Bone Fracture Repair

Question 1

Possible fracture radiology

Answer 1

* 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)

Question 2

What are the possible nature’s of fractures?

Answer 2

Traumatic, Stress, Pathologic (e.g. renal disease)

Question 3

What are the energy levels of trauma?

Answer 3

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.

Question 4

Terms of each.

Answer 4

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

Question 6

Salter Harris Classification

Answer 6

Description of articular fractures. Is epiphysis involved or also some portion of the metaphysis?

Question 7

Overridden

Answer 7

Pull of muscles resulted in fractures moving towards each other.

Question 8

Luxation

Answer 8

Dislocate

Question 9

Gustilo-Anderson Classification

Answer 9

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.

Question 10

Planning for implants

Answer 10

* 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.

Question 11

Why are nutrient foramen important for us to know their locations?

Answer 11

Can be mistaken for a fracture.

Question 12

Blood supply to the bone- what happens after a fracture?

Answer 12

Extraosseous supply of healing bone. Transient. Then normal system is reestablished. Preserve soft tissue attachments and blood supply as much as possible.

Question 13

Direct Bone Union

v.

Indirect Bone union

Answer 13

Internal remodelling. No intermediate cartilage stage/ endochondral ossification

Question 14

Inter-fragmentary Strain Theory

Answer 14

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.

Question 15

Bone is not very tolerant of strain (instability), but what tissues are tolerant?

Answer 15

Haematoma, Granulation Tissue- 100% for both

Cartilage not as tolerant- 15% but more so than bone (<2%)

Question 16

Contact Healing

vs.

Gap Healing

Answer 16

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.

Question 17

Indirect Bone Union

Answer 17

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.

Question 18

aims of a surgeon with a fracture

Answer 18

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

Question 19

Visco-elastic

Answer 19

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

Question 20

Anisotropic

Answer 20

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)

Question 21

Answer 21

Bending and compression= butterfly fracture

Question 22

Answer 22

Torsional forces= spiral crack (~45 degrees)

Question 23

What is meant by bones are NOT pure cylinders? Using the femur as an example.

Answer 23

Differential loading

Question 24

What is a problem with a cast?

Answer 24

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.

Question 25

Tension band wire

Answer 25

Neutralizes tension caused by muscle contraction.

Can also use a plate to neutralize tension forces.

Question 26

Answer 26

Pins with interlocking nails. Implant placed in the neutral axis of the bone. Neutralization of torsional forces and also bending forces.

Question 27

Answer 27

Comminuted fracture- so it cannot withstand force therefore plate is necessary for healing.

Some type of plate fixation.

Question 28

A small increase in the radius of our pin, does what to AMI (area moment of inertia)?

What does an increase in height do?

Answer 28

Radius ^ 4

vs.

AMI (area moment of inertia) of the plate Height^3

Question 29

Comminuted fracture of the tibia- what are we doing here?

Why? 2 reasons!

Answer 29

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.

Question 30

Gardiner’s Approach vs. Carpenter Approach

Answer 30

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.

Question 31

What are the three factors in the fracture assessment score when determining how robust our intervention needs to be? Explain a little on each.

Answer 31