Updated: 10/10/2016

Congenital Dislocation of Patella

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  • A congenital, irreducible, lateral dislocation of the patella
  • Epidemiology
    • incidence
      • rare
    • demographics
      • usually dislocated at birth
        • often missed or misdiagnosed
      • can be reduced at birth with subluxation and later fixed dislocation in childhood
  • Pathophysiology
    • pathoanatomy
      • osseous abnormalities
        • small or absent patella
        • hypoplastic trochlea
        • external tibial torsion
      • soft tissues abnormalities
        • thickened, tight lateral structures including
          • iliotibial band
          • retinaculum
        • tight quadriceps
          • causing superiorly subluxed patella
  • Associated conditions
    • Larson syndrome
    • arthrogryposis
    • diastrophic dysplasia
    • nail-patella syndrome
    • Down syndrome
    • Ellis-van Creveld syndrome
  • Osteology
    • the patella is the largest sesamoid bone
    • ossification
      • males at 4-5 yrs. old
      • females at 3 yrs. old
      • accessory ossification center appears between 8-12 years 
      • separate fragment attached to patella by fibrocartilaginous tissue
  • Function
    • fulcrum for the quadriceps
    • protects the knee joint
      • articular cartilage of patella is thickest in body (up to 1cm)
    • enhances lubrication of the knee
    • see complete knee biomechanics 
  • Blood supply
    • blood supply to patella is predominantly from distal to proximal
    • 6 arteries contribute  
      • from popliteal artery
        • superior lateral geniculate artery
        • superior medial geniculate artery
        • inferior lateral geniculate artery
        • inferior medial geniculate artery
      • from superficial femoral artery
        • supreme geniculate artery
      • from anterior tibial artery
        • recurrent anterior tibial artery
  • History
    • associated syndromes present
  • Symptoms
    • delayed walking
      • can mimic cerebral palsy
  • Physical exam
    • inspection
      • genu valgum
      • knee flexion contractures
      • "smiley face" appearance of knee caps  
      • femoral condyles abnormally prominent
      • small patella which is difficult to palpate laterally
    • motion
      • limited active flexion  
      • as genu valgum worsens, patella subluxes posteriorly causing quadriceps to act as knee flexor 
  • Radiographs
    • recommended views
      • not helpful in children younger than 3 years old because patella is not ossified
      • in children > 3 years of age
        • AP lateral and sunrise   
    • findings
      • dislocated patella
      • hypoplastic trochlea
  • Ultrasound or MRI
    • indications
      • children <3 years of age
        • can help diagnose non-ossified, dislocated patella
  • Nonoperative
    • observation
      • indications
        • for most part not recommended as the condition impairs long term function if left untreated
  • Operative
    • surgical reduction (Andrish technique)
      • indications
        • perform early to allow for trochlear intervention
      • technique (below)
  • Surgical reduction (Andrish technique)
    • soft tissue reduction steps
      • divide and lengthen lateral retinaculum between oblique and transverse layers
      • dissect vastus lateralis from intermuscular septum and advance proximally on quadriceps tendon
      • release distal patellomeniscal ligaments
      • lengthen quadriceps tendon, shorten patellar tendon to correct patellar alta
      • tighten medial structures via medial patellofemoral reconstruction
        • reroute semitendinosus through medial collateral ligament and attach to patella
    • osseous realignment
      • distal realignment usually not needed with adequate release
      • if needed, realignment limited due to tibial tubercle apophysis
        • Roux-Goldthwait is preferred
  • Recurrence

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