ACL Knee Injuries
The anterior cruciate ligament (ACL) is the most commonly injured ligament of the knee. Injury to the ACL is most common among athletes who participate in sports that involve sudden stops, jumping, or changes in direction, such as football, soccer, basketball, downhill skiing, volleyball, and gymnastics. But it can also be injured doing less athletic activities or because of degenerative changes within the ACL that occur as we age.
An ACL injury may require surgery to regain full function of the knee. This will depend on several factors, such as the severity of your injury, your activity level, and the feeling of stability of your knee.
Injured ligaments are classified as sprains and are graded on a severity scale:
- Grade 1: Ligament has been slightly stretched, but is still able to help keep the knee joint stable.
- Grade 2: The ligament has been stretched to the point where it becomes loose. This is often referred to as a partial tear of the ligament.
- Grade 3: Most commonly referred to as a complete tear of the ligament. The ligament has been split into two pieces, and the knee joint is unstable.
Anatomy of the Knee
The anterior cruciate ligament (ACL) is one of four major ligaments that stabilize the knee joint. A ligament is a tough band of tissue that connect the ends of bones together at a joint. The ACL is located in the center of the knee joint where it runs from the backside of the femur (thighbone) to connect to the front of the tibia (shinbone).
The ACL is the main controller of how far forward the tibia moves under the femur. This motion is called anterior translation of the tibia.
If the tibia (shin) moves too far forward, the ACL can tear (rupture). The ACL is also the first ligament that becomes tight when the knee is straightened. If the knee is forced past this point, or hyperextended, the ACL can also be torn.
Other parts of the knee may be injured when the knee is twisted violently. It is not uncommon to also see a tear of the medial collateral ligament (MCL) on the inside edge of the knee, and the lateral meniscus, which is the U-shaped cushion between the outer half of the tibia and femur bones.
You can learn more about the anatomy of the knee by downloading our educational document A Patient’s Guide to Knee Anatomy.
How ACL Knee Injuries Occur
ACL injuries are typically caused by sudden deceleration (slowing down or stopping), hyperextension, or pivoting in place. Sports-related injuries are the most common.
The majority of ACL injuries occur in non-contact sports. Only a small percentage are the result of direct contact with another player or object.
ACL injuries affect both men and women. Female athletes, however, tend to have a higher incidence of ACL injuries than males in certain sports. It has been suggested that differences in anatomy, muscle mass, and training may be the cause of this. Differences in pelvis and lower extremity (leg) alignment, increased looseness in ligaments, and the effects the hormone estrogen can have on ligaments are other suggested causes.
Symptoms of ACL Knee Injuries
The symptoms following a tear of the ACL can vary. Someone with an ACL injury may experience some or all of the following:
- Hearing and/or feeling a “pop” at the time of injury
- Instability, where the knee feels as though it will give out from under you, especially when trying to change direction
- Pain with swelling
- Loss of range of motion
- Discomfort while walking
The pain and swelling from the initial injury typically will usually be gone after 2 to 4 weeks, but the knee may still feel unstable. The symptom of instability and the inability to trust the knee for support are what require treatment. Also, important in the decision about treatment, is the growing realization by orthopedic surgeons that long-term instability leads to early arthritis of the knee.
You can learn more about arthritis of the knee by downloading our educational document A Patient’s Guide to Osteoarthritis of the Knee.
Diagnosing ACL Knee Injuries
Our team of orthopedic surgeons will start with a thorough history and physical exam of your injured knee so that we can understand the severity of the injury. Typically, we will obtain x-rays of your knee to determine if the injury is associated with a broken bone. An MRI scan may also be obtained in order to view the ACL and surrounding soft tissues more clearly.
If you are diagnosed with an ACL injury, your SROSM physician will talk with you about the best course of treatment for you.
You can learn more about ACL injuries by downloading our educational publication A Patient’s Guide to Anterior Cruciate Ligament Injuries.