Anterior cruciate ligament injury

Anterior Cruciate Ligament injury
Diagram of the right knee
Specialty	Orthopedics
Symptoms	Audible "crack" with pain, knee instability, swelling of knee[1]
Causes	Non-contact injury, contact injury[2]
Risk factors	Athletes, females[1]
Diagnostic method	Physical exam, MRI[1]
Prevention	Neuromuscular training,[3] core strengthening[4]
Treatment	Braces, physical therapy, surgery[1]
Frequency	c. 200,000 per year (US)[2]

An anterior cruciate ligament injury occurs when the anterior cruciate ligament (ACL) is either stretched, partially torn, or completely torn.^[1] The most common injury is a complete tear.^[1] Symptoms include pain, an audible cracking sound during injury, instability of the knee, and joint swelling.^[1] Swelling generally appears within a couple of hours.^[2] In approximately 50% of cases, other structures of the knee such as surrounding ligaments, cartilage, or meniscus are damaged.^[1]

The underlying mechanism often involves a rapid change in direction, sudden stop, landing after a jump, or direct contact to the knee.^[1] It is more common in athletes, particularly those who participate in alpine skiing, football (soccer), netball, American football, or basketball.^[1][5] Diagnosis is typically made by physical examination and is sometimes supported by magnetic resonance imaging (MRI).^[1] Physical examination will often show tenderness around the knee joint, reduced range of motion of the knee, and increased looseness of the joint.^[6]

Prevention is by neuromuscular training and core strengthening.^[3][4] Treatment recommendations depend on desired level of activity.^[1] In those with low levels of future activity, nonsurgical management including bracing and physiotherapy may be sufficient.^[1] In those with high activity levels, surgical repair via arthroscopic anterior cruciate ligament reconstruction is often recommended.^[1] This involves replacement with a tendon taken from another area of the body or from a cadaver.^[6] Following surgery rehabilitation involves slowly expanding the range of motion of the joint, and strengthening the muscles around the knee.^[1] Surgery, if recommended, is generally not performed until the initial inflammation from the injury has resolved.^[1] It should also be taken into precaution to build up as much strength in the muscle that the cadaver is being taken from to reduce risk of injury^{[clarification needed]}.

About 200,000 people are affected per year in the United States.^[2] In some sports, females have a higher risk of ACL injury, while in others, both sexes are equally affected.^[5][7] While adults with a complete tear have a higher rate of later knee osteoarthritis, treatment strategy does not appear to change this risk.^[8] ACL tears can also occur in some animals, including dogs.