Chapter 41: Internal Fixation

Question 1

316L stainless steel means what?

Answer 1

Low carbon, 0.03% carbon maximum

Question 2

Weakest point of the orthopedic wire?

Answer 2

Method by which it is secured (knot)

Question 3

Name 4 ways to secure/knot an orthopedic wire?

Answer 3

twist
loop
double loop
cable and crimp cerclage

Question 4

How many twists are necessary for the cerclage knot to be secure?

Answer 4

Only 1 to maintain tension in twist cerclage

(The 1.5 is how many turns of the tensioner in a loop cerclage)

Question 5

For a single loop, how many twists of the tensioner need to be in the loop?

Answer 5

At least 1.5 twists (of the tensioner (it’s a distance thing))

Question 6

Twist knot loosens by what?
Loop knot loosens by what?

(Think basic)

Answer 6

Untwisting
Unbending of the folded arm

Question 7

What method of securing an orthopedic cerclage wire is the best?

Answer 7

Double loop - generates more tension and resists greater load before being classified as loose

Question 8

Pushing a twist knot over to lie flat can result in what % of resting load drop?

Answer 8

45-90% better to just cut it short
vibration at cutting 10%
Resting tension drops below 30N after a collapse of only 1% of diameter of structure

Question 9

Name the principles of cerclage wire use?

Answer 9

• at least 2
• oblique fracture
• Fracture length 2.5-3x bone diameter
• Space half a bone diameter apart
• Circumference of bone must be completely restored (column)

Question 10

Pins and screws AMI?

Answer 10

Radius to the fourth power

Question 11

Plate AMI?

Answer 11

Plate thickness to third power

Question 12

IM pins used alone should fill how much of the medullary canal?

Answer 12

70%

Question 13

2 advantages of not reaming with ILN?

Answer 13

Reduced infection and fat embolisation

Question 14

Ideal % of medullary canal filling for nail for angle stable ILN?

Answer 14

75%

Question 15

Incidence of missed distal locking bolt in angle stable ILN?

Answer 15

1% (up to 28% can be missed in normal nails)

Question 16

Name sections of a screw?

Answer 16

Head, shaft, shank, tip

Question 17

Screw pull-out is determined by which four factors?

Answer 17

Outer diameter
strength of material
core diameter (bending strength of the screw)
AMI (r4)

Question 18

Optimal tightness is what % of the stripping torque?

Answer 18

70%

Question 19

Stripping torque is determined by what?

Answer 19

Thickness and quality of bone engaged and design of screw threads

Question 20

What is the longitudinal and transverse angulation for screws in an LCP?

Answer 20

40 degrees longitudinal and 7 degrees transverse screw angulation

Question 21

In an LCP combi hole, a screw in neutral position moves how much?
In compression?

Answer 21

Neutral: 0.1mm
Compression: 1mm

Question 22

If the opposite cortex can be reconstructed, what is improved?

Answer 22

The AMI of the construct

Question 23

3 Advantages of scalloping edges?

Answer 23

Improved vascularity, reduced AMI of solid section of plate and there is little stress concentration at the screw holes, a bend can be distributed over the whole length of the plate and not just at the screw holes
- Screw hole is also more open allowing for greater angulation of a screw

Question 24

Because the tightest screw experiences the largest load, the strength of construct can increased (up to a point) by increasing what?

Answer 24

Screw torque

Question 25

Plate loosening of a conventional plate will occur if axial load exceeds what?

Answer 25

Frictional force

Question 26

Failure of locking screws requires failure of large areas of bone through _____ force rather than failure of a single screw by axial pullout?

Answer 26

compressive force - cortical bone is much stronger against compressive loads than shear loads

Question 27

You can decrease plate strain and likelihood of plastic deformation and plate failure by doing what (4 things)?

Answer 27

Spanning long segments of bone >3 x length of fractured segment - Limiting screw to hole ratio of <0.5 Limiting distance between bone and plate to 2mm - Leaving 2-3 empty holes over bone defect

Question 28

Why does the smaller head of locking screws not matter vs. cortical screws?

Answer 28

Minimal impact on construct strength because axial pull out is less of a concern for locking screws than for cortical screws

Question 29

What are the polyaxial locking systems?

Answer 29

PAX PLS EvoLox Eickloxx

Question 30

Taragon ILN should not be used in which cat bone?

Answer 30

Humerus (fissures/fractures most common followed by neurovascular damage)

Question 31

The star drive of an LCP screw allows for what % greater insertional torque?

Answer 31

65%

Question 32

Describe a neutralization implant:

Answer 32

Implant used after rebuilding the bone column. Neutralizes the forces on bone. Used in simple fractures or articular where reconstruction is vital. Can damage the blood supply (must be contoured against bone)

Question 33

Describe a bridging implant:

Answer 33

Attaches to the major portions of the proximal and distal fragments to bear the load. Maintains the fracture hematoma usually.

Question 34

Describe a buttress implant:

Answer 34

Supports a fracture near a joint.

Question 35

Fracture planning: What is step 1? Step 2?

Answer 35

Step 1: Can it be reconstructed? (if not, must bridge) Step 2: Should it be reconstructed? (If not, must bridge)