Where the femur and tibia meet is the hinged joint called the knee. The patella protects the joint (kneecap), which lies in front of the knee. The articular cartilage helps to cushion the joint by surrounding the edge of each of the femur, tibia, and the back side of the patella. The meniscuses are two crescent-shaped pillows of fibrocartilage which are found medially and laterally, and help cushion the knee. The ligaments within the joint help with stabilization and balance. There are two collateral ligaments. These ligaments run along either side of the knee and help limit sideways motion. Two cruciate ligaments attach to the femur and tibia, and cross within the knee. The back ligament is called the posterior cruciate ligament (PCL) and helps in preventing the tibia from sliding back on the femur. The patellar tendon is the elastic band-like tendon which runs from the quad down to the tibia. It is the track on which the kneecap runs, and it keeps the patella in place.

Within the knee there are the three main ligaments described above and the ACL. The ACL gets all the publicity because of the problems it causes when it is torn. It is a band of fibrous tissue which connects the tibia to the femur and helps to prevent the tibia from sliding forward on the femur. Muscles surrounding the knee (ie. quadriceps and hamstrings) also help to keep the femur and tibia in place. Being the anterior of the two main ligaments which cross within the joint, the ACL also helps to prevent hyperextension. By preventing the movement of the tibia, and by preventing hyperextension, the ACL also protects the articular cartilage and the meniscal cartilage from tearing.

An ACL injury can happen to anyone. The rate of injury is almost equal through all levels of sports, from beginner, to recreational, to professional athletes. Once torn the ACL doesn't heal itself, so the next question would be "What can be done now?". There are a number of different procedures and ideas on how to treat the injury. Some people choose not to have surgery and continue their regular lives, while others choose the surgery. There are three main methods used today to replace the torn ACL; the patellar tendon graft, semitendinous-gracilis (hamstring) graft, or an allograft (usually a donated Achilles tendon). No matter which method is used, they all have individual advantages and disadvantages.

Tens of thousands of athletes have chosen the patella tendon reconstruction in the past ten years. This is generally because once the patellar tendon heals, there isn't any more complications. The patellar tendon graft is used when the strength of the graft is the main priority. To perform the surgery, there are three main ways in which the knee can be accessed during the surgery. The first is through two main incisions (one medial and one lateral). This method allows for the most accurate positioning. The second is through one main incision down the centre of the knee, and the third is through arthroscope. Each of these methods also have advantages and disadvantages in regards to rehabilitation and long-term results.

Once the incision is made, the patellar tendon is harvested. The middle third of this tendon is measured off, and if it exceeds one centimetre, then just one centimetre of the tendon is cut. Removed, along with the tendon, is a small piece of the patella and a small piece of the tibia. Both bone pieces attach to the patellar tendon. The harvested patella measures 20 x 9 x 7 mm and the harvested tibia measures 30 x 10 x 10 mm. Before the bone is removed, 2 mm holes are drilled into each piece. The bone and tendon are then both removed using a fine oscillating saw.

The next step is to remove 5-10 mm of bone in the tibial tunnel (if necessary) to keep the graft from getting caught during extension. Also the femal notch is sometimes widened in females. Holes are then drilled in the lateral femoral condyle and in the tibia. These holes are widened to fit the bone plugs. The graft is strung into the isometric position and secured with screws. The knee is then brought in to full flexation and extension, making sure that it flows right and is similar to the other leg. Although often a few degrees of extension are lost, the patellar tendon method is the most commonly used today.

The semitendinous method (hamstring method) is generally used when the longevity and simplicity is priority over strength. The incisions used in this method are almost identical to the patellar method, except that an arthroscope is almost always used. A small incision is cut in the back of the knee and the semitendinous tendon is taken out using a tendon stripper. Depending on the method being used, the gracilis tendon may be removed also. Both of these tendons normally attach the hamstring muscles to the lower leg. Once removed, the tendons are then cleaned of muscle.

The semitendinous-gracilis tendon method has been proven on one test to be even stronger than the patellar tendon graft. It involves weaving and looping the two tendons to form a new ACL. This new ACL is then folded over and stapled into place. The recovery from the hamstring method is much easier because there is no disruption to the patellar tendon. Although both the semitendinous and patellar methods are extremely strong, critics say that the easy rehabilitation of the semitendinous is not worth the potential long-term hamstring problems.

The last commonly used method is an allograft. By using tissue from another human, there is no disruption to the hamstring or patellar tendon. An ideal allograft has to meet seven standards. It should duplicate the physiological function of the ACL, it shouldn't create a high infection risk, it should be non-immogenic to the host, there should not be any hyperplastic or alignant transformations, it should be available in different sizes, it should be easy to transplant, and the material of the graft should be able to be stored for long periods of time. The types of allografts that meet these standards are combinations of anterior cruciate ligament-bone, bone-patellar tendon-bone, bone-posterior cruciate ligament- bone, quadriceps tendon-bone, Achilles tendon and freeze dried fascia lata. The selection of which allograft to use depends on the demands that will be placed on the knee.

Each graft can handle a different amount of force. A normal ACL can handle 400 lbs. Normal living activities also apply different levels of these forces on the ACL. Cycling applies 6 lbs, leg squats applies 16 lbs, the lachman test-20 lbs, walking downstairs-20 lbs, level walking-40 lbs, 15 degree isometric contractions-65 lbs, walking down a ramp-100 lbs, active leg extensions-110 lbs, jogging-135 lbs, and active leg extensions with a 7 lbs weight applies 140 lbs. No graft has ever been found to have the same strength as the original ACL, but the patellar tendon method comes the closest, being able to absorb 300 lbs. The semitendinous method can absorb 120 lbs, the illotibial band can absorb 80 lbs, and the fascia lata absorbs 70 lbs. Whichever method is chosen as an allograft, it is up to the tissue bank to make sure that there are no transmissible diseases, the tissue is sterile, the donor is young and that the tissue was retrieved under sterile conditions. If all of these standards are met, the allograft is a very successful procedure.

The strength of any graft is at its maximum when it is first placed in the knee. During the first two weeks the graft loses strength as new blood vessels are formed. This process is called revascularization. Next, it takes about 6 weeks for the graft to regain enough strength for normal activities. It then takes the graft two years to reach full maturity. Full maturity is not needed to resume sports or an active lifestyle, though, and it regains 90% of its strength in the first year.

The first attempts at an ACL reconstruction was in the 1970's. Doctors tried to sew the ligament back together again. These attempts failed. Since then reconstruction has been tried using allografts, xenografts, autografts, synthetetic material and a combination of synthetic and biological material. Along with these methods they used to open up the entire knee, and this also meant the end of any sports career. The procedure which eventually became prominent in the late 1970s and early 1980s was called Lateral Substitution Over the Top (LSOT). This method involved using the illiotibial tract of the thigh. The goal of LSOT was to have limited extension to protect the graft. However this placed limitations on the knee and the lifestyle of the patient. Most patients didn't really like this idea, so the next method to come into practise was the patellar tendon and the other methods used today.

Also 10 years ago, patients over the age of 40 weren't recommended for surgery. They were told to change their lifestyle to accomindate for their ACL deficient knee. Today, age is no longer an issue because of newer methods available, quicker recovery time, and better security. New methods are continuously being tested and new research is always in progress. The future of ACL reconstruction should include a prosthetic and/or augmented biological material. This material should be able to considerably reduce the rehabilitation process because of the little disruption to the joint and by eliminating the need to protect the graft. Another procedure, called the Healing Responce, that doesn't use any screws or pins is being tested. This procedure uses an icepick-like device to poke holes in the bone near the injury. Blood and bone marrow cells are released, clot and form a natural fixation to hold the injured ligament in place. It has been tried on 200 patients in the past two years and so far it has a 95% success rate.

The tearing of the ACL is considered an epidemic. It is the number one reason athletes find themselves on the operating table, with over 100,000 recorded incidences each year. These numbers continue to rise as diagnostic techniques improve and the demands of sport increase. The highest risk sports are skiing and basketball. An average of one in every 200 skiers tears an ACL, and it is difficult to find a women's basketball team that has not experienced at least one tear.

Most of these tears occur without any outside contact. A twisting of the knee, a hard landing or just hyperextension can all easily tear the ACL. Some people feel excruciating pain and are unable to walk without surgery, while others feel no pain at all. If no pain is felt it is usually because the nerve pathways, along with the ACL, have been severed. Most patients do feel a ripping of some sort and hear a 'pop', 'click-clack' or a sound like paper being torn. Also in almost all cases swelling develops within 24 hours of the injury. No matter how they tear the ACL, it often takes a long time for the patient to feel confident with their knee again.

The ACL can't be felt with a finger like a rib or a pulse. Therefore diagnostic techniques had to be developed. From this need came three main tests. They are the anterior drawer test, the lachman test and the pivot shift test. To conduct the anterior drawer test, the patient lies down on his/her back with the hips at a 45 degree angle and the knees at a 90 degree angle, to the table. The doctor then sits on the patient's foot and applies an increasingly firm pull on the calf. If the Tibia pulls forward, almost like a drawer opening, then the test is positive. In the pivot shift test the patient lies slightly on his/her side with the knee fully extended, and muscles relaxed. By applying light stress on the knee and slowly flexing it, the doctor feels for the click or clunk at about 30 degrees for a positive test. The third test is the lachman test. This test is the most popular of the three and can usually give conclusive results. The patient relaxes the leg, and the doctor holds it with one hand on the lower thigh and the other on the upper calf. With hands on opposite sides of the knee, and holding it firmly at 20-30 degrees, the doctor firmly pulls the tibia forward. This test (and the other two) should always be compared to the other knee. If there is any more movement in the affected knee, it indicates a ruptured ACL. The lachman test is more sensitive than the other two tests, but ninety percent of all ACL tears are diagnosed by using one of these tests, or all three.

Once the ACL tear is diagnosed, the patient must decide to treat it surgically or to cope (brace and bear any pain). Reconstruction is not necessarily the best option. The decision generally is based on the lifestyle of the patient and what demands will be placed on the knee. Reconstruction is usually recommended if the patient is young, participates in high-risk sports, has a meniscal tear, other cartilage damage, or if there is limited motion in the knee. Also, if the knee gives out, by the tibia sliding forward on the femur, reconstruction is recommended. This giving out causes a loss of balance and adds stress on the articular cartilage and meniscus, possibly causing tearing.

If reconstruction is decided upon, the selection of which procedure to have is also a difficult process. The most important factor is the activity level of the patient and whether or not the patient is willing to change his/her lifestyle. A high-level athlete puts more demands on the knee than the recreational athlete, so each patient requires an individual treatment plan. The decision should be based on the severity of damage to the knees, the specific athletic activity, the frequency of sports participation, expectations, motivation, willingness to modify activity level, and the willingness to accept an intensive rehabilitation program. The advantages and limitations to each graft have already been listed above.

It doesn't matter who the patient with the ACL deficient knee is, he/she will most likely need a brace. There are three main types of knee braces; prophylactic, rehabilative and functional. The prophylactic knee brace is used to prevent injury to the ligaments of the knee. It is controversial in how useful this brace really is. Some studies show that they could help prevent medial collateral ligament (MCL) injuries, and other studies show that they don't do anything for the knee. There is no evidence that this type of brace can help prevent ACL injuries, and there is actually some biomedical data which proves that prophylactic bracing can increase the chance of ACL injury.

The rehabilitative knee brace is designed to provide protection and controlled movement for a ligament injury that has been treated either operatively or non-operatively. There is some concern expressed about whether this brace can really control passive motion and joint displacing forces, but generally it is a good brace. This brace is usually light, easily applied and adjusted, and provides easy access to the skin. Also, stops on the hinges of the brace allow active and passive motion to be limited.

The functional knee brace is designed to provide stability to a knee with ligament injuries. It is made to control the extra looseness within the knee. Studies about this brace show that it increases the patient's stability, although the greatest benefit was in patients with less laxity and who put lesser demands on the joint. All of the braces may help the knee, but none have ever been able to restore its normal laxity after a tear of the ACL.

The most difficult part about tearing the ACL is the rehabilitation process after reconstruction. In the past this process was extremely long (1-2 years) and was done very passively. In the recent years the time period for the rehabilitation has been decreased to six months for some patients, and the conservative rehabilitation has been replaced by a hard work out. The overall program depends on the physician, the physical therapist and the patient, but two main points are always looked at; immobility must be minimized and the healing tissues must never be overloaded. Generally once the initial pain of the incision subsides the patient can work on passive extension and flexation exercises. This is a relatively new idea (past 5-10 years) as the patient used to be in a cast for 4-6 weeks post-operative. The cast isn't used anymore because of better surgical techniques and graft fixings.

The rehabilitation of the patellar tendon over the hamstring graft is generally much harder. This is usually related to the huge loss in quad strength and the disruption of the patellar tendon. Much of the rehabilitation is waiting for the tendon to heal.

In a recent study of 75 ACL replacement patients between the ages of 45 and 65, only 4% still had pain or swelling five years post operative. None of them had any instability. On the average these patients started biking at 4 months, jogging at nine months, skiing at ten months and tennis after one year for examples of two very different rehabilitation programs. They are both for a patellar tendon graft). Rehabilitation programs have a huge variance in protocol from one to the next, but in all of them the patient must obtain a minimum of 80% of the quadriceps strength in the injured knee as in the normal one, before returning to sports.

There are many different complications that can occur with the ACL replacement surgery, but they are rare. Reasons for the general failure of the graft include trauma, poor fixation, nonatomic placement, inadequate replacement material, failure to use a brace, the use of synthetic replacement, problems with newly tested materials or procedures, extra laxity and articular cartilage degeneration. Early failure of the graft is almost always associated to one of three main incidents; a fall or a twist, fatigue-related failure, or by stretching the graft past its limit. Most reinjuries happen the same way the original ACL was torn (across the middle of the graft), and teenagers are more likely than any other age group to reinjure their knees. There are also some complications directly related to the patellar tendon graft. These problems usually occur when the 'tracking' of the patellar tendon is off. This results in a greater occurance of anterior knee pain, flexation contracture, and extensor weakness.

Then there is arthrofibrosis. This complication causes some debate. Arthrofibrosis can occur when the knee is operated on too early, that is, before all of the swelling of the initial injury goes down. The knee reacts to this, causing stiffness in the joint, but a new study shows that waiting isn't necessarily the best option. These studies show that by operating within the first month of injury, it can reduce cartilage and menisci tearing, in the long run preventing degenerative joint disease. In this study the Italian researchers compared athletes who had received surgery within two weeks of the injury to those who received the same surgery three to twenty-one months after injury. Five years post-operatively they found little difference, except that the earlier treated patients had fewer meniscal and bone lesions, and better overall stability. Whether or not these results are worth the risk of arthrofibrosis is still to be determined

It is difficult to prevent ACL injuries because they can happen to anyone at anytime, but there are a few precautions that have seemed to work. These include a good warm-up, stretch and cooldown, avoiding forceful landings and twisting of the leg, and obtaining and maintaining top conditioned quadriceps and hamstring strength. Also for skiers, the new parabolic ski has been proven to help reduce ACL injuries.

One of the biggest mysteries about the ACL is the difference between the number of injuries seen in women and men. Women seem to tear there the ACL much more frequently then men. In basketball the ratio is four to one and in gymnastics the ratio is almost eight to one. There are many theories as to why the statistics are so lopsided but no one knows for sure. One theory is that women have a weaker quadricep muscle than most men. When the leg muscles aren't as strong, the stress is increased on the ligaments. To prevent this, athletes, especially females should make sure their bodies are in the best condition they can be in. Also some studies show that women rely more on the quads instead of using both the hamstring and quads. This leaves the ligaments vulnerable. One activity that can help to equalize the muscles is jumping rope. This is an excellent activity for female athletes because both the quads and hamstrings have to flex as the athlete hits the ground.

A third theory is that females have different joint structures with less flexibility in their ligaments and more laxity within the knee. Women also tend to have a much narrower femal notch (the notch in which the ACL and PCL run). The female femal notch tends to be more of an 'A' shaped, while the male femal notch tends to be more of a 'U' shape. Some researchers believe that many ACLs are sheared by the narrowness of the femal notch. The women's body also angles in more at the knees because of their wider hips. This may place extra stress on the ACL.

Another theory is that girls are not exposed to the correct motor learning skills at the important times of their development. The neuromuscular co- ordination needed in athletes is not being taught to young girls, and they aren't usually encouraged to learn it. By the time these young girls show an interest in aggressive sports, (usually by Jr. High), it is too late. The consequence could be all of the knee injuries.

Footwear is yet another theory. Sneakers and athletic footwear are continuously improving in grips and ankle support systems. If the ankle can't give on a quick stop, then something else might. That could be an ACL. Also, women in sports generally wear footwear made for a man's foot (ie. soccer cleats, basketball sneakers, ski boots). None of these were made for a women's strength, weight or foot.

Examples of top female athletes who have torn an ACL include Theresa Edwards, Tiffany Woosley and Cheryl Miller. These three basketball players and many other female athletes are constantly pushing the limit of their sport and their knees. The final theory is that female athletes are simply going beyond the capacity of their ligaments to hold the stress. As women's athletics become more up tempo and demanding, a huge rise in ACL tears have occurred. Coincidence? Maybe.

Today ninety percent of all ACL patients return to their previous lifestyle, either through reconstruction surgery or coping. With advancing technology and new procedures, that number can only improve.