AO Trauma NA Master Review: Principles, Classification, and Management of Non-Unions

Faculty, Panel, and Operational Framework

• Webinar: AO Trauma North America Webinar.
• Topic: Non-Union: Let’s Solve It.
• Moderator: Dr. Raymond Wright (University of Kentucky, Lexington, KY).
• Faculty Panelists:
  • Dr. Paul Matuszewski (University of Kentucky, Lexington, KY).
  • Dr. Mitchell Bernstein (McGill University Health Centre, Montreal, QC).
• Core Philosophy: Non-union surgery is systematic. Success relies on identifying the initial failure etiology and restoring biology and mechanical stability.

Core Classification and Diagnostic Principles

Morphological Classification of Sterile Non-Unions

Defining Non-Union vs. Delayed Union

• Clinical Threshold: Lack of progressive osseous bridging across serial radiographs over several months.
• Tibia Benchmarks: Absence of bridging callus across at least two cortices by 4 months indicates a high risk of failure.
• Predictive Value: Early bridging within the first 3 months strongly correlates with progression to union.

Systematic Three-Step Clinical Workup

• Step 1: Identify Etiology: Determine why the fracture failed to heal.
  • Extrinsic host factors: Nicotine use, diabetes, endocrinopathies, nutritional deficiencies, NSAID or narcotic abuse.
  • Intrinsic factors: High-energy trauma, infection, extensive comminution, periosteal stripping, bone loss.
  • Surgeon factors: Hardware mismatch, malalignment, inadequate stability, distraction across fracture gaps.
• Step 2: Address Causes Systematically:
  • Eradicate infection.
  • Correct axis and length discrepancies.
  • Provide rigid mechanical fixation and compression.
  • Deliver biological substrate (autograft, canal reamings, BMP).
• Step 3: Individualize the Treatment Strategy: Tailor the plan to patient compliance, soft-tissue tolerance, systemic reserve, and functional demands.

Case 1: Atrophic Tibial Shaft Non-Union Following Polytrauma

Clinical Presentation

• Demographics: 27-year-old male police officer (state trooper); non-smoker.
• Mechanism: High-energy motor vehicle collision resulting in polytrauma.
• Injury Anatomy: Gustilo-Anderson Type 3A open tibial shaft fracture with a 12–14 cm soft-tissue wound, butterfly segment, and ipsilateral tibial plateau fracture.
• Status at 10 Months: All other fractures healed; persistent midshaft tibial non-union with pain during weight-bearing.
• Exam: Antalgic gait, mid-tibial edema beneath an AFO (worn for traumatic peroneal nerve drop foot), neutral coronal/sagittal alignment, no drainage.
• Laboratories: ESR, CRP, WBC, and endocrine markers normal.

Decision-Making: Why Exchange Nailing Was Selected

• Reaming Biology: Reaming stimulates endosteal blood flow and clears intramedullary scar tissue.
• Local Autograft: Reaming flutes deposit osteogenic cancellous bone paste directly around the non-union.
• Stability Restoration: Upsizing the nail by at least 2.0 mm achieves rigid isthmic cortical contact, eliminating the loose “hot dog in a hallway” problem.
• Contraindicated Action: Avoid “taking down” the non-union site. Disrupting fibrous tissue destroys local progenitor cells and extraosseous blood supply.

Patient Outcome

• Treated with reamed exchange nailing (increasing nail diameter by 2 mm).
• Medial cortical bridging and resolving fracture lines appeared by 6 weeks.
• Complete circumferential bridging across $>3$ cortices confirmed at 3 months.
• Returned to full-duty active police work pain-free at 6 weeks.

Case 2: Diaphyseal Tibial Non-Union with Critical Bone Defect

Clinical Presentation

• Demographics: 34-year-old male motorcyclist struck by a car.
• Injury Anatomy: Gustilo-Anderson Type 3B open tibia fracture managed with debridement, intramedullary nailing, and local rotational flap coverage.
• Status at 12 Months: Persistent localized pain, retained intramedullary nail, well-healed soft-tissue flap.
• Imaging: CT scan demonstrated a 20 mm diaphyseal cortical defect without bony contact.
• Laboratories: Slightly elevated inflammatory markers; vitamin D insufficiency.

The Radiographic Apparent Bone Gap (RABG)

• Definition (Will Lack et al.): Average bone gap measured across medial, lateral, anterior, and posterior cortices on orthogonal radiographs.
• Prognostic Threshold:
  •  < 25 mm: Favorable likelihood of union without extensive segmental intervention.
  • Age 25: High failure rate; requires planned bone reconstruction (Masquelet technique or bone transport).

Frame Reconstruction Strategy (Dr. Mitchell Bernstein)

• Patient refused revision internal hardware due to infection anxiety.
• Removed the intramedullary nail and re-reamed the canal to recanalize marrow spaces.
• Left the soft-tissue wound open during reaming to flush debris out rather than leaving it in the defect.
• Applied a circular hexapod external fixator for rigid multiplanar stability.
• Augmented the defect with autologous anterior iliac crest bone graft (AICBG).
• Applied progressive axial compression across the hexapod struts over 7 months.
• Achieved complete bony consolidation without retained internal hardware.

Case 3: Failed Femoral Exchange Nailing with Endocrine Pathology

Clinical Presentation

• Demographics: Pleasant female schoolteacher; non-smoker; BMI 40.
• Injury History: Closed femoral shaft fracture treated initially with an intramedullary nail, followed by an unsuccessful exchange nailing.
• Status at 8 Months: Severe weight-bearing pain preventing work.
• Exam: Antalgic gait, neutral alignment, no signs of Cushing’s syndrome or hirsutism.
• Radiographs: Metadiaphyseal oligotrophic femoral non-union with loose intramedullary hardware.
• Workup: Inflammatory markers normal; labs revealed elevated TSH, decreased free T4 (hypothyroidism), and severe vitamin D insufficiency.

Biomechanics: Why Exchange Nailing Fails in the Metadiaphysis

• Reamed exchange nails rely on an isthmic cortical fit to control motion.
• In the wide metadiaphysis, even a maximum-diameter nail (15 mm) cannot engage the distant cortices.
• The nail allows residual rotational and angular toggle, leading to persistent mechanical failure.
• Nail dynamization was contraindicated: removal of locking screws in the wide metaphysis promotes shear instability rather than axial compression.

Augmentation Plating Over Retained Nail

• Retained the existing intramedullary nail to preserve gross axial and length alignment.
• Inserted a long, contoured locking plate percutaneously along the lateral tension surface.
• Placed locking and non-locking screws around the intramedullary nail to provide multiplanar stability.
• Delivered autologous cancellous bone graft locally through a small accessory incision.
• Corrected underlying hypothyroidism and initiated high-dose vitamin D supplementation.
• Radiographs confirmed bridging callus at 6 weeks, solid consolidation at 3 months, and mature union at 1 year.

Case 4: Hypertrophic Distal Tibial Non-Union with Varus Deformity

Clinical Presentation

• Demographics: 62-year-old male presenting 4 years post-injury with progressive deformity and pain.
• Surgical History:
  • Index distal tibia ORIF using screws alone (failed).
  • Revised to an intramedullary nail (failed).
  • Revised to an exchange nail with allograft (failed).
• Radiographs & Exam: Large, exuberant “elephant foot” callus with 15° of varus deformity originating from the distal tibia.
• Pathoanatomy: The non-union was biologically active (hypertrophic) but mechanically unstable due to varus malalignment.

Deformity Realignment via Ilizarov / Hexapod Concept

• Exchange nailing and plating cannot correct distal angular deformities within dense hypertrophic bone without extensive osteotomies.
• Removed the failed intramedullary nail and distal hardware.
• Re-reamed the canal to recanalize sclerotic bone.
• Performed an adjacent low-energy percutaneous corticotomy (Ilizarov distraction osteogenesis principle) to stimulate local biology.
• Applied a rigid circular hexapod frame to correct the varus deformity gradually using computer software.
• Maintained rigid stability without inserting new internal implants.
• The hexapod was removed at 6 months, revealing complete bridging callus, restored mechanical alignment, and pain-free weight-bearing.

Technical Controversies and Rapid-Fire Consensus

1. The Role of Nail Dynamization

• Panel Consensus: Essentially obsolete in modern fracture care.
• Highly unpredictable in the tibia; risks acute shortening and rotational collapse.
• Occasionally useful in simple, transverse, isthmic femoral shaft fractures, but rarely indicated in clinical practice.

2. Intraoperative Pathology & Frozen Sections

• Routine frozen sections for polymorphonuclear leukocytes (PMNs) per high-power field are unhelpful in aseptic non-unions.
• Chronic mechanical pseudoarthroses harbor baseline non-specific chronic inflammation that complicates interpretation.
• Send deep intraoperative tissue cultures, but rely on macroscopic inspection and preoperative serologies.

3. Screening for Endocrine and Metabolic Deficits

• Routinely check vitamin D (25-hydroxyvitamin D), calcium, phosphate, PTH, and thyroid profiles (TSH, free T4) in patients with unexplained non-unions.
• Vitamin D deficiency is prevalent; empirically treat with 50,000 IU weekly when deficient.
• Refer to an endocrinologist if multiple screening labs are abnormal or if secondary metabolic bone disease is suspected.

4. Augmentation Plating vs. Blocking Screws

• Blocking (Poller) screws improve nail trajectory during insertion but provide minimal long-term axial stability once a non-union develops.
• Augmentation plating over a retained intramedullary nail provides superior torsional, axial, and angular rigidity in metadiaphyseal non-unions.