HUMAN BITE

Human bite injuries, sometimes referred to as “fight bite” or “clenched-fist” injuries, may present as an innocuous 3–5-mm laceration over the dorsum of the hand at the 3rd, 4th, or 5th metacarpophalangeal (MP) joints. Of primary concern is breach of the joint capsule or flexor tendon sheath on impact through which oral bacteria can enter. Severe complications may occur if the patient does not seek early medical attention or if the wound is dismissed as a simple laceration. Immediate consultation with a hand surgeon is recommended. In cases of “fight bite” wounds, an old adage still applies: “There are two types of bites: the ones you debride and the ones you wish you had debrided.”^1,2

Pathophysiology

• Precarious due to limited vascularization of the MP joint and therefore, limited ability to fight infection
• On impact, an aggressor’s clenched fist will incur the victim’s incisor teeth, causing a skin laceration superficially, providing entry of oral bacterial flora into the wound, the underlying MP joint, and rarely flexor tendon sheath
• Defects within the joint capsule and tendon sheath allow entry of oral bacteria.  If the tooth fractures of the MP joint head then bone infection is possible.
• After attack, the aggressor will extend the hand exacerbating spread of infection to the dorsal spaces of the hand and wrist.  This extension manuever brings the skin and extensor tendon lacerations proximally and isolates the  more distal capsular laceration under the intact portion of the extensor tendon and sets up the iniculated joint for septic arthritis. (see diagram below)
• One mL of human oral inoculum contains 1 x 10⁸  bacteria

Related Anatomy

• The “knuckles”  (common name for the MP joints) are the part of the closed fist that strikes the incisor teeth during a punch to the mouth.
• Flexor tendons and tendon sheaths of the fingers are another closed space that can potentially be inoculated by a human bite.
• Skin

Incidence and Related Conditions

• 11.8/100,000 population a year; 60–75% of all bite wounds are to the hand or upper extremity resulting in a 10% infection rate²
• Most commonly affected are males aged 10–34 years; substrata of females have also been reported.2,³
• Incidence is highest during the summer months.²
• Delayed presentation is not uncommon and is coincident with wound complications.^2,3
• Similar injuries can occur during sporting event.²

Differential Diagnosis

• Cellulitis
• Fracture
• Septic arthritis
• tenosynovitis
• Osteomyelitis
• Foreign body (or broken tooth)

Patient is usually a young male with a history of recent intoxication.  Patients often evade history due to embarrassment or fear of legal repercussions.^1,2 Any laceration over the MP joint remains suspect until proven otherwise.²

• Untreated, human bite wounds can result in septic arthritis, secondary osteomyelitis; deep space infections, stiffness, disability, and in some cases, amputation of a digit.⁵
• Delayed presentation frequently complicates these injuries. 
• Mismanagement of wound care by early wound suturing is also contraindicated and increases the risk of septic arthritis.^2,5

• Favorable outcome can be anticipated human bites receive early aggressive treatment. 
• Patients with delayed presentation can achieve favorable outcomes depending on the severity of infection³ and the success of the surgical and antibiotic treatment.
• Delayed presentation may require more than one debridement and longer hospitalization.³

• Pending the health of victim, appropriate measures may be required to negate transmission of HIV, hepatitis B and C, herpes simplex virus, and human T-cell lymphotrophic virus–1, all of which have been reported.⁴
• Consultation with an infectious disease expert is encouraged.⁵
• Whether structural repair of the MP joint or tendon is secondary in importance to resolution of infection is debated.^1,4
• When patient compliance is an issue, hospitalization should be extended to ensure follow-up. All cases presenting after >7 days post incident also should remain hospitalized for follow-up and IV antibiotics.³
• Infection with methicillin resistant staphylococcus aureus (MRSA) is increasing; patients who are immunocompromised, IV drug users, diabetic or taking steroids are most susceptible.⁵
• Risk of amputation increases by 18% with every 8-day lapse before presentation.
• Hand should be examined in flexed position to align the laceration of the skin, tendon and capsule, thus allowing better visibility of joint capsule and tendon²
• Small laceration over dorsal aspect of 3rd, 4th, and 5th MP joints should be considered possible fight bites.
• Infection risks increase with delayed presentation and/or inadequate management.
• Culture results are typically polymicrobial growth with Staphyloccocus aureas, Eikenella corrodens, beta-hemolytic streptococci, and Corynebacterium species.²
• As many as 50 bacterial species have been isolated from the human oral flora.⁵
• Radiographs may reveal MP joint fracture, septic arthritis, or presence of tooth fragment(s)³
• Before administration of prophylactic antibiotics, a gram stain of the suppurative exudate should be done if present.
• Culture for aerobes, anaerobes and fungi should be done if any sign of infection is evident.

Cited

1. Cheah A, Chong A. Bites to the hand: are they more than we can chew? Singapore Med J 2011;52(10):715-8. PMID: 22009389
2. Perron A, Miller M, Brady W. Orthopedic Pitfalls in the ED: fight bites. Am J Emerg Med 2002;20(2):114-7. PMID: 11880877
3. Dreyfuss U, Singer M. Human bites of the hand: one hundred six patients. J Hand surg Am 1985:10(6):864-9. PMID: 4078274
4. Malahias M, Jordan D, Hughes O, et al. Bite injuries to the hand: microbiology, virology and management. Open Orthop J 2014;8:157-61. PMID: 25067969
5. Osterman M, Draeger R, Stern P. Acute hand infections. J Hand Surg Am 2014;39(8):1628-35. PMID: 25070032
6. McDonald M, Bavaro M, Hofmeister E, Kroonen LT. Hand Infections. J Hand Surg Am 2011;36(8):1403-12. PMID: 21816297

New Articles

1. Malahias M, Jordan D, Hughes O, et al. Bite injuries to the hand: microbiology, virology and management. Open Orthop J 2014;8:157-61. PMID: 25067969
2. Osterman M, Draeger R, Stern P. Acute hand infections. J Hand Surg Am 2014;39(8):1628-35. PMID: 25070032

Reviews

1. McDonald M, Bavaro M, Hofmeister E, Kroonen LT. Hand Infections. J Hand Surg Am 2011;36(8):1403-12. PMID: 21816297
2. Cheah A, Chong A. Bites to the hand: are they more than we can chew? Singapore Med J 2011;52(10):715-8. PMID: 22009389

Classics

1. Perron A, Miller M, Brady W. Orthopedic Pitfalls in the ED: fight bites. Am J Emerg Med 2002;20(2):114-7. PMID: 11880877
2. Dreyfuss U, Singer M. Human bites of the hand: one hundred six patients. J Hand surg Am 1985:10(6):864-9. PMID: 4078274