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Introduction
  • Patella fractures account for 1% of all skeletal injuries
    • occur either by direct impact injury or indirect eccentric contraction
    • male to female 2:1
    • most fractures occur in 20-50 year olds
  • Patella sleeve fracture
    • seen in pediatric population (8-10 year olds)
    • high index of suspicion required
  • Bipartite patella 
    • may be mistaken for patella fracture 
    • affects 8% of population
    • characteristic superolateral position
    • bilateral in 50% of cases
Anatomy
  • Patella is largest sesamoid bone in body
  • Articular cartilage thickest in body (up to 1cm)
  • Most important blood supply to the patella is located at the inferior pol
Classification
  • Can be described based on fracture pattern 
    • nondisplaced
    • transverse
    • pole or sleeve (upper or lower)
    • vertical
    • marginal
    • osteochondral
    • comminuted (stellate)
Presentation
  • Physical exam
    • palpable patellar defect 
    • significant hemarthrosis
    • unable to perform straight leg raise indicates failure of extensor mechanism 
      • retinaculum disrupted
Imaging
  • Radiographs
    • patella alta 
    • fracture displacement
      • best evaluated on lateral x-ray
      • degree of fracture displacement correlates with degree of retinacular disruption
  • MRI 
    • obtain MRI if child has normal xrays but is unable to straight leg raise
Treatment
  • Nonoperative
    • knee immobilized in extension (brace or cylinder cast) and full weight bearing
      • indications
        • intact extensor mechanism (patient able to perform straight leg raise)
        • nondisplaced or minimally displaced fractures
        • vertical fracture patterns
      • early active ROM with hinged knee brace
        • early WBAT in full extension 
        • progress in flexion after 2-3 weeks
  • Operative
    • ORIF with tension band construct
      • indications
        • preserve patella whenever possible 
        • extensor mechanism failure (unable to perform straight leg raise)
        • open fractures
        • fracture articular displacement >2mm
        • displaced patella fracture >3mm
        • patella sleeve fractures in children
      • techniques
        • minifrag lag screw fixation for independent fragments
        • tension bands
          • 0.062 K wires with figure of 8 wire 
          •  longitudinal cannulated screws combined with tension band wires shown to be biomechanically superior 
          • circumferential cerclage wiring 
            • good for comminuted fractures
          • interfragmentary screw compression supplemented by cerclage wiring 
    • partial patellectomy
      • indications
        • comminuted superior or inferior pole fracture measuring <50% patellar height ONLY if ORIF is not possible 
      • techniques
        • quadricep or patellar tendon re-attachment
        • reattachment close to articular surface prevents patellar tilt
        • medial and lateral retinacular repair essential
    • total patellectomy 
      • indications
        • reserved for severe and extensive comminution not amenable to salvage
          • quadriceps torque reduced by 50%
          • medial and lateral retinacular repair essential
Complications
  • Weakness and anterior knee pain 
  • Symptomatic hardware (up to 50%) 
    • most common  
  • Loss of reduction (22%)
    • increased in osteoporotic bone
  • Nonunion (<5%)
    • can consider partial patellectomy
  • Osteonecrosis (proximal fragment)
    • thought to be due to excessive initial fracture displacement
    • can observe these, as most spontaneously revascularize by 2 years
  • Infection
  • Stiffness
 

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