Lecture 15 2/17/25 Flashcards
What are the forces acting on a fracture?
-tension
-compression
-bending
-torsion
What can happen when fractures result from high energy sources, such as projectiles?
liquification of the muscle can occur
What are the unique properties of bone that allow for good fracture healing?
-regeneration capacity
-remodeling of bone in response to stress
How does primary bone healing differ from secondary bone healing?
-primary bone healing involves healing without callus formation and occurs when there is little movement in the fracture gap
-secondary bone healing involves healing with callus formation and occurs with moderate movement in the fracture gap
What are the characteristics of absolute stability?
-fracture is so stable it does not need to form a callus to heal
-allows for direct healing
What are the characteristics of relative stability?
-not as stable; callus is required for healing in order to counter the movement
-allows for indirect healing
-NOT good in joints; can limit mobility with callus formation
How can primordial cells develop into bone?
-directly
-indirectly through cartilage model based on amount of strain in fracture zone
What is strain?
measure of relative movement of the fracture gap under patient loading
How is motion/strain in the fracture gap related to fracture gap size?
inversely proportional
What is the equation for strain?
strain = change in gap width/original width
What are the characteristics of high strain in small gaps?
-small gaps have only a few bridging cells
-any micromotion not contained by absolute stability can exceed the strain tolerance of the involved tissue and destroy the cell structure
What are the characteristics of low strain in large gaps?
-widened gaps have more bridging cells/tissue, allowing the strain to be shared among more cells
-motion no longer creates intolerable strain on individual cells
How much strain is allowed to occur in absolute stability?
around 2 to 5%
How much strain is allowed to occur in relative stability?
around 5 to 20%
What are the characteristics of ultra high stability?
-no movement at all
-lack of movement does not trigger the bone to heal
-results in non-union
What are the characteristics of low stability?
-too much movement
-bone is not able to maintain healing
-results in non-union
What is the required environment for direct bone healing?
-gap less than 2 mm
-no intermediate fibrous tissue
-very little movement
What are the steps of osteonal remodeling?
-osteoclasts cut tunnel into cortical bone
-osteoblasts follow behind and lay down concentric lamellae of bone/osteon
What are the biological requirements for bone healing?
-preservation of blood supply
-anatomical reduction/no gapping
What are the mechanical requirements for bone healing?
-interfragmentary compression/friction
–compression makes gap minimal in size
–friction decreases stability of gap
Which type of fracture cannot undergo primary bone healing?
comminuted
What are the characteristics of relative stability?
-controlled movement at fracture site allows for healing with callus formation
-acceptable reduction is maintained during loading of fractured bone
What are the environmental requirements for indirect bone healing?
-gap greater than 2 mm
-controlled motion
-living bone
What are the steps of indirect bone healing?
-granulation tissue formation
-ingrowth of vessels
-calcification of fibrocartilage
-calcified cartilage progresses to woven bone
-woven bone progresses to lamellar bone
-osteonal remodeling
Why is the callus formation required for osteonal remodeling to occur in indirect healing?
-callus formation establishes absolute stability
-absolute stability is required for osteonal remodeling
What are the steps of indirect bone healing associated with decreases in strain?
-hematoma/granulation: 100% strain
-soft callus: 20% strain
-hard callus: 10% strain
-bone: 2% strain
What are the overall requirements for indirect healing?
-preservation of blood supply
-acceptable reduction
-appropriate length, alignment, and rotation
-movement sufficient to stimulate tissue differentiation while maintaining appropriate strain level
How does strain and stability differ between simple and complex fractures?
-simple fractures have high strain and need absolute stability
-complex fractures have low strain and heal under relative stability
