Osteomyelitis, an infection of bone that leads to tissue destruction and often to debility, can be caused by a wide variety of bacteria (including mycobacteria) and fungi and may be associated with viral infections. Its management must be individualized and depends on numerous factors, including the causative organism, the specific bone involved, vascular supply, nerve function, foreign bodies, recent injury, the physiologic status of the host, and associated comorbidities. The spectrum of the disease can range from extensive (e.g., tibial and vertebral osteomyelitis) to localized (e.g., bone invasion associated with a tooth abscess). Two major classification systems for osteomyelitis are used in making decisions about medical therapy and surgery. Lee and Waldvogel categorized cases as acute or chronic, hematogenous or contiguous, and with or without vascular compromise. The Cierny and Mader classification system for long-bone osteomyelitis encompasses the location and extent of the infection as well as a number of other factors.
Table 126–1 Microorganisms that Cause Osteomyelitis
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Table 126–1 Microorganisms that Cause Osteomyelitis
|Frequently Encountered Bacteria|
Most likely bacterial pathogen
Often metastatic foci with bacteremia
Consider surgery early
|Staphylococci other than S. aureus (coagulase-negative)|
Usually associated with foreign material or implants
|Streptococci||May spread rapidly through soft tissues|
|Enterobacteriaceae (Escherichia coli, Klebsiella, others)|
Considerable variation in antibiotic susceptibility
Increasing antibiotic resistance with overuse
May become resistant to antibiotics during therapy
Increasingly resistant to antibiotics
Frequent successor to other bacteria when initial therapy fails
May be related to contamination
Usually mixed with aerobic bacteria
May be synergistic
Survival dependent on devitalized tissue
|Bartonella henselae||Associated with cat scratches and probably with fleas|
|Brucella species||Prominent in developing countries, especially with unpasteurized milk|
Candida the most likely genus
Considerable variation in susceptibility, depending on species
Surgery may be helpful if infection is invasive
May involve any bone
Vertebral osteomyelitis common in some countries
|Mycobacteria other than M. tuberculosis||Need special culture media to recover|
|Viruses||Associated with some viral infections, including varicella and variola|
The foremost bacterial cause of osteomyelitis is Staphylococcus aureus. Gram-negative organisms such as Pseudomonas aeruginosa and Escherichia coli, coagulase-negative staphylococci, enterococci, and propionibacteria may also be involved. Mycobacterium tuberculosis is a common cause of osteomyelitis in countries with limited medical resources; other mycobacterial species that infect bone include M. marinum, M.chelonei, and M. fortuitum. Fungal etiologies include Candida, Coccidioides, Histoplasma, and Aspergillus species. Noninfectious pathogenic mechanisms that may cause disease mimicking osteomyelitis include avascular necrosis, rheumatoid diseases, neuropathy with chronic trauma, gout, and malignancies.
The precipitating event(s) for osteomyelitis vary greatly. The prosthetic joint implants and stabilization devices that are increasingly being used in orthopedic surgery are associated with complex infections. Trauma is also a common cause of infection, especially when a wound is involved and there is contamination of bone or surrounding tissue along with significant tissue damage or destruction. Even in the absence of an open wound or a compound fracture, damaged tissue and extravasated blood may slow the circulation, establishing a favorable medium for the growth of bacteria that may reach the area through low-level bacteremia from the peripheral venous circulation or from distal lymphatic channels. Bacteremia—whether due to endocarditis or due to seeding from other sites of infection (e.g., abscesses, boils, or vascular devices)—is also a frequent etiologic factor in osteomyelitis. Studies of S. aureus bacteremia indicate a rate of metastatic osteomyelitis approaching 28% if there is a prosthetic joint in place; S. aureus bacteremia can be complicated by the involvement of methicillin-resistant strains (MRSA), which are progressively replacing strains that are more susceptible to antibiotics. The overlapping circulations of the urinary tract and the spine may be a source of vertebral osteomyelitis due to urinary tract pathogens such as E. coli and Klebsiella. Additional predisposing factors include a poor arterial and venous supply, which may limit perfusion to bone to the point of an inadequate response and poor healing, even in patients with normal function. Host factors such as diabetes and its consequences contribute significantly to the development of osteomyelitis through impaired immunity with hyperglycemia, loss of sensation, vascular disease, and renal failure.
In the United States, acute osteomyelitis affects ∼0.1–1.8% of the otherwise healthy adult population. After a foot puncture, 30–40% of adults with diabetes develop osteomyelitis. In this country, there has been a major change in the profile of certain bacterial pathogens, with the emergence of MRSA strains over the last decade. MRSA has become a source of great concern in hospitals, especially after surgery. The morbidity and economic consequences appear to be greater for MRSA osteomyelitis than for osteomyelitis caused by methicillin-sensitive S. aureus strains. However, it is not clear that these poorer outcomes for MRSA are due to new or more destructive virulence factors. Rather, they may simply be the result of a delay in effective antimicrobial treatment.
The types and etiologies of osteomyelitis vary by region and with time. The United States has seen a rise in infections related to the increasing use of orthopedic surgery for correction of deformities and implantation of screws, pins, rods, plates, and prosthetic joints. With the aging of populations and the epidemics of obesity and diabetes in some countries, the frequency of these predisposing factors continues to increase, requiring adaptations in treatment approaches. Any type of instrumentation may lead to infection in a small proportion of cases. Osteomyelitis attributable to orthopedic devices and surgical interventions is considerably less common in countries with limited medical resources, where tuberculosis may be the dominant infection and brucellosis is not unusual. In many of these areas, agricultural injuries, industrial accidents, and war wounds are much more common than in wealthy countries, and the pathogens ...