Patella Dislocation

 

Written By Sabrina Lee, DO, PGY-1; Edited by: Timothy Khowong, MD, MSEd

 

Background

The majority of patellar dislocations occur in young females, specifically teenage athlete girls. There is higher risk in patients under the age of 20 years old. Additionally, 75% of first-time patellar dislocations occur in people under 25 years old.

According to different studies, 30-72% of dislocations are sports-related and 28-39% involve osteochondral fractures. Most common sports or activities that lead to patellar dislocations include soccer, ice hockey, dance, weight lifting, and gymnastics. 


Anatomy

The patella is the largest sesamoid bone in the body. It’s attached to the quadriceps tendon superiorly and the patellar tendon inferiorly. On either side of patella, the joint capsule is comprised of the medial and lateral patellar retinacula, which arise from the vastus medialis and vastus lateralis muscles respectively.

The patella functions to increase the force of the quadriceps during knee extension. During knee extension, the extensor muscles (quadriceps femoris, vastus medialis, vastus intermedius, vastus lateralis), pull the patella laterally. This lateral pulling force actually increases even more during knee flexion. Due to the natural lateral displacement of the patella during quadricep contraction, patellar displacement out of its patellofemoral groove most commonly occurs laterally!

Mechanism of Injury

There are 2 main types of mechanisms that cause patellar dislocations:

  • Type 1: most common

    • A powerful quadriceps contraction with sudden flexion and external rotation of the tibia on the femur

  • Type 2: less common

    • Direct lateral trauma to the patella with the knee in flexion


Risk Factors

These factors can increase risk for patellar dislocations:

  • Athletes (ice hockey, dance, weight lifting, soccer, gymnastics, basketball)

  • Females

    • Females have wider pelvises, which lead to a larger Q angle. Large Q angle can lead to multiple knee problems, including patellar subluxation and dislocation.

  • Conditions with anatomic instability

    • Genu valgum

    • Pes planus

    • Generalized joint laxity

    • Lower extremity misalignment

    • Iliotibial band tightness

    • Patellar subluxation

  • Prior Patellar Dislocations

Clinical Features

  • Patient might state that the knee “gave way” followed by severe pain and they were unable to ambulate

  • Displaced patella (most likely laterally)

    • Also consider the patella might have spontaneously reduced!

  • Knee held in flexion

  • Knee pain, especially with knee extension

  • Additional Findings:

    • Hemarthrosis

    • Knee swelling

    • Tenderness to medial patella

Evaluation

It’s a clinical diagnosis!

Physical Examination:

  • Make sure to perform neurovascular exam distal to the patella

  • You can perform Apprehension Test to assess for patellar dislocation and subluxation

    • Apprehension Test:

      • Knee is placed in 30 degrees of flexion

      • Apply medial pressure, pushing patella laterally

      • While maintaining pressure, flex and extend knee

      • Apprehension Sign: positive test is if pressure causes discomfort and apprehension by the patient (feeling like the knee will dislocate), indicating patellar instability; this is more commonly seen in patellas that have spontaneously reduced

Imaging

  • +/- Knee X-ray (AP, lateral, and sunrise view)

    • It’s technically not required to order an X-ray prior to reduction, unless you have suspicion for a fracture or the diagnosis is unclear

    • If the patella is already relocated, still consider ordering an X-ray to rule out fractures

Xray Below demonstrates dislocated patella with osteochondral fractures.

Management

Mainstay of treatment is to reduce the patella!


Prior to reduction, make sure to give analgesia, such as IV morphine or fentanyl. Sedation may be required but is rarely needed.

Technique for Closed Reduction

  • If there is a single provider (Left image below):

  1. Place hip in mild flexion by raising head of bed (allows quadriceps relaxation)

  2. Gently extend knee with one hand while pushing the patella back into place with the other hand (generally in medial direction is laterally dislocated)

  • If there are two providers (Right image below):

  1. One provider applies slow downward pressure over quadriceps (stretches quadriceps and slowly straightens the leg)

  2. Second provider gently rotates the patella from lateral to anterior

  • Successful reduction is indicated when you feel the patella return to the tibiofemoral tract and there is normal knee flexion and extension.

Yay you did it! After you successfully reduce the patella…

  • Place patient in knee immobilizer or patellar-stabilizing brace with crutches to help with ambulation

    • For first-time patellar dislocation, there are some recommendations that the patient should be splinted in an above knee plaster cast, however supportive data is limited. Uptodate recommends a knee immobilizer or patellar brace.

  • Order X-ray post-reduction to rule out fractures

  • Reassess the knee for signs of ligamentous injuries

Technique with two hands providing lateral to medial force to the patella.

Disposition

When do you consult orthopedic surgery?

  • If you’re unable to reduce patella

  • If there are associated fractures or loose bodies seen on post-reduction X-ray

If you successfully reduced patella, discharge the patient with knee immobilizer and follow-up with orthopedic surgery within 2-3 days

  • Prescribe NSAIDs for pain

  • Allow weight-bearing as tolerated. Limit walking, standing, impact, or repetitive bending if it causes pain

  • RICE (rest, ice, compression, elevation)

  • Encourage ways for prevention of recurrent dislocations, such as:

    • Exercises to stretch and strengthen quadriceps

    • Perform safe exercise techniques

    • Use orthotics for feet support, which impact knee stability

  • Note: It is important to ensure orthopedic follow-up in patients with a history of recurrent patellar dislocations, family history of patellar dislocations, or pediatric patients < 15 years old! These are patient groups that are at high risk of recurrent patellar dislocations so close follow up is necessary.

Complications

  • Associated osteochondral fractures (occurs in 40% of patellar dislocations)

    • Most commonly at: Medial Patellar Facet & Lateral Femoral Condyle

  • Chronic knee pain

    • Dislocation can cause issues with neighboring ligaments, tendons, and structures within the knee capsule, which can lead to ongoing knee pain.

  • Recurrent patellar dislocations

    • Children who are under 16 years old are at higher risk of recurrence, possibly up to 70% risk seen in some studies. If patients have history anatomic instability, they will also be more prone to a recurrent dislocation.

  • Degenerative arthritis

    • Dislocation can damage cartilage, tendons, and ligaments within the knee, which lead to joint instability and abnormal wear and tear.

 
 

References

  1. Fithian DC, Paxton EW, Stone ML, et al. Epidemiology and natural history of acute patellar dislocation. Am J Sports Med. 2004;32(5):1114-1121. doi:10.1177/0363546503260788

  2. Guthrie K. Patellar dislocation. Life in the Fast Lane • LITFL. July 6, 2023. Accessed May 23, 2025. https://litfl.com/patellar-dislocation/. 

  3. Moore BR, Bothner J. Recognition and initial management of patellar dislocations. UpToDate. Accessed May 23, 2025. https://www.uptodate.com/contents/recognition-and-initial-management-of-patellar-dislocations?search=patellar+dislocation&source=search_result&selectedTitle=1~14&usage_type=default&display_rank=1. 

  4. Vermeulen D, van der Valk MR, Kaas L. Plaster, splint, brace, tape or functional mobilization after first-time patellar dislocation: what's the evidence?. EFORT Open Rev. 2019;4(3):110-114. Published 2019 Mar 27. doi:10.1302/2058-5241.4.180016

 
Booth EM