Felon

A felon is a closed-space infection of the distal pulp of the finger. Paronychia, by contrast, centres on the nail fold.

How the pulp is inoculated. The route matters because a bite or oral inoculation changes the microbiology and the antimicrobial cover required:

• Penetrating trauma: a splinter, needle, thorn or puncture
• A bite or oral inoculation
• Iatrogenic puncture, including repeated fingertip testing
• No recalled injury at all, which does not exclude infection

Who is at risk. Four groups are singled out:

• Manual labourers: carpenters, gardeners, mechanics
• Diabetics, through impaired immunity and poor healing
• The immunosuppressed: steroids, chemotherapy, HIV
• Children, through thumb-sucking and foreign-body ingestion

• The paediatric distal phalanx is not a small adult one. The distal phalanx has an open physis with the epiphysis at its base, and the germinal nail matrix lies dorsally, immediately proximal to the physis. A neglected pulp infection or over-aggressive curettage therefore risks the physis (growth arrest/shortening) and the germinal matrix (permanent nail deformity) - so in a child, drainage is adequate but conservative, bone curettage is gentle, and the dorsal matrix/physis are respected.
• Blistering distal dactylitis - the superficial mimic. In children (and occasionally adults) a tense, fluid-filled superficial blister on the volar fat pad of the fingertip, caused by Group A streptococcus (or S. aureus), mimics a felon but is a superficial subcutaneous/epidermal blistering infection, NOT a deep septic pulp compartment. The distinction matters because it is treated by simple deroofing/incision-drainage of the bulla plus oral antibiotics, and does not require the deep septum-disrupting felon I&D. A superficial fluctuant blister (rather than a tensely indurated deep pulp) in a child should raise it.
• Threshold and antibiotics. Children may not localise pain well and can deteriorate quickly, so maintain a low threshold for examination under GA and for imaging; antibiotic choice follows the same anti-staphylococcal (plus MRSA where prevalent) principles, but streptococcal cover is relevant given blistering distal dactylitis.

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• Gout - do not blindly incise a tophus. An acute gouty attack or an eroding tophus of the DIP/fingertip can present with a red, hot, tender, swollen digit that mimics a felon, sometimes discharging chalky white urate rather than pus. Incising a tophus can create a chronic, non-healing, discharging wound. If the story fits (known gout, other tophi, no clear inoculation), aspirate and send for polarising microscopy (negatively birefringent, needle-shaped urate crystals) and check serum urate before committing to a septic incision-and-drainage - the treatment is medical, not a felon drainage.
• The felon that will not settle - think atypical/indolent infection. A pulp or fingertip infection that fails to resolve, recurs, or forms a chronic sinus despite adequate bacterial drainage should prompt consideration of an atypical organism: Mycobacterium marinum (after aquatic / fish-tank / fishing exposure - an indolent granulomatous infection that grows best at lower temperature, needs special mycobacterial culture at ~30-32°C and biopsy, and prolonged antimycobacterial therapy), fungal infection (immunocompromised, gardeners - sporotrichosis), or unusual bacteria. Ordinary swabs and short antibiotic courses miss these, so send tissue for histology plus prolonged/atypical cultures rather than repeating the same drainage.
• Other named mimics to keep in mind. As emphasised throughout, herpetic whitlow (vesicles - do NOT incise; routed to herpetic-whitlow) and non-infective lesions (pyogenic granuloma, glomus tumour, metastasis/rarely subungual melanoma presenting as a "chronic infection") sit in the same differential - the unifying rule is that an atypical, non-purulent, or non-resolving "felon" earns imaging, aspiration/biopsy and the correct culture, not another blind incision.

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The septa. Fibrous bands run from the periosteum of the distal phalanx to the pulp skin. They stabilise the fingertip and divide its fat into lobules, and in infection they can compartmentalise pus into locules that sit against bone and raise tissue tension.

Why an abscess needs drainage. Pus confined in this way means an established pulp abscess cannot be cured reliably by antibiotics alone. Pressure, vascular compromise and direct contact with the distal phalanx explain the risk of necrosis and osteomyelitis. What matters clinically is compartmentalisation, perfusion and proximity to bone, not an exact septal count or an unvalidated pressure threshold.

How it evolves. The findings change as the infection progresses:

• Early cellulitic pain and erythema may precede an abscess
• Increasing tension, fluctuance or a focal collection indicates pus
• Persistent pain, drainage or bone tenderness raises concern for osteomyelitis
• Proximal tenderness or Kanavel signs raise concern for flexor-sheath spread

Microbiology. Staphylococcus aureus is common, but its susceptibility varies by region and exposure, and streptococcal and polymicrobial infections occur. Bites, water or soil exposure, immunosuppression and healthcare contact change the empiric coverage. Send pus or tissue for culture and adapt treatment to local guidance.

By location. The site of maximal swelling guides the incision: a lateral incision goes on the side where the swelling is greatest.

By stage. Staging decides treatment. Abscess formation, bone tenderness, systemic illness and proximal spread determine urgency and imaging; elapsed hours alone do not.

History. A penetrating injury 2-7 days earlier, followed by progressive swelling of the pulp and severe throbbing pain from compartment pressure, worse at night and disturbing sleep. Systemic symptoms are uncommon unless the organism is MRSA or the patient is diabetic.

Examination. The pulp is tense and exquisitely tender, and the erythema is limited to the volar fingertip rather than spreading proximally. Fluctuance may be present but is difficult to elicit because of the septa. Check for Kanavel signs, DIP motion, perfusion and sensation: a felon has no Kanavel signs, which distinguishes it from flexor tenosynovitis, and proximal findings change the urgency and scope of treatment.

Felon or paronychia. The site separates them. A felon is a pulp-space infection of the volar distal phalanx, with severe pulp tenderness and no nail involvement. Paronychia is an infection of the nail fold (perionychium), with nail-fold erythema and pus under the cuticle or nail plate, and it often responds to conservative treatment or simple nail elevation. A subungual collection is a periungual mimic of the same kind:

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The differential. Four conditions sit closest:

A clinical diagnosis. Felon is diagnosed at the bedside: a penetrating injury, severe pulp pain, a tense tender fingertip and erythema limited to the pulp space. In typical cases no investigation is needed before drainage.

Radiographs. AP and lateral films of the finger if the presentation is over 48 hours or there is bony tenderness, looking for bone erosion, periosteal reaction and sequestrum formation. No source cited on this page quantifies how often delayed felons develop osteomyelitis, so image on these clinical grounds rather than on an assumed rate, and remember that radiographic change lags the infection by one to two weeks.

Ultrasound and MRI. Ultrasound can confirm a collection, and selective ultrasound or MRI belongs to the complicated or non-resolving infection. MRI can localise an atypical or non-resolving process when the clinical compartment is uncertain. In the subungual abscess below, ultrasound places the collection between the nail plate and the distal phalanx rather than within the pulp.

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Cultures. Send pus for microscopy, culture and sensitivity at the time of drainage, which allows antibiotics to be tailored, especially for MRSA. Take blood cultures if the patient is systemically unwell or diabetic.

HSV testing. A viral swab for HSV PCR if vesicles are present or the presentation is atypical. Herpetic whitlow mimics a felon but is managed conservatively: incision spreads the virus and worsens the outcome.

Abscess, not the clock. Cellulitis without a collection may be treated non-operatively with close review. Fluctuance, a tense collection, purulence or an ultrasound-confirmed abscess requires prompt drainage. No validated 24- or 48-hour clock replaces examination.

Non-operative treatment. Rarely appropriate, and only for cellulitis without abscess formation or fluctuance, in a cooperative patient who can be observed closely. No trial has quantified how often a non-operative trial succeeds in an established felon; the reviews cited here describe drainage as the treatment once the pulp is tense, so keep the threshold for surgery very low.

Incision and drainage. This is the standard treatment for an established abscess, and the technique is described in the next section. Beyond the collection itself, it is indicated for:

• A fluctuant felon at any stage
• Failed conservative management
• Radiographic osteomyelitis

Antibiotics with drainage. Select antimicrobial therapy from severity, culture, local resistance, allergy, exposure and host factors.

Structures at risk. Four structures are at risk during drainage:

Setup. Supine, with the arm abducted 90 degrees on a hand table. Prepare with Betadine from fingertip to mid-forearm and drape with a window exposing the finger. The upper-arm tourniquet is inflated after exsanguination with an Esmarch or by elevation, to 250mmHg for 20-30 minutes at most.

Anaesthesia. A digital block is preferred: 2% lignocaine without adrenaline, 2-3ml each side of the digit base, then wait 5-10 minutes. Adrenaline is avoided because of the risk of ischaemia. Alternatives are a ring block, a wrist block (median, ulnar and radial nerves) or an axillary block; general anaesthesia for a child or an extensive debridement.

Choosing the incision. The lateral hockey-stick is the preferred technique and the volar longitudinal incision the alternative, but position still follows the collection and the surgeon's safe approach, and no single pattern is universal. Use a longitudinal volar or safe lateral approach appropriate to the collection, and protect the digital neurovascular bundles, the nail matrix and the flexor sheath. Never extend proximal to the DIP flexion crease, which risks entering the flexor sheath, and avoid a transverse volar incision, which crosses the digital nerves.

Never a fishmouth. A transverse incision across the fingertip causes pulp necrosis and an unstable, painful tip.

Lateral (hockey-stick) approach: preferred. It stays lateral to the neurovascular bundle, avoids a volar scar, carries a lower neurovascular risk and drains well.

1. Identify the DIP flexion crease and the midlateral line. Start 5mm distal to the DIP crease on the radial or ulnar side, choosing the side of maximal swelling or pointing.
2. Run the longitudinal limb 15mm parallel to the midlateral line, staying between it and the volar midline.
3. Curve a transverse limb across the fingertip (the hockey-stick) to allow drainage and avoid tip necrosis.
4. Deepen through the dermis to the pulp space with fine scissors or a #15 blade, neither too dorsal (the neurovascular bundle) nor too deep (the DIP joint).

Volar longitudinal approach: the alternative. A central incision 20mm long, starting 5mm distal to the DIP crease and running to the fingertip in the exact midline, between the neurovascular bundles. It leaves a volar scar that can be tender and painful with pinch, and its neurovascular risk is slightly higher if the incision drifts off the midline. Deepen to the pulp, evacuate the pus and break the septa as for the lateral approach.

Drainage and debridement. The same steps follow either incision:

1. Evacuate the pus and send it for MC&S.
2. Break down the fibrous septa with a curved mosquito or small haemostat, sweeping through all compartments. Incomplete drainage leads to recurrence; the aim is to open the infected locules while avoiding indiscriminate injury to viable pulp.
3. Curette out pus and necrotic tissue and irrigate with 500ml normal saline.
4. If bone is exposed, feel it: roughness indicates osteomyelitis. Curette a sequestrum gently, because aggressive curettage weakens the bone.

The wound. Leave it open for drainage and do not close primarily; it needs open drainage for 48-72 hours. Pack lightly with ribbon gauze (iodoform or Vaseline), since tight packing causes pressure necrosis, and insert a 0.25-inch Penrose drain if the cavity is large. A bulky dressing leaves the fingertip exposed for monitoring, and the hand is elevated and protected as needed.

What to exclude. Persistent or severe disease warrants assessment for distal-phalanx osteomyelitis, DIP septic arthritis, flexor-sheath spread, ischaemia, a foreign body and atypical infection. Proximal spread changes the emergency, and painful DIP motion warrants assessment of the joint.

Osteomyelitis. The pulp infection lies directly against the distal phalanx, which creates a real osteomyelitis risk, but no validated 48-hour percentage exists and the incidence is not established by any universal delay threshold. Drain established pus, review cases that do not resolve, image when bone involvement is suspected, obtain deep cultures, and combine source control with organism- and host-specific therapy.

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Antibiotics. Empiric antibiotics are given at a dose and route appropriate to severity, exposure, local resistance and host factors, and adjusted once culture results return. The course runs to a total of 7-10 days.

Packing and drain. Both come out when the cavity and drainage permit rather than on a fixed 48-hour rule; the first review is at 48 hours, with drain removal at 48-72 hours. Close follow-up ensures early detection of complications such as osteomyelitis or chronic sinus formation.

Healing. Early drainage (under 24 hours) is quoted at 98% complete resolution, healing in 3 weeks with minimal scarring. After prompt source control of an established abscess, the outcome depends on tissue viability, the organism and the host: review until drainage and inflammation resolve, and image and re-debride when the response is poor. Complicated or delayed infection varies with osteomyelitis, ischaemia and comorbidity; with osteomyelitis, healing takes 8-12 weeks, longer treatment and reconstruction may be required, and amputation may be required. Do not quote unsupported universal percentages for any of these.

Prognostic factors. Complete source control, viable perfused tissue, no bone, joint or sheath involvement, a susceptible organism and an immunocompetent host favour recovery. Ischaemia, diabetes or immunosuppression, osteomyelitis, proximal spread, a retained foreign body, an atypical organism and inadequate source control count against it.

Function and long-term problems. The figures quoted for recovery:

• Return to work at 4-6 weeks for manual labourers
• Full range of motion in 90% at 8 weeks
• Grip strength recovers toward baseline over about 12 weeks; no series measures a figure for felon recovery, so none is quoted
• Normal two-point discrimination in 85%
• Persistent fingertip tenderness in 5%
• Cold intolerance in 10-15% in the first year
• Nail deformity rare (under 2%) if the nail matrix is avoided
• Recurrence under 2% with adequate initial treatment