What Is A Sprained Knee? | The Complete Guide To Knee Sprains

Written By on November 10, 2021 — Medically Reviewed By Kristopher Ceniza

Written by on November 10, 2021 — Medically Reviewed By: Kristopher Cenzia

We’ve all heard about sprained joints. You may even have had a sprain already – I had two on my left ankle. But, what is a sprained knee, exactly?

Well, a knee sprain occurs when any of the four knee ligaments overstretch. Sprained knees account for 40% of all knee injuries. Some can improve at home, but others will need surgery. This depends on (1):

  • Which ligament was affected: A cruciate ligament? Or a collateral one?
  • The type of sprain: There’s 3 of them.
  • Your lifestyle: An athlete won’t have the same treatment as an office worker.

You’ll find everything you need about knee sprains below, including what it is, its types, and treatments.

Let’s start with the basics:

What is a knee sprain?

A knee sprain happens when knee ligaments get stretched or torn.

These ligaments are bands of strong fibrous tissue around our joints. All your freely movable joints have them – your knees, ankles, wrists, and even your spine.

Ligaments hold bones together, keeping our joints stable. This means ligaments aren’t elastic. If they were, they wouldn’t be able to provide joint stability.

Now, we have four main ligaments to keep the knee joint stable.

These four ligaments support our knee joint

They go from the thigh bone to the shin bone. By stabilizing the knee joint, they also help stabilize the lower leg. These ligaments include:

The cruciate knee ligaments

These are the anterior cruciate ligament (ACL) and the posterior cruciate ligament (PCL). They form an X within the knee joint, giving it stability from front to back.

Knee Force Knee Sleeve

Anterior cruciate ligament (ACL)

Most knee sprains are on the ACL. This injury is common in running and contact athletes. It can happen after changing directions while running or after a direct hit. (2)

An ACL sprain often feels like a “pop” at the moment of injury. The knee can give out afterward. The inflammation tends to appear in the first 24 hours. Some people may have difficulty bearing weight on the injured leg.

Posterior cruciate ligament (PCL)

PCL injuries are uncommon. They happen when an extreme force pushes the shin bone backwards when your knees are bent. Like – God forbid – in car accidents when your knee slams the dashboard. It can happen after falling on your knees, too. (3)

The main symptom is feeling pain behind the knee. Kneeling often makes symptoms worse. Some people may have pain walking downhill as well.

The collateral knee ligaments

These are the medial collateral ligament (MCL) and the lateral collateral ligament (LCL). They are on each side of the knee, limiting side-to-side movements.

Medial collateral ligament (MCL)

This ligament is on the inner side of the joint. It can sprain if the knee bends inward suddenly. Like after changing directions while running.

Symptoms include tenderness and swelling in the area. It can also be painful to walk. Some people may feel knee instability as well. (1)

Lateral collateral ligament (LCL)

This ligament is on the outer side of the knee. This sprain often happens after a direct blow on the inner side of the knee with the leg straight. Symptoms are like an MCL sprain but on the outside of the knee. (4)

Types of knee sprains

We classify knee sprain injuries according to severity. (4)

Additionally, recovery time for sprained knees also depends on how serious the injury is.

Grade I: Mild sprain

In this type of knee sprain, the ligament got stretched but didn’t tear. It’s mildly damaged but you can still do your normal activities:

  • You can bear weight on the injured knee.
  • Your knee feels stable.
  • There’s mild pain and/or swelling.

Most grade I knee sprains get better with home care. This type of knee sprain takes around 4 weeks to heal. (4)

Grade II: Moderate sprain

This is a partial tear of one or more ligaments. Your joint will likely feel unstable with this type of knee injury. Other symptoms of a knee sprain grade II include:

  • Pain and swelling.
  • Joint stiffness.
  • Difficulty walking or bearing weight.

Rest is key here as it reduces the risk of worsening the sprain.

Wearing a knee brace helps as well because it helps protect your injury. Recovery time is around 10 weeks. (4)

Grade III: Severe sprain

This is a complete tear of the ligament. It’s considered a serious injury that needs immediate care. Athletes with grade III sprains may need surgery to go back to sports. (4)

A completely torn ligament often causes these symptoms (4):

  • Decreased movement.
  • Pain, swelling, and stiffness.
  • A feeling like the knee gives out.

Severe sprains take months to heal. The recovery time depends on the lifestyle of the patient. It can take from 4 to 18 months.

Treatments for knee sprains

There are several treatment options for a knee sprain. They depend on the severity of the injury:

Home care

You’ll do this for any sprain. But, it’s likely that you can completely treat a grade I knee sprain at home. To do so, follow the PRICE protocol for the first 3 weeks:

Knee Force Knee Sleeve
  • Protect. Prevent further injury. Wear a knee brace if your therapist recommends you to.
  • Rest. This will promote healing. Avoid physical activities during the first 2-3 weeks after injury.
  • Ice. This can reduce swelling and knee pain. Studies suggest icing the affected leg for 10 minutes, 2-3 times. They found that more than that can hinder recovery.
  • Compression. Wrap the affected joint with an elastic bandage. The compression can reduce inflammation as well. It shouldn’t increase pain. If it does, loosen the bandage a little.
  • Elevation. Elevate the injured leg above your heart several times per day. This will reduce inflammation.

Once the pain improves, try some strengthening exercises. Avoid a sudden increase in physical activity to prevent reinjuries. Going to physical therapy can help you with that:

Physical therapy

Physios are your best allies in recovery, regardless of the severity of your injury.

First, they help you reduce pain and inflammation. Once you feel better, they will give you light stretching and strengthening exercises. Then, they will give you more challenging exercises over time. This is key to getting you back to normal.

If you enjoy exercising or are an athlete, find a physical therapist specializing in sports medicine. They will help you go back to your sport safely!


Grade III sprains may need surgical intervention. Also, people with repetitive sprains or meniscal tears may improve with surgery.

Your doctor will need an MRI first. This will show the damage to the specific ligament.

Most surgeries will be arthroscopic. This is a minimally invasive technique where the surgeon does a few small incisions to insert a camera into your joint and operate.


Can you walk on a sprained knee?

Yes, you can walk on a sprained knee as long as it doesn’t worsen your pain. Don’t walk on a sprained knee if you feel like it gives out. Or if you can’t bear weight on the injured leg.

How do you know if you sprained your knee?

Most people feel a sharp pain in the knee at the moment of injury. You may also feel a popping sound, or like the knee joint gave out under you. It’s common to have inflammation shortly after a knee sprain, too.

What is the fastest way to heal a sprained knee?

That depends on the severity of the knee sprain. In general, the fastest way is resting and following the advice of your therapist and/or doctor. They will know which treatment strategies are best for your case.

Conclusion: What is a knee sprain?

A knee sprain is a common knee injury. It happens when a ligament stretches beyond its capacity. It can be a mild, moderate, or severe knee sprain.

A sprain can also affect any knee ligament, often the ACL or MCL. The best treatments for a knee sprain include home care and physical therapy. (1, 2)


  1. Naqvi, Usker et al. “Medial Collateral Ligament Knee Injuries.” [Updated 2021 Mar 17]. Statpearls. Retrieved on September, 2021: https://www.ncbi.nlm.nih.gov/books/NBK431095/
  2. Evans, Jennifer et al. “Anterior Cruciate Ligament Knee Injuries.” [Updated 2021 Feb 19]. Statpearls. Retrieved on September, 2021: https://www.ncbi.nlm.nih.gov/books/NBK499848/
  3. Raj, Marc et al. “Posterior Cruciate Ligament Knee Injuries.” [Updated 2021 Jan 22]. Statpearls. Retrieved on September, 2021 from: https://www.ncbi.nlm.nih.gov/books/NBK430726/
  4. Yaras, Reed et al. “Lateral Collateral Ligament Knee Injuries.” [Updated 2021 May 4]. Statpearls. Retrieved on September, 2021: https://www.ncbi.nlm.nih.gov/books/NBK560847/
Mitch Torres (PT)
Mitch is a physical therapist, personal trainer, and nutrition coach. Fascinated with the knee joint, Mitch poured that passion into writing about knee pain and how to overcome it with movement. His goal is to teach you how to apply this knowledge into your daily life, so you can keep knee pain away for good.