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