The cruciate ligaments—so named because they crisscross each other—are embedded deep inside the knee joint. The ACL, which connects the femur to the tibia, is only 2 inches in length and 3/4 inch in width, but it is critical in helping to maintain stability. The ACL limits rotation of the knee and restricts the forward motion of the tibia. There are between 100,000 and 250,000 ACL injuries each year. It is more prone to injury than other ligaments and can be stretched or torn by a sudden twisting or torquing motion. For example, losing control of your skis or landing improperly during a basketball game (in which your feet go one way and your knee is turned another way) can result in an injured ACL.

A torn ACL may or may not hurt at the time of injury, depending on the type of injury. Very often, a patient will talk about hearing a pop and suddenly finding that her leg has literally buckled under. Depending on the extent of the injury, stiffness and swelling may persist for some time. In the case of a minor stretch or tear, the injury may resolve itself; however, if the tear is significant, an injured ACL can severely curtail activity.

The PCL is about 2 inches long and slightly wider than the ACL. It connects the femur to the tibia. This ligament restricts the backward motion of the leg and is rarely injured in sports but may be ripped or torn as a result of a traumatic injury such as an automobile accident.

Diagnosis

Physical Examination. Palpating, or feeling, the knee in conjunction with stability testing are the primary ways that a physician can make a quick assessment of an injury without surgical intervention. However, because the cruciate ligaments are deep inside the knee, the physician can’t palpate the area for pain or tenderness. Therefore, unlike tears of the collateral ligaments, which can be graded according to severity (grade 1, the least serious, to grade 3, the most serious), cruciate ligaments cannot be graded in a similar fashion because they cannot be felt.

Stability Tests. The Lachman test (see page 29) is often used to test the ACL. In this test, the doctor puts the leg in full extension and then pulls the tibia forward, almost as if he’s trying to pull the tibia away. If the leg moves 5 millimeters or more from the right to left, it could signify a torn ACL. A KT test quantifies the displacement with a Lachman test. The KT is a handheld machine placed on the tibia as the physician performs the test.

An anterior drawer test is also used to assess the integrity of the ACL. The knee is bent 90 degrees, and the physician pulls the tibia forward. If it moves more than 5 millimeters forward, it strongly suggests a torn ACL.

The posterior drawer test is used to test the PCL. In this test, the physician bends the knee 90 degrees and pushes the tibia back. If the leg moves more than 5 millimeters backward, it strongly suggests a torn PCL.

MRI. An MRI has an accuracy of almost 90 percent in determining a normal or completely torn ACL or PCL. Normally, the ACL or PCL appears as a dark structure that runs from the corresponding origin to its insertion. The MRI, however, is not very good in detailing a partial tear. The partial tear can be diagnosed by arthroscopy.

Arthroscopy. During arthroscopy, the physician can gently pull the ACL to determine the degree of injury and whether it warrants further treatment. However, this is very subjective, and much of the diagnosis depends on the skill and experience of the surgeon.

Treatment

The ACL. There are two courses of treatment for ACL injuries, the nonoperative approach and surgery.

Nonoperative   The physician and patient may opt to try an exercise strengthening program in lieu of surgery.

Surgery   The ACL is surgically reconstructed, and the patient is then put into a rehabilitation program.

The treatment approach depends primarily on the injury and the lifestyle and goals of the patient and any other associated injuries, for example, a concurrent torn collateral ligament or meniscal tear.

Only one-third of all people with a completely torn ACL will be able to build up their muscle strength to the point that they will be able to resume normal activity without surgery. In time, these lucky few will be able to run, jump, ski, play basketball—in short, do whatever they want—with little more than a functional knee brace for added support. The odds of success through exercise alone are not as good for women as it is for men. Born with less muscle strength than men and looser ligaments, most women will not be able to develop enough muscle strength to compensate for the insufficient ligament.

Sedentary younger people who don’t mind curtailing their activities and older, less active people may opt for an exercise strengthening program instead of surgery. Because the injury is not interfering with their lifestyle, there is less urgency to operate. However, an active, athletic person will often choose immediate surgical intervention followed by a rehabilitation program geared at getting her back to full activity as soon as possible.

Lifestyle is only one consideration in choosing treatment; the long-term implications of not surgically correcting the ligament tear is another important factor. Studies show that about 65 percent of all patients with a torn ACL will go on to develop a torn meniscus, which we now know may predispose them to the early onset of arthritis. Although the data are still lacking to directly link a torn ACL with arthritis, the indirect association has been established. Meniscal tears and/or subsequent resection of either all or part of the meniscus in most settings lead to arthritic changes, the primary reason for the trend toward repairing the meniscus. Because 65 percent of people with a torn ACL will eventually develop a torn meniscus, the ACL at least indirectly contributes to the development of arthritis. Consequently, it appears that a reconstruction might play some role in the prevention or minimization of the development of arthritis. The appropriate data, however, necessary to support this hypothesis are still lacking. As the years accumulate, we should eventually have the hard facts to support this assumption.

No matter which treatment option you choose, I want to stress that the recovery process for an ACL injury is not easy. For the patient selecting a nonoperative approach, the rehabilitative process will take approximately 4 months. In fact, the rehabilitative training for a cruciate injury can take anywhere from 3 months to a year and requires a significant time commitment (at least 3 days a week for about 45 minutes each day). However, in most cases, your efforts will be rewarded: surgical intervention along with appropriate rehabilitative training has a success rate of 90 percent, meaning that 90 percent of patients will have a functional knee allowing them to return to their recreational lifestyle.

Surgery

PRIMARY REPAIRS. It seems logical that if you have a torn ligament, the simplest solution would be to suture or sew it back together, a procedure called a primary repair. However, results of resuturing the ligament have been quite dismal. Initially, the patients did well, but over time, the ligament will show symptoms of instability. Reconstruction, or making a new ligament, is now the rule rather than the exception. There is only one situation in which a primary repair of an ACL is appropriate: an avulsion injury in which the ligament remains intact, but it has been pulled off the bone. This type of injury can easily be repaired by simply reattaching the bone avulsion to its previous insertion. An avulsion injury is rare and occurs in skeletally immature individuals (children), whose growth plates are still open. Because the plates are still open—the skeleton is still growing—the attachment to the bone is actually weaker than the ligament itself. Thus the ligament will tear at its weakest link, the attachment to the bone.

RECONSTRUCTION. The most common type of surgery for an ACL injury involves reconstructing the torn ligament with either a healthy tissue (a graft) from the patient, called an autograft; a ligament from a cadaver, called an allograft; or a synthetic ligament.

An Autograft

The most successful type of reconstructive surgery involves using an autograft, which means that the healthy tissue used to reconstruct the damaged ACL comes from the patient’s own body. Typically, the graft is taken from the central one-third of the patellar tendon, which is located just below the kneecap. Although it is less common, the graft can also be taken from the semitendonosis and gracilis tendons, which are located on the inside of the knee. However, studies show that the bone-patellar tendon-bone graft is stronger and heals better and, therefore, whenever possible is the procedure of choice.

Prior to surgery, the patient is given a sedative-hypnotic to induce sleep and then given a general anesthesia. In some cases, depending on the duration of the surgery, the patient might be intubated with a tube and respirator or given a spinal or epidural anesthesia. Patients do not feel anything and are not aware of the surgery.

A small incision (2 to 3 inches) is made to remove the portion of the patellar tendon that is to be grafted. The rest of the procedure is done arthroscopically. The autograft, which becomes the new ACL, is attached to the origin (femur) and inserted to the tibia through drill holes that are cylindrically reproduced to match the size of the bone-tendon-bone graft. The metal screws are a primarily temporary fixation until your own bone fills in and becomes the permanent anchors of the knee. Except in a small percentage of cases, the screws are left in place. In rare cases, one of the screws might become tender to the touch and require removal, which usually would not be done until a year after surgery.

Immediately following the surgery, the new structure is significantly stronger than a normal ACL, but it quickly loses strength as the body begins to fully incorporate the new ligament with the other components of the knee. There are several steps involved in the process of adopting the new ligament to its new location (or, in the case of an allograft, to its new body). First, the body undergoes a process called revascularization in which it passes a new blood supply to the ligament. Without an adequate supply of blood, the ligament cannot survive. This critical stage is followed by another important process called the recollagenization stage. In recollagenization, the body “changes” the collagen of the reconstructed ligament with that of its own collagen. It takes the body approximately 6 to 12 months to fully accept the new ligament. Unfortunately, during the process, the ligament loses approximately 40 to 50 percent of its initial strength. However, because the transplanted ligament was so much stronger than the normal ACL to begin with, the loss of some strength should not interfere with the patient’s ability to return to a functional lifestyle. Although the reconstructed ACL is not a normal ACL, it should be good enough so that the patient can return to a preinjury sports and activity level.

Albeit rare, complications from surgery can include infection (approximately 1 percent); peroneal nerve palsy, which would mean loss of foot function (less than 1 percent); loss of screw fixation at either the tibial or femoral tunnels (less than

1 percent); fracture of the patella (less than 1 percent); and other potential problems that are rare but could make the patient worse.

The gracilis-semitendonosis tendon combination shows a good early result, but with increasing time, this combination does not hold up as well to the bone-patellar tendon-bone combination. This procedure usually requires one incision to harvest the appropriate autograft and several punctures to accommodate the arthroscope and the surgical instruments. It usually lasts less than 2 hours, and most patients are home within 24 hours.

An Allograft

In some cases, a cadaver ligament is used to reconstruct the new ACL, which helps preserve the patient’s own patellar tendon. This procedure, which is called an allograft, works almost as well as the autograft, but it can take longer to heal microscopically—12 to 18 months as compared to 6 to 12 months. Also, there is some evidence to suggest that the allograft might not be as strong as the autograft and may not yield as good a result.

At one time, grafting cadaver ligaments was risky because screening for human immunodeficiency virus (HIV, the AIDS virus) was not performed. During that era, there was one documented case of HIV transmission due to a cadaver ligament transplant. Today, however, screening techniques and specimen tests for these diseases along with superb sterilization techniques have substantially diminished that risk to what is now approximately 1 in 2 million. Even though the risk is minuscule, to be on the safe side, I believe that allografts should be restricted to patients for whom the benefits clearly outweigh any potential risks. For example, an athletic older patient whose tendon may be weakened by age may fare better with an allograft from a younger person. In addition, if a patient has already used his own patellar tendon and requires a second reconstruction, the best choice might be an allograft.

A Prosthesis

By far, the safest and easiest way to reconstruct an ACL would be simply to use a synthetic or man-made ligament. Unfortunately, synthetic ligaments have such a poor track record that they are rarely used in the United States. In the 1980s, a synthetic ligament made out of Gore-Tex was used in ACL reconstructions. Initially, the synthetic ligament worked well, but the success rate at 5 years was below 50 percent. The man-made ligament could simply not withstand the normal stresses placed on the knee and quickly frayed and broke. A new and supposedly vastly improved version of this ligament is now being used in Canada, and I suspect it will be approved for use in the United States soon. Although the early results are encouraging, it will be several years before we know whether this synthetic ligament can withstand the test of time.

Postsurgery and Recovery

After ACL surgery, you will probably spend between 2 and 3 hours in the recovery room. A large bandage and drain will be put on your elevated knee to control bleeding. The dressing is usually removed the day after surgery. A lightweight brace that allows for motion is worn for up to 2 weeks to protect the knee. You can bear weight on your leg the day of surgery. As soon as possible, you will use a continuous passive motion (CPM) machine, which flexes and extends the leg as you lie in your bed. CPM can help prevent the joint from becoming stiff due to inactivity. You will probably be in pain and will be given pain medication as needed. Ice will also help control pain and swelling. At one time patients used to spend up to 48 hours in the hospital, but most insurance companies are now insisting that patients leave within 24 hours.

Over the next 2 to 3 weeks, you may experience night sweats and a fever of up to 101. This is normal and if you’re uncomfortable and your physician agrees, you can bring your fever down with two acetaminophen (Tylenol) or a dose or two of antibiotics to minimize the risk of infection.

In the morning, your knee may feel particularly stiff or painful. An ice pack can help relieve the pain before you begin your therapy.

The average return to sports takes around 6 months, but it can range anywhere between 3 and 12 months, assuming you are diligent about doing your exercises. Your knee will eventually heal with all but a tiny scar remaining. Scar tissue has a tendency to tan darker than normal skin, so if you are out in the sun for a prolonged period of time within the first 12 months after surgery, you might want to cover your knee.

The PCL     PCL injuries are not as well understood as that of the ACL and are currently being studied. As the follow-up studies are becoming available, it becomes apparent that people whose physical examinations or KT evaluations reveal a 1 centimeter or more movement side to side (normal is under 3 millimeters) on a posterior drawer test will probably not do well with an exercise program and will need surgery. The exercise program should stress quadriceps strengthening until both legs are equal in strength. The patients are then healed and can return to their sports. For those whose examination is more than 10 millimeters, a reconstruction using a bone-patellar tendon-bone autograft or allograft or achilles tendon allograft is recommended. To date, there is no consensus of opinion of the superiority of one preparation over the other.

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