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Patient Information

Anterior Cruciate Ligament Reconstruction (ACL)

What is the Anterior Cruciate Ligament?

A healthy knee functions with the help of muscles, cartilage and ligaments; carrying almost the entire weight of the body. Muscles around the knee allow movement and help to provide stability, however it is the ligaments around the knee that are integral to stabilising the joint.
The Anterior Cruciate Ligament (ACL) is a tough band of connective tissue which works to prevent excessive forward movement and twisting of the thigh bone (femur) on the shin bone (tibia). It runs diagonally through the middle of the knee and gives the knee joint about 85% of its stability.

Knee injuries can occur during any sporting activity, however, commonly occurs in sports such as football, netball, skiing and rugby. ACL injuries are one of the most common types of knee injuries, accounting for around 40% of all sports injuries. The ACL can be torn in a number of ways, but a twisting injury is the most frequently seen.

Common causes of an ACL injury include:

  • Knee twisting when landing from a jump
  • Changing direction suddenly e.g when side stepping
  • Stopping suddenly
  • During a collision, such as during a football tackle

When the ACL is torn, the knee usually swells immediately, and patients are unable to play on. They find it difficult to walk. After recovering from the initial injury, the knee can then feel unstable with certain movements and activities which cause the knee to give way. You may find it impossible to do some activities or return to sport. A complete tear of the ACL has minimal ability to heal by itself, however not all patients need to have an ACL reconstruction.

Do I need to have an ACL Reconstruction?

Not all patients will have recurrent instability or giving way within the knee following an ACL rupture. It is entirely reasonable to firstly undergo a period of physiotherapy to strengthen your thigh muscles, core stability and improve balance. Following this a proportion of patients will continue with work and undertake activities reasonably symptom free. 

A further proportion will remain relatively symptoms free following some lifestyle modifications for example, giving up football. The benefit of this approach is that you avoid the risks of surgery and potentially return to normal activities quicker. The downside of physiotherapy is that you may continue to be unstable despite 3 or 4 months of exercises and then need to undergo surgery anyway, delaying your recovery.  
You should also be aware that if you suffer with further episodes of your knee giving way during this period, it could result in damage to other structures within your knee such as joint surface cartilage or meniscus (shock absorber in the knee). Despite this, the medical literature has not shown that ACL reconstruction alters your future risk of arthritis with the knee.

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

  • Your age – older people who are not 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 work or could afford to take time off following surgery whilst your knee is recovering.
  • How unstable your knee is – if your knee is very unstable, you’re at increased risk of doing further damage if you do not have surgery  
  • Whether you have any other injuries – for example, your menisci (small discs of cartilage that act as shock absorbers) may also be torn and may need surgery to repair them, at the same time as the ACL reconstruction.

The aim of surgery is to rebuild the torn ligament and provide you with a stable knee again. This also helps to prevent you having further knee damage going forward in life. This should allow you to return to your normal daily activities. For the majority, a return to sport and other leisure activities is achievable following a period of rehabilitation. This timeframe largely depends on what it is you are hoping to do and whether your preferred sport involves twisting or pivoting. It will also depend on whether you had any additional procedures done at the same time as the ligament reconstruction e.g cartilage repair. You will be expected to follow a strict rehabilitation protocol as set out by your consultant and recognised by your physiotherapy team.

What does the surgery involve?

An ACL reconstruction is an elective procedure (does not involve a medical emergency) and therefore it is important you understand fully the procedure itself as well as the risks and benefits of the operation so you can make a fully informed treatment decision. 
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. Tissues that could be used to replace your ACL are listed below: 

  • part of your hamstring tendons – these run from the back of your knee on the inner side, all the way up to your thigh
  • a strip of your patella 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 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 and is commonly made of a type of polyester

There are various ways of reconstructing the ACL and your surgeon’s team will discuss this with you. At the Royal Orthopaedic Hospital, the vast majority of patients will have their ACL reconstructed using two of the hamstring tendons taken from the same leg. This is called a “hamstring graft” and is harvested at the beginning of your surgery through a small incision over your upper shin (tibia).

Through the same incision, a tunnel is then drilled into the knee at a point where the ACL originates (begins), then using two or three small incisions (less than 1cm) around the front of the knee, a camera is inserted, and a second tunnel is then drilled in the thigh bone (femur). This tunnel starts from inside the knee (where the ACL inserts) and comes out on the outer aspect of the thigh bone. A small incision (less than 5mm) may be present in this area.  The hamstring graft is then pulled into the tunnel and fixed at either end with a small screw and a button. This provides a solid fixation and allows you to rehabilitate sooner.

“Patella Tendon reconstruction” is the second most common method of reconstructing the ACL. This method uses the tendon at the front of your knee (patella tendon) with a portion of bone from the kneecap and the shin bone. This method requires a larger incision to be made, right at the front of the knee but is otherwise performed in a similar fashion to that described above.

Both these methods in time, reproduce the action of the previous ligament and provide the joint with stability. Both have been found to be equally successful, however there are side effects of taking tissue and as a consequence (based on a person’s occupation and requirements), one graft is more suited to one person over another. This should be discussed with your surgeon.

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 45 minutes and 1.5 hours depending on whether or not you have other structures that need to be repaired. The procedure usually requires a maximum of an overnight stay in hospital, however, can sometimes be performed as a day case procedure.

What are the risks of the operation?

All operations involve a certain element of risk. Only you can decide how bad your knee pain and function are and whether it impacts of your daily life enough to commit yourself to surgery and the recovery it involves. The majority of patients who choose to undergo ACL reconstruction make a good recovery and experience no serious complications, however, it is a major surgical procedure, and it is important you understand sometimes problems can occur.

Medical/Anaesthetic Problems

It is difficult to separate the risks of anaesthesia from the risks of the operation and your general health. The risks to you depend on whether you have any other any other illnesses such as heart problems or diabetes. If you are a smoker or you are overweight the risks to you are significantly higher and, in some cases, surgery can be cancelled. Modern general anaesthetic is very safe however there are some common side effects. These include:

  • Sore throat
  • Feeling sick
  • Shivering
  • Headache
  • Damage to teeth, lips or eyes
  • Muscle Pain
  • Excessive drowsiness

Serious complications to general anaesthesia are rare particularly if you are usually fit and well. Rare complications include life threatening allergy to drugs, breathing difficulties and cardiac issues such as heart attacks or stroke.

Infection – Superficial or Deep

A deep infection most often starts when bacteria gain access to the tissues at the time of surgery. This operation is carried out in an ultra-clean air theatre and sterile clothing is worn by the surgical team. You will be given preventative antibiotics at the time of surgery. The risk to you is less than 1%.

You will not be discharged from the hospital unless the appearance of your wound is satisfactory. Once you are home, should you have any concerns about your wound please call us the ward you were discharged from. The risk of a superficial wound infection is 1%

Damage to nerves and vessels

The surgery is carried out next to a number of nerves and blood vessels. Injury to these nerves or vessels occurs in less than one in 100 patients. Any damage identified at the time of surgery will be addressed before the wound is closed. It is reasonably common to have some numbness over the outer aspect of your knee which usually decreases over time.

Swelling, bruising & numbness

Due to the nature of the surgery, there will be some swelling in the knee, which will go down in a few weeks. There will be an area of numbness next to the scar which is entirely normal after surgery. Sometimes, initial bruising can happen, but should settle quickly. Ice packs and high elevation with your leg above the height of your pelvis can help. Do not elevate your leg on a low foot stool.

Blood Clots

Blood clots in the leg (deep vein thrombosis) or blood clots on your lung (pulmonary embolism) are a risk associated with many forms of orthopaedic surgery. The risk to you is less than 1%. The simplest way of reducing this risk is early mobilisation and although you may not be able to put weight through your operated leg, we will encourage you to mobilise with your crutches and to exercise your feet and ankles regularly. You will be given some compression stockings to wear to help minimize the risk to you. Please inform your surgical team or the pre-operative assessment team if you use any form of oral contraceptive pill or hormone replacement as this can increase your risk further. Drugs to thin your blood are not usually recommended as the risk of bleeding tends to outweigh the benefit of blood thinning drugs.

Bleeding (requiring transfusion)

Bleeding is rare, but some bruising may still occur. If a collection of blood results (haematoma), it may need to be drained. Rarely damage can occur to blood vessels behind the knee; this can lead to loss of circulation to the lower leg and foot, which may require further surgery. If you were to lose a lot of blood you may need a transfusion. The risk of this happening to you is less than 1%.

Compartment Syndrome

Compartment syndrome can occur as a result of increased pressure around the muscles of the lower leg as a consequence of bleeding or swelling. This requires extended hospital stay for monitoring and may mean further surgery on your lower leg to release the pressure. The risk to you is less than 0.1%.


Post-operative stiffness can occur as the knee responds to the trauma of the surgery. Sometimes, scar tissue builds up inside the knee, restricting your movement significantly. Here, you might need intensive or water-based physiotherapy, splinting or a further surgical operation to address it.

Ongoing or Unresolved Pain

Sometimes following injury, you may have other problems in the knee joint as well as the ACL deficiency. This could involve cartilage problems or wear and tear on the bone. If this is the case, surgery may not completely abolish all of your knee pain for life. If you have had a bone-patella tendon-bone procedure, you are at slightly more risk of having persistent discomfort over the front of the knee post-operatively. The risk of this is approximately 5-10%.

Graft Failure/Re-tear

There are number of reasons as to why the surgical graft may fail or you may suffer a re-tear of the ACL. This can range from surgical technique through to overaggressive rehabilitation and re-injury. If you were to re-tear the graft or if the graft was not to heal well, you may need a revision procedure. Your surgical team would discuss this at length with you. The risk to you is 5-12% depending on your age, occupation, sport etc.

Irritation from Surgical Hardware

The small screws and buttons used to secure your new ligament in surgery are known as “hardware” or “implants”. Some patients can feel their hardware just under the skin. In some cases, it can irritate the surrounding soft tissues and cause pain or discomfort. For these patients, it is usually recommended the metalwork is removed, but only after careful consideration by your surgeon.

Patella tendon rupture/patella fracture

In bone-patella tendon-bone procedures, there is an increased risk of the residual tendon rupturing and in a very small number of cases patella (kneecap) fracture has been reported. This is more usual to happen in the first 3 months from surgery.

What happens after surgery?

When you wake up, you will have a bandage and you may have a special brace around your knee. If you have had other procedures in combination with your ACL reconstruction, for example, a meniscal repair, you may need to keep this on for up to 6 weeks. You will have a wound that will require some nursing care at 2 weeks after surgery. You must keep this clean and dry until you are asked to see your practice nurse at your GP surgery. Your brace (if you have one) is designed to restrict movement at certain intervals and you will be asked to wear it at all times for the first 4 or 6 weeks. It should be adjusted at particular time scales in your recovery – your nurse, physiotherapist or doctor will explain this to you as applicable. 

You will either be asked not to weight bear on your operated leg or to put partial weight through it when you walk. Both of these requirements mean you will need to use 2 crutches at all times. The physiotherapy team on the ward will talk to you about this. Sometimes you are allowed to weight bear again after 2 weeks. Sometimes we do not restrict you at all. This will be explained to you directly as each case is individual.

You should be prepared to take your recommended pain relief regularly and as advised by your medical team. The immediate few weeks after surgery can be difficult in terms of controlling your pain and swelling. You must also be prepared to work hard at the physiotherapy exercises given to you at the appropriate stages in your recovery. You will have some heat and swelling in the knee which is normal – be prepared to ice your knee regularly in the first 6 weeks of your recovery. 

Ice should not be directly placed onto the skin. An ice pack or a bag of frozen peas should be wrapped in a pillowcase or a damp cloth in order to prevent you burning the skin. Ice packs should only be applied for short intervals (10-15min) at a time, to prevent is causing further tissue damage and more swelling.

You must elevate your leg above the height of your pelvis when you can. This in combination with your compression stockings will also help to reduce swelling.

Following surgery, your knee gradually heals over the course of 6-9 months. You will be seen in outpatients a few weeks after your operation and then followed up until your surgeon is satisfied with your level of recovery for you to be discharged. If you have not received an appointment, it is essential you phone the central appointments office on 0121 685 4186.


You must not drive for 6 weeks following your surgery. Doing so may render your insurance policy invalid. After this you may drive when you are comfortable and safe to do so. Ideally, you will have stopped using crutches and be able to sit comfortably. You should have enough power and bend in your knee to perform an emergency stop. You may get back to driving quicker if you have an automatic car. The law states you should be in complete control of your car at all times. It is your responsibility to ensure this.

Returning to work

You are likely to be away from work for anywhere up to 3 months after surgery. This largely depends on what sort of job it is you do. Desk based workers can often return before, however you should remember that prolonged standing or sitting can make your knee swell and increase your pain. Patients with a more manual profession such as builders or other manual trades may not be fully operational for 4-6 months. Your consultant’s team will advise you.

Sports & Exercise

Your return to leisure activities will be guided by your surgeon and physiotherapist and will depend on how you are progressing and whether you are reaching certain goals. Your therapist will advise you when you are physically capable to deal with different activities and will ensure you progress to a level where it is safe for you to return to certain activities. Sports that involve jumping, cutting, side-to-side sports or full-on contact will be encouraged much later in your recovery; generally, around 9 months to 1 year. As a guide you should be able to use a static bike gently around week 6 and could do a light jog (around 40% pace) on a treadmill at month 4. Swimming is encouraged once you are 3 months on from your operation but should only be front crawl straight leg kick with no breaststroke until you are in your 4th or 5th month of recovery. 

It is vitally important that the rehabilitation programme is followed and that a return to sport does not occur until your physiotherapist agrees. This will be dependent on you reaching certain goals/targets and is not purely based on time. About 85% of all ACL graft re-ruptures occur within two years following surgery. This is thought to be largely due to patients failing to fully recover their muscle strength, core stability, balance and spacial awareness (proprioception).  


Your physiotherapy appointments should begin within two weeks of your operation and these will continue until you are able to return to your normal pre-surgery activities. Whilst you are waiting to see your physio, you should maintain these exercises as often as your pain allows. If you have any questions or need any advice about your exercises then please contact the Physiotherapy Department between 8am - 4pm Monday to Friday on 0121 728 9442.

The Royal Orthopaedic Hospital | T: 0121 685 4000 |