Knee instability

Knee instability happens when your knee buckles, shifts or feels like it's going to give out during everyday movement. Whether your knee feels loose during a workout or gives way while walking down stairs, this condition can make it hard to trust your body and stay active. With the right diagnosis and treatment plan, most people regain strength and confidence in their knee.

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Illustration of a human knee joint with labeled parts including quadriceps, femur, patella, and ligaments.

Anatomy of the knee

Your knee is a hinge joint that connects your thighbone (femur) to your shinbone (tibia). It relies on four main ligaments, the ACL, PCL, MCL and LCL, along with the surrounding muscles, tendons and cartilage, to keep the joint steady during movement.

These ligaments work together to control how far your knee bends, twists and shifts. When one or more of these structures becomes stretched, torn or weakened, the knee can lose its normal stability. That's when you might notice your knee feels unstable, wobbly or prone to buckling, especially during activities like pivoting, climbing stairs or stepping off a curb.

Overview

Symptoms

Knee instability can show up differently depending on the underlying cause, but many people notice a similar pattern of warning signs.

A feeling that your knee will give out or buckle
Knee feels loose, wobbly or unstable during movement
Weakness when standing, walking or climbing stairs
Swelling or discomfort after activity
A sensation of the knee shifting or slipping out of place
Difficulty trusting the knee during sports or exercise

If left unaddressed, knee weakness and buckling episodes can become more frequent, making it harder to stay active without discomfort or worry.

Causes

An unstable knee is often the result of damage to the ligaments, cartilage or muscles that keep the joint steady. Common causes include:

Ligament injuries, such as tears to the ACL, PCL, MCL or LCL
Meniscus tears that affect how the knee absorbs shock
Previous knee dislocations or repeated episodes of the kneecap slipping out of place
Muscle weakness, particularly in the quadriceps and hamstrings, that fails to support the joint
General wear and tear on the joint over time

In some cases, more than one factor contributes to knee instability, so a thorough evaluation helps identify the specific cause behind your symptoms.

Risk factors

Certain factors can make you more likely to develop knee instability. Having one or more of these does not mean you'll experience knee giving out, but it's worth discussing with your care team:

A history of knee injury or previous surgery
Participation in sports that involve pivoting, jumping or sudden stops
Weak thigh or hip muscles
Joint hypermobility or naturally loose ligaments
Prior episodes of the knee buckling or feeling loose

Diagnosis

Diagnosing knee instability starts with a conversation about your symptoms, including when your knee feels unstable and what activities seem to trigger it. Your care team will also perform a physical exam, which may include a knee instability test to check how much the joint shifts or moves compared to normal.

Imaging tests can help confirm what's causing the instability. These may include:

X-rays to check bone alignment and rule out fractures
MRI scans to evaluate ligaments, cartilage and soft tissue
In some cases, additional imaging to assess how the kneecap tracks during movement

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We offer leading-edge treatments for most joint medicine conditions, treating many with medications, bracing, injections and therapy.

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