Nonunion and Bone Defects - Basic Science

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
    
    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
    
    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

Action	Numeric Key	Letter Key	Function Key
Show Bullets		S	Enter (frontside only)
20%	1	N
40%	2	H
60%	3	F	Enter (backside only)
80%	4	E
100%	5	M
Toss	0	T