Patella dislocation

Background

Anatomy of anterolateral aspect of right knee.

• Usual mechanism is blow to extended knee with externally rotated foot
• May also occur with sudden lateral cut or twisting at the ankle or knee
• Acute traumatic dislocations more common in males
• Chronic dislocation seen more commonly in women/teenage girls, typically little or no swelling
  • 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

• Knee dislocation
• Knee fractures
  • Patella fracture
  • Segond fracture
  • Tibial plateau fracture
• Meniscus and ligament knee injuries
• Patella dislocation
• Patellar tendonitis
• Patellar tendon rupture
• Quadriceps tendon rupture

Nontraumatic/Subacute

• Arthritis
• Gout and Pseudogout
• Osgood-Schlatter disease
• Patellofemoral syndrome (Runner's Knee)
• Patellar tendonitis (Jumper's knee)
• Pes anserine bursitis
• Popliteal cyst (Bakers cyst)
• Prepatellar bursitis (nonseptic)
• Septic bursitis
• Septic joint
• DVT

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

See Also

Knee (Main)