Describing a dislocation or fracture
Dislocations and subluxations
A
dislocation is a complete disruption of a joint. The articular surfaces are no
longer in contact. A subluxation is a partial dislocation. Some of the articular
surface is in contact, but the congruence of the two joints has been lost. For
either a dislocation or subluxation the joint needs to be named, and the
direction of the disruption should be described (e.g. an inferior glenohumeral
dislocation).
Fractures
Classification
by quality of bone in relation to load
Fractures
occur when the load to which they are subjected exceeds their intrinsic
strength. A simple traumatic fracture occurs
when an excessive load is applied to normal bone. A pathological fracture is produced when the strength of the bone is
reduced by disease. In this case a force which is within normal limits leads to
a fracture. The disease could be generalised osteoporosis, or a localised lytic
lesion from a metastasis (Table 21.1).
If
bones are subjected to a very large number of loads, none of which alone would
be enough to break the bone, then the mechanical structure of the bone can
gradually fatigue and the bone will then break. This is particularly a problem
for people playing high-level sport and produces a stress
fracture.
Partial
or greenstick fracture. Bones in young people are very flexible. They bend and
then may buckle or partially break, instead of breaking cleanly when overloaded
(as bones in adults do). One characteristic of a greenstick fracture is that
there may be a discontinuity in one cortex of the bone, but not in the other (Fig.
21.3).
Classification
by direction of force
Compression
fractures. If the load applied along the length of a bone exceeds that of its
strength then it may collapse into itself. This is especially common in the
elderly if the bones are osteoporotic, and so are less able to resist a heavy
load. The fracture may be difficult to see. There may only be a small overlap of
the cortical margins of the fracture, while the medulla may look diffusely
radio-opaque (white) because the trabeculae have collapsed into each other.
Overall, the bone will be shortened and may also be angulated.
Avulsion
or distraction fracture. Here the two fragments of bone are pulled apart. In
young patients a ligament or tendon may be stronger in tension than the bone
into which it inserts. If the load is excessive the bone tears apart. These
fractures are particularly common where strong muscles insert into small bones.
Examples are the patella (the quadriceps muscle), the olecranon (triceps) and
the fifth metatarsal head (peroneus tertius).
Spiral
fractures. If a long bone is twisted along its axis a spiral fracture may
result. The length of the spiral is easy to underestimate. It is especially
important to see whether there is any extension into the articular surface of
the bone. The tibia is particularly susceptible to spiral fractures when the
foot is firmly fixed to the ground (by studs or another player’s foot) and the
player’s body continues to twist.
Transverse
fractures. If a long bone is bent along its long axis then a transverse fracture
may result.
Butterfly
fractures. If a bone is struck a direct blow, it is common for a more complex
fracture to result where two break lines spread out obliquely from the point of
contact of the blow, producing a free-floating ‘butterfly’ fragment between
the two fractures.
Comminuted
fractures. Comminuted fractures occur when a large amount of energy is
dissipated into a bone. The bone breaks into fragments which may impact
into each other or separate and become displaced
(Fig. 21.4).
A
long bone is divided into three main zones. The diaphysis is the narrow part of the main shaft. It usually has a
thick cortex and a medulla filled with trabecular bone. The
Classification
of epiphyseal fractures
The
Salter Harris classification of epiphyseal fractures is the simplest and the
commonest used (Table 21.2 and Fig. 21.7).
Grade
1. In this case there is a small crack along the metaphyseal side of the
epiphyseal plate. This side is made up of dying chondrocytes and ossifying
cartilage. The fracture does not affect the blood supply to the epiphyseal plate
nor does it affect the anatomy of the germinal layer. It therefore heals quickly
and without long-term problems, like children’s hone elsewhere.
Grade
2. Here the fracture line again travels along the metaphyseal side of the plate
but, before reaching the far cortex, it breaks out and
Grade
3. In this case the fracture line does not run along the epiphyseal plate at
all. It crosses from the metaphysis to the epiphysis. If it is displaced then it
may heal with a step in the epiphyseal plate. Bony union may occur across the
epiphyseal plate and block further growth, causing a most disfiguring
progressive deformity of the limb if it is not promptly released. The key to the
management of this type of fracture is anatomical reduction if it is displaced.
This type of epiphyseal plate fracture is rare.
Grade
4. Here the fracture line travels along the distal (epiphyseal) side of
the growth plate affecting both the blood supply and the anatomical
integrity of the germinal cells. The fracture line does not travel the whole
length of the epiphyseal plate but deviates off into the epiphysis itself and
out on the articular surface. This is a second reason why this fracture has a
poor prognosis. Not only is the growth plate likely to be damaged, but the
articular surface may be incongruent. This predisposes the joint to early
arthritis. The key to successful management of this type of fracture is
anatomical reduction. This will be best performed by open surgery. Once again,
this type of fracture is rare.
Grade 5. This is a rare and difficult fracture to diagnose. The injury is a severe crush of the epiphyseal plate. The X-ray may only look abnormal in retrospect, and this is indeed how this type of fracture is usually diagnosed. The consequence of complete disruption of the growth plate is complete growth arrest. There is little that can be done to prevent this, or indeed deal with it, once it has occurred
Open fractures.
At the time of a fracture the soft tissues over the bone will
also be damaged. If the skin is broken there is a high probability that at some
time during the accident the fracturing bone came into contact with the
outside world, and so could be contaminated with bacteria. If there is no broken
skin anywhere near a fracture, the fracture can be assumed to be closed
and will initially be free of infection. If, however, there is any break in
the skin anywhere near the fracture it is important that the fracture is
classified as open and treated as such. The bone will need exposing and a
careful search made to allow all dead or contaminated tissue to be removed. The
wound will also need washing out and should be left open. It is always best to
err on the safe side, and if there is any doubt whatsoever to treat the fracture
as ‘open’.
Classification
by position
Bones
have a very strong covering (the periosteum) which is invisible on X-ray. When a
bone breaks the periosteum is torn, but it is unusual for the periosteum to be
completely disrupted. This is very important for othopaedic surgeons because the
periosteum can be used to obtain a good position when reducing a fracture. It
can even act before that. Its elasticity may serve to reduce the fracture after
the trauma. If a fracture is seen to be undisplaced on X-ray, that does not mean
that it was never displaced, it just means that much of the periosteum is
intact. Even displaced fractures usually
have at least part of the sleeve of periosteum intact (on the side of concave
curvature), but once again the displacement at the time of trauma was always
greater than that seen afterwards. This is why apparently innocuous looking
minimally displaced fractures with a small puncture wound over them should be
assumed to be open.
Deciding
whether a fracture is stable or unstable is yet another type of classification,
‘classification by management’.
Stable
fractures are
those which are unlikely to move further. Unstable
fractures are those which will continue to displace if action is not taken
to hold the fracture secure. There is a gradation of stability which depends on
the following factors.
Site.
Fractures in weight-bearing bones are more likely to be displaced by
‘normal’ loads than those in bones which can easily be protected from load,
such as the long bones of the arm.
Shape.
Spiral fractures tend to be unstable, while impacted fractures tend to be very
stable. The more displaced the fracture, the more unstable it is likely to be.
Displacement.
Undisplaced fractures may have the periosteum intact and are therefore stable.
The more displaced the fracture, the more unstable it is likely to be.
Behaviour
of the patient. Patients who are prepared to be careful can maintain the
position of a fracture which would become displaced in a young hard-drinking
male, who is not prepared to take any advice.
International
classifications
The
AO classification is an internationally agreed classification of fractures
using a simple alphanumeric code. The first number relates to the bone (humerus
is 1, radius and ulna are 2, etc.). The second number relates to the position of
the fracture on the bone (1 is proximal, 2 diaphyseal and 3 is distal). The
position number is followed by a letter which defines the severity of the
fracture. For proximal and distal fractures (types 1 and 3) ‘A’ is extra-articular,
‘B’ is partial articular and ‘C’ is intra-articular. For diaphyseal
fractures (type 2) ‘A’ is a simple fracture, ‘B’ is a wedge or butterfly
type and ‘C’ is comminuted or complex. This letter is followed by a further
number which classifies the fracture still further.
Charts
are available to help you to decide the exact classification of each fracture
(see Fig. 21.8)
The
advantage of this classification is that it is international and has been
carefully validated to make sure that, as far as possible, everyone looking at
the same fracture would classify it in the same way. The disadvantage is that a
string of numbers is not very memorable. If you say to most trauma surgeons that
a fracture is a 32B3.2, it is unlikely that they would immediately know that you
were talking about a distal third comminuted fracture of the femur.
A
second problem is that for a classification to be useful it should point to both
treatment and prognosis. One of the key features which determines treatment and
indeed prognosis in a fracture is soft-tissue damage (especially whether the
fracture is open or not). A second major feature is whether a fracture is
displaced or not, as this may make a big difference to any decision on
management. Neither of these two important prognosticators is covered in the
AO classification.