Intramedullary fixation (lewis)

Question 1

Intramedullary fixation

Answer 1

• Most common form of internal fixation
• Don’t apply carelessly
• Intramedullary implants
  
  • Steinmann pins
  • Kirschner wires
  • Rush pins
  • Interlocking nails

Question 2

Intramedullary fixation

Biomechanics

Answer 2

• Three points of fixation
  
  1. Proximal epiphyseal/metaphyseal cancellous bone
  2. Endosteal surface of diaphysis
  3. 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

Question 3

For a comminuted fracture

Answer 3

• 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

Question 4

Intramedullary fixation

Pin points

Answer 4

• 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

Question 5

Intramedullary fixation

Insertion

Answer 5

• 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

Question 6

Intramedullary fixation

The ends

Answer 6

• 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

Question 7

Intramedullary fixtion

Considerations

Answer 7

• 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

Question 8

Intramedullary fixation

Kirschner (‘K’) wires

Answer 8

• 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

Question 9

Intramedullary Fixation

Rush pins

Answer 9

• 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

Question 10

If we can find them we prefer to use K wire with what tip when doing intramedullary fixation?

Answer 10

Chisel tip

Question 11

Intramedullary fixation

Dynamic pinning

Answer 11

• 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

Question 12

Key to dynamic pinning or

cross pinning

Answer 12

• Pins will cross well proximal to fracture line NOT at the fracture line

Question 13

Intramedullary fixation

Interlocking nails

Answer 13

• 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

Question 14

Interlocking nails

Advantages

Answer 14

• 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

Question 15

Interlocking nails

Instrumentation

Answer 15

• 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

Question 16

Key to Interlocking nails

Answer 16

• Adds tons more stability
  
  • rotational forces
  • axial forces

Question 17

Intramedullary fixation

Femur

Answer 17

• Highly preferable to place pins normograde
  
  • Just medial to greater trochanter
  • avoid sciatic nerve
• ‘Over reduction’
  
  • allows better purchase distally
  • prevents anatomic reconstruction
• Easily augmented with external fixation

*dog femurs bow caudally

Question 18

Intramedullary fixation

Tibia

Answer 18

• Normograde (I guess this is the only way) TQ
  
  • craniomedial aspect of tibial plateau
  • extra-articular cranial to menisci
• Do not enter hock distally
  
  • cut off tip of pin
  • don’t drive pin to end of malleolus

*Tibia runs down medial side of leg

Question 19

DO NOT DO INTRAMEDULLARY FIXATION ON:

Answer 19

• Radius
  
  • not amenable to intramedullary fixation
• Stress pinning of physeal fractures is acceptable
  
  • for salter fracture of distal radius (incredibly rare)

Question 20

Intramedullary fixation

Humerus

Answer 20

• Retrograde placement most common
  
  • can do normograde also
• Exits proximally through greater tubercle
• Seated distally in or proximal to medial portion of condyle