Question

Pathophysiological process of osteomyelitis. Please include the cellular, tissue, or organ levels that contribute to the disease process.

Thanks

Answer 1

Pathophysiological process of Osteomyelitis

Osteo - Bone

Myel -  Bone marrow

Itis - Inflammation

Osteomyelitis is the inflammation of bone or bone marrow caused by an infecting organism.

Bacteria reaches the bone through blood stream( hematogenous spread), immunosupressant condition, direct inoculation or through spread from adjacent areas( eg. Diabetic foot ulcer). The bacteria adhere to the bone. Patient specific risk factors like diabetes, increasing age predisposes to acute infection. If acute infection prolongs it results in chronic infection which is characterized by necrotic tissue and sequestra.

Osteomyelitis can either be pyrogenic( pus formation) or non pyrogenic( no pus formation). Staylococcous aureus is the most common cause of pyrogenic Osteomyelitis.

Other organism that causes Osteomyelitis includes Staphylococcus epidermis; Treponema pallidum; Salmonella species; Klebsiella species. Also fungal species like Aspergillus species; Candida ciferri; Blastomycosis also causes Osteomyelitis.

Bacterimia is a common phenomenon. Normally, when bacteria enter into blood flow, recticulo endothelial system phagocyte and eliminate the bacteria but if due to any reason if bacteria survive in the blood, they love to settle in certain areas in the body.

In the case of bones of growing children, bacteria like to settle in metaphysis of long bones. Metaphysis is absent in adults. So in adults, Osteomyelitis commonly seen in vertebrae.

BIOLOGICAL EVENTS THAT OCCURS WHEN BACTERIA ENTER INTO THE BONE

Bone is made up of epiphysis, metaphysis, periosteum,endosteum and articular cartilage.

(Refer the attached image)

When blood reaches the metaphysis of the bones, the area where the arteries meets the veins the vascular pattern become loop shape. Here, the blood flow become very slow and turbulent. This provide favourable environment for the adherence of bacteria. Bacteria express some surface molecules and sticks to the bone and this causes the damage to local tissue. The local tissues and adhered bacteria produce chemical mediators of inflammation. As a result inflammatory reactions occur which leads to formation of pus. Also there will be formation of sequestrum( a piece of dead bone tissue formed within a diseased bone due to chronic Osteomyelitis.