Hyperextended Knee Injury

Written By: Chloe Wilson, BSc(Hons) Physiotherapy
Reviewed by: KPE Medical Review Board

A hyperextended knee is where the knee joint bends too far backwards.

Knee hyperextension can cause pain, swelling and instability and often affects daily activities and sports.

When the knee hyperextends, stress is placed on the knee structures, particularly at the back of the knee.

In severe cases, one or more of the knee ligaments may be over-stretched and either partially or completely tear. This can lead to long-term knee instability if left untreated. 

Here we will look at the common causes, symptoms and associated injuries with a hyperextended knee and then we will go on to look at the best treatment options to ensure a full recovery and reduce the risk of ongoing instability and further injuries.

A hyperextended knee is most commonly caused by a sporting injury but can affect anyone, being caused by anything which forces the knee joint to bend too far backwards.

The most common causes of a hyperextended knee are:

• Awkward Landing: Landing hard from a jump or being unbalanced as you land, particularly if landing on a straight leg, can lead to a hyperextended knee
  
  
• Sporting Tackle: a tackle at the front of the knee that pushes the joint straight backwards can lead to knee hyperextension
  
  
• Skiing: If the front of the skis hit something e.g. a snow bank, the skier’s body often keeps moving forwards while the feet are fixed causing hyperextension of the knee. This is especially likely if the bindings fail to release
  
  
• Running: If you suddenly stop when running, particularly if taking all your weight through one leg, or if your foot gets stuck in the ground, e.g. there is a hole or you are wearing cleats you may experience a knee hyperextension injury. Momentum keeps your body moving forwards while the knee bends backwards, particularly if the foot is fixed
  
  
• Piggyback Ride: If someone jumps on your back for a piggyback ride without warning it can pull you off balance and result in a hyperextended knee

What Prevents Hyperextension of the Knee?

The four knee ligaments, the anterior and posterior cruciate ligaments and the medial and lateral collateral ligaments are the main stabilisers of the knee joint. They are strong ligaments that hold the knee bones together, but if enough force goes through the knee, the ligaments over-stretch and the knee hyperextends.

Women are at greater risk of experiencing a hyperextended knee injury as their ligaments tend to be more lax than men’s which results in an increase likelihood of joint instability. 

1. Knee Pain

Localised knee pain is a common hyperextended knee injury symptom. People usually describe the pain as either a mild ache or sharp pain behind the knee, or occasionally a pinching type anterior knee pain if the structures at the front of the knee have been damaged.

It may range from mild/moderate pain in fairly minor injuries where there is minimal damage to the knee structures to moderate/severe pain if the soft tissues e.g. ligaments have been torn. 

2. Knee Swelling & Bruising

Swelling behind the knee and bruising are common symptoms with knee hyperextension injuries. If one of the ligaments has been completely torn, swelling and bruising will be fairly immediate (within one to two hours) and is often profuse.

If the damage is more minor, such as a grade 1 or 2 ligament sprain or cartilage irritation, the swelling and bruising will slowly develop over 24-48 hours and is usually fairly mild.

3. Knee Instability

Instability is a common hyperextended knee symptoms and the knee joint may feel unstable when standing or walking after a knee hyperextension injury. It may feel like it is going to buckle underneath you or it may actually completely give way.

If the knee gives way it usually indicates that one or more of the knee ligaments has been torn, most commonly the Anterior Cruciate Ligament (ACL).

4. Restricted Knee Movement

Knee movement may be restricted after a knee hyperextension injury due to the build-up of fluid in the joint. The more swelling there is, the more knee stiffness is likely to be a problem.

5. Popping Sound

Knee hyperextension that is accompanied by a popping sound or sensation usually indicates that one of the knee ligaments has ruptured (completely torn). In most cases of hyperextension with knee popping it is the ACL that is torn which will result in immediate swelling and major knee instability.

You may experience, one, some or all of these hyperextended knee symptoms following a hyperextension injury.

ACL injuries are often accompanied by a popping sound. The knee typically has to bend back into at least ten degrees of hyperextension to tear the ACL.

PCL injuries are less common as the PCL is stronger than the ACL. 

In some cases, one of the collateral ligaments at the side of the knee is torn, typically the MCL. With an MCL tear happens the inner side of the knee is generally very tender and there is swelling and bruising on the medial side of the knee.

The ligaments may be damaged in isolation, or multiple ligaments may be injured at the same time. In the most severe cases, all of the ligaments may be torn. When this happens, the joint capsule usually tears as well so there is actually less visible swelling as the swelling isn’t contained in the knee joint.

The meniscus is a special, thick layer of cartilage that lines the knee joint. When the knee hyperextends, it can pinch the cartilage at the front of the knee joint which can cause a meniscus tear.

This usually results in knee pain and swelling and depending on the type of tear, may cause knee locking.

Meniscus tears are notoriously slow to heal without the right treatment due to having a poor blood supply.

RELATED ARTICLE: Knee Meniscus Tears

Applying ice to the knee is a usefeul hyperextended knee treatment tool as it helps to reduce the pain and swelling. The sooner you can get the swelling down, the sooner you will regain your knee movement, strength and stability.

It is important to apply ice correctly – leave it on too long or apply it directly to your skin and you can actually make things worse.

RELATED ARTICLE: Ice Treatment For Injuries 

If you have damaged any of the soft tissues around the knee, such as the ligaments or cartilage, it is advisable to work on a rehab programme with a physical therapist who will be able to give you tailored hyperextended knee exercises.

They will work with you to help you make a full recovery and ensure you aren’t left with any long term instability or pain from your hyperextended knee which could make you more susceptible to further knee problems in the future. 

You can find a whole range of hyperextended knee exercises with guidance on how to do them safely, how to progress and how to get the best results in the knee strengthening exercises section.

In most cases, non-surgical hyperextended knee treatment is suficient, but if you have torn one of the knee ligaments with your knee hyperextension injury, particularly the ACL, you may require surgery to fix the torn tendon. The torn knee ligament is either repaired or replaced with a graft, depending on the severity of the tear.

Recovery tends to be slow but with the correct rehab you should make a full recovery.

You can find out how to tell if you need surgery, what it involves and all about the recovery process in the ACL Surgery section.

The normal range of movement at the knee is 0-135 degrees i.e. fully straight (0^o) to fully bent (135^o). If the knee extends more than 10 degrees past neutral, that is classed as hyperextension.

Genu recurvatum is more common in women due to increased ligament laxity and there is often a genetic link.

There are a number of other things that can cause genu recurvatum syndrome including:

• Ligament Laxity
• Muscle Weakness
• Leg Length Discrepancy
• Medical Conditions: such as Ehlers-Danlos syndrome, Cerebral Palsy and Muscular Dystrophy
• Upper or Lower Motor Neurone Syndrome

Treatment for genu recurvatum usually involves:

1. Medication: if the hyperextension is due to a medical condition
2. Physical and Occupational Therapy
3. Knee Splints, Orthotics & Braces: to provide support to the knee
4. Knee Surgery