Discitis

General Information


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Description:

  • Discitis is infection of bone that can lead to progressive destruction of bone and sequestra
  • Discitis is often difficult to treat; optimal management depends on pathophysiology, microbiology and host immune factors
  • Staphylococcus aureus is most common causative microorganism of discitis


Definitions:

  • Infective osteitis – contamination of bony cortex
  • Infective periosteitis – contamination of periosteal layer that surrounds bone
  • Sequestrum – segment of necrotic bone separated from living bone by granulation tissue
  • Involucrum – layer of living bone formed around dead bone, may become perforated by tracts
  • Cloaca – opening in involucrum
  • Sinuses – tracts reaching skin surface from bone (also called fistula)
  • Brodie abscess – bone abscess with sharply delineated focus of infection, lined by granulation tissue and often surrounded by hard and dense bone


Types:

  • Classification systems
    • Waldvogel classification system for osteomyelitis (used to describe series of 247 patients with osteomyelitis at Massachusetts General Hospital 1963-1966)
      • Hematogenous osteomyelitis in 19%
      • Osteomyelitis secondary to a contiguous focus of infection (including postoperative wound infections, direct puncture wound, or extension from adjoining soft-tissue focus of infection) in 47%
      • Osteomyelitis associated with peripheral vascular disease in 34%
      • Reference – N Engl J Med 1970 Jan 22;282(4):198
    • Cierny-Mader staging system for adults (may be useful for guiding treatment and evaluating prognosis)
      • Anatomic type
        • Stage 1 – medullary osteomyelitis
        • Stage 2 – superficial osteomyelitis
        • Stage 3 – localized osteomyelitis
        • Stage 4 – diffuse osteomyelitis
      • Physiologic class
        • A host – normal host
        • B host – systemic compromise (Bs), local compromise (Bl), systemic and local compromise (Bls)
        • C host – treatment worse than disease
      • Risk factors that affect immune surveillance, metabolism and local vascularity
        • Systemic factors (Bs)
          • Malnutrition
          • Renal or hepatic failure
          • Diabetes mellitus
          • Chronic hypoxia
          • Immune disease or immunosuppression
          • Malignancy
          • Extremes of age
        • Local factors (Bl)
          • Chronic lymphedema
          • Major vessel compromise
          • Small vessel disease
          • vasculitis
          • Venous stasis
          • Extensive scarring
          • radiation fibrosis
          • neuropathy
          • tobacco abuse
      • Reference – Clin Orthop Relat Res 2003 Sep;(414):7
  • Clinical forms of osteomyelitis include
    • Long-bone osteomyelitis caused by hematogenous spread or contiguous to soft tissue infection
    • Open-fracture osteomyelitis (post-traumatic)
      • may occur in 3%-25% of cases, depending on fracture type, degree of soft-tissue injury, degree of microbial contamination and whether antimicrobial therapies (systemic and/or local) given
      • Caused by direct inoculation of bacteria on bone surface at time of trauma, at time of surgery and/or in early postoperative period
      • May also occur as nosocomial infection after treatment of open fracture
      • Untreated infection leads to nonunion, chronic osteomyelitis or amputation
      • Often polymicrobial, such as pathogens from normal skin flora that contaminate wound, microorganisms from contaminated soil or nosocomial pathogens
    • Vertebral osteomyelitis (spondylodiscitis)
      • Most cases hematogenous
        • Sources of infection include skin and soft tissue, infective endocarditis, infected IV site, IV drug abuse, oral cavity and respiratory, gastrointestinal and genitourinary tracts
        • Primary infection site cannot be identified in many cases
        • Infection occurs via segmental arterial circulation of vertebrae
          • Lumbar vertebral bodies commonly involved
          • Infection spreads by direct extension through endplate into disc
          • Posterior and anterior extension may lead to abscesses in epidural, subdural, paravertebral, mediastinal, retroperitoneal or psoas spaces
      • may also occur from direct inoculation from trauma or as complication of spinal surgery
    • Osteomyelitis in patients with diabetes mellitus or vascular insufficiency
    • Osteomyelitis due to infected prosthesis
      • Includes hip replacements, artificial joints (knees, elbows)
      • Usually caused by microorganisms growing in biofilm into organized communities
      • Risk of infection highest first 2 years after implantation but continues at low levels as long as prosthesis in place
      • Most patients present with little or no fever, and painful, unstable joint on exam or x-ray
      • Positive culture of fluid aspirated from artificial joint space before surgery or of bone from bone-cement interface during surgery required for diagnosis
      • Several deep tissue cultures may be useful
      • Staphylococcus aureus and coagulase-negative staphylococci in > 50% cultured bacteria
    • Osteomyelitis due to pressure ulcer
    • Culture-negative osteomyelitis
      • Poorly defined entity
      • Usually indicates presence of purulence, acute histopathologic changes and clinical and radiologic findings suggestive of osteomyelitis, but with negative microbial cultures
      • Duration of symptoms usually longer compared to culture-positive osteomyelitis
      • May be related to
        • Previous antimicrobial use
        • Presence of fastidious microorganisms
        • Presence of microorganisms that require specialized culture media
        • Noninfectious illness
    • Other rare forms
      • Septic arthritis of pubic symphysis
        • Rare infectious complication of various gynecologic and urologic surgeries
        • Most patients present with suprapubic pain and difficulty ambulating
        • Time between surgery and diagnosis can range from 2-18 months
        • May have elevated erythrocyte sedimentation rate, fever and leukocytosis rare
        • Plain x-ray may be normal early, then show pubic bone sclerosis, joint space widening and rarefaction at 6 months
        • Computed tomography scan and magnetic resonance imaging more sensitive in detecting bony changes than plain x-ray
        • Bone scan or In-labeled white blood cell scan very sensitive
        • Treatment includes antimicrobial therapy and surgical debridement if necessary
      • Osteomyelitis of clavicle
        • May be hematogenous or related to subclavian vein catheterization and neck surgery
        • Involvement of sternoclavicular joint area has been described in IV drug users and patients with indwelling IV devices
        • S. aureus is most common cause of infection
        • Patients usually present with clavicular site pain, either acute local pain and swelling or chronic and indolent
        • Fever, localized swelling or mass and soft tissue abscess may be present
        • Duration of symptoms can range from 2 weeks to 18 months
        • Plain x-rays of clavicle may show sclerotic or lytic changes
        • Treatment includes antimicrobial therapy alone (acute cases) or surgical debridement and antimicrobial therapy (chronic cases)
      • Sacroiliac joint infection
        • Uncommon metastatic infection of S. aureus bacteremia
        • IV drug users and patients with indwelling vascular catheters are at risk
        • Patients usually present with acute onset of pain (sacral and/or pelvic) and leukocytosis
        • Blood cultures often positive
        • Evaluate for presence of concomitant infective endocarditis
      • Osteomyelitis of sternum may follow cardiac surgery
      • Osteomyelitis of calcaneus (large heel bone) can follow puncture wounds
      • Acute multifocal osteomyelitis
        • May be associated with skin disorders including acne conglobata or palmoplantar pustulosis
        • Characterized by negative bone cultures and healing over period of several months


Organs involved:

  • Any bone can be affected by discitis, especially
    • Metaphysis of long bones (such as tibia and femur); tibia is most common site of posttraumatic osteomyelitis
    • Vertebral bodies
    • Foot bones


Who is most affected:

  • Hematogenous osteomyelitis seen mostly in prepubertal children and in elderly patients
  • Open fractures occur most often in males aged 11-30 years
  • Osteomyelitis more common in patients with
    • Diabetes
    • Recent trauma
    • Bone surgery
    • Joint replacement
    • Foreign body implant
    • Soft tissue infection


Incidence/Prevalence:

  • Reported incidence ranges from 1/1,000 to 1/20,000


Causes and Risk Factors

Causes:

  • Causative microorganisms for discitis
    • Common
      • Staphylococcus aureus (most prevalent)
      • Coagulase-negative staphylococci
      • Streptococci (such as Haemophilus influenzae, especially in young children)
      • Enterococci
      • Pseudomonas species
      • Enterobacter species
      • Proteus species
      • Escherichia coli
      • Serratia species
      • Anaerobes (Peptostreptococcus species, Clostridium species, Bacteroides fragilis group)
    • Less common
      • Mycobacterium tuberculosis
      • Mycobacterium avium complex
      • Rapidly growing mycobacteria
      • Dimorphic fungi
      • Candida species
      • Aspergillus species
      • Mycoplasma species
      • Tropheryma whippelii
      • Brucella species
      • Salmonella species
      • actinomycetes
  • Causative microorganisms by clinical form of osteomyelitis
    • Hematogenous osteomyelitis (usually monomicrobial)
      • Most common microorganism – S. aureus
      • Other microorganisms include
        • Enterobacteriaceae, group B streptococci, coagulase-negative and other staphylococci in neonates
        • H. influenzae group B in infants and children (incidence of invasive disease decreasing due to routine vaccination in children)
        • Salmonella species, Streptococcus pneumoniae, anaerobic bacteria in patients with sickle cell disease
        • P. aeruginosaCandida species in IV drug users
        • Bartonella henselaeB. quintana in patients with HIV infection
    • Contiguous-focus osteomyelitis
      • Diabetes mellitus, vascular insufficiency, or after contaminated open fracture (polymicrobial)
        • S. aureus
        • Beta-hemolytic streptococci
        • Enterococci
        • Aerobic gram-negative bacilli
        • Anaerobic bacteria
      • Orthopedic fixation devices – S. aureus, coagulase-negative staphylococci
      • Foreign-body associated infection – coagulase-negative staphylococci, Propionibacteriumspecies
      • Following puncture injuries on foot by nails or other sharp objects – P. aeruginosa
      • Following periodontal infection – Actinomyces species
      • Soil contamination
        • Clostridium species
        • Bacillus species
        • Stenotrophomonas maltophilia
        • Nocardia species
        • atypical mycobacteria
        • Aspergillus species
        • Rhizopus species
        • Mucos species
      • Human or animal bites – Pasteurella multocida (cat bite), Eikenella corrodens or other anaerobic bacteria
    • Vertebral osteomyelitis(1)
      • Adults – S. aureus most common
      • Patients with urinary tract infection – aerobic gram-negative bacilli, Enterococcus species
      • Injection drug users – P. aeruginosaS. aureus
      • Following spine surgery
        • Coagulase-negative staphylococci
        • S. aureus
        • Aerobic gram-negative bacilli
      • Infections of intravascular devices – Candida species
      • In endemic regions – Mycobacterium tuberculosisBrucella species
  • Kingella kingae identified in 45% of osteoarticular infections in 131 children in case series (Pediatr Infect Dis J 2007 May;26(5):377)
  • Kingella kingae caused 3 cases of osteomyelitis or septic arthritis in children aged 17-21 months in same day care (MMWR Morb Mortal Wkly Rep 2004 Mar 26;53(11):241 ,Pediatrics 2005 Aug;116(2):e206), commentary can be found in Pediatrics 2006 Jan;117(1):249
  • Mycobacterium haemophilum osteomyelitis described in case report of woman with polycythemia vera(BMC Infect Dis 2006 Apr 10;6:70)
  • Case report of foot ulcer and osteomyelitis due to blastomycosis can be found in CMAJ 2006 Jan 3;174(1):35


Pathogenesis:

  • 3 mechanisms of infection
    • Hematogenous seeding
    • Contiguous spread of infection
    • Direct inoculation of microorganism(s) into intact bone (such as penetrating wound)
  • Trauma, ischemia and foreign bodies increase susceptibility of bone to microbial invasion
  • Initial changes to bone after bacterial inoculation include changes in pH and capillary permeability that result in
    • Regional edema
    • Cytokine release
    • Leukocyte recruitment
    • Decreased oxygen tension
    • Increased local pressure
    • Tissue breakdown
    • Small vessel thrombosis
    • Bone deterioration
  • Infection may spread from medullary cavity into cortex and subperiosteal space and finally into periosteum and adjacent soft tissue
  • Inflammatory process from infection
    • Leukocytes and other inflammatory factors contribute to tissue necrosis and bone destruction
    • Vascular channels compressed and destroyed, and ischemia contributes to bone necrosis


Likely risk factors:

  • Injection drug users (multifocal involvement common) at increased risk for hematogenous long-bone osteomyelitis
  • Diabetic foot ulcer
    • Can result in development of contiguous osteomyelitis, especially if soft tissue infection present > 2 weeks
    • More likely if ulcers large (> 2 cm), deep (> 3 mm) and associated with exposed bone
    • Most cases are mixed infection
  • Patients with
    • Recent trauma
    • Bone surgery
    • Joint replacement
    • Foreign body implant
    • Soft tissue infection
    • Sickle cell disease
  • Immunomodulating and immunosuppressive agents (for example, steroids, methotrexate, tumor necrosis factor inhibitors, interleukin-1 inhibitors)
  • Rheumatoid arthritis (RA)
    • Based on retrospective cohort study
    • 609 adults ≥ 18 years old with RA were matched with 609 controls without RA
    • Mean follow-up 12.7 years in patients with RA vs. 15 years in patients without RA
    • Patients with RA had increased risk of
      • Objectively confirmed infections (hazard ratio [HR] 1.7, 95% CI 1.42-2.03)
      • Infections requiring hospitalization (HR 1.83, 95% CI 1.52-2.21)
      • Any documented infection (HR 1.45, 95% CI 1.29-1.64)
    • Rate ratio for osteomyelitis in patients with RA 1.63 (95% CI 3.39-126.81)
    • Reference – Arthritis Rheum 2002 Sep;46(9):2287
  • Sacral osteomyelitis following laparoscopic sacral colpopexy with synthetic mesh in case report (Obstet Gynecol 2010 Aug;116 Suppl 2:513)


Complications and Associated Conditions

Complications:

  • Sequestrum (large area of bone necrosis)
  • Fistula
  • Complications of vertebral osteomyelitis (spondylodiscitis) include
    • Soft-tissue extension
    • Abscess (paraspinal, epidural, subdural, retropharyngeal, mediastinal, retroperitoneal)
    • Cord compression
    • Meningitis
    • Skeletal tuberculosis


Associated conditions:

  • Septic arthritis
  • Skin and soft tissue infections
  • Infective endocarditis