Human bite wound

Introduction

Between 60% and 75% of all human bite wounds are to the upper extremity. ¹ Approximately 10% of human bite wounds will become infected, with up to 30% in the hand becoming infected. ^{1, 2, 3} The worst bites -- those most likely to become infected -- are the result of a clenched fist to the mouth, the so called “fight bite.”

Anatomy

Human bite wounds to the hand are most often located over the dorsal metacarpophalngeal joint (MCP) due to a clenched fist striking a mouth. The third, fourth, and fifth MCP joints are most frequently involved.

Figure 1. A “fight bite” is most commonly located over the dorsum of the MCP joint.

Pathogenesis

The victim’s teeth may cause only a 3- to 5-mm laceration; however, if the laceration is deep, the teeth may inoculate skin and oral flora deep into the wound. When the fist is subsequently opened, the bacteria are dragged with the soft tissue and extensor tendons into the hand proximally. ³

Figure 2. When the MCP joint is flexed, the skin, tendon, and joint capsule lacerations line up.

Figure 3. When the MCP joint is extended, the skin, tendon, and joint capsule lacerations are not lined up. The tendon laceration is pulled proximally.

Human bite wounds are typically polymicrobial. ^{1, 2} Frequently isolated organisms include:

• Aerobes
  • Staphylococcus aureus
  • Eikenella corrodens (frequently asked test question)
  • ?-hemolytic streptococcus
• Anaerobes
  • Peptostreptococcus spp
  • Prevotella spp
  • Bacteroides spp
• Infections transmitted through bites
  • Hepatitis B and C
  • Herpes
  • Syphilis
  • Tetanus
  • Actinomycosis

Signs of infection usually take 24 to 72 hours to develop. ¹

Natural History

• Incidence of 11.8/100,000 people per year ³
• Incidence peaks between 10 and 34 years of age ³
• Male:Female ratio = 4:1 ³

Clinical Presentation

Patients tend to present 5 to 7 days after injury, once infection has set in. Typical signs and symptoms include:

• Pain, swelling, erythema
• Limited range of motion
• Lymphadenopathy
• Fever

Patients occasionally present prior to onset of infection and may have a benign-appearing laceration. ³

Imaging and Diagnostic Studies

Radiographs should be obtained in fight bites. ^1,3 Look for:

• Proximal phalanx fracture
• Injury to the metacarpal head
• Osteomyelitis
• Tooth fragments

Gram stain and culture for aerobes and anaerobes should also be obtained in all bite wounds. ¹

Treatment

Medical Therapy

• Tetanus toxoid booster PRN ²
• Prophylactic antibiotic regimens, which should be tailored according to culture and sensitivity ²
  • Amoxicillin/clavulinic acid
  • Penicillin and first-generation cephalosporin
  • Penicillin and dicloxacillin
  • Ampicillin and sulbactam (intravenously)

Nonoperative Treatment

• Clean the wound
• Copious irrigation
• Debridement of devitalized tissue ²

Operative Treatment

• Incision and drainage will usually be necessary.
  • In some cases, if the patient presents early and the bite has not created a septic joint, then the cellulitis may be treated with intravenous and/or oral antibiotics.
  • In the usual scenario, an abscess or septic joint has occurred and a formal drainage will be needed.

Outcome

Mennen et al⁴ reported 100 consecutive patients whose finger had been bitten by another person, or who had cut it on a tooth in a fight.

• 82 healed completely
• 18 eventually needed amputation

Amputation is sometimes needed once infection is established in bone or tendon sheath, but most infected joints can be saved. ⁴

Complications

The most common complications of a human bite wound include: ²

• Local infection
• Local abscess
• Lymphangitis
• Tenosynovitis
• Osteomyelitis
• Septic arthritis

Risk factors for pyogenic infection include:

• Delayed treatment
• Inadequate debridement
• Initially suturing the wound.

Rare complications of a human bite wound include: ²

• Endocarditis
• Meningitis
• Brain abscess
• Sepsis with disseminated intravascular coagulation

Pearls and Pitfalls

• Patients may not be honest about the origin of their wound. A high index of suspicion for a fight bite is warranted for any laceration over the dorsal MCP. ³
• Examine the wound with the hand in the clenched position, which will bring the extensor tendon distal. This was the position the injury was created in, so it will be easier to see the tract of the bite and the tendon and capsule penetration.

Controversy

• Small puncture wounds should not be sutured; otherwise, an abscess can form.
• Large wounds that present early may be loosely closed over a drain after the wound has been cleaned and debrided.
• Wounds that present in a delayed fashion (>12 hours) should not be closed unless formally debrided.

References

1. Ball V, Younggren BN. Emergency Management of Difficult Wounds: Part I. Emerg Med Clin N Am. 2007; 25: 101-121.
2. Brook I. Management of human and animal bite wounds: an overview. Adv Skin Wound Care. 2005; 18(4): 197-203.
3. Perron AD, Miller MD, Brady WJ. Orthopedic Pitfalls in the ED: Fight Bite. Am J Emerg Med. 2002;20(2):114-7.
4. Mennen U, Howells CJ. Human fight-bite injuries of the hand. A Study of 100 cases within 18 months. J Hand Surg Br. 1991; 16(4):431-435.