The knees are vulnerable to injury from hard contact or a fall, or just everyday wear and tear. One injury that is common, especially among active people, is a hyperextended knee.

A hyperextended knee means your knee bends too far backward in a straightened position. It’s important not to ignore a hyperextended knee. This injury can reduce your mobility for a few months. But with medical help, it’s treatable.

Even if you’re not sure you’ve hyperextended your knee, always pay attention to knee pain symptoms. And seek medical attention after an injury.

You may know immediately that you’ve hyperextended your knee. You’ll feel pain behind the knee. You may even hear a “pop,” which suggests a torn ligament.

If the hyperextension is serious, you’ll have trouble putting weight on that leg. The knee also becomes difficult to bend. You will likely also have swelling around your knee.

The two main ligaments usually injured in a knee hyperextension are the anterior cruciate ligament (ACL) and the posterior cruciate ligament (PCL). Both ligaments are located in the center of the knee.

The ACL controls the forward movement and the rotation of the shinbone, or tibia. The PCL controls the tibia’s backward movement. These ligaments connect the tibia to the thighbone, or femur. When they’re injured the knee becomes much less stable.

Your knee can become hyperextended if you jump and land badly. It can also happen if you change directions suddenly.

Your knee can also get bent backward from contact. If something or someone hits the front of your knee, the joint can be pushed back too far. That can injure the ligaments and other parts of the knee.

Sometimes your foot can get caught in something and cause you to fall. If the force of the fall pushes your knee in one direction, but your foot can’t follow, that can lead to knee hyperextension.

Gymnasts, skiers, and other athletes are at a higher risk of a hyperextended knee than other people. Older adults with a higher risk of falling are also at an increased risk for hyperextended knees.

Other things that may increase your risk are:

  • weak quadriceps, which are the muscles in your upper leg
  • history of knee injury

Children are more at risk for a bone chip or evulsion fracture if there is a hyperextension injury.

Diagnosis will begin with a visit to your doctor. Your doctor will ask you questions about your injury and then do a physical exam. Part of the exam will include movement of your injured knee. That will allow your doctor to feel for instability in the joint.

You should also be honest about the pain associated with those movements. Part of the exam may also include putting the knee in different positions and applying some pressure as you try to move it.

An X-ray or MRI may provide images of the bone and soft tissue affected by the injury.

Your doctor will determine if one or more ligaments are damaged. It so, the diagnosis is called a ligament sprain. Then the sprain is given a grade.

grade 1 sprainmild, but the ligament is still stable
grade 2 sprain, or partial ligament tearthe ligament has been stretched and is loose
grade 3, or complete tear of the ligamentthe ligament has torn into two pieces

Surgery may be required to repair a partial ligament tear. Surgery will likely be necessary to remedy a grade 3 tear because the knee will be unstable. That could lead to increased pain and re-injury.

Treatment for a hyperextended knee will vary depending on the extent of the damage.

Ice and rest in the days after the injury will help reduce swelling and inflammation. You should also try to elevate the knee as much as possible.

If surgery is required to repair a torn ligament, a piece of tendon from elsewhere in the knee or the hamstring is used to replace the completely torn ligament. General anesthesia is used during this operation. But the procedure is usually done on an outpatient basis.

Physical therapy, including leg muscle strengthening, should follow surgery. It can be a challenging experience. But it’s essential to regaining stability and a full range of motion in the joint.

Learn more: Quad and hamstring exercises to strengthen bad knees »

You may need to wear a knee brace for several months or longer to help stabilize the joint.

It may take months before you achieve a full range of motion and the knee is pain-free. Most kids and adults can return to their normal activities after a hyperextended knee injury. If the sprain is mild, your recovery time will be faster than if you have a more serious injury.

Athletes may be able to continue with their sports. But a major knee injury may place some limits on how far they can push their bodies.

Older adults tend to heal more slowly. They may also have lingering discomfort or stiffness in their knees. That can be minimized with exercise.

The ongoing management of a hyperextended knee will depend on the following:

  • your age
  • your general health
  • the severity of your injury

You may need to stop or reduce your participation in certain sports or activities if they put your knee at further risk of injury. And delay or avoid explosive sports, like basketball or skiing, until you make a full recovery.

Here are some tips to help you manage your recovery:

  • Wear sturdy shoes that provide support.
  • Work with a physical therapist to learn ways to lower your risk for a fall if you are at increased risk for falling due to age or other health conditions.
  • Improve your balance and reduce your risk for a fall by doing exercises like tai chi and yoga.
  • Practice exercises that will strengthen the muscles in your legs. That will help protect your knees from future injuries.
  • Continue exercises learned in physical therapy after you have recovered. They will help keep your knees flexible and strong.