Neha Patil (Editor)

Anterior cruciate ligament

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Dorlands /Elsevier



Anterior cruciate ligament

lateral condyle of the femur

intercondyloid eminence of the tibia

ligamentum cruciatum anterius

The anterior cruciate ligament (ACL) is one of a pair of cruciate ligaments (the other being the posterior cruciate ligament) in the human knee. They are also called cruciform ligaments as they are arranged in a crossed formation. In the quadruped stifle joint (analogous to the knee), based on its anatomical position, it is also referred to as the cranial cruciate ligament. The anterior cruciate ligament is one of the four main ligaments of the knee, and the ACL provides 85% of the restraining force to anterior tibial displacement at 30 degrees and 90 degrees of knee flexion.



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 tibia plateau is a critical weight-bearing region on the upper extremity of the tibia). The ACL attaches in front of the intercondyloid eminence of the tibia, being blended with the anterior horn of the lateral meniscus.


These attachments allow the ACL to resist anterior translation and medial rotation of the tibia, in relation to the femur.


ACL tears are among the most common knee injuries, with over 100,000 tears in the US occurring annually. Most ACL tears are a result of landing or planting in cutting or pivoting sports, with or without contact. Most serious athletes will require an ACL reconstruction if they have a complete tear and want to return to sports, because the ACL is crucial for stabilizing the knee when turning or planting. Reconstruction is most commonly done by autograft, meaning the tissue used for the repair is from the patient’s body. Other times, a cadaver is used for tissue. The two most common sources for tissue are the patellar tendon and the hamstrings tendon. The surgery is arthroscopic, meaning that a tiny camera is inserted through a small surgical cut. The camera sends video to a large monitor so that the surgeon can see any damage to the ligaments. In the event of an autograft, the surgeon will make a larger cut to get the needed tissue. In the event of an allograft, in which material is donated, this is not necessary. The surgeon will make holes in the patient’s bones to run the tissue through, and the tissue serves as the patient’s new ACL. Recovery time ranges between one and two years or longer. A week or so after the occurrence of the injury, the athlete is usually deceived by the fact that he/she is walking normally and not feeling much pain. This is dangerous as some athletes start resuming some of their activities such as jogging which, with a wrong move or twist, could damage the bones. It is important for the injured athlete to understand the significance of each step of an ACL injury to avoid complications and ensure a proper recovery.

Tearing the anterior cruciate ligament can sometimes be part of a knee injury known as “the terrible triad”. This consists of the simultaneous tearing of the anterior cruciate ligament (ACL), medial collateral ligament (MCL) and medial meniscus.

Non-operative treatment of the ACL

The ACL can be treated non operatively with strengthening and rehabilitation and occasionally injections when the ACL is not completely torn and the knee is still stable or if the patient is not doing activities requiring cutting and pivoting or similar actions. The mainstay of ACL non-operative treatment is strengthening of the muscles around the knee, especially the hamstrings. Focused therapy supervised by a physical therapist can be an effective way to accomplish this.

Anterior cruciate ligament surgery is a complex operation that requires expertise in the field of orthopedic and sports medicine. Many factors should be considered when discussing surgery including the athlete's level of competition, age, previous knee injury, other injuries sustained, leg alignment and graft choice. Occasionally, stimulation of the body's natural ability to heal the native ligament, called a “healing response”, is relied upon. More commonly, the ligament must be replaced by a graft from the patient's own tissue or tissue from a cadaver. Graft choice could be confusing, requiring expert counseling from a doctor.

Rehabilitation is crucial to any ACL surgery; complete recovery and return to sports or other activities typically takes six to nine months. Revision ACL surgery will often take nine months to more than a year. During this time, the physical therapist should guide the patient through the rehabilitation process. The early rehab, usually lasting around six weeks, focuses on maintaining full knee motion and preventing scar tissue. The second phase of rehab is directed toward regaining knee strength. Finally, activity-specific rehabilitation is administered. The rehabilitation program can also be composed of aggressive motions and weight-bearing exercises.

If the doctor recommends surgery for ACL, he or she may prescribe "prehab" before operating, as many studies have shown that inducing good motion before the surgery will benefit the patient during recovery.

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. But for adults 18 to 35, 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 two 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. In addition, the quadriceps angle, or Q-angle, between the anterior superior iliac spine and patellar ligament may contribute to the predisposition of ACL tears. There is some evidence that suggests since women are known to have larger Q-angles than their male counterparts, they might be more susceptible to ACL tears.


Anterior cruciate ligament Wikipedia