The decision to have knee surgery will depend on the extent of damage to your anterior cruciate ligament and whether it affects your quality of life.

If your knee doesn’t feel unstable and you don’t have an active lifestyle, you may decide not to have anterior cruciate ligament (ACL) surgery.

However, when deciding whether to have surgery you should be aware that delaying surgery could result in further damage to your knee.

One study of people with ACL tears found that their risk of damaging the injured knee increased by 1% for every month between the injury occurring and surgery.

Things to consider

When deciding whether to have ACL surgery, the following factors should be taken into consideration:

• your age – older people who aren’t very active may be less likely to need surgery
• your lifestyle – for example, whether you’ll be able to follow the rehabilitation programme after having surgery
• how often you play sports – you may need to have surgery if you play sports regularly 
• your occupation – for example, whether you do any form of manual labour
• how unstable your knee is – if your knee is very unstable, you’re at increased risk of doing further damage if you don’t have surgery  
• whether you have any other injuries – for example, your menisci may also be torn and may heal better when repaired at the same time as ACL reconstruction (menisci are small discs of cartilage that act as shock absorbers)

Children

Children can have ACL reconstructive surgery if necessary. However, as they’re still growing, the procedure is likely to be modified to ensure that the growth areas aren’t affected. It’s also a trickier operation and may need to be carried out by a surgeon with a special interest in childhood injuries.

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 that you’re conscious but unable to feel pain.

Your surgeon will discuss the procedure with you and can recommend which type of anaesthetic to use. The operation will take 1-1.5 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 (see below).

Your surgeon will check that your ACL is torn and look for damage to other parts of your knee. If there’s other damage, your surgeon might repair it during the surgery or it may be treated 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 known as an autograft. Tissue taken from a donor is known as 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 femur (thigh bone) and tibia (shin bone). This is usually carried out using a technique known as a 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 there is enough tension in it (that it’s strong enough to hold your knee together).

They’ll also check that 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 that everything is working properly, they’ll use stitches to close the incisions 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.

If you tear the anterior cruciate ligament in your knee, you may need to have reconstructive surgery.

The anterior cruciate ligament (ACL) is a tough band of tissue joining the thigh bone to the shin bone at the knee joint.

It runs diagonally through the inside of the knee and gives the knee joint stability. It also helps control the back-and-forth movement of the lower leg.

ACL injuries

Knee injuries can occur during sports such as skiing, tennis, squash, football and rugby. ACL injuries are the most common type of knee injury, accounting for around 40% of all sports injuries.

You can tear your ACL if your lower leg extends forwards too much. It can also be torn if your knee and lower leg are twisted.

Common causes of an ACL injury include:

• landing incorrectly from a jump
• stopping suddenly
• changing direction suddenly
• having a collision, such as during a football tackle

If the ACL is torn, your knee will become very unstable and lose its full range of movement. This can make it difficult to perform certain movements, such as turning on the spot. Some sports may be impossible to play.

Deciding to have surgery

The decision to have knee surgery will depend on the extent of damage to your ACL and whether it’s affecting your quality of life.

If your knee doesn’t feel unstable and you don’t have an active lifestyle, you may decide not to have ACL surgery.

However, when deciding whether to have surgery it’s important to be aware that a delay could cause further damage to your knee.

Read more about deciding to have surgery.

Before having surgery

Before having ACL surgery, you may need to wait for any swelling to go down and 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 the back of your thigh (hamstrings) are as strong as possible.

If you don’t 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 three weeks after the injury occurred for the full range of movement to return.

You may be referred to a physiotherapist before having surgery. They’ll be able to help you regain the full range of movement in your knee.

Your physio may show you some stretches you can do at home to help keep your leg flexible. They may also recommend low-impact exercise, such as swimming or cycling.

These types of activities will help 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.

Read more about preparing for ACL surgery.

Reconstructive ACL surgery

A torn ACL can’t be repaired by stitching it back together. However, it can be reconstructed by grafting (attaching) new tissue onto it.

The ACL can be reconstructed by removing what remains of the torn ligament and replacing it with a tendon from – for example, the hamstring or patellar tendon.

Read more about how ACL reconstructive surgery is performed.

Risks of ACL surgery

ACL surgery fully restores the functioning of the knee in over 80% of cases.

However, your knee may not be exactly like it was before the injury, and you may still have some pain and swelling in your knee. This may be due to secondary injuries in the knee sustained at the same time as the ACL injury, or afterwards due to the abnormal movement pattern. It usually involves tears or injuries to the cartilage components of the joint.

As with all types of surgery, there are some small risks associated with knee surgery including infection, blood clot, knee pain and knee weakness and stiffness.

Read more about the risks of ACL surgery.

Recovering from surgery

After having reconstructive ACL surgery, a few people may still experience knee pain or instability.

Recovering from surgery usually takes around six months. However, it could be up to a year before you’re able to return to full training for your sport.

Read more about recovering from ACL reconstructive surgery. 

Before having knee surgery, you may need to wait for any swelling to go down and 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 the back of your thigh (hamstrings) are as strong as possible.

If you don’t 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 three 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.

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 or cycling. These types of activities will help 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.

Read more about easy exercises and physiotherapy.

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 that you’re taking, both prescribed and over-the-counter medication (bought from a pharmacy).

You’ll also be asked whether you’ve had anaesthetic (painkilling medication) in the past, and whether you experienced any problems or side effects, such as nausea.

You’ll also be asked some questions about your teeth, including whether you wear dentures, caps or a plate. This is because during the operation a tube may be put down your throat to help you breathe and any loose teeth could be dangerous.

The pre-admission clinic is a good time to ask any questions you have about the procedure. However, 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 are under control, such as high blood pressure (hypertension).
• Keep clean – have a bath or shower before going into hospital and put on clean clothes. This will help 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 that 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 out of hospital.

Read more about having an operation.

Recovering from anterior cruciate ligament (ACL) knee surgery can take up to a year.

After knee surgery, the wound will be closed with stitches. If the stitches are dissolvable, they should disappear after about three weeks.

If your stitches aren’t dissolvable, they’ll need to be removed by a healthcare professional. Your surgeon will advise you about this. They’ll also tell you how to care for your wound. Washing it with mild soap and warm water is usually all that’s required.

Your knee will be bandaged and you may also be given a cryocuff to wear. This is a waterproof bandage that contains iced water to help reduce swelling. You may also be given painkilling medication to control any pain.

You may have painful bruising, swelling and redness down the front of your shin and ankle. This is caused by the fluid inside your knee joint (synovial fluid) leaking down your shin. These symptoms are temporary and should start to improve after about a week.

Rehabilitation

Your surgeon or physiotherapist will be able to advise you about a structured rehabilitation programme. It’s very important that you follow the programme so that your recovery is as successful as possible.

You’ll be given exercises you can start in hospital after your surgery and continue when you get home. The exercises will include movements to bend, straighten and raise your leg. Ask if you’re unsure about how to do any of the exercises.

You’ll also be given crutches to help you move around. You may need to use them for about two weeks, but you should only put as much weight on your injured leg as you feel comfortable with.

Weeks 1-2 of your recovery

For a few weeks, your knee is likely to be swollen and stiff, and you may need to take painkillers.

Your surgeon or GP will advise about the type of pain relief that’s best for you to use. You’ll be advised to raise your leg as much as possible – for example, by putting pillows under your heel when you’re lying in bed.

You may be given a cryocuff to take home with you to help ease the pain and swelling. Ask your surgeon or physiotherapist how often you should use the cryocuff. If you don’t have a cryocuff, you could place a pack of frozen peas wrapped in a towel on your injured knee.

Weeks 2-6 of your recovery

Once the pain and swelling have settled, you may be advised to increase or change your exercises. Your physiotherapist will advise you about what exercises to do. The exercises will help you to:

• fully extend and bend your knee
• strengthen your leg muscles
• improve your balance
• begin to walk properly

After 2-3 weeks, you should be able to walk without crutches.

As well as specific exercises, activities that don’t put much weight on your knee may also be recommended, such as swimming and cycling. 

Weeks 6-24 of your recovery

Six weeks to six months after your knee operation, you should gradually be able to return to your normal level of activity.

You’ll be encouraged to continue with activities such as cycling and swimming, but you should avoid sports that involve a lot of twisting, jumping or turning. This is because you need to allow enough time for the grafted tissue to anchor itself in place inside your knee.

After six months

After six months you may be able to return to playing sport.

Some people may need to take more time to feel confident enough to play sports again, and elite athletes may need longer to return to their previous level of performance.

Returning to work

How quickly you can return to work after having knee surgery will depend on what your job involves.

If you work in an office, you may be able to return to work after 2-3 weeks. If you do any form of manual labour, it could be up to three months before you can return to work, depending on your work activities.

Driving

Your GP will be able to advise you about when you can drive again. This will usually be after 3-4 weeks, or whenever you can comfortably put weight on your foot. 

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

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

However, 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 (less than 1%); you may be given an antibiotic after your operation to prevent infection developing
• blood clot – the risk of a blood clot forming and causing problems is very low (about 1 in 1,000), if you’re thought to be at risk, you may be given medication to prevent blood clots forming
• knee pain – affects up to 18% of 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 (less than 10%) 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. However, subsequent operations are often more difficult and don’t usually have the same long-term success rate as a first tendon repair.

The Map of Medicine is used by doctors throughout the NHS to determine the best treatment options for their patients. NHS Choices offers everyone in England exclusive and free access to this cutting-edge internet resource, which lets you see exactly what your doctor sees.

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Map of Medicine: Knee injuries