ACL Injuries
An anterior cruciate ligament (ACL) injury is one of the most common serious knee injuries, especially in active individuals and athletes. The ACL is a strong band of tissue inside the knee that connects the thigh bone (femur) to the shin bone (tibia). Its main job is to keep the knee stable, particularly during movements that involve pivoting, cutting, jumping, or sudden stops. When the ACL is torn, the knee can feel unstable and unsafe during activity.
At the OrthoIllinois Knee Center, a leading bone and joint provider in northern Illinois, we offer comprehensive knee care. We carefully evaluate all ACL injuries to determine the extent of damage and the best path forward.
An ACL injury occurs when the ligament is stretched or torn. Tears can be partial or complete. A partial tear means some fibers are damaged but the ligament is still intact. A complete tear means the ligament has fully ruptured and can no longer stabilize the knee. Complete tears are more common than partial ones.
The majority of ACL injuries are non-contact injuries. This means the ligament tears without another person hitting the knee. Common causes include:
- Sudden changes in direction
- Quickly stopping while running
- Landing awkwardly from a jump
- Pivoting with the foot planted
Most ACL injuries happen during sports such as soccer, basketball, football, skiing, or lacrosse. However, they can also occur during everyday activities if the knee twists forcefully.
Certain factors can increase the risk of ACL injury. Poor conditioning, muscle weakness, fatigue, and improper movement mechanics all place extra stress on the knee. Some individuals are also at higher risk due to differences in anatomy or neuromuscular control.
An ACL tear often happens suddenly. Many people report hearing or feeling a “pop” at the time of injury. Common symptoms include:
- Rapid swelling within hours
- Significant knee pain
- Difficulty putting weight on the leg
- A feeling that the knee is unstable or “giving out”
- Limited range of motion
Swelling develops quickly because the ligament bleeds into the joint when torn. Even after initial pain improves, instability may continue. The knee may buckle during walking, turning, or going down stairs.
Other structures in the knee are often injured at the same time, such as the meniscus or cartilage. In fact, up to 66% of ACL tears are associated with a meniscus tear. This can cause additional pain, catching, or locking sensations.
Diagnosis begins with a detailed discussion about how the injury happened and a physical examination of the knee. At the OrthoIllinois Knee Center, specialists carefully evaluate knee stability, swelling, motion, and tenderness.
Specific hands-on tests are performed to check whether the shin bone moves too far forward in relation to the thigh bone. Excess movement suggests the ACL is torn.
Imaging studies are used to confirm the diagnosis. X-rays are typically taken first to rule out fractures. While X-rays do not show ligaments, they help identify any bone injury.
Magnetic resonance imaging (MRI) is the most important imaging tool for ACL injuries. MRI clearly shows the ligament and can determine whether it is partially or completely torn. It also reveals other injuries inside the knee, such as meniscus tears or cartilage damage. This information is critical when planning treatment.
A torn ACL does not heal on its own. Without proper management, the knee can remain unstable. Repeated episodes of giving way can lead to further damage to cartilage and menisci, increasing the risk of early arthritis.
Not every ACL tear requires surgery. Treatment depends on factors such as age, activity level, degree of instability, and overall knee health. Some individuals with lower activity demands may do well with physical therapy focused on strengthening and stability training. Others, especially athletes or those who want to return to pivoting sports, often benefit from surgical reconstruction.
Comprehensive knee care means evaluating the entire joint, not just the ligament. At the OrthoIllinois Knee Center, patients receive a thorough assessment and individualized recommendations designed to restore stability, protect long-term joint health, and support safe return to activity.
If you experience sudden knee swelling, instability, or a popping sensation after an injury, prompt evaluation is important. Early diagnosis allows for appropriate treatment planning and reduces the risk of long-term complications.
