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Patellar Dislocations

By Danielle Campagne, MD , Assistant Clinical Professor, Department of Emergency Medicine, University of San Francisco - Fresno

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Patient Education

Patellar dislocations are common and almost always lateral. Diagnosis is clinical; x-rays are taken to exclude fracture. Treatment is reduction and immobilization.

Patellar dislocation is distinct from knee dislocation, which is a much more serious injury.

Most patients are adolescent females and have an underlying chronic patellofemoral abnormality. Many dislocations spontaneously reduce before medical evaluation.

Associated injuries include

  • Osteochondral fracture of the patella or lateral femoral condyle

Complications can include

  • Osteoarthritis

  • In patients with patellofemoral abnormalities, recurrent dislocation or subluxation

Diagnosis

  • Clinical evaluation

  • X-rays to exclude fracture

A patellar dislocation, unless spontaneously reduced, is clinically obvious; ie, the patella is visibly and palpably displaced laterally, and the patient holds the knee in a slightly flexed position and is unwilling to straighten it. If the dislocation has spontaneously reduced, hemarthrosis is often present, and the peripatellar area is usually tender.

Anteroposterior and lateral knee x-rays and patellar views are taken to exclude fracture, even if the dislocation has obviously reduced.

Treatment

  • Reduction

  • Immobilization

Immediate treatment of patellar dislocations is reduction; most patients do not require sedation or analgesia. Reduction is done with the patient's hip flexed. Then practitioners gently move the patella medially while simultaneously extending the knee. When the patella is reduced, a palpable clunk is usually evident and the deformity resolves.

Immediately after reduction, the knee is immobilized with a knee immobilizer or hinged brace with the knee in 20° of flexion.

Patients with osteochondral injury or recurrent instability may require a referral to an orthopedic surgeon for outpatient surgery.

Key Points

  • Patellar dislocations, which are common, are distinct from knee dislocations, which are much more serious.

  • Patellar dislocations occur most often in adolescent females who have an underlying chronic patellofemoral abnormality.

  • A patellar dislocation, unless spontaneously reduced, is usually clinically obvious; take x-rays to exclude fracture.

  • Reduce the dislocation and immobilize the knee.

  • If patients have an osteochondral injury or recurrent instability, refer them to an orthopedic surgeon.

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