Fracture biomechanics and classification Flashcards
What are the forces that must be neutralized for a fracture to heal?
- bending
- torsion
- compression
- tensino
What determines what forces predominate at a fracture site?
- geometry of fracture
2. location of muscle groups
Compression is good for what type of fracture and bad for what other type of fracture?
- good for transverse fracture to reduce motion
2. bad for oblique fracture because fragments shear past
How are fractures classified?
- extent of soft tissue
- degree of cortical disruption
- geometry
- location in bone
- degree and direction of displacement
What does bending cause?
agnulation
What happens to the bone with bending?
- one side is being compressed (concave) and one side is has tension (convex)
Where is the neutral axis of a bone?
usually in the centre of the medullary canal and is where there is neither tension nor compression
What happens if you fix a bone with something that runs down the neutral axis?
the apparatus will be subjected to less bending force than something running down the outside of the bone
What does torsion cause?
rotation
What is torsion
the tendency for a bone or its pieces to twist around long axis
Where does compressino act?
along the long axis of bone and moves ends of bone twoard eachother
What happens if compression is applied to an oblique fracture?
there is overriding–>shear
What does tension cause?
distraction/avulsion fractures of apophyses (olecranon and calcaneus)
What control do casts and splints provide?
- bending
2. ok torsion
What control do wires provide
- good tension
no others
What control do intramedullary pins provide?
- good bending
no others
What control do interlocking nails provide
- bending
- tension
- torsion
- compression
What control do external skeletal fixation provide?
- bending
- tension–but rare use for this
- torsion
- compression
What control do bone plates provide?
good control of all but
weakest in combined compression and bending
What control do bone plates provide?
good control of all but
weakest in combined compression and bending
When does a bone fracture?
when the magnitude of the force placed upon it at a specific site exceeds its ability to resist the force without deforming permanently
What is a closed fracture?
no wound connecting bone to outside world
What is an open fracture
there is a connection with open world
What is a greenstick gracture
bending or folding fracture. the cortex doesn’t actually break all the way through but bones deforms
What is a fissure?
it is a crack and only involves one cortex and is usually longitudinally oriented
What is a saucer?
a divot that gets taken out of one cortex (e.g. horse 3rd metacarpal)
what is a complete fracture?
both cortices are disrupted
What is a depression
e.g. in skull
What is a transverse fracture?
A fracture perpendicular to long axis of bone
Torsion is a big problem, compression good
What is an oblique fracture?
short or long.
What are the two types of oblique fracutre?
short and long (long is more than twice the diameer of the bone
What is a big problem with oblique fractures?
shearing
What is a spiral fracture
a spiral, shearing also a problem
What are types of comminuted fractures?
- butterfly
- highly comminuted
- segmental
- multiple fracture
What two things determine if a fracture is simple or highly comminuted?
- the magnitude of the force and the speed of the force
What does it mean that bone is a viscoelastic force?
it means that its deformation properties depend on loading rate
Distinguish bone breaking between slow and fast application of force?
- slow application: less force before bone bends and breaks
- fast application: more energy absorbed, but more energy so shatters–more concomitant soft tissue damage (high energy)
Where can fractures be located?
- articular
- physeal
- metaphyseal
- diaphyseal (proximal, middle or distal third)
- condylar/suparcondylar/subtronchanteric
Where can fractures be located?
- articular
- physeal
- metaphyseal
- diaphyseal (proximal, middle or distal third)
- condylar/suparcondylar/subtronchanteric
What are to ways you can describe displacement with regard to fracture?
- displaced
2. non-displaced–suggests intact periosteal sleeve
How do you describe displacement?
by referring to the distal fragment location relative to proximal
How can you describe the angle made by fragments?
describe what way the vertex of the angle is pointing
What are 4 causes of fracture?
- traumatic
- pathologic
- fatigue
- iatrogenic
why do we care about fracture classification?
- strong influence on how will heal
