Fact-sheet: Femoropatellar dysplasia


Updated on 09/30/2019 at 6:14 PM

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Definition

Patellofemoral joint malformation

  • Predisposing factor for: patellofemoral chondropathy
  • Patellar dislocation
  • intra-articular foreign body
  • Main factors:
    Femoral trochlear dysplasia
  • Patellar tilt
  • Patellar height
  • TT-TG

Clinical features

3 clinical syndromes:

  • Objective patellar instability
  • Potential patellar instability
  • Painful patellar syndromes

Radiography

  • Femoral trochlear dysplasia: strict lateral radiograph
  • Crossing sign between the trochlear floor line and the anterior border of both condyles
  • Maldague: d < 5 mm
  • Patellar height abnormalities: strict lateral radiograph
  • Caton-Deschamps index: AT/AP = 1
  • Patella alta: AT/AP > 1.2
  • Patellar tilt: strict lateral radiograph
  • Patellar ridge posterior to the lateral facet
  • TT-TG distance abnormalities: distance between the tibial tuberosity and the trochlear groove: D > 20 mm

CT

  • Femoral trochlear dysplasia, stage A: crossing sign
  • Stage B: A + supratrochlear spur + flat trochlea
  • Stage C: B + double contour sign on radiograph + medial facet hypoplasia and convexity of the lateral trochlear facet
  • Stage D: C + supratrochlear spur

Management

  • First-line imaging: AP, lateral, and 30-degree axial (Merchant) views
  • Lateral view: trochlear dysplasia
  • Patellar tilt
  • Patellar height
  • If history of dislocation and radiographic abnormalities: CT
  • Lesion work-up: CT arthrography, MRI, MR arthrography