The anterior cruciate ligament, or ACL, is one of the major ligaments located in the middle of the knee, and runs from the femur (thigh bone) to the tibia (shin bone). It prevents the tibia from sliding out in front of the femur, as well as providing rotational stability to the knee.
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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, with most ACL injuries being complete or near complete tears.
Cause
The anterior cruciate ligament injury is often sports related, and usually occurs when there is an abrupt directional change with the foot fixed to the ground or when a deceleration force crosses the knee (stopping suddenly). Other methods of injury include slowing down while running, landing from a jump incorrectly, and 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 oestrogen on ligament properties.
Symptoms
When you injure your anterior cruciate ligament, you might hear a "popping" noise and you may feel your knee give out from under you. Other typical symptoms include:
- Pain with swelling. Within a few hours, your knee will swell. If ignored, the swelling and pain may resolve on its own. However, if you attempt to return to sports, your knee will probably be unstable and you risk causing further damage to the cushioning cartilage (meniscus) of your knee.
- Loss of full range of motion
- Tenderness along the joint line
- Discomfort while walking.
Diagnosis
Diagnosis of an ACL tear is made by knowing your symptoms, medical history, performing a physical examination of the knee, including the use of specific provocation tests for ACL stability. Other diagnostic tests such as X-rays and MRI scans will give further information, including whether there is an associated fracture, or other injury to the knee (joint cartilage, meniscus, collateral ligament, or capsule).
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Treatment
Treatment for an ACL tear will vary depending upon the patient's individual needs. A torn ACL will not heal without surgery. If the overall stability of the knee is intact, nonsurgical options will be recommended.
Nonsurgical Treatment
Nonsurgical treatment may be effective for patients who are elderly or have a lower activity level. This usually consists of the RICE protocol (Rest, Ice, Compression, and Elevation) to help control initial pain and swelling. Physical therapy is begun as the swelling goes down, with a careful rehabilitation program aimed at restoring function to the knee and strengthen the leg muscles that support it (particularly the hamstrings which insert behind the tibia and dynamically help prevent anterior gliding). A brace may be used to protect your knee from instability in the short term. To further protect your knee, you may be given crutches to keep you from putting weight on your leg.
Surgical Treatment
The young athlete involved in agility or pivoting sports will most likely require surgery to safely return to sports. Most ACL tears cannot be sutured (stitched) back together. To surgically repair the ACL and restore knee stability, the ligament must be reconstructed. This procedure is performed using arthroscopic assistance and small incisions. The torn ligament is replaced with a tissue graft that acts as a scaffold for a new ligament to grow on. Grafts can be obtained from a number of possible sources, including hamstring tendons, patellar ligament/tendon (often with small bone blocks), and more rarely cadaver graft (allograft). As the regrowth takes time, it may be six months or more before an athlete can return to sports. With or without surgery, rehabilitation plays a vital role in getting you back to your daily activities. A physical therapy program will help you regain knee strength and motion.
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