What radiographic and clinical criteria define bone union after plate or intramedullary nail fixation, and when can implant removal be performed?

Radiographic Criteria for Bone Union After Plate or Nail Fixation

Bone union after plate or intramedullary nail fixation is confirmed when bridging callus is visible across at least three of four cortices on orthogonal radiographs, combined with clinical absence of pain and tenderness at the fracture site, typically requiring a minimum of 3-6 months depending on fracture location and complexity.

Radiographic Union Criteria

Standard Radiographic Assessment

• Bridging callus formation across three of four cortices on anteroposterior and lateral radiographs represents the gold standard for radiographic union 1
• Fracture line obliteration or significant callus bridging indicates adequate healing for most long bone fractures 2
• Serial radiographs should demonstrate progressive callus formation without persistent fracture gaps 3

Time to Union by Fixation Type

• Plate fixation: Primary union rates approach 100% for closed fractures, with most achieving union by 3-6 months 2
• Intramedullary nailing: Similar union rates to plating (92.9% vs 95.8%), with comparable healing times of 3-6 months for uncomplicated fractures 2
• Open fractures have significantly higher nonunion rates (all nonunions in one study occurred after open fractures, P=0.0007) and require longer healing times 2

Clinical Criteria for Union

Essential Clinical Signs

• Absence of pain with weightbearing and functional activities at the fracture site 3
• No tenderness on palpation or percussion at the fracture site 1
• Ability to bear full weight without pain or instability 3

Combined Assessment Approach

• Radiographic evidence alone is insufficient; clinical correlation is mandatory 1
• Fracture stability is crucial for bone consolidation and must be maintained throughout healing 1

Timing for Implant Removal

General Principles for Removal

• Implant removal should only be considered after complete radiographic and clinical union is confirmed, typically not before 12-18 months post-fixation 1, 3
• For plate fixation, removal may be performed once solid union is demonstrated with bridging callus on all cortices 3
• Intramedullary nails can remain in situ indefinitely if asymptomatic, as removal is not mandatory after union 1

Specific Timing Considerations

• Minimum 12 months should elapse before considering implant removal to ensure adequate bone remodeling 3
• Earlier removal (before complete remodeling) risks refracture, particularly in high-stress areas 1
• In pediatric populations with conditions like congenital pseudarthrosis, refractures can occur up to 18 years after union, necessitating prolonged implant retention 1

Infection-Related Timing

• In fracture-related infection (FRI), implant retention (DAIR) is only viable within 3-6 weeks of fracture fixation, with success rates of 70-90% 1
• After 10 weeks, DAIR success drops to 51-67%, and implant removal with exchange becomes necessary 1
• Suppressive antibiotic therapy can bridge to bone consolidation before implant removal in infected cases 1

Critical Pitfalls to Avoid

Premature Assessment

• Do not remove implants based solely on time elapsed without confirming radiographic union 3
• Absence of visible fracture line does not equal union; bridging callus must be present 2

High-Risk Scenarios Requiring Delayed Removal

• Open fractures require extended monitoring due to 100% of nonunions occurring in this population 2
• Distal fibula fixation may increase nonunion risk (12% vs 4.1%, P=0.09) and warrants longer observation 2
• Smoking increases nonunion rates and leads to inferior outcomes, requiring extended healing time 1

Malalignment Considerations

• Intramedullary nailing has higher malalignment rates (23%) compared to plating (8.3%), particularly without fibula fixation 2
• Malalignment assessment should occur before declaring union complete, as malunion may require revision 2

Special Considerations

Nonunion Management

• If union is not evident by 6-9 months with persistent pain and no progressive callus formation, consider nonunion and plan revision surgery 4, 3
• Exchange nailing or plate augmentation with bone grafting achieves union in most nonunion cases, with average union time of 8.8 weeks post-revision 3, 5

Implant-Specific Factors

• Intramedullary nails may develop intramedullary bone pedestal formation that complicates future revision if needed 4
• Plate fixation allows for supplemental fixation options without implant removal in complex cases 3, 5