It’s Not Supposed to Bend That Way: What to Know About a Hyperextended Knee

A hyperextended knee injury happens when the knee is bent too far backward. The knee is a hinge joint, meaning it can only move by bending (flexion) or straightening (extension). The normal range of motion for active knee flexion is between 120 and 140 degrees. The knee should be able to fully straighten or extend to 0 degrees, but some people can go slightly beyond that.

When a knee extends beyond 5 degrees, it's called genu recurvatum. This is more common in women and people with conditions that cause joint laxity. But injury can also force your knee into hyperextension, causing soft tissue damage in the joint.

Let's take a closer look at the causes, symptoms, and treatment of a hyperextended knee.

What are the most common causes of a hyperextended knee?

Injury is the most common cause, and it's usually pretty obvious. But some other factors can make hyperextension more likely. It helps to understand which structures stabilize your knee and how they play a role.

Trauma

Athletes who participate in sports that require jumping, quick changes in direction, or direct contact are at higher risk of knee hyperextension. But accidental injuries can cause hyperextension as well. Causes can include:

• Jumping and landing on a straight knee

• A direct blow to the front of your knee

• Being tackled with your foot planted

• Stepping into a hole

• Falling backward with your foot planted

Previous injuries

Many soft tissue structures in and around your knee joint provide stability These include the:

• Anterior cruciate ligament (ACL)

• Posterior cruciate ligament (PCL)

• Joint capsule

• Posterior oblique and posterolateral ligaments

• Collateral ligaments

If any of these structures have been stretched or torn, they can't support your knee as they should. An ACL tear is a common injury, and reconstruction isn't always recommended, especially for older adults. Without the proper rehab, this or other ligament injuries may put you at risk for hyperextension injuries.

Genetics

Some people are born with hypermobile joints, which have increased laxity. Females tend to have more joint laxity than males. Connective tissue disorders, like Ehlers-Danlos syndrome can also affect joint laxity. This results in a higher risk of knee hyperextension. It also increases the risk of ligament injury within your knee.

Neurologic conditions

Neurologic conditions, such as a stroke, can lead to knee hyperextension. This is because of muscle weakness around your knee joint - specifically in your quadriceps, hamstring, and ankle muscles. Weakness in your hamstring and spasticity in your quadriceps, which is common after a stroke, can also cause knee hyperextension.

How do you know if you hyperextended your knee?

If an injury hyperextended your knee, you will often feel pain immediately. Those with a hyperextended knee from joint laxity or weak muscles may not have a history of injury but develop knee pain over time.

The most common symptoms of a hyperextended knee include:

• Pain

• Knee instability or "giving way"

• Swelling

• Bruising

• Limited motion

An injury that hyperextends your knee can stretch, and in some cases, tear the ligaments that support your joint. If this happens, you may hear or feel a "pop." A PCL tear is the most common serious injury associated with hyperextension. A bone bruise can also happen.

How do you treat a hyperextended knee?

If you have pain from a hyperextended knee, your primary care provider or other healthcare professional will evaluate you. They'll look for swelling, bruising, and any signs of instability. They may order an X-ray or MRI to rule out fractures or ligament injuries.

The severity of your injury will determine your treatment. If you have torn a ligament, you may need surgery.

Treatment of a hyperextended knee includes the following:

• Rest: Avoid doing high-impact sports or any activity that increases pain.

• Ice: Use an ice pack a couple of times a day for 15-20 minutes to decrease pain and swelling. Be sure to put a thin towel between the ice and your skin to protect it from cold injury.

• Compression: Wrapping your knee with a light bandage, like an ACE wrap, for a few days will help decrease swelling and provide support.

• Elevation: If your knee is swollen, keep it elevated above the level of your heart.

• OTC pain relievers: A short course (7-10 days) of nonsteroidal anti-inflammatory drugs (NSAIDs) like ibuprofen or naproxen will help decrease pain and inflammation. If you can't take NSAIDs, acetaminophen may help with pain.

• Physical therapy: Exercise is critical to maintain your range of motion and strengthen the muscles that support your knee. A physical therapist can guide you through these exercises. Research has found that strengthening the hamstring and quadriceps muscles is crucial. If you have knee hyperextension from a neurological condition, a physical therapist can help with proprioceptive training to improve knee control and gait.

How long does a hyperextended knee take to heal?

The time it takes to heal a hyperextended knee depends on the severity of your injuries. If no ligaments were injured, your knee should start feeling better with at-home treatment within 2 to 4 weeks.

Ligament injuries take longer to heal. If you overstretched the ligaments or had a partial tear, it will take 1 to 2 months before you can return to normal activities.

More severe injuries and complete ligament tears, especially those that need surgery, can take several months to recover. For example, full recovery and return to sports activities after PCL reconstruction can take 6 to 12 months. A bone bruise after a big injury can also take months to heal.

Can you prevent hyperextended knees?

Some injuries can't be prevented. But knowing what can put you at risk for a hyperextended knee and taking preventive steps can help.

• Exercise:Strengthen the muscles that support your knee, including your hamstrings and quadriceps. Follow a regular stretching program to maintain flexibility. Keeping your leg muscles strong is crucial, especially if you participate in higher-risk activities like football, soccer, and skiing.

• Warmup and cooldown: Do a 5- to 10-minute warmup before activity and a 5- to 10-minute cooldown after to help prevent injuries.

• Consider your posture: Avoid standing with your knees in a hyperextended position. This stresses your knee joint and ligaments, potentially causing pain. This is especially important if you have hypermobile joints. Consider working with a physical therapist to help you retrain how you stand and walk.