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AY BMSc Surgical Fracture Fixation > Pins and nails > Flashcards

Pins and nails Flashcards

1
Q

Which technique has become the principle way to hold long bones of the leg and to a lesser degree the humerus?

A

Intramedullary nails

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2
Q

What care must be taken when imaging intramedullary nail insertion?

A

Radiation dose that the surgeon is subjected to

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3
Q

What are pins also known as?

A

K-wires

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4
Q

Describe the design of a pin

A

Have sharp “trochar points” or occasionlly threaded, self tapping ends

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5
Q

How are pins inserted?

A

Driven into bone fragments by hand driven T-handles or on hand or even air powered drills

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6
Q

When are pins most commonly used?

A

In small bones (e.g. foot and hands)

Occassionally in upper limb long bones in small children

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7
Q

Why are pins generally used in pairs?

A

To minimise the rotatory element in the final pin/bone construct

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8
Q

When might pins be used in conjunction with flexible wire?

A

To achieve compression between 2 small bone surfaces (e.g. patella fracture)

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9
Q

What 2 ways is flexible wire used?

A

Cerclage (static)

Tension band 9dynamic)

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10
Q

How are flexible wires used as cerclage?

A

Encircles or crosses the fragments pushing them together (e.g. cracked long bone)

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11
Q

Why have nails replaced cerclage in most situations?

A

Do less damage to the blood supply if used properly

Are much more robust

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12
Q

Give an example of when cerclage is useful

A

Around cracked fragments of bone around endoprostheses - during hip reviison surgery sometimes deliberately crack femur to remove primary prosthesis - cerclage can be used to maintain a medullary cavity so that the new prosthesis can still be inserted

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13
Q

How do wires work as a tension band?

A

Utilises the power of surrounding muscles to produce compression at a fracture site (e.g. patellar, olecranon and medial malleolar fractures) - the more the muscles work the more stable the fracture will be

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14
Q

Why is tension banding a useful way of rehabilitating damaged joints?

A

Movement promotes stability and encourages joint nutrition and cartilage as well as bone recovery

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15
Q

Why when using cerclage wires is it important, where possible, to work beneath the periosteum?

A

To avoid damage to blood supply

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16
Q

Why are wires still used extensively in spinal surgery?

A

It can be threaded through restricted holes and its versatility can produce powerful fiation

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17
Q

What is the principal reason that wire has fallen out of routine use?

A

Its awkwardness is use and the need to twist it properly (over-twisting causes breakages)
Also surgeons find other techniques more elegant

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18
Q

How do intramedullary nails work?

A

Placed in the medullary canal and fucntion as a form of internal splint which stabilises long bone fractures with minimal damage to the surrounding soft tissues

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19
Q

What are the advantages of intramedullary nails?

A

Minimal damage to surrounding soft tissues
Uusally withstand axial and bending stresses
Can achieve rotatory control when combined with screws and playes
Can be mobilised early after surgery with weight bearing before bony union

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20
Q

What is the antegrade technique?

A

Nail is inserted into the bone from one end whilst not disturbing the fracture site ata all

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21
Q

What is essential when attempting antegrade technique?

A

X-ray image intensifier

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22
Q

What is the retrograde technique?

A

Fracture site is opened by soft tissue dissection and the fracture end delivered into the wound for reaming and insertion of the nail

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23
Q

What is reaming?

A

Widening of the intramedullary canalthrough paring off the inner surface of the bone

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24
Q

What are current developments in nail design centred around?

A

Whether to ream or use nails which are solid and thinner so they they can be inserted without damage to the inner blood supply

25
Q

Which patient groups in particular benefit from early aggressive medullary fixation?

A

Elderly

Multiply injured people

26
Q

Which 3 factors determine the effectiveness of a nail?

A

The material it is made of
How much of the nail is in contact with the bone
Dimensions and shape of the nail (and its wall thickness if ti is hollow_

27
Q

What material are most nails made of?

A

Stainless steel

28
Q

Why are most nails made of stainless steel?

A

Good strength and stiffness characteristics
Easy to handle during manufacturing
Well tolerated by body tissues

29
Q

Why is titanium not a good material for nails?

A

More susceptible to weakening either if a hole is drilled across it or if it is accidentally abraded during insertion or locking

30
Q

What is notch sensitivity?

A

If a material is accidentally abraded during insertion or locking

31
Q

What is the working length of a nail?

A

The length of a nail that transmits load from one main fragment of a fractured bone to the other

32
Q

Why is the working length of a nail important?

A

The stiffness of a nail in both rotation and bending is related inversely to its working length

33
Q

How is a nail anchored to the bone in a multifragmentary shaft fracture?

A

Via cross-locking screws

34
Q

How does working length affect the relative movement between the main bone fragments?

A

The longer the working length - the greater the relative movement between the main bone fragments

35
Q

Why are nails which are inserted across a multifragmentary shaft fracture less able to resist bending and torsional forces?

A

Bone is gripped solely by the nails proximal and distal screws = LONGER working length (equal to the distance between top and bottom locking screws)
So less able to resist bending and torsional forces

36
Q

Why are solid nails stronger than hollow nails of the same diameter?

A

More metal for their volume

37
Q

How can the grip of hollow nails be optimised?

A

Chose a size which will grip the inside of a reamed bone, whatever its size, along a large length of its internal diameter
Curve nails roughly to conform to the shape of the bone for which they are designed

38
Q

How can the bending stiffness of hollow nails be increased?

A

Increase thickness of walls

39
Q

What is the advantage of having a somewhat flexible nail?

A

Has a little “give” on insertion making it easier to put in and will allow nail to deform slightly to conform to the natural shape of the bone

40
Q

How is the stiffness related to the diameter of the nail?

A

Stiffness = proportional to the diameter raised to the fourth power

41
Q

How is the bending strength related to the diameter of a nail?

A

varies with the third power of the diameter

42
Q

How are the strength and stiffness of a nail related?

A

As nails get a bit stronger they get considerably more stiff

43
Q

How can stiffness be reduced in a nail?

A

Using a longitudinal slot in the wall

44
Q

What is the disadvantage of a longitudinal slot in the wall of a nail?

A

Loses some overall bending strength and especially torsional strength

45
Q

Describe the typical design of most nails

A

Curved according to the shape of the bone
Slotted along their length
Wall thickness of 1.2mm

46
Q

What are the 5 ideal indications for nailing?

A

Transverse and short oblique fractures of the tibial and femoral shafts
Comminuted fractures of tibia and femur (providing cross locking capabilities are available)
Pathological shaft fractures (esp in osteoporotic bone)
Delayed or non-union of the shafts of the femur or tibia
Selected open fractures

47
Q

What are the contraindications to nailing?

A

Children (nail may damage growth plates)

When there is a fracture involving an adjacent joint

48
Q

What are the 3 configurations nails can be used in?

A

Simple nail with no additions
With screws (situated obliquely or at right angles to the axis of the nail and passing through holes in the nail)
With plates

49
Q

In what fractures are nails particularly used in association with plates?

A

To treat fractures of the proximal and distal femur

50
Q

Why are simple nails good?

A

Maintains fairly accurate, but not necessary precise, anatomical alignment
Permits early weight bearing

51
Q

Which 3 bones are simple nails mst commonly used in?

A

Femur
Tibia
Humerus

52
Q

How can the effective working length of a nail be increased?

A

By adding cross screws

53
Q

Why is using cross screws good?

A

Increases effective working length of a nail
Ensure good rotatory control (independent of the contact between nail and bone)
Increases the length of long bones which can be nailed

54
Q

Why are the upper and lower ends of the femur problematic in fracture fixation?

A

Femur is constantly being bent under load because of the 135 degree offset of the femoral neck (creates an angle of about 7 degrees between the axis of the femur and the tibial plateau when the tibial plateau is orientated horizontally, parallel with the ground)

55
Q

Which group are fractures of the femoral neck common?

A

Old age (particularly osteoporotic women)

56
Q

How does an extracapsular femur fracture tend to sit?

A

Proximal fragment to keel over medially and the femur to shorten

57
Q

What dictates the degree of displacement of an extracapsular femur fracture?

A

The degree of damage to the medial part of the upper femoral shaft

58
Q

How is medial ffragmentation of the upper femur treated? Why?

A

Impractical to restore
Add extra support to lateral side with a plate
Nail the remaining proximal femoral neck
(fem neck is effectively rejoined to the shaft by a nail acting as a cantilever against the buttressed lateral femoral cortex)

59
Q

What are the complications of nailing?

A

Centre around difficulty of insertion

  • Reamers can get stuck or penetrate through outside of the bone
  • Nail can be inserted in wrong position
  • Rotatory misalignment is common
  • Infection

AY BMSc Surgical Fracture Fixation (5 decks)

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