7 reasons for knee buckling: symptoms, diagnosis and treatment

Imagine running to catch that bus your late for and your knee gives way! Or whilst playing your favourite sport, you experience your knee buckling underneath you.

Having your knee give way can be a scary thought. Not many people think about the reasons why your knee gives way until it happens to them.

It’s at this point that knowing what’s going on and how to fix it becomes very important.

Prefer to skip ahead?

1. ACL Injury

2. Osteoarthritis

3. Torn Meniscus

4. Ligament Tears

5. Patella Instability

6. Quadriceps Insufficiency

7. Synovial Plica Syndrome

8. Other Causes For Knee Buckling

This article is about highlighting the main reasons your knee gives way. Starting with the most common reasons, and then working down to those that may not occur so frequently.

The aim is not only to inform you, but to help you do what you need to overcome this condition.

Let’s start from the top with the number one reason that your knee gives way!

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ACL tear - animated showing the inside of ACL tear
The Joint Clinic [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)]

ACL injuries are very common and can have lasting effects on your knees. The Medical Journal of Australia reports that in Australia, there are upwards of 17,000 injuries per year.

Looking at the statistics you can see that the rate of ACL injury is only increasing with increased population and participation in cutting sports such as netball and soccer.

The amount of reconstructions being performed are also increasing, with Australia currently having the highest amount of ACL reconstructions in the world.

Graph of the incidence of ACL injuries in Australia

Common symptoms:

Acute ACL tears are usually obvious. Some people describe a loud snap that can be heard from several meters away. Within 30 minutes there will be swelling which could make the knee twice its normal size.

Normal symptoms of an ACL tear include:

  • Knee swelling
  • Knee giving way
  • Loss of range into knee flexion and extension
  • Pain during walking

Giving way or buckling of the knee occurs because the ACL’s main function is to stop the shin bone from sliding forward during twisting movements. Without the support of this ligament, the shin will move forward and cause the knee to buckle.


There has been a change in trends for in the management of ACL injuries as further research emerges. It was normal up until a few years ago to operate on all knees to restore normal function and stop the knee buckling.

Now a trial of non-surgical management is recommended for at least 3 months before a decision about surgery is made. This is because there are now high-level studies that show even athletes can return to high level sport without an ACL.

Many clinicians now advocate for conservative therapy because there is a big chance it will be successful. Even if conservative therapy isn’t a success, (meaning your knee continues to give way) you can always have the surgery later with no increased risk of damaging the knee.

It may be beneficial in the early stages to trial a knee brace to help avoid the knee giving way. We have recommended one brace from Amazon here:

ACL brace

If you do opt for surgery, there are some common side-effects after the operation, numbness in the knee being one of them.

Rehabilitation for ACL injury is unique as every person will present differently. However, there are some core elements which will remain the same, these involve:

  • Lower limb and core strengthening
  • Running and cutting drills
  • Lower limb control during jumping and single leg tasks
  • Sport specific drills as you improve
  • Education on safe return to sport and load management

ACL taping can also be part of the management of this condition, click here to watch ACL taping in youtube.

It will also be important to start a graded return to running program. You can find out details of how to grade up your running with pain here.

For further information on ACL injuries, please see our ACL injury page.

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#2 – Osteoarthritis

With the baby boomer generation coming of age, we are seeing a rise in the total number of people with knee osteoarthritis.

This is a condition that generally progresses as we age and is characterised by the break-down of healthy cartilage in your knee. Other signs include the formation of osteophytes which are little bony spurs on the outside of the joint and the breakdown of ligaments in the knee.

Keep in mind, some people will have arthritic changes on X-ray and NO pain. This brings me to explaining some of the common symptoms for arthritis

Common symptoms:

Symptoms of arthritis will progress as the condition worsens (this may take years, there is no way of knowing medically), they typically include:

  • Morning pain and stiffness
  • Stiffness and pain when standing after prolonged sitting
  • Cracking, grinding
  • Swelling and gradual loss of range
  • Knee buckling (giving way) and locking can be rarer symptoms

Although having your knee giving way is a rarer symptom of osteoarthritis, it is important to take note. Mechanical symptoms like knee buckling, means the knee is not stable and these symptoms warrant a referral to your local orthopaedic surgeon.


Unfortunately, there isn’t yet a long-term cure for knee osteoarthritis currently. But don’t think that all hope is lost, because there is good evidence that weight loss as small as 5% can reduce symptoms by up to 50%.

Exercise is the current gold standard treatment for knee osteoarthritis. A good starting point is general cardiovascular fitness and quadriceps strengthening.

You can find a basic quadriceps exercise here.

Sometimes simple braces can help to reduce swelling when the arthritis is aggravated, we would recommend something like this:

Knee compression sleeve for OA

If this isn’t working, then surgical management may be considered. The best surgical solution at current, is to eventually replace the knee with an operation called the total knee replacement.

Total knee replacement surgeries are very common and usually provide excellent results. Some risks associated will be numbness after surgery, and the risk of infection.

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#3 – Torn Meniscus

Chart showing different meniscal tears including: vertical, bucket-handle, transverse, degeneration

Meniscal tears can be associated with giving way of the knee. There are many different types of meniscal tears, but the ones associated with giving way of the knee are usually the bigger ‘bucket handle’ type tears.

Meniscal tears are usually sustained with twisting movements under load. They can occur with forceful movements, but sometimes they can result from something as simple as getting up from sitting. For some patients it will feel like the back of the knee gives way.

Usually acute meniscal tears will happen to younger people, and these are more likely to be bigger bucket handle tears. As we age, our meniscus are more prone to tearing, but these are more degenerate tears as a result of osteoarthritis.

Common symptoms:

If the tear is sizeable, then it is possible that locking and giving way of the knee occur. Other symptoms will involve, pain with weightbearing, swelling, inability to fully straighten the knee.


For large bucket handle tears, surgery is usually required to mend the tear and try to preserve as much of the meniscus as possible. If the knee isn’t giving way and locking, then it is appropriate and safe to trial physiotherapy and see how it goes.

A ligament tear can take up to 12 months to heal because of the poor blood supply to the meniscus to don’t be concerned if it’s not better in a couple of weeks. By 3 months you should be make progress but may still have pain associated.

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#4 – Ligamentous tears of the knee

Man with ligamentous knee injury getting helped by another player

The knee has four major stabilising ligaments that give it stability through range. One I previously mentioned is the ACL. If you have tears in the other 3 ligaments, you may also experience giving way of the knee.

PCL (posterior cruciate ligament)

Right next to the ACL, on the inside of the knee, we also have a PCL. This ligament helps to stop your shin bone from hyperextending.

This ligament is usually injured with dashboard car injuries, where the shin is forced into the dash and the knee hyperextends.

If your PCL is torn, you won’t feel stable when you fully straighten the knee and the knee can give out backwards and buckle.

MCL (medial collateral ligament)

The major inside stabiliser of the knee is your MCL. This ligament stops the knee from buckling inwards.

The MCL is damaged when your knee is forced inwards. As you are forced into being knock kneed, the MCL is stretched and can partially or fully tear.

LCL (lateral collateral ligament)

Much like the MCL, your LCL stops the knee from bowing outwards. It is put under strain when there is a force that pushes the knee out, like a kick to the inside of the knee.


The solution to ligament injuries heavily relies on how much of the ligament is torn. For most of these the first step would be to get appropriate imaging like an MRI to assess the damage.

Small and medium sized tears can usually be helped with bracing the knee first, followed by physiotherapy and progressive exercises. Braces would need to have support on the inside and outside of the knee like these:

Hinged ROM brace

If the ligaments are fully torn they will usually require surgery to fix it.

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#5 – Patella instability

Patella instability - photo of knee dislocation with player lying on the field of play.

Patella instability is defined by constant dislocations of your knee cap. It can be difficult to manage, and I have had patients whose knee will dislocate up to two and three times a day.

This condition affects between 7-49 people out of every 100,000. The knee cap usually dislocates outwards and after your first dislocation you are much more likely to dislocate again.

Common Symptoms:

The most problematic part of patella instability is the knee cap dislocating. This will usually happen in the early phase of knee bend as there is not much groove for the knee cap to sit in.

Sometimes as your knee dislocates, your knee gives way at the same time. This is due to the sudden loss of power of your quadriceps muscle as it attaches onto the knee cap.

Other symptoms could include grinding, clicking and discomfort or pain in the knee. If left untreated it can lead to kneecap pain at the front of the knee, commonly known as patellofemoral pain.


If the knee is constantly giving way or buckling, then surgery may have to be considered. I would still always give strengthening a go first, because if this works it will save you money and potentially prevent any problems resulting from surgery.

If you want to try strengthening, you need to make sure your knee control is just right. Online physiotherapy will be perfect to help in this journey as we can construct an exercise program that will be perfect for your needs.

Some basic exercises to start with would be squats and side bridges. From here you would move closer to single leg strength exercises and motor control around the hip.

Surgical options would include a repair of your MPFL (medial patella-femoral ligament), a tibial tuberosity transfer or a lateral retinaculum release.

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# 6 – Quadriceps insufficiency

Your quadriceps muscle is located on the front of your thigh. It’s the major muscle responsible for straightening the knee.

Sometimes your knee gives way because of a lack of strength in this muscle – also called an insufficiency. There can be numerous reasons for this muscle being weak:

  • Pain inhibition (if your knee is very sore, your brain can switch of the quadriceps muscle)
  • Weakness post-surgery – ACL or TKR, or meniscus repairs
  • Nerve impingement in the back
  • Deconditioning from lack of use – with people who are very sedentary

Common Symptoms:

With quadriceps insufficiency you will feel like your thigh muscles are weak. You may not really trust your leg and would prefer to use crutches or other walking aids. Your knee might lock backwards into extension and if it comes unlocked the knee buckles.

If you have weakness due to pain inhibition, there may be associate injuries with your knee causing your quadriceps to not work as well.


The major treatment for quadriceps insufficiency is strength training. Now your body is very good at cheating as your attempting to strengthen weak muscles. I remember having a young fit guy who could still climb stairs with no use of his quadriceps!

The key in early strength training is isolation. You want to really isolate the quadriceps, so they can’t get out of doing the work.

I have attached a video for my favourite exercise to begin with in quadriceps training below:

When your quadriceps strength is improving its often good to begin a more generalised strength program. We have some exercises including calf raises to strengthen your calves in our Achilles Tendinopathy ulimate guide.

Also if the calves are weak and causing concern, taping can help to keep some stability through the ankle. And it’s important to know what shoes to wear for support!

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# 7 – Synovial Plica Syndrome

These are folds in the membrane around your joint in the knee. They are thought to be left over material from the development stage of birth. Kind of like your appendix, they don’t serve much of a purpose except to get irritated in some people.

Usually the plica will get caught in the front and inside part of your knee. It can get caught rubbing against your knee cap through movements which involve bending the knee.

Synovial plica syndrome is more common in the younger years of life up to about 30 years old. There is wide variation in the exact prevalence of this condition, however it’s thought to occur in about 10% of the population. (I think it could be less than this)

Common symptoms:

Your knee giving way is not a common symptom of this condition. The reason I included this diagnosis is people will report a ‘pseudo-locking’ where the knee feels like it locks. This is also often described as giving way.

Other common symptoms include:

  • Knee pain
  • Clicking, clunking, catching
  • A popping sensation with squats or loaded knee bends

These symptoms will usually be activity dependent, however there may be an aching that remains after.


This condition will commonly occur due to a lack of quadriceps strength and control around the knee joint. Look at the quadriceps insufficiency section for an exercise to help get your quadriceps strength back.

Often this will respond well to Physiotherapy, including taping, exercise, load management (load mx blog) and some over the counter pain killers. This condition can be treated via online physiotherapy as the mainline treatment will involve exercises on hip and knee control.

If physiotherapy isn’t giving full pain relief the next option would be a cortisone injection. I would recommend only trying one of these as there is no further benefit to try additional doses and they can affect tendon integrity over time.

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Other Causes For Knee Buckling

Osteochondral Lesion (OCD)

An osteochondral lesion is where a piece of cartilage is torn or broken away from the knee joint. This causes a small ‘hole’ in the cartilage, where usually it’s smooth.

People with OCD will experience pain in the knee, occurring usually with weight-bearing. They can experience knee buckling due to the uneven nature of the cartilage.

Other symptoms may include a dull ache in the knee, especially after activity.

Osteochondral lesions often require surgery to treat them as cartilage doesn’t have good blood supply.

The Bottom Line

Knee buckling can be due to all sorts of ailments. We went through some of the main culprits, but there are still more like multiple sclerosis that can give you knee buckling symptoms.

If you have knee buckling, feel free to book your consultation with Click Physiotherapy for a video conference and we can discuss treatment of this with you in person!

Frequently Asked Questions about knee buckling:

Why does my knee buckle?

Buckling in the knee caused due to a number of different reasons including; meniscal damage, weak muscles, arthritis, ligament damage and more.

How do I prevent my knee giving way?

This will depend on the reason for your knee giving way. Giving way can be treated with physiotherapy to strengthen muscles in conditions like ACL injuries or arthritis, however the knee may need surgical management if there is major instability in the knee.

When do I see a doctor if my knee gives way?

If you are concerned about your knee, it is a good idea to see your doctor. They can help diagnose the cause of giving way and then refer you for the most appropriate treatment.

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