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Anterior Cruciate Ligament Reconstruction


For knee injuries to reconstruct the anterior cruciate ligament (ACL), this website aims to give you information on the ACL structure and function, what an operation entails including postoperative rehabilitation. After reading this information if you have any further questions please contact us.

What is the ACL?

The cruciate ligaments are a pair of extremely strong, thick ligaments in the centre of your knee joint. You have an anterior cruciate ligament and a posterior cruciate ligament (PCL) and they form a cross, this is where the name cruciate is derived. The ACL lies in front of the PCL running from the outer aspect of the femur (thigh) to the inner aspect of the tibia (shin). The direction of the fibres is as if you had your hands in your pockets.

Functions of the ACL
The primary functions of the ACL are;

  • To prevent forward translation of the lower leg (tibia) on the femur (thigh)
  • To control outward rotation of the lower leg when you have your knee in a bent position
  • Helps to control the small rolling and gliding movements that occurs in the knee to allow for smooth motion

ACL Injury

If the ACL is injured excessive movement occurs with the lower leg moving forward and outwards when the knee is flexed. This will lead to the knee 'giving way' or 'collapsing' on any activities that involve twisting or turning. ACL tears can often go undiagnosed as, although the knee is swollen and painful immediately following the injury, this often resolves over 5-10 days. After this period of recovery there may be no pain but a feeling of instability with any attempted return to sports with activities such as sudden changes in direction or stopping suddenly.

At the time of injury other structures may have been damaged; most commonly this is the meniscus ("cartilage"), other ligaments or the smooth articular cartilage that covers the end of the femur or tibia. If you have sustained other damage within the joint it may lead to a less optimal outcome.

No matter how successful the operation, it is important to understand that surgery to reconstruct your ACL cannot give you a normal knee, as it can never truly replicate the ACL that you had anatomically and physiologically. However surgical reconstruction can allow you to function normally and return to sports with no instability or risk of further damage to structures inside the knee.

At present there is no evidence that ACL reconstruction decreases the incidence or progression of degenerative change (osteoarthritis). However by stabilising the knee and reducing further damage to articular cartilage and meniscus it is reasonable to assume that the ACL reconstruction may have a protective effect.


An MRI (magnetic resonance imaging) scan is not absolutely essential to diagnose an acute ACL tear as an accurate and detailed history and clinical examination is more reliable. MRI can however confirm the diagnosis and give additional information on injuries to other ligaments and structures within the knee. On MRI the ACL appears as a uninterrupted dark band. If damaged there is disruption or complete absence of this band. Although there is good correlation for diagnosis MRI scanning is not 100% accurate. Occasionally an examination under anaesthetic and arthroscopy ("keyhole surgery") is necessary to confirm the diagnosis of ACL rupture and, more importantly, assess the extent of injury.

The scan on the left shows an intact ACL on MRI. This is the black structure in the centre of the picture running diagonally upwards from left to right. The scan on the right demonstrates a complete rupture of the ACL.

Surgical procedure

The ACL will not heal itself and it is not currently possible to repair a torn one. Therefore, an alternative tissue must be used to replace it.

There are 3 main types of grafts available:

  • Using the patient's own tissues (autograft)
  • Using another person's tissue (allograft)
  • Using artificial material

Using the patient's own tissue is by far the preferred way. However there may be times when this is not possible and this would be clearly explained if necessary.

The two choices for graft tissue are:

Hamstring tendon graft (the gracilis and semitendinosus tendons)
Kneecap (patella) tendon graft

The hamstring tendon graft is usually the preferred graft choice for a number of reasons. It does not disrupt the mechanism by which the knee is straightened. It has been shown to result in less post-operative pain over the front of the knee, less discomfort when kneeling post-operatively and a reduced loss of full extension (straightening) of your knee. The hamstring graft also more closely reproduces the forces of an intact ACL.

The hamstring tendons used can be felt on the inner aspect of the thigh at the back of the knee. You will manage perfectly well without them and in fact research now shows that they grow back to some extent.

Surgery to reconstruct the ACL is carried out via an arthroscopy and a small incision on the inner aspect of your lower leg just below your knee. The arthroscope allows additional surgery (i.e. trimming of meniscal ("cartilage") tears) to be performed at the same time

Most ACL reconstructions are performed under general anaesthetic although the procedure can be undertaken under "local" or "regional" anaesthesia. In most patients the knee is not put into plaster or braced at any time after surgery.

Timing of reconstruction

Often patients, especially if sporty, are keen to proceed with reconstructive surgery immediately after injury. They feel this will lead to earlier return of function. Unfortunately this is not so. The best results of surgery are gained after full rehabilitation of the knee prior to surgery, so as to regain a full range of motion, especially straightening, and good quadriceps strength. This will minimize the potential risk of post-operative stiffness. The optimum time from injury (or arthroscopy) to reconstructive surgery is 4-6 weeks. This time may be longer if other structures are damaged. In this time it is important to understand that although the swelling decreases and movement returns in this period, the ligament will not heal. The knee is unstable and at risk of further damage if high risk sports involving pivoting are attempted.

The day of surgery

You will come in on the day of your surgery having starved (i.e. no food or liquids) for approximately 6 hours prior to your anticipated surgery time. Nursing staff and a physiotherapist will assess you, explain post-operative procedures and measure you for crutches. You will also be requested to complete some questionnaires relating both to your general health as well as your knee.

Your Surgeon will examine your knee to ensure it is ready for surgery. He / she will also mark the leg to be operated on. This is also your chance to ask any last minute questions. The anaesthetist will visit you to explain the anaesthetic and post-operative pain control.

The immediate period after surgery

You will wake up from the anaesthetic in the recovery area of the operating theatre. The knee will be in a tight bandage and you will have a blue Cryocuff sleeve on top. The Cryocuff contains ice cold water and helps control swelling of the knee in the early post-operative period. Your leg will also be placed on a continuous passive motion (CPM) machine in the recovery ward. This machine slowly flexes your knee up to 900 and aids the early movement of the knee after surgery. On return to the ward, you will rest until the following day on the CPM.

The next day all attachments are taken down i.e. drips, patient control anaesthesia, CPM etc. and the dressing on your knee is reduced to allow you to start your exercises. The physiotherapist will instruct you on exercises to gently flex the knee, gain full hyper-extension (straightness) and strengthen your quadriceps. You will walk with the aid of crutches putting as much weight through your operated leg as is comfortable. There is no limitation to weight bearing and you will not require a brace. The Cryocuff sleeve remains on while at rest and is removed for exercises and mobilising.

You are normally in hospital for 1 night and discharged when you are safe with crutches and your Consultant is happy with the range of movement of your knee. In this early phase you will continue with the exercise you were taught in hospital. These exercises are vitally important for the best possible results.

You are advised to continue using the Cryocuff at home until you return to clinic approximately 10-14 days after surgery for removal of any sutures or clips. You are referred to start outpatient physiotherapy at this time.

In this initial 10-day period after surgery it is quite common to experience bruising and swelling in the calf, the front of the shin or inner thigh from the site of your hamstring graft. This can appear quite alarming but is not serious. You may also experience some numbness over the front of the shin or around the scar; this is normal and sensation will usually return over a period of time.

Rehabilitation and physiotherapy

Physiotherapy is vitally important if there is to be a successful outcome of the ACL reconstruction. It takes a great deal of effort, commitment and time. If you do not feel you can commit yourself fully, it is probably best not to undergo the operation, as you will have less favourable result.

In general, a brief outline of stages and goals after the reconstruction are;

  • Protected movement for weeks 1-6
  • Gym activities and swimming for weeks 6-12
  • Light jogging and golf at 3-4 months
  • Non-contact sports training at 6 months
  • Full return to contact sports at 9 months

Associated with this document is also a guide to your rehabilitation protocol. Progress after the reconstruction is based on the time involved in the formation and maturation of the new ligament and on functional goals. All patients advance at different rates but the time factors are the average basis upon which progression is made. Progression too early may jeopardise your new ligament and cause it to rupture. At all stages you should be guided by your Consultant or Physiotherapist. If you have any specific queries about your rehabilitation please contact either your Consultant or your Physiotherapist.

Please be aware that this protocol relates only to a standard "isolated" ACL reconstruction. If there is other ligament or cartlidge damage, the rehabilitation may vary from this protocol.

Brief Rehabilitation Protocol
Associated with this document is a detailed rehabilitation protocol relating to ACL reconstruction.  However a precis of the protocol is as follows:

Stage 0- prior to surgery
It is crucial that prior to an ACL reconstruction the knee is fully rehabilitated.  There should be no significant effusion (swelling of the knee), the muscle tone should be good and there should be a full range of movement including full hyperextension and flexion.

Stage 1 (0-2wks)
The main objective in the initial two week period after surgery is to reduce swelling, regain muscle control, restore a normal walking pattern and regain the ability to extend and flex the knee.  Use of Cryocuff for cold compression very useful and beneficial.  Aim to acheive short regular periods of exercises (little and often) rather than in one period of the day.

You will walk with crutches initially, gradually increasing weight bearing on the knee and try to walk without a limp.  It is crucially important to be able to fully extend and lock your knee as soon as possible.  This helps the quadriceps muscle above the knee to pump blood and reduce swelling as well as enabling a normal walking pattern.  Exercises include static contractions of the quadriceps, gentle bending as well as hamstring and calf stretches.

Stage 2 (2-6 weeks)
Now the aim is to stop using crutches, gain confidence and strengthen the knee whilst restoring full movement, especially extension.  You can use a static bicycle with no resistance, continue quadriceps strengthing and hamstring curls with no resistance.

Stage 3 (6-12wks)
Upto now the knee has only been bent, straightened and the swelling reduced.  The graft fixation has now begun to occur biologically and is thus a little stronger than in the initial six weeks.  You will now be able to progress to proprioceptive training to help improve balance and co-ordination.  Proprioception effectively means co-ordination.  At this stage the exercises will include wobble boards and the mini-trampet.  At the  gym you can swim, using a static bicycle and the leg press.  At the same time progressive quadriceps and hamstring strengthening will continue.

Stage 4 (3-6mths)
You can continue in the gym, gradually stepping up intensity.  Continue with proprioception and agility skills ie hopping in several directions.  Start light jogging on a treadmill  when sufficient strength and control of the knee has been acheived.  Return to golf starting with the driving range at about 4 months after the reconstruction.

Stage 5 (6-9mths)
Return to short specific training in a non-contact fashion.  Use the 3 months to increase your level of fitness and be in good condition to compete when you are able to return to full sports after 9 months.

Stage 6 (9-24mths)
Although you should safely be able to return to contact sport activities at 9 months after your reconstruction, it is important to continue with the exercises as outlined above, especially the proprioceptive work.  Many professional sports persons note that although they can return to sport at 9 months, they do not feel fully rehabilitated until 24 months have passed as they learn to use the knee again.

Possible risks & complication

There is no surgical procedure that is free from complications.  ACL reconstruction, especially recently, has a very good record of safety and success, but complications can occur.  These can include:

  1. Stiffness of the knee.  The knee may have difficulty gaining full extension or flexion.  This is reduced with early physiotherapy and a great deal of effort from the patient.  Sometimes it may be necessary to manipulate the knee under anaesthetic or carry out an arthroscopy to break down adhesions if the knee does become stiff.
  2. Persistent pain over the front of the knee.  There may be persistent numbness on the inner aspect of the leg, or the front of the leg, and rarely an area develops tiny "shocks" when lightly touched.
  3. Persistent swelling of the knee
  4. Deep venous thrombosis (DVT).  Heparin is giving routinely to avoid DVT.  Unless the procedure is an emergency, patients should not be taking the oral contraceptive pill for 6 weeks prior to surgery.  Finish your current pack and take other contraceptive precautions until after your operation.  It is also advisable not to take HRT at the time of surgery.  Please ask for advice if necessary.
  5. Infection of the knee.  This is a rare but extremely serious complication.  Antibiotics are given during and shortly after the operation to minimise the risk.
  6. Failure of the graft.  The knee may start to give way again.  This may occur within a short time of the operation or after a considerable period.  The 5 year success rate in preventing instability is approximately 90%.

Please contact the hospital at which you underwent surgery if you are at all concerned that there is a problem.  In particular, act immediately if you develop a fever, severe pain or significant wound problems.

If you have any questions about ACL repair, please ask your consultant.

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