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 hour and 1 hour and 30 minutes, and will usually require an overnight stay in hospital.

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.

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 include: 

• 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 (artificial) 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 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.

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.

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.