External Fixation

Question 1

What is the general indication for external fixation?

Answer 1

Soft tissue concerns - primary or damage control

Question 2

What are the advantages of external fixation

Answer 2

• soft tissue sparing
• early WB

Question 3

What are the disadvantages of external fixation

Answer 3

• psychology
• weight
• infection
• cost

Question 4

What is the rate of infection in external fixation

Answer 4

20-100%

Question 5

What happens if bone is lengthened too slow

Answer 5

Bone develops a callus, preventing distraction

Question 6

What happens if bone is lengthened too fast

Answer 6

There are traction injuries to neurovascular structures and bone which reduced the likelihood of bone consolidation

Question 7

What are the factors of tension-stress effect

Answer 7

• stability of fixator
• distraction rate and frequency (for high frequency instruments, you have to irrigate in order to increase the thermal necrosis threshold)
• osteotomy type and position

Question 8

How long after the osteotomy do you have to wait before you start to distract?

Answer 8

5-7 days

Question 9

What is the ideal rate for lengthening a bone

Answer 9

1 mm a day in four 0.25mm intervals (ie a quarter turn)

Question 10

What is a consequence of excess motion or distraction too quickly

Answer 10

Pseudoarthrosis

Question 11

What is a tensioning device

Answer 11

Stiffens wires and increase stability at bone interface

Question 12

How much tension is needed in cancellous bone

Answer 12

90kg

Question 13

How much tension is needed in tibia and metatarsals

Answer 13

100-110kg

Question 14

What are the steps in inserting a Schanz pin

Answer 14

• drill into bone
• insert Shanz pin
• attach pin to ring with fixation bolt
• rings

Question 15

What are the steps in inserting a wire

Answer 15

• no need to predrill
• insert wire
• secure wire to ring with fixation bolt
• tension the unsecured side
• secure free side to ring with fixation bolt to capture tension
• tensioning device

Question 16

What are the four general principles of external fixation

Answer 16

• soft tissue sparing
• gradual correction
• safe zones
• construct stability

Question 17

What are the factors affecting construct stability

Answer 17

• number of pins and trans osseous wires
• pin and wire diameter
• pin spread
• multiplanar orientation
• distance of connecting bar from mechanical axis of bone
• proximity to segment in need of immobilizing
• tensioned wires
• limit use off connecting components
• reducing thermal necrosis

Question 18

What are the different types of external fixation?

Answer 18

• unilateral frames - pins
• multiplanar from - pins
• circular frame - wires
• hybrid frames - wires and pins
• Taylor spatial frame - wires and pins struts,