Updated: 6/14/2021

Congenital Dislocation of Patella

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  • summary
    • Congenital Dislocation of Patella is a rare congenital knee condition that presents with an irreducible, lateral dislocation of the patella.
    • Diagnosis is confirmed clinically with genu valgum, knee contractures and presence of a patella that is dislocated posterolaterally.
    • Treatment is surgical reduction and stabilization in majority of cases.
  • 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
  • Etiology
    • 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
  • Anatomy
    • 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
  • Presentation
    • 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 posterolaterally causing quadriceps to act as knee flexor
  • Imaging
    • 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
  • Treatment
    • 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)
  • Techniques
    • 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
  • Complications
    • Recurrence
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