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Knee injuries - Causes and treatment

Knee injuries are very common, especially if you take part in sport. Your knee is a complex joint. Sometimes the bones of your knee can be damaged but it's more likely that you will injure soft tissues such as ligaments. Injuries can often be treated with physiotherapy but you may need surgery if you damage your knee more seriously.

What are knee injuries?

The most common knee injuries are:

  • a sprain - overstretching one or more ligaments through twisting or wrenching
  • a strain - a tendon or muscle is overstretched
  • torn ligaments
  • a torn meniscus
  • bleeding in your knee joint - this is usually caused by a torn ligament

Knee injuries
Illustration showing a healthy left knee

Knee ligament injuries

Ligaments connect one bone to another within your joints and help provide stability and flexibility.

Medial collateral ligament

This is on the inside of your knee and is taut when your leg is straight. It's a strong ligament but can be sprained or completely ruptured (torn) if you twist your straightened leg at the same time as being knocked sideways.

Anterior cruciate ligament

The anterior cruciate ligament (ACL) runs from the outside of the back of your thigh bone to the inside of the front (anterior) of your shin bone. Cruciate means in the form of a cross. The two cruciate ligaments cross over each other - the ACL crosses in front of the posterior cruciate ligament. Together they help to stabilise front to back movements of the knee.

Your ACL is about half the strength of your medial collateral ligament (MCL). It's the most commonly injured knee ligament in sport.

Posterior cruciate ligament

The posterior cruciate ligament (PCL) runs from the inside edge of your thigh bone to the back (posterior) of your shin bone.

Lateral collateral ligament

The lateral collateral ligament (LCL) is like a thin cord that runs from the bottom of your thigh bone to the top of your shin bone on the outside of your knee. It's not usually damaged on its own and you may need to have it repaired if you are having surgery on other damaged ligaments.

Other soft tissue injuries

The soft tissues around the knee can also be injured. Soft tissue means any tissue in your body that isn't bone.

If you do a sport that involves twisting your upper leg while your foot is planted on the floor, you may tear a meniscus. Your menisci are two crescent-shaped discs of shock-absorbing cartilage. In older people whose menisci are more likely to be worn down, a tear can result from even a very minor injury.

Your patellar tendon (also called patellar ligament) connects your kneecap to your thigh muscle. If your knee is bent too far back, this tendon may tear.

Symptoms of knee injuries

The symptoms for most ligament injuries will be similar, no matter which one has been damaged. These include:

  • pain
  • swelling
  • instability

If you completely rupture your ACL, you may hear a popping sound. You may also feel something snap inside your knee, as if it has given way.

A meniscus injury will be painful on either the inside or outside of your knee joint (depending on which meniscus is damaged) and you may have some swelling. Your knee may lock or feel as if it's catching.

If you damage your patellar tendon you won't be able to straighten your leg properly. You will probably also have pain, swelling and weakness.

Causes of knee injuries

You may injure your knee if:

  • it receives an impact or is moved beyond its usual range of movement, for example if you have a fall or land awkwardly
  • you do a sport that combines running, jumping and stopping with quick changes of direction such as football
  • you have a condition such as osteoarthritis
  • if your knees hit the dashboard in a car accident - PCL damage is sometimes called the "dashboard injury" as this is how it often occurs with the knee being hit directly from the front


Your doctor will examine you and do different tests depending on which ligament he or she thinks is injured.

With MCL injuries, your doctor will try to find out how badly the ligament is damaged by seeing how far your lower leg can be moved outwards while holding your upper leg still. There are three grades of injury.

  • Grade 1 is a sprain.
  • Grade 2 is a partial tear.
  • Grade 3 is a complete tear.

You will usually be tested for an ACL injury by your doctor pulling your lower leg forward with your thigh held still and your leg bent.

If your doctor thinks you may have injured your PCL, he or she will probably ask you to lie on your back with your legs raised so that your thighs point straight up, and then ask you to bend your knees at right angles. If your lower leg sags towards the floor, the PCL is probably torn.

Your doctor may ask you to try movements such as stepping or hopping. He or she may feel for fluid in the joint by pressing gently over your kneecap, especially if your knee is not severely swollen. Other checks that you may have include an X-ray (to rule out a broken bone) and an MRI scan (this uses magnets and radiowaves to produce images of the inside of your body).

Treatment of knee injuries

All soft tissue injuries to the knee should receive the same immediate first aid treatment. This follows the RICE procedure.

  • Rest the injury initially, then reintroduce movement so you don't lose too much muscle strength.
  • Ice packs or a bag of frozen peas wrapped in a towel should be applied to your knee to reduce swelling and bruising. You shouldn't apply ice directly to your skin as it can give you an "ice burn" - place a cloth between the ice and skin.
  • Compress the joint by bandaging it to support the injury and help decrease swelling.
  • Elevate the knee and keep it supported.

Further treatment will vary according to which ligaments you have damaged and how badly. It will also depend on how much sport you do. If you don't put much demand on your knee, resting it and following a programme of strengthening physiotherapy exercises may be sufficient.


In some situations, you may need to have surgery to repair the damage. This is likely to be the case if:

  • you have a grade 3 MCL injury
  • you have damaged your ACL and do a lot of sport, you may need a reconstruction operation - this involves taking a graft of tendon (usually from your kneecap) to replace the damaged ligament
  • damage to your PCL means your knee is too unstable for you to play sport
  • you have torn your patellar tendon
  • your knee remains painful or locks after a meniscus injury

Prevention of knee injuries

There are some precautions you can take to try to reduce the risk of damaging your knee ligaments.

  • Exercise regularly to maintain a good level of fitness. This will mean your muscles are stronger and better able to support your joints. If you have not been active for a while, start gently and gradually increase the intensity.
  • Spend five to 10 minutes warming up before exercising and cooling down afterwards. Stretch out your muscles once they are warmed-up - don't do this while they are cold as you could damage them - and then again after you have cooled down. This reduces the risk of injuring yourself and helps to prevent stiffness later.

Further information


  • Villar R. Knee problems. 1st ed. London: Thorson's Health Series
  • Sherry E, Wilson S. Oxford Handbook of Sports Medicine. 2nd ed. Oxford: Oxford University Press, 1998: 406-422
  • Sprains and strains. NHS Library for Health. Clinical Knowledge Summaries.
    accessed 21 August 2007
  • Osteoarthritis. Arthritis Research Campaign
    accessed 9 February 2007
  • MacAuley D. Oxford Handbook of Sport and Exercise Medicine. 1st ed. Oxford: Oxford University Press, 2007: 212-230
  • Knee injury - meniscus cartilage tear. NHS Library for Health. Clinical Knowledge Summaries
    accessed 19 February 2007
  • McLatchie G. Understanding sports and exercise medicine. 1st ed. Oxon: Family Doctor Publications in association with the British Medical Association, 2000
  • Starting to exercise. Bandolier
    accessed 13 February 2007

Why not find out what more BUPA can do for you?

For more information about discounted BUPA private medical insurance for members of approved fitness centres, please call BUPA today on 0800 600 500 and quote A711.

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