If you have cracking or popping that does cause pain or swelling, though, see a doctor. It can be a sign of:

  • Meniscus tears. The meniscus is a rubbery C-shaped disc that cushions your knee and acts as a shock-absorber. It also helps spread weight evenly so your bones don’t rub together. Tears to the meniscus are often caused by sudden twisting or other things you might do while playing sports. In young people, tears usually happen during a traumatic event, but as we age the meniscus can tear more easily.
  • Cartilage injury or wear. Sometimes the cartilage covering of our bones can be injured, causing a piece to break off and catch in our joint. Typically the knee will respond to this injury by swelling or catching. Cartilage in your knee can also wear thin or break down, commonly known as arthritis. Some people say it feels like their knees are grinding when they move. Osteoarthritis is the most common kind of arthritis. It usually affects middle-aged and older people.

What’s happening when your knee goes snap, crackle, and pop

A question I am asked a lot is, “I hear clicking and popping in my knee, is this something that I should be concerned about?”

Joint noise in the form of crackling, clicking or popping is very common. It may be from simple soft tissue catching or more serious damage to the bearing surface of the joint, the articular cartilage. What I tell my patients is that unless it is causing pain, swelling or the knee is giving way, it is nothing to worry about. If it’s painful, then I’ll investigate further.

No worries: Sometimes this noise is due to tiny air bubbles inside the joint fluid, which build up with changes in joint pressure. The bubbles make a noise when they burst. This is called cavitation. Another cause for painless popping in the knee is when the ligaments and tendons catch as they go over a bony lump and pop when they snap back into place. Or the clicking and popping may be caused by catching on soft tissue or scar tissue within the knee. Most of the time these noises are natural and do not mean that you will develop arthritis or be prone to injury.

Some concern: However, when the popping sounds are accompanied by swelling and pain, or they produce a catching sensation or the knee gives way, then those are times when we worry about a possible injury within the knee. A physician should examine the knee to help make a clear diagnosis.

There are a number of possible explanations for the popping. The noise and pain may be a mechanical symptom, which feels like something is caught in the knee as it moves back and forth. This kind of popping is often a sign that you have a meniscus tear or that a small piece of loose cartilage is caught in the knee. You would most likely feel this kind of popping pain come and go.

Painful popping could also be because of osteoarthritis, where the smooth cartilage has worn down and the bones cause friction when they rub against one another. This painful popping would be more persistent.

Another common problem that results in a popping or grinding sensation is roughness on the undersurface of the patella that used to be called chondromalacia and is often labeled as patellofemoral pain syndrome, or runner’s knee. Often you may feel the popping, grinding or crunching more than you can hear it. To feel this, try squatting with your hand flat over the front of your knee.

Real worry: When a patient says to me, “Doc, I heard a pop and my knee swelled,” it is definitely a cause for concern. If there is a pop at the time of injury, the knee has almost certainly been damaged in this case. You have most likely injured either your ligaments — anterior cruciate ligament, posterior cruciate ligament or medial collateral ligament — or the meniscus or articular cartilage. The knee will usually swell up with these kinds of injuries.

If there is pain, swelling or giving way of the knee, then we will do a careful exam, history, and, very often, an X-ray and/or an MRI to study the cartilage and the soft tissue within the knee and determine if the tissues need to be repaired. If the important tissues of the knee are torn, then we will plan to repair that tissue. Sometimes careful physical therapy alone can fix the problem and help you avoid surgery.

So remember, if you hear clicks and pops in your knee but feel no pain or swelling, don’t worry. It is normal. If you have pain, instability or swelling, make sure you check it out to avoid further damage to the joint. The philosophy on this has changed from “rest your knee and wait until you are older for a joint replacement” to fixing the problem by repairing or replacing the missing cartilage so that you may never develop arthritis or need a knee replacement.

If you are experiencing undiagnosed knee pain, use our self-diagnosis symptom checker tool to learn more about your injury.

Knee Pain and Popping

Written By: Chloe Wilson, BSc(Hons) Physiotherapy
Reviewed by: KPE Medical Review Board

Knee pain and popping is a common problem. It’s that tell-tale snap, crackle, pop making your knees sound like a bowl of rice krispies.

Many people find they hear strange noises such as knee clicking when they do things such a squatting down or getting up from kneeling.

In many cases, it is more of a nuisance than a real problem, but in some cases, it may be a sign of an underlying problem in the knee.

Knee popping in itself is very common and can be caused by a number of things. It may be as simple as little bubbles of gas popping in the knee or indicate a problem in the soft tissues such as a ligament tear.

Another term commonly used for popping in the knee is “crepitus”, which essentially means a noisy joint, whether it be popping, clicking, cracking or snapping.

What Causes Knee Pain And Popping?

Knee popping and clicking can be caused by a number of things. It may be something simple like the ligaments catching on a bony lump and “snapping” back in to place or gas bubbles popping.

But in some cases, knee popping is linked to a more serious injury such as ligament or cartilage tear.

Here we look at the top 8 causes of knee popping and how to treat them.

Types of Knee Popping

Knee clicking and popping noises in the knee usually fall into one of three categories:

1) Pain-Free Popping Knee: Popping noises in the knee often occur without any pain, in which case they are nothing to worry about

2) Painful Popping Noise at time of Injury: Sometimes when the knee is injured e.g. twisting awkwardly, there is a sudden, loud “pop” at the same time indicating damage to part of the knee

3) Recurrent Painful Popping Noises not Caused by an Injury: Knee pain and popping can come on gradually with no obvious cause. It may happen sporadically or frequently depending on the cause.

Knee Popping No Pain

If knee popping occurs without any associated pain, it is usually due to either a build up of gas bubbles inside the joint which burst, or ligaments/tendons snapping over the joint. There is generally nothing to worry about with this type of knee crepitus.

1) Gas Bubbles

Changes in joint pressure can cause tiny bubbles of gas to slowly form in joints. When these gas bubbles burst quickly, they make a popping sound, in a similar way to when you pop bubble-wrap.

The technical term for this is cavitation. There is no harm in this case of knee popping no pain, and the myth that it makes you prone to arthritis is unfounded.

2) Ligaments/Tendons

Ligaments and tendons are soft tissues that are positioned around all the joints in our body. Sometimes when you move a joint (e.g. your knee), a ligament or tendon may stretch slightly as it goes over a small bony lump and then snaps back into place making a knee clicking sound.

Again, there is no harm with this type of knee clicking if there is no pain, and despite what people often say, it doesn’t make you more prone to knee problems.

Knee Popping with an Injury

Was there is a loud “pop” as you twisted or bent your knee? Knee popping pain at the time of injury usually indicates damage to one of the ligaments.

The two most common ligament injuries that produce knee pain and popping are ACL (Anterior Cruciate Ligament) and MCL (Medial Collateral Ligament) injuries, usually caused by twisting the knee awkwardly.

1) ACL Injury

What is It? The ACL (the ligament which sits in the centre of the knee) gets over-stretched and tears, either fully or partially. Sudden knee pain and popping at the time of injury usually indicates a complete tear of the ACL.

How Does It Happen? The ACL typically gets damaged when there is a hard blow to the side of the knee (e.g. sporting tackle), sudden twisting or deceleration, or when the leg bends backwards too far

Symptoms? Approximately 50% of ACL tears are accompanied by a popping sound at the knee associated with immediate swelling and pain. The other classic sign of an ACL tear is the knee repeatedly giving way. The knee pain and popping usually only occurs at the time of the injury, there isn’t typically any recurrent knee clicking or popping afterwards

Treatment? ACL Injury treatment will depend on the extent of the tear but usually involves exercises, knee braces and/or surgery

You can find out loads more in the ACL Injuries section including information on rehab, surgery and how to prevent ligament injuries.

2) MCL Injury

What is It? The Medial Collateral Ligament on the inner side of the knee gets over-stretched and tears

How Does it Happen? The MCL usually gets torn when a force gores through the outside of the knee e.g. tackle, or sudden twisting e.g. skiing

Symptoms? Typical symptoms of an MCL tear include inner knee pain and popping/tearing sensation, swelling, instability, difficulty bending the leg

Treatment? MCL tears are usually treated with a combination of knee exercises, tubigrip, knee braces and friction massage

You can find out more about the causes, symptoms and treatment options in the MCL Injury section.

Ongoing Knee Pain and Popping

Sometimes knee pain and popping develops over time, without any obvious injury. In these instances, the knee clicking/popping tends to happen frequently and is usually due to one of these conditions:

1) Cartilage/Meniscus Tear

What is It? A tear in the meniscus, the special cartilage that lines the joint.

What Causes the Noises? When the meniscus tears, small fragments of it can catch in the knee as it moves which results in knee clicking

Associated Symptoms: knee pain, locking (knee gets stuck), swelling

Frequency? Knee pain and popping from a meniscus tear tends to come and go, rather than happening all the time as the torn fragment moves around the joint

Treatment? Exercises or surgery depending on type and severity of tear

Visit the Meniscus Tear section to find out more about this common cause of knee pain and popping.

2) Arthritis

What is It? Osteoarthritis is wear and tear of the cartilage that lines the knee joint accompanied by the formation of bone spurs, known as osteophytes

What Causes the Noises? As the cartilage thins, the joint surface becomes rough and friction occurs between the bones resulting in crepitus and knee popping pain.

Who Does it Affect? Arthritis is the most common cause of knee pain and popping in people over the age of 50 and develops gradually over time

Associated Symptoms: Toothache type pain, stiffness (particularly in the morning) and swelling

Frequency? With arthritis, knee pain and popping, clicking and crepitus tend to be persistent rather than coming and going

Treatment? Exercises, knee brace, injections, surgery

Find out everything you need to know about this causes of a popping knee in the Arthritis section.

3) Chondromalacia Patella

What is It? Chondromalacia Patella is irritation and inflammation of the cartilage lining the back of the patella (kneecap)

What Causes the Noises? The friction between the back of the kneecap and the underlying femur (thigh bone) seen in chondromalacia patella can cause knee pain and popping

Who Does it Affect? Healthy, often sporty adolescents and young adults. Chondromalacia Patella is more common in women than men

Frequency? It tends to be a more constant problem. The knee clicking/crepitus can usually be felt as well as heard when you put your hand over the front of the knee and bend and straighten the knee joint

Treatment? Exercises, knee strap, taping, ice, medication

Find out more about the causes, symptoms and treatment options in the Chondromalacia Patella section.

4) Runners Knee

What is It? Runners Knee is a problem in how the kneecap moves which causes an ill-defined ache around the knee aka anterior knee pain or patellofemoral pain syndrome. It doesn’t just affect Runners though!

What Causes the Noises? In Runners Knee, the patella rubs against the femur which is often associated with a grinding sensation when the knee moves

Who Does it Affect? It is usually worse with prolonged activity e.g. running, coming downstairs or after prolonged inactivity e.g. office workers

Frequency? Knee pain and popping tends to come and go with Runners Knee

Treatment? Exercises, orthotics, ice, rest

Find out everything you need to know in the Runners Knee section.

Knee Popping Treatment

Treatment for knee pain and popping will depend on the underlying cause of the noises, but will generally include strengthening exercises, physical therapy and possibly wearing a knee brace. In some rare cases, surgery may be required.

You can find out loads more about these common causes of knee pain and popping including the best treatment options for each, by using the links above.

And remember, if you have knee clicking but it doesn’t cause you any pain, don’t worry. It is usually entirely normal and nothing to worry about. You may find that strengthening your leg muscles actually eliminates the noise – see the strengthening exercises section for ideas on where to start.

Knee Popping By Activity

Knee Popping When Extending: Knee popping when you straighten your knee is usually due to gas bubbles (not usually painful), plica syndrome or patellofemoral pain syndrome.

Knee Popping and Pain When Bending: If you get knee popping and pain when bending your knee e.g. squatting down, it is most likely due to a problem with the knee cartilage such as a meniscus tear or chondromalacia patella.

Knee Popping When Extending And Bending: If you get knee pain and popping with both knee flexion and extension, it is likely that there is damage to the joint surface such as cartilage damage or knee arthritis. If there is no pain, it is likely to be gas bubbles popping.

Knee Popping With Twisting: Sudden knee pain and popping when you twist is usually doe to a knee ligament injury, most often an ACL injury and/or MCL tear. If the knee swells up or feels unstable after hearing a pop as you twisted, seek medical attention immediately.

Knee Popping When Walking: Almost all the possible causes of knee popping that we’ve looked at here can cause knee pain and popping when walking, be it arthritis, runners knee, cartilage tear or ligament injury. There will usually be other symptoms associated here that will lead to a clearer knee pain diagnosis.

Knee Popping No Pain: If there is no pain with your knee popping, chances are it is a simple case of gas bubbles bursting inside the joint which is completely harmless. Keeping active and strengthening the knee muscles can sometimes help to reduce the frequency of knee popping.

Common Questions About Knee Popping

1. Will Knee Popping Go Away?

In most cases, knee pain and popping will settle down, but how long this takes will depend on what is causing the popping noise. Soft tissue injuries usually heal in 6-12 weeks. Most people notice their knee popping settles down within 3 months of working on knee strengthening exercises.

If there is no pain with the popping, then it is highly likely the popping noises will continue as there isn’t a mechanical problem to be fixed. Bit rest assured, there is no increased risk of knee problems later in life.

2. Is Knee Popping Bad

In most cases, knee popping is not a serious problem, it is simply bubbles of gas popping, or tendons snapping over small, bony lumps.

However, knee popping can be serious if there is a sudden popping noise from the knee at the time of injury, which typically indicates a significant injury to one of the knee ligaments.

3. Why Do Knees Crack When Squatting?

Many people complain of popping, cracking, or crunching noises when they squat down. The technical term for this is cavitation or crepitus, which simply put means “joint noise”. Caused by a change in pressure inside a joint, gas bubbles of carbon dioxide form, and when they burst, you get the familiar cracking sound.

4. How Do I Crack My Knee Safely?

If your knee feels like it locks up sometimes, you may find that releasing the pressure in the joint helps. This is only appropriate if there is no knee pain and you have not recently injured your knee.

  • Lie down somewhere comfortable
  • Stretch your leg out until your knee is straight, toes pointing towards the ceiling
  • Keeping your leg straight initially, lift your leg up as high as is comfortable and then slowly bend your knee in and out until you hear a small pop.

Safety Advice

The best way to diagnose your particular symptoms is to see a doctor but here I have shared with you the more common causes for knee pain and popping. Always see your doctor for a thorough examination to rule out any serious injury if you have knee pain and popping.

  1. Knee Pain Guide
  2. Symptoms
  3. Knee Popping

Page Last Updated: 09/24/19
Next Review Due: 09/24/21

Knee Symptoms
January 20, 2020

Knee Pain Diagnosis
March 11, 2019

Knee Treatment
September 12, 2019

1. Clinics In Orthopedic Surgery Journal: Noise around the Knee. February 2018

2. WikiHow: How to Keep Your Knees from Popping and Cracking. July 2018

3. Physical Therapy In Sport: Implications of knee crepitus to the overall clinical presentation of women with and without patellofemoral pain. September 2018

4. Musculoskeletal Science and Practice: People’s beliefs about the meaning of crepitus in patellofemoral pain and the impact of these beliefs on their behaviour: A qualitative study. April 2017


I am a 21-year-old woman and I have a problem with my knee.

If I bend down to pick something up or even if I kneel down, my knee clicks quite loudly. Sometimes when it clicks it is also very painful.

I have to carefully try and straighten my leg or even get somebody to do it for me as it hurts a lot.

When I finally manage to straighten it, there is a very loud thump or click and it feels as if something is actually clicking back into place, but after this, the pain gradually subsides until the next time.

I do not know what it could be and whether it requires medical attention or not?

I fell on my knee about 6 years ago, but I don’t think it could be that.

Do you have any ideas of what it could be?


This sounds like a torn cartilage or meniscus.

These tough, smooth moulded cushions between the bones of your knees absorb shocks and allow the bones to glide easily over each other to provide smooth, frictionless movement.

A twisting injury of the knee can partially tear the cartilage leaving a loose flap of it floating in the fluid inside the joint or becoming trapped between the moving bones.

If this happens, a loud clicking or clunking can be felt and from time to time, swelling of the knee (water on the knee) can be seen and felt.

Pain is variable, depending on how big the tear is and its position at any given time.

A doctor’s examination can readily confirm a cartilage tear by manipulating the joint and rotating it in both the flexed and straight position.

If it is present, an arthroscopy procedure can be arranged whereby a narrow telescope is inserted into the knee to view the torn cartilage and remove all or part of it through the keyhole incision already made.

Yours sincerely

The NetDoctor Medical Team

Last updated 01.10.2014

What’s to know about crepitus of the knee?

There are various causes of crepitus.

Air bubbles

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

Share on PinterestCrepitus 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.

Torn cartilage

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.

Symptoms include:

  • swelling
  • stiffness
  • 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.

The Centers for Disease Control and Prevention (CDC) estimate that 49.6 percent of adults aged 65 years and above were living with a diagnosis of arthritis between 2013 and 2015.

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.

Options include:

  • lifestyle modifications, such as weight loss and exercise
  • medication
  • 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.

Five signs of a potentially serious knee injury:

Your knee twists, you hear a pop, and now you have knee swelling and pain when bending your knee. Perhaps you were struck by another player and have bruising, but no swelling. Are these severe knee injuries? When should you consider seeing a Sports Medicine Doctor following a knee injury? Let’s go over 5 things that trained professionals look for to determine if your knee injury is serious.

As an active athlete or competitor, you know that severe knee injuries are common. Both contact and non-contact knee injuries can be severe. This post will cover five signs to look for to help determine if you might have a severe knee injury. In general, the most common and worrisome finding is immediate, significant swelling.

Even though most of the injuries I see in the office turn out to be mild, it is essential for you to know what the warning signs are to look for a potentially severe knee injury.

1. Your Knee Is Swollen

Swelling in the knee immediately or shortly after an injury is a common sign that indicates you may have sustained a serious knee injury. In many cases, the swelling is due to blood. The bleeding will stop, but the swelling will remain. Blood in the joint is called a hemarthrosis. Blood in the knee joint can cause a lot of pain due to inflammation. If we suspect that you have blood in your knee joint, that often means that you sustained a severe injury. The bleeding is usually due to something inside the knee tearing.

Common causes of swelling after a severe knee injury include:

  1. A tear of the ACL
  2. Patella or kneecap dislocation
  3. A meniscus tear: specifically a Bucket-Handle Tear.
  4. An MCL tear
  5. Injury to the articular cartilage.

Over 70% of athletes with a swollen knee who felt a pop while running and pivoting will have an ACL tear or a patella dislocation. Patella (kneecap) dislocations are more common than you think. All of you dread an ACL tear. But most of you are surprised when we see you in the office and tell you that your kneecap dislocated. Most dislocated kneecaps will reduce spontaneously on the field. That means that the kneecap will go back into place on its own.

Patellar dislocations may hurt just as much as an ACL tear. Because patella dislocations are such a common sports injury we wrote this post to go into far more detail about them.

With any of the above issues, most of you will find it very difficult to walk without severe knee pain. Crutches, icing, and elevation are beneficial in these cases. These knee joint injuries need to be evaluated for an X-ray. Fractures are rare, but they do occur. Very few knee injuries will require a brace unless you want to use it for comfort. The most important reason for seeing a sports medicine physician after an injury that causes swelling is to look for these most common severe injuries.

Many of these severe knee joint injuries should be evaluated sooner rather than later. The initial treatment will be a reliable examination to arrive at a diagnosis, which will be followed with an MRI to confirm the diagnosis. Depending on what we think you injured, we may consider rest, physical therapy, or surgery.

2. Your Knee Is “Locked” And You Can’t Straighten It

If you had a knee injury and you are not able to fully straighten the leg, we may tell you that you have a locked knee. A locked knee is simply a knee that cannot fully straighten. There are different reasons a locked knee might occur. In some patients, the swelling and inflammation can prevent you from fully straightening the knee. In others, a meniscus tear has flipped into the middle of the joint and is causing mechanical locking. You cannot straighten it with the meniscus in that position.

Many athletes who have a locked knee will also find it very painful to bend the knee too. They may feel sharp knee pain when bending which can occur when these bucket handle meniscus tears move.

The most common cause of a locked knee is a unique meniscus tear called a bucket handle tear. A bucket handle tear is considered a serious knee injury and will require surgery to fix the tear. The reason these tears are serious is that a large piece of the meniscus tears flips over and becomes stuck in the middle of the knee joint. You need that meniscus to protect the knee. The vast majority of bucket-handle tears can be repaired. So the sooner we start the treatment process, the better the outcome might be after a meniscus repair.

Although we discuss bucket handle tears here. Not all locked knees will be found to have a bucket handle tear. In older athletes, a flap tear, or different types of meniscus tears typically occur. These types of tears are also essential to identify early on. Most bucket handle tears are repairable. The torn bucket handle should not be removed from the knee, if at all possible. These tears, which cause a locked knee, are often very large. If the piece is removed and not repaired, then you have a significant chance of developing osteoarthritis. These bucket handle tears do not require emergency surgery, but they are urgent, and you should see a sports medicine doctor if you feel like something is preventing you from straightening your knee all the way.

3. Your Knee Feels Unstable, or You Felt a Pop

Torn ACL

Most ACL tears and patella dislocations occur from a twisting, non-contact injury. A typical story is that you were turning or twisting hard, and you felt a pop. As I mentioned earlier, most patella dislocations will reduce or go back into their usual place on their own. But if your patella remains dislocated the knee will look strange.

If you felt or heard a loud pop as you twisted or turned to avoid another player, then you may have torn your ACL. Other causes of popping include a patella or kneecap dislocation. If you felt or heard a loud pop in your knee, then there is a strong chance that you have a severe knee injury. Most ACL injuries and patella dislocations are non-contact injuries. A running back turning to head upfield. A striker moving laterally to avoid the defense. These are familiar stories when we see high school and college athletes who have torn their ACL.

This post dives further into the immediate management of suspected ACL injuries.

Once again, another prevalent severe knee injury following a loud pop is a patella dislocation. They are more common than most people think. Everyone has heard of an ACL tear, but most are not aware that the patella or kneecap can dislocate. Many patella dislocations will spontaneously reduce or go back into place. That means that the patella was only dislocated for a second or two. Patients with a patella dislocation often require an MRI to see if you injured the cartilage on the patella when it dislocated. Surgery to repair the patella ligaments is usually not necessary for a first dislocation. This post provides more information about patella dislocations.

4. You Have Significant Weakness Trying To Straighten Your Knee

Severe weakness when trying to straighten the knee, even a few days after the injury, could mean that you suffered a severe tendon injury. Common causes of weakness include patella dislocations, patella tendon tears, and quadriceps tendon tears. Patella tendon and quadriceps tendon tears are not common in youth or collegiate sports, but we will see a few of these every year.

In older weekend warriors who are wondering why their knee is weak after a serious injury, patella tendon and quadriceps tendon injuries are far more common. If you are over 35 and felt a loud pop in your knee while pushing off during tennis, or basketball then you need to consider that you have seriously injured your patella or quadriceps tendon(s).

After an injury to one of these large, critically important tendons, you will find that the knee will feel unstable. You will think that the knee is unable to support your weight without giving way. You should be promptly evaluated by a Sports Medicine physician to determine the type of injury you had. Both quadriceps and patella tendon injuries require surgery to repair these large essential tendons.

We discuss the management of patella tendon injuries in this post. The management of quadriceps tendon tears is very similar.

Patella dislocations occur mostly in younger athletes. Most patella dislocations happen when the knee is bent, the athlete is twisting, and then they are struck on the inner side of the knee. The patella will usually snap back into place, but the damage is done. Any suspected patellar dislocation should be evaluated by a sports medicine physician since patella dislocations can cause injuries to the cartilage or the ligaments which hold the patella in place.

5. You Have Significant Difficulty Walking

Of course, many knee injuries make it painful and hard to walk. For people with severe knee injuries, it is usually very hard if not impossible to walk. You will often need to be helped off the field and require crutches. Anyone who is placed on crutches should be considered to have a serious knee injury until an Orthopedic Surgeon evaluates you. In many of these cases, an urgent X-ray is useful to rule out a fracture if the athlete can not put any weight on the knee.

Take-Home Message:

Now you know what to look for if you are worried that you might have a serious knee injury.

  • Your knee is swollen
  • You felt a pop
  • Your knee is locked and will not straighten
  • You have a significant weakness when trying to straighten the knee.
  • You have persistent, significant difficulty walking or putting weight on your leg.

Knee injuries are common across all sports. Most knee injuries are mild, and the athlete can expect to return to play relatively soon. Identifying the serious or severe knee injuries and acting quickly can make all the difference when it comes to getting you back in the game and minimizing your risk of further damage.

Disclaimer: this information is for your education and should not be considered medical advice regarding diagnosis or treatment recommendations. Some links on this page may be affiliate links. Read the full disclaimer.

Knee pain is a very common problem for patients who come to my office. There are a lot of things that can cause knee pain. One of the more frequent causes of knee pain is a torn cartilage, also known as a meniscus tear. A torn meniscus is often noticed after an injury, such as a twisting injury, after stepping in a hole or after a fall from a height. Sports can frequently injure the knee due to the high forces placed on the knee during impact with another player, impact with the ground, or just the rotational stress from planting the foot and twisting around the non moving leg. However a meniscus tear can also occur without a onetime injury, and may occur due to repetitive activity or from wear and tear over time.

A lot of times patients will feel a sharp stabbing pain with a torn meniscus as they take a step. Also, they may have the feeling that the knee will lock up or will give out. This gives them the concern that their knee is unstable and will not hold them up. These symptoms can be worsened by squatting or climbing stairs. The knee will also feel unstable when trying to rotate or pivot, giving a feeling of “shifting” within the knee. For this reason, a brace can be useful to help secure the knee.

In the long run, surgery may be needed for a meniscus tear in an active otherwise healthy individual. With modern technology we can address these with newer arthroscopic techniques. This is usually an outpatient surgery. There are some situations when it may not be practical to perform surgery for a meniscus tear. For example, if the patient’s age is not appropriate for the surgery or if there is too much arthritis in the joint, surgery on the torn meniscus in this situation may not offer the benefit desired. Other options may be considered, such as medications, exercises, therapy, ice / heat, injections or sometimes joint replacement if the knee is completely worn out.

Because there are other problems that can cause knee pain (e.g. patellofemoral pain, arthritis, ACL tear, inflammation), it is important to be fully evaluated for your knee pain. With a proper diagnosis a course of treatment can be laid out for you to get you back on your feet again.

Painful Pops and Cracks in Knees

A knee that decides to “pop” or make cracking sounds can be quite alarming. I think that all of us at one time or another have kneeled down and had our knees make a loud noise, but no pain occurs. In the majority of instances, though, this is a harmless soft tissue band that rubs in an unusual way within the knee joint, makes a sound, but doesn’t hurt or cause any damage. On the other hand, what is being described in this question deals with a painful “crack” or “pop” in the knee. There are multiple possible causes of this.
The knee joint internally is covered with cartilage – the same pearly white covering that we see on the end of a turkey or chicken bone. This cartilage protects the joint as we flex, bend, and straighten the knee for millions of cycles over our lifetimes. If this cartilage becomes worn or frayed, the normal smooth sensation that accompanies bending the knee can become rough – leading to catches or popping sensations. If the cartilage becomes severely damaged (almost like having a pothole on a highway) then severe painful catches and swelling can occur.
Other possible causes of “mechanical” symptoms in the knee include meniscus tears or loose bodies in the knee. The meniscus is another type of cartilage that acts as the shock absorber of the knee. The medial meniscus lies on the inner aspect of the knee between the cartilage ends of the thigh bone and leg bone, while the lateral meniscus is on the outer side. For someone with a history of a knee-twisting injury or accident, tears of the meniscus are quite common. If the tear is severe enough, then the knee can actually lock solidly in one position — leaving the person unable to bend or straighten without a physicians help. Luckily, these severe tears are not common, but smaller tears, leading to a catching sensation and pain, are seen routinely in an orthopedic surgeon’s office.
Loose bodies are small fragments of cartilage or other tissue that move freely around the joint and cause complaints of popping and catching. Theses are normally seen well with MRI or x-ray, and patients respond very well to small surgeries that remove the fragments.
Finally, for young, active patients with these complaints (and no history of injury), the most common diagnosis involves the knee cap. As patients work out on the elliptical machine or stair master, for instance, the kneecap is moving back and forth through a groove on the end of the thigh bone. If the knee cap isn’t covered by a smooth surface of cartilage (a condition called chondromalacia) the popping and catching can be painful and frustrating. If the knee cap has poor muscular control, then it even may start to jump out of the groove causing a “my knee just popped out” sensation. Both of these problems may be accompanied by swelling, pain and inability to be active.
In all of these situations, it’s important to consider the following: mechanical symptoms (popping, catching, or locking) that follow an injury to the knee or that are noted with significant swelling need to be addressed by a health care provider. Many times, knee x-rays and MRI’s help to confirm a diagnosis. Otherwise, keeping the quadriceps (thigh) muscles strong with exercises and possibly physical therapy can alleviate many of these complaints.

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