A felon is an infection that occurs within the closed-space compartments of the fingertip pulp. The swelling leads to intense throbbing pain. The surrounding tissues are at risk for ischemia if the blood flow is compromised by compression from edema and pus formation. Treatment involves incision and drainage of the infected pulp space and oral antibiotics. If left untreated the underlying bone, joint, or tendons may become infected.
Any injury to the fingertip may predispose to a felon including minor cuts, foreign body penetrations, splinters, and paronychias. Staphylococcus aureus is the most common bacteria associated with felons. Gram-negative organisms can be found in immuno-suppressed individuals.
Felons, along with paronychias, account for almost one-third of hand infections. Felons most commonly occur in the first and second digits of the hand. They are most commonly caused by penetrating trauma. However, anything that introduces bacteria into the digital pulp can lead to felon formation. Splinters, puncture wounds, bits of glass, abrasions, or bites can all be inciting factors. Paronychias are another common cause.
A felon is an infection that occurs within the closed-space compartments of the fingertip pulp. The infection may initially start as cellulitis which can progress to abscess formation if not treated early. The compartments of the fingertip are divided by vertical fascial strands known as ‘septae’ which run from the periosteum of the distal phalanx to the skin. These fibrous septae provide structural support to the pulp and form small compartments. Blood flow may be compromised when edema and infection form in these non-compliant compartments which in turn can lead to skin and pulp necrosis. The swelling in these small compartments causes the severe pain associated with felons. Septae may also impede complete drainage after and an incision and drainage procedure if they are not properly separated. If not properly treated, felons can progress to osteomyelitis, tenosynovitis, and septic arthritis.
The patient may recall trauma to the finger, but often no inciting source is identified. The patient may describe that they first noticed erythema of the finger tip, which later became edematous and painful. The pain may be mild at first but rapidly progress to severe and throbbing.
The presenting symptoms include tissue tension, throbbing pain, edema, and erythema of the fingertip pulp at the distal phalanx. Typically the edema will not extend proximally to the distal phalanx due to the compartments defined by the septae. The pain is often severe and worse in the dependent position. Spontaneous drainage may occur due to the pressure in the fingertip, which may result in temporary relief. However, if not properly incised and drained, the abscess will reform.
The diagnosis can often be made based on clinical exam. The distal phalanx may be erythematous and edematous with tense tissues and fluctuance. The fingertip may be extremely tender to the touch. It is important to note any bony abnormalities and assess for signs of ischemia. Imaging should be performed if there is a history of foreign body penetration. Imaging can also identify fractures, osteomyelitis, and gas formation in the tissues which may lead to an alternative diagnosis. A gram stain and culture of any discharge or drainage should be obtained to help guide antibiotic therapy.
If abscess formation has not yet occurred and the felon is in the cellulitis stage, it can be treated with anti-staphylococcal and anti-streptococcal antibiotics. Warm water or saline soaks, and elevation of the fingertip will also aid in recovery. If abscess formation has occurred, or if tension or fluctuance are present, incision and drainage must be performed to drain infected material and maintain venous blood flow to the finger. Due to the fibrous septae forming multiple compartments, it may be difficult to fully drain a felon and debridement in an operating room may be necessary.
A digital block should be performed prior to incision and drainage. Bupivacaine has the advantage of a longer lasting anesthetic effect than lidocaine. A finger tourniquet can be used to decrease bleeding and aid in visualization of structures. The area of maximal swelling and tenderness should be located for optimal drainage. For deep felons, a single lateral incision should be made. The incision should be made at least 0.5 cm distal to the DIP in order to avoid injury to the flexor tendon sheath, digital neurovascular structures, nail matrix and to avoid contracture. The incision should extend parallel to the nail plate. It is important to maintain a distance of 0.5 cm from the nail plate to avoid injury. The incision should be made on the nonoppositional side of the appropriate digit. The incision should be made on the ulnar aspect of digits 2, 3, or 4 and on the radial aspect of digits 1 and 5. The depth of the incision should be to the dermis. The incision should be extended to the end of the nail. For complete drainage, it is often necessary to use blunt dissection to separate the finger septae with a small blunt hemostat. If there is necrotic tissue present, it should be excised, and the abscess should then be decompressed and irrigated. The wound should be packed, and the finger should be splinted.
A volar longitudinal incision can be used for superficial felons. The same precautions as stated above should be followed. It is not recommended to use the “fish-mouth” incision, the “hockey stick” or the transverse palmar incision, as these incisions have been associated with complications such as neurovascular damage and painful scarring.
Packing should be removed in 48 to 72 hours, and the finger should be re-examined by a physician. If there is an improvement and the wound appears to be healing, the packing should be removed, and the wound can be allowed to close by secondary intention. If there is no improvement within 12-24 hours, or if the felon is extensive or recurrent, a surgical consult may be needed.
The patient should receive a tetanus shot if not up to date. A first-generation cephalosporin or anti-staphylococcal penicillin to cover S aureus and streptococcal organisms should be prescribed for 7-10 days. Doxycycline, trimethoprim/sulfamethoxazole, or clindamycin can be added if there is suspicion for MRSA. If the felon was a result of a bite wound, or if the patient is immunosuppressed, coverage for E corrodens may be indicated. Gram stain should be used to guide therapy when available.