OSTEOMYELITIS
Osteomyelitis is defined as an inflammation of the bone caused by an infecting organism. The infection may be limited to a single portion of the bone or may involve numerous regions, such as the marrow, cortex, periosteum, and the surrounding soft tissue. The infection generally is due to a single organism, but polymicrobial infections can occur, especially in the diabetic foot.
The root words osteon (bone) and myelo (marrow) are combined with -itis (inflammation) to define the clinical state in which bone is infected with microorganisms.
Large areas of dead bone or sequestra may be formed when the medullary and periosteal blood supplies are reduced. Reactive new bone may form around infected bone and is termed involucrum. Established or chronic infection comprises a nidus of infected dead bone or scar tissue and an ischemic soft tissue envelope. If established osteomyelitis is not medically and surgically treated, it leads to an indolent refractory infection.
CLASSIFICATION
Osteomyelitis can be classified by:-
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· duration – acute, subacute, or chronic, depending on the duration of symptoms. The time limits defining these classes are arbitrary, however.
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· Pathogenesis – exogenous or hematogenous. Exogenous osteomyelitis is caused by trauma (open fractures), surgery (iatrogenic), or contiguous spread from infected local tissue. The hematogenous form results from bacteremia.
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· host response type – pyogenic or nonpyogenic.
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· site – spine, hip, tibia, foot, etc. extent – size of defect type of patient – infant, child, adult, or compromised host
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Bone infections are classified etiologically by the Waldvogel system (1–3) as-
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· hematogenous osteomyelitis or
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· osteomyelitis secondary to a contiguous focus of infection. Contiguous focus osteomyelitis has been further subdivided into-
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§ osteomyelitis with or without vascular insufficiency.
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In the Waldvogel classification, osteomyelitis may be acute or chronic. Acute disease is characterized by a suppurative infection accompanied by edema, vascular congestion, and small vessel thrombosis. The vascular supply to the bone is compromised as the infection extends into the surrounding soft tissue.
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Systemic and local factors that affect immune surveillance, metabolism, and local vascularity
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Systemic (Bs) Local (Bl)
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Malnutrition Chronic lymphedema
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Renal, hepatic failure Venous stasis
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Diabetes mellitus Major vessel compromise
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Chronic hypoxia Arteritis
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Immune disease Extensive scarring
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Malignancy Radiation fibrosis
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Extremes of age Small vessel disease
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Immunosuppression or immune deficiency Neuropathy
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Asplenic patients
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HIV=AIDS
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ETOH and=or tobacco abuse
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a HIV, human immunodeficiency virus; AIDS, acquired immunodeficiency syndrome; ETOH, Alcohol abuse.
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· Acute hematogenous osteomyelitis is primarily a disease in children.
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· Direct trauma and contiguous focus osteomyelitis are more common among adults and adolescents than in children.
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· Spinal osteomyelitis is more common in persons older than 45 years.
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TABLE 5-1. Comparison of Acute and Subacute Hematogenous Ostemyelitis
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