Anatomic
Double-Bundle ACL Reconstruction
Patient
Information Handout / Frequently Asked Questions
Freddie H. Fu, MD, DSc (Hon), DPs (Hon)
Marvin Y. Lo, MD
Margaret S. Lo, MD
Mathew W. Pombo, MD
Rebecca Singleton, PA-C
What is the ACL and what does it
do?
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The
anterior cruciate ligament (ACL) is a ligament that connects the femur to the
tibia in the center of the knee joint.
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When
athletes “blow out” their knees – this is the ligament that is commonly torn.
§
The
ACL is important during daily activities but absolutely critical
to the stability of the knee during sports.
What is the native anatomy of
the ACL?
§
The
ACL is made up of two functional bundles of tissue, the anteromedial (AM) and
posterolateral (PL) bundles. These bundles are first seen during fetal
development and persist throughout life. [1]
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The AM
bundle of the ACL primarily controls anterior (forward) movement of the tibia
underneath the femur, and the PL bundle controls rotational stability of the
knee, such as in pivoting, twisting, running, and jumping. [9,10]
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In
other words, each bundle has a different function, and this is reflected in the
anatomy. When the knee is straight the AM and PL bundles are parallel. As the
knee is flexed, the two bundles cross each other:
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Here
is a closer look at the femoral attachment sites – we can see the upper margin
of the ACL attachment site (intercondylar ridge) and the bifurcate ridge (probe
on ridge) which separates the insertion sites of both the AM and PL bundles.
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Interestingly
– different animals have different numbers of ACL bundles – likely a reflection
of Darwinian selection.
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This
is seen in both the bone and soft tissues. Above is a comparison of the human
bony ridge (left) for ACL insertion, on the right is the bony ridge of the ACL
in monkeys – reflecting different ACL bundles.
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Here
is a goat with 3 bundles on the left, and a rhesus monkey also with 3 bundles
on the right.
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Here
are some normal human knees showing both the AM and PL bundles of the ACL - on
MRI scan and during arthroscopy:
Are ACL tears common?
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ACL
tears are very common. Over 200,000 ACL tears occur each year in the
How is an ACL tear diagnosed?
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Tear
of the ACL can be diagnosed by a history of trauma to the knee (contact or
non-contact) and physical examination. MRI scan can confirm the diagnosis:
§
At the
time of arthroscopic surgery, severe stretch-out or complete tear of the AM and
PL bundles of the ACL can be seen, as pictured below:
Is surgery absolutely necessary
for my ACL tear?
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No.
There are some patients who are able to function without an intact ACL. These
patients modify their activity, by eliminating pivoting and cutting movements
and sports, in order to minimize subluxation, or “giving away” episodes.
However, sometimes during regular activities the ACL-deficient knee can
subluxate, resulting in painful episodes with swelling.
§
Importantly,
there is a risk for damage to the menisci (cartilage shock absorbers) and
articular coating cartilage inside the knee joint with each subluxation event.
This damage can lead to degenerative arthritis.
§
Because
of these concerns, a majority of active patients elect to undergo ACL surgery
when the ligament tears.
Can the ACL be repaired or does
it have to be reconstructed?
In
general, the fibers of the ACL cannot be sewn back together again (repaired).
This is due to severe stretch-out and irreversible damage to the ligament
sustained at the time of injury. Therefore, the damaged ligament must be
removed and replaced with a new one.
I just tore my ACL—when will I
be ready for surgery?
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In
general, there are three criteria that must be met before the ACL can be
surgically reconstructed:
1) Swelling in the knee must go down to
near-normal
2) Range-of-motion (flexion and extension) of
the injured knee must be nearly equal to the uninjured knee
3) Good Quadriceps muscle control must be
present (able to do a straight-leg raise)
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Usually
it takes a couple of weeks after injury before ACL reconstruction can be
performed.
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The
presence of any associated injuries to the knee joint involving cartilage,
meniscus, or other ligaments may change the time-frame for surgery.
What are the key variables to
consider when thinking about ACL reconstruction (what do we mean by anatomic
reconstruction, and what is double bundle reconstruction)?
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Anatomic
reconstruction - everybody has different anatomy – therefore in order to truly
reconstruct the ACL – it is important to approximate each individuals native
anatomy - both in tunnel size and
location
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Single
vs. Double bundle ACL surgery – (see below)
What is the surgical technique
for ACL reconstruction?
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In the
majority of
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Usually,
the surgeon will perform a notchplasty first to chip off a piece of bone in the
joint (see below), which Dr. Fu believes is unnecessary. Then a drill guide
will be used to drill one tunnel each on the tibial and femoral side, followed
by passing through one graft.
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This
standardized technique does historically provide good results. Dr. Fu has
performed over 5000 Single-Bundle ACL reconstructions in this manner at UPMC
from 1982-2003 (21 year experience).
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However,
many feel that we can make improvements. More importantly, Dr. Fu believes that
the surgery should be individualized to each patient because everyone has a
different native anatomy.
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At
UPMC, and in many medical centers around the world, “Double-Bundle” ACL
reconstruction is now performed. Dr. Fu
has performed over 500 Double-Bundle reconstructions since 2003, with excellent
results.
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Double-Bundle
surgery reconstructs both the AM and the PL bundles. [20]
Why is Anatomic
Double-Bundle ACL reconstruction performed instead of Single-Bundle?
The
answer to this question is based on a significant amount of scientific
evidence:
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The
ACL is composed of two functional bundles, the anteromedial (AM) bundle and the
posterolateral (PL) bundle, not just one. [1]
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Between
10% and 30% of patients complain of pain and residual instability following
Single-Bundle ACL reconstruction. [2-7]
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Arthritis
has been observed on x-rays in up to 90% of patients at long-term follow-up
after Single-Bundle ACL reconstruction. [8]
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Single-Bundle
ACL reconstruction does not adequately restore normal knee stability,
particularly tibial rotation [11-16]
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Anatomic
Double-Bundle reconstruction better restores knee stability compared to
Single-Bundle reconstruction. [12,14,16,17]
To
better understand how “Double-Bundle” ACL reconstruction has evolved from
“Single-Bundle” surgery, one should consider a door hinge. A door with one
hinge is like a Single-Bundle reconstruction—it will open and close, but the
hinge is required to do too much work. Over time it will loosen and the door
will wobble. In comparison, a Double-Bundle reconstruction is like a door with
two or three hinges. The work is shared between the hinges, and the door can
open and close smoothly for long periods of time without falling apart. One
hinge doors can be seen in log cabins, while in Medieval times two hinges were
used. Today’s doors have three hinges, representing an evolution in design.
The principles of
anatomic double bundle ACL reconstruction surgery
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Reproducing
the anatomy of ACL by reconstructing both the AM and PL bundles.
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Reproducing
the insertion sites of ACL by identifying them carefully and measuring their
sizes, followed by drilling the bone tunnels precisely where they belong
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Reproducing
the tension pattern of each bundles of the ACL by fixing them at their
respective angles
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A La
Carte surgery (ie. individualizing each surgery for each patient)
In regards to A La
Carte surgery, how much variation is there?
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Here
is an example of two patients - similar age and height
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This
is a measurement of the tibial insertion points which dictate the tunnel and subsequent
graft size (see below)
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As we
can see, the tibial insertion sites here are markedly different - 17mm on the
left picture and only 12mm on the right.
What are the details of the surgery?
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For
ACL reconstruction, we typically use four small incisions:
o
Three
arthroscopic incisions:
o
One
tibial incision for the bone tunnels
o
Occasionally,
an additional incision is made on the lateral (outer) aspect of the knee joint
over the femur to help secure the grafts.
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ACL
reconstruction usually takes 60 to 90 minutes.
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First,
the insertion sites of both bundles (AM and PL) of the old ACL are first marked
on the femur and tibia.
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The
injured ACL is then removed with arthroscopic equipment.
§ The insertion areas of the AM and PL bundle are measured to decide what graft size to use for each patient.
- Care is taken to place the new tissue grafts in the exact position of the original bundles of the ACL, creating an “Anatomic” reconstruction.
- For each
bundle of graft tissue (AM and PL) one tunnel is created in the femur and
one in the tibia (total = 4).
- Each tunnel
measures anywhere from 5 to 9mm in diameter and dictates final graft size
- Guide wires
are placed first, to ensure correct tunnel placement, and then the bone is
drilled to create the tunnels.
- The grafts
are then passed through the tunnels and fixed to the femur and tibia with
a combination of special fasteners, screws and sometimes staples:
- MRI and X-rays after surgery show the
Double-Bundle ACL reconstruction:
- After Double-Bundle reconstruction, we have found most patients to have excellent range-of-motion, typically equal to the other knee. These results are better than with the Single-Bundle ACL reconstruction, and can be seen as early as 1 to 3 months after surgery:
Is it possible to tear just one
bundle?
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Yes –
this is rare but does happen
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Clinically
an isolated tear of the:
- AM bundle leads to anterior-posterior instability
- PL bundle leads to rotatory instability
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In
this case we can save the intact bundle and “augment” the ACL with a single
bundle reconstruction – either the AM or PL… whichever one is torn
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On the
left is a picture of a PL intact, AM (only) reconstruction
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On the
right is a picture of a AM intact PL (only) reconstruction
Do we perform single bundle ACL
reconstruction?
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Yes –
we perform single bundle ACL reconstruction in approximately 20 % of the
patients.
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Except
for the one bundle tear described above, there are a few more scenarios that we
prefer to perform single bundle surgery, including
- Patient has a small native ACL insertion site, which will
be identified during the surgery
- Patient is still growing and their growth plate is not
closed
- Patient has severe arthritic changes
- Patient who is suffering from multiple ligament injury
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However,
unlike the traditional ACL surgery, our single bundle surgery is performed in
an anatomic fashion. We will carefully investigate the rupture pattern of the
ACL and identify the native ACL insertion site, just like we do in double
bundle ACL surgery. Then, the tibia and
femur bone tunnels are placed at the center of the native insertion site.
Where do the grafts for ACL
reconstruction come from?
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The
graft tissue can come from your own body (autograft) or from a cadaver
(allograft). At UPMC we most commonly use Hamstring Tendon when autograft is
chosen.
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Disadvantages
to autograft primarily relate to harvest-site morbidity as well as potential
loss of function from the tissue taken.
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Multiple
types of allograft tissue are commonly used including Hamstring tendon,
Tibialis tendon, and Achilles tendon.
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Allograft
tissue is comprehensively screened by tissue banks for diseases such as
Hepatitis and HIV, and overall is a safe option for graft tissue. Disease
transmission is very uncommon. [19]
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For
Double-Bundle ACL reconstruction, allograft tissue is commonly used.
Postoperative
Instructions