The document provides an overview of fracture healing, detailing biological and mechanical factors that influence the process. It discusses Perren's strain theory, explaining how different levels of interfragmentary strain affect healing pathways, such as direct and indirect healing. Additionally, it covers fixation techniques, factors leading to nonunion, and management strategies for complications like pseudoarthrosis.

1. Fracture Healing and
Mechanical stability
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2. Contents
 Introduction
 Perren`s strain theory
 Fracture healing
 Indirect Healing
 Direct healing
 Fixation techniques and stability
 Nonunion and Management

3. Introduction
 Fracture healing -
 Biological environment –
 Age
 Nutritional status
 Blood supply
 Metabolic
 Mechanical stability –
 Absolute
 Relative
 Surgical procedure Alters biological environment
 Selection of fixation Alters mechanical environment
Outcome

4. Mechanical Stability -
Absolute stability - Direct
healing
Relative stability - Indirect
healing
Interfragmentary strain theory / Perren`s
strain theory

5. Parren's strain theory
Strain
 Relative deformation of a material when a given
force is applied
 Relative changes in the fracture gap divided by
original fracture gap = L / L
 Stability determines the Strain at the fracture site
Stable fixation – less strain
Unstable fixation – high strain
Large gap fracture – less strain
Cross section of the fracture-
L= original gap
length
L= change in
the gap
length

6. Fracture gap strain VS cells response
 The degree of inter fragmentary strain appears to govern the
cellular response.
 Each of these tissues is able to tolerate a different amount of
strain:
 Granulation tissue: up to 100%
 Fibrous connective tissue: up to 10 -17%.
 Fibrocartilage: 2–10%.
 Lamellar bone: < 2%

7. Perren's strain theory….
 When the inter fragmentary strain is <2% bone repair occurs by direct healing
 While for intermediate amount of IFS (5–10%) the fracture heals by indirect healing.

8. Stain theory of healing –Indirect healing
Fracture Strain is high
Strain become less,
stimulate soft callus
formation
Strain become less
Transition
from soft to
hard callus
Indirect
Fracture
healing
Granulation tissue
formation

9. Indirect
Healing
Hematoma formation
-Immediate
-immobilization of the fracture
-facilitate the movement of
inflammatory cells and mediators
Acute inflammatory phase
 < 1 week
 Remove the injuries agents/
necrotic bone
 Granulation tissue formation

10. Indirect Healing…
Soft callus stage - 2-3 weeks
Periosteum - Intramembranous
ossification –
MPC – chondrocytes – cartilage
MPC – fibroblast – ECM
Replacement of the granulation tissue
by fibrous tissue and cartilage.

11. Hard callus formation
Hard callus stage – 3-4 Months
Starts as soon as soft callus bridge the gap
intramembranous + endochondral ossification
Callus formation –
Lowest strain – at periphery of callus
Increase production of the hard callus reduce
the strain center part of the fracture

12. Indirect Healing
Remodeling Stage
 Months to years
 Conversion of woven bone
into lamellar bone
 Formation of Medullary cavity
 Return of biomechanical
property
 Influenced by wolf law –
Remodeling based on stress

13. Stain theory of healing…pseudo arthrosis
Complete instability
 Callus is unable to form because
the strain is too much for it to
tolerate.
 The more strain-tolerant fibrous
tissue forms
 Bone ends are sealed over with
cortical bone
 Formation of false joint with
synovial fluid in the gap

14. Hypertrophic nonunion
Unstable fracture
 Excess callus formation unable to reduce the IFS
 Creates a hypertrophic non union

15. Direct Healing
 Anatomically reduced rigid fixed fractures
 Formation of cutting cones
 >100,000 remodeling units work at time
 Direct osteonal remodeling
 Without callous
 Activation resorption by osteoclasts osteoid formation by osteoclasts
Primary osteons Mineralization

16. Direct Healing….
Healing process dependent on gap size
<0.01mm – Contact healing
0.01mm – 1mm – gap healing
Gap healing
 Gap is filled with woven bone by
osteoblast
 Then haversian remodeling begins with
cutting cones traversing the new bone
in the fracture gap.
Larger gaps
filled with fibrous tissue and under goes
secondary ossification

17. FIXATION TECHNIQUES AND STABILITY

18. Relative stability
Intramedullary nailing
 Load sharing device
 Inter fragmentary micro motion
 Fracture gap strain is usually 2-10%
 Body responds by forming more soft callus
to try and decrease the strain
 Fixation of diaphyseal fractures – strength
and less duration

19. Relative stability
Bridge plating technique
 Comminated fractures
 Strain is get divided within these
fragments
 Less strain favors indirect healing
 External fixation
 POP cast
 Traction

20. Absolute stability
Compression plating
technique
• Fracture site strain is so low <2%
• Low strain inhibit callus formation
• Direct healing will occur
• Fixation of Articular fractures

21. Absolute stability
 TBW
 Lag screw fixation

22. Interfragmentary
strain,
Nonunion and
Management

23. Nonunion ….
 Fracture is fixed rigidly but a gap is present
 Direct healing may not be able to bridge the gap
 The lack of strain may inhibit callus formation
and secondary healing
 Predispose to non-union
 Management –
 Increase the flexibility
 Reduce the gap by compression

24. Nonunion….
a- Hypertrophic nonunion after
unlocked intramedullary nail
b – Instability due to short unlock nail
creating a resorption cavity
C- Additional stability gained by over
reaming and insertion of a thicker and
longer dynamically locked nail

25. Valgus osteotomy – Femoral neck
fracture
Strain is high because of
high shear force
Valgus osteotomy
changes the shear force
into compressive force

26. Management of
pseudo arthrosis
 If bone resection need Oblique
osteotomy is preferred rather
than transverse osteotomy
 Limited compression can be
obtained with a plate
 ``Compression in to the axilla``
technique with a plate and lag
screw

27. Thank You