Contrary to events frequently seen in action movies, bare fisted fighting often results in serious injury to both the receiver and the deliverer of a closed fist to the face. The third most common bite injury seen in emergency rooms are human bites, and the majority of these occurs as the result of a closed fist directed against a human tooth. Only dog and cat bites are more common.
Approximately 10-15% of human bite wounds become infected; multiple factors contribute to this high incidence. Patients often delay before seeking medical attention, and even then, may be deceptive about the mechanism of injury. Wounds are often more complicated than appreciated at presentation, and may be managed inadequately. In the pre-antibiotic era, or in areas of the world without adequate medical resources, human bite injuries to the hand may result in amputations in as many as 20%.
Human saliva contains as many as 100 million organisms per milliliter, and may contain 190 different species. Moreover, most of these injuries occur on the hands, and hand wounds of any cause have a higher infection rate than do similar wounds in other anatomic locations. Furthermore, the possibility of transmission of hepatitis B, hepatitis C, herpes simplex virus (HSV), syphilis, tuberculosis, actinomycosis, and tetanus have been reported. While it is possible to transmit the human immunodeficiency virus (HIV) through human bites, the probability of this is very low. It is critical to appreciate the high risk of infectious complications, and early aggressive treatment is mandatory to prevent serious wound infection and its associated complications.
Clenched-fist injuries occur as the closed fist strikes the teeth of another individual with sufficient force to create a small wound, usually 3-8mm in length. The injury most commonly occurs over the dorsal surface of the middle finger metacarpophalangeal (MCP) joint (knuckle closest to the hand) of the dominant hand. Potential injuries include joint penetration, metacarpal fracture, and extensor tendon laceration. Injury to the digital nerve or artery is rare. Layers of tissue at this area include skin, the extensor tendon mechanism, the joint capsule, and then the joint. While these layers line up at the moment of impact, they move differentially as the fist is opened acting like the closing of sliding doors closing off the depths of the wound, and affording opportunity for a deep wound infection to develop. This also makes adequate irrigation of the wound more difficult. These are the most serious human bite wounds, and they require the most aggressive treatment.
Commonly isolated aerobic bacteria include Eikenella corrodens and Staphylococcus, Streptococcus, and Corynebacterium species. Staphylococcus aureus is isolated in up to 30% of infected human bite wounds and is associated with some of the most severe infections and, consequently, the highest complication rates.
Eikenella corrodens, a slow-growing gram-negative bacillus frequently associated with chronic infection and abscess formation, is isolated in 30% of human bite wounds as well. Commonly isolated anaerobes include Bacteroides and Peptostreptococcus species. Morbidity of human bites is primarily related to infection and its sequelae, leading to permanent functional and/or cosmetic impairment.
When questioned as to the nature of their injury, patients will often mislead the examiner out of embarrassment or fear of legal repercussion. Because explanations offered for such wounds often are misleading, extreme caution is necessary. While a careful history may elicit the truth from the patient, experienced emergency physicians often treat suspicious injuries as bites regardless of the history.
If a child receives a small laceration to the scalp or forehead during unwitnessed horseplay, it is important to ascertain whether a tooth caused the wound if complications are to be avoided.
Treatment involves emergent surgical intervention in addition to medications. These wounds must be carefully cleaned. The doctor will surgically extend the wound and will extensively irrigate the wound, possibly using high pressure saline and debride it. It is important to evaluate damage to the tendon mechanism as well as penetration of the joint and to perform x-rays to rule out fractures or foreign objects in the wound.
These wounds are usually not closed because the structures in the hand form many small closed spaces that make it easy for infection to be trapped and then spread. Emergency room doctors often consult surgical specialists if a patient has a deep closed-fist injury or one that appears already infected.
The doctor will make sure that the patient is immunized against tetanus, which is routine procedure for any open wound. A study released in June 2004 showed that routine use of antibiotics for human bites may not be necessary, as physicians try to minimize overuse of antibiotics. Superficial wounds in low-risk areas may no longer need antibiotic treatment, but more serious human bites to high-risk areas such as the hands should be treated with antibiotics to prevent serious infection. Patients with closed-fist injuries may need inpatient treatment and intravenous antibiotic therapy. Theoretically, penicillin treats oral pathogens and may suffice for prophylactic treatment, as Staphylococcus species probably infect bite wounds only secondarily. Once a human bite is infected, beta-lactamase–producing staphylococci must be addressed. Eikenella corrodens may not be covered by first-generation cephalosporins. Additionally, Eikenella species are resistant to clindamycin, penicillinase-resistant semisynthetic penicillins, and metronidazole. A broad-spectrum antibiotic, rather than combination therapy, is the usual choice for infected bite wounds. In an in vitro study of 50 infected human bites, Talan et al found that amoxicillin-clavulanic acid and moxifloxacin demonstrated excellent activity against common isolates.
With early and appropriately aggressive care, the outlook after these injuries is, generally, good. Inadequate or delayed treatment, however, can result in very serious consequences.
-- Lee, MD