Anterior cruciate ligament

The anterior cruciate ligament (ACL) is a cruciate ligament which is one of the four major ligaments of the human knee. In the quadruped stifle (analogous to the knee), based on its anatomical position, it is also referred to as the cranial cruciate ligament.

The ACL originates from deep within the notch of the distal femur. Its proximal fibers fan out along the medial wall of the lateral femoral condyle. There are two bundles of the ACL—the anteromedial and the posterolateral, named according to where the bundles insert into the tibial plateau. The ACL attaches in front of the intercondyloid eminence of the tibia, being blended with the anterior horn of the medial meniscus. These attachments allow it to resist anterior translation and medial rotation of the tibia, in relation to the femur.

The anterior cruciate ligament is part of what is known as “the terrible triad”. This consists of the tearing of the anterior cruciate ligament (ACL), medial collateral ligament (MCL), and medial meniscus all at one time.

Injury
The ACL is quite commonly injured in athletes of varying sports. These situations are often remedied by surgery followed by several months of physical therapy.

A 2010 Los Angeles Times review of two medical studies discussed whether ACL reconstruction was advisable. One study found that children under 14 who had ACL reconstruction fared better after early surgery than those who underwent a delayed surgery. For adults 18 to 35, though, patients who underwent early surgery followed by rehabilitation fared no better than those who had rehabilitative therapy and a later surgery.

The first report focused on children and the timing of an ACL reconstruction. ACL injuries in children are a challenge because children have open growth plates in the bottom of the femur or thigh bone and on the top of the tibia or shin. An ACL reconstruction will typically cross the growth plates, posing a theoretical risk of injury to the growth plate, stunting leg growth or causing the leg to grow at an unusual angle.

The second study noted in the L.A. Times piece focused on adults. It found no significant statistical difference in performance and pain outcomes for patients who receive early ACL reconstruction vs. those who receive physical therapy with an option for later surgery. This would suggest that many patients without instability, buckling or giving way after a course of rehabilitation can be managed non-operatively. However, the study points to the need for more extensive research, was limited to outcomes after 2 years, and did not involve patients who were serious athletes. Patients involved in sports requiring significant cutting, pivoting, twisting, or rapid acceleration or deceleration may not be able to participate in these activities without ACL reconstruction. The randomized control study was originally published in the New England Journal of Medicine.

ACL Injuries in Women
Women have been known to suffer ACL injuries more frequently than men; current research gives some explanations for this. The joint through which the anterior cruciate ligament passes, along with the actual size of the anterior cruciate ligament, is significantly smaller in women than in men. This makes it more susceptible to damage. Along with these aspects, women tend to not activate their hamstring muscles as much as their male counterparts during certain cutting movements causing less stability in the knee joint.