Updated: 7/20/2019

Nonunion

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Introduction
  • A nonunion is an arrest in the fracture repair process
    • progressive evidence of non healing of a fracture of a bone
    • a delayed union is generally defined as a failure to reach bony union by 6 months post-injury
      • this also includes fractures that are taking longer than expected to heal (ie. distal radial fractures)
    • large segmental defects
      • should be considered functional non-unions 
  • Pathophysiology
    • multifactorial
      • most commonly, inadequate fracture stabilization and poor blood supply lead to nonunion
      • infection
        • eradication needs to occur along with the achieving fracture union
      • location
        • scaphoid, distal tibia, base of the 5th metatarsal are at higher risk for nonunion because blood supply in these areas
      • pattern
        • segmental fractures and those with butterfly fragments
        • increased risk of nonunion like because of compromise of the blood supply to the intercalary segment
Classification
  • Types of nonunion
    • septic nonunion
      • caused by infection
      • CRP test as the most accurate predictor of infection 
    • pseudoarthrosis
    • hypertrophic nonunion  
      • caused by inadequate stability with adequate blood supply and biology
      • abundant callous formation without bridging bone 
      • typically heal once mechanical stability is improved 
    • atrophic nonunion
      • caused by inadequate immobilization and inadequate blood supply
    • oligotrophic nonunion
      • produced by inadequate reduction with fracture fragment displacement
Presentation
  • Symptoms
    • important to discern injury mechanisms, non operative interventions, baseline metabolic, nutritional or immunologic statuses and use of NSAIDs and/or nicotine containing products
    • assess pain levels with axial loading of involved extremity 
  • Physical exam
    • important to complete a thorough neurovascular exam, including the status of the soft tissue envelope
    • assess mobility of the nonunion
    • assess extremity for the presence of deformity
Imaging
  • Radiographs
    • plain radiographs are the cornerstone for evaluation of fracture healing; four views should be included
    • full length weight bearing films should obtained if a limb length discrepancy is present 
  • CT
    • if the status of union is in question, a CT scan should be obtained; hardware artifact may limit utility of the CT scan
Treatment
  • Nonoperative
    • fracture brace immobilization 
    • bone stimulators
      • contraindications include synovial pseudoarthroses, nonunions that move and greater than 1 cm between fracture ends
  • Operative
    • infected nonunion
      • often associated with pseudoarthrosis
      • chance of fracture healing is low if infection isn't eradicated
      • staged approach often important
      • modalities
        • need to remove all infected/devitalized soft tissue
          • use antibiotic beads, VAC dressings to manage the wound 
        • with significant bone loss, bone transport may be an option
        • muscle flaps can be critical in wound management with soft tissue loss
    • pseudoarthrosis
      • may be found in association with infection
      • joint capsule may be encountered with operative exposure
      • modalities
        • removal of atrophic, non-viable bone ends
        • internal fixation with mechanical stability
        • maintenance of viable soft tissue envelope
    • hypertrophic nonunions
      • often have biologically viable bone ends
      • issue with fixation, not the biology
      • modalities
        • internal fixation with application of appropriate mechanical stability
    • oligotrophic nonunions
      • often have biologically viable bone ends
      • may require biological stimulation
      • modalities
        • internal fixation 
    • atrophic nonunions
      • often have dysvascular bone ends
      • mobile
      • modalities
        • need to ensure biologically viable bony ends are apposed 
        • fixation needs to be mechanically stable
        • bone grafting 
          • autologous iliac crest  (osteoinductive) is gold standard
          • BMPs
          • osteoconductive agents (ie. crushed cancellous chips, DBM)
        • establishment of healthy soft tissue flap/envelope
Techniques
  • Bone stimulators
    • four main delivery modes of electrical stimulation
      • direct current
        • decrease osteoclast activity and increase osteoblast activity by reducing oxygen concentration and increasing local tissue pH 
      • capacitively coupled electrical fields (alternating current, AC)
        • affect synthesis of cAMP, collagen and calcification of carilage
      • pulsed electromagnetic fields
        • cause calcification of fibrocartilage
      • combined magnetic fields
    • bone simulators work through induction coupling, which stimulates bone growth through the following direct effects 
      • increasing expression of BMP7
        increasing expression of BMP7
      • increasing expression of BMP2
      • increasing expression of TGF-beta1
      • increasing expression of osteoblasts proliferation
      • increasing expression of BMP2
        increasing expression of TGF-beta1
        increasing expression of osteoblasts proliferation

 

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