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Introduction
  • Sleeve fracture occurs between the cartilage "sleeve" and main part of the patella and ossific nucleus 
  • Epidemiology
    • demographics
      • occurs most commonly in children 8 to 12 years of age
        • when patellar ossification is nearly complete
  • Pathophysiology
    • mechanism of injury
      • indirect injury caused by powerful contraction of the quadriceps muscle applied to a flexed knee
    • pathoanatomy
      • disruption can occur distally, laterally, or proximally
Anatomy
  • Ossification
    • does not begin until 3 to 5 years of age.
    • most patellar fractures occur in adolescents when ossification is nearly complete
    • incomplete coalescence of a superolaterally located accessory center of ossification results in bipartite patella (often confused with fracture)
Presentation
  • History
    • indirect injury
    • not associated with direct blow to the knee
  • Symptoms
    • severe knee pain
  • Physical exam
    • inspection
      • soft-tissue swelling
      • a high-riding patella implies that the extensor mechanism has been disrupted
      • hemarthrosis of the knee joint is often present
    • palpation
      • palpable gap at the lower end of the patella 
    • motion
      • active extension of the knee is difficult; especially with resistance
      • inability to weightbear
Imaging
  • Radiographs
    • recommended views
      • AP and lateral of knee
    • findings
      • small flecks of bone adjacent to inferior pole
      • diagnosis may be missed because the distal bony fragment is not readily discernible on radiographs
      • patella alta
        • for distal fractures (most common)
      • patella baja
        • for proximal fractures
  • MRI
    • indications
      • may be useful for diagnosing a sleeve fracture when the diagnosis is not clear from the clinical and plain radiographic findings
Treatment
  • Nonoperative
    • cylinder cast for 6 weeks
      • indications
        • nondisplaced fractures with intact extensor mechanism
  • Operative   
    • open reduction and internal fixation (modified tension band technique)
      • indications
        • displacement more than 2-3mm
        • majority require ORIF
        • may be performed with sutures through drill holes
Technique
  • Open reduction and internal fixation
    • approach open reduction - periosteal sleeve (white arrow) and inferior pole cartilage (asterisk) opposite cancellous bone of the main patella (black arrow).
      • parapatellar to knee 
        • approach the inferior pole of the patella through a 7-cm medial parapatellar incision
        • make incision over the distal aspect of the approach directly over the inferior pole of the patella 
    • repair
      • repair of the torn medial and lateral retinaculum along with the use of sutures through the cartilaginous and osseous portions of the patella often suffice
    • fixation
      • once anatomic reduction of articular surface achieved, fracture can be stabilized using modified tension band wiring around two longitudinally placed Kirschner wires (A) Patellar “sleeve” fracture. (B) and (C) demonstrate AP and lateral x-ray of the knee after reduction and fixation with Kirschner wires and tension band wiring
    • post-operative care
      • place in cast with knee in mild degree of flexion
      • remove cast at ~3 weeks and start ROM exercises
Complications                                                                                                                                     
  • Patella alta
  • Extensor lag
  • Quadriceps atrophy
 

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