1. Least Effective Exercises Slideshow
2. Dehydration Slideshow
3. First Aid Care and Pain Relief for Minor Injuries

Medical Author:

Benjamin Wedro, MD, FACEP, FAAEM

Benjamin Wedro, MD, FACEP, FAAEM

Dr. Ben Wedro practices emergency medicine at Gundersen Clinic, a regional trauma center in La Crosse, Wisconsin. His background includes undergraduate and medical studies at the University of Alberta, a Family Practice internship at Queen's University in Kingston, Ontario and residency training in Emergency Medicine at the University of Oklahoma Health Sciences Center.

View Full Profile

Medical Editor:

William C. Shiel Jr., MD, FACP, FACR

William C. Shiel Jr., MD, FACP, FACR

Dr. Shiel received a Bachelor of Science degree with honors from the University of Notre Dame. There he was involved in research in radiation biology and received the Huisking Scholarship. After graduating from St. Louis University School of Medicine, he completed his Internal Medicine residency and Rheumatology fellowship at the University of California, Irvine. He is board-certified in Internal Medicine and Rheumatology.

View Full Profile

In this Article

• What is the function of the knee joint?
• What is a torn anterior cruciate ligament (ACL)?
• What causes a torn ACL?
• What are symptoms and signs of a torn ACL?
• How is a torn ACL diagnosed?
• What is the treatment for a torn ACL?
• How long does it take to recover from a torn ACL?
• Can ACL tears be prevented?
• Torn Anterior Cruciate Ligament (ACL) At A Glance
• Patient Comments: Torn ACL - Causes
• Find a local Doctor in your town
• Torn ACL Index

The ACL arises from the front of the medial femoral condyle and passes through the middle of the knee to attaches between the bony outcroppings (called the tibia spine) that are located between the tibia plateaus. It is a small structure, less than 1 ½ inches long and ½ inch wide. But regardless of its size, the anterior cruciate ligament is vital in preventing the thighbone (femur) from sliding backward on the tibia (or, from the other point of view, the tibia sliding forward under the femur). The ACL also stabilizes the knee from rotating, the motion that occurs when the foot is planted and the leg pivots.

Without a normal ACL, the knee becomes unstable and can buckle, especially when the leg is planted and attempts are made to stop or turn quickly.

Most anterior cruciate ligament injuries occur due to trauma, usually in a sport or fitness activity. The ligament gets stretched or tears when the foot is firmly planted, the knee locks and twists or pivots at the same time. This commonly occurs in basketball, football, soccer, and gymnastics, where a sudden change in direction stresses and damages the ligament. These injuries are usually noncontact, occur at low speed, and occur as the body is decelerating

ACL injuries may also occur when the tibia is pushed forward in relation to the femur. This is the mechanism of injury that occurs because of a fall when skiing, from a direct blow to the front of the knee (such as in football), or in a car accident.

Women are more prone to ACL injuries than men. Women have slightly different anatomy that may put them at higher risk for ACL injuries:

• The intercondylar notch at the end of the femur is narrower in women than men. When the knee moves, this narrower space can pinch and weaken the ACL.



• Women have a wider pelvis than men and this causes the femur to meet the tibia at a greater angle (called the Q angle). This increases the force applied to the ACL with any twisting motion, increasing the risk of damage.



• Women may have a greater imbalance in the strength of the quadriceps muscle in relation to the hamstrings. This increases the stress on the ACL to stabilize the knee and potentially causes it to fail.