Principles of holding fracture
There
are two main ways in which a fracture can be held which make a profound
difference to the way in which the fracture heals. Rigid fixation blocks the normal callus formation of bone healing.
The bone appears to be unaware that there is a fracture if there is no movement
at the fracture site. As the bone undergoes normal physiological remodelling,
the fracture cleft is gradually obliterated by new bone. This takes about a
year. During that time the fixation must share the loads normally taken by the
bone. Most implants fatigue under the repetitive load imposed by the human body,
and will soon fail if the bone does not heal and take over its original
function. Fracture healing is therefore a race against time: the bone must unite
before the implant fails or the construct will collapse. Nonrigid fixation (such
as plaster of Paris) allows limited movement and loading of the fracture site.
The aim is to allow movement and load to stimulate
callus
formation without allowing the fracture to re-displace. This delicate balancing
act depends on the quality of the fixation, the type of fracture and the
compliance of the patient (Fig. 21.11).
When
a hone breaks there is disruption of periosteum, cortical bone, trabecular bone
and the blood vessels which run in the periosteum and the medulla. There is
haemorrhage and immediate release of cytokines. This signals to cells locally
that damage has occurred. These cytokines attract macrophages which start the
cleaning-up process. They also attract undifferentiated stem cells which migrate
in and start differentiating into fibroblasts and bone-producing cells. These
stem cells probably come from the periosteum and the endosteum, and normally lie
latent.
The
haematoma around the fracture is invaded with small capillaries while the
macrophages remove the haematoma itself. At the same time connective tissue is
laid down. The connective tissue slowly organises.
This
pattern of layers of organised tissue appears first as a collar arising from the
periosteum close to the end of each broken bone. The collars appear to grow
towards the collar on the other bone. Eventually, the spurs of callus meet and
bridge the fracture site. They become increasingly thick and strong
fibrocartilage stabilises the fracture. This period, which in the adult occurs
over the first few weeks after the fracture, is described as the fracture
becoming sticky. It may still be possible to angulate the fracture but it is no
longer possible to translate the fracture (move it from side to side).
Meanwhile, in the fracture cleft itself, osteoclasts continue to resorb
haematoma and other dead tissue and to eat away the broken bone ends. This can
result in the fracture becoming more obvious on X-ray over the first few weeks
and can indeed make fractures visible which were initially invisible (e.g. the
scaphoid). The callus of fibrous cartilage around the fracture cleft becomes
calcified and then ossified (so that it is visible on X-ray). Ossification
starts at the bone ends but in the centre of the fracture cleft, where oxygen
levels may be very low, cartilage may be laid down initially rather than bone.
This cartilage is then replaced by bone (endochondral
ossification). It is not clear whether the callus is derived from the
haematoma or from the periosteum, but it is clear that movement stimulates the
production of a callus.
While
the fracture can no longer be angulated with normal loads, and it
is not painful to try, the
fracture is said to be clinically united. On
X-ray, when the strands of ossified callus can he seen to be stretching
continuously from one bone end to another, the fracture is said to be radiologically
united. In neither case is the fracture at full strength yet, but at this
stage limited activity can be undertaken safely. Finally, the callus forms a fat
cuff of woven bone from one bone end to the other. This callus is at least as
strong as the bone around it because biomechanically it has widened the diameter
of the tube and this confers extra strength. This stage is called consolidation.
Over
the next months the woven bone is replaced by Haversian cortical bone which
remodels over the following years.
Rigid
immobilisation. If the fracture is rigidly immobilised with a plate there is no
stimulus for callus formation. Macrophages remove the haematoma and the dead
bone ends. The normal process of remodelling produced by osteoclasts tunnelling
through the bone and osteoblasts laying down new bone in their wake gradually
obliterates the fracture cleft and reconstitutes normal hone. This process is
slow and even in a young patient may take up to a year. If the fixation of the
fracture is not completely rigid then some callus will form rapidly, but the
patient may be able to resume near-normal function because the fracture is held
stable if not immobile by the fixation. This partial rigidity therefore offers
the best of both worlds, with rapid biological healing combined with the
benefits of early mobilisation of the patient.
Types
of fixation
Fixation
can be divided into external and internal. Implants which are fitted directly on
to or put down the inside of the bone and are then covered with soft tissues and
skin are classified as internal fixation. Those
where the mechanical strength of the construct is outside the skin are defined
as external
fixation.
Types
of internal fixation
Screws
can be used to hold plates on to bone or can be used in their own right to hold
bone fragments together. In orthopaedics,
screws have been standardised to an agreed set of diameters. The threads of the
screws also come in two standard forms, one for cortical and the other for
cancellous bone. The size of these threads and their pitch (the distance between
each thread) is specifically designed to give the best possible grip in healthy
human bone. The drills, which create the holes for these screws, are also
standardised to allow as snug a fit of the screws as possible without putting
undue load on the bone. ‘Taps’ are also supplied which cut the grooves in
the bone to take the threads of the screws. Tables are available in every
orthopaedic theatre to show which drill should be used for which screw.
Lagging
If
a screw is to be used to compress two hone fragments together it is important
that the thread of the screw should only grip the distal fragment in which the
tip of the screw is embedded. As the screw is tightened the shoulder of the
screw (the part that tapers in under the head) presses down on the proximal
fragment and compresses the two fragments together. If the thread of the screw
engages with the proximal fragment the screw can actually hold the fragments
apart. There are techniques used to ensure that the fragments are drawn together
as the screw is tightened. First, a screw can be used which has no proximal
thread, just a smooth shaft. This is known as a ‘lag’ screw. An alternative
strategy is to use
Plates
The
plates come in several sizes, each designed to be used with a standard set of
screws. They are designed to fit on to the curved surface of bone and to be held
there by screws. The plates can be used for several purposes and there are
specific plates designed for each function (Fig. 21.14).
Buttress
plates. Buttress plates prevent one fragment of hone slipping on another. They
are especially useful in oblique fractures in load-bearing bones where they will
stabilise what is a very unstable fracture configuration.
Dynamic
compression plates (DCP). Dynamic compression plates have oval screw holes in
them with tapered walls. If the screw holes are drilled into the bone at one end
of these holes (there are drill guides to assist in doing this) then the plate
slides along the bone as the screw is tightened home. If the plate has already
been firmly fixed to the other fragment then the slip can be used to compress
the fragments of bone tightly together. This has the benefit of stabilising the
construct by increasing the area of contact. It also appears to stimulate
healing by putting the bone edges in close apposition.
Neutralisation
plates. Neutralisation plates are used to prevent bone ends from being
distracted. They can therefore be used to resist angular forces by being placed
on the side of a bone which goes into tension when load is applied (the side
that opens when the fracture bends). Plates with screws are excellent at
resisting tension and this is how they are used in neutralisation. Plates have
very little resistance to bending and so should never be put on the side of the
bone which is in compression and which will go into concave angulation when load
is applied.
Wires
Wires
are much less traumatic than plates and screws. They can be used temporarily to
hold fragments reduced while plates and screws are applied. They can also be
used to resist shear where loads are not great. They are especially useful in
children’s fractures where plates and screws could damage the epiphyseal plate
(Fig. 21.13). Wires can cross the growth plate without causing long-term
effects, and if left protruding from the skin can be removed when the fracture
is secure without the need for a further anaesthetic.
Kapanji wires are
a technique which can be used in fractures where impaction may have left a
defect which leaves the fracture unstable when reduced. After the fracture has
been disimpacted and reduced, wires are introduced into the fracture cleft on
the side of the defect. As soon as the tip of the wire is in the medulla the
wire is tilted so that its tip travels proximally and embeds on the inside of
the far cortex. One or more wires placed in this way substitute for the
Figure of eight wiring allows
a strong wire suture to be woven over the cortex of bone which is in tension.
The construct is not prominent and so fits well subcutaneously and is commonly
used on the olecranon and on the patella (Fig
21.14).
Nails
Intramedullary
nails. Implants driven down the medulla of a long bone suffer from a significant
mechanical disadvantage because they must be narrower than the hone into which
they are introduced. Nevertheless, the medulla can provide a natural guide for
the implant and introducing the nail into one end of the bone (under image
intensifier control) minimises the risk of infection from opening the
fracture, and preserves the periosteal blood supply. In recent years the scope
of intramedullary nails has been increased enormously by
the introduction of the locking nail. This
system has holes through the nail at each end. Using jigs or an image
intensifier,
screws can be passed through the bone, the hole in the nail and out through the
opposite cortex of the bone. This produces a construct which holds the bone
rigidly and is especially resistant to twisting. It allows an intramedullary
nail to be used for a far greater range of long-bone fractures. Some of the
newer nails can now be passed down the medulla without requiring any reaming in
advance, the unreamed nails. This
makes the operation quicker and reduces the trauma to the patient.
In
summary, internal fixation can allow very accurate reduction of fractures under
direct vision, and allows strong and stable fixation so that the patient can
rapidly return to everyday activities with the minimum of inconvenience. The
disadvantage is that the patient requires carefully planned and complex surgery
which carries a risk of infection if sterile technique is not strictly adhered
to.
earlier
mobilisation of the patient. Internal fixation is technically demanding,
requires a large range of implants and instruments, and is best performed in
ultraclean theatres as infection is a disaster. Internal fixation requires
careful preplanning and the best surgery is performed if the fractures are
drawn out on stencils first, and the problems of reduction and obtaining
mechanical stability planned in advance. This includes size and type of plates,
and position of screws. Only in this way can the operation be performed quickly
and cleanly (minimising the risk of tissue damage and infection) so that the
strongest fixation is obtained.
Internal
fixation is best performed under a tourniquet, if possible, in order to obtain a
blood-free view. There are complications inherent in using a tourniquet such
as cuff damage to nerves as a result of inflation to an excessive pressure, and
problems of reperfusion injury if the cuff is left up too long.
Exposure
of the fracture may damage the soft-tissue attachments to the bone and produce
avascular fragments, which will delay or even prevent fracture union.
Soft-tissue dissection should therefore be kept to a minimum, but must be
adequate to obtain a clear view and access. All incisions should be designed so
that they can be extended safely if necessary — extensile exposure.
The
risk of infection can be minimised by cleaning out open fractures and leaving
them open, with the fractures stabilised until it is certain that all dead and
contaminated tissue has been removed. Only when they are clean should they be
closed (delayed primary closure). When
internal fixation is used infection is minimised by performing quick, tidy and
well-planned surgery, and by adhering to strict theatre discipline on theatre
sterility. Surgery should be covered by three doses of a broad-spectrum
antibiotic which has good activity against Staphylococcus
(the commonest infective organism) and Streptococcus
(the second most common).
Internal
fixation can also leave unsightly scars, and these should be planned to minimise
cosmetic deformity without compromising access.
Drills
and screws can damage nerves and vessels. Drill guards should always be used to
prevent soft tissues being inadvertently dragged into a spinning drill. When the
drill is cutting into the far cortex the hand that the surgeon is using to hold
the drill should have a straight finger resting on the limb through which the
drill is passing, and only light pressure should be applied to the drill so
that when the drill then comes out through the far cortex it will not suddenly
penetrate deep into the soft tissues on the far side of the bone, where it
might perforate a nerve or vessel.
Removal
of internal fixation
Implants
for internal fixation are made of surgical-grade stainless steel and should not
corrode. Nevertheless, the alloys contain transitional metals such as chromium
and vanadium whose salts are allergenic, toxic and may even be carcinogenic.
Despite this, there is little evidence that metalware left in patients for
long periods causes any chemical or even allergic problems. Children should have
metalware
removed
if it is likely to compromise growth. It should be removed as early as possible
because periosteal bone grows rapidly over the plates and makes their removal
difficult. Internal fixation also shields the bone around it from load, and so
may cause local osteoporosis. The load passing down the bone may then peak at
the end of a plate (a stress raiser) and
cause a fracture. Internal fixation of a fracture next to an old plate already
embedded in the bone is very difficult to manage. Despite this, it is now normal
practice to leave plates and even intramedullary nails in the patient unless
there is a specific reason why they should be given another anaesthetic and he
subjected to a further operation to remove them.
External
fixators
An
alternative way to holding a fracture is to insert pins and wires into the bone
on each side of the fracture, and to attach these to an external frame which
provides the structural integrity. Fixators can be as simple as a set of pins
incorporated into a plaster through single- and double-bar fixators, to ring
fixators holding the bone through tensioned wires (Fig.
21.15). There is a
trade-off between cost, ease of fitting, adjustability, rigidity and convenience
to the patient (Table 21.5).
The
choice of fixator will depend on what is available and the use to which it is to
be put.
Uses
of an external fixator
Emergency
use of the external fixator
Fixators
are used for two main reasons in an emergency.
Pelvis.
They can be used to stabilise an unstable pelvic fracture to try to reduce
life-threatening haemorrhage from the pelvic veins. Closing and stabilising an
open pelvis fracture may reduce bleeding by reducing movement of the pelvic
veins. This may stabilise clots and reduce haemorrhage. Closing the pelvis may
increase the intrapelvic pressure and tamponade the veins to reduce bleeding. A
bar fixator attached to pins inserted into the pelvic wings will need to be
used. The bar should be set as low as possible to give enough room over the
abdomen should a laparotomy be needed.
Neurovascular
compromise. If a limb has an unstable fracture and has lost its blood supply
the skeleton needs to be stabilised before the vascular repair can be performed.
One option is to insert a stent and
provide a temporary blood supply to the limb while a definitive orthopaedic
fixation is performed. An alternative is to use an external fixator which can be
applied quickly to stabilise the fracture so that the vascular surgeon can start
work with the minimum of delay. The disadvantage of this approach is that an
external fixator may not be the optimal way of stabilising that particular
fracture, but once it has been applied the risk of infection from the pin tracks
makes a conversion to a plate or an intramedullary nail potentially risky.
Soft
tissue damage. If there is extensive damage to the soft tissues then it may not
be possible to achieve good cover of the bone. If bone is contaminated and/or
exposed internal fixation may not be advisable. Under these circumstances an
external fixator may offer the best option. The position of the pins can be
planned with the plastic surgeons to enable them to rotate flaps without the
fixator or the pins getting in the way.
Leg
lengthening and correction of deformity. Over the last decade one of the great
advances in orthopaedics has been the discovery that bones can be lengthened
gradually — callostasis.
Segments of bone can be
moved across defects and, if the periosteum is left as intact as possible, new
bone will be laid down in the defect — bone
transport.
In
order for the pins of the fixator to be able to move through the soft tissues as
the bones move they need to be very thin, and it is now routine to use wires
which gain their rigidity by being tensioned on a ring (the Ilizarov
technique). The key to the technique is to move the bone so slowly that new
bone can be laid down in its track, but not so slowly that the bone unites and
prevents any further distraction. The fixation pins must be positioned to avoid
damaging vital structures as they carve through the soft tissues. Care must also
be taken to avoid overstretching nerves and vessels, and to avoid contractures
caused by ligaments, tendons and muscles failing to extend in concert with the
bone.
Determining
union
Clinical
union
A
bone is clinically united when putting load on the fracture produces no
detectable movement and no pain. The fracture site will not yet be as strong as
the bone around it, but it is united.
Radiological
union
This
is not the same as clinical union. It occurs when the callus around the fracture
can be seen to pass from one broken bone end to the other without a gap
between. The fracture across the medulla of the bone may still be visible, but
the callus around the bone is continuous. The bone should now be able to cope
with normal loads, but will not be as strong as the bone around it. From a
management point of view, it is the time when movement and loading of the limb
should be increased to build up muscle power, mobility and proprioception. If
the patient plays sport or works in a job involving heavy labour they should not
return to this unless the bone is protected, or until the fracture has
consolidated (Fig. 21.16).
Consolidation
Consolidation
takes much longer than union, and is defined as the time when the process of
fracture healing is complete and the strength of the hone has risen to normal
levels or even beyond. The formation of callus around a fracture creates a
strong cuff. The diameter of this cuff is greater than the diameter of the bone
itself, and so a consolidated fracture can be stronger than the original bone (Fig.
21.17).
Restoring
function
When
a fracture occurs, there will be damage to soft tissues. Muscles may be bruised
or torn. Ligaments may be ruptured, joints filled with blood, and nerves and
blood vessels damaged. The original philosophy in orthopaedics was that the
key to management of fractures was immobilisation, and of injury was rest. This
has now all changed. Fractures are stabilised to allow mobilisation of the limb
and the patient. Rigid fixation of the fractures actually inhibits callus
formation and slows healing. However, stabilisation of the fractures allows the
patient to start moving the soft tissues to promote healing and reduce
stiffness. It also allows the patient to return to a normal independent life
sooner. Physiotherapy is a key element in the rehabilitation of trauma cases.
It:
• allows early mobilisation of the limb while
ensuring that loads are not so excessive that the fixation will fail;
• provides instruction and advice to the patient on
their own rehabilitation;
• builds the patient’s confidence;
• re-trains proprioception so that the feedback loops
between sensors of joint position and tendon load start to co-ordinate with
motor nerves serving the muscles.