12 – Fracture Biomechanics and Classification Flashcards
What affects how fractures form?
- The bone involved
- Location within the bone
- Age, species, breed of the patient
- Nature of injury
- Forces acting on the fracture
What are some forces that can cause and act on a fracture?
- Compression
- Tension
- Bending
- Torsion
Compression
- Depends on the type of fracture
- *shearing is NOT a force, but is a result of a force
o Bad for cutting off blood vessels
Tension
- Result in DISTRACTION
- Most common at apophyses, where large muscle masses pull on bone when the limb is bearing weight
- Ex. triceps/olecranon, quadriceps/tibial tuberosity, gluteals/greater trochanter
What is an avulsion?
- Fracture caused by a tensile force
*‘little piece’
Bending
- Happens when a force is applied perpendicular to the long axis of a bone
- Can also result from compression when the proximal and distal ends of the bone are offset
- *results in ANGULATION
Compression and tension sides of a bone (bending)
- When a bending force is applied to a bone, the cortices are compressed on the concave side and distracted on the convex side (‘tension’)
Torsion
- Twisting force applied to a bone
- *results in ROTATION
Most (but not all) fractures are acted upon by a combination of forces: healing process
- Forces that will act upon a fracture once the pieces are realigned are the forces that will need to be NEUTRALIZED in order for the fracture to heal
What forces do we need to control
-compression
-bending
-torsion (especially since ulna is also broken)
(not tension)
-bending
-tension
-will have compression on one side (with tension on the other side)
-NO torsion worries (anconeal process holding it in place)
(mandible)
- not torsion (mandible is held in place)
- not compression (proximal and distal parts are held in place)
- not tension
- *BENDING
What do casts/splints control?
- Good against bending
- Fair against torsion
- Do virtually nothing for compression or tension
What do intramedullary pins control?
- Good against bending, but that is it
What do wires control?
- Help to control tension and produce compression
- Ineffective against other forces
What do interlocking nails control?
- Good against all forces
What do external skeletal fixators control?
- Good against all forces as long as appropriately strong configuration is chosen
What do bone plates control?
- Good against all forces
What are some questions you will ask to figure out how to repair a fracture?
- Is the fracture open or closed?
- What is the fracture geometry and degree of comminution?
- What part of which bone is the fracture in?
- In which direction are the fragments displaced?
Closed fracture
- No wounds connects the bone with the outside world
Open fracture
- There is or has been a connection between bone and outside world
What are the lowest degree of comminution fractures?
- Greenstick: bend and ‘frays’ on the one side
- Fissure: little crack
Saucer fracture
Complete fracture
- 2 separate pieces
