Unit 6a: Fractures Flashcards
Why might fractures, in general, be getting treated earlier when they could heal by themselves?
More cost effective (reduced hospital stay)
What are the 2 most important mechanical properties of bone?
Strength
Stiffness
What does ‘anisotropic’ mean?
A material has different properties depending on the direction it is loaded
What types of load are long bones most resistant to/
Strongest in compression
Then tension
Weakest in shear
What is the the location and mode of fracture determined by?
The geometry and structure of the bone
The loading mode
The laoding rate
In tension and compression what is the stiffness of a bone proportional to?
The cross sectional area of the bone
larger the area, stiffer the bone
What affects a bone’s mechanical behaviour in bending?
Cross-sectional area
Distribution of bone tissue around a neutral axis
What is the second moment of area?
A measure of the fficiency of a shape to resist bending
What is second moment of area also called?
Moment of inertia
What does a larger second moment of area indicate about a bone?
It is stronger and stifeer ``
Why do long bones have a high second moment of area for the amount of bone material and why is this beneficial?
Because much of the bone tissue is distributed at a distance from the neutral axis - means they are more resistant to bending
What factors affect bone strength and stiffness in torsional loading?
The cross-sectional area
Distribution of bone tissue around a neutral axis
What is the polar moment of inertia?
Th efficiency of a shape to resist torsional loads
Why does the proximal tibia have a higher polar moment of inertia than the distal tibia despite its smaller cross-sec area?
Much of the bone tissue is distributed away from the neutral axis
Where does torsional fracture of the tibia most commonly occur?
Distally
Would an accompanying fibula fracture under torsional load take place lower or higher than the tibia?
Higher (within proximal third) - weakest point
What type of bone is found mid-diaphysis?
Cortical bone
What type of bone makes up the metaphyses?
Cancellous bone
Which type of bone is significantly weaker under axial compressive loading?
Cancellous bone
Give 2 fractures of tibial fracture caused by the weakness of cancellous bone under axial compressive loading?
Supracondylar fracture
Tibial plateau fracture
In adults, in pure bending which side of the bone will fail first and why?
Convex side (as bone is weaker in tension)
In children, in pure bending which side of the bone will fail first?
Concave side
What fracture pattern usually results from pure bending?
Transverse fracture pattern
What fracture pattern results from pure compression?
Oblique
What fracture pattern occurs when bending is superimposed on axial compression and why?
“Butterfly segment”
Bending causes transverse, compression causes oblique
Protruding oblique surface impacts the other surface
What fracture pattern results from pure torsion?
Spiral fracture
What angle is the fracture at compared to the axis about which the torque is applied?
45 degrees
What causes the fracture line in a spiral fracture?
Failure of the bone in tension perpendicular to the crack
Where do fractures occur in pure axial compression and why?
Close to or within the metaphyses - because cancellous bone is weaker than cortical bone
What type of loading causes most long bone fractures?
Combination of more than one mode of loading
How does loading rate affect bone strength?
Stronger at a higher loading rate
How does the energy absorption capacity of bone compare when it is loaded to failure by impact compared to slowly?
Impact energy absorption can be twice as high as when it is loaded slowly
What pattern is caused by high energy fractures?
Comminuted fracture with sever soft tissue damage
What pattern is likely to be caused by a low energy fracture?
Spiral fracture
What is a haematoma and why does it occur after fractures?
Collection of blood - occurs because broken bone and damaged soft tissues bleed and cause a build up of blood around the damaged area
