The anterior cruciate ligament (ACL) is one of the four main ligaments in the knee and also one of the most commonly injured knee ligaments. It’s primary function is to prevent forward slippage of the tibia from the femur, but it also provides rotational stability to the knee joint. It is estimated that there are 100,000 – 200,000 ACL injuries per year. The vast majority of these are due to non-contact knee injuries. The mechanism of injury is usually deceleration of the knee joint coupled with cutting, pivoting, or side-stepping maneuvers. Certainly, involvement in sports is a risk factor, but ACL injuries can also occur outside of sports or even in those individuals who are not particularly athletically-inclined. Females also have a higher risk for injury compared to males. It has been proposed that this is due to several factors: physical conditioning, muscular strength, and neuromuscular control. Other hypothesized causes of this gender-related difference in ACL injury rates include pelvis and lower extremity (leg) alignment, increased ligamentous laxity, and the effects of estrogen on ligament properties.

Immediately after the injury, patients usually experience pain and swelling, and the knee feels unstable. Within a few hours after a new ACL injury, patients often have a large amount of knee swelling, a loss of full range of motion, pain or tenderness along the joint line and discomfort while walking. Evaluation usually begins with an examination by an athletic trainer, physical therapist or physician. X-rays are necessary to rule out fractures and examination will assess ligament integrity. Most ACL injuries are suspected based on the facts surrounding the injury and clinical examination, but an MRI will confirm if there is indeed a tear of the ligament or other associated injuries.

What happens naturally with an ACL injury without surgical intervention varies from patient to patient and depends on the patient’s activity level, degree of injury and instability symptoms. Partial ACL tears will not heal spontaneously but the patient may be able to function without pain or instability with proper rehabilitation. Complete ACL ruptures have a much less favorable outcome without surgical intervention. After a complete ACL tear, some patients are unable to participate in cutting or pivoting-type sports, while others have instability during even normal activities, such as walking. There are some rare individuals who can participate in sports without any symptoms of instability. This variability is related to the severity of the original knee injury, as well as the physical demands of the patient.

ACL tears are not usually repaired using suture to sew it back together, because repaired ACLs have generally been shown to fail over time. Therefore, the torn ACL is generally replaced by a substitute graft made of tendon.

Active adult patients involved in sports or jobs that require pivoting, turning, or hard cutting as well as heavy manual work are encouraged to consider surgical treatment. This includes older patients who have previously been excluded from consideration for ACL surgery. Activity, not age, should determine if surgical intervention should be considered. In young children or adolescents with ACL tears, early ACL reconstruction creates a possible risk of growth plate injury, leading to bone growth problems. The surgeon can delay ACL surgery until the child is closer to skeletal maturity or the surgeon may modify the ACL surgery technique to decrease the risk of growth plate injury. A patient with a torn ACL and significant functional instability has a high risk of developing secondary knee damage and should therefore consider articular cartilage, collateral ligament, joint capsule, or a combination of the above. Then “unhappy triad,” frequently seen in football players and skiers, consists of injuries to the ACL, the MCL, and the medial meniscus. In cases of combined injuries, surgical treatment may be warranted and generally produces better outcomes. As many as half meniscus tears may be repairable and may heal better if the repair is done in combination with the ACL reconstruction.

Dr. Wahl, D.O.