Before having knee surgery, you may need to wait for any swelling to go down and for the full range of movement to return to your knee.

You may also need to wait until the muscles at the front of your thigh (quadriceps) and back of your thigh (hamstrings) are as strong as possible.

If you do not have the full range of movement in your knee before having surgery, your recovery will be more difficult.

It's likely to take at least 3 weeks after the injury occurred for the full range of movement to return. Your GP may refer you to a physiotherapist to help you prepare for surgery.

Physiotherapy

Physiotherapists, or physios, are healthcare professionals who use physical methods, such as massage and manipulation, to encourage healing. A physio will be able to help you regain the full range of movement in your knee.

Optimising the muscle function in the knee will help to ensure a more successful outcome after surgery. It may also provide the knee with sufficient stability so that surgery may not always be necessary.

Your physio may show you some stretches you can do at home to help keep your leg flexible.

They may also recommend low-impact exercises, such as swimming for fitness or cycling. Visit the website of charity Cycling UK for advice. These types of activities will improve your muscle strength without placing too much weight on your knee.

You should avoid any sports or activities that involve twisting, turning or jumping.

Pre-admission clinic 

Before having anterior cruciate ligament (ACL) surgery, you'll be asked to attend a pre-admission clinic. You'll be seen by a member of the team who will look after you while you're in hospital.

A physical examination will be carried out and you'll be asked about your medical history. You may also need to have some investigations and tests, such as a knee X-ray.

You'll be asked about any tablets or other types of medication you're taking, both prescribed and bought over the counter from a pharmacy.

A member of your care team will also ask about any anaesthetic you've had in the past and whether you experienced any problems or side effects, such as nausea.

They'll also ask you some questions about your teeth, including whether you wear dentures, caps or a plate.

This is because a tube may be put down your throat to help you breathe during the operation, and any loose teeth could be dangerous.

The pre-admission clinic is a good time to ask any questions you have about the procedure. But you can discuss any concerns with your surgeon at any time.

Read more about preparing for surgery.

Preparing for hospital

It's a good idea to be fully prepared before going into hospital for surgery. Below is a list of things to consider if you're about to have an operation.

Do your homework 

Find out as much as you can about your operation and what it involves. Information or a video about the procedure may be available at your hospital.

Ask your surgeon if you're unsure about anything.  

Other medical problems

Ask your GP to check that any other medical problems you have, such as high blood pressure (hypertension), are under control.

Keep clean

Have a bath or shower before going into hospital, and put on clean clothes. This will reduce the chances of taking unwanted bacteria into hospital.

Eating before your operation

Anaesthetics are often safer if your stomach is empty, so you'll usually have to stop eating several hours before your operation.

You should be given more advice about this during your pre-admission clinic.

Prepare for returning home

Stock up on food that's easy to prepare, such as tinned foods and staples like rice and pasta. You could also prepare meals and put them in the freezer.

Put things you'll need, such as books and magazines, where you can easily reach them.

Arrange help and transport

Ask a friend or relative to take you to and from hospital. You'll also need to arrange for someone to help you at home for a week or two after you come back.

Read more about having an operation.

A number of methods can be used to reconstruct an anterior cruciate ligament (ACL). The most common method is to use a tendon from elsewhere in your body to replace the ACL.

You'll either have a general anaesthetic, which means you'll be totally unconscious during the procedure, or a spinal anaesthetic, where anaesthetic is injected into your spine so you're conscious but unable to feel pain.

Your anaesthetist will discuss the procedure with you and can recommend which type of anaesthetic to use.

The operation will take between 1 and 1.5 hours, and will usually require an overnight stay in hospital.

Examining your knee

After you've been anaesthetised, the surgeon will carefully examine the inside of your knee, usually with a medical instrument called an arthroscope.

Your surgeon will check that your ACL is torn and look for damage to other parts of your knee. Any other damage found might be repaired during the surgery to your ACL or after your operation.

After confirming that your ACL is torn, your surgeon will remove the graft tissue, ready for relocation.

Graft tissue

A number of different tissues can be used to replace your ACL. Tissue taken from your own body is called an autograft. Tissue taken from a donor is called an allograft.

A donor is someone who has given permission for parts of their body to be used after they die by someone who needs them. 

Before your operation, your surgeon will discuss the best option with you.

Tissues that could be used to replace your ACL are listed below. 

• a strip of your patellar tendon – this is the tendon running from the bottom of the kneecap (patella) to the top of the shin bone (tibia) at the front of your knee
• part of your hamstring tendons – these run from the back of your knee on the inner side, all the way up to your thigh
• part of your quadriceps tendon – this is the tendon that attaches the patella to the quadriceps muscle, which is the large muscle on the front of your thigh
• an allograft (donor tissue) – this could be the patellar tendon or Achilles tendon (the tendon that attaches the back of the heel to the calf muscle) from a donor
• a synthetic graft – this is a tubular structure designed to replace a torn ligament

The most commonly used autograft tissues are the patellar tendon and the hamstring tendons. Both have been found to be equally successful.

Allograft tissue may be the preferred option for people who are not going to be playing high-demand sports, such as basketball or football, as these tendons are slightly weaker.

Synthetic (man-made) tissues are currently used in certain situations, such as revision surgery and multi-ligament injuries.

The graft tissue will be removed and cut to the correct size. It will then be positioned in the knee and fixed to the thigh bone (femur) and shin bone (tibia).

This is usually carried out using a technique called knee arthroscopy.

Arthroscopy

An arthroscopy is a type of keyhole surgery. It uses a medical instrument called an arthroscope, which is a thin, flexible tube with bundles of fibre-optic cables inside that act as both a light source and camera.

Your surgeon will make a small incision on the front of your knee and insert the arthroscope.

The arthroscope will illuminate your knee joint and relay images of your knee to a television monitor. This will allow the surgeon to see the inside of your knee clearly.

Additional small incisions will be made in your knee so that other medical instruments can be inserted. The surgeon will use these instruments to remove the torn ligament and reconstruct your ACL.

Your surgeon will make a tunnel in your bone to pass the new tissue through.

The graft tissue will be positioned in the same place as the old ACL and held in place with screws or staples that will remain in your knee permanently.

Final examination

After the graft tissue has been secured, your surgeon will test that it's strong enough to hold your knee together.

They'll also check your knee has the full range of motion and that the graft keeps your knee stable when it's bent or moved. 

When the surgeon is satisfied everything is working properly, they'll stitch the incisions closed and apply dressings.

After the procedure, you'll be moved to a hospital ward to begin your recovery.

Read more about recovering from knee surgery.

In more than 80% of cases, surgery to repair an anterior cruciate ligament (ACL) fully restores the functioning of the knee.

ACL surgery will improve the stability of your knee and stop it giving way. You should be able to resume normal activities after 6 months.

But your knee may not be exactly like it was before the injury. You may still experience some pain and swelling in the replacement ligament.

If other structures in your knee are also damaged, it may not be possible to fully repair them.

As with all types of surgery, there are some risks associated with knee surgery.

They include:

• infection – the risk of infection is small: you may be given an antibiotic after your operation to prevent infection developing
• blood clot – the risk of a blood clot (embolism) forming and causing problems is very low: if you're thought to be at risk, you may be given medication to prevent blood clots forming
• knee pain – affects some people who have ACL surgery and is more likely to occur when the patellar tendon is used as graft tissue; you may have pain behind your kneecap or when kneeling down or crouching
• knee weakness and stiffness – some people experience long-term weakness or stiffness in their knee

After ACL surgery, there's also a small chance that the newly-grafted ligament will fail and your knee will still be unstable.

If the first operation is unsuccessful, further surgery may be recommended. But subsequent operations are often more difficult and do not usually have the same long-term success rate as a first tendon repair.