Intramedullary fixation (lewis) Flashcards
1
Q
Intramedullary fixation
A
- Most common form of internal fixation
- Don’t apply carelessly
- Intramedullary implants
- Steinmann pins
- Kirschner wires
- Rush pins
- Interlocking nails
2
Q
Intramedullary fixation
Biomechanics
A
- Three points of fixation
- Proximal epiphyseal/metaphyseal cancellous bone
- Endosteal surface of diaphysis
- Distal epiphyseal/metaphyseal cancellous bone
- Resistant to bending forces
- proportional to diameter of pin4
- No resistance to compression, torsion or tension (unless a locked nail)
- Little resistance to shear
- Unsuitable for sole method of stabilizing comminuted fractures
3
Q
For a comminuted fracture
A
- Use an interlocking nail (if available)
- locking scres through nail creates more stability (rotational stability)
- OR add adjunctive fixater
- two pins: nagates rotational stability and prevents axial collapse
4
Q
Intramedullary fixation
Pin points
A
- Don’t use threaded pins for intramedullary fixation
- Chisel point used to make a pin bounce and deflect
- Trocar used most commonly (for intramedullary fixation I think)
- often cut off tip of pin to keep from piercing hock joint
5
Q
Intramedullary fixation
Insertion
A
- Manually with Jacobs chuck or low-speed power drill
- Normograde
- Pin is inserted at one end of bone
- Driven across the fracture site
- Retrograde (easier)
- Pin inserted through the fracture site
- Driven out one end of bone
- Reduced and driven across the fracture site
- Sometimes end up in joint
- Cant do if it’s a closed fracture
6
Q
Intramedullary fixation
The ends
A
- End cut flush with bone
- less irritation
- difficult to retrieve
- End cut and countersunk
- no irritation
- difficult to retrieve
- ‘Tied-in’ (articulated)
- contributes to stability
- Prevents migration
- Easily retrieved
- Increased morbidity
- Usually used in complex fractures
7
Q
Intramedullary fixtion
Considerations
A
- May be contraindicated in infection
- Lewis says no, bone will heal with good blood supply
- Often inadequate if used along, particularly with comminution
- we are better than this now, don’t do
- Pin migration
- fixation failure
- articular damage
- No applicable to all bones
8
Q
Intramedullary fixation
Kirschner (‘K’) wires
A
- Small diameter (0.8-1.6mm), flexible, trocar tipped pins
- Divergent transcortical
- interfragmentary implants
- Intramedullary implants in small dogs and cats
- Used in manner of ‘Rush’ pins
9
Q
Intramedullary Fixation
Rush pins
A
- Curved, elastic pins
- provides dynamic three point fixation
- True rush pins rarely used
- Kirschner wires or small diameter Steinmann pins often used a rush pins
10
Q
If we can find them we prefer to use K wire with what tip when doing intramedullary fixation?
A
Chisel tip
11
Q
Intramedullary fixation
Dynamic pinning
A
- Dynamic intramedullary cross pins
- ‘in the manner of Rush pins’
- Stress pinning
- Pins are inserted at an angle such that pins deflect off endosteal cortical surfaces
- May provide added strenth
- Commonly used in metaphyseal or physeal fractures
12
Q
Key to dynamic pinning or
cross pinning
A
- Pins will cross well proximal to fracture line NOT at the fracture line
13
Q
Intramedullary fixation
Interlocking nails
A
- Nails positioned within medullary cavity
- Screws penetrate cortex-nail-cortex
- At least one screw (preferably two)
- proximal and distal to fracture
- Screw placement determined with a guide jig
*big diameter nails (6-8mm nails) think about buffy! LOL
14
Q
Interlocking nails
Advantages
A
- Controls bending, rotational & axial forces
- Situated in central mechanical axis
- Placed following closed or open reduction
- Application relatively fast and eash
- Economical when compared with plating
15
Q
Interlocking nails
Instrumentation
A
- Jig
- lines holes in nail parallel with holes in jig
- Proximal end of nail special
- Nail extension
- has a screw
*know which nail to use before implanting it
