Anterior cruciate ligament reconstruction is a surgical tissue
graft replacement of the anterior cruciate ligament, located in the knee,
to restore its function after anterior cruciate ligament injury. The torn
ligament is removed from the knee before the graft is inserted. The surgery is
performed arthroscopically. Types of grafts
Two alternative sources of replacement material for ACL reconstruction are
commonly utilized: Autografts, and
Allografts. Since the tissue is one's own in an
autograft the probability of rejection is minimal.
Sterilization and redundant donor screening process make allografts a
generally safe choice for patients; however, risks remain. Irradiation of
donor content to remove infectious agents potentially weakens the selected
tendon, although for ACL surgery the weakened tendon is generally as strong
as the replaced ligament. Infection may also require removal of the graft.
Synthetic tissue suitable to ACL reconstruction has also been developed.
Few data exist on its strength or reliability.
= Allograft= The patellar tendon, anterior tibialis
tendon, or Achilles tendon may be recovered from a cadaver and used as an
allograft in reconstruction. The Achilles tendon, due to its large size,
must be shaved to fit within the joint cavity. There is a slight chance of
rejection, which would lead to more surgery to remove the graft and replace
it. = Autograft=
An accessory hamstring or part of the patellar tendon are the most common
donor tissues used in autografts. Quadriceps tendon can also be used if
the patellar tendon has been harvested in a previous surgery.
Hamstring tendon Hamstring autografts are made with the
semitendinosus tendon either alone, or accompanied by the gracilis tendon for a
stronger graft. The semitendinosus is an accessory hamstring, and the gracilis is
actually not a hamstring, but an accessory adductor. The two tendons are
commonly combined and referred to as a four strand hamstring graft, made by a
long piece which is removed from each tendon. The tendon segments are folded
and braided together to form a quadruple thickness strand for the replacement
graft. The braided segment is threaded through the heads of tibia and femur and
its ends fixated with screws on the opposite sides of the two bones.
Unlike the patellar tendon, the hamstring tendon's fixation to the bone
can be affected by motion in the post-operative phase. Therefore,
following surgery, a brace is often used to immobilize the knee for one to two
weeks while the most critical healing takes place. Evidence suggests that the
hamstring tendon graft does just as well, or nearly as well, as the patellar
tendon graft in the long-term. Many patients struggle with recovery
after a hamstring graft procedure. Problems include strengthening of the
quadriceps, T-band and calf. Proper healing procedures and medical care are
essential to regain strength. The main surgical wound is over the
upper proximal tibia, avoiding the typical pain sensation when one kneels
down. The wound is typically smaller than the patellar tendon graft and hence
less pain after the operation. A new technique for minimal-invasive
harvesting from the back of the knee has been developed in the last years. This
technique is faster, easier and produces a significantly smaller wound.
Unfortunately, this less invasive procedure can still cause nerve damage
around the scar and throughout the distal portion of the leg. In an effort
to fix this issue, surgeons have tested different incision directions in an
effort to decrease nerve damage and sensory loss near the incision site. A
study published in Knee Surgery Sports Traumatology Arthroscopy about whether
vertical, transverse or oblique cuts result in the least amount of nerve and
sensory damage came to the conclusion that, “With the oblique incision, the
direction of incision is almost parallel to the infrapatella branch of the
saphenous nerve, thus the risk of injury to that nerve is the lowest.”
There seems to be some controversy as to how well a hamstring tendon regenerates
after the harvesting. Most studies suggest that the tendon can be
regenerated at least partially, while still being inferior in strength to the
original tendon. Advantages of using a hamstring graft
includes its high “load to failure” strength, the stiffness of the graft,
and the low postoperative morbidity. It has shown that the natural ACL can
withstand a load of up to 2160 Newtons.By using a hamstring graft, this
number doubles. The "load to failure" is twice as high as the natural ACL,
helping to decrease risk of becoming injured again. The stiffness of a
hamstring graft also contributes to this risk factor. If the graft is stretching
out instead of staying stiff, this increases the shift between the tibia
and the fibula. In comparison to the stiffness of the natural ACL, the
hamstring graft quadruples. Therefore, using a hamstring graft for a torn ACL
has a variety of benefits including stability and recovery purposes,
decreasing the chance of re-injury. Patellar tendon
The patellar tendon connects the patella to the tibia. The graft is taken from
the injured knee, but in some circumstances, such as a second
operation, the other knee may be used. The middle third of the tendon is used,
with bone fragments removed on each end. The graft is then threaded through holes
drilled in the tibia and femur, and finally screwed into place.
The graft is slightly larger than a hamstring graft, however graft size is
not a determinant of outcome. The most important factor in determining the
outcome is correct graft placement. The disadvantages include: 1. Increased
wound pain. 2. Increased scar formation as compared to a hamstring tendon
operation. 3. Risk of fracturing the patella during harvesting of the graft.
4. Increased risk of tendinitis. 5. Increased levels of pain with activities
that require kneeling years after post op. In general, some or all of these
disadvantages could be attributable to the phenomenon of post-operative
patellar tendon shortening. = Choice of graft=
Type Typically, age and lifestyle choices
help decide the type of graft to be used for ACL reconstruction. The overall
factors in knee stability are correct graft placement by the surgeon and
treatment of other menisco-ligament injuries in the knee, rather than type
of graft. The advantages of an allograft are that
the patient does not sustain additional injury through removal of a tendon, thus
improving recovery time, and that total procedure time is slightly reduced.
Disadvantages are the risk of infection from foreign bodily materials and
perhaps a slightly weaker graft. Site
No ideal graft site for ACL reconstruction exists. Surgeons have
historically regarded patellar tendon grafts as the "gold standard" for knee
stability, however the procedure suffers a slightly higher complication rate,
including knee pain when lunging. Hamstring grafts historically had
problems with fixation slippage and stretching out over time. Modern
fixation methods avoid graft slippage produce similarly stable outcomes with
easier rehabilitation, less anterior knee pain and less joint stiffness.
Although there is generally less experience with the use of tibialis
anterior grafts, preliminary data has shown no difference in short-term
subjective outcomes between tibialis anterior allografts and patellar tendon
allografts. Stem Cell Treatment during ACL Surgery
Recently, autologous stem cell transplantation using mesenchymal stem
cells has been used to improve recovery time from ACL surgery, especially for
athletes. MSCs are multipotent stem cells, meaning they can differentiate
into multiple cell types. In the case of mesenchymal stem cells, these cell types
include osteoblasts, adipocytes, or chondrocytes. Ligament tissue mainly
consists of fibroblasts and extracellular matrix. The fibroblast is
the main cell type but the extracellular matrix is made of collagen with
proteoglycans. These fibroblasts are in charge of maintaining and regenerating
new tissue. When introducing MSCs to induce new ligament growth, there are
several factors that a tissue engineer must consider. Ligament cells differ in
size, respond to different cues in the cell environment, and express different
cell surface markers, limiting the number of clinical treatments for
accelerated repair of ACL tissue to MSCs and primary fibroblasts obtained from
other ACL tissue. According to a study performed by Ge et al., the
proliferation rate and collagen production were greater with MSCs than
fibroblasts. Therefore, most modern stem cell injections use MSCs to promote
faster repair of the ACL and allow people such as athletes to return to
their previous form faster than ever before.
In order for MSCs to differentiate into an ACL, they must be placed in a proper
scaffold on which to grow and also must be in a bioreactor which will maintain a
normal physiological environment for the cells to reproduce and proliferate
effectively. The scaffold must have the mechanical properties of a healthy ACL
to sustain the ligament while it is in its primary form and maintain normal
knee movement. It must also be biodegradable so that as the ligament
grows, the scaffold degrades proportionally and eventually disappears
altogether when the ligament has physiological mechanical properties.
Scaffolds that are used for ACL growth include collagen, silk, gelatin,
poly-lactic acid, and glycosaminoglycins. Mechanical
properties of the scaffolds are further enhanced through braiding and twisting
of the scaffold materials. The bioreactor is the environment in
which the ACL will grow. It has to have similar properties to a knee joint so
that when it is inserted into the body, it is not reject as foreign which could
cause infection. Therefore, it has to have compatible pH levels, oxygen
concentration levels, metabolite levels, and temperature as well as be sterile.
Recovery Initial physical therapy consists of
range of motion exercises, often with the guidance of a physical therapist.
Range of motion exercises are used to regain the flexibility of the ligament,
prevent or break down scar tissue from forming and reduce loss of muscle tone.
Range of motion exercise examples include: quadriceps contractions and
straight leg raises. In some cases, a continuous passive motion device is used
immediately after surgery to help with flexibility. The preferred method of
preventing muscle loss is isometric exercises that put zero strain on the
knee. Knee extension within two weeks is important with many rehab guidelines.
Approximately six weeks is required for the bone to attach to the graft.
However, the patient can typically walk on their own and perform simple physical
tasks prior to this with caution, relying on the surgical fixation of the
graft until true healing has taken place. At this stage the first round of
physical therapy can begin. This usually consists of careful exercises to regain
flexibility and small amounts of strength. One of the more important
benchmarks in recovery is the twelve weeks post-surgery period. After this,
the patient can typically begin a more aggressive regimen of exercises
involving stress on the knee, and increasing resistance. Jogging may be
incorporated as well. After four months, more intense
activities such as running are possible without risk. After five months, light
ball work may commence as the ligament is nearly regenerated. After six months,
the reconstructed ACL is generally at full strength, and the patient may
return to activities involving cutting and twisting if a brace is worn.
Recovery varies highly from case to case, and sometimes resumption of
stressful activities may take a year or longer.
The reconstructed ACL has a high success rate. Studies show that cases in which
the ACL retears are generally caused by a traumatic impact. Some studies
indicate that wearing a brace during athletic activity does not reduce
probability of re-injury to the ACL, but a study of active post-ACL replacement
skiers shows a 64% reduction in re-injury likelihood by using a knee
brace after recovery. A sufficiently traumatic impact to retear the ACL is
unlikely to be mitigated by the use of a brace.
Recovery Progression Recovery is a four phase progression.
= Phase 1= The goals of this phase are to:
Eliminate swelling due to inactivity Progress from partial weight bearing to
full weight bearing exercises Regain normal range of motion
Increase quadriceps strength Increase hamstring strength
Some equipment that can be used and exercises that can be performed are:
Use of Cryo-cuff - provides cold compression
Isometric Contraction of Quads Quad Sets
- stand against wall, push extended knee against rolled towel
- progress to straight leg raised to 30deg.
Wall Slides - To increase knee flexion
Assisted Knee Flexion Towel Squeeze
- Sit in chair, squeeze rolled towel between knees for 5 seconds. Relax &
repeat. VMO Strengthening Exercise
Supported Bilateral Calf-Raises walk without crutches
= Phase 2= The goals of this phase are to:
Regain full knee extension Restore knee flexion to +130°
Perform a full squat properly Regain good balance and control
Reestablish proper gait Some exercises that can be performed
are: Mini squats
- Progress to full squats → single-leg half squat
Mini Lunges - Progress to full lunges
Leg Press - Double-leg → single
Step-ups - lateral & forward
Bridges - Double-leg → single
- Floor → Swiss ball Hip Abduction w/ Theraband
Hip Extension w/ Theraband Wobble board
- Assisted → un-assisted → eyes closed Stork Stand
- Assisted → un-assisted → eyes closed → unstable surface
Static Proprioceptive hold/ball throwing Functional Exercises that can be
performed at this time include: - Walking
- Bike - Roman Chair
= Phase 3= The goals of this phase are to:
Regain full range of motion Regain full strength and power
Increase agility allows for adaption to direction change,
acceleration and deceleration Be able to perform restricted
sports-specific drills Begin plyometric drills
Some exercises that can be performed are:
Continue exercises from Phase 2, progress as necessary
Jump & Land drills - Jump from block & stick landing
- Double-leg landing → single-leg Plyometric Drills
- Jumping over blocks, sideways & forward
- Hopping up & down steps/stairs = Phase 4=
The goal of this phase is a return to activity, however it requires an ability
to perform some functional performance tests such as:
Agility Tests Illinois Agility Test
Zig Zag Agility Test These tests are used to test the ability
of the knee to withstand cutting and planting maneuvers
Standing Vertical Jump Here you jump straight in the air from a
standing start and land on two feet as stable as possible.
Heiden Hop Test Here you essentially jump as far as
possible with the uninjured leg and land on the injured leg. Your ability to
stick the landing is indicative of good knee function.
Isokinetic Testing This is used to evaluate muscle
strength. The individual should have at least 90%
quadricep strength of the uninjured leg They should also have equal hamstring
strength to their uninjured leg as well Cost and logistics of the procedure
The cost of ACL surgery in the US is an unfortunate reality which affects
whether or not a patient proceeds with the operation. The average out-of-pocket
cost of ACL reconstruction is $2,339.43, according to a 2010 survey of ACL
surgery patients. Insurance companies may or may not cover the various
billable components of ACL reconstruction, which may include:
pre-op appointments, pre-op physical therapy, ACL reconstruction by the
surgeon, an assistant's charge, anesthesia, the hospital or facility
fee, rental fees for cryotherapy, prescriptions, transportation, crutches
or wheel chair fees, leg brace fees, post op visits, and a physical therapy
rehab program. Despite the complexity of the procedure
and numerous doctor visits involved, 80% - 90% of patients who have had the
surgery said they had favorable results. References
External links