ACL Injuries

The knee joint is composed of three primary bones: the femur (thigh bone), tibia (shin bone), and patella (kneecap). Inside the knee, two essential ligaments, the anterior cruciate ligament (ACL) and the posterior cruciate ligament (PCL), cross each other to form an X-shape. Together, these ligaments help control the knee’s front-to-back motion and rotational stability.

The ACL sits at the front of the knee joint, connecting the femur to the tibia, while the PCL is located at the back. The ACL’s primary function is to prevent the tibia from sliding forward in relation to the femur and to stabilize the knee during twisting or rotational movements.

The ACL is not only responsible for stabilizing the knee but also contains nerve fibers that help the brain perceive the knee’s position, a function known as proprioception. These nerve fibers, along with blood vessels that provide nutrition to the ligament, play a vital role in the overall function of the knee joint. When the ACL is injured, both stability and proprioception are compromised, leading to difficulties in balance and movement.

ACL injuries commonly occur during activities that involve sudden changes in direction, sharp twisting motions, rapid deceleration, or awkward landings from jumps. High-risk sports such as soccer, basketball, football, skiing, and lacrosse are particularly associated with ACL tears due to the dynamic and fast-paced movements they require.

Women athletes, especially those participating in college sports like soccer and basketball, are at a higher risk of ACL injuries. Research suggests that women are up to four times more likely than men to suffer ACL tears, possibly due to anatomical and hormonal differences, as well as variations in muscle strength and movement patterns.

Other causes of ACL injuries include direct contact or collision, as seen in football or car accidents, where a sudden force impacts the knee, causing the ligament to rupture.

• A “Pop” Sound: Many individuals report hearing or feeling a “pop” in their knee at the time of injury.
• Sudden Knee Buckling: The knee may give way or buckle, indicating a loss of stability.
• Severe Knee Pain: Intense pain occurs right after the injury, often requiring the person to stop activity.
• Swelling and Inflammation: The knee typically swells within hours due to bleeding into the joint.
• Limited Range of Motion: Stiffness and difficulty bending or straightening the knee are common after an ACL injury.
• Instability: Even after the initial pain subsides, the knee may feel unstable, particularly during activities that involve pivoting or changing direction. Ignoring these symptoms or continuing to engage in physical activities with an unstable knee can lead to further damage, such as meniscus tears or cartilage injuries.

To diagnose an ACL injury, healthcare providers use a combination of a detailed medical history, physical examination, and imaging tests. The Lachman test and anterior drawer test are commonly performed during a physical exam to assess the knee’s stability.

In addition to physical tests, imaging studies such as X-rays and magnetic resonance imaging (MRI) are crucial for confirming the diagnosis. While X-rays are used to rule out bone fractures, MRIs provide detailed images of soft tissues, including the ACL, meniscus, and cartilage. Because ACL injuries are often accompanied by other knee injuries, an MRI helps in evaluating the full extent of the damage.