Updated: 6/27/2019

Human Bite

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  • Epidemiology
    • incidence
      • third most common bite behind dog and cat
    • demographics
      • more common in males
    • location
      • typically dorsal aspect of 3rd or 4th MCP joint
        • "fight bite"
  • Pathophyiology
    • mechanism
      • most often result of direct clenched-fist trauma (from tooth) after punching another individual in the mouth
      • can also result from direct bite (i.e. child biting another child)
    • pathoanatomy
      • tooth penetrates capsule of MCP joint
        • flora (bacteria) from mouth enter joint
        • bacteria become trapped within joint as fist is released from clenched position
          • bacteria now caught under extensor tendon and/or capsule
    • microbiology
      • typically polymicrobial 
      • most common organisms
        • alpha-hemolytic streptococcus (S. viridans) and staphylococcus aureus
        • eikonella corrodens in 7-29%
        • other gram negative organisms
  • Associated conditions
    • extensor tendon lacerations
      • can be missed due to proximal tendon retraction
  • History
    • direct clenched-fist trauma to another individual's mouth 
      • often overlooked
      • must have high index of suspicion as patients often unwilling to reveal history
      • consider the injury a "fight-bite" until proven otherwise
    • possible delay in presentation until symptoms become intolerable
  • Symptoms
    • progressive development of pain, swelling, erythema, and drainage over wound
  • Physical exam
    • fight bite
      • small wound over dorsal aspect of MCP joint
        • wound often transverse, irregular
        • typically 3rd and/or 4th MCPs, but can involve any digit 
        • erythema, warmth, and/or edema overlying wound and joint
        • ± purulent drainage
      • must assess for integrity of extensor tendon function
      • possible pain with passive ROM of MCP joint
      • typically no involvement of volar/flexor surface of digit
      • neurovascular status typically preserved
  • Radiographs
    • indicated to assess for foreign body (i.e. tooth fragment) and for fracture
  •  Culture
    • not routinely obtained in ED due to contamination
    • deep culture obtained in OR
      • aerobic and anaerobic
  • Operative
    • I&D, IV antibiotics
      • indications
        • fight bite
        • joints or tendon shealths are involved
      • antibiotics
        • IV antibiotics directed at Staph, Strep, and gram-negative organisms
          • ampicillin/sulbactam (unasyn)
        • PO antibiotics upon discharge for 5 to 7 days
          • amoxicillin/clavulanic acid (augmentin)
      • debridement
        • debridement of wound and joint capsule
        • wound left open for drainage
        • obtain gram stain and culture

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