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Surgery > Sx fx fixation > Flashcards

Sx fx fixation Flashcards

1
Q

Indications of IM pins

A
  • simple fx of humerus, femur + tibia

+/- cerclage wire

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2
Q

Advantages of IM pins

A
  • cheap
  • quick and simple w/ no special training
  • effective when used in appropriate situations
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3
Q

compare normo and retrograde placement methods of IM pins

A
  1. Normograde: Advancement from one end of bone to other - preferred dt decreased change of injury to adjacent jt and important ST structures.
  2. Retrograde: pin driven from fx through one end of bone and then driven back into opposite end of the bone. Contraindicated in tibial fractures.
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4
Q

4 main fracture forces

A
  1. Compression
  2. Rotation
  3. Bend
  4. Tension
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5
Q

which biomechanical force(s) do IM pins resist

A

bending

if used w/ cerclage wire on spiral/long oblique fractions give some resistance to low mag compression/rotation

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6
Q

contraindications of IM pins

A
  1. Open fxs/comminuted/infected
  2. Radius
  3. As primary method of repair in comminuted fxs or fx where rotational and compressive forces are significant
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7
Q

biological factors of IM pin placement

A
  • placed closed = do not disrupt blood supply HOWEVER

usu. concurrent use of cerclage wire which SIGNIF DISRUPTION of soft tissue and blood supply thus POOR BIOLOGY

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8
Q

What are the 7 principles of IM pin placement?

A
  1. Properly assess fx so that IM pins are not used in inappropriate situations
  2. Pin size should be approx 70-80% size of medullary canal
  3. Ensure pin is seated as deeply as possible into distal cancellous bone
  4. Cut the end of the pin protruding from the bone as short as possible.
  5. Normograde placement
  6. Do not use IM pins in open/infected fxs
  7. Not in radius!!
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9
Q

Describe how you ‘properly assess fxs’ so that IM pins are not used in inappropriate situations

A
  1. high fx assessment score and low overall load w/ min. rotation and axial compression and high fx biology
  2. Interdigitating transverse fxs and long oblique/spiral fxs in small to medium sized young animals that are appropriately managed post-op.
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10
Q

why is the IM pin size to medullary canal ratio important?

A

the larger the pin the greater the strength provided yet may delay reformation of the medullary artery if too large

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11
Q

what is the exception to the 70-80% size of medullary canal rule? (IM pins)

A

Tibial IM pins ~50-60% medullary diameter so that pin can bend on entry and avoid damaging the stifle joint

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12
Q

what is the risk of retrograde placement of IM pins in the femur?

A

sciatic nerve damage

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13
Q

what is the risk of retrograde placement of IM pins in the tibia?

A

absolute contraindication –> damages stifle joint

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14
Q

why are pins contraindicated in the radius?

A
  • shape of bone: cranial bow, craniocaudal compression of radius –> medullary canal too small for pin to be stable and not compromise the medullary revascularisation
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15
Q

Why should casts and splints not be used to reinforce intramedullary pins?

A

the added weight of the cast can produce a fulcrum effect which increases the bending force in the fx site

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16
Q

If an IM pins needs reinforcement it is probably….

A

the wrong choice anyway!

- remove pins OR add ESF if possible to provide some rotational and axial stability and resist bending loads

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17
Q

how are IM pins used to support plates?

A
  1. The IM pin increases resistant to bending forces and plate fatigue –> useful in highly comminuted fractures.
  2. IM pin smaller - 40% diamater
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18
Q

how are IM pins used to support ESFs?

A

Type 1 ESFs tied-in to IM pin for humerus and stifle fractures –> added resistance to bending

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19
Q

IM pins are rarely ever effective when used alone –> they should virtually always be combined with?

A

cerclage wire

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20
Q

action of cerclage wire

A
  • produces interfragmentary compression and helps neutralise compression and rotational forces produced by weight-bearing
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21
Q

8 principles of cerclage wire application

A
  1. Must be strong enough (wide gauge)
  2. Must be perpendicular to long axis of the bone.
  3. Tight and applied directly against the bone w/ no soft tissue entrapment
  4. Non-circular bone not suitable (ie. radius, ulna, proximal humerus/tibia)
  5. Place cerclage wide 5mm from the f line and spaced every 10mm apart
  6. Place a minimum of 2 wires –> only suitable for long oblique fxs where length is a least 2x diameter of bone shaft.
  7. In areas where the diaphysis is conical avoid cerclage wires or combine w/ a K-wire to stop migration
  8. Loop cerclage is better but if twist cerclage method - don’t bend over twist or cut twist to less than 3 full twists.
22
Q

Why is placement of only 1 cerclage wire contraindicated?

A

acts as a fulcrum and increases the likelihood of failure by bending forces

23
Q

how are tension band wires used?

A

used to convert axial tension force (distraction) into a compression force

24
Q

indications for tension band wires

A

any fx or osteotomy of a traction apophysis - placed as a figure of 8

25
Q

5 principles of tension band wires

A
  1. Use 2 K wires to maintain reduction and to prevent rotation of the fx or osteotomy fragment and to anchor th tension band wire around. K wires should be perpendicular to fx line, parallel to each other and long enough to penetrate cortex.
  2. Drill hole in bone shaft should ideally be the same distance from the fx line as the size of the fx fragment
  3. Avoid having soft tissue interposed btwn the tension band wire and the K wires as this will lead to soft tissue necrosis and loosening
  4. Tension band wire should be a figure of 8
  5. Unlike cerclage wire tension band wires do NOT need to be overtightened –> as a dynamic force and not static
26
Q

how do the forces provided by tension band wires differ from cerclage wires?

A

tension bands provide dynamic compression whereas cerclage compression is static

27
Q

3 components of an ESF

A
  • fixation pins
  • clamps
  • connecting bars
28
Q

type 1 ESF characteristics

A
  1. Unilateral, uniplanar
  2. least rigid - 10x weaker than type III
  3. Simple humerus/femur fx w/ high fx assessment scores + IM pins support
29
Q

type 2 ESF characteristics

A
  1. Bilateral, uniplanar
  2. Very strong
  3. Radius and tibia fxs
30
Q

type 3 ESF characteristics

A
  1. Bilateral, biplanar

2. strongest

31
Q

maximum duration of ESF

A

12wks

32
Q

re. ESFs: the stability of the pin-bone interface relates to the:

A
  1. Amount of force that the transfixation pin has to carry

2. Method of pin insertion

33
Q

11 principles of ESF application

A
  1. Predrill holes for pin placement (thermal necrosis)
  2. Use +ve profil pins
  3. 3-4 pins either side of fracture lines
  4. Pin diameter should not excessed 20% bone diameter
  5. Avoid soft tissue tension on pins
  6. Slow speed insertion of pines w/ power drill (thermal necrosis)
  7. Ensure body of pin has engaged both cortices
  8. Avoid ‘no go’ or high morbidity areas and pin placement
  9. Ensure 2cm clearance btwn skin ad clamps
  10. Ensure post-op care!! (packing w/ gauze, sterile bandage changes)
  11. Dynamise dissassembly
34
Q

Define: Dynamisation of ESFs

A

progressive staged disassembly of ESF to increase load in healing fx and inc. speed and strength of remodelling

35
Q

Explain the process of ESF dynamisation

A

Rads 6-8wks post-op
1. Considerable bridging callus then remove a los of the ESF
2. Little bridging callus –> remove a small amount of the ESF
3. No bridging callus –> undo fixation clamps and manipulate fx —> if unstable then ESF has insuff. stability (OR other reason for delayed union)
If stable –> retighten ESF and give more time.

Which pieces to remove?

  1. Any loose pins
  2. if Type II and III - remove one side of bilateral frame
  3. Leave IM pin and connection until last
36
Q

options for reinforcement of bridging plate fractures

A
  1. Large plate size
  2. Plate-rod
  3. Orthogonal plates
  4. Dual bone fixation
  5. Leg lengthening plate
37
Q

advantages of plate-rod reinforcements

A
  1. Biological: normograde placement aids indirect fx reduction –> min. sx damage to the fx envelope
  2. Biomechanical: inc. stiffness + strength, inc. resistance to implant failure through fatigue
  3. Simple and maintains reduction –> facilitates indirect fracture reduction
38
Q

indications for bridge plate fixation

A
  • comminuted fractures where anatomical reconstruction not possible
39
Q

give 2 scenarios where orthogonal plate placement may be indicated

A
  1. other leg amputated

2. open fracture of heavy dog (prolonged healing expected)

40
Q

what are the advantages of bone plating

A
  1. Neutralise all forces
  2. Allow an early return to function
  3. Do not req. removal
41
Q

relative disadvantages of bone plating

A
  1. More expensive/technically challenging

2. “less biologic” (however MIPI/OBDNT approaches)

42
Q

what can result if a bone plate is ‘too strong/large’

A

stress protection –> osteoporosis of bone

43
Q

what rule dictates the length of bone plates?

A

minimum of 3 screws on either side of the fx line

44
Q

which side of the bone must the bone plate be placed?

A

related to biomechanics of bone shape –> one side gets compressive forces whilst other gets tension forces.
Must plate the side getting tension forces thus converting them to compressive forces.
If placed on compressive side –> exacerbate tension force and causes failure

“Tension band principle”

45
Q

what do dynamic compression plates allow?

A

static compression of fx site

46
Q

ID the neutral and loading positions of screws on DCPs?

A

neutral position is at bottom of slide/incline

loading position is at the top of the slide which results in compression when tightened

47
Q

3 ways to use a DCP

A
  1. Compression
  2. Neutralisation
  3. Buttress
48
Q

indications for compression plating

A
  1. Non-comminuted simple transverse/ v. short oblique fxs
49
Q

indications for neutralisation plating

A
  1. Long oblique fractures

2. Simple comminuted anatomically reconstructible in combo w/ lag screws (interfragmentary compression)

50
Q

describe order/action of screws when compression plating

A
  1. First screw next to fx line is neutral
  2. Second screw on other side of fx line is compressive
  3. Rest of the screws are neutral

Surgery (22 decks)

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