UNIT 6E: External Fixators

Question 1

What is the basic structure of an external fixator?

Answer 1

Pins drilled into the bone to which a metal beam is attached in parallel to the long axis of the bone

Question 2

What are the advantages of external fixators?

Answer 2

Allows access to the soft tissues

Very versatile

Question 3

List 5 uses of external fixation in orthopaedics

Answer 3

Limb lengthening

Limb shortening

Joint fusion (arthrodesis)

Correction of angulatory or rotatory deformity

Bone segment transportation

Question 4

How can post-trauma use of external be divided?

Answer 4

Temporary or definitive

Question 5

Which type of injuries in temporary external fixation most useful?

Answer 5

Open fractures with extensive soft tissue damage

Question 6

What are the benefits of temporary external fixation?

Answer 6

Access to the tissues

Elevation of the limb

Fixation technique can be changed once soft tissues have healed

Can be used in lie threatening situations where speed is essential

Question 7

What are the common sites for application of external fixation?

Answer 7

Tibia
Femur
Humerus

Question 8

What are 2 principles to be considered when constructing frames/

Answer 8

The bone/frame construct should be stable (i.e. not rigid)

Pin placement must not tether soft tissues or restrict access to wounds

Question 9

What are bilateral frames?

Answer 9

Bone pins positioned so they cross both cortices and pass through the skin and sofft tissues on both sides of the limb

Question 10

What are the issues with bilateral frames?

Answer 10

Cause soft tissue tethering

Limit limb motion (painful and limits rehab)

Question 11

Describe the design of a unilateral frame

Answer 11

ass through the skin on one side of the limb - enter the proximal corted - end by just passing through the opposite cortex

Question 12

What are the advantages of unilateral frames?

Answer 12

Confer adequate stability
Permit mobilisation

Excellent access to wound

Keep soft tissue tethering to a minimum

Question 13

Why is fracture stability rather than rigidity more desirable?

Answer 13

Rigidity may inhibit bone healing (balance so callous formation is not inhibited and fracture alignment is maintained)

Question 14

What 6 factors determine the stability of an external fixator?

Answer 14

The configuration of the frame

The degree of contact between the bone ends

he extent of the soft tissue injury

The quality of the bone/pin interface

The degree to which the clamps have been properly tightened

The total number of pins used

Question 15

Which direction of strain is thought to be a good stimulus for healing bone?

Answer 15

Strains along the long axis of the bone

Question 16

If there is no movement at the fracture site what does not form?

Answer 16

Callous

Question 17

What is dynamisation?

Answer 17

The modification of the construct which permits the transition of forces across a fracture without allowing distraction of the fragments

Question 18

When is dynamisation usually used?

Answer 18

When soft tissues are well on the way to healing

The simple unilateral frame is to be used for definitive fracture control

Question 19

What are 5 advantages of external fixators?

Answer 19

Can be assembled and fitted quickly

Can be adjusted later

Beam can be removed to take very clear x-rays or to feel stability of the fracture

Most fixators are versatile and can be used in many sites

Gives excellent access to soft tissues

Question 20

What are 3 disadvantages of external fixation?

Answer 20

Bone/pin interface infection

Loosening

Soft tissue thering

Question 21

How is an infected external fixator pin site treated?

Answer 21

Change to method of treatment

Question 22

Why do bending forces cause loosening rather than damage to the pin?

Answer 22

The pin is stiffer than the bone

Question 23

How can soft tissue tethering be reduced?

Answer 23

Strategic positioning of the pins

Question 24

Which structure becomes tethered typically in external fixation of femur fractures?

Answer 24

QQQuadriceps muscle

Question 25

What complications can occur in the fixator itself?

Answer 25

Modular components may work loose

Loss of fracture stability

Question 26

What is a sign that pins may be loosening?

Answer 26

Painful pins

Question 27

How should old loose infected pin sites be investigated and how does this affect treatment?

Answer 27

X-rays - if sequestra (areas of dead bone) which may be ring shaped are present these should be drilled out and the wound cleaned

Question 28

How are tight infected pin sites treated?

Answer 28

May be retrieved by aggressive wound cleaning (surgery if necessary) and systematic antibiotics

Question 29

What considerations should be taken to avoid soft tissue tethering on insertion?

Answer 29

Pass through as little muscle as possible

Joint position

Question 30

Are fixators crossing joints good or bad?

Answer 30

Bad - will cause joint stiffness - should be removed as soon as possible

Question 31

What should be done to minimise the incidence of malunion and nonunion?

Answer 31

Regular check ups (clniically and with x-rays)

Question 32

If infection is present but the external fixator is holding the fracture in a stable configuration and the bone pins are not involved how should it be treated?

Answer 32

Local surgery and systemic antibiotics until union

Question 33

What material is being investigated for fixation devices that dissolve away?

Answer 33

Polyglycolates