Recent Blog Articles
Using weight loss or sports supplements? Exercise caution
Not yet ready for cataract surgery? Try these tips
Back to the future: Psychedelic drugs in psychiatry
Children not yet vaccinated against COVID-19? What to do
HIV rates rising: Could new forms of PrEP help?
Careful! Scary health news can be harmful to your health
Post-pandemic weight loss: There’s an app for that
Cognitive behavioral therapy for insomnia by telemedicine: Is it as good as in-person treatment?
Prediabetes diagnosis as an older adult: What does it really mean?
Is blood sugar monitoring without diabetes worthwhile?
What Is It?
A knee sprain is an injury of the ligaments, tough bands of fibrous tissue that connect the bones of the upper and lower leg at the knee joint. The knee joint has four major ligaments.
- Anterior cruciate ligament (ACL) — The ACL and the posterior cruciate ligament (PCL) bridge the inside of the knee joint, forming an "X" pattern that stabilizes the knee against front-to-back and back-to-front forces. The ACL typically sprains during one of the following knee movements: a sudden stop; a twist, pivot or change in direction at the joint; extreme overstraightening (hyperextension); or a direct impact to the outside of the knee or lower leg. These injuries are seen among athletes in football, basketball, soccer, rugby, wrestling, gymnastics and skiing.
- Posterior cruciate ligament (PCL) — The PCL works with the ACL to stabilize the knee. It most often sprains because of a direct impact to the front of the knee, such as hitting the knee on the dashboard in a car crash or landing hard on a bent knee during sports. In athletes, PCL injuries are most common among those who play football, basketball, soccer and rugby.
- Medial collateral ligament (MCL) — The MCL supports the knee along the inner side of the leg. Like the ACL, the MCL can be torn by a direct sideways blow to the outside of the knee or lower leg, the kind of blow that can happen in football, soccer, hockey and rugby. The MCL can be injured by a severe knee twist during skiing or wrestling, particularly when a fall twists the lower leg outwards, away from the upper leg.
- Lateral collateral ligament (LCL) — The LCL supports the outer side of the knee. It is the least likely knee ligament to be sprained because most LCL injuries are caused by a blow to the inside of the knee, and that area usually is shielded by the opposite leg.
Like other types of sprains, knee sprains are classified according to a grading system:
To continue reading this article, you must log in.
Subscribe to Harvard Health Online for immediate access to health news and information from Harvard Medical School.
- Research health conditions
- Check your symptoms
- Prepare for a doctor's visit or test
- Find the best treatments and procedures for you
- Explore options for better nutrition and exercise
I'd like to receive access to Harvard Health Online for only $4.99 a month.Sign Me Up
Already a member? Login ».
As a service to our readers, Harvard Health Publishing provides access to our library of archived content. Please note the date of last review or update on all articles. No content on this site, regardless of date, should ever be used as a substitute for direct medical advice from your doctor or other qualified clinician.