The most common knee problems are:

• A sprain 
• A strain
• Torn ligaments 
• A torn meniscus
• Arthritic conditions such as Osteoarthritis (OA), Rheumatoid arthritis (RA)

Knee Ligament Injuries

1. 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.

2. 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.

3. 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.

4. 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

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

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

Treatment

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.

In the case of a mild injury, treatment may involve only the use of a compressive support brace for the knee.

In the case of more serious injuries, the patient may be required to wear a knee brace for six weeks or longer. The splint will allow the knee to flex or extend, but will limit or prevent the knee from moving in a particular plane dependent upon the type and severity of damage.