Introduction, epidemiology, and clinical manifestations

Osteomyelitis is a common term for bone infection, although noninfectious inflammation of bones and adherent structures exist. Strictly speaking, osteomyelitis implicates affection of bone and marrow. The term osteitis would be often more appropriate because no one knows how much infection is inside the marrow in a given episode. As for any infection, physicians like to create big groups of disease headed as acute (AO) and chronic osteomyelitis (CO), although this distinction does not much determine daily clinical practice. For physicians, a commonly accepted definition of AO is a recent bone infection with systemic inflammatory response, while CO requires minimal symptom duration of 6 weeks to 3 months. Another classification system is the presence of a sinus tract, sequestra, or involucra, which are anatomico-pathologic hallmarks of chronic infection. Finally, surgeons have their classification schemes, based on practical aspects of the surgical approach, of which the Cierny-Mader classification is one of the most frequent. The terms acute or chronic are not used in this classification. Generally, surgeons understand a CO as infection requiring surgery, with already established sequestra and bone deformities.

AO is a hematogenous infection that occurs mostly in prepubertal children and in the elderly and is usually located in the metaphyseal area of long bones (children) or in the spine (elderly). It is the result of a local proliferation of bacteria within bone after a septicemic storm. Alternatively, AO can originate locally following trauma or orthopedic surgery (surgical site infection). In contrast, CO has two origins. It may result from either a neglected sequel of AO, or from the continuous spreading of chronic ulcers in paraplegics, bedridden patients, or diabetic patients with foot problems. Epidemiology of osteomyelitis is heterogeneous with variability among involved bones, pathogens, and settings. For example, resource-poor countries may reveal a higher proportion of tuberculous osteomyelitis or CO due to post-traumatic origin compared to resource-rich countries, as well as a higher prevalence of foot osteomyelitis among elderly patients.