What is Anterior Cruciate Ligament (ACL)
An ACL injury is the tearing of the anterior cruciate (KROO-she-ate) ligament, or ACL, inside your knee joint. An ACL injury most commonly occurs during sports that involve sudden stops and changes in direction such as basketball, soccer, tennis and volleyball.
Immediately after an ACL injury, your knee may swell, feel unstable and become too painful to bear weight. Many people hear or feel a “pop” in their knee when an ACL injury occurs.
Depending on the severity of your ACL injury, treatment may include surgery to replace the torn ligament followed by rehabilitation exercises to help you regain strength and stability. If your favorite sport involves pivoting or jumping, a proper training program may help reduce your chances of an ACL injury.
Causes of Anterior Cruciate Ligament (ACL)
The anterior cruciate ligament can be injured in several ways:
- Changing direction rapidly
- Stopping suddenly
- Slowing down while running
- Landing from a jump incorrectly
- Direct contact or collision, such as a football tackle
Several studies have shown that female athletes have a higher incidence of ACL injury than male athletes in certain sports. It has been proposed that this is due to differences in physical conditioning, muscular strength, and neuromuscular control. Other suggested causes include differences in pelvis and lower extremity (leg) alignment, increased looseness in ligaments, and the effects of estrogen on ligament properties
Signs and Symptoms Anterior Cruciate Ligament (ACL)
Symptoms of an acute ACL injury may include the following:
- Feeling or hearing a “pop” sound in the knee
- Pain and inability to continue activity
- Swelling and instability of the knee
- Development of a large hemarthrosis
Anatomy of Anterior Cruciate Ligament (ACL)
Three bones meet to form your knee joint: your thighbone (femur), shinbone (tibia), and kneecap (patella). Your kneecap sits in front of the joint to provide some protection.
Bones are connected to other bones by ligaments. There are four primary ligaments in your knee. They act like strong ropes to hold the bones together and keep your knee stable.
These are found on the sides of your knee. The medial collateral ligament is on the inside and the lateral collateral ligament is on the outside. They control the sideways motion of your knee and brace it against unusual movement.
These are found inside your knee joint. They cross each other to form an “X” with the anterior cruciate ligament in front and the posterior cruciate ligament in back. The cruciate ligaments control the back and forth motion of your knee.
The anterior cruciate ligament runs diagonally in the middle of the knee. It prevents the tibia from sliding out in front of the femur, as well as provides rotational stability to the knee.
What Happens if you have ACL injury?
If you have a sudden (acute) anterior cruciate ligament (ACL) injury, you typically know when it happens. You may feel or hear a pop, and the knee may give out, causing you to fall. The knee swells and often is too painful or unstable for you to continue any activity.
An ACL injury can cause small or medium tears of the ligament, a complete tear of the ligament (rupture), a separation of the ligament from the upper or lower leg bone (avulsion), or a separation of the ligament and part of the bone from the rest of the bone (avulsion fracture). When any of these occur, the lower leg bone moves abnormally forward on the upper bone, with a sense of the knee giving out or buckling.
How an anterior cruciate ligament (ACL) injury is treated and how it heals depends on:
- The condition of the ACL before the injury. This includes prior injuries, partial tears, ACL deficiency, and changes due to age.
- The general condition and health of the rest of your knee before this injury.
- The amount of damage or injury to the ACL. Injuries are usually grouped into grade I, II, or III sprains (tears) according to the amount of damage.
- Other injuries to the knee joint, such as to the cartilage or menisci, or to bones in the knee.
- Your age, how active you are, and how committed you are to treatment and rehabilitation (rehab).
- The time of diagnosis. If the ACL diagnosis is not made soon after the injury, the knee may be further damaged with use.
An ACL injury may develop into long-lasting and recurrent (chronic) ACL deficiency that leads to an unstable knee the knee buckles or gives out, sometimes with pain and swelling. This can occur if you had an ACL injury in the past and didn’t know it or if your ACL has not been treated or has been treated unsuccessfully. ACL deficiency can cause damage to the joint, including osteoarthritis. But not everyone with an ACL injury gets ACL deficiency.
People with minor ACL injuries usually begin treatment with a physical rehab program. Rehab exercises build strength and flexibility in the muscles on the front of the thigh (quadriceps) and strengthen and tighten the muscles in the back of the thigh (hamstrings). Most people return to their normal activities after a few weeks of rehab.
Description of Anterior Cruciate Ligament (ACL)
About half of all injuries to the anterior cruciate ligament occur along with damage to other structures in the knee, such as articular cartilage, meniscus, or other ligaments.
Injured ligaments are considered “sprains” and are graded on a severity scale.
Grade 1 Sprains. The ligament is mildly damaged in a Grade 1 Sprain. It has been slightly stretched, but is still able to help keep the knee joint stable.
Grade 2 Sprains. A Grade 2 Sprain stretches the ligament to the point where it becomes loose. This is often referred to as a partial tear of the ligament.
Grade 3 Sprains. This type of sprain is 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.
Partial tears of the anterior cruciate ligament are rare; most ACL injuries are complete or near complete tears.
Treatment of ACL Overview
The goals of treatment for an anterior cruciate ligament (ACL) injury are to:
- Restore normal or almost normal stability in the knee.
- Restore the level of function you had before the knee injury.
- Limit loss of function in the knee.
- Prevent injury or more damage to other knee structures.
- Reduce pain.
- Prevent osteoarthritis.
You’ll need to work with your doctor to decide whether you should have several months of rehabilitation (rehab) or surgery with rehab. Not all ACL tears need surgery.
Treatment right after an injury
If you know you have injured your ACL, the first treatment consists of:
- First aid to reduce swelling and pain. This may include resting the knee, applying ice, using gentle compression with an elastic bandage, elevating the leg, and taking pain medicines, such as acetaminophen or nonsteroidal anti-inflammatory drugs (NSAIDs).
- Using crutches and/or splints in the first few days. If crutches or splints are used for too long, the muscles will become weaker from too little activity. Then movement of the knee will become stiff and restricted.
- Strength and motion exercises to help prepare you for treatment.