Fracture Biomechanics Flashcards
What is stress? Strain?
external force applied to any cross-sectional area
deformation of a loaded material as compared to its normal form, typically measured in length
What is stiffness?
ability of a material’s ability to resist an applied force (stress)
What is deformation? What is the difference between elastic and plastic?
change in shape due to application of a force (stress)
- ELASTIC: reversible change in shape, where material is able to return to its original shape when load is removed
- PLASTIC: permanent change in shape, where material does not return to original shape when a load is removed
What is a yield point? Ultimate failure point?
point when material begins to deform plastically, where strain exceeds the material’s ability to recover and render it permanently deformed (between elastic and plastic)
when material cannot withstand anymore strain and fails
Stress-strain curve:
- elastic region = bone able to return to original shape
- past yield point = becomes plastic and unable to return to its original shape
What are the 5 forces applied to bone?
- tension
- compression
- torsion
- shearing
- bending
What is compression?
2 opposing forces meet each other on the bone, pressing down/up
What is torsion?
2 opposing forces twist in opposite directions around the bone
What is bending?
forces applied at the ends of bones cause the formation of a compression/tension zone
What are the 2 types of bone?
CANCELLOUS - spongy bone typically located at the ends of bones within the metaphysis and epiphysis, acting as the major shock absorber
CORTICAL - dense, and solid bone primarily located at the diaphysis that only requires 2% strain for failure
What is bone porosity? What does it mean when it is high and low?
ratio of open space to total bone within a bone
- HIGH = long elastic phase and lower yield point (cancellous)
- LOW = steep and short plastic phase, very brittle (cortical)
How does the compression and tension affect cortical bone?
higher compression pressure compared to tension pressure
- osteons are disintegrated with compression
- osteons slide past one another with tension
What is a bone’s anatomic axis? Mechanical axis?
line drawn proximal to distal in intramedullary canal, bisecting the bone in half
load axis - line passing through points of load-bearing points
What kind of fracture is caused by tension?
transverse fractures
What fracture is caused by compression?
oblique
What fracture is caused by torsional forces?
spiral - low energy, shear stress in axial and transverse directions propagating along the tensile stress line
What fracture is caused by bending forces? How is the radius most commonly affected?
butterfly fragment
inner compression, outer tension
What is viscoelasticity?
ability of the viscoelastic material to handle a load placed upon it, depending on the rate at which a load is applied and strain is induced
What is the difference between open and closed fractures?
OPEN = wound near the fracture, either due to the bone or an exterior wound
CLOSED = no breach of soft tissue
What is required to supply a complete description of fractures?
orthogonal - VD/CC, lateral
What’s the difference between Type I and Type II open fractures?
I - wound smaller than 1 cm (puncture), typically created by a bone fragment from the inside that penetrates the skin then retracts + mild/mod soft tissue contusion; simple treatment
II - open wound larger than 1 cm (external source) + soft tissue trauma without extensive soft tissue damage or flaps/avulsions - fracture is typically minimally comminuted
Type I open fracture:
- wound < 1 cm
- fragment causing wound not seen
- wild soft tissue trauma
Type II open fracture:
- larger wound and soft tissue involvement compared to Type I
- no flaps or avulsions