Ch. 41 and 41 Internal and External Fixation Flashcards
How does a plate or implant used for a fracture with anatomic resconstruction aid?
the implant acts as a neutralization implant
what are the principles of biological osteosynthesis?
- indirect fracture reduction using limited surgical approaches with minimal disturbance of the hematoma
- fracture stabilization using bridging implants rather than anatomic reconstruction and rigid fixation
- limited reliance on secondary implants
- limited, if any, use of bone grafts
what is the relationship of tensile strength to size of wire?
related to the cross sectional area = pi x radius^2
what size wire is 18 gauge? what is its relative tensile strength
18 gauge is 1 mm and has a relative tensile strength of 1 - it is what we use to compare things to
what size wire is 16 gauge and what is its relative tensile strength?
- 2 mm
1. 4 tensile strength
what size wire is 20 gauge and what is its relative tensile strength?
0.8 mm and 0.64x
what size is 22 gauge wire and what is its relative tensile strength?
0.6 mm and 0.36x
what size is 24 gauge wire and what is its relative tensile strength?
0.5 mm and 0.25x tensile strength
what is the loop tension and load resisted before loosening for a twist cerclage
70 N
270 N
what is the loop tension and load resisted before loosening for a single loop cerclage?
165 N and 260 N
that is the loop tension and load resisted before loosening for a double loop cerclage?
390 N and 662 N
what is a Morse taper?
the screw-cone peg that was the locking bolt of the first generation angle stable interlocking nail
The area moment of intertia in the solid section of an 8 mm interlocking nail is approximately ___ times that of a 3.5 mm DCP and ___ times that of a Broad 3.5 DCP
The area moment of intertia in the solid section of an 8 mm interlocking nail is approximately 6.8 times that of a 3.5 mm DCP and 3.5 times that of a Broad 3.5 DCP
what are the four advantages of an ILN?
- placed in neutral axis so subjected to compressive forces instead of bending
- greater AMI for ILN than for a plate - the plate is to the third power bc it is a rectangle but the ILN is to the fourth power because it is a cylinder - so the AMI goes up much faster as you increase in implant size for an ILN than plate
- stability in torsion and compression with the locking of the nails
- eliminates any risk of screw pull out
where is an ILN the weakest?
when bending occurs in a plane parallel to he long axis of the nail cannulation
–> decreasing cannulation size results in a stronger nail
As an example, a 6 mm nail accepting a 2.7 instead of 3.5 screw lead to a 52 fold increase in nail fatigue… but then those screws broke easily so finally someone made a bolt
what percent of the medullary canal should you fill with an ILN?
70%
what does it mean to secure a nail in dynamic mode?
only place bolts in one fragment
requires that a fracture be load sharing to try this
what two factors determine pull out strength of a screw?
the outer diameter and the strength of the material into which it is placed
what determines the bending strength of a crew?
the core diameter
what percentage of a screws’ stripping torque is the optimal tightness of a screw?
70%
how much more torque can be applied for a star head vs hexagonal head?
65% more
how much angulation can be given for a locking screw in the PAX securos system?
10 degrees
for bridge plating, what is the recommended plate span ratio for comminuted versus simple fractures?
2-3 times the length of the fracture if comminuted
8-10 times the length of the fracture if simple
what is the best age to apply elastic plate osteosynthesis?
younger than 5-6 months
what percent of the canal should be used for the IM pin in a plate rod construct?
35-40%
BEcause for every 10% in canal filling, plate strain is decreased by 20% but you don’t want more than 40% or there is too much rigidity
how does the traditional positive profile transfixation pin compare to the Duraface negative profile pin in terms of stiffness, pin strength, and resistance to cyclic fatigue?
Duraface has 55% increase in stiffness, 54% increase in strength and 2.3-4.9 times increase in cyclic fatigue
which will add more stability to an ex fix frame, a diagonal or articulating bar? what is the difference between the two?
a diagonal crosses the fracture gap
an articulating bar does not
a diagonal will add more stability than an articulating bar
by how much will adding an ex fix to an ILN decrease torsional compliance and bending compliance?
adding an ex fix to an ILN decreases torsional compliance by 25% and bending compliance by 60%
how big should the acrylic bar be in a free form ex fix?
acrylic bars should be 2-2.5 times the diameter of the bone
alternatively, they should be 3-4 times the size of a stainless steel bar to reach a similar stiffness
where along the bone should you place ex fix transfixation pins in relation to the joints or fracture?
place pins 3/4s of the bone diameter away from adjacent joints and 1/2 of the bone diameter away from the fracture line
what strategies can be used to strengthen the pin bone interface junction and pin pull out strength?
- pin type - use threaded pins
- pin size - threaded portion should be 20-30% of the bone diameter
- pin placement - central placement through the widest part of bone available
- insertion technique - low speed <300 rpm and pre drill
what strategies can decrease the load and bending forces per pin in an ex fix?
- adequate pin number - 3-4 pins per fragment
- decrease pin working length - place clamp with bolt toward patient and no more that 1 cm from surface of skin
- pin configuration and frame stiffness - far-near-near-far pin placement, multiplanar frame, augmentations (articulation, diagonals, intramedullary pin)
