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Updated: Jan 23 2024

Nonunion and Bone Defects

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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
    • Laboratory evaluation
      • CBC, ESR, CRP
        • must rule out infectious etiology
      • total protein and serum albumin 
      • vitamin D, TSH, PTH
        • Vitamin D deficiency is the most commonly encountered nutritional deficiency (60-70%)
  • 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
          • synovial pseudoarthroses
          • mobile nonunions
          • 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
        • 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
        • 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
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