One of the most common knee injuries is an ACL injury. An ACL injury is a tear or sprain of the anterior cruciate ligament (ACL) — one of the strong bands of tissue that help connect your thigh bone (femur) to your shinbone (tibia).
ACL injuries most commonly occur in athletes who participate in high demand sports that involve sudden stops or changes in direction, jumping and landing — such as soccer, badminton, basketball, football and downhill skiing.
Many people hear a pop or feel a “popping” sensation in the knee when an ACL injury occurs. Your knee may swell, feel unstable and become too painful to bear weight.
Depending on the severity of your ACL injury, treatment may include rest and rehabilitation exercises to help you regain strength and stability, or surgery to replace the torn ligament followed by rehabilitation. A proper training program may help reduce the risk of an ACL injury. Once torn, an ACL cannot regrow or heal on its own.
Contents
- What is the structure of my Knee and What is the role of ACL?
- What causes a torn ACL?
- What are the risk factors for ACL injury?
- How can I prevent ACL injury?
- ACL tear is not always complete
- What are the signs and symptoms of ACL tear?
- First Aid after ACL tear.
- When to see a Doctor?
- What tests and procedures diagnose a torn ACL?
- Treatment
- Non-surgical
- Surgical
What is the structure of my Knee and ACL? (Anatomy)
Bones. Three bones meet to form your knee joint: your thighbone (femur), shinbone (tibia), and kneecap (patella). Your kneecap sits in front of the joint to provide some protection.
Ligaments. Bones are connected to other bones by ligaments. There are four primary ligaments in your knee. They act like strong ropes to hold the bones together and keep your knee stable.
1. Collateral Ligaments: These are found on the sides of your knee. They control the sideways motion of your knee and brace it against unusual movement.
a) Medial collateral ligament (MCL) runs along the inside of the knee. It prevents the knee from bending in.
b) Lateral collateral ligament (LCL) runs along the outside of the knee. It prevents the knee from bending out.
2. Cruciate Ligaments: These are found inside your knee joint. They cross each other to form an “X” with the anterior cruciate ligament in front and the posterior cruciate ligament in back.
a) The cruciate ligaments control the back-and-forth motion of your knee.
b) The anterior cruciate ligament runs diagonally in the middle of the knee. It prevents the tibia from sliding out in front of the femur, as well as provides rotational stability to the knee.
Muscles. The major muscles of the thigh also act as stabilizers: the quadriceps in the front of the leg and the hamstrings in the back.
What causes a torn ACL?
ACL injuries often happen during sports and fitness activities that can put stress on the knee:
- Suddenly slowing down and changing direction (cutting) rapidly
- Pivoting with your foot firmly planted
- Landing awkwardly from a jump
- Stopping suddenly
- Receiving a direct blow to the knee or having a collision, such as a football tackle
ACL injuries often occur with other injuries. For example, an ACL tear often occurs along with tears to the MCL and the shock-absorbing cartilage in the knee (meniscus).
What are the Risk factors for ACL injury?
There are a number of factors that increase your risk of an ACL injury, including:
- Being female — possibly due to differences in anatomy, muscle strength and hormonal influences
- Participating in certain sports, such as soccer, football, basketball, gymnastics and downhill skiing
- Poor conditioning
- Using faulty movement patterns, such as moving the knees inward during a squat
- Wearing footwear that doesn’t fit properly
- Using poorly maintained sports equipment, such as ski bindings that aren’t adjusted properly
- Playing on artificial turf
How can I prevent ACL injury?
Proper training and exercise can help reduce the risk of ACL injury. A sports medicine physician, physical therapist, athletic trainer or other specialist in sports medicine can provide assessment, instruction and feedback that can help you reduce risks.
Programs to reduce ACL injury include:
- Exercises to strengthen the core — including the hips, pelvis and lower abdomen — with a goal of training athletes to avoid moving the knee inward during a squat
- Exercises that strengthen leg muscles, particularly hamstring exercises, to ensure an overall balance in leg muscle strength
- Training and exercise emphasizing proper technique and knee position when jumping and landing from jumps
- Training to improve technique when performing pivoting and cutting movements
ACL tear is not always complete!
Injured ligaments are considered “sprains” and are graded on a severity scale.
Grade 1 Sprains. The ligament is mildly damaged in a Grade 1 Sprain. It has been slightly stretched, but is still able to help keep the knee joint stable.
Grade 2 Sprains. A Grade 2 Sprain stretches the ligament to the point where it becomes loose. This is often referred to as a partial tear of the ligament.
Grade 3 Sprains. This type of sprain is most commonly referred to as a complete tear of the ligament. The ligament has been split into two pieces, and the knee joint is unstable.
Partial tears of the anterior cruciate ligament are rare; most ACL injuries are complete or near complete tears.
An ACL avulsion occurs when the ACL is torn away from either the femur or the tibia. This type of injury is more common in children than adults.
About half of all injuries to the anterior cruciate ligament occur along with damage to other structures in the knee, such as articular cartilage, meniscus, or other ligaments.
What are symptoms and signs of a torn ACL?
When you injure your anterior cruciate ligament, you might hear a “popping” noise and you may feel your knee give out from under you. Other typical symptoms include:
- Pain with swelling. Within 24 hours, your knee will swell. If ignored, the swelling and pain may resolve on its own. However, if you attempt to return to sports, your knee will probably be unstable and you risk causing further damage to the cushioning cartilage (meniscus) of your knee.
- Loss of full range of motion
- Tenderness along the joint line
- Discomfort while walking
First Aid after suspected ACL Injury
- Raise your leg above the level of the heart
- Put ice on the knee
- Take over the counter pain relievers, such as nonsteroidal anti-inflammatory drugs (such as ibuprofen)
- Do NOT move your knee if you have had a serious injury.
- Use a splint to keep the knee straight until you see a doctor.
- Do NOT return to play or other activities until you have been treated.
When to see a doctor?
Seek immediate care if any injury to your knee causes signs or symptoms of an ACL injury. The knee joint is a complex structure of bones, ligaments, tendons and other tissues that work together. It’s important to get a prompt and accurate diagnosis to determine the severity of the injury and get proper treatment.
Also, get immediate medical attention if the foot is cool and blue after a knee injury. This means that the knee joint may be dislocated, and blood vessels to the foot may be injured. This is a medical emergency.
What tests and procedures diagnose a torn ACL?
Physical Examination and Patient History
During your first visit, your doctor will talk to you about your symptoms and medical history.
During the physical examination, your doctor will check all the structures of your injured knee, and compare them to your non-injured knee. Most ligament injuries can be diagnosed with a thorough physical examination of the knee.
In addition to performing special tests for identifying meniscus tears and injury to other ligaments of the knee, the physician will often perform the Lachman’s test to see if the ACL is intact.
Imaging Tests
X-rays. Although they will not show any injury to your anterior cruciate ligament, x-rays can show whether the injury is associated with a broken bone.
Magnetic resonance imaging (MRI) scan. This study creates better images of soft tissues like the anterior cruciate ligament. However, an MRI is usually not required to make the diagnosis of a torn ACL.
Normal ACL MRI 
MRI in ACL Tear
Treatment
Treatment for an ACL tear will vary depending upon the patient’s individual needs.
1. Nonsurgical Treatment
A torn ACL will not heal without surgery. But nonsurgical management of isolated ACL tears is likely to be successful or may be indicated in patients:
- With partial tears and no instability symptoms
- With complete tears and no symptoms of knee instability during low-demand sports who are willing to give up high-demand sports
- Who do light manual work or live sedentary lifestyles or are elderly
- Whose growth plates are still open (children)
Nonsurgical options are:
- Bracing. Your doctor may recommend a brace to protect your knee from instability. To further protect your knee, you may be given crutches to keep you from putting weight on your leg.
- Physical therapy. As the swelling goes down, a careful rehabilitation program is started. Specific exercises will restore function to your knee and strengthen the leg muscles that support it.
Possible disadvantages of nonsurgical treatments
The long-term outcome for patients who are treated non surgically varies.
- Those who return to unrestricted activity are likely to experience some knee instability.
- Pain may be associated with the physical therapy regimen.
- In the absence of an intact ACL – even when no other injury is present – the menisci (pads of cartilage that cushion the bones that meet at the knee joint) have a higher risk of injury.
- If a tear forms in one or both menisci of the knee, pain and swelling may occur.
- More importantly, a damaged meniscus increases a patient’s risk of developing osteoarthritis of the knee later in life.
2. Surgical Treatment
ACL surgery is generally recommended if:
- You’re an athlete and want to continue in your sport, especially if the sport involves jumping, cutting or pivoting
- More than one ligament is injured
- You have a torn meniscus that requires repair
- The injury is causing your knee to buckle during everyday activities
- You’re young (though other factors, such as activity level and knee instability, are more important than age)
ACL Reconstruction (Rebuilding the ligament). Most ACL tears cannot be sutured (stitched) back together. To surgically repair the ACL and restore knee stability, the ligament must be reconstructed. Your doctor will replace your torn ligament with a tissue graft. This graft acts as a scaffolding for a new ligament to grow on. Grafts can be obtained from several sources-patellar tendon, hamstring tendons, quadriceps tendon or cadaver graft-depending on what’s best for you. Because the regrowth takes time, it may be six months or more before an athlete can return to sports after surgery.
Procedure. Surgery to rebuild an anterior cruciate ligament is done with an arthroscope using small incisions. Arthroscopic surgery is less invasive. The benefits of less invasive techniques include less pain from surgery, less time spent in the hospital, and quicker recovery times.