Felon

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.[5][6]

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 and are most commonly caused by penetrating trauma. However, anything that introduces bacteria into the digital pulp can lead to the formation of a felon. Puncture wounds, penetration of foreign bodies such as splinters or bits of glass, abrasions, or bites can all be inciting factors. Paronychias (skin infection around the nail) is another common cause.[7][8]

Felons are relatively common, particularly among adults. They can occur at any age but are more frequently seen in adults due to increased manual labor or exposure to trauma. Certain demographic factors, such as occupation and lifestyle, may influence their prevalence. For example, people who have occupations involving manual labor have a higher incidence of felons due to increased exposure to traumatic injuries or repetitive microtrauma to the hands and fingers. Co-morbidities influence the prevalence of felons as well; certain medical conditions (eg, diabetes mellitus, peripheral vascular disease, or immunosuppression) may predispose individuals to develop felons due to impaired wound healing or compromised circulation and immune function.

Trauma to the fingertip and poor hand hygiene are significant risk factors for felon development. They allow bacteria, particularly Staphylococcus aureus, to colonize the skin and enter the fingertip tissue through breaks in the skin. While felons can occur throughout the year, seasonal variations in incidence may occur, with higher rates observed during warmer months when outdoor activities and manual labor are more common. The incidence of felons may vary geographically based on factors such as climate, socioeconomic status, access to healthcare, and occupational patterns.

Pathophysiology

A felon infection 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 fingertip pulp and form small compartments. Blood flow may be compromised when edema and infection form in these noncommunicating compartments, leading to pulp and skin necrosis. Swelling in these small compartments causes the severe pain associated with felons. Septae may impede complete drainage after an incision and drainage procedure if they are not properly separated. If left untreated, felons can progress to osteomyelitis, tenosynovitis, and septic arthritis.

Histopathology

Histopathological examination of a felon typically reveals acute suppurative inflammation characterized by infiltration of neutrophils, abscess formation with necrotic debris, tissue destruction, and vascular changes—including vasodilation and increased vascular permeability. Fibrin deposition may be present, and granulation tissue formation may occur in chronic cases. These findings are consistent with the infectious nature of a felon and aid in confirming the histological diagnosis.[9]

History and Physical

The presenting symptoms of a felon are usually pain and redness. The patient may recall trauma to the finger, but often, the inciting source is not identified. The patient may describe that they first noticed erythema of the fingertip, which later became edematous and painful. The onset of pain may be mild at first but rapidly progresses to severe throbbing pain and worse in the dependent position.

The presenting signs include tissue tension, non-pitting edema, and erythema of the fingertip pulp at the distal phalanx of the affected finger. Typically, the edema will not extend proximally to the distal phalanx due to the compartments defined by the septae. Spontaneous drainage of the felon may occur due to the pressure within the fingertip pulp. While that may provide temporary relief, the abscess will reform if not properly incised and drained.[10]

Evaluation

The diagnosis can often be made based on a clinical exam of the affected digit. The distal phalanx may be erythematous and edematous with tense tissues and fluctuance. The fingertip may be incredibly tender to the touch. 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 tissue gas formation, possibly leading to an alternative diagnosis. A Gram stain and culture of any discharge or drainage will help guide antibiotic therapy. Biopsy sampling for histopathology is very rarely needed for diagnosis.[11]

Treatment / Management

Management of the felon will depend on the severity of the infection. If the felon is in the cellulitis stage without abscess formation, 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 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 drain a felon fully, and debridement in an operating room may be necessary.[12][13][14](B3)

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 maximal swelling and tenderness area should be located on the volar aspect for optimal drainage. For deep felons, a single lateral 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 essential 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 fingertip septae with a small blunt hemostat. Any necrotic tissue must be excised, and the abscess should be decompressed and irrigated. Finally, the wound should be packed, and the finger should be splinted.[15]

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 24 to 48 hours following the procedure, 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 to 24 hours, or if the felon is extensive or recurrent, a surgical consult may be needed.[16]

An age-appropriate tetanus toxoid-containing vaccine ("tetanus shot") should be administered to all patients who cannot confirm a history of 3-dose primary vaccination series and have received the most recent dose within the past 5 years. The patient should be prescribed a 7 to 10-day course of antibiotics, such as a first-generation cephalosporin or anti-staphylococcal penicillin, to cover S aureus and streptococcal organisms. Doxycycline, trimethoprim/sulfamethoxazole, or clindamycin can be added if there is suspicion of methicillin-resistant Staphylococcus aureus (MRSA). If the felon resulted from a bite wound or if the patient is immunosuppressed, coverage for Eikenella corrodens may be indicated. When available, gram stain and culture of any discharge or drainage should be used to guide therapy.

Differential Diagnosis

The differential diagnoses for felons include:

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

Prognosis

The prognosis largely depends on early recognition, timely medical intervention, and the patient's overall health status. When promptly addressed, most cases of felons respond well to treatment, which typically involves incision and drainage of the abscess along with antibiotic therapy. Recurrence is uncommon but may occur if the infection is not entirely resolved or if predisposing factors such as trauma or compromised immune function are present. Overall, with proper management, the prognosis for felons is generally good, and most patients can expect complete resolution of symptoms and restoration of fingertip function.

Complications

Delayed or inadequate treatment may lead to the progression of the infection and the development of complications. Tissue necrosis, abscess extension into surrounding structures (such as tendons, joints, or bone), and systemic spread of infection can occur.[17] Severe cases can result in permanent tissue damage, loss of function, or even sepsis, a life-threatening condition characterized by widespread infection and organ dysfunction. Additionally, if the infection is not completely eradicated, there is a risk of recurrence or the formation of chronic, non-healing wounds. Proper management of felon, including timely incision and drainage of abscesses and appropriate antibiotic therapy, is essential to minimize the risk of complications and ensure optimal patient outcomes.