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).

  Classification by anatomical site

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 metaphysis is the flare at each end between the diaphysis and the epiphyseal (growth) plate. It has thinner cortical bone and its medulla is, again, filled with trabecular bone. The ends of a long bone beyond the epiphyseal plate are called the epiphyses (singular epiphysis). They are covered mainly by articular cartilage but may have a cuff of thin cortical bone. In infants and children, in whom the bones are still growing, the epiphyseal plate will be open. The plate is weaker than the bone around and so fractures tend to track along it or even across it. Epiphyseal fractures are important because they can have a poor prognosis. Fractures into the joint (articular fractures) are also important because they carry a very poor prognosis if they are not anatomically reduced (Fig. 21.6).

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 tracks down into the metaphysis. This is by far the most common epiphyseal fracture, and for the same reason as given above has a good prognosis. Even if the fracture is markedly displaced the prognosis remains good. In children the bone will remodel and grow straight over the next year, especially if no rotatory abnormality is involved. In fact, one of the greatest risks in a grade 2 fracture is causing growth arrest by damaging the growth plate while reducing the fracture, especially if this is attempted after a few days when the fracture may already be uniting.

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’.

  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.