Understanding ACL Injuries

May 22, 2025

Understanding ACL Injuries

Understanding ACL Injuries

The Anterior Cruciate Ligament (ACL) is one of the most commonly injured structures in the knee, especially among athletes. Understanding how these injuries occur, who is most at risk, and the prevalence of ACL injuries can help patients and providers better prepare for prevention, diagnosis, and treatment.

Types of ACL Injuries

ACL injuries are classified by severity:

Grade I (Sprain): The ligament is mildly damaged and slightly stretched, but still provides adequate stability to the knee.
Grade II (Partial Tear): A rare occurrence where the ligament is stretched to the point of being loose but not completely torn.
Grade III (Complete Tear): The ligament is split in two and no longer stabilizes the knee. This is the most common form of ACL injury requiring surgical intervention.

ACL injuries often occur in conjunction with damage to other knee structures such as the menisci, cartilage, or other ligaments (especially the MCL and LCL).

Mechanisms of Injury

The majority of ACL injuries are non-contact and result from:

Sudden deceleration or stopping
Rapid change in direction (cutting or pivoting)
Improper landing from a jump
Twisting the knee while the foot is firmly planted

Contact injuries may occur from direct blows to the outside of the knee, especially in collision sports, but are less common.

Who is Most at Risk?

Several groups are at increased risk of ACL injury:

Athletes in sports such as soccer, basketball, football, skiing, and gymnastics
Females, who are 2 to 8 times more likely to sustain ACL injuries than males in similar sports due to biomechanical, hormonal, and neuromuscular factors
Youth athletes, especially during late adolescence when athletic activity intensifies and growth-related changes occur
Individuals with previous ACL injuries, as the risk of reinjury or injury to the opposite knee is significantly elevated

How Common Are ACL Injuries?

ACL injuries are common in active populations:

Over 200,000 ACL injuries occur annually in the United States.
Approximately 100,000 ACL reconstruction surgeries are performed each year.
Recreational and competitive athletes are especially affected, with higher rates in sports involving pivoting and jumping.
Return-to-sport rates vary: around 65-90% return to some level, but fewer than 55-65% return to their pre-injury level of performance.