Friday, January 15, 2010

Osteomyelitis





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:-
·    duration - acute, subacute, or chronic, depending on the duration of symptoms. The time limits defining these classes are arbitrary, however.
·    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.
·    host response type - pyogenic or nonpyogenic.
·    site - spine, hip, tibia, foot, etc. extent - size of defect type of patient - infant, child, adult, or compromised host
Bone infections are classified etiologically by the Waldvogel system (13) as-
·    hematogenous osteomyelitis or
·    osteomyelitis secondary to a contiguous focus of infection. Contiguous focus osteomyelitis has been further subdivided into-
§ osteomyelitis with or without vascular insufficiency.
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.
Cierny and Mader proposed a classification system for chronic osteomyelitis based on host factors and anatomical criteria. This system is described further in the section on chronic osteomyelitis.


Systemic and local factors that affect immune surveillance, metabolism, and local vascularity
Systemic (Bs)                                                                                           Local (Bl)
Malnutrition                                                                   Chronic lymphedema
Renal, hepatic failure                                                                      Venous stasis
Diabetes mellitus                                                       Major vessel compromise
Chronic hypoxia                                                           Arteritis
Immune disease                                                          Extensive scarring
Malignancy                                                                      Radiation fibrosis
Extremes of age                                                           Small vessel disease
Immunosuppression or immune deficiency                    Neuropathy
Asplenic patients
HIV=AIDS
ETOH and=or tobacco abuse
a HIV, human immunodeficiency virus; AIDS, acquired immunodeficiency syndrome; ETOH, Alcohol abuse.
Race : There is no increased incidence of osteomyelitis based on race.
Sex : Male-to-female ratio is approximately 2:1.
Age : In general, osteomyelitis has a bimodal age distribution.
·   Acute hematogenous osteomyelitis is primarily a disease in children.
·   Direct trauma and contiguous focus osteomyelitis are more common among adults and adolescents than in children.
·   Spinal osteomyelitis is more common in persons older than 45 years.


TABLE 5-1. Comparison of Acute and Subacute Hematogenous Ostemyelitis
Acute
Subacute
WBC count
Frequently elevated
Frequently normal
ESR
Frequently elevated
Frequently elevated
Blood cultures
50% positive
Rarely positive
Bone cultures
90% positive
60% positive
Localization
Metaphysis
Diaphysis, metaphysis, epiphysis, cross physis
Pain
Severe
Mild to moderate
Systemic illness
Fever, malaise
No
Loss of function
Marked
No or minimal
Prior antibiotics
Occasional
30%-40%
Initial radiograph
Bone normal
Frequently abnormal