Patellar Dislocation

What Is It, Causes, Diagnosis, Treatment, and More

Author: Alyssa Haag

Editors: Ahaana Singh, Ian Mannarino, MD, MBA

Illustrator: Aileen Lin


What is a patellar dislocation?

A patellar dislocation, also known as a patella dislocation, occurs when the patella, or the kneecap, slips out of its normal position. The patella typically rests in a groove, known as the trochlear groove at the end of the thigh bone (femur). It is primarily held in place by two main structures: the medial patellofemoral ligament and the tendon of the quadricep muscles.

When the knee bends and straightens, the patella moves up and down within the groove. Sometimes the patella may slide too far to one side or the other, and when this occurs, the patella may completely or partially dislocate. Dislocation tends to move the patella bone in the lateral direction, away from the body.

Patellar dislocation is a relatively uncommon knee injury. Only accounting for approximately 2–3% of all knee injuries, patellar dislocations most commonly affect young and active individuals, with a higher risk among adolescent females and athletes.

What causes the patella to dislocate?

Patellar dislocations occur most commonly as a result of trauma, usually a non-contact twisting injury, which can commonly occur while swinging a baseball bat. As the upper body twists to hit the ball, the opposite leg usually remains planted and may result in the twisting and consequent dislocation of the patella. Additionally, a patellar dislocation can occur due to a direct blow to the part of the knee closest to the middle, or midline, of the body (also called the medial aspect of the knee). 

Children with cerebral palsy (a group of disorders that affect the balance and posture of individuals) and Down syndrome (a disorder marked by developmental delays and mild to moderate learning disability) are prone to having recurrent dislocations due to increased imbalance and muscle weakness.

How do you diagnose patellar dislocation?

Diagnosis of a patellar dislocation includes a thorough review of patient history, physical examination, and diagnostic imaging. Most commonly, individuals will usually describe pain following trauma to the knee. Other common symptoms include feeling as though the knee “gives away”, or collapses, and hearing a popping sound while walking. Individuals may also experience swelling of the knee. 

Examination of the knee by a medical professional usually includes a test called the patellar apprehension test. To perform the patellar apprehension test, the provider applies an external force on the side of the patella closest to the midline of the body and assesses for pain and excessive sliding of the kneecap. If the pain is manageable, flexibility and extension of the knee will also often be evaluated. 

In order to confirm diagnosis and develop a treatment plan, the provider may also order X-rays. If more detailed images are necessary, an MRI may also be required to visualize the patellar tendon and quadriceps muscle more clearly.

How do you treat patellar dislocation?

Initial treatment of patellar dislocation usually consists of a “reduction,” or putting the patella bone back in place with the application of pressure. After reduction, various conservative, or traditional, interventions for patellar dislocation include wearing a brace to stabilize the knee as it heals; reducing weight bearing on the knee joint by using crutches; and attending physical therapy to assist in regaining complete knee range of motion.

If a patellar dislocation occurs more than once or if—despite the conservative interventions—the knee joint still remains unstable, surgical treatment may be recommended. 

Pain relievers may also be prescribed throughout the treatment process to control excessive pain.

How long does it take for a dislocated patella to heal?

It can usually take about six weeks to fully recover from a dislocated patella using nonsurgical treatment. If, on the other hand, surgery is required for the dislocated patella, recovery may take six months to a year. Although the individual’s range of motion may be regained after six months, healthcare practitioners often will not recommend a complete return to sports yet. Paying attention to one’s own body and listening to medical advice is imperative for the long-term healing of the dislocation.

What are the most important facts to know about patellar dislocation?

Patellar dislocations occur when the patella, the bone of the kneecap, slides out of its typical location. To diagnose a patellar dislocation, thorough review of patient history, physical examination, and imaging may be necessary. Treatments usually focus on conservative management, such as immobilization and minimizing weight bearing. However, with recurring dislocations or with minimal improvement of patellar instability following traditional interventions, surgery may be recommended. Recovery can take about six weeks with conservative treatments, and up to one year with surgery.

Related links

Meniscus tear
Patellar tendon rupture

Resources for research and reference

Hayat, Z., El Bitar, Y., & Case, J. L. (2020). Patella Dislocation. In StatPearls [Internet]. Retrieved December 4, 2020, from https://www.ncbi.nlm.nih.gov/books/NBK538288/

Patellar Dislocation and Instability in Children (Unstable Kneecap). (2019). In OrthoInfo. Retrieved November 6, 2020, from https://orthoinfo.aaos.org/en/diseases--conditions/patellar-dislocation-and-instability-in-children-unstable-kneecap/

Tunney, D. P. (2017). Patellar Apprehension Test. In MedSchool.co. Retrieved November 6, 2020 from https://medschool.co/exam/knee/patellar-apprehension-test