ACL for web by gegeshandong



There are 2 cruciate ligaments inside the knee joint (anterior and posterior – so named because they
cross each other as they pass through the joint). They are found inside the capsule (the outer lining) of
the knee joint (but lie outside the inner synovial membrane so are not bathed in synovial fluid).

The anterior cruciate ligament (ACL) is one of the major stabilisers of the knee and is one of the most
commonly injured structures. It lies in the centre of the joint so cannot be palpated directly and its
primary function is to prevent forward shearing and/or inward rotation of the tibia. Individuals who
sustain an injury of the ACL often complain of signs of instability or of the knee 'giving way' during
changes of direction (often with the foot planted while the individual turns in the direction of the
                                                 injured knee) or sudden deceleration or acceleration
                                                 (anterolateral rotatory instability).

                                                 The ACL is attached from the top of the tiba, passing
                                                 upwards, backwards and laterally to attach to the
                                                 underside of the femur. In the image the ACL can be
                                                 seen laying in the centre of the joint one the patella has
                                                 been removed.

                                               Detailed anatomical inspection reveals the ACL is
                                               composed of 3 primary bundles. Each bundle will resist
                                               anterior translation to a greater or lesser extent at
                                               different points in range (e.g. the posterolateral bundle
                                               resists anterior translation mainly at 30 degrees of knee
                                               flexion whilst the anteromedial bundle is the primary
restraint to movement with the knee flexed to 90 degrees).

The ACL has a significant blood supply (from the genicular
arteries) – hence rupture of this ligament will invariably
lead to a significant haemarthrosis (blood inside the knee
joint) – immediate or very quick (within minutes) swelling
of the knee is a characteristic sign of an acute rupture of
the ACL.

Both cruciate ligaments do receive a small nerve supply
from the tibial and common peroneal nerves –
proprioceptors have been repeatedly observed and
occasionally nociceptors have also been identified. Pain is
not usually a dominant feature ACL injury due to its poor
nerve supply – in many cases subjects may develop ACL
failure and be totally unaware of it ever having occurred –
this is sometimes an incidental finding when examining the knee for other pathologies.

Causes of Injury

Injuries of the ACL can occur as a result of contact from an external force (extrinsic injury - e.g.
hyperextension of the knee or being tackled from behind whilst playing football) or due to internal
stress from sudden deceleration or cutting maneuvers forcing the joint into abnormal torsional positions
(intrinsic injury - e.g planting the foot to suddenly change direction and the studs stick in the ground
blocking movement of the lower leg).

                                                       Irrespective whether the cause is an extrinsic or
                                                       intrinsic injury the ACL may be partially or
                                                       completely torn and the ensuing signs and
                                                       symptom will in part depend upon the extent of the


                                                      Clinically the injuries of the anterior cruciate
                                                      ligament are suspected when there been a history
                                                      of rotational or hyperextension trauma. This may
                                                      be either a contact or a non-contact injury. The
subject may describe pain at the time of the injury but, due to the insensitivity of the ACL. This is not
often the case unless other secondary structures are also injured. A sudden development (within an
hour) of tense swelling of the knee is common for a traumatic ACL rupture but some individuals who
develop a gradual fraying of the ACL as a result of repeated low load injuries may have little or no

Typically, individuals will complain of instability, in particular when running and turning. This is known as
‘antero-lateral rotational instability’. Occasionally, there may be locking of the knee if the torn stump of
the ACL moves in between the joint surfaces.

The ACL may be either partially or completely ruptured.

Clinical assessment can involve a number of tests to assess the integrity of the ACL:-

        Anterior draw test – the affected knee is flexed to 90 degrees. The clinician then pulls the tibia
        forward – an anterior slip of the tibia would indicate a partial or complete tear of the ACL. This
        can be modified to increase or decrease loading of secondary restraints. The result can be grade
        from grade I (up to 5mm greater draw when compared to the uninjured side), grade II (5 to
        10mm greater draw when compared to the uninjured side), grade III (more than 10mm greater
        draw when compared to the uninjured side).

        (For videos of the anterior drawer test click here

        Lachman test – the knee is held at 30 degrees of knee flexion and the tibia is drawn anteriorly.
        An anterior slip of the tibia is suggestive of a partial or complete tear of the ACL. This is often
        graded based on the degree of anterior slip – Grade I - up to 5mm more slip compared to the
        injured side, Grade II -5-10mm more anterior slip than the uninjured side, Grade III –greater
        than 10mm anterior more than the uninjured side. Variants of the Lachman’s test have been
        also described (such as the Alternative Lachman Test, Drop Leg Lachman Test or the Prone
        Lachman Test) and suggested as demonstrating greater sensitivity.

        (For videos of the Lachman test click here

        A more complex test is called the pivot shift test, in which greater stresses are put on the knee
        as it is straightened by the clinician from a bent and inwardly rotated position. If the knee
        "gives," this is an indication that other stabilizing structures inside the knee must be torn
        besides the ACL. This test can sometimes only be done when the knee is completely relaxed.
        Because of this it may best be observed under anesthesia during the surgical procedure.

        (For videos of the Pivot Shift test click here

Recent biomechanical evidence would suggest that the Anterior Draw test and Lachman test assess
different bundles of the ACL – as the anteriomedial bundle is under greater tension when the knee is
flexed to 90 degrees the anterior draw test is most significant in assessing this section, where as the
Lachman test is more indicative of injury of the posterolateral or intermediate bundles (for an excellent
review of ACL biomechanics see Amis and Dawkins, 1991 (

Confirmatory diagnosis can be made by either arthroscopic assessment (keyhole surgery) or MRI
(magnetic resonance imaging) scans.

Early diagnosis is important to reduce the likelihood of damage to secondary restraints and early
implementation of a suitable management strategy.


As describe above, pain may not necessarily be an indicator of ACL injury as the ligament is relatively
insensitive with few or no pain nerve endings (nociceptors). The classic symptoms an individual will
describe are those of instability – the knee will ‘give way’ when loaded and the individual is twisting.
Swelling may also be significant if the injury is a single event macrotrauma – this is a tense swelling
which, when aspirated often contains blood (haemarthosis). Multiple microtraumas to the ACL usually
leads to a small amount of swelling (effusion) within the knee and there may be no identifiable
mechanism of injury.

Intermittent locking may also occur if the stump of the torn ACL should fall in between the articular

Some individuals may have no symptoms – it has been reported that up to 1/3 of individuals with ACL
deficiency have no subsequent loss of function (click on the links below for key articles by F.R. Noyes)


Whilst until relatively recently it was considered that the only option was that reconstruction was the
most appropriate course of action even in the absence of any signs of instability to avoid the
development of osteoarthritic changes. However, there is a significant lack of evidence that early
reconstruction prevents arthritic changes.

It has been shown that individuals sustaining an injury or rupture of the ACL typically fall into one of 3
groups (see Noyes 1983). 1/3 of subject will have little or no symptoms (copers), 1/3 can avoid surgical
intervention if activities are modified (adapters) – e.g. stop playing sport involving twisting, 1/3 will
require surgical intervention usually involving reconstruction (non-copers).

There are 3 basic options in the management of the ACL deficient knee:-

Conservative management

Once the knee has settled down from the injury, this requires an intensive rehabilitation programme to
regain full movement, strength, flexibility and co-ordination. Progression should be staged to avoid
further injury and sport should only be resumed when strength is equivalent to the uninjured leg and
there has been no evidence of instability. You may find that you progress to a certain level and cannot
move on thereby having to limit some activities in the future.

Wait and see approach - In this case you may consider surgery in the future if necessary. A conservative
protocol will be initiated but if there is any episode of instability then reconstruction occurs. The
advantage of this approach is that you will not undergo surgery unnecessarily however, there is always
the risk that the episode of instability that promotes surgery, may cause further damage in the joint. The
disadvantage of this approach is that you may spend months in rehab only to find that you need surgery
anyway, thus increasing the time from injury to full recovery. The fact is, that the higher the level of
activity you want to participate in, the higher the likelihood you will eventually require surgery.
Immediate reconstructive surgery - It is now generally accepted that even if the preferred course of
action is surgery, it is advisable to wait until the acute post-injury phase has settled - usually 4-6 weeks.
Post-operative recovery will be easier if the swelling in the knee has gone, if there is full movement and
reasonable muscle control. Professional sportsmen and women will usually take this option primarily
because they need to be back playing in the shortest possible time. They cannot afford to spend 3-4
months in rehab only to find that the knee gives way as soon as they start serious training.

Which option is right for you? You may be given conflicting advice but ideally you should understand the
alternatives and be able to make your own informed choice. Unfortunately, in the real world, options
may be limited by availability and accessibility of surgery.

Copers and Adapters

These groups often require conservative management to maintain stability and re-education of the
knee. Emphasis is often placed on strengthening the hamstring group more than the quadriceps as their
tone can maintain the tibia in a correct alignment during dynamic activities.

Modification of activities may be necessary if the individual complains of recurrent instability on
rotational activities. Co-ordination activities

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