II. Epidemiology

  1. Most common Knee Injury seen in children
  2. More common in teenage girls and young women
    1. Associated with increased Q-Angle (see below)

III. Mechanism

  1. Forceful deceleration with concurrent knee rotation or
  2. Valgus force with strong quadriceps contraction
    1. Results in lateral Patella displacement out of groove

IV. Predisposing factors

  1. Miserable Malalignment Syndrome
  2. Tight lateral Retinaculum
  3. Patella Alta
  4. Patella hypermobility
  5. Vastus lateralis hypertrophy

V. Symptoms

  1. Anterior knee ripping or tearing sensation at injury
  2. Knee flexes with dislocation
  3. Patella relocates with knee extension
  4. Subluxation associated with giving way sensation
  5. Dislocation is associated with severe pain

VI. Signs

  1. Knee held in semi-flexed position
  2. Palpable Patella deviated from normal position
    1. Lateral Patellar Dislocation is more common than medial dislocation
  3. Dislocation
    1. Concurrent osteochondral Fracture in 28-52% patients
    2. Associated with Anterior Cruciate Ligament Tear
  4. Subluxation
    1. Instability and weakness
    2. Reluctant to bear weight
  5. Predisposing factors
    1. Examine for predisposing factors listed above
    2. J-Sign
    3. Quadriceps angle (Q-Angle) >15 degrees

VII. Radiology: Knee XRay

    1. Merchant and Infrapatellar views (knee flex 45)
    2. Anteroposterior, Notch, and lateral views
  2. Interpretation
    1. Often normal
    2. Medial Patella avulsion Fracture
    3. Osteochondral Fracture

VIII. Management

  1. Patella reduction (if still dislocated)
    1. Pre-reduction XRay not needed if isolated Patella dislocation (consider a post-reduction XRay)
    2. Administer IV Analgesics or Anesthesia
    3. Maneuver (two providers)
      1. One provider gently extends knee
      2. Second provider applies gentle pressure to relocate the Patella (medial pressure to relocate a laterally dislocated knee)
  2. Bracing and taping
  3. Alter aggravating activity
  4. Physical Therapy and Rehabilitation
    1. Soft tissue and Patellar mobilization
    2. Muscle Strength
      1. Vastus medialis oblique
      2. Gluteus
      3. Foot and ankle
  5. Consider immobilization
    1. Indications
      1. First Patella dislocation and
      2. No significant Vastus Medialis disruption
    2. Technique
      1. Immobilize for 6 weeks
      2. Knee in full extension
      3. Foam pad protects Vastus Medialis
      4. Lateral support holds Patella medially
  6. Maintenance
    1. Patellar stability program after rehabilitation
  7. Surgery Indications
    1. Inadequate improvement in 6 months
    2. Osteochondral Fracture

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Related Studies

Ontology: Patellar subluxation (C1839733)

Concepts Finding (T033)
English Patellar subluxation