Severe Knee Pain

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

Find out all about the most common causes of severe knee pain

Severe knee pain can be extremely unpleasant and cause a great deal of anxiety.

If you are in excruciating knee pain it can make sleep very difficult, affect daily activities, stop you from doing the things you love and make it very hard to relax. 

The first step to take if you are suffering from severe knee pain is to find out what is causing it. It may be something fairly simple that can be easily fixed, or it may be something more serious that needs some intervention.

The second step is to get the pain under control so that you can get through day to day and get some sleep.

What Causes Severe Knee Pain?

In most cases, severe knee pain comes on suddenly. It is typically accompanied by other symptoms such as swelling, instability, hot, red skin or there may be an obvious deformity of the leg, depending on the underlying cause.

Here we will look at the common causes of severe knee pain. We will look at how they present to help you work out what is going on and then what you can do to treat it.

We will also look at what signs to watch out for that indicate there is something serious going on that requires immediate medical attention.

Severe Knee Pain & Swelling

Severe knee pain accompanied by knee swelling usually indicates a problem inside the knee joint. It will typically have come on very suddenly with an injury but in some cases, it may build up over over a few days. The swelling may be fairly constant or come and go. So what could it be?

1) Knee Ligament Tear

Severe knee pain accompanied by swelling typically indicates damage to one of the four knee ligaments. The cruciate ligaments (ACL and PCL) and found in the middle of the knee joint and the collateral ligaments are found on either side of the joint (MCL on the inner side, LCL on the outer side). 

Overstretching results in tears in the ligament which causes swelling and bleeding in the knee. The more fibers that are damaged, the greater the swelling.

Ligament tears can cause mild, moderate or severe knee pain, depending on the severity of the injury

There are three grades of ligament tear:

Grade 1: Where only a few fibers are torn. There is usually mild pain and swelling but no instability

Grade 2: More fibers are torn but the ligament is still intact. There may be moderate – severe pain and swelling and some mild instability

Grade 3: Complete rupture of the ligament. There is usually sudden, excruciating knee pain and swelling, often accompanied by instability

The greater the degree of damage, the more severe the symptoms and the quicker they will develop. Ligament tears are often a result of twisting injuries or the knee being pushed out of position e.g. in a sporting tackle. You can find out lots more about the symptoms, diagnosis and treatment of ligament injuries in the knee sprain section

2) Meniscus Tear

The knee joint is protected by a special layer of cartilage known as the meniscus. If the meniscus is torn, it causes bleeding and inflammation in the joint. 

A meniscus tear can cause knee pain, swelling and locking

Depending on the location and extent of the damage to the cartilage, this can cause severe knee pain and swelling as well as limiting knee movement. Symptoms often build up over a couple of days.

There are two main causes of meniscus damage. There may be wear and tear where the meniscus thins and frays, usually associated with arthritis and aging. Alternatively a twisting injury, typically when the foot is fixed to the floor and the knee is slightly bent, will often tear part of the meniscus. 

The pain tends to be worse when trying to bend the knee or take any weight on it. A classic symptom of a meniscus tear is locking at the knee joint – where the leg gets stuck in a certain position, unable to move.

You can find out all about the common causes, symptoms, diagnosis and treatment in the meniscus tear section. 

3) Knee Arthritis

Knee arthritis is a common cause of severe pain and swelling in people typically over the age of 70. Wear and tear on the joint leads to bone and cartilage damage which irritates the joint and causes swelling. 

Arthritis is a common cause of flare ups of severe knee pain, particularly in the over 70's

The symptoms of arthritis often fluctuate with people swinging between good periods with minimal symptoms to flare ups where there may be excruciating knee pain and swelling. In many cases, symptoms may be mild to moderate and can be managed with medication, exercises, knee supports and diet, but if the pain becomes so severe that it affects your sleep or majorly limits your daily activities, then surgery may be necessary. 

In the arthritis section you will find loads of information about the different types of arthritis, the causes, symptoms, stages and best treatment options.

Severe Pain With Obvious Deformity

If severe knee pain is accompanied by an obvious deformity there is most likely a fracture (break) or dislocation on one of the knee bones. If this is the case, you will usually be able to pinpoint the time it happened – there will have been a fairly major trauma such as a fall, hard tackle or RTA, and you will have excruciating knee pain. Bones don’t just break or dislocate without you knowing it.

1) Knee Fractures

In most cases, if you have fractured one of the knee bones there will be sudden, immediate severe knee pain and swelling.

Patella fractures cause severe knee pain and deformity

You may have noticed a popping or cracking sound at the time of injury and it will often be difficult to take weight through the leg. If you have fractured one of the leg bones, you may notice a hard lump under the skin, or the may have even penetrated the skin.

Patella fractures of the kneecap tend to occur when you fall onto the front of your knee from a height or during an RTA. Find out more in the kneecap injuries section.

In some cases, there may be a small hairline fracture of one of the bones. In this case, again you will usually be able to pinpoint a time of injury, but the pain and swelling may gradually build up over a couple of days.

2) Dislocation

Kneecap dislocations can causes severe knee pain and obvious deformity. The kneecap typically dislocates outwards

If you have dislocated the knee, in most cases it is the kneecap that dislocates, usually to the outer side of the knee. There will be a very obvious lump on the outer side of the knee and it will be extremely painful and difficult to move the knee. 

It is extremely difficult to dislocate the tibiofemoral knee joint, requiring a massive force. It is much more common do dislocate the patellofemoral joint (kneecap). You can find out more in the patella dislocation section.

If you suspect you have fractured or dislocated one of your knee bones, seek urgent medical attention immediately

Severe Knee Pain & Instability

Severe knee pain associated with instability usually indicates a ligament rupture, typically affecting the ACL

Severe knee pain is often accompanied by instability. There may be two things going on. Firstly, if the knee gives out completely i.e. collapses when you have weight on it so that you stumble or fall, it is most likely that you have ruptured one of the knee ligaments, such as the ACL.

The ligaments are the main stabilising structures in the knee, so if they rupture the knee will often give way, particularly when you are twisting or turning. Ligament ruptures typically occur during twisting injuries and are often accompanied by an audible pop or cracking noise.

The second possibility is that the body is trying to protect itself from further damage. When you take weight on the injured leg the pain can be so severe that it feels like the knee is going to buckle or give out, but it doesn’t actually collapse. This usually means there is damage inside the joint, but it is unlikely to be ligament damage.

If the knee is giving way regularly, it is important to get it looked at by your doctor as each time it gives way, you risk further damage to the knee joint. You can find out lots more in the knee ligament injury section.

Swollen, Red & Hot Knee

Severe knee pain that comes on suddenly and accompanied by swelling, redness and heat is most likely due to one of these:

1) Gout Knee

If your knee suddenly started to swell, looks red, feels hot to touch and you have excruciating knee pain the most likely cause is gout. 

Gout causes severe knee pain. Symptoms usually come on suddenly over a few hours and the knee is extremely painful, red, hot and swollen.

The symptoms of gout usually develop very quickly, usually at night time when our body temperature drops, and there is sudden, severe knee pain. High levels of uric acid lead to the formation of crystals in the joint which causes inflammation.

With gout, the skin around the knee often looks red and shiny and there may be lumps underneath the skin. The pain is often so severe that it is difficult to walk. Gout attacks usually last a couple of weeks but episodes frequently recur.

You can find out everything you need to know about gout and how to treat it in the gout knee section.

2) Septic Arthritis

Septic arthritis can cause severe knee pain and is caused by a bacterial infection in the joint. It most commonly affects the knees and feet and may affect more than one joint at a time. Septic arthritis typically causes severe knee pain, swelling and redness and the joint feels hot to touch.

Symptoms come on fairly quickly over a few hours/days and may make it difficult to move the knee or take any weight through it. It often makes you feel quite unwell and you may develop a fever. Septic arthritis is usually diagnosed by a blood test and treated with antibiotics.

3) Cellulitis

Cellulitis develops when bacteria enter the body through a cut or scrape causing an infection. There may be only very minor damage to the surface of the skin around the knee such as a small graze or tiny cut, but that is enough for the bacteria to enter the body. The area will appear red, hot, swollen, be tender to touch and there may be severe knee pain. You may feel generally unwell with a fever and nausea and lymph nodes may become enlarged.

Cellulitis does not get better on its own, it requires antibiotics, so if you feel cellulitis is the cause of your severe knee pain, see your doctor immediately

When To See Your Doctor

Any incidence of severe knee pain should be checked out by your doctor particularly if: 

1) Your knee looks deformed
2) You can’t put any weight through the leg
3) Your knee movements are limited – can’t fully bend or straighten the knee
4) You have severe knee pain, especially at night or when resting
5) Your knee keeps giving way
6) You feel unwell or have a fever
7) There is redness or the knee feels hot
8) There is major swelling around the knee
9) Your symptoms persist or get worse
10) You have pain, swelling, redness, tingling or numbness in the calf 

What Else Could It Be?

If you are still not sure what is causing your severe knee pain, visit the knee pain diagnosis section where we help you work out what is going on by thinking about the location of the pain (e.g. front, back or side of the knee).

Alternatively, in the knee symptoms guide we look at other symptoms typically linked with knee pain such as pain when running or bending, knee locking, sharp pain or pain on the stairs. And remember, if you are suffering from severe knee pain, get checked out by your doctor.

  1. Knee Pain Guide
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  3. Symptoms
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  5. Severe Knee Pain

Page Last Updated: 09/20/19
Next Review Due: 09/20/21

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1. Clinical Journal Of Pain: The influence of knee pain location on symptoms, functional status and knee-related quality of life in older adults with chronic knee pain: data from the Osteoarthritis Initiative. June 2017

2. BMC Musculoskeletal Disorders: Management of chronic knee pain: A survey of patient preferences and treatment received. September 2008

3. British Journal of General Practice: Defining knee pain trajectories in early symptomatic knee osteoarthritis in primary care: 5-year results from a nationwide prospective cohort study. 2016

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