Updated: 5/16/2021

Human Bite

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  • summary
    • Human Bite wounds are associated with infections of the hand due to presence of various aerobic and anerobic pathogens.
    • Diagnosis is made by history and presence of open wounds most commonly over the dorsal aspect of the 3rd or 4th MCP joint.
    • Treatment is generally surgical debridement and antibiotics (must protect against aerobic and anaerobic bacteria).
  • Epidemiology
    • Incidence
      • human bite wounds to the hand consist of approximately 2% of bite wounds
        • 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"
  • Etiology
    • 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
  • Presentation
    • 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
  • Imaging
    • Radiographs
      • indicated to assess for foreign body (i.e. tooth fragment) and for fracture
  • Studies
    • Culture
      • not routinely obtained in ED due to contamination
      • deep culture obtained in OR
        • aerobic and anaerobic
  • Diagnosis
    • Clinical
      • diagnosis is made with careful history and physical examination
  • Treatment
    • 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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