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Anterior Cruciate Ligament (ACL) Injuries
One of the most common knee injuries is an anterior cruciate ligament sprain or tear. Athletes who participate in high demand sports like soccer, football, lacrosse and basketball are more likely to injure their anterior cruciate ligaments.
If you have injured your anterior cruciate ligament, you may require surgery to regain full function of your knee. This will depend on several factors, such as the severity of your injury and your activity level.
Anatomy
The Anterior Cruciate Ligament (ACL) is a major ligament located inside the knee and provides a large amount of stability to the joint. The ACL crosses (Cruciate is latin for "crossing") through the knee joint from front to back and prevents the Tibia from moving forward on the Femur.
An injury to the anterior cruciate ligament can be a debilitating musculoskeletal injury to the knee, seen most often in athletes. Non-contact tears and ruptures are the most common causes of ACL injury. ACL injury more commonly causes knee instability than does injury to other knee ligaments. Injuries of the ACL range from mild, such as small tears, to severe when the ligament is completely torn.
Description
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.
Cause
ACL injuries occur when an athlete rapidly decelerates, followed by a sharp or sudden change in direction (cutting). ACL failure has been linked to heavy or stiff-legged landing; as well as twisting or turning the knee while landing, especially when the knee is in the valgus (knock-knee) position.
Women in sports such as basketball, tennis, soccer, and lacrosse are significantly more prone to ACL injuries than men. The discrepancy has been attributed to differences between the sexes in anatomy, general muscular strength, reaction time of muscle contraction and coordination, and training techniques. Recent studies suggests hormone-induced changes in muscle tension may also be an important factor, but there is no clear correlation. Women have a relatively wider pelvis, requiring the femur to angle toward the knees. Recent research also suggests that there may be a gene variant that increases the risk of injury.
Symptoms
Symptoms of an ACL injury include hearing a sudden popping sound, swelling, and instability of the knee (i.e., a "wobbly" feeling). Pain is also a major symptom in an ACL injury and can range from moderate to severe. Continued athletic activity on a knee with an ACL injury can have devastating consequences, resulting in massive cartilage damage, leading to an increased risk of developing osteoarthritis later in life.
Examination
The pivot-shift test, anterior drawer test and the Lachman test are used during the clinical examination of suspected ACL injury. The ACL can also be visualized using a magnetic resonance imaging scan (MRI scan).
An ACL tear can present with a popping sound heard after impact, swelling after a couple of hours, severe pain when bending the knee, and buckling or locking of the knee during movement.
Though clinical examination in experienced hands is highly accurate, the diagnosis is usually confirmed by MRI, which has greatly lessened the need for diagnostic arthroscopy. MRI has a higher accuracy than clinical examination in detecting ACL tears when multiple ligaments are torn.
Anterior drawer test
The anterior drawer test for anterior cruciate ligament laxity is one of many medical tests used to determine the integrity of the anterior cruciate ligament. It can be used to help diagnose sprains and tears. The test is performed as follows: the patient is positioned lying supine with the hip flexed to 45° and the knee to 90°. The examiner positions himself by sitting on the examination table in front of the involved knee and grasping the tibia just below the joint line of the knee. The thumbs are placed along the joint line on either side of the patellar tendon. The index fingers are used to palpate the hamstring tendons to ensure that they are relaxed; the hamstring muscle group must be relaxed to ensure a proper test. The tibia is then drawn forward anteriorly. An increased amount of anterior tibial translation compared with the opposite limb or lack of a firm end-point indicates either a sprain of the anteromedial bundle of the ACL or a complete tear of the ACL. This test should be performed along with other ACL-specific tests to help obtain a proper diagnosis.
Lachman test
The knee is flexed at 30 degrees. Examiner pulls on the tibia to assess the amount of anterior motion of the tibia in comparison to the femur. An ACL-deficient knee will demonstrate increased forward translation of the tibia at the conclusion of the movement. The Lachman test is recognized by most authorities as the most reliable and sensitive clinical test for the determination of anterior cruciate ligament integrity, superior to the anterior drawer test commonly used in the past. To do this, lay the patient supine on an examination table. Put the patient's knee in about 20–30 degrees flexion, also according to Bates' Guide to Physical Examination the leg should be externally rotated. The examiner should place one hand behind the tibia and the other on the patient's thigh. It is important that the examiner's thumb be on the tibial tuberosity. On pulling anteriorly on the tibia, an intact ACL should prevent forward translational movement of the tibia on the femur ("firm endpoint").
This test can be done in an on-the-field evaluation in an acute injury setting, or in a clinical setting when a patient presents with knee pain. In either situation, ruling out fracture is important in the evaluation process. Also when evaluating the integrity of the ACL, it is important to test the integrity of the MCL.
Pivot shift test
Person lies on one side of the body as the knee is extended and internally rotated. The evaluator applies stress to lateral side of the knee, while the knee is being flexed. A crash felt at 30 degrees flexion indicates positive test.
Treatment
Treatment for an ACL tear will vary depending upon the patient's individual needs. For example, the young athlete involved in agility sports will most likely require surgery to safely return to sports. The less active, usually older, individual may be able to return to a quieter lifestyle without surgery.
Nonsurgical Treatment
A torn ACL will not heal without surgery. But nonsurgical treatment may be effective for patients who are older or have a very low activity level. If the overall stability of the knee is intact, your doctor may recommend simple, nonsurgical options.
Bracing. Your doctor may recommend a brace to protect your knee from instability. To further protect your knee, you may be given crutches to keep you from putting weight on your leg.
Rehabilitation. As the swelling goes down, a careful rehabilitation program is started. Specific exercises will restore function to your knee and strengthen the leg muscles that support it.
Surgical Treatment
Rebuilding the ligament. Most ACL tears cannot be sutured (stitched) back together. To surgically repair the ACL and restore knee stability, the ligament must be reconstructed. Your doctor will replace your torn ligament with a tissue graft. This graft acts as a scaffolding for a new ligament to grow on.
Grafts can be obtained from several sources. Often they are taken from the patellar tendon, which runs between the kneecap and the shinbone. Hamstring tendons at the back of the thigh are a common source of grafts. Sometimes a quadriceps tendon, which runs from the kneecap into the thigh, is used. Finally, cadaver graft (allograft) can be used.
There are advantages and disadvantages to all graft sources. You should discuss graft choices with your own orthopaedic surgeon to help determine which is best for you.
Because the regrowth takes time, it may be six months or more before an athlete can return to sports after surgery.
Procedure. Surgery to rebuild an anterior cruciate ligament is done with an arthroscope using small incisions. Arthroscopic surgery is less invasive. The benefits of less invasive techniques include less pain from surgery, less time spent in the hospital, and quicker recovery times.
Unless ACL reconstruction is treatment for a combined ligament injury, it is usually not done right away. This delay gives the inflammation a chance to resolve, and allows a return of motion before surgery. Performing an ACL reconstruction too early greatly increases the risk of arthrofibrosis, or scar forming in the joint, which would risk a loss of knee motion.
Prevention
Research has shown that the incidence of non-contact ACL injury can be reduced anywhere from 20% to 80% by engaging in regular neuromuscular training that is designed to enhance proprioception, balance, proper movement patterns and muscle strength. Many of our sports teams have incorporated these techniques into their pre-season training and as part of their in-season warm up routines. If you would like to know more about what you can do to prevent the chances of an ACL injury, stop by the Athletic Training Room.
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