Expertise provided by Amit Momaya, MD, Orthopaedic Surgeon, UAB Medicine
Disclaimer: This expertise is shared based on a typical injury and not intended to diagnose or provide an outlook on Lindsey Vonn’s situation.
What is an ACL injury?
An anterior cruciate ligament (ACL) injury occurs when one of the knee’s primary stabilizing ligaments is stretched or torn. The ACL runs diagonally through the center of the knee and plays a key role in controlling rotation and preventing the shin bone from sliding forward relative to the thigh bone. When it is torn—whether partially or completely—the knee often loses its normal stability. This can make activities that involve pivoting, cutting, or sudden changes in direction feel difficult or unsafe, and many people experience the sensation of the knee “giving out.” ACL injuries are common in sports that require quick deceleration, jumping, or rapid directional changes, but they can also occur during everyday activities with the right twisting force.
How does an ACL tear usually happen?
This injury most commonly occurs via a non-contact mechanism in which the athlete plants and cuts or lands from a jump. It is common in football, soccer, and basketball.
What are the immediate symptoms of an ACL tear?
Immediate signs of an ACL tear often include a noticeable popping sensation, rapid swelling, and the feeling that the knee suddenly gave way.
How is an ACL tear diagnosed?
Diagnosis is typically made based on the patient’s history and a physical exam—most notably the Lachman test, where the shin bone is gently pulled forward relative to the thigh bone—and is then confirmed with an MRI.
Does an ACL tear require surgery?
The injury typically requires surgery to reconstruct the ACL and restore stability in the knee.
What does recovery from an ACL tear typically look like?
Recovery typically progresses through gradually increasing range of motion and strengthening over time. In most cases, rehabilitation involves structured and often intensive physical therapy, especially for individuals planning to return to sports. Therapy focuses on restoring knee stability, rebuilding strength, improving balance, and retraining proper movement mechanics. Bracing is commonly used during the early phases of recovery to support the knee, and some athletes choose to continue wearing a brace even after returning to sport for added confidence and protection.
When can someone return to play or activity?
The average return to play timeline is approximately 9-12 months.
Can ACL tears be prevented?
ACL tears can’t be completely prevented, but the risk can be significantly reduced through targeted neuromuscular training programs. Structured injury‑prevention routines—such as the FIFA 11+ program—focus on strengthening, balance, landing mechanics, and agility, all of which help lower the likelihood of an ACL injury.
When should someone see a sports medicine specialist?
When an individual experiences a sudden pop, knee shift, or swelling in the knee, it is important to visit a board certified orthopedic surgeon to further evaluate the injury. Call 205-930-8339 to make an appointment.
Learn more about sports medicine at UAB Medicine