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About your knee...  "torn ACL????"                  (Updated 3/20/05)

The doctor has just told you that your ACL (anterior cruciate ligament) is torn.  What does this mean?  Ligaments are structures that hold bones together.  They not only stabilize the knee joint, but more importantly they guide the motion of the knee.  Therefore, the loss of a ligament results in instability, i.e.:  a knee that gives out or gives way, but also a knee that does not move normally. This may or may not cause problems for your knee in the future, depending upon your activity level, and associated damage to the knee:  past, present, and future.

First a few words about anatomy.....
"Cruciate" means crossing - and the anterior cruciate ligament is injured in your knee.  The ACL has a mate, the PCL.  Anterior means front; posterior means back.  Thus you have injured the "front criss-crossing ligament"  in the very center of your knee joint.  Because the ACL is located in the very heart of your knee joint and is bathed by the fluid of the joint, it will not heal on its own.  Additionally, your menisci ("cartilage's - the shock absorbers") are structures that lie as spacers between the bones that make up the knee joint.  About half the time when one injures the ACL, one will simultaneously tear the knee cartilage.  Tearing the knee cartilage may cause pain at the joint lines and such symptoms as locking, catching, popping, and swelling.

 

Now about function....
The ACL is a stabilizer.  Without this stabilizer the knee may give out and the normal motion or "dynamics" of the knee joint is irreversibly altered.  This leads to abnormal motions of the knee joint. The function of the ACL is to prevent the lower leg bone (tibia) from coming forward relative to the thigh bone (femur).  More importantly, it also prevents an abnormal rotation of the thigh bone on the leg bone with the foot planted, such as when cutting and pivoting. This may occur with the knee near full extension (straight) particularly when attempting to cut, land from a jump, decelerate, or change directions.  This is called the "pivot shift phenomenon".  Without the ACL, the knee may shift or giveaway when one attempts to pivot, especially in sports involving twisting motions - like football, soccer, lacrosse, basketball, skiing, softball, baseball, dancing, etc., but also may cause problems occasionally during day-to-day activities.

The meniscus cartilage is an important shock absorber of the knee and transmits load or force from one bone to the other.  When it is torn, the ends of the bones are more sensitive to forces and the waxy surface cartilage covering that caps the bone ends in the joint can deteriorate faster; this end result is "osteoarthritis" or wear and tear of the knee at an early age, especially in active, athletic people.

When the ACL is torn, it is almost never heals, and will not grow back.  It is usually gone for good.  The ACL has back up ligaments, but these have a relatively minor role, and they cannot usually sustain the forces of sports and vigorous activity.  Generally, therefore, these back-up ligaments  stretch out with time, and the knee becomes looser.

Putting all of this together, the end result of an "ACL deficient knee" is progressive:

(1) loosening or laxity (a knee that gives out more frequently with time);

(2) torn meniscus cartilage (loss of shock absorbers); and

(3) arthritis (a deterioration of  the surface of the joint - the hyaline cartilage). 

These changes are dependent upon one's weight, age, and activity level.  Generally, the more active, younger, and heavier one is, the greater likelihood and speed of deterioration.  Arthritis also depends upon genetic (inherited) factors.

Numerous papers and studies in the orthopedic literature have documented the natural history or outcome of a neglected ACL deficient knee.  Poor results, i.e., continued instability and deterioration of the knee, are noted for many of those who attempt to return to high activity levels.

On the other hand, there are studies to support conservative treatment.  However the consensus is, successful conservative treatment of the ACL deficient knee includes:  activity modification, i.e., restricting turning, twisting, and cutting sports, in favor of activities such as cycling, straight ahead jogging on even terrain, cross country skiing, etc.  Another important element of conservative treatment is muscle strengthening - FOR LIFE.  A consistent program emphasizing quadriceps and especially hamstring strengthening exercises is essential.  Bracing is often advocated  for the ACL deficient knee in combination with rehabilitation and activity modification, but this is controversial.  Numerous sports braces are on the market, however, documentation is lacking and definitive recommendations based on clear-cut scientific data are limited. They may prevent further injury.

Therefore, the alternatives for your knee include:  (1)  benign neglect (no treatment); (2)  "conservative aggressive" treatment, i.e., activity modification with avoidance of twisting sports, strengthening program especially for the hamstrings, and possibly bracing); and (3)  surgery, to rebuild the ligament.  Usually, when the ligament is disrupted it is in a very high explosive fashion.  Suffice it to say that direct repair of the torn ends are fraught with technical difficulties and outcomes are generally unsatisfactory.  Therefore, when one elects a surgical procedure to "reconstruct" the ACL, we are talking about the replacement of the ligament with another structure.

"Change your life or change your knee."

Surgery for ACL reconstruction is a complex concept.  There are probably 100 procedures described to restore knee stability after this ligament is injured.  They fit two basic categories, replacing the ligament in its original position (intra-articular) vs. making modifications on the outside of the knee joint to compensate for the loss of the ligament (extra-articular).  Extra-articular repairs are a thing of the past. Nowadays, most young active individual's are best served by an intra-articular ACL replacement. The choices for replacement are basically three categories:  autograft (tissue obtained from another site in the same individual's leg), allograft (tissue obtained from a donor, i.e., a cadaver), and a synthetic man-made substitute.  Each of these categories has its own advantages and disadvantages.

The autograft is the "gold standard", and most commonly used method of reconstruction.  Obviously, an autograft sacrifices tissues from elsewhere in the limb, with potential future repercussions, such as "donor morbidity", weakness, pain, tendonitis, stiffness, etc.  The two main autografts usually utilized are the patellar tendon or hamstring tendon.  In a small proportion of individuals use of the patellar tendon can result in increased post-operative "grinding" and pain behind the knee cap, quadriceps weakness and atrophy, patellar tendonitis, or very, very rarely a catastrophic complication such as patella fracture or rupture of the remaining portions of the patella tendon. Fortunately, most of the time these problems are not noted, and there are no donor site problems.  Suffice it to say however, that sacrificing a portion of the patella tendon to use as a new ACL takes away from the prime and only extensor of the knee, the quadriceps mechanism.  There is no back up "machinery" to extend the knee.

On the other hand, there are numerous hamstring muscles and tendons. The prime hamstrings are the biceps, and the semimembranosus.  These are not used as donors. The secondary or lesser "hamstrings" such as the semitendinosus and the gracilis can be utilized with no significant loss of hamstring function nor strength.  One doesn't typically miss the donated hamstrings.

In order to avoid so called "donor morbidity", allografts have been advocated as a potential source of the ACL replacement.  A tissue is harvested from a cadaveric donor (a dead person), and is harvested in a sterile fashion to avoid contamination by bacteria, and is then frozen. The donor is screened for historical risk factors for such infectious diseases as hepatitis, syphilis, and AIDS.  Furthermore, the donor's blood and tissues are tested for these diseases.  All donor material must test negative.

Transfer of the AIDS (HIV) virus from tissue donors to recipients despite negative tests, according to reports by the CDC in Atlanta and by the Red Cross, is an extremely rare phenomenon.  Testing has improved substantially, and thousands of allografts have been done safely. AIDS IS CERTAINLY A SMALL BUT THEORETICAL POSSIBILITY, with risk estimates at 1 in 800,000 to 1 in a 1,000.000. Another concern about allograft is the potential for tissue rejection.  Unlike the heart, kidneys, and other transplanted tissue, transplanted bone and tendon is froze, thereby eliminating its "antigenicity", which is the capacity to induce a rejection by the host.  Therefore,  fresh sterilely harvested and frozen allograft tissue appears to be a safe and effective form of ACL reconstruction, with an acknowledged  risk for potential of transmitting infectious disease including: AIDS, hepatitis, syphilis, bacterial infections, and a minimal risk of rejection. Studies to date appear to show allograft tissues are strong and heal in a fashion similar to autografts, but perhaps more slowly and incompletely.  They may stretch out more, and may take longer to heal.

Finally, the other option is synthetic substitution.  Synthetics include:  Goretex, Dacron, and the LAD (ligament augmentation device) prosthesis.  These appear to work well on the  short term, however, they appear to stretch and tear over the long term. There is no man-made tissue that permanently can stand up to long term wear and tear within the human body. It appears that ACL synthetic substitutes are no exception to the rule.  They cannot be recommended for a long-term good result. Results with biologic tissues, such as autografts and allografts, appear to provide a higher proportion of long-term successful results. Synthetics have fallen out of favor.

Surgery for the  ACL replacement is usually done as an outpatient (in-out same day).  Surgery takes anywhere from 1-1/2 to 2-1/2 hours, depending upon the need for associated procedures such as repair of a torn meniscus (cartilage) or other ligament work.  The surgery is typically performed in an arthroscopic fashion.  Small incisions must be made to construct tunnels in the bones through which the graft is passed such that it ends up being in a similar position to the old ACL.  The incisions are kept very small and cosmetically, these are generally very acceptable.  The days of a long scar traversing the front of the leg are gone.  Other advantages of an arthroscopic technique are decreased post-operative pain and decreased drying effect on the waxy surface cartilage of the end of the bone thereby reducing the chance of late arthritis.  Arthroscopic techniques also enable precise work, especially with regard to proper placement of the graft.

The risks of this surgery include, but are not limited to the following:
The chance that the procedure will not work, or that the graft will fail, or the graft may stretch out, or that it may be reinjured, and the knee will then remain loose and symptomatic (3-5%); the risk that the procedure will work "too well" and the knee will be stiff with loss of significant range of motion (less than 2%). These possibilities are reduced with a good therapy program, a compliant obedient patient who follows the post-operative rehabilitative rules, and an excellent physical therapist. In general, stiffness is rarely a problem, but if present, usually responds to another arthroscopic procedure to remove scar tissue, and/or manipulate the knee to attain motion. Small amounts of permanent motion loss may be normal however, and rarely present functional problems.  Additional risks and potential complications include: injury to blood vessels and nerves about the knee (less than 1%); blood clots in the legs, "thrombosis", which may break off and go to the lungs, "embolism" (less than 1%); infection (less than 1%) - this could potentially render the graft non-functional; the need for future hardware removal should it become symptomatic (3%); and the minimal though theoretical possibility of acquired diseases using allografts.  It is common to have small areas of diminished sensation in front of the knee after knee surgery,   but this does not usually present a problem.

Some injuries that occur along with the ACL tear are irreversible, such as injuries to the surface cartilage of the knee joint, and injuries to the menisci (shock absorbers), which may not be able to be repaired and require removal. Therefore, a good rule of thumb is if the knee was rated 10 before the injury, the best surgery can do is restore it to an eight or nine. 

An ACL-injured knee will never be completely normal, no matter what.

Approximate cost for ACL reconstruction (including:  surgery center fees, surgeon's fees, physical therapy, brace (if necessary), etc.) is $10-15,000.00.

The three factors that determine a good outcome after reconstructive surgery include:  an experienced surgeon, a compliant ambitious patient, and a knowledgeable physical therapist.  If any one of these factors is deficient, the outcome is likely to be less than optimal. Physical therapy will allow the knee to regain its range of motion and strength over a prolonged period of time, in a safe fashion.

It takes 9 to 12 months for a reconstructed ACL to completely heal and regain its strength.

Regardless of how good the knee feels, it may not be ready to accept full activity until at least 4-6 months has elapsed, whether an allograft or an autograft is done, providing good motion and strength has been achieved in rehabilitation.

Therefore, it is extremely important that the patient and the therapist follow the physician's guidelines for post-operative rehabilitation.  This will usually require a period of anywhere from one to two weeks of crutch walking, the use of a post-operative exercises to keep the knee straight, and return to activity only when range of motion and strength have returned to normal and enough time has elapsed to allow the graft to mature.  The ACL-reconstructed knee has been protected in a brace in the past, but over the past decade, the value of these braces have been increasingly questioned.  Brace use now remains an option, but is not routinely necessary.  Braces still have a role in patients attempting to return to risky activities without surgery, but they are not a panacea.

The prognosis for this injury is generally good, considering the usual results of arthroscopic reconstruction, a knowledgeable therapist, and ambition and hard work on the part of the patient. 

Even if the surgery is done well, the therapy is meticulous, and the patient is compliant, complete healing cannot always be guaranteed.

This discussion does not encompass every single factor and consideration regarding your knee problem.  The information here is not exhaustive and all inclusive, these are the highlights. This will serve as a means of educating you about your knee and hopefully stimulating some thoughts and questions on your part. With this information you will now be more knowledgeable about the problem and hopefully this will help you make a decision about how you wish to proceed with your knee. If you have any other questions, please ask your doctor.

Arthroscopic view of ACL reconstruction.

 


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Dan Wnorowski, M.D.

 

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