Patellar dislocation

Last updated: October 13, 2023

Summarytoggle arrow icon

The patella is the largest sesamoid bone in the human body. It is located within the quadriceps femoris tendon and acts as a fulcrum to increase the force exerted on the tibia. In patellar dislocation, the patella slips out of the femoral trochlear groove, usually laterally. Patellar dislocation usually occurs following torsion of a semiflexed knee; less frequently, dislocation is the result of direct trauma to the patella. Recurrent dislocation may be associated with underlying biomechanical abnormalities such as medial patellofemoral ligament injury. In some patients, the condition is congenital. Patellar dislocation is primarily a clinical diagnosis, but x-rays should be obtained in all patients to rule out concomitant osteochondral fractures. Joint aspiration and/or further imaging (e.g., MRI or CT scan) may be indicated based on physical examination and/or x-ray findings. Many first episodes of patellar dislocation can be managed conservatively, but surgical treatment is often indicated for concurrent fractures or major soft tissue lesions, failure of conservative management, or recurrent dislocations.

Definitiontoggle arrow icon

Epidemiologytoggle arrow icon

  • Sex: >
  • The first episode of patellar dislocation typically happens before the age of 20 years.
  • Up to 45% of patients will have recurrent patellar dislocations after the first episode.

Epidemiological data refers to the US, unless otherwise specified.

Etiologytoggle arrow icon

Traumatic patellar dislocations [4]

  • Non-contact (most common): usually due to a twisting injury when the knee is simultaneously in flexion and under valgus strain
  • Direct contact: usually due to a direct sideward impact on the patella (e.g., during contact sports or a car accident)

Risk factors for recurrent dislocations [4]

Over 90% of patellar dislocations result from a twisting injury when the knee is simultaneously in flexion and under valgus strain, often during an activity such as sports or dance, rather than from direct traumatic contact. [4][6]

Clinical featurestoggle arrow icon

Subtypes and variantstoggle arrow icon

Congenital (fixed) patellar dislocations [3]

Diagnosticstoggle arrow icon

For the approach to a painful swollen knee of unclear etiology, see “Acute internal knee derangement.”

Clinical evaluation [2][6]

Imaging [2][6][11]

Full knee x-ray series

Lipohemarthrosis in the presence of normal knee x-rays suggests an underlying osteochondral fracture. [5][12]

Additional imaging

Treatmenttoggle arrow icon

There are currently no consensus guidelines for the management of patellar dislocation. The decision to proceed with conservative versus surgical management may vary based on patient and provider preferences. [2][4]

Conservative management [1][2][4]

The patella often relocates spontaneously, making manual reduction unnecessary. [1]



Surgery [1][2][4]

Complicationstoggle arrow icon

We list the most important complications. The selection is not exhaustive.

Referencestoggle arrow icon

  1. Smith TO, Donell S, Song F, Hing CB. Surgical versus non-surgical interventions for treating patellar dislocation. Cochrane Database Syst Rev. 2015.doi: 10.1002/14651858.cd008106.pub3 . | Open in Read by QxMD
  2. Weber AE, Nathani A, Dines JS, et al. An Algorithmic Approach to the Management of Recurrent Lateral Patellar Dislocation. J Bone Joint Surg. 2016; 98 (5): p.417-427.doi: 10.2106/jbjs.o.00354 . | Open in Read by QxMD
  3. Casey Imbergamo, Ryan Coene, Matthew Milewski. Management of Fixed Dislocation of the Patella. Journal of the Pediatric Orthopaedic Society of North America. 2020; 2 (2).doi: 10.55275/jposna-2020-122 . | Open in Read by QxMD
  4. Chan Gao, Aaron Yang. Patellar Dislocations: Review of Current Literature and Return to Play Potential. Curr Phys Med Rehabil Rep. 2018; 6 (2): p.161-170.doi: 10.1007/s40141-018-0187-8 . | Open in Read by QxMD
  5. Duthon VB. Acute traumatic patellar dislocation. Orthop Traumatol Surg Res. 2015; 101 (1): p.S59-S67.doi: 10.1016/j.otsr.2014.12.001 . | Open in Read by QxMD
  6. Jain NP, Khan N, Fithian DC. A treatment algorithm for primary patellar dislocations. Sports health. 2011; 3 (2): p.170-4.doi: 10.1177/1941738111399237 . | Open in Read by QxMD
  7. Bunt CW, Jonas CE, Chang JG. Knee Pain in Adults and Adolescents: The Initial Evaluation. Am Fam Physician. 2018; 98 (9): p.576-585.
  8. Calmbach WL, Hutchens M. Evaluation of patients presenting with knee pain: Part II. Differential diagnosis. Am Fam Physician. 2003; 68 (5): p.917-22.
  9. Smith TO, Davies L, O’Driscoll ML, Donell ST. An evaluation of the clinical tests and outcome measures used to assess patellar instability. Knee. 2008; 15 (4): p.255-262.doi: 10.1016/j.knee.2008.02.001 . | Open in Read by QxMD
  10. Ahmad CS, McCarthy M, Gomez JA, et al. The Moving Patellar Apprehension Test for Lateral Patellar Instability. Am J Sports Med. 2009; 37 (4): p.791-796.doi: 10.1177/0363546508328113 . | Open in Read by QxMD
  11. ACR Appropriateness Criteria: Acute Trauma to the Knee (Revised 2019). Updated: August 23, 2016. Accessed: August 23, 2019.
  12. Stefancin JJ, Parker RD. First-time Traumatic Patellar Dislocation. Clin Orthop Relat Res. 2007; 455: p.93-101.doi: 10.1097/blo.0b013e31802eb40a . | Open in Read by QxMD
  13. Duncan ST, Noehren BS, Lattermann C. The Role of Trochleoplasty in Patellofemoral Instability. Sports Med Arthrosc. 2012; 20 (3): p.171-180.doi: 10.1097/jsa.0b013e31826a1d37 . | Open in Read by QxMD

Icon of a lock3 free articles remaining

You have 3 free member-only articles left this month. Sign up and get unlimited access.
 Evidence-based content, created and peer-reviewed by physicians. Read the disclaimer