Osteomyelitis

Osteomyelitis
Osteomyelitis in cancer. Image courtesy of Professor Peter Anderson DVM PhD and published with permission © PEIR, University of Alabama at Birmingham, Department of Pathology
ICD-10	M86
ICD-9	730
DiseasesDB	9367
MedlinePlus	000437
eMedicine	ped/1677
MeSH	C01.539.160.495

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Associate Editor-In-Chief: Cafer Zorkun, M.D., Ph.D. [2]

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Overview

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.

Etiology

• Newborns (younger than 4 mo): S aureus, Enterobacter species, and group A and B Streptococcus species
• Children (aged 4 mo to 4 y): S aureus, group A Streptococcus species, Haemophilus influenzae, and Enterobacter species
• Children, adolescents (aged 4 y to adult): S aureus (80%), group A Streptococcus species, H influenzae, and Enterobacter species
• Adult: S aureus and occasionally Enterobacter or Streptococcus species

In children, the long bones are usually affected. In adults, the vertebrae and the pelvis are most commonly affected.

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, infectious root-canalled teeth, other disease or drugs (e.g. immunosuppressive therapy).

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, internal fixation of fractures or root-canalled teeth. 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. Often, the body will try to create new bone around the area of necrosis. The resulting new bone is often called an involucrum.

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, the vertebra, the maxilla and the mandibular bodies are especially susceptible to osteomyelitis. [4]

Causes

The vast predominance of hematogenously seeded osteomyelitis is caused by Staphylococcus aureus. Escherichia coli, Salmonella paratyphi, 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. The most frequent cause is from infection of an incision from surgery.

Complete Differential Diagnosis of Associated Conditions

• Bacteroides
• Decubitus
• Diabetic angiopathy
• E.Coli
• Gastrointestinal infection
• Klebsiella
• Otitis
• Pneumonia
• Pseudomonas
• Serratia
• Sinusitis
• Skin infection
• Staphylococcus aureus
• Staphylococcus epidermidis
• Streptococcus pyogenes
• Streptococcus pneumoniae
• Tonsilitis
• Urinary tract infection
• Vasculitis

Diagnostic Findings

• Conventional radiographic evaluation of acute osteomyelitis is insufficient because bone changes are not evident for 14–21 days after the onset of infection.
• Although MR imaging is the accepted modality of choice for the early detection and surgical localization of osteomyelitis, in the emergency department, CT is usually more readily available for establishing the diagnosis.
• At CT, features of bacterial osteomyelitis include overlying soft-tissue swelling, periosteal reaction, medullary low-attenuation areas or trabecular coarsening, and focal cortical erosions.

MRI

Images courtesy of RadsWiki

Patient #1 Extensive calcaneal osteomyelitis. Note soft tissue ulceration and cellulitis

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  T1
• 
  STIR
• 
  T1
• 
  STIR
• 
  T1 fat sat contrast
• 
  T1 fat sat contrast

Bone Scan

Patient #2

Images courtesy of RadsWiki

• 
  Blood pool
• 
  Delayed

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Osteomyelitis and Chondritis of Vertebrae

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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.

Prior to the widespread availability and use of antibiotics, blow fly larvae were sometimes deliberately introduced to the wounds to feed on the infected material, effectively scouring clean.[5]

See also

• Brodie abscess

External Links

• Goldminer: Osteomyelitis

Additional Resources

• Template:MerckManual
• Template:Chorus

Template:WikiDoc Sources