A knee sprain refers to torn or overstretched ligaments, the tissues that hold bones together. If you have a sprained knee, the structures within the knee joint that connect the thigh bone to the shin bone have been injured.
A knee sprain is painful and can create other problems over time, including arthritis.
The knee has four main ligaments: two that stabilize its front and back, and two that stabilize side-to-side movement.
Knee sprains are named for the specific ligament that has been torn or injured:
- The anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL) provide stability to forces coming from the front or back. The two form an “X” across the joint.
- The lateral collateral ligament (LCL) runs along the outside of the knee and helps keep it stable on the side.
- The medial collateral ligament (MCL) runs along the inside of the knee.
Depending on which ligament was sprained, you may experience different symptoms. For an ACL sprain, you may hear a pop at the time you’re injured and feel as though your knee can’t support you.
If you have a PCL sprain, the back of your knee may hurt, and it might be worse if you try to kneel on it.
For LCL and MCL sprains, your knee may seem as though it wants to buckle toward the opposite direction from the injured ligament and will likely be tender where the injury happened.
Most people with knee sprains will experience at least some of the following:
- muscle spasms
Any activity that forces your knee out of its natural position can cause a sprain.
The ACL is often injured when you play a running or contact sport like soccer, basketball, football, or gymnastics, usually as a result of jumping or twisting suddenly.
It can also occur if you over-straighten your knee to an extreme degree or if you get struck by something in the knee or lower leg.
The PCL can be injured in a car collision when your knee hits the dashboard, or in a sport where the front of your knee is hit while it’s bent. Falling hard on your knee can also cause a PCL sprain.
You can sprain your LCL if you receive a blow to the inside of your knee. This is less common than the other types of sprains because your other leg protects this area.
An MCL sprain is usually caused by something hitting your leg from the side, or a fall that causes your lower leg to twist outward from your thigh.
The doctor will test the ligaments by stressing the individual ligaments to see if there’s any instability or if the joint is stable.
If you injure your knee, see a doctor as soon as possible. This is especially important if you can’t stand up, feel as though your knee will collapse, or your leg looks swollen or bulgy.
The doctor will examine your knee, look for swelling and bruising, and ask you to move it around to determine your mobility. They’ll compare it to your uninjured knee.
They’ll also want to know what you were doing when the injury happened, whether you heard a pop, and how long it took to become painful.
You may also be given imaging tests. An X-ray will show if there’s a broken bone, but other imaging methods allow the physician to see different, non-bony structures inside your knee. This includes the ligaments and other tissues that support it.
Knee sprains are rated by severity. An overstretched ligament is grade 1. A partially torn ligament is grade 2. A ligament that’s severely torn or separated is considered grade 3.
The treatment your doctor recommends will depend on the severity of your injury and what part of your knee was damaged.
A doctor may recommend over-the-counter pain relievers like acetaminophen. If the pain is debilitating, you may be prescribed stronger medication.
You’ll want to avoid doing anything that overstresses your knee and can risk you hurting it further. This includes playing sports.
While sitting or sleeping, you can also prop your leg up on pillows to get it higher than your heart to help reduce the swelling.
An ice pack on the knee for 20 minutes every few hours can reduce swelling (but check with a doctor first, especially if you have diabetes). The ice will also help pain and can stop any bleeding inside the joint.
An elastic bandage can also help with swelling, but be sure not to wrap your knee too tightly because it can cut off your blood circulation.
If the wrap makes the pain worse, your knee starts to get numb, or your lower leg swells up, loosen the bandage.
The doctor may give you a brace to protect your knee and stabilize it while it heals. This will keep you from moving it too much or over-stretching it.
Knee sprain exercises and physical therapy
A doctor or physical therapist may recommend exercises based on the extent of your injury and where you are in your recovery:
- leg lifts
- thigh strengthening
- bending your knees
- raising up on your toes
- thigh and calf stretches
- weight training with hamstring curl and leg press equipment
If the ligament is torn, you may need surgery. This process usually involves reattaching the torn ligament or replacing it with a piece of healthy tendon.
The surgeon will make a few small incisions and drill little holes in your calf and thigh bones. The graft is attached to the bones, which will grow around it.
It will take several weeks or even months before you’re able to resume your normal activities, and you’ll need a program of progressive physical therapy to restore your range of motion.
A knee sprain is considered healed when there’s no more pain or swelling, and you can move your knee freely.
Many grade 1 and 2 knee sprains heal within two to four weeks. People who need surgery, however, may take as long as four to six months to recover.
About 80 to 90 percent of people with ACL injuries and 80 percent of those with PCL injuries will experience a full recovery. MCL and LCL sprains tend to heal quite well. However, some people with sprained ACL or PCL ligaments can develop arthritis in their knee over time.
Because your knee bears your body weight and determines how well you’re able to move around, make sure you take proper care of a knee sprain. Getting medical care early and following your doctor’s instructions are important.
While most knee sprains will heal without surgery, avoid the temptation to go back to your normal activities or playing sports without letting your knee heal completely. That can cause problems later on.
Performing the recommended physical therapy exercises can help you get back to doing what you love.