1. Delayed healing—causes and treatment principles
Published: July 2013
David Elliott, UK
AOT Basic Principles Course

2. Learning outcomes List factors leading to nonunion
Understand the difference between delayed union and nonunion
Discuss how these complications might be avoided in fracture management
Outline the principles of treatment of nonunion
Teaching points:
Highlight the impact of disrespect of biomechanics and biology in leading to delayed healing.

3. Definition of disturbed bone healing
Delayed union—failure to consolidate within the normally expected time for fracture types and location
Nonunion—the opinion of the treating surgeon is that healing will not occur without intervention
Pseudoarthrosis—Formation of a false joint where a fibro-cartilaginous cavity is lined with synovial membrane

4. Contact healing
Fracture healing
Primary bone healing with osteonal reconstruction is not really healing
It is the bone going about its usual business of remodelling
Gap healing

5. Secondary (indirect) bone healing
True healing process is driven by inflammatory response to injury
Described in four stages:
Inflammation
Soft callus
Hard callus
Remodelling

6. Requirements for bone healing
Bone healing organ (BHO) is a hypothetical temporary structure
Postulating its existence helps us understand the reasons for failure of bone healing
BHO is derived from fracture hematoma and migrating pluripotential stem cells
Appropriate mechanical environment
The bone healing organ (BHO) is a hypothetical temporary structure, but postulating its existence helps us understand the reasons for failure of bone healing.
BHO is derived from fracture hematoma and migrating pluripotential stem cells.
Appropriate mechanical environment

7. Bone healing organ (BHO)

8. Bone healing organ (BHO)
Formation adversely affected by:
Open fracture
High energy (soft-tissue disruption)
Subcutaneous bone, intraarticular bone
Surgery?

9. Bone healing organ (BHO)
Performance adversely affected by:
Presence of carbon monoxide (smoking)
Poor blood supply (microvascular disease)
Infection
High strain environment (instability)

10. Bone healing organ (BHO)
Type of tissue formed is dependent on the mechanical environment
Interfragmentary Strain Theory of Fracture Healing—Stephan Perren (1975)

11. Interfragmentary Strain Theory
Strain:  = L/L (measured in %)
Tissue cannot be formed by the BHO if the interfragmentary strain is greater than the yield tolerance of the tissue concerned

12. Yield tolerances
Bone = 2%
Cartilage = 10%
Granulation tissue = 100%

13. Effect of increasing displacement
 = < 2% bone formation
 = 2–10% cartilage formation
 = 10–100% granulation tissue

14. Effect of increasing fracture gap
 = 10–100% granulation tissue
 = 2–10% cartilage formation
 = < 2% bone formation

15. Angular displacement (bending)

16. Angular displacement (bending)
 = 100%
 = 0%
Asymmetrical strain

17. Four directions of displacement = octahedral strain calculation
There is an app for this calculation: Hooke’s Stress and Strain Calculation.

18. Thinking in terms of the individual cells of the BHO

19. Thinking in terms of the individual cells of the BHO

20. Thinking in terms of the individual cells of the BHO

21. Clinical relevance

22. Clinical relevance

23. Clinical relevance

24. Clinical relevance

25. Clinical relevance

26. Radiology of nonunion
X-rays are blocked by the dense nuclei of metallic atoms
In bony tissue, these are calcium ions
Callus is not radio-opaque until mineralization occurs
Mineralization cannot occur in any zone of a fracture gap until the local strain is 2% or less
Amount and distribution of callus is a radiological marker of the strain environment at the fracture
X-rays are blocked by the dense nuclei of metallic atoms, in bony tissue, these are calcium ions.
Callus is not radio-opaque until mineralization occurs.
Mineralization cannot occur in any zone of a fracture gap until the local strain is 2% or less.
Therefore, the amount and distribution of callus is a radiological marker of the strain environment at the fracture.

27. These two fractures are established, aseptic, mobile nonunions
These two fractures are established, aseptic, mobile nonunions. The patients are of similar age and have both had two previous procedures.
The fracture on the left has no mineralized callus indicating high strain. The fracture on the right has mineralized callus indicating that there has been a period of low strain in some zones of the fracture gap.
At operation both bone ends were fully vascularized in both cases.

28. Treatment of nonunion Restore alignment Stabilize with durable implant
Prevention

29. Alignment Essential to equalize the strain across the fracture gap
Osteotomy may be needed to move the plane of the fracture line closer to perpendicular to the mechanical axis (antishear)

30. Stability
Essential to achieve low interfragmentary strain in order to permit bone formation
Default options
Reamed IM nail for lower limb diaphyseal nonunion
Compression plates for upper limb and metaphysis

31. Exchange nailing
First option in diaphyseal femoral and tibial nonunion
Nonunion occurs because of instability or malreduction
Both must be addressed to heal the fracture
As shown in these x-rays, in this case a larger diameter nail, with stronger polyaxial distal locking bolts, achieved sufficient stability for the nonunion to heal.

32. Compression plating
Implants must be preloaded to achieve a stabilizing compressive force
Prebending the plate and using load screws in the elliptical hole of an LCP may have to be supplemented with a tension or compression device
Lag screws are unlikely to generate sufficient compressive force to adequately stabilize the nonunion
Implants must be pre-loaded to achieve a stabilizing compressive force at the nonunion.
Standard techniques of pre-bending the plate and using load screws in the elliptical hole of an LCP may have to be supplemented with a tension/compression device.
Lag screws, with or without a neutralization plate, are unlikely to generate sufficient compressive force to adequately stabilize the nonunion.

33. Compression plating Longstanding humeral shaft nonunion.
Debridement of pseudarthrosis, creation of “axilla”, plate fixed proximally with locking screws, compression achieved by use of eccentrically placed load screws distally.
This resulted in rapid healing.

34. Circular fixators
Advantage of transferring force along the mechanical axis of the bone
Can store large amounts of energy = large preload = stability at nonunion site
Patient already had exchange nailing with fibular osteotomy. Simple 2-ring frame, note bend in tensioned wires storing energy to compress nonunion site.
This resulted in rapid healing.

35. What about bone grafting?
Many surgeons no longer use cancellous autograft as an adjunct to surgery
Removing existing implants and restoring alignment lead to the formation of a fresh bone healing organ
Considerable doubt as to whether the benefits outweigh the extra morbidity
Many surgeons in the field of nonunion surgery no longer use cancellous autograft as an adjunct to surgery.
The procedures necessary to remove existing implants and restore alignment will lead to the formation of a fresh bone healing organ.
The addition of remotely harvested non-structural autograft may provide local substrate but there is now considerable doubt as to whether the benefits outweigh the extra morbidity.
References:
Ramoutar DN, Rodrigues J, Quah C, et al. Judet decortication and compression plate fixation of long bone non-union: Is bone graft necessary? Injury Dec;42(12):

36. What about non-surgical treatments?
Structure of bone is known and understood right down to an atomic level
It must be possible to influence the chemical reactions or manipulate the microscopic physical/electrical environment
However, clinically relevant experimental data is extremely difficult to produce
Bone is a hierarchical nanocomposite, the structure of which is known and understood right down to an atomic level.
It must be possible to influence the chemical reactions or manipulate the microscopic physical/electrical environment BUT clinically relevant experimental data is extremely difficult to produce due to lack of numbers of homologous cases.

37. Prevention of nonunion
Attend AO course and faithfully follow the principles learned
Embrace the concept of the BHO
Understand why some fractures heal faster than others and some not at all
Importance of soft-tissue handling
Advantages of indirect reduction and minimal access techniques
Use large diameter IM nails where possible
Do not use an all-locked LCP in simple fracture patterns without a tension or compression device
Attend AO course and faithfully follow principles learned.
Embrace the concept of the “bone healing organ” it will help you understand why some fractures heal faster than others and some not at all. It will make you appreciate the importance of soft tissue handling and the advantages of indirect reduction and minimal access techniques.
Use large diameter IM nails where possible.
Do not use an all locked LCP in simple fracture patterns without the addition of a tension or compression device.

38. Take-home messages
Understanding how the local strain environment influences bone formation is crucial
Restoration of alignment and stable fixation with a durable implant
In plate fixation, some energy must be stored (preload) in the construct to confer sufficient stability to allow healing
More research is needed on nonsurgical treatment
Prevention is better than cure
Understanding how the local strain environment influences bone formation is crucial when assessing and treating nonunions.
Cornerstones of treatment are restoration of alignment and stable fixation with a durable implant.
In plate fixation there must be some energy stored (preload) in the construct to confer sufficient stability and allow healing.
More research needed on nonsurgical treatment.
Prevention is better than a cure.