Bone Fracture Repair Flashcards
Possible fracture radiology
* general anaesthesia is often req’d to obtain good quality radiographs due to potentially painful positive
* minimum of two orthogonal views (at 90 degrees of each other)
* radiography of the contralateral limb may be useful (comparison)
What are the possible nature’s of fractures?
Traumatic, Stress, Pathologic (e.g. renal disease)
What are the energy levels of trauma?
Low energy (non-displaced fracture), high energy (comminuted fracture- displaced or even shattered), very high energy (gunshot- soft tissue overlying the bone important because that is where blood supply comes from to heal the bone).
* Healing will change depending on how much energy has gone into causing the break. AND affects the stability of the fracture and might influence how we treat the fracture.
Terms of each.
Simple= one fracture line
Oblique= longer than one bone diameter or not
Segmental= segment of diaphysis that has a complete cortical rim
Comminuted= MUSH- fragments- they are not complete- no complete diaphyseal there
Avulsion= normally occur at sites of muscle attachment
Depressed fractures= flat bones, typically of the skull
T and Y fractures= Fractures of the elbow- normal fossa- Straight across or Y pattern
Salter Harris Classification
Description of articular fractures. Is epiphysis involved or also some portion of the metaphysis?
Overridden
Pull of muscles resulted in fractures moving towards each other.
Luxation
Dislocate
Gustilo-Anderson Classification
With open fractures.
Type I- wound < 1 cm (least severe)- bone fragment has often poked through
Type II- wound > 1 cm but lots of soft tissue damage, flap or avulsion
Type III- more severe- extensive soft tissue injury. Is there adequate soft tissue for closure (3 different levels)
** Important because they introduce contamination. Bones and screws left for the rest of the animal’s life unless they cause a problem. Except bacteria can adhere to surface of the implant with a sludge that protects them from antibiotics and the body’s immune system. So typically we don’t give antibiotics for the rest of the animal’s life.
Planning for implants
* Bone stock- have we got enough bone for the particular implant (metal stabilizer)
* Bone size
* What fracture forces?
* Which type?
* What size?
Hole should not be greater than 30% of the bone.
Why are nutrient foramen important for us to know their locations?
Can be mistaken for a fracture.
Blood supply to the bone- what happens after a fracture?
Extraosseous supply of healing bone. Transient. Then normal system is reestablished. Preserve soft tissue attachments and blood supply as much as possible.
Direct Bone Union
v.
Indirect Bone union
Internal remodelling. No intermediate cartilage stage/ endochondral ossification
Inter-fragmentary Strain Theory
New gap size vs. what the original gap size was. New bone cannot form if strain between two fragments is > 2%. Strain is high when the change in length is high. If original length of the gap is small, strain is also high.
Think of
Strain= change in length (gap size)/ original length (gap size)
e.g. broken tibia, moving around, unstable, high strain. If you fix tibia but you still have a gap, then there is strain. As long as less than 2%, new bone can form.
Bone is not very tolerant of strain (instability), but what tissues are tolerant?
Haematoma, Granulation Tissue- 100% for both
Cartilage not as tolerant- 15% but more so than bone (<2%)
Contact Healing
vs.
Gap Healing
Contact Healing- Bones are together and healing. Compressed together, rigidly stable then we get new bone forming. Occurs with osteoclasts and osteoblasts- oriented parallel to long axis of the bone. Dont see much callus.
CLINICALLY UNCOMMON. REALISTICALLY USUALLY A MIXTURE.
vs.
Gap healing- we still have bone ends close together less than I mm. But because of a gap- it is more disorganized- not parallel. WOVEN BONE deposited- DISORGANIZED. Subsequently has to be remodelled so it TAKES LONGER.
Indirect Bone Union
Becasue intrafragmentary strain is too high this is what happens. So tissues that are tolerant of high strain form and are laid down further away from the central axis of the bone. They impart stability to the fracture. Therefore strain decreases and NOW BONE CAN FORM!
** callus deposition is a response to instability and results in increasing stability.
aims of a surgeon with a fracture
Preserve vascular supply of the healing bone, provide stability vs. forces acting at the fracture site.
FORCES MUST BE OVERCOME for the fracture to heal.
Thoracic Limbs 30% BW
Pelvic limbs 20% BW at slow walk
5 x this with running and jumping
Visco-elastic
Amount of deformation to rate of loading
Energy stored during deformation is released at time of yield (fracture)
Amount of soft tissue damage is proportional to energy released
When the sum of forces acting on the bone > stiffness = fracture
Bone is anisotropic (fine architecture)
* stronger when loaded longitudinally vs. transversely
* stronger in compressive vs. tension
Anisotropic
Stronger when loaded longitudinally vs. transversely
Stronger in compression vs. tension
The forces acting on bone determine the conformation of the fracture.
Compression = oblique fractures 30-45 degrees angle to the direction of compressive force
Tensile force= transverse fractures- straight across- perpendicular to tensile load
Bending= transverse fractures (think of bone on a bar)
Bending and compression= butterfly fracture
Torsional forces= spiral crack (~45 degrees)
What is meant by bones are NOT pure cylinders? Using the femur as an example.
Differential loading
What is a problem with a cast?
Generally poor at countering forces at the fracture site. Instability is still present. Must immobilize the joint above and below the fracture. Can cause rubbing. Sometimes can become more expensive than a bone plate if you charge properly for each change.
ONLY IN ANIMALS where rapid uncomplicated healing anticipated.
Tension band wire
Neutralizes tension caused by muscle contraction.
Can also use a plate to neutralize tension forces.
Pins with interlocking nails. Implant placed in the neutral axis of the bone. Neutralization of torsional forces and also bending forces.
Comminuted fracture- so it cannot withstand force therefore plate is necessary for healing.
Some type of plate fixation.
A small increase in the radius of our pin, does what to AMI (area moment of inertia)?
What does an increase in height do?
Radius ^ 4
vs.
AMI (area moment of inertia) of the plate Height^3
Comminuted fracture of the tibia- what are we doing here?
Why? 2 reasons!
Using a plate, interlocking nail, and external skeletal fixation
WHY??
Always a race between implant failing- and healing. THEY ALWAYS FATIGUE AND WILL EVENTUALLY BREAK.
Gardiner’s Approach vs. Carpenter Approach
New approach is Gardiner’s Approach. Want to make sure joint surfaces and rotational alignment is the same BUT we dont’ care about the little bits of bone. We want to disturb the soft tissue and vascular supply as little as possible for healing.
What are the three factors in the fracture assessment score when determining how robust our intervention needs to be? Explain a little on each.
