The knee is one of the most important joints. It enables you to walk, squat, and climb steps. A knee sprain can seriously affect your quality of life by making these everyday movements difficult and painful. This common injury occurs when the connective tissues in your knee stretch or tear.
Athletes are especially prone to knee sprains, but this injury can happen to anyone. Fortunately, a knee sprain is treatable, and most people recover.
Discover the causes, symptoms, and treatment for this disorder.
What Is a Knee Sprain?
The human knee is a complex joint that contains three bones: the femur, patella, and tibia. Ligaments are rope-like pieces of tissue that attach these three bones and stabilize your knee. Your knee has four main ligaments belonging to two different categories, each with different functions.
Collateral ligaments. These connecting tissues support the sides of your knee and allow the joint to move from side to side. These ligaments include the:
- Medial collateral ligament (MCL). This ligament attaches the femur to the tibia along the inside of your knee.
- Lateral collateral ligament (LCL). This tissue runs along the outside of your knee. It links your femur to the fibula, a small bone in your leg.
Cruciate ligaments. These two ligaments cross inside your knee joint in an “X” shape. They allow your knee to move forward and backward without moving too far sideways. The two cruciate ligaments are the:
- Anterior cruciate ligament (ACL). This tissue stretches diagonally across the middle of your knee and attaches the femur to the tibia. The ACL is your knee’s weakest and most commonly injured cruciate ligament.
- Posterior cruciate ligament (PCL). This fiber lies behind the ACL and stabilizes your shinbone. The PCL is less prone to injury than the ACL.
An injury to any of these ligaments can cause a knee sprain.
What Causes a Knee Sprain?
A knee sprain can be caused by any movement or trauma that stretches your ligament too far, causing it to tear. Common knee sprain causes include:
- A hard blow to the knee (for instance, while playing sports)
- A car crash
- Changing direction rapidly while moving
- Landing awkwardly after a fall or jump
- Putting too much pressure on the knee
- Twisting the knee
Most knee sprains only affect one ligament. However, multiple ligaments may be injured during a traumatic event like a car accident or a long fall.
What Are the Symptoms of a Knee Sprain?
If you sprain your knee, you will probably notice the injury immediately. Knee sprain symptoms include:
- An altered gait
- Bruising
- Difficulty bending your knee
- Instability in your knee
- Limping
- Pain or discomfort
- Swelling
You may also feel a “snapping” sensation inside your knee when your ligament tears.
If you experience severe pain or if your symptoms persist even after treating your knee at home, you should see your doctor.
How Is a Knee Sprain Diagnosed?
Your healthcare provider can use several methods to diagnose a knee sprain, including:
Physical examination. Your doctor will test your ability to move and put weight on your knee during a physical exam. They may watch while you walk across the room to see if you have a limp. You may also be asked to bend and straighten your leg while seated. Based on your range of movement, your doctor can determine which part of the knee is injured.
X-ray. An X-ray won't display a stretched or torn ligament, but it can show fluid that may have collected around your knee due to a sprain. This test can also find other possible causes of knee pain, like arthritis or a broken bone.
Magnetic resonance imaging (MRI). An MRI provides a clear image of the damaged parts of your knee and shows how severely the joint is injured.
Ultrasound. An ultrasound shows your soft tissues, so it can help your doctor diagnose injuries in your ligaments and tendons.
What’s the Treatment for a Knee Sprain?
The best knee sprain treatment depends on the severity of your injury.
At-home knee sprain care for mild injuries can include the R.I.C.E. method:
- Rest. Limit your physical activity as much as possible to avoid putting weight on your injured knee.
- Ice. Wrap an ice pack in a cloth and apply it to your knee a few times daily for 20 minutes per session. This method can help reduce swelling.
- Compression. Wrapping your knee in a soft bandage can help stabilize the joint and prevent further damage.
- Elevation. Prop your knee up to minimize swelling.
More severe knee sprains may require treatment from a doctor, like:
- Nonsteroidal anti-inflammatory drugs (NSAIDS): These medications reduce inflammation and pain.
- Brace. A cast or knee brace can hold bones in place and keep your knee from moving too much while it heals.
- Physical therapy. A physical therapist can prescribe specific exercises to help you use your knee again and regain strength in your legs.
- Surgery: If you injure multiple ligaments or have a severe sprain, your doctor may recommend surgical reconstruction. During this complex surgery, your surgeon may use grafts or tissues taken from cadavers or a living donor to rebuild your knee.
How Long Does It Take to Recover From a Knee Sprain?
Knee sprain recovery time depends on the severity of your injury. If you have a Grade 1 sprain, your ligament stretches but doesn’t tear. This injury will often heal in one to two weeks following proper at-home treatment.
A Grade 2 sprain occurs when you partially tear your ligament. It may take a month or longer to recover from this moderate injury.
You will likely have a longer recovery period if you need surgical reconstruction following a Grade 3 sprain. Surgical patients typically need crutches for 6 to 8 weeks following their procedure and may need to see a physical therapist for rehabilitation.
How Do I Prevent a Knee Sprain?
You may be unable to avoid some types of trauma that cause knee sprains, like car accidents or falls. However, you can take simple steps to protect your knees during physical activity. These preventative measures include:
- Core-strengthening exercises
- Running drills, like running backward or in a zigzag pattern (though you should avoid doing this recklessly, or you might accidentally twist your knee)
- Strengthening your leg muscles by doing lunges and squats
- Stretching your calves, hamstrings, and other leg muscles before playing sports
Keeping your legs strong and learning about the common causes of a knee sprain can help you avoid this painful injury. Your knees play an important role in your mobility, so taking good care of this essential joint is more than worth the effort.