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BMSc - Applied Ortho Semester 2 > Implant technology - unit 6B deck 3 > Flashcards

Implant technology - unit 6B deck 3 Flashcards

1
Q

what bones are IM nails used in

A

weight bearing long bones - femur and tibia

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2
Q

what are the indications for IM nailing

A
  1. Transverse and short oblique fractures of the tibial and femoral shafts,
  2. Comminuted fractures of tibia and femur, provided cross locking capabilities are available
  3. Pathological shaft fractures, especially in osteoporotic bone,
  4. Delayed or non-union of the shafts of the femur or tibia,
  5. Selected open fractures, in the hands of surgeons experienced in the management of trauma.
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3
Q

why is IM nailing used so much

A

provides stable fixation with minimal damage to soft tissues

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4
Q

what are contraindications for IM nailing

A
  • In children as the nail may damage growth plates
  • When there is a fracture involving the adjacent joint
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5
Q

what are the 3 configurations IM nails can be used in

A
  1. As a simple nail with no additions,
  2. In association with screws situated obliquely or at right angles to the axis of the nail and passing through holes in the nail,
  3. In association with plates, particularly to treat fractures of the proximal and distal femur.
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6
Q

what are nails within medullary cavities provide and what do they allow

A

maintaining a fairly accurate anatomical alignment whilst permitting early weight bearing

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7
Q

When does an IM nail only work ? and what part of the bone are the effective ?

A

Only if it is in contact with the bone - they are only effective in the middle part of long bones

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8
Q

What is the effect of adding cross screws to an IM nail ?

A
  1. This increases the effective working length of the nail
  2. It also helps ensure good rotatory control
  3. It also increases the length of bone which can be nailed
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9
Q

Why do the upper and lower ends of the femur present a particular problem in fracture fixation?

A
  • The femur is being constantly bent when under load because of the 135 degree offset of the femoral neck
  • which in turn creates an angle of about 7 degrees between the axis of the femur and the tibia
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10
Q

who commonly gets fractures of the femoral neck

A

old age women suffering osteoporosis

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11
Q

due to the shaping and loading of the femur, what is the tendency to happen after a femoral neck fracture

A
  • For the proximal fragment to keel over medially and for the femur to shorten
  • The degree of displacement depends on the degree of damage to the medial part of the upper femoral shaft
  • In order to correct the deformity and permit early weight bearing its necessary to re-orientate the broken fragment
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12
Q

In practice, restoration of the medial fragmentation of the upper femur is impractical - what is done instead

A

an extra support is added to the lateral side of the femur in the form of a plate and from the plate is hung a nail, which is placed up the remaining proximal femoral neck.

femoral neck is effectively rejoined to the shaft by a nail acting as a cantilever against the buttressed lateral femoral cortex

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13
Q

what are complications of IM nailing

A
  • reamers used to widen the medullary cavity can get stuck or penetrate through to the outside of the bone
  • nail can be inserted in the wrong orientation and rotatory misalignment is common
  • infection - very difficult to treat
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14
Q

what does an external fixators consist of

A

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

beam and pins provide a means of support which stabilises the fracture and permits access to the soft tissues during wound healing

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15
Q

what were external fixators designed for and what do they allow for

A

Designed to help in the treatment of difficult and extensive wounds which involved fractures

They stabilise the bone, allowing soft tissue to be dealt with, application of dressings by the nurses is easier, more complicated surgery to damaged blood vessels and skin grafting or even complex plastic surgery can be performed

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16
Q

what are the two categories of external fixators use

A
  • orthopaedic use
  • post-trauma use
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17
Q

what are the orthopaedic uses of external fixation

A
  1. limb lengthening
  2. limb shortening
  3. joint fusion (arthrodesis)
  4. correction of angulatory or rotatory deformity
  5. bone segment transportation
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18
Q

what are the 2 categories of post traumatic use of external fixation

A
  1. temporary
  2. definitive
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19
Q

when is temporary external fixation used

A
  • In open fractures with extensive soft tissue damage
  • In these situations bone healing is unlikely to occur until the blood supply to the soft tissues has recovered and the wounds have healed.
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20
Q

Give some examples of situations where temporary external fixation is used

A

In life threatening situations where speed is essential e.g. stop bleeding following unstable pelvic fractures or in poly-trauma

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21
Q

what does temporary external fixation allow

A
  • Maintains stability of the bone whilst
  • Allow safe access to the soft tissues for dressings and further surgery.
  • Provides an easy way of achieving elevation of the limb
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22
Q

what will happen with temporary external fixation after the soft tissues have healed

A

The external fixation technique may be changed for another treatment, such as nailing (surgical), or cast bracing (non-surgical)

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23
Q

what is meant by definitive external fixation

A

It is when an external fixation is used for soft tissue healing and right through to fracture healing

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24
Q

what is dynamisation of an external fixator ?

A

Release of the fixator to allow axial (proximal-distal) movement.

Need to ensure that pin placement does not interfere with soft tissue during mobilisation and to ensure that the external fixation construct can perform other functions such as the sliding of one fracture fragment relative to another to stimulate callus formation.

25
Q

What is the difference between temporary and definitive external fixation?

A

Temporary usage is commonly associated with open fractures where the damage to the soft tissues is extensive (then diff method usually used e.g. IM nailing). Definite external fixation may be used until soft tissue healing and right throughto fracture healing

26
Q

External fixation frames may be confugred in a variety of ways, what are the 2 key principles to bear in mind ?

A
  1. The bone/frame construct should be stable (i.e. not rigid)
  2. Pin placement must not tether soft tissues or restrict access to wounds
27
Q

in the past, bilateral frames were used for EF, what does this method consist of and why is this method not used anymore

A
  • Bone pins are positioned so that they crossed both cortices and passed through the skin and soft tissues on both sides of the limb
  • This causes unacceptable soft tissue tethering and limit limb motion
  • This is painful and limits rehabilitation so that joints become unnecessarily stiff.
28
Q

Currently unilateral frames are used for EF, what does this consist of and why are they used ?

A

They pass through the skin on one side of the limb, enter the proximal cortex and end by just passing through the opposite cortex

They confer adequate stability to fractures whilst permitting mobilisation, good access to wounds and also keep soft tissue tethering to a min

[however their pins must still be carefully placed so that soft tissue damage and tethering are minimised]

29
Q

Occasionally, unilateral frames do not give adequate stability [bone might be too soft] - what can be done instead

A

A or V frames - where pins are sited at right angles to each other through the same side of the limb

30
Q

what are unilateral frames designed to do

A

hold bones in functional alignment whilst soft tissues heal and sometimes until the fracture is fixed or healed sufficiently to permit protected or unprotected weight bearing

31
Q

Why is the aim of external fixation to achieve stability not absolute rigidity ?

A
  • Achieve fracture stability, NOT absolute rigidity (total or near total rigidity may inhibit bone healing)
  • Desired stability is somewhere between total instability and rigidity so that healing by callous formation is not inhibited and fracture alignment is maintained.
32
Q

what is stability of an external fixator determined by

A
  • The configuration of the frame
  • The degree of contact between the bone ends (depends on trauma extent)
  • The extent of the soft tissue injury (depends on trauma extent)
  • The quality of the bone/pin interface (depends on care in pin placement and quality of the bone)
  • The degree to which the clamps have been properly tightened (can be caused by oversight, should be checked regularly during Tx)
  • The total number of pins used.
33
Q

what should be achieved at reduction when using an EF and why

A
  • Bone to bone contact between the main fragments should be achieved, if at all possible, w/out affecting alignment as this maintains load sharing between the frame and the bone
  • If there is no contact between bone ends (which may be inevitable if there has been gross bone loss) then the frame alone, with a minor contribution from the soft tissues, will be responsible for the stability of the limb
34
Q

When a fracture fixator complex is loaded there will be movement (or strain) what type of strains are a good stimulus for bone healing?

A

Strains which occur along the long axis of the bone promote bone healing and formation

The size of the strain required is very small and movement between fragments of 0.5 to 1 mm (micro-movements)

35
Q

Strains of what size may inhibit bone healing ?

A

in excess of 2 mm

36
Q

What does no movement at all do to bone healing ?

A

inhibits callous formation

==> It is therefore felt that ideally stability should be sufficient to permit a little axial strain.

37
Q

Define dynaminisation

A

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

38
Q

when is Dynamisation usually used

A
  • when the soft tissues are well on the way to healing,
  • when the simple unilateral frame is to be used for definitive fracture control.
39
Q

What are the advantages of using external fixators

A
  1. They can be assembled and fitted to the body fairly quickly which may be of value in emergencies
  2. They can be adjusted later if the position of the bones is not anatomically acceptable after the first application.
  3. The beam of the fixator can be removed to take very clear x-rays or to feel the stability of the fracture.
  4. Most fixators are versatile enough to be used in many sites without changing the basic model so keeping down stocks in store.
  5. It gives excellent access to the soft tissues
40
Q

What are the disadvantages of external fixation

A
  • The bone/pin interfaces are a potential site of infection
  • Pin loosening
  • Soft tissue tethering by pins between skin and bone is inevitable to a greater or lesser degree.
41
Q

what increases the risk of the bone/pin interface becoming infected

A
  • If the patient walks on the fixator
  • Pin loosening

If a pin has become infected then the fixator may not work well, if so the method of treatment has to be changed however these options are limited

42
Q

what increases the risk of pins loosening

A

Greatly increased risk if weight bearing is applied

  • Great bending forces are exerted on the pins about a fulcrum at the bone pin interface.
  • This leads to stresses and strains at the interface which usually result in damage to the bone rather than the pin, which of course loosens the pin.
  • Once pins loosen, if no further action is taken, further loosening is inevitable.
43
Q

What will reduce soft-tissue tethering of pins in external fixators

A

Strategic positioning of the pins

[Tethering results in inhibited voluntary movement and discomfort]

44
Q

what are the categories of complications of external fixation which can arise

A
  1. fixator complications
  2. bone/pin interface complications
  3. complications directly from the fracture itself
45
Q

What fixator complications may develop when using an external fixator and therefore what should be done

A

The modular components may work loose

==> Stability in all planes must be considered after application of the fixator and altering the configuration should be considered if testing demonstrates instability.

46
Q

What are the bone/pin interface complications which can develop when using an external fixator ?

A
  1. Pins may loosen
  2. Pins may become infected
  3. Carelessly inserted pins can cause soft-tissue tethering
47
Q

What are painful pins likely to be ?

A

Loose

48
Q

Generally, loose pins cannot be tightened and should be re-sited.

True or false?

A

True

49
Q

what is the care management plan for pins in external fixators to help prevent infection?

A
  • Pin tracks should be cleaned regularly and kept dry.
  • Patients should be instructed in keeping pin sites clear of dried exudate with clean cotton buds.
  • If any dressing is applied it should be dry.

[In general antiseptic creams or lotions tend to keep pin sites too moist and do not prevent infection unless there is also regular cleaning.]

50
Q

What should be done for a loose infected pin in an external fixator ?

A

Infection treated but the pin site should be resited

51
Q

If sequestra (area of dead bone - appears ring shaped) are seen at old infected pin sites on x-ray what should be done ?

A

Should be drilled out and the wound cleaned

52
Q

How may Tight infected pin sites may be retrieved?

A

Aggressive wound cleaning (surgically if necessary) and systematic antibiotics

53
Q

What should be considered to help avoid soft-tissue tethering of pins in external fixators ?

A

Pin site should pass through as little muscle as possible. Muscle tethering leads to pain, and limited movement can lead to joint stiffness because of limited rehabilitation.

Need to consider joint position when applying pins

54
Q

what will fixators that cross joints cause

A

Some joint stiffness - these fixators should be removed as soon as possible, even if only temporarily for rehabilitation.

55
Q

what are the complications may arise directly from the fracture seen in external fixation

A
  1. Malunion
  2. Non-union
  3. Infection - if the EF is holding the fracture is in a stable configuration and the bone pins are not involved, the infection can be treated by local surgery and systemic antibiotics until union. If EF unstable, then need to change to more stable structure
56
Q

When is dynamisation normally used?

A
  • The soft tissues are well on the way to healing.
  • The simple unilateral frame is to be used for definitive fracture control.
57
Q

What are three main disadvantages of external fixation?

A
  1. The bone/pin interfaces are a potential site of infection and if the pins loosen, the risk of infection increases.
  2. Pin loosening is a real possibility especially if weight bearing is applied.
  3. Soft tissue tethering by pins between skin and bone is inevitable to a greater or lesser degree.
58
Q

What are external fixations advantages over other techniques?

A
  • They can be assembled and fitted to the body fairly quickly which may be of value in emergencies and in treating people with multiple injuries.
  • They can be adjusted later if the position of the bones is not anatomically acceptable after the first application.
  • The beam of the fixator can be removed to take very clear x-rays or to feel the stability of the fracture.
  • Most fixators are versatile enough to be used in many sites without changing the basic model so keeping down stocks in store.
  • It gives excellent access to the soft tissues.

BMSc - Applied Ortho Semester 2 (25 decks)

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