Nonunion and Bone Defects

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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
  - smoking
  - 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 the infection isn’t eradicated
    - a staged approach is often important
    - modalities
      - need to remove all infected/devitalized soft tissue
        
        use antibiotic beads, and 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
    - the 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
    - the issue with fixation, not the biology
    - modalities
      - internal fixation with the 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 the gold standard
        
        BMPs
        
        osteoconductive agents (ie. crushed cancellous chips, DBM)
      - establishment of healthy soft tissue flap/envelope