Yasmin Dhar, M.D.
Orthopedic Surgeon and Sports Medicine Specialist
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Anterior Cruciate Ligament Tears
What is the Anterior Cruciate Ligament or "ACL"?
The anterior cruciate ligament (ACL) is one of the main stabilizing ligaments in the knee. Running through the knee from the front of the tibia (shin bone) to the back of the femur (thigh bone), it assists with proper movement of the joint and prevents abnormal slippage of the bones. Abnormal slippage can create an unstable knee that “gives way” or “buckles” during activity.
How is the ACL injuried?
While the ligament can be injured with a direct blow to the knee, it is more common to tear the ligament when pivoting or twisting on a planted foot or by hyperextending the knee.
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How do I know my ACL is torn?
Usually, a tear to the ACL results in sudden pain, giving way of the knee, or a combination
of both. Many people report hearing a “pop” in their knee when the injury occurred.
The knee usually swells within 1-3 hours of the injury. A doctor can examine the knee and
is usually able to identify any ligaments that are injured. The ligament will feel loose or you
will have pain during the examination. If there is a lot of swelling, the doctor may want to
drain the fluid from your knee. If the fluid is red (meaning there is blood in the knee joint),
you most likely tore your ACL.
Do I need X-rays, MRI or other tests?
A set of X-rays is usually ordered to make sure that there are no broken bones. MRIs can be helpful. Usually the doctor will know what is wrong just from examining you, but MRIs are helpful if there is any doubt whether your ACL is injured (if there was too much pain or swelling to examine you) or to check for additional damage in the knees.
Is there usually other damage to the knee when the ACL is torn?
Other ligaments in the knee can be injured when there is an ACL injury. These may need to be repaired, but many times can heal adequately without surgery. The most common injury that occurs with an ACL tear is a cartilage tear (meniscus tear). Some meniscus tears can be repaired, but most must be trimmed back so that the torn edges are smooth. Occasionally, a badly torn meniscus has to be removed. If the meniscus can be repaired, it is usually done at the time of the ACL surgery. Even though it is possible it may not heal, it is probably best to try and repair a meniscus tear in conjunction with an ACL surgery. Another common injury that can occur with an ACL tear is damage to the cartilage on the joint surface. Damage to these surfaces is very serious and in some cases is the worst part of the injury. Depending on the extent of damage, it may require a more complex surgery.
Does a torn ACL have to be fixed with surgery?
The ACL cannot heal on its own, but not all tears of the ACL need to be fixed. It depends on your activity level. People participating in activities where they plant their feet and twist or cut are susceptible to having an unstable knee and may be better off with surgery. People with strenuous jobs may also need surgery. People who are unwilling or unable to modify their activities and desire an unrestricted lifestyle are encouraged to consider the surgery to have the best chance of returning to their previous lifestyle. On the other hand, people who do not perform many cutting or pivoting activities or lead a sedentary lifestyle may be able to get by with physical therpay and a brace. However, even someone with a sedentary lifestyle may experience giving way with simple activities such as going down stairs or stepping off a curb. In these cases, surgery is needed to restore normal everyday activities and to prevent further damage to the knee.
If I don't fix my ACL, am I likely to hurt my knee again or get arthritis?
Even if the knee joint does not become unstable (give way), it will still be loose after an ACL injury. This will make you more prone to tearing your meniscus in the future. While there is no direct evidence showing that people who tear their ACL develop arthritis, the ACL injury itself may contribute to the early onset of arthritis in your knee. People who experience recurrent episodes of their knee buckling or giving out may be damaging their cartilage further.
How is the ACL fixed?
The ACL cannot heal itself and it cannot be stitched together, so it needs to be reconstructed or replaced with arthroscopic techniques. In ACL reconstruction, a replacement graft is precisely positioned in the joint at the site of the former ACL and then fixed to the thigh and lower leg bones with screws or other fixation techniques. There are currently several options for replacement grafts. Choices for the type of replacement graft include autograft (using your own tissue) or allograft (cadaver donor tissue).
What is the difference between autografts and allografts?
Autografts can come from your patella tendon or the hamstring tendons. The graft choice to be used is determined by you and your surgeon. All of these graft options offer a strong graft, secure fixation and excellent long–term results. The results show that people are able to return to their activities with few complications. Since the graft comes from your own body, there is no chance of infectious disease transmission or rejection. Allografts are donor tissues taken from tissue banks. They are also strong grafts with excellent long-term results. Because the surgeon is not taking the tissue from your body, the surgical time and operative pain are less. This allows for easier rehabilitation in the early postoperative stages. Although there is a risk of infectious disease, donor tissue is received only from reliable tissue banks. The tissue is rigorously screened and treated to prevent the spread of infectious disease. The risk of contracting an infectious disease from an allograft is very low. Although rejection of the graft is possible, the risk of this is extremely low because the tissue is not living material.