What Is a Hyperextended Knee?

Knee hyperextension occurs when the knee joint bends backward beyond its normal range of motion. Depending on the severity, this injury can cause damage to the ligaments or tendons that support this area of your leg. It can also lead to pain and several other symptoms.

This article will outline the most common causes of knee hyperextension, its typical symptoms, and the most effective diagnosis and treatment techniques.

Causes

Knee hyperextension most often occurs in athletes playing sports or in people participating in physically demanding forms of exercise.

One of the most common causes of this condition is a backward-directed blow to the front of the knee joint. Tackle football or soccer players are particularly susceptible.

Direct blows to the leg are not the only cause. Other common causes include landing awkwardly on your leg after a jump or overextending your knee after falling from an elevated surface.

Regardless of the mechanism, bending your knee backward beyond its normal limits can significantly damage several structures in the leg. The most commonly affected areas include:

• The anterior cruciate ligament (ACL)
• The posterior cruciate ligament (PCL)
• The posterolateral corner (PLC) of the knee

The medial collateral ligament (MCL) and the meniscus—may also be affected. This is more likely if some degree of knee rotation or twisting occurs during the hyperextension injury.

Symptoms

Depending on the severity of your injury, several symptoms may result from knee hyperextension. The most frequent ones include:

• A popping sensation during the injury
• Acute pain in the joint, especially in the area behind the knee (popliteal fossa)
• Bruising, redness, or warmth in the leg
• Sudden swelling immediately after the injury
• Instability or giving way of the leg
• Difficulty walking

These complaints can vary widely based on the anatomical structures affected and the severity of the knee hyperextension. Because of this, any new or worsening symptoms that occur after this type of injury should be evaluated immediately by a healthcare professional.

Diagnosis

Following a knee hyperextension injury, it is extremely important to have your leg evaluated by a healthcare professional who can perform a comprehensive examination and determine the nature of your injury. During this process, several different diagnostic tools may be used.
These include:

• Physical examination: Multiple different leg movements are performed to help determine the integrity of the structures in your leg.
• Magnetic resonance imaging (MRI): This test provides a clear image of the soft tissue structures in the knee (ligaments, tendons, and meniscus) to assess for any damage.
• X-ray: This form of imaging is occasionally needed to look for concurrent bone damage after a traumatic hyperextension injury.

Treatment

Mild knee hyperextension can usually be treated conservatively.

After the initial incident, a healthcare provider may advise you to ice and elevate the leg to reduce swelling or inflammation. NSAID (nonsteroidal anti-inflammatory drug) pain relievers, such as Advil or Motrin (ibuprofen) and Aleve (naproxen) may also be suggested.

Other possible treatment options include:

• Wearing a knee brace: This device helps stabilize the leg and can reduce the strain on an injured ACL, PCL, or PLC.
• Physical therapy (PT): A therapist will focus on strengthening the affected leg to improve its stability. They will also help restore any lost range of motion and improve your ability to walk, run, and jump.
• Electrical stimulation or pneumatic compression: This may be utilized to control your pain and swelling.

More significant hyperextension injuries may ultimately require surgical correction. This typically involves an arthroscopic reconstruction of the damaged structure with a graft from another area of the body (or from a cadaver).

Following this operation, extensive physical therapy is usually necessary to rehabilitate the knee.

Prognosis

Individuals who sustain minor knee hyperextension injuries can usually recover following conservative treatment. This is especially true for people who do not experience any instability after the injury or who don’t choose to participate in more physically demanding forms of exercise.

Most people undergoing an arthroscopic reconstruction after a hyperextension injury can also recover fully. Several potential complications are worth noting, however.

Failure rates for surgical posterolateral corner reconstructions are reported to be as high as 38% in some studies. A similar systematic review found that roughly 9% of ACL reconstructions ultimately fail or need surgical revision. In addition, up to 73% of people who had their ACL surgically reconstructed showed signs of osteoarthritis in the joint at a 20-year follow-up.

Summary

Knee hyperextension injuries occur when the knee bends backward beyond its normal limits. This problem can happen to anyone but is most common in athletes who land awkwardly or who experience a blow to the leg.

Depending on the severity, several different anatomical structures may be damaged, including the knee’s tendons or ligaments. Mild hyperextension injuries are treated conservatively, while major ones may require arthroscopic surgery.