ANTERIOR CRUCIATE
LIGAMENT TEARS
Anatomy
 The
anterior cruciate ligament is a thick band of tissue
which has two major strands that extend from the lower
leg bone (tibia) to the thigh bone (femur). This ligament
is very important for maintaining stability of the
knee. When it is injured or torn the patient feels
the instability of the knee when they turn or pivot.
This instability is particularly problematic when participating
in pivoting sports such as soccer and football. The
ligament sits just in front of its counterpart, the
posterior cruciate ligament, directly in the middle
of the knee joint.
Mechanism
of Injury
Most anterior cruciate ligament
tears occur during a sporting activity and usually
in younger patients. When you consider the number of
sport hours played, they are more common in women.
There have been a variety of reasons proposed for this,
such as muscle imbalance and slight variations in the
anatomy of the knee joint in women compared to men.
The most common sports are football and basketball
in younger patients; skiing injuries predominate in
older patients. It is, however, possible to injure
the anterior cruciate doing a variety of activities.
We’ve seen bilateral ACL tears in a weight lifter
who was doing an incline bench and popped both his
knees at the same time when bench-pressing 350 pounds.
It can also be a work-related injury. Interestingly,
most people would expect that it is due to contact,
but this is not true. Mostly it is a non-contact deceleration
where the athlete suddenly turns to the opposite side
of the planted and injured knee. As the patient turns
and pivots the ligament tears. In basketball it is
usually a result of a hyperextension and internal rotation
of the tibia on the femur, associated with deceleration.
Usually the patient will feel
a sudden pop in their knee immediately in injury to
the knee. Surprisingly, sometimes the knee will not
get very swollen, although it certainly can. The injury
is often missed because the physical examination requires
some experience and training. It might actually be
easily missed in the initial stages.
 Natural
History of the Torn Anterior Cruciate Ligament
If left untreated the laxity which
is immediately present only becomes worse. The other
structures of the knee try in vain to provide some
stability to the knee. Over time and with more usage
these other structures stretch out as well, resulting
in increased instability and then associated meniscal
(cartilage) tears. There is an incidence of approximately
1 in 3 patients who at the time of the anterior cruciate
ligament tear will tear their cartilage as well. This
progresses with time because in an untreated knee the
knee is unstable and produces greater stress on the
cartilage. Up to 80% of the knees will eventually develop
a cartilage tear. The smooth Teflon lining of the knee
which is known as articular cartilage is often damaged
at the time of the ACL tear. If left untreated, this
will again progressively wear at the knee, causing
an increased rate of osteoarthritis development. The
patients will alter their gait and will develop a rather
specific quadriceps avoidance gait because when they
contract their quads during normal walking its slides
the tibia forward which is usually stopped by the anterior
crucial ligament. The patient will naturally and unconsciously
try to prevent this. All these problems mean that the
knee will progress to late degenerative changes and
osteoarthritis much earlier than in a normal knee.
There is not good evidence that bracewear alone will
decrease the rate of re-injury to the knee. However,
in older and non-active patients there is definitely
a role for non-operative treatment by simply modifying
their activities and avoiding all situations where
they may pivot and damage their knee further.
Mechanics
The anterior cruciate is the main
factor causing resistance to the anterior displacement
of the tibia on the femur. This is demonstrated when
the orthopedic surgeon pulls the tibia forward on the
femur performing a test of the anterior cruciate ligament.
The tibia will displace much further forward than it
should when the ACL is torn. The ligament is tight
when the knee is in full extension and has the least
amount of tension at approximately 45’ of flexion.
Because there are different bands to the anterior cruciate
ligament different areas of the anterior cruciate tighten
at different angles of the knee.
Physical
Examination
 Examination
immediately at the time of injury will reveal usually
at least mild swelling of the knee, but not necessarily.
The best test is called a Lachman Test where each of
the examiner’s hands are placed just above and
just below the knee joint. The lower bone is brought
forward with the knee angled at approximately 15’ and
the examiner assess the end point. Usually, there is
a firm endpoint with an intact ACL when the tibia is
pulled forward. When the ligament is torn that endpoint
is no longer present. The examiner will also look for
increased excursion of the tibia forward on the femur.
A Drawer Test is when the knee is flexed to 90’.
Essentially, the same test is performed. It is more
difficult in an acute situation to perform this test
because usually the athlete’s knee is too sore
to allow the knee to bend to 90’. A Pivot Shift
is a test where the knee is brought from an extended
position into flexion. Usually the knee will show a
slight and subtle shift as the tibia rotates on the
femur and shifts back into proper position. It is actually
subflexed in the full extended knee position and returns
to its natural position as the knee is flexed. As it
returns to its natural position there is a "pivot
shift" which takes experience to detect.
Associated injuries are always
assessed for at the same time. Joint line tenderness
representing torn cartilage and tenderness over the
lateral knee which may reflect tearing of the collateral
ligaments. O’Donohue’s "terrible triad" injury
involves not only the ACL, but also the medial meniscus
and the medial collateral ligament. It is unfortunately
fairly common.
Treatment
Originally it was felt that the
knee should be repaired surgically as soon as possible.
Now, most orthopedic surgeons feel that the swelling
should subside and the patient should work to improve
range of motion with physiotherapy for 2-3 weeks. Once
this is accomplished the patient can then proceed to
an anterior cruciate ligament reconstruction. As stated
earlier, surgery does not have to be performed on a
sedentary older patient, but it is almost always recommended
to a younger, active athlete that they should have
anterior crucial tear repaired. With modern techniques
it is performed as an outpatient – the patient
is discharged from the hospital the same day. The patients
will leave the hospital on crutches wearing a knee
immobilizer for approximately 10 days while they are
up and getting around. When the immobilizer comes off,
the patient usually will use a passive motion machine
that moves the knee through flexion and extension.
Physical therapy is started immediately post-operatively.
Treatment of a torn anterior crucial ligament in the
older patient usually consists of physical therapy
and exercise training as well as potentially brace-wear
for some activities.
Surgical
Treatment Options
 There
have been many options described for the surgical treatment
of the anterior cruciate ligament. The most popular
and currently recognized as the gold standard at this
point is an operation where the middle one third of
the patella tendon is used as a graft. It is virtually
impossible to repair the ligament that is torn. The
torn ACL is simply removed and the replaced with the
patella tendon graft. Two thirds of the patella tendon
is left behind and it will repair itself, not compromising
the function of the knee. At each end of the patella
tendon a bone block is also taken; one piece from the
tibia, and the other from the patella (kneecap). These
two bony blocks are inserted into holes that are drilled
into the tibia and femur and held into place with screws,
which provide stabilization of the ligament graft.
There are other tissues that can
be used to substitute for the anterior crucial ligament.
Most commonly the second choice are hamstring tendons
which are weaved into a graft close to the size of
the anterior crucial ligament. We have also used quadriceps
tendon and allograft. An allograft is donated cadeaver
tissue which is freeze dried until the time of usage
upon which time it is thawed out and trimmed to size
and used as an ACL substitute. The advantage of an
allograft operation is that there is a smaller incision
required, the rehab is shorter, and less painful. The
disadvantage is that it is not quite as strong as a
graft formed from the patient’s own tissue.
Risks, Complications
and Alternatives to Surgery
Any time an operation is performed
no matter how small or major there are going to be
a risks. With anterior cruciate surgery the most common
risks are infection, blood clots in the legs, failure
of the graft, stiffness of the knee, and persistent
pain and instability. There are other rare complications
such as neurovascular injury and medical complications
both general and related to the anesthetic. All would
have to be understood and accepted by the patient prior
to the surgery. In particular, all of these should
be discussed with your surgeon pre-operatively. Unfortunately,
there is no way to perform any surgery without some
risks, but the results of anterior cruciate surgery
are better than 90-95% effective. Even if a complication
does occur it can usually be treated and resolved.
Long Term
Prognosis
With an anterior cruciate ligament
repair, the patient’s long-term prognosis without
any other associated significant injury is excellent.
It certainly carries a much better prognosis than when
the knee if left untreated. The patient can usually
return to any activity that he was doing pre-operatively
and many athletes have gone on to excel again at their
chosen sport.
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