Kodi K. Azari
I. Human Bites
Epidemiological studies demonstrate that the hand suffers over 80% of human bites, with the average victim being a male in his twenties. Human bites to the hand account for 25% to 30% of hand infections annually, and over 42 species of bacteria have been cultured from the human mouth. Although most bites are intentionally inflicted as the result of altercations, etiologies of child abuse or domestic violence must be considered.
Most commonly, a clenched hand strikes a tooth, resulting in potential direct damage to overlying skin, subcutaneous tissues, extensor tendons, muscles, and bone; secondarily, bacterial inoculation of the extensor tendon mechanism, bone, and joint space can occur. Following injury, extension of the hand allows for proximal migration of inoculated bacterium, as the extensor mechanism returns to its resting position.
A gnawing-type bite mechanism to an open hand results in a crush component that can appear to have limited hand tissue involvement, but with limited dorsal skin thickness over superficially placed extensor tendons, significant damage can occur. Open hand injuries can also effect damage to the palmar surface of the hand, with skin and subcutaneous tissue loss, but with the palm’s thicker, glaborous skin, and densely adherent fascia, less involvement of the hands’ blood supply, flexor tendon mechanism, musculature, and skeleton is seen.
Though a full history should be obtained at the time of patient interview, the mechanism of injury, position of the hand at the time of injury, and patient-specific conditions such as tetanus immunization and immunosuppressed states (steroids, diabetes, cancer, and HIV) play a large role in focused workup of the bitten patient.
Physical examination should include full vascular, neurological and musculotendinous evaluation. Cutaneous physical examination manifestations can range from a single puncture-type injury, to large avulsed flap segments, each carrying the possibility of significant short-term and long-term sequelae, the most common of which is infection.
Hand infections develop as the result of a bacterial inoculum and the inability to clear the infection in the hand tendons and deeper structures. Hand infections can range from a mild cellulitis to a paronychia/eponychial infection, to significant purulent tenosynovitis or necrotizing fasciitis.
Involvement near joint spaces can result in the development of septic arthritis with cartilaginous and bony destruction; therefore, all injuries near joints,
especially the metacarpo-phalangeal joint, should be managed as if the joint is involved until effectively ruled out. Wound extension to accurately identify tendinous injuries may be needed.
Differential diagnosis of patient complaints and physical examination findings will guide laboratory examinations. Uncomplicated cellulitis does not require blood-work, but ascending cellulitis unresponsive to oral antibiotics or demonstrating lymphangitic spread should have a CBC to track white blood cell count, and blood cultures to rule out bacteremia. Drainage of any fluid collection should have both aerobic/anaerobic culture and sensitivity studies performed in order to assist with antibiotic therapy.
Initial plain film x-rays are useful to rule out any concomitant osseous injury or foreign bodies; if patients develop infectious complications, x-rays can be useful baselines for osteomyelitis workup, or identification of bony destruction in septic arthritis.
The incidence of human hand bites far exceeds the number that receives medical attention. Most bites to the hand should be treated as a contaminated wound and treated with irrigation and appropriate debridement.
Bite wounds should be allowed to close by secondary intention.
The patient’s tetanus immunization status should be updated as warranted
For complicated bites involving more than simple skin and subcutaneous tissue injury, therapy then becomes injury directed: Skeletal integrity needs to be restored following identification of fractures, control or repair of vascular and neural injuries, and repair or debridement of musculo-tendinous injuries.