Some of the most common knee injuries are sprains or tears of the ACL (anterior cruciate ligament). Any knee injury can be painful, but ACL injuries are especially debilitating, often leaving the patient unable to walk without surgery. If you’ve experienced a traumatic knee injury leading to instability, there’s a chance you’ve injured your ACL. 
 

What is the anatomy of the knee?

The knee is a hinge joint and the largest joint in our body. It consists of three bones that meet and move against each other: the femur (thigh bone), the tibia (shin bone), and the patella (kneecap). These bones are connected by ligaments that keep the knee stable. Collateral ligaments are on the side of the knee and control sideways motion. Cruciate ligaments exist inside the knee, crossing in an “X” formation and controlling forward and backward motion.
 

What purpose does the ACL serve?

The ACL is a cruciate ligament that runs diagonally through the middle of the knee. It prevents the tibia from sliding in front of the femur and provides rotational stability during quick, pivoting activities. This function is one of the main reasons why ACL injuries are more common in athletes who practice quick start and stop motions, such as skiers, football players, basketball players and soccer players. 
 

Types of ACL injuries:

The knee is one of our most resilient joints, but if any of its bones, ligaments or tissues break, tear or sprain with enough force, ACL injuries may occur, resulting in damage to the other soft tissues of the knee joint. Injured ligaments are called sprains, even if they have completely torn. 

Types of ACL injuries include:

Grade 1 Sprains: The ACL has been slightly overstretched but is still functioning to keep the knee stable. 
Grade 2 Sprains: The ACL has been stretched to the point where it has become loose and can no longer provide proper stability to the knee. 
Grade 3 Sprains: The ACL has completely torn into two pieces and can no longer stabilize the knee joint. 
 

How do I know if I’ve injured my ACL?

One of the most common symptoms of a torn or sprained ACL is hearing an immediate “popping” sound and feeling your knee give out from under you. The popping sound and sensation are among the most unmistakable signs that your ACL has sustained significant trauma. 
 

Other symptoms of an ACL injury:

Along with the trademark “popping” sound, other symptoms of a torn ACL include:

• Severe pain with swelling within 24 hours
• Loss of mobility
• Pain while walking
• Knee instability

ACL injuries are typically the result of:

• Quickly changing direction
• Stopping suddenly
• Incorrect landing after a jump or fall
• Direct collision, such as a football tackle or hard fall

When to see a doctor:

ACL injuries almost always require medical intervention. If you hear or feel a “popping” sensation in your knee or experience severe swelling and pain, schedule an appointment with The Steadman Clinic. Our world-renowned surgeons and orthopaedic specialists can help develop a detailed diagnosis and treatment plan for your ACL tear.