January 1997
The Anterior Cruciate Ligament
by Diana Garroway
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The anterior cruciate ligament (ACL ) is the most important
ligament within the knee. Injury of this ligament is serious and there
is more than one procedure and opinion on how it should be treated.
Although there are no answers to the questions of why it affects some
people and not others, questions like what can be done to fix the tear,
how to come back to sports, and how to prevent it from happening again,
all can be answered. Twenty years ago the tearing of the ACL was the
end of an athletic career. Now it is just another obstacle to work
through.
Where the femur and tibia meet is the hinged joint called the
knee. The patella protects the joint (kneecap), which lies in front of
the knee. The articular cartilage helps to cushion the joint by
surrounding the edge of each of the femur, tibia, and the back side of
the patella. The meniscuses are two crescent-shaped pillows of
fibrocartilage which are found medially and laterally, and help cushion
the knee. The ligaments within the joint help with stabilization and
balance. There are two collateral ligaments. These ligaments run along
either side of the knee and help limit sideways motion. Two cruciate
ligaments attach to the femur and tibia, and cross within the knee. The
back ligament is called the posterior cruciate ligament (PCL) and helps
in preventing the tibia from sliding back on the femur. The patellar
tendon is the elastic band-like tendon which runs from the quad down to
the tibia. It is the track on which the kneecap runs, and it keeps the
patella in place.
Within the knee there are the three main ligaments described above
and the ACL. The ACL gets all the publicity because of the problems it
causes when it is torn. It is a band of fibrous tissue which connects
the tibia to the femur and helps to prevent the tibia from sliding
forward on the femur. Muscles surrounding the knee (ie. quadriceps and
hamstrings) also help to keep the femur and tibia in place. Being the
anterior of the two main ligaments which cross within the joint, the
ACL also helps to prevent hyperextension. By preventing the movement of
the tibia, and by preventing hyperextension, the ACL also protects the
articular cartilage and the meniscal cartilage from tearing.
An ACL injury can happen to anyone. The rate of injury is almost
equal through all levels of sports, from beginner, to recreational, to
professional athletes. Once torn the ACL doesn't heal itself, so the
next question would be "What can be done now?". There are a number of
different procedures and ideas on how to treat the injury. Some people
choose not to have surgery and continue their regular lives, while
others choose the surgery. There are three main methods used today to
replace the torn ACL; the patellar tendon graft, semitendinous-gracilis
(hamstring) graft, or an allograft (usually a donated Achilles tendon).
No matter which method is used, they all have individual advantages and
disadvantages.
Tens of thousands of athletes have chosen the patella tendon
reconstruction in the past ten years. This is generally because once
the patellar tendon heals, there isn't any more complications. The
patellar tendon graft is used when the strength of the graft is the
main priority. To perform the surgery, there are three main ways in
which the knee can be accessed during the surgery. The first is through
two main incisions (one medial and one lateral). This method allows for
the most accurate positioning. The second is through one main incision
down the centre of the knee, and the third is through arthroscope. Each
of these methods also have advantages and disadvantages in regards to
rehabilitation and long-term results.
Once the incision is made, the patellar tendon is harvested. The
middle third of this tendon is measured off, and if it exceeds one
centimetre, then just one centimetre of the tendon is cut. Removed,
along with the tendon, is a small piece of the patella and a small
piece of the tibia. Both bone pieces attach to the patellar tendon. The
harvested patella measures 20 x 9 x 7 mm and the harvested tibia
measures 30 x 10 x 10 mm. Before the bone is removed, 2 mm holes are
drilled into each piece. The bone and tendon are then both removed
using a fine oscillating saw.
The next step is to remove 5-10 mm of bone in the tibial tunnel
(if necessary) to keep the graft from getting caught during extension.
Also the femal notch is sometimes widened in females. Holes are then
drilled in the lateral femoral condyle and in the tibia. These holes
are widened to fit the bone plugs. The graft is strung into the
isometric position and secured with screws. The knee is then brought in
to full flexation and extension, making sure that it flows right and is
similar to the other leg. Although often a few degrees of extension are
lost, the patellar tendon method is the most commonly used today.
The semitendinous method (hamstring method) is generally used when
the longevity and simplicity is priority over strength. The incisions
used in this method are almost identical to the patellar method, except
that an arthroscope is almost always used. A small incision is cut in
the back of the knee and the semitendinous tendon is taken out using a
tendon stripper. Depending on the method being used, the gracilis
tendon may be removed also. Both of these tendons normally attach the
hamstring muscles to the lower leg. Once removed, the tendons are then
cleaned of muscle.
The semitendinous-gracilis tendon method has been proven on one
test to be even stronger than the patellar tendon graft. It involves
weaving and looping the two tendons to form a new ACL. This new ACL is
then folded over and stapled into place. The recovery from the
hamstring method is much easier because there is no disruption to the
patellar tendon. Although both the semitendinous and patellar methods
are extremely strong, critics say that the easy rehabilitation of the
semitendinous is not worth the potential long-term hamstring problems.
The last commonly used method is an allograft. By using tissue
from another human, there is no disruption to the hamstring or patellar
tendon. An ideal allograft has to meet seven standards. It should
duplicate the physiological function of the ACL, it shouldn't create a
high infection risk, it should be non-immogenic to the host, there
should not be any hyperplastic or alignant transformations, it should
be available in different sizes, it should be easy to transplant, and
the material of the graft should be able to be stored for long periods
of time. The types of allografts that meet these standards are
combinations of anterior cruciate ligament-bone, bone-patellar
tendon-bone, bone-posterior cruciate ligament- bone, quadriceps
tendon-bone, Achilles tendon and freeze dried fascia lata. The
selection of which allograft to use depends on the demands that will be
placed on the knee.
Each graft can handle a different amount of force. A normal ACL
can handle 400 lbs. Normal living activities also apply different
levels of these forces on the ACL. Cycling applies 6 lbs, leg squats
applies 16 lbs, the lachman test-20 lbs, walking downstairs-20 lbs,
level walking-40 lbs, 15 degree isometric contractions-65 lbs, walking
down a ramp-100 lbs, active leg extensions-110 lbs, jogging-135 lbs,
and active leg extensions with a 7 lbs weight applies 140 lbs. No graft
has ever been found to have the same strength as the original ACL, but
the patellar tendon method comes the closest, being able to absorb 300
lbs. The semitendinous method can absorb 120 lbs, the illotibial band
can absorb 80 lbs, and the fascia lata absorbs 70 lbs. Whichever method
is chosen as an allograft, it is up to the tissue bank to make sure
that there are no transmissible diseases, the tissue is sterile, the
donor is young and that the tissue was retrieved under sterile
conditions. If all of these standards are met, the allograft is a very
successful procedure.
The strength of any graft is at its maximum when it is first
placed in the knee. During the first two weeks the graft loses strength
as new blood vessels are formed. This process is called
revascularization. Next, it takes about 6 weeks for the graft to regain
enough strength for normal activities. It then takes the graft two
years to reach full maturity. Full maturity is not needed to resume
sports or an active lifestyle, though, and it regains 90% of its
strength in the first year.
The first attempts at an ACL reconstruction was in the 1970's.
Doctors tried to sew the ligament back together again. These attempts
failed. Since then reconstruction has been tried using allografts,
xenografts, autografts, synthetetic material and a combination of
synthetic and biological material. Along with these methods they used
to open up the entire knee, and this also meant the end of any sports
career. The procedure which eventually became prominent in the late
1970s and early 1980s was called Lateral Substitution Over the Top
(LSOT). This method involved using the illiotibial tract of the thigh.
The goal of LSOT was to have limited extension to protect the graft.
However this placed limitations on the knee and the lifestyle of the
patient. Most patients didn't really like this idea, so the next method
to come into practise was the patellar tendon and the other methods
used today.
Also 10 years ago, patients over the age of 40 weren't recommended
for surgery. They were told to change their lifestyle to accomindate
for their ACL deficient knee. Today, age is no longer an issue because
of newer methods available, quicker recovery time, and better security.
New methods are continuously being tested and new research is always in
progress. The future of ACL reconstruction should include a prosthetic
and/or augmented biological material. This material should be able to
considerably reduce the rehabilitation process because of the little
disruption to the joint and by eliminating the need to protect the
graft. Another procedure, called the Healing Responce, that doesn't use
any screws or pins is being tested. This procedure uses an icepick-like
device to poke holes in the bone near the injury. Blood and bone marrow
cells are released, clot and form a natural fixation to hold the
injured ligament in place. It has been tried on 200 patients in the
past two years and so far it has a 95% success rate.
The tearing of the ACL is considered an epidemic. It is the number
one reason athletes find themselves on the operating table, with over
100,000 recorded incidences each year. These numbers continue to rise
as diagnostic techniques improve and the demands of sport increase. The
highest risk sports are skiing and basketball. An average of one in
every 200 skiers tears an ACL, and it is difficult to find a women's
basketball team that has not experienced at least one tear.
Most of these tears occur without any outside contact. A twisting
of the knee, a hard landing or just hyperextension can all easily tear
the ACL. Some people feel excruciating pain and are unable to walk
without surgery, while others feel no pain at all. If no pain is felt
it is usually because the nerve pathways, along with the ACL, have been
severed. Most patients do feel a ripping of some sort and hear a 'pop',
'click-clack' or a sound like paper being torn. Also in almost all
cases swelling develops within 24 hours of the injury. No matter how
they tear the ACL, it often takes a long time for the patient to feel
confident with their knee again.
The ACL can't be felt with a finger like a rib or a pulse.
Therefore diagnostic techniques had to be developed. From this need
came three main tests. They are the anterior drawer test, the lachman
test and the pivot shift test. To conduct the anterior drawer test, the
patient lies down on his/her back with the hips at a 45 degree angle
and the knees at a 90 degree angle, to the table. The doctor then sits
on the patient's foot and applies an increasingly firm pull on the
calf. If the Tibia pulls forward, almost like a drawer opening, then
the test is positive. In the pivot shift test the patient lies slightly
on his/her side with the knee fully extended, and muscles relaxed. By
applying light stress on the knee and slowly flexing it, the doctor
feels for the click or clunk at about 30 degrees for a positive test.
The third test is the lachman test. This test is the most popular of
the three and can usually give conclusive results. The patient relaxes
the leg, and the doctor holds it with one hand on the lower thigh and
the other on the upper calf. With hands on opposite sides of the knee,
and holding it firmly at 20-30 degrees, the doctor firmly pulls the
tibia forward. This test (and the other two) should always be compared
to the other knee. If there is any more movement in the affected knee,
it indicates a ruptured ACL. The lachman test is more sensitive than
the other two tests, but ninety percent of all ACL tears are diagnosed
by using one of these tests, or all three.
Once the ACL tear is diagnosed, the patient must decide to treat
it surgically or to cope (brace and bear any pain). Reconstruction is
not necessarily the best option. The decision generally is based on the
lifestyle of the patient and what demands will be placed on the knee.
Reconstruction is usually recommended if the patient is young,
participates in high-risk sports, has a meniscal tear, other cartilage
damage, or if there is limited motion in the knee. Also, if the knee
gives out, by the tibia sliding forward on the femur, reconstruction is
recommended. This giving out causes a loss of balance and adds stress
on the articular cartilage and meniscus, possibly causing tearing.
If reconstruction is decided upon, the selection of which
procedure to have is also a difficult process. The most important
factor is the activity level of the patient and whether or not the
patient is willing to change his/her lifestyle. A high-level athlete
puts more demands on the knee than the recreational athlete, so each
patient requires an individual treatment plan. The decision should be
based on the severity of damage to the knees, the specific athletic
activity, the frequency of sports participation, expectations,
motivation, willingness to modify activity level, and the willingness
to accept an intensive rehabilitation program. The advantages and
limitations to each graft have already been listed above.
It doesn't matter who the patient with the ACL deficient knee is,
he/she will most likely need a brace. There are three main types of
knee braces; prophylactic, rehabilative and functional. The
prophylactic knee brace is used to prevent injury to the ligaments of
the knee. It is controversial in how useful this brace really is. Some
studies show that they could help prevent medial collateral ligament
(MCL) injuries, and other studies show that they don't do anything for
the knee. There is no evidence that this type of brace can help prevent
ACL injuries, and there is actually some biomedical data which proves
that prophylactic bracing can increase the chance of ACL injury.
The rehabilitative knee brace is designed to provide protection
and controlled movement for a ligament injury that has been treated
either operatively or non-operatively. There is some concern expressed
about whether this brace can really control passive motion and joint
displacing forces, but generally it is a good brace. This brace is
usually light, easily applied and adjusted, and provides easy access to
the skin. Also, stops on the hinges of the brace allow active and
passive motion to be limited.
The functional knee brace is designed to provide stability to a
knee with ligament injuries. It is made to control the extra looseness
within the knee. Studies about this brace show that it increases the
patient's stability, although the greatest benefit was in patients with
less laxity and who put lesser demands on the joint. All of the braces
may help the knee, but none have ever been able to restore its normal
laxity after a tear of the ACL.
The most difficult part about tearing the ACL is the
rehabilitation process after reconstruction. In the past this process
was extremely long (1-2 years) and was done very passively. In the
recent years the time period for the rehabilitation has been decreased
to six months for some patients, and the conservative rehabilitation
has been replaced by a hard work out. The overall program depends on
the physician, the physical therapist and the patient, but two main
points are always looked at; immobility must be minimized and the
healing tissues must never be overloaded. Generally once the initial
pain of the incision subsides the patient can work on passive extension
and flexation exercises. This is a relatively new idea (past 5-10
years) as the patient used to be in a cast for 4-6 weeks
post-operative. The cast isn't used anymore because of better surgical
techniques and graft fixings.
The rehabilitation of the patellar tendon over the hamstring graft
is generally much harder. This is usually related to the huge loss in
quad strength and the disruption of the patellar tendon. Much of the
rehabilitation is waiting for the tendon to heal.
In a recent study of 75 ACL replacement patients between the ages
of 45 and 65, only 4% still had pain or swelling five years post
operative. None of them had any instability. On the average these
patients started biking at 4 months, jogging at nine months, skiing at
ten months and tennis after one year for examples of two very different
rehabilitation programs. They are both for a patellar tendon graft).
Rehabilitation programs have a huge variance in protocol from one to
the next, but in all of them the patient must obtain a minimum of 80%
of the quadriceps strength in the injured knee as in the normal one,
before returning to sports.
There are many different complications that can occur with the ACL
replacement surgery, but they are rare. Reasons for the general failure
of the graft include trauma, poor fixation, nonatomic placement,
inadequate replacement material, failure to use a brace, the use of
synthetic replacement, problems with newly tested materials or
procedures, extra laxity and articular cartilage degeneration. Early
failure of the graft is almost always associated to one of three main
incidents; a fall or a twist, fatigue-related failure, or by stretching
the graft past its limit. Most reinjuries happen the same way the
original ACL was torn (across the middle of the graft), and teenagers
are more likely than any other age group to reinjure their knees. There
are also some complications directly related to the patellar tendon
graft. These problems usually occur when the 'tracking' of the patellar
tendon is off. This results in a greater occurance of anterior knee
pain, flexation contracture, and extensor weakness.
Then there is arthrofibrosis. This complication causes some
debate. Arthrofibrosis can occur when the knee is operated on too
early, that is, before all of the swelling of the initial injury goes
down. The knee reacts to this, causing stiffness in the joint, but a
new study shows that waiting isn't necessarily the best option. These
studies show that by operating within the first month of injury, it can
reduce cartilage and menisci tearing, in the long run preventing
degenerative joint disease. In this study the Italian researchers
compared athletes who had received surgery within two weeks of the
injury to those who received the same surgery three to twenty-one
months after injury. Five years post-operatively they found little
difference, except that the earlier treated patients had fewer meniscal
and bone lesions, and better overall stability. Whether or not these
results are worth the risk of arthrofibrosis is still to be determined
It is difficult to prevent ACL injuries because they can happen to
anyone at anytime, but there are a few precautions that have seemed to
work. These include a good warm-up, stretch and cooldown, avoiding
forceful landings and twisting of the leg, and obtaining and
maintaining top conditioned quadriceps and hamstring strength. Also for
skiers, the new parabolic ski has been proven to help reduce ACL
injuries.
One of the biggest mysteries about the ACL is the difference
between the number of injuries seen in women and men. Women seem to
tear there the ACL much more frequently then men. In basketball the
ratio is four to one and in gymnastics the ratio is almost eight to
one. There are many theories as to why the statistics are so lopsided
but no one knows for sure. One theory is that women have a weaker
quadricep muscle than most men. When the leg muscles aren't as strong,
the stress is increased on the ligaments. To prevent this, athletes,
especially females should make sure their bodies are in the best
condition they can be in. Also some studies show that women rely more
on the quads instead of using both the hamstring and quads. This leaves
the ligaments vulnerable. One activity that can help to equalize the
muscles is jumping rope. This is an excellent activity for female
athletes because both the quads and hamstrings have to flex as the
athlete hits the ground.
A third theory is that females have different joint structures
with less flexibility in their ligaments and more laxity within the
knee. Women also tend to have a much narrower femal notch (the notch in
which the ACL and PCL run). The female femal notch tends to be more of
an 'A' shaped, while the male femal notch tends to be more of a 'U'
shape. Some researchers believe that many ACLs are sheared by the
narrowness of the femal notch. The women's body also angles in more at
the knees because of their wider hips. This may place extra stress on
the ACL.
Another theory is that girls are not exposed to the correct motor
learning skills at the important times of their development. The
neuromuscular co- ordination needed in athletes is not being taught to
young girls, and they aren't usually encouraged to learn it. By the
time these young girls show an interest in aggressive sports, (usually
by Jr. High), it is too late. The consequence could be all of the knee
injuries.
Footwear is yet another theory. Sneakers and athletic footwear are
continuously improving in grips and ankle support systems. If the ankle
can't give on a quick stop, then something else might. That could be an
ACL. Also, women in sports generally wear footwear made for a man's
foot (ie. soccer cleats, basketball sneakers, ski boots). None of these
were made for a women's strength, weight or foot.
Examples of top female athletes who have torn an ACL include
Theresa Edwards, Tiffany Woosley and Cheryl Miller. These three
basketball players and many other female athletes are constantly
pushing the limit of their sport and their knees. The final theory is
that female athletes are simply going beyond the capacity of their
ligaments to hold the stress. As women's athletics become more up tempo
and demanding, a huge rise in ACL tears have occurred. Coincidence?
Maybe.
Today ninety percent of all ACL patients return to their previous
lifestyle, either through reconstruction surgery or coping. With
advancing technology and new procedures, that number can only improve.
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Copyright 1998. Diana Garroway. All rights reserved. (Jimbo's ACL
Journal).