Patellar dislocation

Patellar instability occurs when the kneecap doesn't stay properly aligned within its normal groove at the front of the knee, causing it to partially slip out of place or fully dislocate. This condition can bring pain, swelling and a sense that your knee is unstable or giving way, especially when standing, walking or climbing stairs. With the right diagnosis and treatment plan, most people regain confidence in their knee and return to the activities they enjoy.

Find a specialist

Find a location

Detailed diagram of the human knee joint with labeled structures including the patella and ligaments.

Anatomy of the knee

The patella, or kneecap, is a small triangular bone at the front of the knee. It sits within a groove at the end of the femur, or thighbone, and glides up and down as you bend and straighten your leg. Ligaments and soft tissues along the inner and outer sides of the patella help keep it centered in this groove, while the quadriceps muscles provide additional control during movement.

When these stabilizing structures are healthy and balanced, the kneecap tracks smoothly within the groove. If they become weakened or damaged, the patella can shift out of alignment, leading to subluxation or dislocation.

Overview

Symptoms

You may be experiencing patellar instability if you notice:

Knee pain, especially when standing up from a seated position
A sensation of the knee buckling or giving way
Recurrent kneecap subluxations or dislocations
Swelling, bruising or sharp pain following a dislocation
Visible deformity of the knee after injury
Changes in sensation, such as numbness, below the knee after dislocation

Symptoms may worsen over time if the instability isn't addressed, so early evaluation matters.

Causes

Patellar instability often results from a combination of structural and muscular factors rather than a single cause. Common contributors include:

Anatomical differences, such as a shallow femoral groove or an abnormal patella shape
Flat feet or fallen arches that affect knee alignment
An increased Q angle, which changes how the quadriceps pull on the kneecap
Muscle imbalance or weakness in the quadriceps
A previous patellar dislocation or ligament injury
Abnormal wear in the joint, including patellofemoral arthritis

These factors can cause the kneecap to track abnormally, increasing the risk of repeated subluxations or complete dislocations.

Risk factors

Certain factors can raise your chances of developing patellar instability, though having one or more of these doesn't mean you'll experience the condition:

A shallow or irregularly shaped femoral groove
Flat feet or fallen arches
Weak or imbalanced quadriceps muscles
A history of prior kneecap dislocation or ligament injury
Existing joint wear, such as patellofemoral arthritis

Knowing your personal risk factors can help your care team guide you toward the right activity level and treatment plan.

Diagnosis

Our orthopedic and sports medicine specialists take a patient-centered approach to diagnosing patellar instability. Your evaluation may include a detailed medical history and physical examination, an assessment of knee alignment, strength and tracking, X-rays to evaluate bone structure and patellar position, and MRI or CT scans to assess soft tissue injury and joint anatomy. We explain findings clearly, so you understand your diagnosis and treatment options.

View treatment options

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

Explore treatments