What is an Anterior Cruciate Ligament (ACL) Injury?
The anterior cruciate ligament, or ACL, is located inside the knee joint, more or less behind the patella (kneecap) when looking at the joint from the front. It is a major ligament that connects the tibia of the lower leg to the femur of the upper leg. The ACL and PCL form a cross (or crux, hence “cruciate”) across the knee joint, which spans the knee joint from front to back. It is referred to as the anterior ligament because it is connected to the front half of the top of the tibia, whereas the posterior cruciate ligament is connected to the rear half. The cruciate ligaments play important roles to help to keep the tibia and femur stabilized together. This ensures concentric range of motion of the leg.
Damage to the ACL can have serious repercussions for normal function and movement and limits some activities. Once sustained, ACL injuries may have an impact on the stability of the knee joint, particularly as they often occur in conjunction with injury to other important components of the joint. These may include the medial collateral ligament and the medial or lateral meniscus, a thick layer of cartilage also located between the femur and tibia.
Estimates indicate that ACL damage accounts for upwards of 50% of all ligament injuries.
Causes of Anterior Cruciate Ligament Injuries
The anterior cruciate ligament may be damaged in a number of ways, including:
• Over-extension of the limb
• Exertion of excessive forces or pressure on the leg, which may be encountered during activities such as dismounting from a horse or landing from a jump
• Blunt force from contact sports, such as football or rugby
• Excessive turning outward of the bones of the leg, which may occur in the execution of a specific movement, as a result of poor technique in doing so, or by accident
ACL ligament injuries are mostly prevalent during activity. They have a higher incidence in women, due to pelvic architecture and commonly found hip muscle imbalances, which results in a more exaggerated knee angle. This may increase adverse forces and pressure on the knee joint, and thus on the ACL.
Sports and activities in which ACL injuries are relatively common include:
• Martial arts
ACL injuries may be linked to muscle strength imbalances, which can increase the load and strain on the knee joint.
Other factors or behaviors may also affect the risk of ACL injury. Examples of these include:
• Excessive flexion of the ankle
• Female hormone levels, as defined by the menstrual cycle
• Increased internal rotation of the hip
• Increased external rotation of the tibia
• Lower angles of flexion in the upper body, hip, or knee
• Reduced core strength and orientation relative to the knee joint
• Weakness of the knee joint
• Variations in the structure of the femur or tibia where ligaments are attached
Treatments for Anterior Cruciate Ligament Injuries
ACL injuries may be treated by surgical reconstruction of the ligament. Suturing the ruptured ligament has been tried in the past but it is not the standard of care for most cases. Reconstruction involves replacing the damaged ACL with tissue from the patient (autograft) or tissue from the tissue bank (allograft). A discussion with your surgeon will help you decide which option is best for you. Physical therapy is a necessary component of rehabilitation after reconstruction surgery. For those whose ACL damage is not severe enough, or enough of a concern for patients to undergo surgery, non-operative therapy is also available. This may include physical therapy and education to avoid re-injury in the future.
The anterior cruciate ligament supports the knee joint and contributes to normal flexion and rotation. An injury to this structure may result in decreases in normal function and performance, particularly in a competitive sporting or athletic capacity. Treatments for ACL damage may include physical therapy and surgery to reconstruct the ligament. A consultation with your orthopedic specialist can provide guidance to manage your ACL injury, depending on its severity and effects on your occupation and personal life.
- Bates NA, McPherson AL, Rao MB, Myer GD, Hewett TE. Characteristics of inpatient anterior cruciate ligament reconstructions and concomitant injuries. Knee surgery, sports traumatology, arthroscopy : official journal of the ESSKA. 2014.
- Prodromos CC, Han Y, Rogowski J, Joyce B, Shi K. A meta-analysis of the incidence of anterior cruciate ligament tears as a function of gender, sport, and a knee injury-reduction regimen. Arthroscopy : the journal of arthroscopic & related surgery : official publication of the Arthroscopy Association of North America and the International Arthroscopy Association. 2007;23(12):1320-1325.e1326.
- Alentorn-Geli E, Myer GD, Silvers HJ, et al. Prevention of non-contact anterior cruciate ligament injuries in soccer players. Part 1: Mechanisms of injury and underlying risk factors. Knee surgery, sports traumatology, arthroscopy : official journal of the ESSKA. 2009;17(7):705-729.
- Alentorn-Geli E, Myer GD, Silvers HJ, et al. Prevention of non-contact anterior cruciate ligament injuries in soccer players. Part 2: a review of prevention programs aimed to modify risk factors and to reduce injury rates. Knee surgery, sports traumatology, arthroscopy : official journal of the ESSKA. 2009;17(8):859-879.
- Renstrom P, Ljungqvist A, Arendt E, et al. Non-contact ACL injuries in female athletes: an International Olympic Committee current concepts statement. British journal of sports medicine. 2008;42(6):394-412.
- Viggiano D, Corona K, Cerciello S, Vasso M, Schiavone-Panni A. The kinematic control during the backward gait and knee proprioception: insights from lesions of the anterior cruciate ligament. Journal of human kinetics. 2014;41:51-57.
- Noyes FR, Barber-Westin SD. Anterior cruciate ligament graft placement recommendations and bone-patellar tendon-bone graft indications to restore knee stability. Instructional course lectures. 2011;60:499-521.
- Tiamklang T, Sumanont S, Foocharoen T, Laopaiboon M. Double-bundle versus single-bundle reconstruction for anterior cruciate ligament rupture in adults. The Cochrane database of systematic reviews. 2012;11:Cd008413.
- Sohn OJ, Lee DC, Park KH, Ahn HS. Comparison of the Modified Transtibial Technique, Anteromedial Portal Technique and Outside-in Technique in ACL Reconstruction. Knee Surgery & Related Research. 2014;26(4):241-248.
- Carmont MR, Scheffler S, Spalding T, Brown J, Sutton PM. Anatomical single bundle anterior cruciate ligament reconstruction. Current Reviews in Musculoskeletal Medicine. 2011;4(2):65-72.
- Carey T, Oliver D, Pniewski J, Mueller T, Bojescul J. Anterior cruciate ligament augmentation for rotational instability following primary reconstruction with an accelerated physical therapy protocol. Journal of surgical orthopaedic advances. 2013;22(1):59-65.
- Grindem H, Eitzen I, Engebretsen L, Snyder-Mackler L, Risberg MA. Nonsurgical or Surgical Treatment of ACL Injuries: Knee Function, Sports Participation, and Knee Reinjury: The Delaware-Oslo ACL Cohort Study. The Journal of bone and joint surgery. American volume. 2014;96(15):1233-1241.