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Anterior Cruciate Ligament
Anterior Cruciate Ligament ( ACL )
An ACL injury is a tear or sprain of the anterior cruciate (KROO-she-ate) 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.
Depending on the severity of your ACL injury, treatment may include rest and rehabilitation exercises to help you regain strength and stability, or surgery to replace the torn ligament followed by rehabilitation. A proper training program may help reduce the risk of an ACL injury.
Diagnosis
During the physical exam, your doctor will check your knee for swelling and tenderness — comparing your injured knee to your uninjured knee. He or she may also move your knee into a variety of positions to assess range of motion and overall function of the joint. Often the diagnosis can be made on the basis of the physical exam alone, but you may need tests to rule out other causes and to determine the severity of the injury. These tests may include:
- X-rays. X-rays may be needed to rule out a bone fracture. However, X-rays don’t show soft tissues, such as ligaments and tendons.
- Magnetic resonance imaging (MRI). An MRI uses radio waves and a strong magnetic field to create images of both hard and soft tissues in your body. An MRI can show the extent of an ACL injury and signs of damage to other tissues in the knee, including the cartilage.
- Ultrasound. Using sound waves to visualize internal structures, ultrasound may be used to check for injuries in the ligaments, tendons and muscles of the knee.
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Causes
Ligaments are strong bands of tissue that connect one bone to another. The ACL, one of two ligaments that cross in the middle of the knee, connects your thighbone to your shinbone and helps stabilize your knee joint.
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
When the ligament is damaged, there is usually a partial or complete tear of the tissue. A mild injury may stretch the ligament but leave it intact.
Risk factors
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
Prevention
Proper training and exercise can help reduce the risk of ACL injury. A sports medicine physician, physical therapist, athletic trainer or other specialist in sports medicine can provide assessment, instruction and feedback that can help you reduce risks.
Programs to reduce ACL injury include:
- 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.