The Anterior Cruciate
Ligament (ACL) is the most commonly injured ligament of the knee. The
ligament is most commonly injured during an athletic activity. Due to the
fact that sports are an increasingly important part of day to day life in
the United States, the number of ACL injuries have steadily increased over
the past few decades. This injury has received a great deal of attention
from orthopedic surgeons over the past 15 years and very successful
operations to reconstruct the torn anterior cruciate ligament have been
invented.
Anatomy
Remember that the ACL controls how far forward the tibia
moves in relation to the femur. If the tibia moves too far the ACL can
rupture. The ACL is also the first ligament that becomes tight when the
knee is straight. If the knee is forced past this point, or hyperextended,
the ACL can also be torn. This tearing of the ligament results in the loud
pop and the feeling of instability in the knee. The ACL may not be the
only ligament injured when the knee is twisted violently, such as in a
clipping injury in football. It is not uncommon to see both the medial
collateral ligament (MCL) and the ACL injured.
Causes
The major cause of injury to the ACL is sports related. The types of
sports which have been associated with ACL tears are numerous. Those
sports requiring the foot to be planted and the body to change direction
rapidly (such as basketball) carry a high incidence of injury. Football,
of course, is frequently the source of an ACL tear. Football combines the
activity of planting the foot and rapidly changing direction AND the
threat of bodily contact. Downhill skiing is another frequent source of
injury, especially since the introduction of ski boots that come higher up
the calf. These boots move the forces caused by a fall to the knee rather
than the ankle or lower leg. The ACL injury usually occurs when the knee
is forcefully twisted, or hyperextended. Many patients recall hearing a
loud pop when the ligament tears, and feel the knee give away.
There has been a dramatic increase in the number of females who suffer an
ACL tear. This is in part due to the rise in women's athletics, but
studies have shown that female athletes are more likely to suffer this
injury when compared to their male counterparts. It is uncertain why this
is the case. Initially, it was thought that females were at higher risk
because of differences in training intensity. But more evidence suggests
that there may be a difference in the anatomy of the female knee, or the
female ligament may not be as strong due to the effects of the female
hormone estrogen. These factors may lead to a higher risk of ACL injury
for the female athlete.
Symptoms
How does a torn anterior cruciate ligament cause problems?
The symptoms following a tear of the ACL are not always the same in
different people. Usually, there is swelling of the knee within a short
time following the injury. This is due to bleeding into the knee joint
from torn blood vessels in the damaged ligament. The instability caused by
the torn ligament leads to a feeling of insecurity and giving way of the
knee, especially when trying to change direction on the knee. The knee may
feel like it wants to bend to far backwards.
The pain and swelling from the initial injury will usually be gone after 2
to 4 weeks, but the instability remains. The symptom of instability, and
the inability for the patient to trust the knee for support is what
requires treatment. Also important in making decisions about which way the
knee should be treated is the growing realization by orthopedic surgeons
that long term instability leads to early arthritis of the knee. (These
two images illustrate the degenerative arthritis present after
longstanding ACL deficiency, both in the x-ray films and in the artist's
rendition based on the x-rays.) Many orthopedic surgeons feel that by
treating the instability and performing a reconstruction of the ligament,
the risk of developing wear and tear arthritis in the knee can be reduced.
Diagnosis
How do we look into this problem?
The history and physical examination is probably the most important tool
in diagnosing a ruptured or deficient ACL. In the acute injury, the
swelling is a good indicator. A good rule of thumb that orthopedic
surgeons use is that any tense swelling that occurs within two hours of a
knee injury usually represents blood in the joint, or a hemarthrosis. If
the swelling occurs the next day, the fluid is probably from the
inflammatory response. Placing a needle in the swollen joint and draining
as much fluid as possible, gives relief from the swelling and provides
useful information to your doctor. If blood is found when draining the
knee, there is about a 70% chance it came from a torn ACL.
X-Rays of the knee to rule out a fracture may also be ordered on the
initial examination. Ligaments and tendons do not show up on x-rays, but
bleeding into the joint also occurs when a fracture through the knee joint
is present, or when portions of the joint surface are chipped off.
Probably the most accurate test without actually looking into the knee, is
the MRI scan. The MRI (Magnetic Resonance Imaging) machine uses magnetic
waves rather than x-rays, to show the soft tissues of the body. With this
machine, we are able to "slice" through the area we are interested in and
see the anatomy, and injuries, very clearly. This test does not require
any needles or special dye, and is painless.
In some cases, arthroscopy may be used to make the definitive diagnosis -
if there is a question about what is causing your knee problem.
Arthroscopy is a type of an operation where a small fiberoptic TV camera
is placed into the knee joint, allowing the orthopedic surgeon to look at
the structures inside the knee joint directly. The vast majority of ACL
tears are diagnosed without resorting to surgery, and arthroscopy is
usually reserved to treat the problems identified by other means.
Treatment
How do we treat this problem?
Initial treatment for ACL injury includes crutches and rest until the
swelling resolves. The knee joint may be aspirated to remove the blood in
the joint. Aspirated means simply putting a needle in the knee joint and
draining out the blood.
Once, the initial pain and swelling begins to resolve, physical therapy
will probably be initiated to regain as much of the normal range of motion
as possible. One of the problems that tearing the ACL causes, is that
small proprioceptive nerve endings in the ligament are torn as well. These
nerves are there to give the brain information about where the body is in
3D space. For instance, these nerves are what makes it possible for you to
touch your nose with your eyes closed. The joints rely on these nerves to
fine tune the muscles' actions that allow the joint to function properly.
A good physical therapy program will help retrain these nerves as they
repair themselves, and will strengthen certain muscles that will take over
some of the functions of stabilizing the knee joint from the loss of the
ACL.
To help replace the stability of the knee due to the loss of the ACL, an
ACL brace may be suggested. These braces are fairly effective at
preventing the knee from giving way during strenuous activity. Most of
these braces must be fitted by a certified orthotist, a physical
therapist, or physician. They are NOT the type you can buy at the
drugstore. Most orthopedists will recommend wearing a brace for at least 1
year after a reconstruction, so even if you decide to have surgery, a
brace is a good investment.
If the symptoms of instability are not controlled by a brace and
rehabilitation program, then surgery may be suggested. Most surgeons now
favor reconstruction of the ACL using a piece of tendon or ligament to
replace the torn ACL. Today, this surgery is most often done using the
arthroscope. Incisions are usually still required around the knee, but the
joint itself is not opened. The arthroscope is used to perform the work
needed on the inside of the knee joint. Most patients can expect at least
one night in the hospital, although more and more surgeries are being done
outpatient, where you leave the hospital the same day.
In the typical surgical reconstruction, the torn ends of the ACL must
first be removed. Once this has been done, the type of graft that will be
used is determined. One of the most common tendons used for the graft
material is the patellar tendon. This tendon connects the kneecap
(patella) to the lower leg bone (tibia). Another very common graft that is
used is to combine two of the hamstring muscle tendons that attach to the
tibia just below the knee joint - the gacilis tendon and the
semitendinosis tendon. Studies have shown that these two tendons can be
removed without really affecting the strength of the leg. There are other,
much bigger and stronger hamstring muscles that can take over the function
of the two tendons that are removed.
If the patellar tendon is used, about one third of the patellar tendon is
removed, with a plug of bone at either end. The bone plugs are rounded and
smoothed. Holes are drilled in each bone plug to place sutures that will
pull the graft into place. The next procedure is to prepare the knee to
place the graft. The intracondylar notch is enlarged so that there is no
rubbing on the graft. This process is referred to as a notchplasty. Once
this is done, holes need to be drilled in the tibia and the femur to place
the graft. These holes are placed so that the graft will run between the
tibia and femur in the same direction as the original anterior cruciate
ligament. The graft is then pulled into position using sutures placed
through the drill holes. Screws are used to hold the bone plugs in the
drill holes.
Other types of materials are also used to replace the torn ACL. In some
cases, an allograft is used. An allograft is tissue that comes from
someone else. This tissue is harvested from tissue and organ donors at the
time of death and sent to a tissue bank. There the tissue is checked for
any type of infection, sterilized, and stored in a freezer. When needed,
the tissue is ordered by the physician and used to replace the torn ACL.
The advantage of using allograft is that the surgeon does not have to
disturb or remove any of the normal tissue from your knee to use as a
graft. The operation is also usually takes less time because the graft
does not to be harvested from your knee.
After surgery, a physical therapist will be contacted to begin your
rehabilitation program. You will probably be involved in some type of
rehabilitation for 6 months after surgery to ensure the best result from
your anterior cruciate ligament reconstruction. The first 6 weeks
following surgery expect to see the physical therapist about three times a
week. Following the initial period, you may be placed on a home program
and monitored by the therapist.
