Anterior Cruciate Ligament (ACL)
John Nolan, Jr, MD - Orthopaedic Sports-Medicine Injuries
One of the most dreaded injuries in sports is a tear of the ACL. From professional football to high school basketball, increasing numbers of athletes are injuring their anterior cruciate ligament, resulting in the loss of at least a season of competition and usually requiring surgery and an extensive rehab program.
“Weekend warriors”, non-athletes and individuals engaged in every day strenuous activities can also tear their ACL.
The ACL is a complicated three dimensional structure that runs from the front portion of the tibia bone (shin), and insets into the back lateral wall of the femur (thigh). It provides stability to the knee by preventing excessive movement between the tibia and the femur and it provides rotational stability of the knee.
Other important structures that contribute to the stability and function of the knee include the medial (inside) and lateral (outside) collateral ligaments, which connect the femur to the tibia on either side of the knee. In addition, the medial and lateral menisci are “C” shaped cartilage structures that sit atop the tibia and provide both cushioning and extra stability.
Once the ACL has been injured, the secondary stabilizing structures of the knee can quickly become overstressed, resulting in gross ligamentous laxity and a knee that is unstable even during activities of daily living.
There are several ways that the ACL can be injured. The most common is a twisting injury when the upper leg turns to cut and the foot is fixed on the ground. Other common scenarios including a “clipping” type injury or landing on a hyperextended knee. While ACL injuries are frequently seen during football games, any sport or activity that involves twisting, turning, jumping, or any type of contact can result in an injury. The individual often describes feeling a sudden pop with loss of control of the knee. An athlete is rarely able to continue playing after an ACL tear, and frequently has to be helped off the field by others. Over the next 24 hours significant swelling occurs resulting in a palpable collection of blood in the knee known as a hemarthrosis. This swelling causes increased pain and stiffness in the knee and usually results in the individual seeking prompt medical attention.
The diagnosis of an ACL tear can frequently be made simply by examining the knee. In addition to a hemarthrosis, special tests demonstrate laxity of the ACL. An anterior drawer test is performed by having the doctor try to pull the tibia forward with the knee in the flexed position. The “Lachman” test is a similar test done with the knee in about 30 degrees of flexion, and is considered the most sensitive test for an ACL injury. Additional tests may be done to look for injuries to other structures in the knee, and x-rays are usually ordered to rule out the presence of a fracture. Finally, in many cases the doctor will want to check an MRI both to confirm the diagnosis of an ACL tear as well as check for other associated injuries.
Treatment of an ACL injury depends on the severity of the tear, the presence of other knee injuries, and the age and anticipated activity level of the patient. Patients with incomplete tears and those who are less active often elect nonsurgical treatment. This includes a course of physical therapy, activity modification, and the use of bracing when performing certain activities. Although age is not a specific determining factor, older patients, particularly those with some knee arthritis, are often good candidates for nonsurgical care.
Surgical treatment is recommended in most patients when the injury is complete and the goal is to return to athletic activity. It is not possible to repair the ligament once it has been torn. In a small percentage of cases the ligament is torn off the tibia with a piece of bone and can be directly repaired. In most cases the tear is in the middle of the ligament, and the ligament must be removed and replaced by another structure to recreate the ligament. This is called an ACL reconstruction.
The Surgical Procedure
A graft is chosen and shaped to match the patients ACL. Tunnels are drilled in the tibia and femur and the graft is then placed in and fixed with pins or screws. The procedure, which used to require one or more large incisions and several days in the hospital, is now almost always done through an arthroscope with tiny incisions, and frequently is done as an outpatient. Other injuries, such as meniscus tears, are also fixed at the time of the arthroscopy. Postoperative rehabilitation includes range of motion and strengthening exercises under the direction of a trainer or physical therapist. Patients can frequently return to normal activities within a few weeks, but return to sports is usually delayed for six to twelve months.
Progress to Date
There have been dramatic improvements in surgical techniques over the last twenty years which have resulted in both faster recovery and better long term results. Most research at the present time resolves around determining the best choice and proper placement of the grafts. Graft choices include using a portion of the patient’s patellar tendon or hamstring from either the injured or opposite knee, or using a sterilized cadaver graft. Graft placement options revolve around where to place the ligament into the femur, and whether to use one larger ligament or two smaller grafts to try to more accurately replicate the function of the native ACL. As of today, there is no conclusive evidence that one method is superior to another, and the decisions are made on the basis of surgeon and patient preference and surgeon experience.
The results of ACL reconstruction are generally very good. No reconstruction technique exists that is as good as the patient’s own natural ACL. There is an increased risk of premature arthritis as a result of the injury with or without surgery, and while most athletes can return to competitive sports they are often a step slower than before the injury. Most patients are able to resume a much more active lifestyle with fewer restrictions and with fewer residual symptoms after the ACL is reconstructed and rehabbed, and it is almost always recommended for young and athletically inclined patients. I would encourage all patients faced with this injury to have a thorough discussion with your doctor regarding the best treatment options for your specific circumstances.