ACL Tear
Anterior Cruciate Ligament Tear
Anatomy and Function
The anterior cruciate ligament (ACL) attaches from the anterior tibia (shin bone) to the femoral (thigh bone) intercondylar notch. As seen on the diagram, it lies just anterior to (in front of) the posterior cruciate ligament (PCL). Both ligaments are named based on their insertion site on the tibia. On the femoral side, it attaches in the posteromedial aspect of the lateral femoral condyle. The average length is 33 mm (1.3 inches) and the width is 11 mm ( 0.43 inches). The anatomy and footprint of the ligament are very important in reconstruction.
The primary function of the ACL is to limit anterior translation (forward sliding) of the tibia on the femur in the knee joint. It secondarily aids in limiting the pivot of the knee joint. It has two bundles: an anteromedial (AM) and posterolateral (PL) bundle. The anteromedial bundle is taught in flexion (knee bending) and the posterolateral bundle is taught in extension (knee straightening). Recent evidence has shown that the AM bundle may play a large role in anterior-posterior translation (forward to backward motion) of the knee, and the PL bundle in rotational stability. (23412155)
Epidemiology
Anterior cruciate ligament (ACL) injuries are among the most common sports injuries in America. Close to 200,000 reconstructions are performed annually. (25086064)
Signs and Symptoms
The ACL injury typically occurs during a twisting injury at the knee. It often occurs in competitive sports, and does not always have to include a direct blow to the knee. Sometimes it can occur with a misstep during pivoting.
You may often hear a “pop” and have knee swelling. Most of the time this accompanies a great deal of pain where you may be unable to place weight on the injured leg. This can be followed by the inability to fully flex (bend) or extend (straighten) the knee.
Some other things that could mimic an ACL injury could be a fracture (broken bone), dislocation, meniscus tear, cartilage injury, or other ligament injury.
If this type of injury occurs to you, you should seek immediate medical attention for appropriate diagnosis and treatment.
Diagnosis
An astute clinician may be able to pick up this injury based on history and physical exam alone. Sometimes a knee arthrometer may be used to detect the side to side difference in anterior translation of the tibia.
An x-ray (plain radiograph) may show a “Segond fracture” which is the avulsion of the anterolateral ligament. This is a secondary injured ligament which often signifies an ACL tear.
Often times, your doctor may order an MRI (magnetic resonance imaging) study of your knee to make the definitive diagnosis. This can be very helpful as a surgical plan, as it will also show any other injury that occurred to your knee involving the meniscus, cartilage, or other ligaments. Be sure to disclose to your physician if you have any metal implants, a pacemaker, or any fear of enclosed places, as this can affect your ability to get an MRI.
Treatment
Initial treatment should include rest, ice, compression, and elevation. Try to keep it elevated above the level of your heart. Be sure not to put ice directly on your skin, and place it over a protective plastic or cloth. Anti-inflammatory medications such as ibuprofen and naprosyn can be initiated if it is safe for you to take these drugs and you do not have any impaired kidney function. Tylenol should be taken as well if your liver function is normal.
An x-ray should be obtained if you are unable to place weight on your knee due to pain. This is to make sure there is no dislocation and no bones are broken. Try to immobilize your knee and keep it protected until you seek medical attention.
When you get to your provider, then you will most likely get more information on your injury and the diagnosis. This will help guide you decide whether or not to have surgery for your injury.
Deciding Whether or Not to Have Surgery
Depending on the degree of the tear, a torn ACL has very limited healing capacity. In general, a torn ACL cannot be repaired. Therefore, it must be reconstructed using different tissue from either your own body (autograft) or donor cadaver (allograft) tissue.
In general, without a functional ACL, patients should not participate in cutting-sports where side-to-side movements are done with the knee. These sports include but are not limited to soccer, tennis, baseball, basketball, and football. Though the body tries to adapt to ACL deficiency, it is not able to overcome it. (24837218) If you are able to safely undergo physical rehabilitation and you do not wish to return to cutting-sports, then you don’t need to have your ACL reconstructed. However, even if you don’t wish to return to cutting sports, and your knee remains unstable, then surgery would be necessary. (25438034)
Some other factors that would require surgery to get better include a torn meniscus, a multiple ligament knee injury, and failure of nonoperative management. Please refer to those sections on our website to learn about those injuries.
In certain European countries, there are studies where exceptional physical therapy have allowed certain athletes to return to sports without getting an ACL reconstruction. In the United States, an ACL reconstruction is recommended if you wish to return to a cutting sport in addition to any other necessary procedures.
Graft Choice
This is an area of heavy research. There are very specific patient and surgeon factors which ultimately will result in the greatest success for athletes. In general, autografts (using your own tissue) has the proven track record to have the highest chance for success without re-tearing the graft. Although in certain circumstances, an allograft (donor tissue) may be a better choice due to patient factors such as age, bone, and tissue quality.
An evidence-based ACL Graft Selector utilizing risk data from a community-based registry is currently being developed.
Surgical Technique
Femoral Nerve Block
Though getting a nerve block is relatively low-risk. Long term complications can include temporary or permanent nerve parasthesias (numbness and tingling), and muscle weakness. A recent study showed that patients who do get a nerve block had worse knee function and strength compared to those that did not receive a block. In addition they did take longer to return to sport with a nerve block. (25466410)
Anatomic ACL Reconstruction
The ACL attaches on the tibia in line with the posterior aspect of the anterior horn of the lateral meniscus. This is an important landmark for surgeons during ACL reconstruction to try to match the native anatomy of the patient. (23571132) The latest evidence suggests that the best outcomes for success are anatomic ACL reconstruction where the patient’s anatomy is restored. (25086574) (25239931)
Single Bundle versus Double Bundle
There is no difference in outcome scores, complications, or failure rates between single bundle versus double bundle repair.(23152258)
Pysical Therapy
Though your surgeon may have done an excellent job reconstructing the ACL, it is ultimately up to you and your body to let it heal.
We are currently in the process of building our SportsHealth.info Physical Therapy protocols. If you are a licensed therapist and would like to contribute, please contact us.