One form of malunion is the malrotation of a bone, which is especially common after femoral and tibial fractures. Complications of fractures may be classified into three broad groups, depending upon their time of occurrence. These are as follows –

Immediate complications – occurs at the time of the fracture. Early complications – occurring in the initial few days after the fracture. Late complications – occurring a long time after the fracture. Pathophysiology
The natural process of healing a fracture starts when the injured bone and surrounding tissues bleed, forming a fracture hematoma. The blood coagulates to form a blood clot situated between the broken fragments. Within a few days, blood vessels grow into the jelly-like matrix of the blood clot. The new blood vessels bring phagocytes to the area, which gradually removes the non-viable material. The blood vessels also bring fibroblasts in the walls of the vessels and these multiply and produce collagen fibres. In this way, the blood clot is replaced by a matrix of collagen. Collagens rubbery consistency allows bone fragments to move only a small amount unless severe or persistent force is applied.At this stage, some of the fibroblasts begin to lay down bone matrix in the form of collagen monomers. These monomers spontaneously assemble to form the bone matrix, for which bone crystals (calcium hydroxyapatite) are deposited in amongst, in the form of insoluble crystals. This mineralization of the collagen matrix stiffens it and transforms it into bone.
Cause
Risk factors
More than 70% of cases are recorded in people with at least one of these clinical situations: immunosuppression, diabetes, alcoholism/drug abuse/smoking, malignancies, and chronic systemic diseases. For reasons that are unclear, it occasionally occurs in people with an apparently normal general condition.Necrotizing fasciitis can occur at any part of the body, but it is more commonly seen at the extremities, perineum, and genitals. Only a few of such cases arise from the chest and abdomen. Trauma is the usual cause of the infection, such as from intravenous drug injection, insulin injection, animal and insect bites, catheter insertion over the skin, or a fistula connecting skin to the internal body organs. Skin infections such as abscess and ulcers can also complicate necrotizing fasciitis. Spreading of infection through blood has been suggested for those with streptococcal pharyngitis. For infection of the perineum and genitals (Fournier gangrene), trauma, surgery, urinary tract infection, stones, and Bartholin gland abscess are the usual causes.The risk of developing necrotizing fasciitis from a wound can be reduced by good wound care and handwashing. Bacteria
Types of soft-tissue necrotizing infection can be divided into four classes according to the types of bacteria infecting the soft tissue. This classification system was first described by Giuliano and  his colleagues in 1977.Type I infection: This is the most common type of infection, and accounts for 70 to 80% of cases. It is caused by a mixture of bacterial types, usually in abdominal or groin areas.