The knee is a vulnerable joint prone to injury because its stability decreases as it bends. One common knee injury is the anterior cruciate ligament injury, often referred to simply as the ACL injury.
What is the ACL?
The anterior cruciate ligament (ACL) is one of two ligaments inside the knee joint. It runs from the top of the tibia (shin bone) diagonally into the end of the femur (thigh bone). The ACL’s job is to prevent the tibia from sliding too far forward under the femur. Put simply, the ACL keeps the knee stable.
What is an ACL Injury?
An ACL injury is any trauma to the ligament that prevents it from properly stabilizing the knee. ACL injuries can be mild or severe—ranging from a sprain to a partial tear or a complete tear:
- Sprain: This is a minor trauma to the ligament, where the fibers are stretched.
- Partial Tear: A partial tear involves more serious trauma to the ligament and means that some, but not all, of the fibers are torn.
- Complete Tear: This is a severe ACL injury where the ligament has torn completely or the ligament and part of the bone separate from the rest of the bone.
What Causes ACL Injury?
An ACL injury occurs when the knee is sharply extended beyond its normal range of motion—including when the knee is bent backward, twisted, or bent side to side. If more than one of these movements occurs simultaneously, the chance of injury is even higher. An ACL injury can also be the result of contact (being hit by a person or object), which causes the knee to extend beyond its normal range.
ACL injuries often occur during sports, particularly sports with a lot of stop-and-go movements, jumping, or change in direction. The injury can happen when the foot is firmly planted, the knee is bent, and a sudden change in direction happens or when the foot is firmly planted and a sudden force hits the knee.
Some common sports associated with ACL injuries are: football, basketball, soccer, and skiing. These sports require movements that cause the femur to pivot on the tibia. ACL injuries are common in skiing because the length of the ski adds extra force to the twisting motion. Physical contact, like that involved in football, can have serious consequences for the ACL. A hard hit on the football field can result in a torn ACL.
Sports aren’t the only cause of ACL injuries. Some people injure their ACLs in simple accidents like falls or missteps—such as missing a step on the stairs or stepping off a curb.
Symptoms of ACL Injury
You may have heard people talk about the dreaded “pop” they heard when they injured their knee. It’s true that many people feel or hear the knee pop when they tear their ACL; however, that’s not the only symptom—and an absence of a pop doesn’t mean there isn’t a tear.
Symptoms of an ACL injury include:
- Feeling or hearing a “pop” in the knee at the time of injury
- Pain, particularly on the outside and back of the knee
- Limited mobility due to pain and/or swelling
- Instability-The knee buckles or gives out
It is important to note that the ability to walk does not mean that you don’t have a serious injury to your ACL. You can walk with a torn ACL, but the knee joint is unstable and you are unlikely to be able to perform movements needed for sports such as skiing or basketball. Left untreated, an ACL injury can lead to serious problems, including osteoarthritis that results from bone rubbing on bone.
Diagnosis of ACL Injury
Doctors use a variety of tools to diagnose an ACL injury. First, a doctor will discuss the history of the injury and evaluate your symptoms. Your doctor can also perform a physical examination to assess stability and movement in the knee joint.
Your doctor may order X-rays, but those only show damage to bone, so you may also need an MRI (magnetic resonance imaging), which shows damage to ligaments, tendons, and muscles. Finally, your doctor may use a technique called arthroscopy, which is a minimally invasive surgical procedure that allows your doctor to insert surgical instruments through a tiny incision and visually examine the inside of the knee.
Treatment of ACL Injury
For starters, you’ll want to treat an ACL injury the way you would any acute injury—with RICE to control swelling:
- Rest: Rest the knee by staying off of it and/or using crutches
- Ice: Ice the injured area several times a day
- Compression: Wrap the knee in an elastic bandage
- Elevation: Elevate the leg by propping it above your heart
However, it’s important to have a doctor examine your knee. Untreated ACL injuries can have lasting consequences. Depending on the severity of your ACL injury, your doctor will use one of the following treatment techniques:
Non-surgical: A complete ACL tear will not heal by itself; however, some people can do well without surgery. Patients who might want to consider skipping surgery include:
- Older patients
- Less active patients
- Patients who are willing and able to decrease or change their activity
- Patients who avoid pivoting sports
- Patients who opt out of surgery are more likely to re-injure themselves. They can experience further damage to ligaments, meniscus tears, and osteoarthritis. The patients with the highest quality of life after opting out of surgery are those who undergo good rehabilitation with physical therapy. This approach is not recommended for complete tears, but can be used in partial tears.
ACL-Anterior Cruciate Ligament Reconstruction
Some patients will choose to undergo a surgical procedure called ACL reconstruction. This is appropriate for:
- Younger, more active patients
- Patients who participate in sports with pivoting (soccer, basketball, football, skiing)
- Patients with injuries involving more than one ligament
- Patients with concomitant meniscal tears
Patients typically undergo ACL reconstruction about three weeks after injury—once swelling is reduced and range of motion is adequate. The procedure involves removing the damaged ACL and replacing it with tissue, called a graft. The graft can come from the patient or from donor tissue. ACL reconstruction is almost always performed arthroscopically.
Rehabilitation and Recovery from ACL Injury
Whether a patient opts for a non-surgical approach or an ACL reconstruction, a good physical therapy program is critical for recovering from an ACL injury.
Patients who choose the non-surgical route will need a physical therapy program that focuses on strengthening the surrounding musculature of the knee. These muscles can then help to stabilize the knee joint in the absence of the ACL. These patients also can benefit from a knee brace with a rigid frame.
Patients who undergo surgery must commit to several months of rehab following the procedure. This rehab occurs in phases beginning with range of motion, followed by building strength, and then adding sports-specific exercises. For best surgical results, it is imperative that patients commit to following the structured rehabilitation protocol outlined by their doctor and physical therapist.