Why is my knee unstable?

What is knee instability?

Knee instability is a feeling of  a knee that "looses" lacks support, or feels like it's moving abnormally.¹ The knee may appear to move forward, sideways, or "spin" unpredictably. This feeling can result from various types of injuries, especially as a result of cruciate ligament damage¹. 

It can appear after trauma², for example a fall, a wrong movement or a shock during a sports activity, but also in everyday life.

What are the symptoms of knee instability?³

The symptoms of knee instability can vary from person to person. They are not always present at the same time. Some appear during exercise, others in everyday life. Here are the most common signs.

A feeling of instability or "knee giving out"

This is often the first sign felt. The knee may feel weak, unreliable. Some people speak of apprehension, with the fear that the knee will not hold. Others describe real episodes where the knee dislocates, sometimes to the point of dislocation of the patella.

Knee locks

The knee can lock suddenly, flexion, or extend. This makes it seem like it's impossible to bend or fully extend the leg for a few moments. These blockages can be related to the menisci or the patella, depending on their mechanism.

Pain

Pain is not systematic, but it is common. It can appear at rest or especially during physical activities, such as walking, climbing stairs or sports. It is often located around the knee and its intensity can vary.

Swelling of the knee (effusion)

The knee can swell after exertion or trauma. This swelling reflects the presence of fluid in the joint. It may be accompanied by a feeling of tension or stiffness.

If you recognize one or more of these symptoms, it is important to talk to a healthcare professional. Putting into words what you feel helps to better understand the origin of the instability and to adapt the treatment.

What is the cause of a weak knee?

A weak knee is rarely linked to a single cause. It most often results from an association between joint injury and a disorder of muscle control.⁴

Ligament damage, such as a ruptured anterior cruciate ligament, or pathologies such as osteoarthritis of the knee, change the mechanical stability of the joint.⁴ But pain also plays an important role. It disrupts the functioning of the muscles and nervous system, which normally ensure a permanent adjustment of movement.⁴

To protect itself, the body sets up compensatory movements. Gait changes, support is different, and loads on the knee are poorly distributed.⁴ These adaptations can maintain the feeling of instability and promote new episodes of a weak knee.

How to identify the possible origin of knee instability?  

The identification of the origin of knee instability is largely based on the ligament or structure affected⁵. Each ligament plays a specific role in stability.

• Anterior cruciate ligament (ACL): often involved in pivoting or sliding forward sensations, especially after trauma with rapid swelling.
• Posterior cruciate ligament (PCL): responsible for backward instability, sometimes more discreet on a daily basis.
• Lateral ligaments : involved in instabilities on the sides of the knee.
• Complex instabilities : several ligaments can be affected simultaneously after a major trauma.

The clinical examination, with specific tests depending on the affected ligament, supplemented if necessary by imaging, makes it possible to specify the origin of the instability and to guide the management.

Knee giving up and pain: what is the link?

Knee pain and instability are closely linked. Pain changes the information sent to the brain and disrupts the control of the muscles around the knee. These become less effective at stabilizing the knee joint.

Over time, instability can in turn increase the stress on the knee and maintain pain. Persistent pain may then set in. This is why the treatment must focus on the injury, the pain and the control of movement.⁶

How to treat knee instability?

Treatment depends primarily on the affected ligament, the severity of the damage and your lifestyle.

Some instabilities, in particular isolated damage to the lateral collateral ligament, are most often treated without surgery, by rehabilitation. The wide variety of procedures used to treat patients with posterolateral instability makes it difficult to reach a consensus on the most effective approach. Surgery may be considered, but other methods may also be considered, such as reconstruction by tendon graft in the case of chronic damage⁵.

For the anterior cruciate ligament, functional or surgical treatment may be offered depending on the instability and your goals.5 We invite you to consult our article: How is a cruciate ligament rupture treated?

For the medial collateral ligament, treatment with the RICE protocol followed by temporary immobilization and the use of crutches to control pain is recommended. However, it is also recommended to put weight on the leg as soon as the pain allows.5

Complex instabilities sometimes require more comprehensive surgical management.

In any case, rehabilitation is an essential step in regaining a more stable knee.

How do you strengthen a weak knee?⁷

Strengthening a weak knee is not just about building muscle. It's about regaining good control of movement.

Strengthening the thigh muscles, working on balance and coordination, as well as re-educating everyday gestures are essential. These exercises should be progressive and adapted to your situation. Consistency is key, often over several months.

Being accompanied by a health professional makes this process safer and allows you to regain more confidence in your knee.