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Microbiology 65: Infections of Bones, Joints and Muscles
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Infection of bones = osteomyelitis
o Hematogenous, environmental, or soft tissue/joint spread
Hematogenous osteomyelitis =
o Pathogenesis:
 Primarily in childhood and adolescence
 Likely in traumatized bone
 Metaphysis predisposed to infection (vascular supply)
 Sludging of blood ideal for bacterial growth
 In adults, starts in intervertebral disc and spreads adjacently
o Diagnosis and Treatment:
 Local pain and systemic signs -> parenteral antibiotics (4-6 weeks) and surgical
drainage
 CT scans useful to guide drainage
 Blood cultures and bone aspirate obtained
 Most infected with S. aureus
 Use β-lactamase resistant penicillin (naficillin/oxacillin) or 1st generation
cephalosporin (cefazolin)
 If MRSA, vancomycin
 Salmonella may infect sickle-cell children; P. aeurginosa, Candida albicans, and
oral flora in drug users, E. coli and enterococci in adults with urinary tract
obstruction
o Infants -> metaphysis of long bone (may rupture), subperiosteal abscesses common,
new bone at inappropriate site (involucrum), may affect bone growth
o Children -> contained within metaphysis, arteriole occlusion and capillary clot formation
(necrosis), sequestrum can form
o Adults -> vertebral bodies (disc space to other vertebrae), complications of spinal
epidural or psoas abscess
 S. aureus most common, also enteric Gram neg bacteria, viridans strep,
Mycobacterium tuberculosis and enterococci
 Aspiration or needle biopsy of disc space
 If neurologic changes occur, urgent surgical drainage
Osteomyelitis 2° to Contiguous Foci of Infection = trauma, insertion of orthopedic hardware
(bacteria reside in biofilms on surface of foreign bodies sheltering from antibiotics)
o S. aureus, Gram – bacilli, or fungi infrequently cured without removal of device
o S. aureus most common, Gram neg bacteria (P. aeruginosa) or coag neg staphylococci
Osteomyelitis in Diabetes = vascular disease and neuropathy, skin and soft-tissue ulceration
may penetrate into bone (may require amputation)
o Polymicrobial -> S. aureus, streptococci, enterococci, and Gram neg bacteria common
o Debridement of necrotic bone and soft tissue and adjunct antimicrobials
o Without definitive culture results -> wide range antibiotics
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Chronic Osteomyelitis = can remain dormant, exacerbations from purulent drainage, antibiotic
therapy useful, can cause progressive destruction
Joint Infections
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Swollen, red, warm, painful joint with fever -> septic arthritis
Noninfectious inflamm joint disease from gout, pseudogout, RA, CT disease or viruses
Infection supported by high WBC (neutrophils), Gram stain +, absences of other causes
Inflammatory reaction in synovial fluid from serum protein, phagocytes, and microorganism
interaction
Bacterial infections more common and have higher WBCs in fluid (neutrophils)
o S. aureus most common in all, H. influenza type B, in kids, Kingella kingae in kids < 2,
gonococcus in sexually active adults
Treatment:
o High dose antibiotic therapy parenterally
o Drain synovial fluid (aspiration before surgery)
 Open drainage in hip joint to prevent necrosis of head of femur
o Complete therapy with oral agent
o 3-4 treatment
Muscle Infections
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Myalgias prominent in viral illness, rikettsial infections, osteomyelitis, endocarditis
Involvement of microorganism is indirect (acute-phase response) -> accelerated catabolism of
muscle (by macrophage products monokins, IL1 and TNF)
o Symtoms from increase prostaglandin E2 synthesis, IL1 and TNF hypothalamic
interaction (fever)
 Aspirin helps solve fever
Specific muscle infections:
o Invaded from either contiguous site or hematogenous spread
o Crepitus (gas in muscle) suggest gas gangrene from Clostridum perfringens
o Generalized muscle pain and peripheral eosinophilia, pork -> trichinosis
Treatment:
o Directed toward eradication of organism once identified
o Drainage of abscesses and surgical debridement may be neccessary