The anterior cruciate ligament (ACL) is probably the most commonly injured ligament of the knee. In most cases, the ligament is injured by people participating in athletic activity. The most common method of injurying the ACL is with a “plant and pivot” maneuver, occuring is sports such as football, soccer, and basketball. This injury has received a great deal of attention from orthopedic surgeons over the past 15 years, as the amount of sport related injuries have increased.
Where is the ACL, and what does it do?
Ligaments are tough bands of tissue that connect the ends of bones together. The ACL is located in the center of the knee joint where it runs from the backside of the femur (thighbone) to connect to the front of tibia (shinbone). The ACL runs through a special notch in the femur called the intercondylar notch and attaches to a special area of the tibia called the tibial spine.
The ACL is the main knee stabilizer, preventing excessive motion at the knee joint between the femur (thigh bone) and tibia (leg bone). If these two bones move further apart than the ACL is capable of stretching, it will tear or rupture.
How do ACL injuries occur?
The major cause of injury to the ACL is sports. The types of sports that have been associated with ACL tears are numerous. Those sports requiring the foot to be planted and the body to change direction rapidly (such as basketball) carry a high incidence of injury. Football is also frequently the source of an ACL tear. Football combines the activity of planting the foot and rapidly changing direction or pivoting thus leading to a torn ACL. Downhill skiing is another frequent source of injury, especially since the introduction of ski boots that come higher up the calf. These boots move the impact of a fall to the knee rather than the ankle or lower leg. An ACL injury usually occurs when the knee is forcefully twisted or hyperextended. Many patients recall hearing a loud “pop” when the ligament is torn, and they feel the knee give way or buckle when weight is applied.
Illustration of an ACL and MCL Tear (figure A), Meniscus Flap Tear (figure B), Cartilage injury (figure C)
The number of women suffering ACL tears has dramatically increase. This is due in part to the rise in women's athletics. But studies have shown that female athletes are two to four times more likely to suffer ACL tears than male athletes in the same sports.
What does a torn ACL feel like?
The symptoms following a tear of the ACL can vary. Usually, the knee joint swells within a short time following the injury. This is due to bleeding into the knee joint from torn blood vessels in the damaged ligament. The instability caused by the torn ligament leads to a feeling of buckling and giving way of the knee, especially when trying to change direction on the knee. The knee may feel like it wants to slip backwards. Many times, even with a complete tear of the ACL, normal every day activities and even straight ahead sports such as jogging, biking or swimming that do not involve changing direction quickly can be performed without difficulty.
The pain and swelling from the initial injury will usually be gone after two to four weeks, but the knee may still feel unstable. The symptom of instability and the inability to trust the knee for support are what require treatment. Also important in the decision about treatment is the growing realization by orthopedic surgeons that long-term instability leads to early arthritis of the knee.
How do doctors identify ACL injuries?
The history and physical examination are probably the most important ways to diagnose a ruptured or deficient ACL. In the acute (sudden) injury, the swelling is a good indicator. A good rule of thumb that orthopedic surgeons use is that any tense swelling that occurs within 2-4 hours of a knee injury usually represents blood in the joint, or a hemarthrosis. Draining the swollen joint or aspirating the knee gives relief from the swelling and provides useful information. If blood is found when draining the knee, there is about a 70 percent chance it represents a torn ACL. This fluid can also show if the cartilage on the surface of the knee joint was injured. During the physical examination, your doctor will determine how badly the ACL was injured and whether other knee ligaments or joint cartilage were injured.
X-rays of the knee will be performed in the office to rule out a fracture. Ligaments and tendons do not show up on X-rays, but bleeding into the joint can result from a fracture of the knee joint, or when portions of the joint surface are chipped off. Magnetic resonance imaging (MRI) is probably the most accurate test for diagnosing a torn ACL without actually looking into the knee. The MRI machine uses magnetic waves rather than X-rays to show the soft tissues of the body. This machine creates pictures that look like slices of the knee. The pictures show the anatomy, and any injuries, very clearly. This test does not require any needles or special dye and is painless.
In some cases, arthroscopy may be used to make the definitive diagnosis if there is a question about what is causing your knee problem.
Arthroscopy is an operation that involves inserting a small fiber-optic TV camera into the knee joint, allowing the orthopedic surgeon to look at the structures inside the joint directly.
The vast majority of ACL tears are diagnosed without resorting to this type of surgery, though arthroscopy is sometimes used to repair a torn ACL.
NONSURGICAL Treatment: Initial treatment for an ACL injury focuses on decreasing pain and swelling in the knee. Rest and mild pain medications, such as acetaminophen (Tylenol®), can help decrease these symptoms. You may need to use crutches until you can walk without a limp. Most patients are instructed to put a normal amount of weight down while walking. The knee joint may need to be drained with a needle (mentioned earlier) to remove any blood in the joint.
Most patients receive physical therapy after having an ACL injury. Therapists treat swelling and pain with the use of ice, electrical stimulation, and rest periods with your leg supported in elevation. Exercises are used to help you regain normal movement of joints and muscles. Range-of-motion exercises should be started right away with the goal of helping you swiftly regain full movement in your knee. This includes the use of a stationary bike, gentle stretching, and careful pressure applied to the knee by the therapist. Exercises are also given to improve the strength of the hamstring and quadriceps muscles. As your symptoms ease and strength improves, you will be guided in specialized exercises to improve knee stability.
An ACL brace may be suggested. This type of brace is usually custom-made and not the type you can buy at the drugstore. It is designed to improve knee stability when the ACL doesn't function properly. An ACL brace is often recommended when the knee is unstable and surgery is not planned. As mentioned, a torn ACL that isn't corrected often leads to early knee arthritis. There is no evidence that an ACL brace will prevent further damage to the knee due to wear and tear arthritis. The ACL brace may help keep the knee from giving way during moderate activity. However, it can give a false sense of security and won't always protect the knee during sports that require heavy cutting, jumping, or pivoting. Many orthopedists will also recommend wearing a brace for at least one year after a surgical reconstruction, so even if you decide to have ACL surgery, a brace is probably a good investment.
SURGERY Treatment: If the symptoms of instability are not controlled by a brace and rehabilitation program, then arthroscopic surgery may be suggested. Symptoms of instability include recurrent giving way, swelling and/or pain. The main goal of surgery is to keep the tibia from moving too far forward under the femur bone and to get the knee functioning normally again.
Even when surgery is needed, we ideally like patients to attend physical therapy for several visits before the surgery. This is done to reduce swelling and to make sure you can straighten your knee completely and gain strength. This will speed recovery after surgery.
Reconstruction of the ACL is performed using a piece of tendon to replace the torn ACL. This surgery is always done with the aid of the arthroscope. Tiny incisions are made around the knee, but the surgery doesn't require the surgeon to open the joint. The arthroscope is used to view the inside of the knee joint as the surgeon performs the work.
An allograft is tissue that comes from someone else. This tissue is harvested from tissue and organ donors at the time of death and sent to a tissue bank. The tissue is checked for any type of infection, sterilized, and stored in a freezer. When needed, the tissue is ordered by the surgeon and used to replace the torn ACL. The allograft (your surgeon's choice of graft) can be from the tibialis tendon or Achilles tendon (the tendon that connects the calf muscles to the heel). The advantage of using an allograft is that the surgeon does not have to disturb or remove any of the normal tissue from your knee to use as a graft. The operation also usually takes less time because the graft does not need to be harvested from your hamstring.
REHABILITATION / RECOVERY
Nonsurgical rehabilitation for a torn ACL will typically last six to eight weeks. Therapists apply treatments such as electrical stimulation and ice to reduce pain and swelling. Exercises to improve knee range of motion and strength are added gradually. If your doctor prescribes a brace, your therapist will work with you to obtain and use the brace.
You can return to your sporting activities when your quadriceps and hamstring muscles are back to nearly their full strength and control, you are not having swelling that comes and goes, and you aren't having problems with the knee giving way.
Post-operative Rehabilitation: You will take part in a formal physical therapy after ACL reconstruction. You will be involved in a progressive rehabilitation program for four to six months after surgery to ensure the best result from your ACL reconstruction. At first, expect to see the physical therapist two to three times a week. If your surgery and rehabilitation go as planned during the first six weeks, you may only need to do a home exercise program and see your therapist every few weeks over the four to six month period.