An ACL injury is a tear or sprain of the anterior cruciate ligament (ACL) — one of the strong bands of tissue that help connect your thigh bone (femur) to your shinbone (tibia).

ACL injuries most commonly occur during sports that involve sudden stops or changes in direction, jumping and landing — such as soccer, basketball, football and downhill skiing.

Many people hear a pop or feel a “popping” sensation in the knee when an ACL injury occurs. Your knee may swell, feel unstable and become too painful to bear weight.

Symptoms include:

• A loud pop or a “popping” sensation in the knee
• Severe pain and inability to continue activity
• Rapid swelling
• Loss of range of motion
• A feeling of instability or “giving way” with weight bearing

ACL injuries often happen during sports and fitness activities that can put stress on the knee:

• Suddenly slowing down and changing direction (cutting)
• Pivoting with your foot firmly planted
• Landing awkwardly from a jump
• Stopping suddenly
• Receiving a direct blow to the knee or having a collision, such as a football tackle

There are a number of factors that increase your risk of an ACL injury, including:

Being female — possibly due to differences in anatomy, muscle strength and hormonal influences

Participating in certain sports, such as soccer, football, basketball, gymnastics and downhill skiing

Poor conditioning

Using faulty movement patterns, such as moving the knees inward during a squat

Wearing footwear that doesn’t fit properly

Using poorly maintained sports equipment, such as ski bindings that aren’t adjusted properly

Playing on artificial turf

You can prevent ACL injury by:

• Exercises to strengthen the core — including the hips, pelvis and lower abdomen — with a goal of training athletes to avoid moving the knee inward during a squat

• Exercises that strengthen leg muscles, particularly hamstring exercises, to ensure an overall balance in leg muscle strength

• Training and exercise emphasizing proper technique and knee position when jumping and landing from jumps

• Training to improve technique when performing pivoting and cutting movements

• Training to strengthen muscles of the legs, hips and core — as well as training to improve jumping and landing techniques and to prevent inward movement of the knee — may help to reduce the higher ACL injury risk in female athletes.

ACL injury is treated through one or more treatment alternatives, namely:

• RICE
• Rehabilitation
• Surgery