| Line 64: |
Line 64: |
| | ==[[Skin Repair|Repair in the Skin]]== | | ==[[Skin Repair|Repair in the Skin]]== |
| | | | |
| − | ==Repair in the Bones== | + | ==[[Fractures|Repair in the Bones]]== |
| − | ===Causes of Fracture===
| |
| − | * The causes of fracture fit into two distinct categories:
| |
| − | *# '''Fracture of trauma'''
| |
| − | *#* 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.
| |
| | | | |
| | ==Repair in the Respiratory Tract== | | ==Repair in the Respiratory Tract== |