Anterior cruciate ligament injury
An anterior cruciate ligament injury occurs when the anterior cruciate ligament (ACL) is either stretched, partially torn, or completely torn. The most common injury is a complete tear. Symptoms include pain, an audible cracking sound during injury, instability of the knee, and joint swelling. Swelling generally appears within a couple of hours. In approximately 50% of cases, other structures of the knee such as surrounding ligaments, cartilage, or meniscus are damaged.
| Anterior Cruciate Ligament injury | |
|---|---|
| Diagram of the right knee | |
| Specialty | Orthopedics |
| Symptoms | Audible "crack" with pain, knee instability, swelling of knee |
| Causes | Non-contact injury, contact injury |
| Risk factors | Athletes, females |
| Diagnostic method | Physical exam, MRI |
| Prevention | Neuromuscular training, core strengthening |
| Treatment | Braces, physical therapy, surgery |
| Frequency | c. 200,000 per year (US) |
The underlying mechanism often involves a rapid change in direction, sudden stop, landing after a jump, or direct contact to the knee. It is more common in athletes, particularly those who participate in alpine skiing, football (soccer), netball, American football, or basketball. Diagnosis is typically made by physical examination and is sometimes supported by magnetic resonance imaging (MRI). Physical examination will often show tenderness around the knee joint, reduced range of motion of the knee, and increased looseness of the joint.
Prevention is by neuromuscular training and core strengthening. Treatment recommendations depend on desired level of activity. In those with low levels of future activity, nonsurgical management including bracing and physiotherapy may be sufficient. In those with high activity levels, surgical repair via arthroscopic anterior cruciate ligament reconstruction is often recommended. This involves replacement with a tendon taken from another area of the body or from a cadaver. Following surgery rehabilitation involves slowly expanding the range of motion of the joint, and strengthening the muscles around the knee. Surgery, if recommended, is generally not performed until the initial inflammation from the injury has resolved. 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.
About 200,000 people are affected per year in the United States. In some sports, females have a higher risk of ACL injury, while in others, both sexes are equally affected. While adults with a complete tear have a higher rate of later knee osteoarthritis, treatment strategy does not appear to change this risk. ACL tears can also occur in some animals, including dogs. The most common knee injury in dogs is ACL or CCL rupture.