Implant Technology Unit 6b Flashcards
(147 cards)
1
Q
what are the 2 methods of fixing fractures
A
internal fixation
- bone screws and plates, IM nails
external fixation
2
Q
what are the materials commonly used for fracture fixation and what must be considered
A
stainless steel
- commonly used
- strong, inexpensive and easy to manufacture
- however, stainless steel plates don’t tolerate stress reversals very well
titanium
- strong, inexpensive, biologically more inert than stainless steel
- less likely to cause allergies
plates and screws must be of the SAME material, otherwise galvanic corrosion of the implants is likely to occur.
3
Q
how does a screw work in fracture fixation
A
hold two broken fragments together
may be used in isolation or in combo with plates
4
Q
what is a screw
A
mechanism that produces linear motion as it is rotated
screw in ortho consists of a helix shaped thread on a shaft.
turn the head and the screw will move through a stationary object.
The object may be made of a material, such as cancellous bone, which is softer than the screw, so that the screw can create its own thread as it passes through. This requires a suitably designed tip.

5
Q
how does a screw work
A
fixes together two (or more) objects by compressing them against each other
6
Q
what is required for a screw to be able to fix together two objects
A
1 - that the head of the screw is wider than the diameter of the shaft so that it pushes Block 1 against Block 2
2 - thread does not grip Block 1
7
Q
how can it be assured that the thread does not grip block 1
A
1 - either the screw must have no thread on the section nearest to the head, where it touches Block 1
2 - or if a screw thread is present, Block 1 must have a pre-drilled hole in it which is larger than the screw thread
8
Q
what are the 3 components of a screw
A
head
shaft
tip
9
Q
what are the 3 factors that determine the strength of a screw fixation
A
- strength of the screw material
- strength of the object material [bone in ortho]
- design of the screw thread
10
Q
what are the 2 functions of the head of a screw
A
1 - provides a buttress to stop the whole screw sinking into the bone. Buttress can be made bigger by placing a washer between the head and the bone, thus spreading the load over a larger area. This is used in soft bone.
2 - provides a connection with the screwdriver. It is the interface which transmits to the screw the twisting force applied by the person putting in the screw. The screw turns and advances forwards in response to a twisting force (or torque) so it is important that torque can be applied effectively.
11
Q
what is the shape of the connection on the head of the screw in bone screws and why
A
hexagonal, because
1 - it gives an effective coupling unlikely to be damaged in the screwing process.
2 - the very positive interlock between screwdriver and screw makes it easy to use. No axial force is required to retain the driver in the head. This is an advantage in tight corners
12
Q
what is another aspect of the screw head design
A
the shape of the undersurface
- most standard bone screws this is rounded
- this allows max area of contact between screw head and bone after countersinking, thus reducing the risk of a zone of excessive stress which may crack the bone
13
Q
why is careful screw design important
A
try to avoid causes of high stress called stress raisers
14
Q
in the shaft of a screw, what are the diameters to consider
A
1 - the core diameter, which is the smallest diameter of the threaded section of the shaft.
2 - the shaft diameter, which is the diameter of the shaft where there is no thread.
3 - the thread diameter, which is the diameter of the widest part of the threaded
section.
15
Q
what is the strength of the screw determined by
A
determined by the smallest diameter
the greater the smallest diameter, the stronger the screw will be
[In some screws the thread diameter is bigger than the shaft diameter (in a cancellous bone screw for example). In others the thread diameter is the same as the shaft diameter (in some partially threaded cortical bone screws for example).]
16
Q
what are the 3 aspects of the thread
A
shape
depth
pitch
17
Q
what is the function of the thread
A
inclined plane which is rotated in the thread hole in the bone so that the screw moves forward in response to being twisted
18
Q
most bone screws have symmetrical threads - true or false - and why are they designed this way
A
false
- asymmetrical threads
they are flat on the upper surface in contact with the bone and rounded underneath
provide a wide surface on the pulling side and little frictional resistance on the underside
thus, more of the torque is used in pulling two objects together and less is wasted on simply overcoming friction during insertion of the screw
19
Q
what is the depth of the thread
A
half the difference between the thread diameter and the core diameter
20
Q
what determines how well a screw resists being pulled out of bone
A
The amount of thread in contact with the bone
21
Q
what depth of thread is preferred in weak cancellous (spongy) bone
A
deeper thread as this will capture more material between the threads
thus, increase the resistance of the screw to pulling out
22
Q
what is the pitch of a screw
A
the linear distance travelled by the screw for a complete (360 degree) turn of the screw
[not so critical in influencing holding strength]
23
Q
what is tapping
A
process of cutting a thread
24
Q
what is a self tapping screw
A
A screw which has a cutting tip that enables it to cut its own “female” thread track, as it is being inserted
All cancellous screws are self-tapping
25
what is special about the malleolar screw
it's self-drilling which means that it can drill a hole in the cancellous bone without the need to use a separate drill bit.
Its trocar shaped tip provides a suitable cutting edge to allow it to act as a drill, although in practice this is seldom done.
26
what can a screw do in soft, cancellous bone
screw may be permitted to ‘force’ a thread track without the need for a tapping instrument
[not possible in hard cortical bone because too much torque would be required, risking jamming or breaking the screw]
27
What advantages do hexagonal and star head screws have over cross head screws?
Good coupling so no damage to screw heads. Positive interlock between screwdriver and screw
28
Why are cortical screws not self-tapping?
Self tapping would cause damage to the bone and make screw impossible to insert due to excessive torque required.
29
what to tapping instruments and self-tapping screws have
flutes
| - i.e. channels which provide a route for cuttings to escape
30
why do cortical screws have no flutes
because bone can grow in to the flute and so make removal difficult
31
what is lagging
process of compressing two objects together
[screws area a means of compressing objects together]
32
what is the purpose of screws in bone fixation
stabilisation of fragments provides a basis for early mobilisation of the limb
prevent excessive movement of metal implants which could lead to failure through metal fatigue.
33
Screws can achieve a lag effect in two ways: one are lag screws, how does this work
- partially threaded only at the section nearest the tip.
- When a partially threaded cancellous screw is placed in a hole the size of the core that has been drilled in the first bone fragment A, the screw will firstly cut its own thread in fragment A and then in the second bone fragment B, using the corkscrew tip
- unthreaded shaft then slides through the hole in the first fragment until the head touches the surface of bone A
- As the screw advances the head pulls fragment A towards fragment B (which now contains the threaded part of the screw).
- In this way the two pieces of cancellous bone have been compressed (lagged) together.
34
Screws can achieve a lag effect in two ways: one is how the screws are inserted, how does this work
- technique allows any screw to act as a lag screw, even if it is threaded along all its shaft
- If a hole (the gliding hole) is slightly larger than the screw thread diameter is made in cortical bone fragment A, then the screw will slip through the hole without any need to twist it with a screwdriver.
- If a hole (the thread hole) equivalent to the screw core diameter is made in fragment B and then tapped to match the dimensions of the screw thread, the screw will now advance by gripping the bone of the second fragment.
- When the screw head makes contact with the surface of fragment A and the screw is further twisted, the two fragments of cortical bone are compressed (lagged) together.
35
what is essential to ensure when using lagging as a fixation technique
- to position screws accurately
| - so forces generated are evenly distributed across fractures, otherwise distortion of bone is easily possible
36
what are the situations that screws may be used
- to prevent sideways displacement of fragments
i. e screws commonly used along around joints to hold cancellous bone fragments together
- to hold a plate against bone
i. e. When cortical bone is being fixed, screws alone are not very effective in controlling large bending forces. Screw fixation is therefore usually supplemented by a plate. The screws and plate share the load with the reconstructed bone.
- to increase the grip of an IM nail on the bone
- To permit displacement in an axial direction
- As part of an external fixator assembly
37
when are screws and plates used together
- screws are used to hold the plate firmly to the bone so that the load is shared between the reconstructed bone and the plate
- used in upper limb to fix forearm fractures
- used around joints where complete reconstruction of the cancellous bone is not possible, so that the fragments of bone cannot be rigidly held together with screws alone
38
when is complete reconstruction of cancellous bone not possible
- particularly violent fractures
- soft bone found after a delay of a few days between injury and surgery
- bone is unnaturally soft as it may be in old age
39
when are plates used
in situations where fracture stability can be achieved and enhanced by compression at the fracture site by forcing bone fragments together
screw fixation can be reinforced or protected by plate
40
what is osteosynthesis
reconstruction of a fractured bone by surgical and mechanical means
should be complete so that the shape of the bone is restored with few or no defects in overall bony architecture
41
how does plates help with osteosynthesis
helps to maintain the restored bony shape
When the bone is loaded, for example by muscle activity, the bone and plate share the load.
42
what can happen in complex fractures that can hinder healing
complete anatomical restoration, incorporating all the pieces in the fixation, may be achieved only at the risk of damaging the blood supply to the fragments
43
what happens in complex fractures in regards to plates and what is it called
two main bony shaft fragments may be linked by means of a plate to restore bone length and alignment
small fragments in between are left unfixed but their blood supply is left undisturbed and they retain the potential to heal as part of the overall healing of the bone
[called "bridging technique"]
44
what is the design and structure of plates
plates are flat and relatively thin
must be as compact as possible and sufficiently malleable to allow shaping
means that they have limited capabilities to resist an applied load when stressed in certain directions
45
how does the structure of bone differ from structure of a ortho plate
bone is hollow tube and generally resists bending equally well in any direction
however, its overall strength depends very much on its wall thickness
thin walled bones are weaker than thick walled bones
46
what is the aim of plate fixation
achieve load sharing between plate and bone until the healing bone is strong enough to take all the load efficient i.e. when the fracture is united
[If load sharing is satisfactorily achieved then the plate is relatively safe from failure, which is normally due to metal fatigue]
47
what happens if the plates takes most of the load
plate will be prone to bending
can happen if there is a defect or gap at the fracture site
- normally due to fractured bone not been accurately re-assembled
plate bends backwards and forwards as the incomplete bone-plate construct is loaded
backwards and forwards cyclical movement known as stress reversal
- likely to result in early fatigue failure of the plate
48
what factors should be considered to prevent bending of the plate
- system of fixation with plates and screws should, together with the bone, form as stable a construct as possible,
- ensure as little damage as possible should be done to the blood supply to the bone [so healing of fracture complex takes place as quickly as possible
- plate should be placed in a position relative to the broken bone that it is minimally stressed
- plate should be placed so there is min soft tissue damage
- plate should be made of materials which are strong as possible and which can tolerate the fatigue effects of stress reversals
49
what is the main cause of fatigue fracture
Stress reversals due to inadequate load sharing, i.e. the bone not taking enough of the applied load.
50
what are indications for use of plates
- when anatomical alignment must be restored accurately
- where the use of screws alone is inadequate (because large bending forces distort # fixed only by screws)
- when load sharing may be achieved with confidence
51
what can be done if loading sharing between bone and the plate cannot be guaranteed
bone graft may be added at the site of any deficit.
preferably taken from elsewhere on the patient (an autogenous graft)
will encourage the healing of defects
will accelerate the healing of the bone before the plate becomes at risk from fatigue failure.
52
what areas of the body commonly require the use of a plate
around joints
- failure to restore a joint surface may lead to OA
bones of forearm
pelvis
- esp around acetabulum
on the face and the jaw
53
what can be done with plate-screw combos to make them more efficient
can be places strategically to make them more effective so that they are less likely to fail
i.e. using a plate on the tension side of a fracture opposite to where muscles remain intact
54
what is eccentric loading
when bones are not loaded evenly along their axes
can occur in a fracture if the soft tissue are stripped off one side of the bone while remaining intact on the other side
- produce a tendency for a loaded bone to distort more on one side than the other.
55
how can a plate help with eccentric loading
If a plate is fixed on the side tending to open - the tension side - then this will counteract the eccentric load, compressing the fragments together at the side under the plate.
The eccentric load will continue to compress the bone fragments together on the side of the bone opposite to the plate
Fracture is compressed throughout the bone cross section and the plate suffers an equal and opposite force - tension.
56
in what areas of the body is bone compression achieved using wires as tensions bands
around the olecranon of the elbow
patella
57
wherever possible where should plates be placed
tension side of a fracture
[may not always be possible for anatomical reasons, such as the need to respect the blood supply of the bony fragments or the risk of tendons]
58
what else can be done to improve the use of plates
contouring a plate before use, so that it is bent slightly more concave than the bone [will encourage compression of the bone opposite the site of attachment of the plate]
aids in load sharing between plate and bone and, by forcing the rough fracture fragments together across the whole cross- section of the bone, it adds greatly to stability.
59
what is disadv of plating technique
Tissue stripping may damage blood supply
will delay healing and contribute to risk of infection
60
what are the function of K wires
maintain fragments in alignment by pushing them or holding them together, depending on the fragments fitting together like a jigsaw puzzle so that their shape and interlock contribute to the bone/pin or bone/wire construct.
61
when are IM nails used and what is used along side them by the surgeon
hold long bones of the leg [and sometimes humerus]
x-ray intensifier - permits the surgeon to take freq "snapshots" of a bone during an op so that they can check progress of a nail as it passes through the bone
62
what is the shape of pins
sharp "trochar points" or occasionally threaded, self tapping ends and are driven into bone fragments by hand driven T-handles or by hand
63
when are pins commonly used
small bones or occasionally in upper limb long bones in small children
foot and hand bones in adults commonly
64
is it important the no. of pins used ?
not that important
but generally pins used in pairs in order to minimise the rotatory element in final pin/bone construct
65
when may pins and flexible wires be used in conjunction
to achieve compression between two small bone surfaces, e.g. in patella fracture
66
what are flexible wires used for
to induce compression
67
what are the two ways to use flexible wires
- used statically by encircling or crossing the fragments (cerclage), pushing them together so that the cleavage lines produced by the fracture are pushed together
- used dynamically as a tension band, utilising the power of surrounding muscle to produce compression at a fracture site
[useful in patella fractures]
68
what are examples of flexible wires being used statically
used in repairing long bones which have been cracked
also cerclage of cracked fragments of bone around endoprostheses is useful
i.e. during revision hip surgery ometimes useful to deliberately crack open the femur to facilitate removal of the primary prosthesis and its surrounding cement; afterwards the femur can be reconstituted with cerclage wires, maintaining a medullary cavity so that the new prosthesis can still be inserted.
69
what have in recent years replaced cerclage in most situations and why
nails
| - as nails do less damage to the blood supply is used properly and are much more robust
70
where are sites, other than the patella, that the flexible wires work as dynamic compression
olecranon
medial malleous of the ankle
71
how does dynamic compression by flexible wires work
Muscle contractions working against the fulcrum caused by the wire holding the fragments together immediately under the wire produce compression at the far side of the fracture fragments
the more the muscles work, the firmer the fracture is compressed and the more stable it will be.
[ideal way of rehab damaged joints as movement promotes stability and encourages joint nutrition and cartilage as well as bone recovery]
72
what is essential to ensure when working with wire
to work beneath the periosteum as otherwise the blood supply will be damaged
also to avoid over-twisting the wire which would cause a weak or potentially loose fixation
73
What is a cerclage wire?
A wire that crosses or encircles a fracture fragment
74
where is a intramedullary (IM) nail places and what does it work to do
in the medullary canal of a fractured bone and functions as a form of internal splint which stabilises long bone fractures with minimal damage to the surrounding soft tissues
75
IM nails are sturdy and round in shape, what does this mean
that they can withstand axial and bending stresses
76
what can be achieved by combining nails with screws and plates
rotatory control of the bone can be achieved and length maintained
Limbs with nailed fractures may be mobilised early after surgery, with weight bearing before bony union.
77
what is the name of modern nailing technique and what does it entail
antegrade technique
- the nail is inserted into the bone from one end whilst not disturbing the fracture site at all
- does little damage to surrounding soft tissue or blood supply
- x-ray image intensifier is essential
78
what is the name of the old nailing technique and what does it entail
retrograde technique
- the fracture site was opened by soft tissue dissection and the fracture end delivered into the wound for reaming and insertion of the nail
79
what is development of new IM nails designs centred around
whether it is necessary to widen the intramedullary canal through paring off the inner surface of the bone (reaming) or whether to use nails which are solid and thinner so that they may be inserted without damage to the inner blood supply of bones (unreamed technique).
80
why is IM nailing used so much
shown that early aggressive medullary fixation dramatically reduces injury mortality and post-operative morbidity
81
what are the 3 important considerations of the design of IM nails
- material of which it is made
- how much of the nail is in contact with the bone for any particular fracture
- dimensions and shape of the nail [and its wall thickness if it is hollow]
82
what are most nails made of
stainless steel
- has good strength and stiffness characteristics
- easy to handle during the manufacturing process
- well tolerated by the body tissues
83
why is titanium not used for nails
more susceptible to weakening either if a hole is drilled across it, or if it is accidentally abraded during insertion or locking - known as notch sensitivity.
84
what is the working length of a nail
the length of a nail that transmits load from one main fragment of a fractured bone to the other
85
why is the working length of a nail important
as the stiffness of a nail in both rotation and bending is related inversely to its working length
i.e. a longer working length and it is easier to bend and twist [the tube analogy]
86
what does it mean if a IM nail has a firm grip on the endosteal surface of the bone immediately above and below a transverse fracture
that it will have a short working length
i.e. the ability of the nail to resist bending and torsional forces will be high
87
in what scenarios does IM nail have a long working length
if a nail is inserted across a multifragmentary shaft fracture, the nail must be anchored to the bone via cross-locking screws.
If gripping of the bone is solely by virtue of the nail’s proximal and distal locking screws, then it will have a longer working length equal to the distance between top and bottom locking screws
88
what does a long working length of a IM nail mean
will be less able to resist bending and torsional forces
The longer the working length, the greater the relative movement between the main bone fragments.
89
nails can either be solid or hollow - what is the difference
Solid nails are stronger than hollow ones of the same diameter simply because they have more metal for their volume
Solid nails may be thinner than hollow ones but they require cross screws to get a grip on the hollow bone.
Hollow nails are supplied in a range of diameters so that a size can be chosen which will grip the inside of a reamed bone, whatever its size, along a large length of its internal diameter.
90
nails can be curved to conform roughly to the shape of the bone for which they are designed - how are femoral nails shaped compared to tibial nails
femoral nails are gently curved in an arc over their whole length whereas the tibial nail has a sharper angulation one third of the way down from the top.
91
Hollow nails are less stiff in bending than solid ones, although their stiffness may be altered by making the walls thicker or thinner - what makes them stronger?
The thicker the wall the stronger and stiffer the nail.
92
what is an adv of a slightly flexible nail
will have a little “give” in it on insertion which will make it easier to put in and will permit the nail to deform slightly to conform to the natural shape of the bone.
93
why are very stiff nails not ideal either
may damage the bone if there is any discrepancy between the shape of a nail and that of the bone - this situation may arise because nails are of a standard shape and people are not
94
what is one way of reducing stiffness of a nail
to put a longitudinal slot in the wall of a nail
makes it much more flexible but does so at the cost of it losing some overall bending strength and, especially, torsional strength
95
what is normally the design and dimensions of a nail
usually curved according to the shape of the bone involved and slotted along their length
wall thickness of 1.2 mm
longitudinal slot
gives an optimal balance between strength and flexibility and permit good contact between nail and femur
96
Why are some nails made less stiff by the use of a longitudinal slot?
so they are easier to insert
97
what bone are IM nails used in
weight bearing long bones
| - femur and tibia
98
what are the indications for nailing
- transverse and short oblique fractures of the tibial and femoral shafts,
- comminuted fractures of tibia and femur, provided cross locking capabilities are
available,
- pathological shaft fractures, especially in osteoporotic bone,
- delayed or non-union of the shafts of the femur or tibia,
- selected open fractures, in the hands of surgeons experienced in the management of trauma.
99
why is IM nailing used so much
provides stable fixation with minimal damage to soft tissues
100
what are contraindications for nailing
in children as the nail may damage growth plates
also when there is a fracture involving the adjacent joint
101
what are the 3 configurations IM nails can be used in
- as a simple nail with no additions,
- in association with screws situated obliquely or at right angles to the axis of the nail and passing through holes in the nail,
- in association with plates, particularly to treat fractures of the proximal and distal femur.
102
what are nails within medullary cavities useful at doing
maintaining a fairly accurate anatomical alignment whilst permitting early weight bearing
103
what do nails need to work
to be in contact with the bone
and are only effective in the middle part of long bones
104
how can the effective working length of a nail be increased
by adding cross screws
| - increases the length of long bones which can be nailed
105
what areas of bone present problems in fracture fixation
upper and lower ends of the femur
- 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 when the tibial plateau is orientated horizontally, parallel with the ground.
106
who commonly gets fractures of the femoral neck
old age women suffering osteoporosis
107
due to the shaping and loading of the femur, what is the tendency to happen after a femoral neck fracture
for the proximal fragment to keel over medially and for the femur to shorten
degree of displacement depends on the degree of damage to the medial part of the upper femoral shaft
need to re-orientate the broken fragment
108
In practice, restoration of the medial fragmentation of the upper femur is impractical - what is done instead
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
109
what are complications of nailing
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
110
what are the main functions of cross screws
They hold apart bone fragments.
| They provide rotatory control.
111
what does external fixators consist of
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
112
what were external fixators designed for
to help in the treatment of difficult and extensive wounds which involved fractures
Stabilise the bone, allowing soft tissue to be dealt with
- application of dressings by the nurses was easier, more complicated surgery to damaged blood vessels could be performed, skin grafting or even complex plastic surgery could be preformed
113
what are the two categories of external fixators use
orthopaedic use
post-trauma use
114
what are the orthopaedic use of external fixation
limb lengthening
limb shortening
joint fusion (arthrodesis)
correction of angulatory or rotatory deformity
bone segment transportation
115
what are the 2 categories of post traumatic use of external fixation
temporary
definitive
116
when is temporary external fixation used
in open fractures with extensive soft tissue damage
| - bone healing is unlikely to occur until the blood supply to the soft tissues has recovered and the wounds have healed.
117
what does temporary external fixation allow
maintains stability of the bone whilst access is safely gained to the soft tissues for (a) dressing and (b) further surgery.
providing an easy way of achieving elevation of the limb
118
what will happen with temporary external fixation after the soft tissue has healed
external fixation technique may be changed for another treatment, such as nailing (surgical), or cast bracing (non-surgical)
119
what situations is temporary EF used
life threatening situations where speed is essential.
stop bleeding following unstable pelvic fractures
poly-trauma
120
what is meant by definitive EF
used for soft tissue healing and right through to fracture healing
121
what is dynamisation
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.
122
what are the two principles of configuration of modular EF frames
the bone/frame construct should be stable (i.e. not rigid)
pin placement must not tether soft tissues or restrict access to wounds
123
in the past, bilateral frames were used for EF, what does this method consist of and why is this method not used anymore
bone pins are positioned so that they crossed both cortices and passed through the skin and soft tissues on both sides of the limb
cause unacceptable soft tissue tethering and limit limb motion
- This is painful and limits rehabilitation so that joints become unnecessarily stiff.
124
currently unilateral frames are used for EF, what does this consist of
pass through the skin on one side of the limb, enter the proximal cortex and end by just passing through the opposite cortex
confer adequate stability to fractures whilst permitting mobilisation, good access to wounds and also keep soft tissue tethering to a min
have their pins carefully placed so that soft tissue damage and tethering are minimised.
125
occasionally, unilateral frames do not give adequate stability [bone might be too soft] - what can be done instead
A or V frames
| - where pins are sited at right angles to each other through the same side of the limb
126
what are unilateral frames designed to do
hold bones in functional alignment whilst soft tissues heal and until the fracture is fixed or healed sufficiently to permit protected or unprotected weight bearing
127
what is the aim of EF frames
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.
128
what is stability in EF determined by
(a) the configuration of the frame,
(b) the degree of contact between the bone ends,
[depends on trauma]
(c) the extent of the soft tissue injury
[depends on trauma]
(d) the quality of the bone/pin interface
[depends on care in pin placement and quality of the bone]
(e) the degree to which the clamps have been properly tightened
[can be caused by oversight, should be checked regularly during Tx]
(f) the total number of pins used.
129
what should be achieved at reduction with the idea of using a EF for holding
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
130
what is thought to be a good stimulus for bone healing
strains along the long axis of the bone
- movement between fragments of 0.5 to 1mm
- [movements in excess of 2mm may inhibit healing]
- no movement at all inhibits callous formation
131
what can Dynamisation be defined as
the modification of the construct which permits the transition of forces across a fracture without allowing distraction of the fragments.
132
when is Dynamisation usually used
when the soft tissues are well on the way to healing,
when the simple unilateral frame is to be used for definitive fracture control.
133
what are adv of using EF
- can be assembled and fitted to the body fairly quickly, which is useful in emergencies
- can be adjusted later if position of the bones is not anatomically acceptable after first application
- beam of the fixator can be removed to take clear x-rays or to feel the stability of the #
- Most fixators are versatile enough to be used in many sites w/out changing the basic model so keeping down stocks in store.
- gives excellent access to the soft tissues
134
what are disadv of using EF
- bone/pin interface are potential site of infection
- pins loosening [also increases the risk of infection]
- soft tissue tethering by pins between skin and bone [is inevitable to a greater or lesser degree]
135
what increases the risk of the bone/pin interface becoming infected
if the patient walks on the fixator
If a pin has become infected then if the fixator does not work well and the method of treatment has to be changed then the options are limited
136
what increases the risk of pins loosening
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.
137
what are the categories of complications of external fixation
fixator complications
- loosening of the modular components
- all components should be regularly tightended
bone/pin interface complications
complications from the #
138
what needs to be considered after application of the fixator
stability in all planes and altering the configuration should be considered if testing demonstrates instability.
139
what does a painful pin in EF mean
the pin is loose
generally, loose pins cannot be tightened and should be re-sited
140
what is the care management plan for pins
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.
In general antiseptic creams or lotions tend to keep pin sites too moist and do not prevent infection unless there is also regular cleaning.
If any dressing is applied it should be dry.
141
what is sequestra
area of dead bone
- may be ring-shaped
- if present should be drilled out and the wound cleaned
142
Tx for infected pin sites
aggressive wound cleaning (surgically if necessary) and systematic antibiotics
143
what needs to be considered when positioning the pins
Carelessly inserted pins can cause soft tissue tethering.
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
- ankle should be kept in the plantigrade position so that muscle tethering does not induce the patient to adopt an equinus posture
144
what will fixators that cross joints cause
some joint stiffness
these fixators should be removed as soon as possible, even if only temporarily for rehabilitation.
145
what are the complications from the # seen in EF
malunion
non-union
infection
- if the EF is holding the # 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
146
When is dynamisation normally used?
The soft tissues are well on the way to healing.
The simple unilateral frame is to be used for definitive fracture control.
147
List three complications that can occur with external fixation.
Pins may loosen.
Pin tract infection.
Soft tissue tethering.
