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OSTEOMYELITIS
Definition:
Osteo- derived from the Greek word osteon meaning bone, myelo meaning marrow and –it is meaning inflammation, simply means an infection of the bone or bone marrow that results in inflammation, necrosis and formation of new bone. Types:

1.Acute osteomyelitis
-Bone infection develops within two weeks of an initial infection, injury or the onset of the underlying disease. 2.Sub-acute osteomyelitis
-Bone infection develops within one to two months of an initial infection, injury or the onset of the underlying disease. 3.Chronic osteomyelitis
-- Bone infection develops within two months or more of an initial infection, injury or the onset of the underlying disease. Classification:
1.Hematogenous
-Through bloodstream
-Blood borne spread of infection
-Involves rich red marrow
-In children and infants: the long bone

2.Contagious focus
-Extension from adjacent tissue infection

3.Direct infection to the bone or exogenous
-Microbes gain entry to the bone through open fractures, penetrating wounds, or contamination in surgical procedure -Implanted items may also cause infection
Etiology:
Osteomyelitis is caused by:
Contiguous spread
Blood borne organisms
Open wounds
Most common causative agent: Staphylococcus aureus

Risk factors:
Gender(male)
Poorly nourished
Elderly
Children
Obese
Patients who have impaired immune system
Patients with chronic illnesses (e.g. Diabetes, rheumatoid arthritis) Patients receiving long tern corticosteroid therapy or other immunosuppressive agents

Anatomy and physiology:

Bone
Each long bone consists of a central shaft called the diaphysis, and the two ends, each called an epiphysis. A thin layer of articular cartilage covers the end of the epiphyses where the bone articulates with other bones. A long bone that is still growing has an epiphyseal plate, and the diaphysis. The epiphyseal plate is the site of growth in bone length. When bone growth stops, the cartilage of each epiphyseal plate is replaced by bone and is called an epiphyseal line. Bones contain cavities such as the large medullary cavity in the diaphysis, as well as smaller cavities in the epiphyses of long bone and in the interior of other bones. These spaces are filled with either yellow or red marrow. Marrow is the soft tissue in the medullary cavities of the bone. Yellow marrow consists mostly of fat. Red marrow consists of blood forming cells and is the only site of blood formation in adults. Children’s bones have proportionately more red marrow than do adult bones. As the person ages, red marrow is mostly replaced by yellow marrow. In adults, red marrow is confines it the bones in the central axis of the body and in the most proximal epiphyses of the limbs. Most of the outer surface of bone is coveres by dense connective tissue called the periosteum, which contains blood vessels and nerves. The surface of the medullary cavity is lined with a thinner connective tissue membrane, the endosteum. The periosteum and the endosteum contain osteoblasts, which function in the formation of bone, as well as in the repair and remodelling of bone. When osteoblasts become surrounded by matrix, they are referred to as osteocytes. Bone is formed in thin sheets of extracellular matrix called lamellae, with osteocytes, located between the lamellae. Osteocytes are located within spaces called lacunae. Cell processes extend from the osteocytes across the extracellular matrix of the lamellae within canals called canaliculi. There are two major types of bone, based on their histological structure. Compact bone is mostly solid matrix and cells. Cancellous bone consists of a lacy network of bone with many small, marrow-filled spaces Blood production in red marrow

blood cell formation, also called Hematopoiesis, or Hemopoiesis, red blood cell [Credit: Micro Discovery/Corbis]continuous process by which the cellular constituents of blood are...
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