Knee

Patellar Dislocation

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Patellar Dislocation, Patellar Subluxation

  • See Also
  1. Knee Dislocation
  • Definitions
  1. Patellar Subluxation
    1. Excessive Patella laxity in movement with typically lateral displacement
  2. Patellar Dislocation
    1. Severe subluxation with complete displacement of the Patella outside the trochlear groove
    2. Patella does not spontaneously relocate
  • 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)
  • Mechanism
  1. Forceful deceleration with concurrent knee rotation or
  2. Valgus force with strong quadriceps contraction
    1. Results in lateral Patella displacement out of trochlear groove
  • Risk factors
  1. Miserable Malalignment Syndrome
  2. Tight lateral Retinaculum
  3. Patella Alta
  4. Patella hypermobility
  5. Vastus lateralis hypertrophy
  • 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
  • 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
  • Imaging
  1. Knee XRay
    1. Views
      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
  2. MRI Knee without Contrast
    1. Indications
      1. Osseous loose body on XRay
      2. Large joint effusion (hemarthrosis)
    2. Findings
      1. Osteochondral defect
      2. Medial Patellofemoral Ligament (MPFL) Tear
  • Differential Diagnosis
  1. Knee Dislocation
    1. Knee spontaneous reduction prior to presentation may be misdiagnosed as Patella subluxation
    2. Knee Dislocation may occur with low energy mechanism (esp. in Obesity)
    3. Knee Dislocation is a risk for vascular injury, and missed dislocation risks limb loss
  • 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. Non-weight bearing
      4. Foam pad protects Vastus Medialis
      5. 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
    3. Medial Patellofemoral Ligament (MPFL) Tear resulting in recurrent subluxation or dislocation
  • Complications
  1. Osteochondral Fracture
  2. Medial Patellofemoral Ligament (MPFL) Tear
    1. May result in recurrent Patella subluxation or dislocation
  • References
  1. Rashidzada (2020) Crit Dec Emerg Med 34(11): 12-3