If there is clear evidence of instability of the knee based on the
examination under anesthesia, the hamstring tendons are harvested
first. Because hamstring harvest is so critical the tourniquet is
inflated with the knee maximally flexed with the extremity
exsanguinated. The pes anserinus is palpated and a 3 cm longitudinal
incision is made over this; this incision is made so it can be extended
proximally for harvest of the central third of the patella tendon if
that were needed. The lateral arthroscopic portal is made just adjacent
to the lateral border of the patella tendon and just superior to the
joint line. The medial portal is established after the arthroscope has
been placed in the lateral portal. A spinal needle is then introduced
in the anticipated position of the medial portal, just adjacent to the
medial border of the patella tendon. The portal placement can be fine
tuned by using the spinal needle to establish exact position prior to
making the incision. A superolateral portal is utilized for outflow.
This is established 1-2 cm superior and lateral to the patella.
Pathologic Surgical Findings
The injured ACL must be visualized and palpated during arthroscopy. Meniscal and chondral injuries are commonly seen at surgery.
Intraoperative Decisions Based on Pathology
If a partial ACL injury is present, the decision to reconstruct the
ligament should be based more on the examination under anesthesia
rather than the diagnostic arthroscopy, which can be confusing when
examining a partially injured ligament with a lax remnant. A decision
often must be made to repair or remove torn meniscal tissue. This
should be based on the location of the tear, the condition of the torn
tissue, the chronicity of the tear, and the age of the patient. In the
setting of ACL reconstruction, meniscal repair is a more viable option.
Procedure
Hamstring tendon harvest
After the tourniquet is inflated, the pes anserinus is identified
through a longitudinal incision. The sartorius fascia is identified and
then incised between the gracilis and the semitendinosus in line with
their fibers. The sartorius fascia is then dissected off the surface of
the semitendinosus and the gracilis. This is fascia is thin and often
adherent to the superficial surface of the hamstring tendons. The
semitendinosus and gracilis are then released as a combined unit as
distal as possible on the tibia. The division of the two tendons can be
identified on the undersurface of the two tendons. Once this division
is identified the natural split is extended distally. A separate clamp
is then placed on the free end of each of the tendons. The tendons are
then pulled with the clamp to deliver as much of the tendon outside the
wound. This is done with the extremity if the figure-of-four position.
This allows for clear identification of the gastrocnemius attachments
of the tendons. The attachments are then released. The tendons are then
palpated proximally to make certain there are no remaining attachments
or adhesions. At this point the tendon stripper is passed in line with
the tendons.
Graft preparation
The harvested hamstring tendons are then stripped of all muscle
tissue and trimmed to the same length. The hamstring tendons are then
looped over themselves to double their thickness. The total length
should optimally be at least 10 cm when the grafts are doubled. At this
point a #2 Bunnel nonabsorbable suture is placed in the last 2-3 cm of
each of the tendon ends. Care is taken to pull all slack out of each
suture pass. The looped semitendinosus and the looped gracilis tendons
are then pulled through a tunnel sizer. The diameter is usually between
7 and 9 mm in diameter; this should be a very snug fit. The tendons can
then be placed on a tensioning device to allow potential creep to be
taken out of the system. The tendons must be kept moist to prevent
desiccation; this is done with a saline soaked gauze.
Tunnel preparation
An arthroscopic pump is utilized for joint distention, joint
irrigation, and joint hemostasis. Dilute epinephrine is placed in the
bags of arthroscopic fluid to aid in hemostasis. The tourniquet is
rarely used for this portion of the surgery and deflated after the
graft harvest. Once the portals are established, soft tissue is
debrided form the origin and insertion of the native ACL with a large
diameter motorized shaver. All remaining native ACL tissue is removed
as well. In the acute situation a notchplasty is rarely required.
However, the soft tissue must be adequately removed to allow
visualization of the over-the-top position on the femur. This may
require removal of a small amount of bone. In the chronic situation
where bone has overgrown in the femoral notch, a formal notchplasty may
be required. A tibial aiming guide is used to place the tibial
guidewire in the posterior central portion of the tibial footprint. The
starting point on the tibia is at a point 45 degrees off the midline.
The guide is usually set between 45 and 50 degrees of angulation. If
the graft is on the shorter side, the angle can be slightly decreased
to ensure that the graft exits the tibial tunnel. The guidewire is then
overdrilled with the appropriate sized (based on the graft diameter)
drill or reamer. A cannulated soft tissue plug is then placed in the
tibial tunnel to prevent leakage of fluid and maintain joint
distention. The knee should be held in approximately 90 degrees of
flexion while drilling the femoral tunnel. If the tibial tunnel has
been drilled at a more shallow angle, however, more than 90 degrees of
knee flexion may be required for proper femoral tunnel angulation. If
the knee is held in less than 90 degrees of flexion, there is a greater
chance of blowing out the posterior femoral cortex and the guidewire
will exit too proximal on the femur, likely out of the sterile field.
The guidewire is placed transtibial through a femoral offset guide,
with no more than a 5 mm offset; it is fine if the posterior wall is
blown out on the femur unless interference screw fixation is planned.
The guidewire is drilled through the anterolateral femoral cortex and
stopped at this point. The wire does not yet exit the skin.
Approximately 25-30 mm of hamstring graft is typically placed in the
femoral tunnel. With EndoButton femoral fixation, an extra 10 mm is
drilled beyond the anticipated amount of tissue placed in the femoral
tunnel to allow flipping of the EndoButton. Therefore the depth is
typically to 35-40 mm with the appropriate sized drill or reamer. Care
must be taken not to drill through the anterolateral cortex with this
larger drill. If this occurs, the EndoButton cannot be used and
alternative mode of fixation must be employed. The remainder of the
tunnel is drilled with a 4.5 mm drill; this tunnel exits completely
through the anterolateral cortex. The apertures of each of these
tunnels are then chamfered smooth with the shaver where friction is
going to be exerted on the graft. This includes the posterior aspect of
the tibial tunnel and the anterior aspect of the femoral tunnel. The
total length of the femoral tunnel is measured with a depth gauge. This
length is subtracted from the amount of graft planned to be placed in
the femoral tunnel (25-30 mm). This resulting number is the length of
the EndoTape required to span the distance from the anterolateral
cortex to the start of the graft material. If closed loop EndoTape is
used approximately 3-4 mm is added to this number to account for the
looped graft around the tape.
Graft passage and fixation
The appropriate sized closed loop EndoTape is selected. The
hamstring tendons are passed through the loop of EndoTape and the
lengths of all the graft strands are equalized. If interference screw
fixation is planned, it is recommended to tubulize the graft or bring
all the strands together with a running absorbable suture; this will
help keep the strands from wrapping around the interference screw as it
is inserted. Two marks are made on the graft relative to the aperture
of the femoral tunnel; one at the point where the EndoButton should be
flipped and a second at the point where the graft will finally come to
rest after the EndoButton has been flipped. This again is typically at
25-30 mm. A #5 and #2 suture are placed in the outer holes of the
EndoButton for graft flippage. The length of these sutures should be
maximized. A transtibial slotted guidewire is placed through the
tunnels and exits outside the anterolateral thigh. The #5 and # 2
flipping sutures are pulled through the knee with the guidewire. The
graft is then pulled into position with the #5 suture. The EndoButton
should be visualized at it is pulled through the knee to make certain
the #5 suture end of the EndoButton is leading. Once the mark is hit on
the graft, the EndoButton is flipped by pulling the #2 suture. The
graft is then pulled back into position and the second mark should be
visualized at the aperture of the femoral tunnel. The knee is then
cycled through a range of motion at least 20 times with maximal tension
on the ends of the graft exiting the tibial tunnel. The graft can be
evaluated for isometery at this point. A second #2 suture can be placed
in the outer hole of the EndoButton and this can be left to trail out
of the tibial tunnel. This suture would facilitate removal of the
EndoButton if that were needed for some reason. With the knee in 30
degrees of flexion, with maximal tension a blunt threaded interference
screw the same diameter as the tunnel is placed anterior to the limbs
of the graft. This effectively shortens the points of fixation of the
graft but does not provide adequate fixation. Therefore, the fixation
is augmented with a suture button, staple, or screw and washer.
Dressings, Braces, Splints, or Casts
A simple sterile non-adherent dressing with a compression stocking
is placed after surgery. A cryocuff is placed directly over the
dressing and a full length hinged knee brace locked at 30 degrees of
flexion for the first week are placed in the operating room.
Graft harvest difficulties can be problematic as the surgeon is
becoming comfortable with the anatomy of the pes anserinus and the
hamstring tendons. It is mandatory that the surgeon receive training on
this harvest technique and practice on a cadaver specimen. Some of the
problems harvesting the tendons include the failure to identify the
semitendinosus and gracilis distally as they coalesce; in this case
more proximal identification is helpful. Another problem stems from not
releasing the attachments of the tendons to the gastrocnemius resulting
in premature amputation of the tendon at this attachment. Another error
could stem from not passing the tendon stripper parallel to the
direction of the tendon resulting in premature amputation of the
tendon. Finally it is helpful if the tendon stripper is not too sharp.
Tunnel malposition typically with the femoral or tibial tunnel too
anterior. This malposition can result in graft impingement resulting in
failure of loss of extension. Malposition can also reduce the isometry
of the graft resulting in failure. Stiffness especially if the surgery
is done too early or the rehabilitation program is inadequate. Donor
site morbidity is uncommon after hamstring harvest, The patients may
often have a sensation of a pulled hamstring with a pop and ecchymosis
distally where the harvested hamstring is attempting to scar. This
usually happens within the first six weeks as the patient becomes more
active.