The anterior cruciate ligament (ACL) is one of the main restraining
ligaments of the knee (see anatomy).
The ACL is sited in the centre of the knee and runs from the back
of the femur to the front of the tibia and acts to prevent excessive
forward movement of the tibia. The Anterior cruciate ligament’s
main role, however, is to keep the knee stable during rotational movements
like twisting, turning or side-stepping activities.
Injuries to the ACL typically occur during a non-contact twisting
movement and a popping sensation can often be felt or heard. Immediate
swelling often occurs due to bleeding into the knee (a haemarthrosis).
Other injuries to the knee can occur at the same time including meniscal
tears (cartilage) or damage to the joint surface.
The ACL also provides important information to the muscles around
the knee (proprioception), which are involved in protecting the knee
during activities. These ‘balancing’ mechanisms are reduced
when the ACL is injured although some of this function can be restored
with an appropriate exercise programme supervised by a sports physiotherapist.
If the ACL is torn the knee is likely to give way with twisting activities
and if this is associated with knee swelling, it is likely that damage
has been done to the joint surface and/or meniscal cartilage. Continued
damage will eventually result in osteoarthritis.
« An MRI scan of a normal ACL»
« An MRI scan of a torn ACL»
« An arthroscopic view of a torn ACL »
Anterior Cruciate
Ligament (ACL) Symptoms
The symptoms of patients with an injury to the ACL include a feeling
of instability or giving way. They may involve swelling and pain.
Typically this will be with twisting activities, however a small proportion
of patients become so unstable that even simple activities may cause
giving way. There are also a small proportion of patients who are
able to return to pivoting activities without giving way.
Anterior Cruciate
Ligament (ACL) Diagnosis
A ruptured ACL can normally be diagnosed from the history of the injury
and confirmed with specific tests at the time of your examination.
The diagnosis can be difficult in some cases (especially fresh injuries
where examination may be too uncomfortable and those with other injuries
to the knee); in these cases the diagnosis can usually be confirmed
by MRI scan. A torn ACL cannot be seen on x-ray.
Anterior Cruciate
Ligament (ACL) Treatment
Surgery is not required for all ACL injuries. Some patients with this
injury choose to alter their lifestyle in order to avoid activities
which make the knee give way. A small proportion of patients are able
to continue with their activities without major problems. These "copers"
are typically (but not always) patients with lower physical activity
levels, who do not participate in pivoting/twisting activities.
Conservative treatment of an ACL injury involves a supervised physiotherapy
programme concentrating specifically on:
Strength – all muscles around the knee must
be strengthened especially the hamstrings. These muscles can then
take over some of the ACL’s role in knee stability.
Balance and proprioception - as the ACL has
an important role in providing information to the muscles and
brain about the position of the knee joint, specific re-training
of other nerves is performed to help compensate.
Functional Knee Braces are sometimes prescribed to
help patients with damaged ACL’s. Their benefits are not fully
understood although they may help with proprioception (see above).
They are expensive and may not provide much in the way of support
to knee stability.
Anterior Cruciate
Ligament (ACL) Surgery
« An animation of ACL reconstruction»
« Roll your mouse over the image to start
the animation again »
Following an ACL rupture your surgeon may decide, after discussion
with you, that reconstruction is appropriate.
ACL reconstruction is the commonest ligament reconstruction performed
around the knee. ACL reconstruction is an attempt to replace the stabilizing
function of the anterior cruciate ligament. The ACL reconstruction
procedure involves removing the remains of the damaged ACL and replacing
it with another form of soft tissue, called a graft.
A number of grafts are available for use to replace the ACL.
The two commonest graft techniques are to use two “hamstring
tendons” – the semitendinosus and gracilis muscle tendons
– or a so called BTB (bone tendon bone, or patella tendon graft).
The preference of the Yorkshire Knee Clinic Surgeons is to use hamstring
grafts as first choice. The evidence in the medical literature is
that there is little or nothing to choose between these two main grafts
in terms of results.
Other grafts are available in more unusual situations.
« An arthroscopic view of an ACL graft
»
Anterior cruciate ligament reconstruction is usually performed using
arthroscopic (keyhole) surgery. There is however a small (4 to 5 cm)
incision below the knee where the tendons for the graft are harvested
from. The basic technique of anterior cruciate ligament reconstruction
is to identify the correct insertion points on the femur and tibia
for the ACL. At these insertion points tunnels of an appropriate size
to match the graft are drilled through the bone. The graft is then
pulled up through the bone and is secured using either screws, pins,
staples or other specialised anchoring devices.
ACL reconstruction may be performed either as day case or overnight
surgery.
In patients who are having the operation for appropriate reasons and
who comply with rehabilitation (6-8 months), there is a 90 to 95%
chance of a good result: that is, where stability is restored enough
for the patient to undertake activities, including sports, that they
were previously unable to.
Complications include infection (<1% significant), nerve damage
(a numb patch of skin, quite common over a small area, but rarely
a problem), stiffness (uncommon) and failure of the graft due to re-injury
or unexplained failure.
