Felon

Felons are closed-space infections of the fingertip pulp.[1, 2]  

Fingertip pulp is divided into numerous small compartments by vertical septa that stabilize the pad. Infection occurring within these compartments can lead to abscess formation, edema, and rapid development of increased pressure in a closed space. This increased pressure may compromise blood flow and lead to necrosis of the skin and pulp. The infection may lead to osteomyelitis and other serious life and limb threatning diseases. 

Frequency

United States

Felons may account for up to 15% to 20% of all hand infections; howevever, a large retrospective review found this infection accounting for 5% of all hand infections that underwent incision and drainge.[3]  Therefore, it is likely that they account for an even small number of hand infections. The thumb and second digit are the most commonly affected digits. Often, a felon may develop from a localized fingertip infection such as a paronychia. 

Mortality/Morbidity

Left untreated, osteomyelitis, tenosynovitis, and septic arthritis may result. In addition, the infection can lead to fingertip destruction through spontaneous decompression toward the skin. 

Given the severity of the pain and swelling patients usually present within the first several days and have a favorable prognosis. With early treatment, the prognosis is excellent with possible minor complications such as pain, sensitivity of the fingertip, pulp atrophy and deformity.

A felon presents as pain and swelling to the fingertip. It is generally on the volar aspect and usually does not extend proximally past the distal interphalangeal joint(DIP).

Penetrating trauma often precedes a felon. Wooden splinters, thorns, glass, repeated fingersticks in diabetics or minor cuts are common predisposing causes, yet no history of penetrating trauma is discovered in approximately 50% of patients. Infection also may spread from a paronychia.[4]  

The infection often begins as cellulitis, which is initially confined by the tough fibrous septa that course throughout the pad. At this stage, patients may report pain, redness, and swelling. 

If resolution does not occur, abscess formation is accompanied by progression of swelling and intense throbbing pain. There is usually not significant pain with range of motion at the DIP joint. 

A felon is characterized by a fingertip pad that is erythematous, tensely swollen, and very tender to palpation. There may be an associated puncture wound or paronychia.

Usually, due to the septae, the infection is usually contained to the pulp of the fingertip. If the infection has spread to the flexor tendon sheath, bone or joint, spreading of the infection may be visible.[4]  The point of maximal fluctuance may be on the volar aspect, raadial or ulnar surfaces.

Staphylococcus aureus is the most common cause of a felon and is often methicillin-resistant (MRSA).[5, 6, 7, 3]

Streptococcal specias are one of the other leading causes of a felon. 

Gram-negative organisms have been reported in immunosuppressed patients. Lancet-induced trauma from fingertip blood glucose measurements have been implicated as an etiology.

Eikenella corrodens has been reported in persons with diabetes who bite their fingernails.[5, 8, 9]

Perform Gram stain and culture on any fluid removed from the wound.

Radiographs should be obtained if there is a history of penetration with a radiopaque foreign body, if the history is unclear or if there is concern for underlying bone involvement.

Radiographic evaluation should be performed in severe cases and in immunocompromised patients if there is concern for osteomyelitis, joint involvement or any other concerning symptoms.

Serum tests are generally not indicated.

If there is concern that the patient needs definitive treatment in the operating room or has osteomyelitis, a complete blood count, basic metabolic profile, erythrocyte sedimentation rate and c-reactive protein may be performed. Blood cultures can also be obtained if providing intravenous antibiotics or if there is concern for sepsis.

There are no randomized trials to guide the treatment of a felon.

Treatment is guided by whether or not there is an associated abscess. However, this is often a rapidly spreading infection and therefore unless presenting very early, strong consideration should be made to incision and drainage.

If there is no abscess, treatment can be with oral antibiotics for low risk patients or IV antibiotics for high risk infections. Treatment should include MRSA coverage. If MRSA is not suspected a first generation cephalosporin is appropriate. If MRSA is suspected, trimethoprim/sulfamethoxazole would be appropriate for outpatient treatment or vancomycin for inpatient treatment.[10]

Adequate early treatment of a felon can prevent abscess formation and other serious complications.

Administer antibiotics with activity against methicillin-resistant Staphylococcus.

Decompression is almost always indicated.

Prior to incision, several steps can be performed to aid in adequate drainage.

A digital block provides adequate local anesthesia.

The limb can be exsanguinated by holding at 90º for 5 minutes and then applying a forarm tourniquet.[11, 12]

Incision and drainage:

Multiple incisions have been proposed for the incision and drainage of a felon, however no randomized trials exist. Most experts recommend either a unilateral longitudinal approach, a volar approach or a hockey stick appropach.[4]

All attempts should be made for the incision to be in the area of maximum swelling and tenderness. The incision should not cross the distal interphalangeal (DIP) joint to prevent formation of a flexion contracture at the DIP flexion crease. Probing is not carried out proximally to avoid extension of infection into the flexor tendon sheath.

A longitudinal incision in the midline is effective without serious iatrogenic complications that are observed with other traditionally recommended incisions. Incisions should ideally made on the opposite side of the pinching surface unless the point of maximal fluctuance is on the pinching surface. The incision should be made on the ulnar side of digits 2,3,4 and the radial side of digits 1 and 5. 

When using the longitudinal approach, it should begin doral to and 0.5cm distal to the DIP flexion crease and extend distally. Care should be made not to violate the tendon sheath. The wound should be deepend along a plane until the abscess is entered. Using tenotomy scissors or a hemostat care should be made to break up all involved septa.[13]

 A wik may be placed in the incision to allow continued drainage for 2-5 days.[14]

Daily soaks in warm soapy water or dilute povidone-iodine solution can be used.

Other approaches not discussed are associated with a variety of complications.

An orthopedist or hand surgeon should be consulted for more complex cases, especially when there is concern for osteomyelitis or flexor tenosynovitis, or immunocompromised patients.

Because of the potential for complications, prompt follow-up should be arranged in all cases. Surgical consultation should be obtained if there is no improvement within 12-24 hours of conventional therapy. If patients are unable to follow-up they should be advised to return for a wound check within 24-48 hours.

If treated early, drainage, elevation, and oral antibiotics may be adequate. Appropriate follow-up should always be arranged. Severe infections and complicated cases may require hospitalization for intravenous antibiotics and surgical drainage.

The most common organism involved is S aureus, accounting for around 80% of cases. Empiric coverage for MRSA is recommended. Gram stain, if available, should be used to guide therapy.

Provide tetanus prophylaxis if appropriate.

If drainage and antibiotic therapy yield no improvement within 12-24 hours, consultation with a surgeon is recommended.

Potential complications of felon include fingertip necrosis, osteomyelitis, and/or flexor tenosynovitis.

The goals of pharmacotherapy are to treat infections and prevent further complications.

Class Summary

Empirical coverage for S aureus and streptococcal organisms should be provided. While a first-generation cephalosporin or antistaphylococcal penicillin has traditionally been recommended, the rapid emergence of community-acquired methicillin-resistant S aureus (CA-MRSA) requires treatment with drugs more likely to be effective against this agent. Trimethoprim/sulfamethoxazole or clindamycin should be added for this coverage. Coverage for E corrodens may be indicated for immunosuppressed patients and bite wounds. Tailor antibiotics to cultures and sensitivities. Continue antibiotics for 7-10 days.

Dicloxacillin (Dycill, Dynapen)

Bactericidal antibiotic that inhibits cell wall synthesis; DOC to treat infections caused by penicillinase-producing staphylococci. May be used to initiate therapy when staphylococcal infection is suspected.

Cephalexin (Keflex, Biocef)

Another alternative antibiotic. First-generation cephalosporin that inhibits bacterial replication by inhibiting bacterial cell wall synthesis. Bactericidal and effective against rapidly growing organisms forming cell walls.

Trimethoprim/sulfamethoxazole

Inhibits bacterial growth by inhibiting synthesis of dihydrofolic acid.

Clindamycin

Semisynthetic antibiotic produced by 7(S)-chloro-substitution of 7(R)-hydroxyl group of parent compound lincomycin. Inhibits bacterial growth, possibly by blocking dissociation of peptidyl tRNA from ribosomes, causing RNA-dependent protein synthesis to arrest. Widely distributes in the body without penetration of CNS. Protein bound and excreted by the liver and kidneys.

Amoxicillin and clavulanate

Amoxicillin inhibits bacterial cell wall synthesis by binding to penicillin-binding proteins. Addition of clavulanate inhibits beta-lactamase producing bacteria.

Good alternative antibiotic for patients allergic or intolerant to the macrolide class. Usually is well tolerated and provides good coverage to most infectious agents. Not effective against Mycoplasma and Legionella species. The half-life of oral dosage form is 1-1.3 h. Has good tissue penetration but does not enter cerebrospinal fluid.

For children >3 months, base dosing protocol on amoxicillin content. Due to different amoxicillin/clavulanic acid ratios in 250-mg tab (250/125) vs 250 mg chewable-tab (250/62.5), do not use 250-mg tab until child weighs >40 kg.

Nafcillin (Unipen)

Indicated for severe infections.

Treats infections caused by penicillinase-producing staphylococci. Used to initiate therapy in any patients with possible penicillin G-resistant staphylococcal infection. Do not use for treatment of penicillin G-susceptible staphylococcal organisms.

Use parenteral therapy initially in severe infections. Severe infections may require very high doses.

Change to oral therapy as condition improves.

Because of occasional occurrence of thrombophlebitis associated with the parenteral route, particularly in elderly patients, administer parenterally only for a short term (24-48 h) and change to oral route if clinically possible.

Doxycycline

Broad-spectrum, synthetically derived bacteriostatic antibiotic in the tetracycline class. Almost completely absorbed, concentrates in bile, and is excreted in urine and feces as a biologically active metabolite in high concentrations.

Inhibits protein synthesis and, thus, bacterial growth by binding to 30S and possibly 50S ribosomal subunits of susceptible bacteria. May block dissociation of peptidyl t-RNA from ribosomes, causing RNA-dependent protein synthesis to arrest.

Provides good coverage against Spirochetes, many gram-negative organisms, anaerobic organisms, atypical bacteria, and many gram-positive organisms.

The finger should be soaked 3-5 times daily in soapy water or dilute povidone-iodine solution per expert recommendations.

Provide follow-up care within 2 days.

Remove packing in 2-5 days

 

Osteomyelitis involving the diaphysis of distal phalanx is a common complication.

The most serious complication of felon is acute tenosynovitis, which may result from contiguous spread of infection. This can be iatrogenic from inadvertent nicking of the flexor tendon sheath during drainage.

Other complications include skin necrosis, deformity of the fingertip, septic arthritis, and instability of the finger pad.

Prognosis is excellent when treated early and appropriately. Patients may have pain, sensitivity or deformity for upwards of 6-months.