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Understanding Your Knee Anatomy and How the ACL Can Get Torn

Understanding Your Knee Anatomy and How the ACL Can Get Torn

As the largest joints in your body, your knees take a lot of strain and pressure every day, bearing your weight while you stand, walk, and perform lots of other activities. That ability to bear weight while remaining flexible and mobile is due to the complex anatomy that characterizes the joints.

The anterior cruciate ligament (ACL) is a key part of that anatomy, and unfortunately, it’s also one of the most commonly injured parts of the knee. 

In this post, James M. Lee Jr., MD, at Orange Orthopaedic Associates reviews some basic knee anatomy, focusing on ACL injuries to help you seek medical treatment as early as possible.

Knee anatomy 101

Your knee joint forms where the thighbone (femur) meets with the shinbone (tibia). A third bone — the patella or kneecap — is also part of the joint and plays a key role in joint function. 

The fibula, a smaller bone in your lower leg, plays no direct role in joint function, but it does form an attachment for one of the four main ligaments in the knee.

Ligaments are tough, fibrous bands that join bones. In the knee, the primary ligaments include:

All four ligaments work to help the knee move while stabilizing the joint.

The ACL and PCL cross in the center of the knee. The ACL specifically prevents the lower bone (tibia) from sliding in front of the femur, while also providing the knee’s rotational movement and stability.

How ACL injuries happen

ACL injuries typically happen when the ligament stretches beyond its limits and sometimes tears. These injuries are most commonly associated with rapid changes in direction that cause extreme rotational pressure on the ligament. They’re also associated with:

Many ACL injuries involve damage to other knee structures, including other ligaments or the knee cartilage.

Like other ligament sprains, ACL injuries are graded according to their severity. 

Grade 1

Grade 1 sprains are the mildest type of ACL injury. In these sprains, the ACL is stretched, but not torn. You may have mild pain and swelling, but the joint itself remains stable.

Grade 2

Grade 2 ACL injuries include partial ligament tears, where the ligament is torn partway through. In these injuries, the ligament may be too stretched or weakened to support normal knee stability.

Grade 3

Also called a complete ACL tear, grade 3 sprains involve tears that extend all the way through the ligament. The ligament may be torn in half or it may be torn from its attachment on the bone. These are the most serious injuries involving significant pain and knee instability.

Treating ACL tears

Some milder ACL tears respond to rest, ice application, and physical therapy to promote healing and restore normal knee function. But more severe injuries require surgery to repair or replace the damaged ligament.

If your ACL injury requires surgery, you have physical therapy afterward to strengthen the knee and stabilize the joint. Your recovery time depends on many factors, including your activity level, your age, and the severity of the tear.

ACL tears can be serious, but with the right treatment, you can get back to the activities you love. 

To learn more about ACL injuries and their treatment, book an appointment online or over the phone today with our team at Orange Orthopaedic Associates in West Orange and Bayonne, New Jersey.

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