Author, Donkey, Bureaucrats, Administrators
53,803
edits
Changes
Healing and Repair - Pathology (view source)
Revision as of 18:33, 27 February 2011
, 18:33, 27 February 2011→Repair in the Bones
Line 64:
Line 64:
===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===
−* 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.
−
−* 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.
==[[Skin Repair|Repair in the Skin]]==
==[[Skin Repair|Repair in the Skin]]==
−==Repair in the Bones==
+==[[Fractures|Repair in the Bones]]==
−[[Image:fracture repair.jpg|thumb|right|150px|Fracture repair (Courtesy of BioMed Archive)]]
−===Complications===
−==Repair in the Respiratory Tract==
==Repair in the Respiratory Tract==