Continuing Education Activity

A felon infection occurs within the closed-space compartments of the fingertip pulp. The swelling leads to intense throbbing pain. If the blood flow is compromised by compression from edema and pus formation, the surrounding tissues are at risk for ischemia. 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. This activity describes the pathophysiology of felons and highlights the role of the interprofessional team in its management.

Objectives:

• Identify the presentation of felons.

• Determine the causes of felons.

• Determine the treatment options for felons.

• Communicate the importance of care coordination among interprofessional team members to improve outcomes for patients affected by felons.

Introduction

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 risk 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. The underlying bone, joint, or tendons may become infected if left untreated.[1][2]

Etiology

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 immunosuppressed individuals.[3][4]

Epidemiology

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.[5][6]

Pathophysiology

A felon is an infection that occurs within the closed-space compartments of the fingertip pulp. The infection may initially start as cellulitis, progressing 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 noncompliant compartments, which 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 an incision and drainage procedure if they are not properly separated. If not properly treated, felons can progress to osteomyelitis, tenosynovitis, and septic arthritis.

History and Physical

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 fingertip, which later became edematous and painful. The pain may be mild at first but rapidly progresses 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.

Evaluation

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, possibly leading to an alternative diagnosis. A gram stain and culture of any discharge or drainage should be obtained to help guide antibiotic therapy.

Treatment / Management

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, as well as elevation of the fingertip, will also aid in recovery. If abscess formation has occurred, or if tension or fluctuance is 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.[7][8][9]

A digital block should be performed before incision and drainage. Bupivacaine has the advantage of a longer-lasting anesthetic effect than lidocaine. A finger tourniquet can decrease bleeding and aid in the 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 to avoid injury to the flexor tendon sheath, digital neurovascular structures, and nail matrix and to avoid contracture. The incision should extend parallel to the nail plate. Maintaining a distance of 0.5 cm from the nail plate is important to avoid injury unless there is an obvious paronychia, which should also be drained. For complete drainage, it is often necessary to use blunt dissection to separate the finger septae with a small blunt hemostat. If necrotic tissue is 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 24 to 48 hours, and a physician should re-examine the finger. If there is an improvement and the wound appears to be healing, the packing should be removed, and the wound can be closed 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.

If the patient is not up to date, the patient should receive a tetanus shot. 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 of MRSA. If the felon resulted from 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.

Differential Diagnosis

The differential diagnoses for felons include the following:

• Cellulitis
• Dermatomyositis
• Fingertip injuries
• Granuloma annulare
• Hematomas from pulse oximetry
• Herpetic whitlow
• Pyogenic granuloma
• Paronychia
• Reiter syndrome

Enhancing Healthcare Team Outcomes

A felon is a common presentation, and healthcare workers should be familiar with its management. Mild cases can be treated with warm soaks and an antibiotic, but if fluctuance is present, drainage is required. Before making an incision, it is important to know the anatomy of the fingertip to avoid causing any iatrogenic injury. The outcomes for most patients are excellent.