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− | * [[Diaphyseal Fractures - Small Animal]] | + | ===Causes of Fracture=== |
− | * [[Fractures - Bovine]] | + | * The causes of fracture fit into two distinct categories: |
− | * [[Fractures - Equine]] | + | *# '''Fracture of trauma''' |
− | * [[Non-diaphyseal Fractures - Small Animal]] | + | *#* Breakage of normal healthy bone due to excessive stress pressure of short duration. |
| + | *# '''Pathological fracture''' |
| + | *#* Breakage of bone weakened by some underlying metabolic, inflammatory or neoplastic condition. |
| + | |
| + | ===Description of a Fracture=== |
| + | * There are various terms to describe a fracture's appearance. |
| + | * Separation of the ends of the fracture may be '''complete''' or '''incomplete'''. |
| + | * When there is no penetration of the overlying skin, a the fracture is described as '''closed'''. |
| + | * When the sharp ends penetrate the overlying skin, the fracture is '''compound'''. |
| + | ** In this scenario there is the danger of introducing infection. |
| + | *'''Comminuted''' describes a fracture where there are multiple small fragments of bone at the site of breakage. |
| + | * Where the edges of the fracture are impacted into each other, the fracture is said to be '''compressed'''. |
| + | * When one side of the fracture is depressed below the plane of the other, the term '''depressed''' is used. |
| + | ** This occurs in the flat bones of the skull. |
| + | * '''Microfractures''' are fractures that are only visible on histological section as cracks in the bone. |
| + | ** Grossly, there might be evidence of some haemorrhage in the area. |
| + | |
| + | ===Fracture Repair=== |
| + | [[Image:fracture repair.jpg|thumb|right|150px|Fracture repair (Courtesy of BioMed Archive)]] |
| + | * On breakage, there is rupture of the periosteal, cortical and medullary vessels, causing: |
| + | ** A blood clot in the breakage area. |
| + | *** Fibrin is the important component. |
| + | ** Local necrosis of tissue supplied by these vessels. |
| + | *** This lowers the local pH. |
| + | * The fate of the blood clot depends upon its location. |
| + | ** The periosteal portion is lysed and disappears; |
| + | ** The medullary portion is removed by macrophages. |
| + | * The necrotic material is removed by phagocytosis. |
| + | ** Necrotic [[Bone Marrow - Anatomy & Physiology|bone marrow]] is removed by [[Macrophages|macrophages]]. |
| + | *** This is a fairly rapid process. |
| + | ** Osteoclasts remove necrotic bone. |
| + | *** This is a slow process. |
| + | * On the periosteal side, the periosteum proliferates into the clot. |
| + | ** Forms a fibrous collar around the bone called the soft callus. |
| + | * The cells in the inner aspect of the soft callus, particularly those near the fracture fragments, differentiate into osteoblasts. [[Image:fracture callus.jpg|thumb|right|150px|Fracture callus (Courtesy of BioMed Archive)]] |
| + | ** Grow across the divide between the two fragments, laying down coarse woven bone. |
| + | * The woven bone laid is known as the hard callus. |
| + | ** This periosteal coarse bone is of utmost importance in repair. |
| + | *** It is responsible for much of the strength of the fracture repair. |
| + | ** This is replaced over a period of time by mature compact bone. |
| + | *** Aligns itself according to the stresses applied to it. |
| + | * Periosteal cells that are further away from the fracture fragments differentiate into cartilage-producing cells. |
| + | ** Produce a cone of cartilage between the two fragments. |
| + | *** As the local pH changes to more alkaline conditions, this cartilage undergoes calcification, with invasion by blood vessels and osteoblasts. |
| + | **** The cartilage is replaced by bone - endochondral ossification. |
| + | * On the medullary side, the endosteum proliferates and invades the clot, laying down bone. |
| + | ** This bone may totally occlude the medulla and is later remodelled to reconstitute a patent lumen. |
| + | |
| + | ===Complications=== |
| + | * There are several possible complications that may arise in the repair of bone. |
| + | # Inadequate immobilisation of the fractured ends will lead to incomplete repair by callus formation. |
| + | #* An intervening mass of fibrocartilage remains, forming a false joint. |
| + | #** In some cases the false joint can even appear to form a synovial lining. |
| + | #* If the fractured ends are sufficiently far apart, no substantial callus forms. |
| + | #** The intervening space is taken up by connective tissue organisation. |
| + | # Failure to align the fractured ends in proper apposition to one another will produce excessive callus. |
| + | #* This takes a longer time to be remodelled by the adult compact bone. |
| + | # [[Healing and Repair - Pathology#Description of a Fracture|Comminution]] delays healing due to persistent irritation. |
| + | # Infection delays healing due to the effects of the toxins on theproliferating cells. |
| + | #* May give rise to a systemic infection affecting the rest of the body. |