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Anterior Cruciate Ligament (ACL) Injury
The anterior cruciate ligament (ACL) is a cruciate ligament
which is one of the four major ligaments of the human knee.
In the quadruped stifle (analogous to the knee), based on
its anatomical position, it is referred to as the cranial
cruciate ligament.
The ACL originates from deep within the notch of the distal
femur. Its proximal fibers fan out along the medial wall of
the lateral femoral condyle. There are two bundles of the
ACL—the anteromedial and the posterolateral, named according
to where the bundles insert into the tibial plateau. The ACL
attaches in front of the intercondyloid eminence of the
tibia, being blended with the anterior horn of the lateral
meniscus. These attachments allow it to resist anterior
translation of the tibia, in relation to the femur.
The ACL is important in maintaining stability in the knee
during dynamic activities such as cutting, turning, pivoting
and changing direction. The ACL prevents the anterior
translation of the tibia beneath the femur.
An anterior cruciate ligament, or ACL, injury is a tear in
one of the knee ligaments that joins the upper leg bone with
the lower leg bone. The ACL keeps the knee stable. See a
picture of the knee and the ACL.
Injuries range from mild, such as a small tear, to severe,
such as when the ligament tears completely or when the
ligament and part of the bone separate from the rest of the
bone.
Without treatment, the injured ACL is less able to control
knee movement, and the bones are more likely to rub against
each other. This is called chronic ACL deficiency. The
abnormal bone movement can also damage the tissue (cartilage
) that covers the ends of the bones and can trap and tear
the pads (menisci) that cushion the knee joints. This damage
can lead to osteoarthritis.
Sometimes other knee ligaments or parts of the knee are also
injured. This includes cartilage such as the menisci , or
bones in the knee joint, which can be broken.
Your ACL can be injured if your knee joint is bent backward,
twisted, or bent side to side. The chance of injury is
higher if more than one of these movements occurs at the
same time. Contact (being hit by another person or object)
also can cause an ACL injury.
An ACL injury often occurs during sports. The injury can
happen when your foot is firmly planted on the ground and a
sudden force hits your knee while your leg is straight or
slightly bent. This can happen when you are changing
direction rapidly, slowing down when running, or landing
from a jump. This type of injury is common in soccer,
skiing, football, and other sports with lots of stop-and-go
movements, jumping, or weaving. Falling off a ladder or
missing a step on a staircase are other likely causes. Like
any other body part, the ACL becomes weaker with age. So a
tear happens more easily in people older than age 40.
Symptoms
Hearing a "Pop":
People who suffer an ACL tear usually report hearing a
"pop" at the time of the injury. Most people are
surprised at how loud this can be, and many bystanders
have heard this from the sideline of a football or
soccer game. Even if you don't hear the pop, usually
people will feel the sudden shift in the joint.
Knee Giving Out/Instability:
The ACL is critical to the stability of the knee joint,
and when an ACL tear occurs, the joint is usually
unstable. This means that the knee joint has a tendency
to give out. Giving out or instability usually occurs
with cutting or pivoting movements common in many
sports. However, in some patients with an ACL tear,
instability can occur with even simple movements while
walking or getting into a car.
Swelling and Pain:
Swelling of the knee joint occurs in almost all patients
with an ACL tear. This swelling is usually quite large,
and occurs rapidly -- within minutes -- of the injury.
The swelling that occurs with a torn ACL is actually a
hemarthrosis, meaning the knee joint is filled with
blood. The ACL has a blood vessel within the ligament
that is torn at the time of injury, causing the knee to
fill with blood.
Pain associated with an ACL tear is common, although can
vary depending on associated damage in and around the
knee joint. Much of the pain of an ACL tear is due to
the swelling of the joint.
Diagnosis
Your doctor can assess the ligaments of your knee with
specific tests. The most commonly used tests to determine
the presence of an ACL tear include:
-
Lachman Test
The Lachman test is performed to evaluate abnormal
forward movement of the tibia. By pulling the tibia
forward, your surgeon can feel for an ACL tear.
-
Pivot Shift Maneuver
The pivot shift is difficult to perform in the
office, it is usually more helpful in the operating room
with a patient under anesthesia. The pivot shift
maneuver detects abnormal motion of the knee joint when
there is an ACL tear present.
Test Results:
Your physician will also evaluate x-rays of the knee to
assess for any possible fractures, and a MRI may be ordered
to evaluate for ligament or cartilage damage. However, MRI
studies may not be needed to diagnose an ACL tear. In fact,
the physical examination and history are just as good as a
MRI in diagnosing an ACL tear!
Although people often refer to the surgery as an "ACL
repair," it is better called an "ACL reconstruction." The
anterior cruciate ligament, once completely torn, cannot be
repaired. The options for ACL reconstruction are:
-
Using the central 1/3 of the patellar tendon, the tendon
connecting the knee cap (patella) to the shin bone
(tibia), to fashion a new ligament. When the graft is
'harvested,' a piece of the bone of the patella and
tibia is also taken. Thus the attachments of the tendon
to the bone are not disturbed. When the graft is placed
into the knee, this allows for 'bone to bone healing.'
This is felt by many surgeons to be the most secure
graft type. The primary disadvantage is knee pain
following the surgery; this may persist for years.
-
Using a portion of the hamstring tendon. The hamstring
muscle group (in the back of the thigh) has tendon to
spare. Some of the tendon can be harvested to create a
graft. The advantage of the hamstring tendon is that
there is less disturbance in harvesting the graft, and a
much lower incidence of knee pain after surgery.
However, many surgeons question the stability of this
graft.
-
Finally, many patients now opt for donor tissue grafts.
These usually use the patellar tendon of a cadaver,
similar to using your own as described above. The
problem with this is the sterilization process that
kills the living cells of the graft. This means the
healing time of the graft is longer and less reliable.
There is a very small risk of infection, as is the case
with any donor tissue. The advantage is that this
procedure can be done entirely arthroscopically, and
there is much less post-operative pain.
The best decision for ACL surgery varies from person to
person and surgeon to surgeon. It is important to discuss
the ACL reconstruction options with your doctor. Your
surgeon may have a preferred technique and it is important
to take that into consideration. Most studies show little
difference between the patellar tendon and hamstring grafts
in the long run. The donor tissue grafts are slightly less
reliable, but because it involves a smaller surgery, and
none of the complications associated with graft harvesting,
many patients still prefer this method for ACL
reconstruction.
After anterior cruciate ligament (ACL) surgery, move
your ankles up and down an average of 10 times every 10
minutes. Continue this exercise for two to three days to
help blood circulation and to prevent blood clots from
forming in yourlegs. If you develop acute pain in the back
of your calf, tell your doctor. This could be an early sign
of clots.
-
Elevate leg - Keep your operated leg elevated at
a minimum of a 45-degree angle. Prop your leg on
cushions or pillows so your knee is at least 12 inches
above your heart for the first three to five days after
surgery. Keep your leg elevated if your knee swells or
throbs when you are up and about on crutches. Don't put
pillows behind your knee because this limits motion of
the knee. Place pillows under your heel and calf.
-
Take pain medication - Expected pain and
discomfort for the first few days. Take pain medications
as your doctor advises. These could be over-the-counter
painkillers, such as ibuprofen or acetaminophen, or
stronger narcotic drugs.
-
Bend knee - Slowly begin bending your knee.
Straighten your leg and bend your knee. If necessary,
place your hands behind your knee for assistance bending
your knee. The goal is to achieve a range of motion of 0
to 90 degrees by the time you return for your first
post-operative visit a week after surgery.
-
Monitor for fever - A low-grade fever — up to 101
degrees Fahrenheit or 38.3 Celsius — is common for four
or five days after surgery. If your temperature is
higher or lasts longer, tell your doctor. Your
temperature should go down with acetaminophen.
-
Remove bandage - The dressing on your knee is
usually removed the day after surgery. There may be some
minor fluid drainage for two days. Sterile dressings or
bandages may be used during this time. After surgery,
keep the wound clean and dry. Take sponge baths until
the sutures are removed.
Rehabilitation
Your rehabilitation program to restore range of motion to
your knee begins the moment you wake up in the recovery
room. During the first week after surgery, most patients are
encouraged to lift their legs without assistance while lying
on their backs. These are called straight leg raises.
By the end of the second or third week, patients usually
walk without crutches.
Sessions with a physical therapist usually begin seven to 14
days after surgery. During physical therapy, weight bearing
is allowed if you did not have a meniscus repair.
A range of motion of 0 to 140 degrees is a good goal for the
first two months.
Don't work your quadriceps early on because this can stretch
the ACL graft. Stationery bike riding or lightweight leg
presses are recommended during the first three months after
surgery. These exercises strengthen the quadriceps while
using the hamstrings to protect the ACL graft.
Don't swim or run for five months. You can swim with your
arms, without paddling your feet, at about two to three
months after surgery.
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