The Anterior Cruciate Ligament

The Anterior Cruciate Ligament

What is a cruciate ligament?

The knee, which is the largest joint in the body, relies on four ligaments, as well as muscles and tendons, to function properly. There are two ligaments on the sides of the knee: the Medial Collateral Ligament (MCL) and the Lateral Collateral Ligament (LCL). In addition the knee contains two crossed ligaments, which run through the center of the knee: the Anterior Cruciate Ligament (ACL) and the Posterior Cruciate Ligament (PCL).

The ACL prevents the tibia, or shinbone, from sliding forward at the knee and the PCL prevents the tibia from shifting back, or posterior. The ligaments hold the knee together, providing the stability which allows for cutting, pivoting and rapid stops and starts.

How are the ligaments injured?

Injuries to the cruciate ligaments generally, but not always, take a great deal of force. Football players and skiers are prone to such injuries by virtue of the great forces involved in these sports. However, more ACL injuries occur with sudden stopping, twisting or pivoting in sports such as basketball and soccer. Also, these injuries tend to occur in greater numbers in female athletes. Generally, with an ACL injury the individual often feels the knee shift and/or hears a pop and the knee swells rapidly.

PCL injuries more often occur with falls, motor vehicle accidents or trauma directed to the front of the flexed (bent) knee and the swelling is often not that impressive. Fortunately, PCL injuries occur much less often than ACL injuries and are generally less disabling.

Can the ACL heal without surgery?

While injuries to the MCL, LCL and PCL may often heal without surgery the ACL has limited potential for healing. Tears of the ACL may often lead to a loose or unstable knee that easily 'gives out' with various activities. The treatment of the injured ACL depends on a number of factors such as age, desired activity level, and the amount of healing that takes place in the knee.

Although most tears are complete, sometimes the ACL simply stretches and in other cases it tears fully but scars down, or reattaches, close to its original position and continues to provide some stability to the knee. In almost one third of ACL injuries the ligament may continue to provide sufficient stability so that the knee will not be appreciably unstable. Such individuals may advance back to limited sports with rehabilitation and occasionally bracing. In another one third the knee may be moderately loose or unstable. These individuals generally can go about their normal daily activities without problems but will be unable to resume sports without the knee 'giving out'. The last one third, unfortunately, are very unstable and easily 'give out' with activities of daily living, such as walking or coming down stairs.

In younger and more athletic individuals we are inclined to recommend surgery to restore the stability of the knee as these individuals remain at greater risk to further damage the knee with a return to sports – especially activities those involving sudden cutting, pivoting, or deceleration. An older, or less athletic, individual may choose to modify his or her life style to protect the knee from further damage by avoiding these activities.

What is a torn cartilage?

The other important structures within the knee are the menisci. "Menisci" is the plural form of the Latin word "meniscus". There are two menisci within the knee – the medial meniscus and the lateral meniscus. These structures are round, rubber-like fibro cartilage spacers that act like washers or shock absorbers within the knee. When someone says that they have a "torn cartilage," they are describing a tear of a meniscus. Without a normal functioning meniscus people often develop early arthritis in the involved knee. Tears of the "cartilage," or meniscal tears, occur frequently in association with tears of the cruciate ligaments and often result in pain on the inner or outer aspect of the injured knee.

After someone injures their knee how do you make the diagnosis?

There is nothing better than a thorough history and physical examination for the evaluation of the injured knee. With a complete disruption of the ACL the knee generally swells, or fills with blood, rapidly. Patients also often recall a popping sensation or sound at the time of the injury and may even feel the knee shifting in and out of a place. Often the initial examination may be quite difficult due to pain and spasm. In such cases a period of ice, rest and anti-inflammatory medications may be indicated followed by another examination in a week or two when the exam is less painful. Looseness, or laxity, on examination confirms a ligament injury, while popping and/or tenderness along the joint line is suggestive of a torn "cartilage" or meniscus. X-rays are obtained to rule out the occasional fracture and Magnetic Resonance Imaging (MRI) scans are often ordered, although they are not one hundred percent accurate.

How is an injury to the ACL treated?

The decision as to whether surgery is indicated is not based solely upon the presence or absence of a tear on an MRI scan but rather on whether the knee is loose or unstable on examination. The athletic goals, or desires, of the patient also play a significant role in the decision making.

As stated earlier, some patients occasionally tighten-up and are able to eventually resume all of their normal activities without surgery. Others may be fairly stable but continue to have pain and swelling and are candidates for an arthroscopic or limited incision surgery. Those individuals who end up with mild laxity or instability have the option of avoiding certain athletic activities, permanently, and thereby may be able to avoid surgery. These people may choose to operate on their lifestyle rather than on their knees. Those individuals who are obviously loose can be expected to continue to have problems with the knee and therefore should seriously consider ACL reconstructive surgery.

In the past before the development of modern surgical techniques, ACL injuries were often career ending injuries for athletes. Some athletes, however, continued to play with an unstable knee and eventually tore the cartilage in their knees and developed early arthritis. Most of these former 'greats' now have artificial knees! The goal of treatment is to prevent further episodes of instability or giving way. In the older or less active individual this is often accomplished with bracing and activity modification. If one can avoid episodes of giving way they can often protect the knee from further injury and early arthritis. The dilemma is to decide who can modify their lifestyle to prevent giving way and who will be unable to do so and therefore should undergo surgery to correct the instability. In most cases, the younger and more athletic individuals should seriously consider surgery.

Why not use a brace instead of surgery?

Special custom ACL braces are often prescribed for the older or less vigorous athlete as well as those whose instability or laxity is only mild. The braces limit some of the excess motion, or instability. In individuals with more significant laxity, as well as those athletes involved in more demanding sports, these braces however remain ineffective. In general the braces do not protect the knee from further damage in individuals who resume high demand sports. If the braces really worked we would see professional athletes using them instead of surgery.

What's the bottom line?

If one has an injury to the Anterior Cruciate Ligament that results in laxity or instability the individual must avoid those activities which cause the knee to give out or undergo surgery to correct the instability. A failure to do so results in further episodes of giving way during which time further meniscal and articular cartilage damage occurs resulting in early and irreparable damage and eventual arthritis.

If you are interested in the details of the surgery please review Anterior Cruciate Ligament Surgery.