A felon is an abscess of the distal pulp or pad of the fingertip (1,2,3,4,5,6,7). The most commonly affected digits are the thumb and index finger (8). Unlike a paronychia, a felon is a deep soft-tissue infection that involves the distal pulp of a finger or thumb and may not communicate with skin until late in the course. Incision and drainage are often required to prevent the spread of infection to bone and to relieve pain. Several techniques have been advocated, all of which involve surgical drainage with as little interruption to the vascular, neurologic, and structural components as possible. No technique has been definitively shown to be best.

A felon may occur in any age group. The emergency or primary care physician with experience in minor surgical procedures may perform the procedure on the cooperative patient with regional anesthesia alone. For uncooperative patients, procedural sedation may be necessary (see Chapter 33).

The distal finger consists of a relatively closed compartment bounded by the nail and skin on the dorsal and distal aspects, by skin on the palmar surface, and by the flexion crease of the distal interphalangeal joint proximally (Fig. 116.1). The pulp of the fingertip is divided into small compartments by 15 to 20 fibrous septae that run from the periosteum to the skin. These septae are most dense at the flexor crease, at the fingertip, and on each side at the dorsal-palmar junction. The septae are least dense at the center of the touch pad. The flexor digitorum profundus tendon inserts at the proximal one third to middle of the distal phalanx. Blood is supplied by digital arteries, which lie parallel and lateral to the phalanx. The digital nerves lie palmar and superficial to the arteries. Both arteries and nerves begin to arborize just beyond the distal phalangeal epiphysis.

A felon is caused by inoculation of bacteria into the fingertip from a minor puncture wound, splinter, or fissure and can go unnoticed by the patient until the severe throbbing pain and localized swelling begin. A felon may arise when an untreated paronychia spreads into the pad of the fingertip (4). Cases have also been reported of iatrogenic felon formation as the result of repeated finger sticks (4,9). Young children and diabetic patients, who commonly undergo finger sticks to obtain blood, are therefore at increased risk for developing a felon.

Infection in the pulp of the fingertip may progress in several ways. Inflammation and edema cause increased pressure in the relatively noncompliant compartments. As pressure rises, the arteries collapse, and tissue necrosis, including necrosis of the periosteum and cancellous bone (osteitis), may ensue (10). The epiphysis is spared, as its blood supply is outside the closed space, which allows regeneration of eroded bone in children. The extent of regeneration depends on the virulence of the organism and the patient’s age (10). The fibrous septae, being least dense in the central area of the finger pad, may allow abscess extension to overlying skin. In this case, a draining sinus may result (1). Rarely, the abscess located deep in the pulp may dissect around the side of the phalanx and cause an associated paronychia.

Although the bacteriology in children has not been extensively studied, the primary pathogens consist of skin flora, especially Staphylococcus aureus. Oral flora are also common in children who suck their fingers or thumb. Recently, methicillin-resistant S. aureus has been reported in felons (11,12). Complications of an untreated felon include tenosynovitis, flexion contracture, septic arthritis, and osteomyelitis (13,14,15,16,17).

Felons are characterized by intense throbbing pain made worse by dependent position and localized distal pulp swelling and redness. Compared to a paronychia, the pain caused by a felon is usually more intense. The swelling does not extend proximal to the distal interphalangeal joint (1). Differential diagnoses include herpetic whitlow (18) (distinguished by the presence of vesicles and a history of recurrence), osseous metastasis (19), and superficial abscess extension from a paronychia.

Early in the infection, before frank pus formation, the need for incision and drainage may be obviated with immobilization, elevation, oral antibiotics, and warm water or saline soaks (4,8,17,20,21). A tense fingertip should be surgically decompressed even when no frank pus drainage or fluctuance is present, as ischemic necrosis of deep tissues may precede skin necrosis and pus drainage (21,22). Once abscess formation has occurred, treatment of this deep space infection involves timely incision and drainage, appropriate antibiotic therapy, elevation and immobilization, and close follow-up. “Fish mouth,” through-and-through, “hockey stick” or “J,” and transverse palmar incision techniques are not recommended, as they are more likely to result in painful sensitive scars and damage to neurovascular structures (4,20,23,24).