The anterior cruciate ligament (ACL) is one of the most commonly injured ligaments of the knee.
According to the American Academy of Orthopaedic Surgeons (AAOS), an estimated 200,000 ACL injuries occur annually, and 100,000 ACL reconstruction surgeries are performed each year.
As one of the four primary ligaments of the knee, the ACL connects the front top part of the shinbone to the back bottom part of the thigh bone and keeps the shin from sliding forward. It also provides rotational stability to the knee.
The ACL keeps the knee hinged together and functioning properly with the help of the posterior cruciate ligament (PCL), which like the ACL, is also a crossed ligament in the center of the knee.
There are two additional ligaments on the sides of the knee called the medical collateral ligament (MCL) and the lateral collateral ligament (LCL), as well as multiple muscles, tendons, and secondary ligaments.
ACL injuries tend to happen more often in people who play high-impact sports where rapid pivoting and turning are common, such as basketball, football, skiing, and soccer.
AAOS reports that about 70 percent of ACL tears happen without direct contact to the knee. In these instances, the tears tend to happen when a person is running and quickly changes direction, suddenly twists or cuts, or if they hyperextend their knee coming down from a jump.
However, a direct hit to the knee, such as during a football tackle, can also cause ligaments to tear.
Female athletes who play pivoting sports are 2 to 10 times more likely than male athletes to sustain a knee ligament injury, such as an ACL injury, according to the AAOS.
This may be due to differences in physical conditioning, muscular strength, and neuromuscular control. It might also be due to pelvis and lower leg alignment, a wider pelvis, or other anatomical differences.
Most ACL tears occur in the middle of the ligament or when the ligament is pulled off the thigh bone. The tears form a gap between the torn edges and do not heal on their own.
Damage to the meniscus, articular cartilage, or other ligaments in the knee also occurs in about half of ACL injuries.
An unhappy triad is the most common multi-ligament injury it involves injury to the ACL, MCL, and medial meniscus. Some people also experience bruising on the bone beneath the cartilage surface.
Many people tend to feel or hear a popping in their knee when they injure their ACL. They may also experience a brief hyperextension of the knee joint causing the knee to bend backward.
After the injury, most people have to stop the activity they were doing, and the knee usually swells for a few hours.
There are different severities of ACL sprains, which are categorized in the following way:
Grade I sprain: Pain with minimal damage to the ligaments, but still able to help keep the knee joint stable.
Grade II sprain: More ligament damage and mild looseness of the joint, often called a partial tear.
Grade III sprain: The ligament is completely torn and the joint is very loose or unstable.
In 2008, the Journal of the American Academy of Orthopaedic Surgeons reported that most ACL injuries occur in those between the ages of 15 to 45 because this group has an active lifestyle and greater participation in sports.
However, other studies show a rise in the number of reported ACL tears in children, with the injury seen in kids as young as age two.
The true incidence of ACL tears in children is not known, and it isnt clear if the increase is related to kids being more active in sports such as soccer, or other factors like increased awareness by physicians and better diagnostic techniques.
While some ACL injuries are not preventable, the following may help minimize the risk:
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Most anterior cruciate ligament (ACL) tears occur in the middle of the ligament or when the ligament is pulled off the thigh bone.
The tears form a gap between the torn edges, and they do not heal on their own. Symptoms of a torn ACL may include the following:
Knee Popping: Many people feel or hear a popping in their knee when they injure their ACL.
Knee Hyperextension: Some people feel a brief hyperextension of the knee joint when they injure their ACL, which occurs when the knee is bent backward.
Knee Swelling: A large amount of swelling usually occurs within six hours of an ACL injury and may increase for two days before it gradually subsides.
Knee Pain and Discomfort: After the injury, most people have to stop whatever activity they were doing. They feel pain or tenderness in the joint area, especially when they put weight on the injured leg.
They may also feel a loss of full range of motion and an uncomfortable feeling when walking, as well as the sensation that their knee is unstable or giving in under pressure.
To diagnose an ACL injury, a physician will examine your knee by comparing the structures of your injured knee to your non-injured knee, and seeing which parts stay in proper position when pressure is applied in different directions.
In most cases, this will allow your doctor or orthopedist to determine which ligaments are injured.
When swelling makes it difficult for a healthcare provider to diagnose a tear, further tests may be recommended, including:
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Most anterior cruciate ligament (ACL) tears occur in the middle of the ligament or when the ligament is pulled off the thigh bone.
The tear forms a gap between the torn edges of the ACL, and the tear doesnt heal on its own. Surgery is the only way to completely repair a torn ACL.
Whether surgery is required depends on a variety of factors including:
Some people who are elderly or inactive may choose not to have surgery if they can return to limited activity after rehabilitation or by wearing a brace. Younger people who want to maintain an active lifestyle or return to competitive sports are more likely to opt for surgery.
People who decide not to have reconstructive surgery may experience further injury to the unstable knee joint.
Additionally, many people who experience an ACL tear will, years later, show signs of osteoarthritis in the knee, but studies show that reconstruction can help reduce this rate.
Your surgeon will want you to regain full range of motion in the knee before surgery, which can take two weeks or longer from the time the tear occurred. He or she will also want you to have quadriceps control and reduced swelling.
Most surgeons believe that putting off surgery until your knee has met these criteria can speed postoperative rehabilitation.
Reconstruction surgery is the most common technique used to treat a torn ACL.
During this surgery, the torn ACL is replaced with a new ligament taken from an organ donor (cadaver graft) or from one of your other tendons around the knee.
These other tendons might include the hamstring at the back of the thigh, the quadriceps tendon, which runs from the kneecap into the thigh, or the patellar, which attaches the bottom of the kneecap to the top of the shinbone.
Once a graft is chosen, the surgeon will perform arthroscopic surgery, making small incisions in the leg using a pencil-shaped instrument that holds a camera called an arthroscope. With the arthroscope, the surgeon can see inside of the knee.
Using the camera as a guide, the surgeon then drills holes in the thigh bone and shinbone and passes the new ligament through these holes to anchor it in place with screws or other devices.
Incisions are then closed with stiches, tape, or staples. As time goes on, the new graft becomes a living ligament in your knee.
The following are potential complications of ACL reconstruction surgery:
Martha M. Murray, MD, of Boston Childrens Hospital, and Braden C. Fleming, PhD, of Brown University, are leading the research for a sponge scaffold that wouldnt require any grafts or holes drilled into bones.
The scaffold works like a sponge, holding the blood between the two torn ends of the ACL long enough for the cells and tissue around it to grow into each other, stimulating healing to the surrounding ligaments.
This technique, which uses whats often called platelet-rich plasma or PRP, is currently under investigation for rotator cuff injuries, elbow tendonitis, Achilles tendon repairs, and other medical procedures, in addition to ACL injuries.
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Youll need time to recover and rehabilitate after experiencing a torn anterior cruciate ligament (ACL).
How much time depends on the severity of the tear and how you decide to treat it.
Since ACL tears form a gap between the torn edges that do not heal on their own, surgery is the only way to completely repair a torn ACL.
However, for those who decide not to have surgery, nonsurgical treatment may be helpful, particularly for people who maintain a very low activity level. Your doctor may recommend the following options if the overall stability of your knee is still intact:
Bracing and crutches: A brace can protect your knee from instability, and crutches can help keep you from putting weight on your leg.
Physical therapy: As the swelling goes down, a rehabilitation program that involves physical therapy and exercise can help restore full range of motion to your knee and strengthen the leg muscles around it.
Immediately following surgery, you will be told to ice and elevate your knee. You may also be prescribed anti-inflammatory and pain medications, as well as given crutches to use until you can walk without them.
Your doctor will give you detailed instructions on how to care for your knee once youre home.
If you work at a desk, you may be able to return to work in one or two weeks, but if you perform physical labor, you may need to take off for three to six months.
Physical therapy is an important part of recovery that includes stretching, balancing, and strength training exercises.
After surgery, youll most likely participate in a physical-therapy program (guided by a professional physical therapist) for about 6 to 12 months, depending on your tear and the level of activity you want to reach.
If youre an athlete, rehabilitation may take longer to get you in physical condition to participate in your sport or activity.
The first part of physical therapy will focus on returning proper range of motion to the ACL joint and the muscles that surround it, including the quadriceps and hamstrings. Once this is achieved, youll be given a strengthening program that focuses on increasing stress across the ligament.
In the last phase of rehabilitation, your physical therapist will assess which activities, if any, still create pain, discomfort, or instability in your knee joint, and will establish ways to work around such activities.
Studies have shown that more than 90 percent of people are able to return to sports and workplace activities after surgery without symptoms of knee instability, according to The American Orthopaedic Society for Sports Medicine.
Youll be able to play sports again with or without a brace after your leg strength, balance, and coordination have returned to near normal. The time it takes to reach this point varies from person to person.
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