Acute Osteomyelitis: Etiology, pathogenesis
It is an inflammation of the bone and marrow (osteo- means bone and myelo – marrow), commonly in children and adolescents
Route: Hematogenous spread – most common in long and vertebral bones extension from contagious site- otitis media, dental caries and direct implantation-compound fracture
All types of organisms possible; however, pyogenic organisms most notably Staphylococcus aurous represent 80 – 90% of pyogenic osteomylitis. Others include pseudomonas, Klebsiella, Salmonella in sickle cell anemic patients.
Sites: Any bone may be affected but the metaphysics of long bones (distal femur, proximal tibia and humorus) adjacent to actively growing epiphyses and the vertebral column are most often involved.
The location of the lesions within specific bones is influenced by the vascular circulation, which varies with age. In the neonate, the metaphysical vessels penetrate the growth plate resulting in frequent infection of the metaphysis, epiphysis or both.
In children, localization of microorganisms in the metaphysics is typical.
In adults, the epiphyscal growth plate is closed and the metaphysical vessels reunitewith their epiphyses counterparts, which provide a route for bacteria to seed in theepiphysis and subchondral regions.·
The susceptibility of the metaphysis to acute osteomylitis is in part, explained by the dilated vascularature of the marrow spaces where sluggish blood flow provides an idealsite for multiplication of bacteria. Then acute inflammatory response with exudation follows with venous and arterial thrombosis. These reaction increases intravenous pressure with a resultant bonenecrosis. Infection spreads rapidly through marrow spaces which perpetuates the Haversian systems of the metaphysical cortex, elevates the periosteum and forms a sub-periosteal abscess in children and adolescents as opposed to adults periosteum that is adherent to the bone.
Accession of both peri-osteal and endo-osteal vessels lead to segmental bone necrosis of some or all of the diaphysis, the portion of dead bone is known as a sequestrum.·
Small sequestra especially in children tend to be completely absorbed by osteoclastic activity. Large sequestra form a nidus for episodes of infection. In the presence of a sequestrum, the periosteal reactive woven or laminar bone may be deposited as asleeve of living tissue known as involcrum, around the segment of devitalized bone (sequestrum). The involcrum around sequestrum is usually irregular and perforated.·
In infants, acute ostemylitis may complicate acute arthritis through infrequent it also occurs in adults. The picture is different in children. The patient complains of fever, sever pain and tenderness aggravated by any movement, ESR elevated, leukocytosis. Complications include septicemia, septic arthritis, alteration in growth rate, chronic osteomylitis
Figuring out if a person has osteomyelitis is the first step in treatment. It’s also surprisingly difficult. Doctors rely on X-rays, blood tests, MRI, and bone scans to get a picture of what’s going on. A bone biopsy helps determine the type of organism, typically bacteria, causing the infection so the right medication can be prescribed.