Patella dislocation

Background

Anatomy of anterolateral aspect of right knee.
  • Usual mechanism is blow to extended knee with externally rotated foot[1]
  • May also occur with sudden lateral cut or twisting at the ankle or knee
  • Acute traumatic dislocations more common in males[2]
  • Chronic dislocation seen more commonly in women/teenage girls, typically little or no swelling[2]
    • May be associated with hemarthrosis
  • Chronic dislocation more common in females
    • Typically little or no swelling

Clinical Features

patella dislocates laterally
  • Patella usually displaced laterally
  • Knee held in flexion
  • Pain

Differential Diagnosis

Knee diagnoses

Acute knee injury

Nontraumatic/Subacute

Evaluation

  • Clinical diagnosis
  • May consider pre-reduction x-ray if concern for fracture (not required)

Management

Relocation with lateral pressure on dislocated patella
  • Reduce
    • Generally do not need x-rays prior to reduction
    • Sedation rarely required
      • Single dose of pain medication may facilitate relaxation

Techniques for closed reduction

  • Single operator
  1. Place the hip in mild flexion by raising head of bed
    • This facilitates relaxation of the quadriceps
  2. Gently extend the knee with one hand while pushing the patella back in place with the other hand
  • Two operators
  1. One provider applies slow downward pressure over quadriceps
    • This stretches the muscle and slowly straightens the leg
  2. Second provider gently rotates the patella lateral to anterior
  • Place patient in knee immobilizer
  • Provide NSAIDs
  • Obtain radiographs to rule out associated fracture (consider including sunrise view)
  • Allow weight-bearing as tolerated

Complications

  • Commonly associated fractures:
    • Medial patellar facet
    • Lateral femoral condyle

Disposition

  • If unable to reduce or if fracture or loose bodies (i.e. osteochondral fracture) are seen on post-reduction radiographs, consult orthopedic surgery
  • If patella successfully reduced, discharge with knee immobilizer and orthopedic follow up within 1 - 2 weeks

References

  1. ↑ Review of Orthopaedics, 6th Edition, Mark D. Miller MD, Stephen R. Thompson MBBS MEd FRCSC, Jennifer Hart MPAS PA-C ATC, an imprint of Elsevier, Philadelphia, Copyright 2012
  2. ↑ 2.0 2.1 Fithian DC, Paxton EW, Stone ML, Silva P, Davis DK, Elias DA, White LM. Epidemiology and natural history of acute patellar dislocation. AJSM 2004;32:1114-1121

See Also

Knee (Main)

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