The term malunion is applied to a bone that has united soundly but in the wrong position (Fig. 7.5). This sounds alarming but does not always matter greatly. Fractures of the clavicle almost always unite with a little shortening and overlap, which is quite acceptable and does not affect the functional result, but in fractures where the fragments are pulled apart by the unopposed action of different muscle groups, the functional result of malunion is poor.

Cross-union. Cross-union, in which two adjacent bones become linked by new bone, is a variety of malunion. Cross-union in the forearm blocks pronation and supination.

If the healing process fails, the bone ends do not unite and remain separate. This is a serious problem in a weight-bearing bone but may cause less disability in other situations, such as a fractured metacarpal. Two types of non-union are seen: (1) hypertrophic, and (2) atrophic.

Hypertrophic non-union is characterized by a massive cuff of bone around the ends of the fractures that looks a little like an elephant’s foot (Fig. 7.6a). These fractures are trying desperately to heal and can be helped to do so by realigning the limb and preventing movement between the bone ends. Prevention of movement can be done by rigid internal fixation, or intramedullary or extramedullary stabilization.

Atrophic non-union shows rounding of the bone ends (Fig. 7.6b), sometimes so marked that the tips of the bone ends resemble pencils, and the medullary cavity may be closed. This is indicative of a poor blood supply to the bone ends.

A pseudarthrosis forms in some patients (Fig. 7.7). If there is no sign of osteogenesis, treatment must aim to ‘kick start’ this by bone grafting with fresh cancellous bone or marrow.

A fracture with delayed union takes longer to unite than normal but eventually does so. It is important to distinguish delayed union from non-union, as delayed unions will unite with time and attention to correct immobilization of the fracture fragments. Non-unions, however, may need operative intervention in order to allow the bone ends to unite. Separation of the two types can be difficult. Unless there are positive signs of non-union, such as closing of the medullary cavity of the fragments, which makes the diagnosis easy, or an improvement between one radiograph and the next, diagnosis rests on comparing the rate of bone union with the normal rate of healing of a fracture in the same situation.

Fractures can be classified in many ways but the simplest and most practical was the ancient classification of the old military surgeons who regarded all fractures as simple or compound.

Potentially infected fractures can now be treated and immediate amputation is a thing of the past, but anaerobic bacteria are just as lethal as ever. Any fracture beneath a contaminated wound should be regarded as ‘compound’ in the ancient sense and treated energetically (p. 132 and p. 312).

Modern treatment of ‘compound’ fractures is so effective that the term is no longer applicable. Apart from this, fractures with intact skin can be far from ‘simple’ to treat and ‘compound’ may be confused with complicated, comminuted or multiple. ‘Simple’ and ‘compound’ have been replaced by ‘ closed’ and ‘ open’ but ‘compound’ is sometimes used to describe how the skin has been damaged (Fig. 7.8). A fracture in which the skin has been penetrated by a bone fragment from inside the leg is sometimes referred to as ‘compound from within’ to distinguish it from a true open fracture and to emphasize the potential danger.

Fractures can also be classified according to the shape of the fragments and this is helpful in deciding management (Fig. 7.9).

Transverse fractures are the result of a direct blow or a pure angular force applied to the bone. The shape of the bone ends helps transverse fractures to stay aligned more easily than fractures which do not fit together so neatly.

Oblique or spiral fractures. Most long bone fractures are caused by a violent twisting movement about the long axis of the bone rather than the sideways bending which causes a transverse fracture. A sharp twist to the leg while the foot is stuck in a rabbit hole produces a spiral fracture of the tibia, even if radiographs suggest that the fracture line is oblique. In fact, oblique fractures are rare and are almost always a radiological artefact.

The fragments of a spiral fracture are more difficult to balance against each other than the square end of a transverse fracture and are very unstable. The bone spikes damage blood vessels, nerves or skin and the tips of the spikes can themselves break off to produce a triangular fragment known as a ‘butterfly’ fragment.

Crush fractures. A fracture in which cancellous bone is squashed or crushed presents a difficult problem because there are no fragments left to manipulate back into position. If the fracture site is opened up and the cortex of the bone replaced in its normal position, a large cavity remains and the bone can only be restored to its normal shape by packing the space with bone graft or holding the sides of the cavity apart by external fixation.

Crush fractures are typically seen in the lumbar vertebrae, tibial plateaux and calcaneum.

Greenstick fractures. When a green stick breaks, it does not snap cleanly but bends so that one ‘cortex’ buckles while the other remains intact. If the force is very great, one side may snap while the other remains intact – try it. If a green stick fractured in this way is straightened it bounces back slightly but will not hold its correct position.

Fractures of long bones in children behave in the same way. The compressed cortex first buckles to produce a ‘buckle’ fracture. If the force continues, the cortex under tension will fracture (Fig. 7.10). Because of the resilience of the bone, reduction is only possible if the fracture is made complete or if three-point pressure (p. 127) is applied. Fortunately, fractures in children remodel well enough to restore the normal anatomy and the deformity of most greenstick fractures can be accepted.

Bones can be broken by a direct blow and many patterns are seen. A sharp blow on the front of the knee may shatter the patella into many small fragments held together by soft tissue, like a boiled sweet broken in its wrapper (p. 254), but the fragments of a tibia fractured in a road traffic accident will be widely separated.

More fractures are caused by indirect violence than direct violence. In this type of trauma, usually a twisting injury, no violence is applied to the site of the fracture itself. Open fractures are therefore uncommon, although the bone fragments can penetrate the skin from inside, making the fracture ‘compound from within’.

Pathological fractures occur through abnormally weak bone. Tumours, cysts and osteoporotic bone are common sites of pathological fractures (Fig. 7.12).

Repeated small bending stresses will break any material (Fig. 7.13