Osteomyelitis

Osteomyelitis
Specialty	Rheumatology, podiatry

Osteomyelitis is an infection of bone or bone marrow, usually caused by pyogenic bacteria or mycobacteria. It can be usefully subclassifed on the basis of the causative organism, the route, duration and anatomic location of the infection.

Presentation

Generally microorganisms may be disseminated to bone hematogenously (i.e., via the blood stream), spread contiguously to bone from local areas of infection, such as cellulitis, or be introduced by penetrating trauma including iatrogenic causes such as joint replacements or internal fixation of fractures. Leukocytes then enter the infected area, and in their attempt to engulf the infectious organisms, release enzymes that lyse bone. Pus spreads into the bone's blood vessels, impairing the flow, and areas of devitalized infected bone, known as sequestra, form the basis of a chronic infection. On histologic examination, these areas of necrotic bone are the basis for distinguishing between acute osteomyelitis and chronic osteomyelitis. Osteomyelitis is an infective process which encompasses all of the bone (osseous) components, including the bone marrow. When it is chronic it can lead to bone sclerosis and deformity.

Because of the particulars of their blood supply, the tibia, the femur, the humerus, and the vertebral bodies are especially prone to osteomyelitis.

Etiology

Acute osteomyelitis almost invariably occurs in children. When adults are affected, it may be because of compromised host resistance due to debilitation, intravenous drug abuse, disease or drugs (e.g. immunosuppressive therapy).

Treatment

Osteomyelitis often requires prolonged antibiotic therapy. IV antibiotics are generally used to combat the infection, with a course lasting a matter of weeks or months. A PICC line or central venous catheter is often placed for this purpose. Osteomyelitis also may require surgical debridement. Severe cases may lead to the loss of a limb. Initial first line antibiotic choice is determined by the patient's history and regional differences in common infective organisms. American artist Thomas Akins in 1875 depicted a surgical procedure for osteomyelitis in a famous oil painting titled "The Gross Clinic", now part of Jefferson Medical College.

Causes

The vast predominance of hematogenously seeded osteomyelitis is caused by Staphylococcus aureus. Escherichia coli, and streptococci are other common pathogens. In some subpopulations, including intravenous drug users and splenectomized patients, Gram negative bacteria, including enteric bacilli, are significant pathogens.

Staphylococcus aureus is also one of the most common organisms seen in osteomyelitis seeded from areas of contiguous infection, but here Gram negative organisms and anaerobes are somewhat more common, and mixed infections may be seen.

Systemic mycotic, or fungal infections may cause osteomyelitis. The two most common are Blastomyces dermatitidis and Coccidioides immitis.

In osteomyelitis involving the vertebral bodies, about half the cases are due to Staphylococcus aureus, and the other half are due to tuberculosis (spread hematogenously from the lungs). Tubercular osteomyelitis of the spine was so common before the initiation of effective antitubercular therapy that it acquired a special name, Pott's disease, by which it is sometimes still known.

See also

• Brodie abscess

References

• 5-54b. at The Merck Manual of Diagnosis and Therapy Professional Edition
• Wrong Diagnosis Osteomyelitis - Statistics on Osteomyelitis in England
• 00298 at CHORUS