Anterior cruciate ligament
|Anterior cruciate ligament|
Diagram of the right knee. Anterior cruciate ligament labeled at center left.
|Latin||ligamentum cruciatum anterius|
|From||lateral condyle of the femur|
|To||intercondyloid eminence of the tibia|
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 medial meniscus.
These attachments allow the ACL to resist anterior translation and medial rotation of the tibia, in relation to the femur.
ACL tears are one of the most common knee injuries, with over 100,000 ACL 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. 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. That camera sends video to a large monitor so 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 1-2 years or longer.
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 physical therapy supervised by a knee doctor can be an effective way to accomplish this.
Anterior cruciate ligament surgery is a complex surgery that requires expertise in the field of 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 body's natural ability to heal the native ligament, called a “healing response” surgery is resorted to. More commonly the ligament needs to 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. ACL surgery typically takes 6 to 9 months for complete recovery and return to sports or such activity. Revision ACL surgery will often take 9 months to more than a year. During this time, the doctor should guide the patient through the rehabilitation process. The early rehab, usually lasting around 6 weeks, will focus on maintaining full knee motion and preventing scar tissue. The second phase of rehab will then be directed towards regaining knee strength. Finally, sport or the patient's activity specific rehabilitation activities are administered before the patient returns to the occupational activities like sports. The rehabilitation program can also be composed of aggressive motions, weight bearing exercises, and a speedy recovery for athletes to return to their sport.
If the doctor recommends surgery for ACL, he may prescribe rehab before surgery as many studies have shown that having good motion before the surgery will benefit the patient after surgery.
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. 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. 
||This section contains a gallery of images.|
- Anterior cruciate ligament reconstruction
- Anterior drawer test
- Lateral collateral ligament
- Medial collateral ligament
- Posterior cruciate ligament
- Unhappy triad
- "Canine Cranial Cruciate Ligament Disease" (PDF). Melbourne Veterinary Referral Centre. pp. 1–2. Archived from the original (PDF) on 19 July 2008. Retrieved September 8, 2009.
- Ellison A, Berg E. Embryology, anatomy, and function of the anterior cruciate ligament. Orthop Clin North Am 1985;16:3-14. PubMed Abstract
- "The Unhappy Triad". Retrieved December 12, 2012.
- Stein, Jeannine (2010-07-22). "Studies on ACL surgery". The Los Angeles Times. Archived from the original on 25 July 2010. Retrieved 2010-07-23.
- "ACL Tears: To reconstruct or not, and if so, when?". howardluksmd.com. Retrieved 2010-07-23.
- Frobell, Richard B.; Roos, Ewa M.; Roos, Harald P.; Ranstam, Jonas; Lohmander, L. Stefan (2010). "A Randomized Trial of Treatment for Acute Anterior Crut Tears". New England Journal of Medicine 363 (4): 331–342. doi:10.1056/NEJMoa0907797. PMID 20660401.
- "ACL Injuries in Women". Retrieved December 12, 2012.
- Anatomy photo:17:02-0701 at the SUNY Downstate Medical Center - "
r Extremity: Knee Joint"
- Anatomy figure: 17:07-08 at Human Anatomy Online, SUNY Downstate Medical Center - "Superior view of the tibia."
- Anatomy figure: 17:08-03 at Human Anatomy Online, SUNY Downstate Medical Center - "Medial and lateral views of the knee joint and cruciate ligaments."
- lljoints at The Anatomy Lesson by Wesley Norman (Georgetown University) (antkneejointopenflexed)