What are knee ligaments?
The knee ligaments are bands of tissue that connect your thigh bone in your upper leg (femur) to your lower leg bones (tibia and fibula).
What do the knee ligaments do?
Knee ligaments have several important jobs. They:
- Absorb shock when the foot strikes a surface.
- Connect the thigh bone to the lower leg bones.
- Keep the bones in the proper position.
- Prevent the knee from twisting or collapsing.
- Stabilize the knee joint.
- Stop the knee from moving in any unsafe or unnatural directions.
What are knee ligaments made of?
Ligaments are made of:
- Collagen, a protein that binds tissues in animals.
- Connective tissue.
- Elastic fibers that are slightly stretchy.
What are the ligaments of the knee?
There are two main types of ligaments in your knee:
- Collateral ligaments: The two collateral ligaments are like straps on each side of your knee. The medial collateral ligament (MCL) is on the inner side of your knee. It attaches the thigh bone (femur) to the shin bone (tibia). The lateral collateral ligament (LCL) is on the outer side of your knee. It connects your femur to your calf bone (fibula). The collateral ligaments prevent the knee from moving side to side too much.
- Cruciate ligaments: The two cruciate ligaments are inside your knee joint and connect your femur to your tibia. They cross each other to create an X. The anterior cruciate ligament (ACL) is located toward the front of the knee. The posterior cruciate ligament (PCL) is behind the ACL. The cruciate ligaments control the way your knee moves front to back.
Conditions and Disorders
Can I injure a knee ligament?
An injury to a knee ligament is called a sprain or a tear. Many knee sprains are mild, but torn knee ligaments can be severe.
Knee ligament injuries are common, especially in athletes. The ligaments can be overstretched or torn when:
- Force is applied to the back of the knee when the joint is partly flexed.
- Force is applied to the front of a bent knee (sometimes called “dashboard injury” because it’s common in car accidents).
- Force is applied to the side of the knee when the foot is on the ground (for example, during a tackle).
- The knee is hyperextended (straightens too much), usually by force.
- The knee joint twists in an unnatural way (for example, when playing basketball or skiing).
How can a healthcare provider tell if I’ve injured a knee ligament?
If you seek medical attention for a knee injury, a healthcare provider may:
- Ask you about your symptoms and when they started.
- Conduct a physical exam by looking at the injured knee, assessing how it moves and comparing it to the other knee.
- Order imaging tests if necessary, such as MRI, to take pictures of the knee ligaments.
- Take X-rays to rule out a broken leg bone, kneecap (patella) or other problem.
How are knee sprains and tears classified?
A healthcare provider will grade your injury by how severe it is and what symptoms you have:
- Grade 1: A grade 1 injury to a knee ligament is a minor sprain. The ligament is overstretched or just slightly torn. With a grade 1 knee strain, you’ll have minimal pain, swelling or bruising. You’ll still be able to put weight on the affected leg and bend the knee.
- Grade 2: A grade 2 knee sprain is a moderate (partial) tear of the ligament. Signs include bruising, swelling and some pain. With a grade 2 injury, you’ll have some difficulty putting weight on the leg or bending the knee.
- Grade 3: A grade 3 injury is a complete tear or rupture of the knee ligament. Grade 3 injuries often involve more than one knee ligament. With this level of injury, you will experience severe bruising, swelling and pain. You won’t be able to put weight on the leg or bend the knee.
Can a person damage more than one ligament at a time?
It’s possible to damage more than one knee ligament at the same time. These injuries can be very serious, as they can interrupt blood supply to your leg or damage nerves that help control your leg.
What are the common treatments for knee injury?
Treatment for a knee sprain or torn ligament can vary greatly, depending on:
- How long you’ve had symptoms.
- How many knee ligaments are injured.
- Severity of the injury (grade 1, 2 or 3).
- Whether pain or inability to put weight on your knee is interfering with your life.
- Whether the injury weakens the knee and puts you at risk for more injuries in the future.
Treatment may range from nonsurgical to surgical:
- RICE: rest, ice, compression with an elastic bandage and elevation.
- Nonsteroidal anti-inflammatory drugs (NSAIDs).
- Assistive devices (for example, crutches to help you keep weight off the knee).
- Immobilization (such as a knee brace).
- Physical therapy.
- Surgery by an orthopedic surgeon to repair or rebuild the damaged ligament(s).
How can I prevent knee ligament injuries?
Not all knee injuries can be prevented. But you can take steps to keep your knee ligaments safer, especially during exercise:
- Avoid sports that involve tackling, such as football and rugby.
- Exercise on level surfaces to decrease the chances you’ll twist a knee.
- Maintain a healthy weight to reduce pressure on the knees.
- Vary your exercise routine, combining weight training and aerobic activities (cardio).
- Warm up before you exercise, increase intensity gradually and stretch afterward.
- Wear shoes that fit well.
- Wear all appropriate safety equipment for any sports you play.
Frequently Asked Questions
When should I see a healthcare provider for a sprained knee?
Damage to a knee ligament can weaken the knee joint, increasing the chances that you’ll injure yourself again.
Talk to a healthcare provider if you have:
- Looseness or weakness in the knee.
- Loss of feeling in the knee or leg.
- Pain on the inside or outside of the knee.
- A popping or snapping noise.
- Repeat knee injuries.
- Swelling around the knee joint.
- Trouble putting weight on that leg.
A note from Cleveland Clinic
Knee ligaments are bands of tissue that connect the thigh bone in the upper leg to the lower leg bones. There are four major ligaments in the knee: ACL, PCL, MCL and LCL. Injuries to the knee ligaments are common, especially in athletes. A sprained knee can range from mild to severe. Talk to a healthcare provider if you have a severe knee injury or repeat injuries. Proper diagnosis and treatment can help prevent pain and future injuries.
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