Biomechanics Of IM Nailing

Question 0

When should an IM nail be used?

Answer 0

Long bone shaft fractures
Meta/diaphyseal instability
Nonunions/malunions
Arthrodesis of knee or ankle

Question 1

What is an IM nail? What does it do? When should it be used?

Answer 1

Internal splint
Load sharing LARDQ
Relative stability 
Maintain alignment
Enables active muscular function
Long bone fracture standard of care

Question 2

Contraindications for IM nails

Answer 2

Soft tissue damage at entry site
Poor bone quality
Infection
Pediatric growth plates

Question 3

Cautioned use for IM nails

Answer 3

Metaphyseal fractures

Polytrauma pts

Question 4

Kuntschers nail limitations

Answer 4

Only for stable, mid shaft fractures

2% of all femur fractures

Question 5

Generations of interlocking nails

Answer 5

1st: transverse GK
2nd: cephalomedullary RT
3rd: advanced trigen

Question 6

What determines the number of screws placed in an IM nail?

Answer 6

Fracture pattern and location. More screws near the fracture site. Fill central holes to prevent levering of the long bone-shorten working length. Empty screw hole=weakest link.

Question 7

What are the interlocking modes?

Answer 7

Static and dynamic

Question 8

Static interlocking screw characteristics.

Answer 8

Screw closest to the fracture prevents motion
No gliding or rotation
Used for all femurs fractures, comminuted or unstable fractures

Question 9

Dynamic interlocking screw characteristics

Answer 9

Screw furthest from fracture site allows gliding along nail axis
No rotation but micromotion
Some tibia fractures - transverse or short oblique

Question 10

How distal/proximal can a fracture be for nailing?

Answer 10

At least 5cm away from the closest interlocking hole.
Too much movement around the screw construct can cause malfunction and breakage–not intended for heavy loading.
If possible use a bigger nail to fill metaphysical area
Broaden angularity of screws-more stable

Question 11

What materials can be used for nails?

Answer 11

Stainless steel (very stiff)
Titanium (less stiff-like normal bone stiffness)

Question 12

Tighter bow means:

Answer 12

Less nail-to-bone contact
Less friction
Easier insertion/removal
Reduced transferral of load

Question 13

Straighter wider bow means:

Answer 13

Better transferral of load
More contact
More risk of fracture during insertion

Question 14

How to select and implant?

Answer 14

Diameter: ream 1-1.5 sizes larger than nail
Femur: 1.5-2
Tibia: 1.0-1.5
Length: go long if possible

Question 15

Things to consider while nailing

Answer 15

Implant selection
Round vs fluted
Load transferral

Question 16

Choice TO nail:

Answer 16

Depends on fracture configuration

especially and proximal and distal ends

Question 17

Choice OF nail:

Answer 17

Depends on fracture location
Associated with musculoskeletal injuries
Obesity