ACL – Anterior Cruciate Ligament Injury

Nev Davies
Reading Children’s Orthopaedic Unit

Anterior Cruciate Ligament (ACL) Injury
Patient information

Quick Fact Sheet

  • The Anterior Cruciate Ligament (ACL) is one of the important ligaments that stabilises the knee joint by connecting the thigh bone (femur) to the shin bone(tibia). It plays a particular role when playing sports that involve side-stepping movements e.g. football, rugby, netball and basketball.
  • Unfortunately, the number of ACL injuries seen in clinics is increasing, particularly in young people under the age of 20 years old.
  • ACL injuries occur most commonly playing sport.
  • Sometimes other ligaments and/or structures in the knee can be damaged at the same time e.g cartilages.
  • A knee specialist can usually diagnose an ACL injury from a clinical assessment and an MRI scan helps to confirm the diagnosis.
  • Treatment options for an ACL injury need to be discussed carefully as not everyone requires an operation.
  • Whatever treatment is decided, physiotherapy is paramount to getting a good result.
  • Surgery for ACL injuries involves reconstructing the ligament and has been improved over the last 40 years. It is now done via a keyhole technique usually as a day case, under a general anaesthetic.
  • Injuring your ACL does put your knee at risk of early wear and tear (arthritis) in later life.
  • Prevention programs work and need to be implemented in the UK to help stop young people injuring their knees.

Anterior Cruciate Ligament (ACL) Reconstruction

Introduction – What is the ACL?

The ACL is one if the main structural ligaments, that controls the stability of the knee, particularly in pivoting and side-stepping movements – i.e. playing sports such as football, rugby, netball, as well as in dance and ballet. It also has important receptors (proprioceptors), within its tissue, that gives clever, involuntary feedback to the brain and hence help the muscles control the knee. It runs from the top of the notch in the femur (thigh bone), inwards and downwards to the front of the flat plateaux of the tibia (shin bone) (see picture 1).

Picture 1a – sketch of ACL Picture 1b – arthroscopic (keyhole) picture of normal healthy ACL

Picture 2a – twisting mechanism Picture 2b – ACL rupture at arthroscopy

Timing of Surgery

The timing of ACL reconstruction is variable depending on the individual situation. Factors that affect this timing include possible damage to other structures within the knee, particularly the meniscal shock absorbing cartilages and also making sure the knee has been prehabilitated by the physiotherapists ie: the knee is ‘ready’ for the operation.
The preoperative physio sessions are crucial to ensure that:
1. The swelling has settled
2. The range of movement has returned to normal
3. The muscles have been reactivated (particularly the quadriceps muscles)

History of ACL Surgery

In the late 1970s and early 1980s some of the pioneers of ligament surgery started off by trying to repair these ruptured ACLs by essentially stitching them back together. Patients stayed in hospital for a week after surgery, and were often in full leg plasters for up to 6 weeks ! We have come a long way with the development of keyhole techniques, day-case units, enhanced recovery and emphasis on early rehabilitation. In those early days, the results were not that good, with only about one third of patients getting better and developing a stable knee – this meant quite quickly repair techniques were abandoned, and reconstruction (i.e. removing the damaged ligament and replacing it with a graft) came strongly into favour. Reconstruction quickly became the main surgical option for this injury in the late 1980s and remains so today.

What is involved with the surgery ?

Over the last 30 years this ACL reconstruction surgery has been refined and improved tremendously. Nowadays we perform lots of these operations and generally it is a very good procedure – it is done essentially ‘keyhole’, takes about an hour to do, and patients go home the same day with crutches and a set of exercises to get the knee moving straight away. At the start of the operation, an examination under anaesthetic (EUA) reveals as very wobbly knee. (click here for a video showing a wobbly knee)

The first part of the operation is an arthroscopy (inserting a fibre optic camera) to look around and probe all the other structures within the knee to check they are normal and have not been damaged. This includes the articular surface cartilage of the joint (the smooth tissue that covers the ends of bones at joints), and the meniscal shock absorbing cartilages (the cartilages that absorb movement at the joint between the bones). Usually damage to these structures would be expected, as they are picked up on the MRI scan, but occasionally an associated injury is found at this time. Any issue identified can be dealt with there and then before beginning the ACL reconstruction.

(Please read my additional information leaflet on meniscal injuries and chondral injuries here)

In 90% of my patients (children and adults) I use a hamstring tendon graft to make a new ligament. We collect two of the hamstring tendons from the same leg and having made special tunnels in both bones, we thread the tendons across the knee, forming a new ligament. They are held in place by a special fixation device (endobutton) in the femur (thigh bone) and a screw in the tibia (shin bone) in order to make the tension nice and firm. We fold them over to make a 4-string graft that is as strong as the original ligament. When I repeat the EUA at the end of the surgery, the knee is rock solid stable.


Picture 3:

acl graft cartoon

4-String ACL Graft
sitting across the knee

What is the after care?

After waking up in the recovery your child will come back to the ward and rest with their leg elevated. At the end of the operation a wool and crepe wrap bandage is applied, snug but not tight. It should be worn for 48 hours and can then be reduced to a tubigrip dressing, which we give you to take home. The physios visit, and when ready, get your child up on crutches and confident hopping about. After they have been to the toilet successfully and have had something to eat and drink, you will be able to go home (usually a few hours post operatively). It is advised to elevate the leg on pillows for the first 72 hours and to start gentle exercises as recommended by the physios. Ice packs (frozen peas wrapped in a tea towel will do) can help significantly with reducing swelling, bruising and can help with pain relief. Ice packs should be used for 10 mins at a time several times a day. State of the art compression cryocuffs (ice duvets) are available to hire in the post-operative period. (Click here for details) You should give your child regular pain killers – Calpol and Ibuprofen together as per dosage instructions for at least 3-5 days.

What is the rehabilitation like after surgery?

Rehabilitation is a big commitment postoperatively and gaining a good relationship and mutual trust of your physiotherapist is as important as with your surgeon. The time commitment is substantial and prolonged (12-18 months) It is only suggested your child returns to contact sports (match fitness) when they have satisfied all the specific return to sport criteria. This includes a barrage of strength, balance and flexibility tests on both legs to make sure the risk of re-injury to the operated leg but also the good leg is minimised. Returning to sport prior to this or not following the rehabilitation course puts the knee at massive increase of reinjury.

It is important to see your child’s physio regularly to start with in the post-operative period. I see patients in my clinic at 6 weeks post op to check on early progress, go through my operative findings and pictures, and get check X-rays to look at the tunnel positions. Further reviews with X-rays are at 6 months and then 12 months post op to check growth areas and to make a formal return to sport plan.

What are the success rates of surgery?

As an honest UK knee surgeon, I tell all my families undergoing an ACL reconstruction the following:

  • the benefits of the surgery
  • the likely natural history of the condition if we were not to do the surgery
  • the non-operative alternatives
  • the risks involved (both general risks with any surgery and specific risks to ACL)
  • the likely success rates, particularly the chance of returning to pre-injury level sports

In my hands, 80% of my patients having an ACL reconstruction get back to their original pivoting sports. Regarding re-injury and re-rupture of an ACL graft, the overall percentage quoted in the literature is around 5% but, unfortunately this is significantly higher (up to 25%) in the adolescent high-risk patient group. The other unfortunate fact is regardless of treatment path (operative or non-operative) 50% of patients will have developed some signs of early wear and tear in their knees (arthritis) at 10 years post injury, and hence are likely to have ongoing symptoms and problems in the future.

The National Ligament Registry

This is a UK database for patients undergoing ACL reconstruction in our country. It was designed by surgeons to enable accurate documentation of type of surgery, and outcome of patients following surgeries.  These are called PROMs (patient reported outcome measures) Registries are powerful tools in medicine which help doctors to improve the care they can give to their patients. Although it is not compulsory, I strongly encourage my patients and families to allow us to enter your operative and follow up data. For more information visit the website, which is also a fantastic patient information resource.

What are the risks of ACL reconstruction ?

General Risks of any surgery:
  • Scars Everyone (100%) gets a scar and most fade over time. Some patients with particular skin types can develop bumpy scars.
  • Pain, Bruising and Swelling (~90%) Some slight discomfort and bruising is to be expected following every type of surgery. You will be given medication advice to control pain post operatively. Ice packs in the first 48 hours can help significantly. An increased pain response (complex regional pain syndrome) <1% has been reported in a few cases after ACL surgery but is very rare.
  • Numbness around the scars (~70%) Some local numbness around the scar is normal and as things heal, it usually improves with time.
  • Infection (1-2%) The wound sites may become infected. This usually settles with oral antibiotics. Very occasionally a further operation may be needed. Antibiotics are given at the time of the surgery and ‘deep’ infection within the knee joint is very rare. If this occurs a further operation would be required to wash out the joint.
  • Blood clots (Deep Vein Thrombosis) (<0.1% in children) These can occur in the lower legs following any surgery, although are almost unheard of in children under 16 years old.
Specific Risks to ACL surgery :
  • Graft rupture (5-25%) The graft may rupture after further (often minor) trauma. Further surgery may then be necessary. (revision reconstruction)
  • Growth Disturbance (dependant on age of patient) Any patient with growth remaining will be carefully monitored to check there is no uneven growth occurring.
  • Ongoing symptoms (mostly dependant on damage to other structures in the knee) Persistent swellings, pain or mechanical symptoms may require further exploratory arthroscopy if not settling after several months.
  • Early Arthritis – 50% at 10 years This is very dependent on lots of other variables, some controllable, some not.

I can’t emphasise enough how important it is to make sure we have gone through any questions you may have before we proceed with surgery.

In Summary:

  • Unfortunately, ACL injuries, particularly in youngsters are on the increase
  • We see lots of young people with these injuries, sometimes associated with other damaged structures within the knee e.g. shock absorber cartilages
  • Surgery is usually recommended for most young patients but not essential
  • Rehab takes about a year to get back into competitive match sports
  • Good pre- and post-operative physio plays as big a part in outcome as good surgery.
  • Preventing reinjury and damage to the other leg is also key in the future.


If you have any further questions, please don’t hesitate to contact us!

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    I had a knee arthroscopy to removed and clean up damaged cartilage after 6 years of repeated injury and dislocation from playing sport. I had been putting off the idea of surgery, but it was a great decision to finally get it seen to. I couldn't be happier with the results so far, and in less time than expected. Running, squats and climbing stair caused pain, and a lot more cracking than a 22 year old's knee should have! Now 2 weeks after the op, and following the physio exercises given after the operations, I am driving and climbing/ descending stairs without a problem and on the road to a full recover and hoping to get back to regular exercise within the next few weeks.

    I came to see you approximately four years ago and talked through the pros and cons of having an ACL replacement following an ACL rupture in my right knee I suffered playing an ill- advised game of beach volley ball on holiday in Antigua. I went ahead with the operation which you successfully performed at the Dunedin Hospital in Reading, I got on with my rehab and I now just wanted to let you to know that I will be running the London Marathon in three weeks (and raising money for Whizz-Kidz a disability charity for young people.) This letter is just a belated thank you for enabling this to happen.

    Mr Davies is a fantastic surgeon he put in a half knee joint in my right knee I have no problem with it ever since the operation in August last year. I have no more pain in my knee at all. I would recommend him to anyone.

    Mr Nev Davies has a very pleasant manner and was easy to talk to. The service provided was efficient, quickly identified the problems I had and was able to recommend treatment close to where I live.


    • General Medical Council (GMC) Membership
    • Royal College of Surgeons of England (RCS(Eng.))
    • British Medical Association (BMA)
    • British Orthopaedic Association (BOA)
    • British Society of Children's Orthopaedic Surgery (BSCOS)
    • British Association of Surgery of the Knee (BASK)
    • AO European Trauma Group
    • British Orthopaedic Sports Trauma and Arthroscopy Association (BOSTAA)