What is It: A knee sprain is where one of the four knee ligaments overstretches and potentially tears
Symptoms: Typical symptoms of a sprained knee include ligament pain (may be anywhere around the knee), swelling, instability, difficulty bending and straightening the knee
Causes: A force through the knee or sudden twisting of the joint
Other names: Ligament tear, knee strain
Treatment: PRICE, exercises. Occasionally surgery is required
A knee sprain simply means that one of the knee ligaments has been overstretched and that some or all of the fibres have been damaged.
This usually occurs when there is a force through the knee e.g. a
tackle in sport or sudden twisting of the knee e.g. when falling
awkardly or quickly changing direction.
There are four ligaments in the knee joint, any of which can be sprained.
In the centre of the joint are the two cruciate ligaments - anterior and posterior (ACL & PCL). At the sides of the joints are the two collateral ligaments - the medial and lateral (MCL & LCL).
The cruciate and collateral knee ligaments work together to keep the knee joint stable and protect it from injury.
Any movement that overstretches the knee can result in a knee sprain. It may affect one of more of the ligaments depending on the severity of the injury.
Let's look at the most common causes of a knee sprain and which ligament tends to be affected:
1) ACL Sprain
Sudden twisting of the knee, or hyperextension (where the knee bends back too far) typically injures the ACL
2) PCL Sprain
A force through a bent knee e.g. a fall onto a bent knee, car accident where the knee hits the dashboard often results in a PCL injury. These account for less than 20% of knee ligament injuries
3) MCL Sprain
If there was a force through the outer side of the knee pushing the knee inwards, particularly if the foot was fixed to the ground, then it often results in a MCL injury
4) LCL Sprain
If there was a blow to the inner side of the knee pushing it outwards, then it is likely to have caused a LCL injury
If the force is great enough, more than one ligament may be damaged as well as the knee cartilage. The most common combination is an ACL and MCL tear.
Knee sprains can be classified into three grades, depending on the amount of damage to the ligament:
Grade 1: a few fibres (less than 10%) are damaged/torn. Usually heals naturally
Grade 2: more fibres are torn but the ligament is still intact
Grade 3: the ligament is ruptured i.e. completely torn. May require surgery
The most common symptoms of a sprained knee are pain, swelling, bruising and stiffness which may make it difficult to move the knee and/or walk. With more severe injuries, there may also be some instability around the knee causing it to give way.
Symptoms may develop immediately after an injury, but sometimes they don’t appear until a couple of days later.
The location of the pain can help to determine which knee ligament you have sprained.
1) Medial Knee Pain: pain on the inner side of the knee usually indicates a Medial Collateral Ligament tear - see MCL Tear
2) Lateral Knee Pain: pain on the outer side of the knee usually indicates a Lateral Collateral Ligament tear
3) Widespread Pain and Instability: Most likely an ACL (most common) or PCL tear. If there was a "popping" noise, it is most likely an ACL tear
4) Severe Swelling: If there is a great deal of swelling, you may have injured more than one ligament
If you are given a diagnosis of a sprained knee, it is worth asking some questions to find out more.
You want to find out from your doctor:
1) Which ligament is damaged?
2) What grade knee sprain is it?
3) What treatment do they recommend?
4) Is there anything you need to avoid?
5) Is it safe to drive?
Usually, the best course of action is to follow the PRICE principles (Protect, Rest, Ice, Compress, Elevate) to reduce pain and swelling and to speed up healing.
Visit the PRICE treatment section to find out how to safely and effectively use all the different aspects.
Then when you feel able (usually in just a few days), start some exercises to regain the strength, movement and function of your knee. This is really important to make sure you make a full recovery and don't leave yourself at risk of further injuries due to ongoing instability.
You can find in-depth guidance on
exercises and how to progress them appropriately to get back to full
function following a sprain visit the
knee strengthening exercises
You might find that wearing a knee brace helps to reduce any pain and instability after a knee sprain. Usually a basic knee brace will be sufficient, costing as little as $4/£7. If you need a bit more support, advanced knee braces work well. Click the links to find out more about knee brace options.
If you have already been discharged by your doctor and all you have been told is that you have a sprained knee, it is almost certainly not too serious, and is likely a grade 1 or 2 sprain.
Grade 3 tears (also known as a rupture), can often be treated in the same way as grade 1 & 2 sprains, although they will take longer to heal. However, sometimes surgery is advisable if the knee keeps giving way, despite trying exercises.
The most common knee ligaments to sprain are the MCL and ACL. The least common is a PCL injury.
There are a number if different causes of knee pain, some that come on following a specific incident, others build up gradually with no obvious cause.
If your knee pain was caused by a specific incident such as a fall, visit the Common Knee Injuries section. If your knee pain has come on gradually over time, go to the Common Knee Conditions section.
If you think it might not be a knee sprain and you want help working out what is wrong with your knee, visit the Knee Pain Diagnosis section.
Page Last Updated: 21/9/18
Next Review Due: 21/9/20