Closed-Space Pulp Infection | Surgical Emergency | High Pressure Compartment
- Fibrous septae create closed compartments - high pressure causes tissue necrosis
- Urgent drainage within 24-48 hours prevents osteomyelitis and flexor sheath involvement
- Never use fishmouth incision - causes pulp necrosis and unstable fingertip
- S. aureus most common organism - empiric flucloxacillin until cultures
- Neurovascular bundles run along radial and ulnar borders - avoid midlateral incisions at these zones
- “Felon = closed-space infection confined by vertical fibrous septa (unlike paronychia = perionychial)
- “Kanavel signs absent (distinguishes from flexor tenosynovitis)
- “Lateral incision avoids volar scar and neurovascular injury
- “Drains removed at 48 hours - prolonged drainage causes chronic drainage sinus
Clinical Imaging
Imaging Atlas
Closed compartment with 15-20 vertical fibrous septa from periosteum to skin. High pressure causes tissue necrosis, bone erosion, and spread to adjacent structures (flexor sheath, DIP joint).
24-48 hour window for drainage. Delay beyond 48h increases osteomyelitis risk to 10-15%. Pus under pressure erodes bone and spreads proximally.
Lateral or volar longitudinal incision - Never fishmouth! Fishmouth causes pulp necrosis and unstable painful fingertip. Break down all septa during drainage.
Osteomyelitis (10-15%), flexor tenosynovitis (5%), septic DIP arthritis (3%), fingertip necrosis (from inadequate drainage or wrong incision). Aggressive early drainage prevents all.
| Presentation | Timing | Treatment | Key Pearl |
|---|---|---|---|
| Early felon (under 24h), tense pulp, no fluctuance | Under 24 hours | Trial of IV antibiotics + elevation + observation | May abort with early antibiotics - but low threshold for drainage |
| Established felon (24-48h), fluctuant, severe pain | 24-48 hours | URGENT incision and drainage + IV antibiotics | This is the standard scenario - drainage mandatory |
| Late felon (over 48h), bony tenderness, systemic signs | Over 48 hours | Drainage + sequestrectomy + prolonged antibiotics | Assume osteomyelitis - need X-ray and debridement |
SEPTAFibrous Septa Anatomy
Hook:SEPTA = the partitions that create the problem - must break them ALL during drainage!
FELONFelon vs Paronychia Distinction
Hook:FELON = Fingertip Emergency requiring Lateral incision Or Necrosis follows!
BONESComplications of Felon
Hook:BONES at risk if you delay drainage or use wrong incision!
Overview and Epidemiology
A felon is a closed-space infection of the pulp space of the distal phalanx. The unique anatomy - with 15-20 vertical fibrous septa running from periosteum to skin - creates multiple small compartments that cannot decompress. Rising pressure causes microvascular thrombosis, tissue necrosis, bone erosion, and potential spread to adjacent flexor sheath and DIP joint. Early drainage (within 24-48 hours) prevents these devastating complications.
- Minor penetrating trauma (80%): splinters, needles, thorns
- Bite injuries (10%): human or animal bites
- Hematogenous spread (5%): rare, diabetics
- Iatrogenic (5%): fingerstick blood glucose testing
- Manual laborers: carpenters, gardeners, mechanics
- Diabetics: impaired immunity, poor healing
- Immunosuppressed: steroids, chemotherapy, HIV
- Children: thumb-sucking, foreign body ingestion
Pathophysiology and Mechanisms
The pulp space of the distal phalanx is compartmentalized by 15-20 vertical fibrous septa running from the periosteum of the distal phalanx to the skin. These septa contain fat lobules, nerves, and vessels. When infection enters this closed space, pressure builds rapidly. Unlike cellulitis (which spreads along tissue planes), a felon is confined and pressure rises until tissues rupture or necrosis occurs. Pressure can reach 30-40 mmHg - sufficient to cause bone erosion and vascular thrombosis.
| Structure | Location | Risk During Drainage | Protection Strategy |
|---|---|---|---|
| Neurovascular bundles | Radial and ulnar borders of finger | Injury during lateral incision if too dorsal/volar | Keep incision between midlateral line and volar midline |
| Flexor digitorum profundus tendon | Volar to DIP joint | Inadvertent entry into flexor sheath | Do not extend incision proximal to DIP flexion crease |
| Distal phalanx bone | Central pulp space | Osteomyelitis from pressure necrosis | Early drainage prevents bone involvement |
| DIP joint | Deep to pulp space | Septic arthritis from proximal spread | Urgent drainage prevents joint extension |
- S. aureus (70%): most common, flucloxacillin
- MRSA (10-15%): increasing, needs vancomycin
- Streptococcus (10%): Group A or B
- Polymicrobial (5%): bite injuries, anaerobes
- 0-12h: Bacterial inoculation, inflammatory response
- 12-24h: Abscess formation, pressure rises
- 24-48h: Tissue necrosis begins, bone erosion starts
- Over 48h: Osteomyelitis (10-15%), proximal spread (5%)
Classification Systems
Anatomical Classification
| Type | Location | Features | Preferred Incision |
|---|---|---|---|
| Central Felon | Central pulp space | Most common (70%), symmetric swelling, midline tenderness | Volar longitudinal or lateral hockey-stick |
| Radial Felon | Radial side pulp | Eccentric swelling, maximal tenderness radial side | Radial lateral hockey-stick incision |
| Ulnar Felon | Ulnar side pulp | Eccentric swelling, maximal tenderness ulnar side | Ulnar lateral hockey-stick incision |
Classification by location guides incision placement - choose lateral incision on side of maximal swelling.
Clinical Presentation
- Penetrating injury 2-7 days prior (splinter, thorn, needle)
- Severe throbbing pain - worse at night, disturbs sleep
- Progressive swelling of fingertip pulp
- Systemic symptoms uncommon unless MRSA or diabetic
- Tense, tender pulp space - exquisitely painful to palpate
- Erythema limited to volar fingertip (not proximal)
- Fluctuance may be present (but difficult to elicit due to septa)
- No Kanavel signs (distinguishes from flexor tenosynovitis)
Felon = pulp space infection (volar distal phalanx). Paronychia = nail fold infection (perionychial). Key differences: felon has severe pulp tenderness, no nail involvement, requires surgical drainage. Paronychia has nail fold erythema, pus under cuticle or nail plate, often responds to conservative treatment or simple nail elevation.
| Condition | Key Distinguishing Features | Management Difference |
|---|---|---|
| Paronychia | Nail fold erythema, pus visible under cuticle, no pulp involvement | Conservative or simple nail elevation |
| Flexor tenosynovitis | Kanavel signs: flexed posture, fusiform swelling, pain on passive extension, tenderness along flexor sheath | Urgent flexor sheath irrigation |
| Cellulitis | Diffuse erythema, no localized abscess, spreads along lymphatics | IV antibiotics, no drainage |
| Herpetic whitlow | Vesicles, burning pain, history of HSV, no pus | Conservative - DO NOT INCISE |
Investigations
Investigation Protocol
Felon is a clinical diagnosis. Classic presentation: penetrating injury history, severe pulp pain, tense tender fingertip, erythema limited to pulp space. No investigations needed to proceed with drainage in typical cases.
X-ray finger (AP and lateral) if presentation over 48 hours or bony tenderness. Look for osteomyelitis signs: bone erosion, periosteal reaction, sequestrum formation. Present in 10-15% of delayed cases.
Send pus for MC&S at time of drainage. Allows antibiotic tailoring (especially for MRSA). Blood cultures if systemically unwell or diabetic.
Viral swab for HSV PCR if vesicles present or atypical presentation. Herpetic whitlow mimics felon but requires conservative management - incision spreads virus and worsens outcome.
Management
Conservative Management (Rarely Appropriate)
Indications:
- Presentation under 12 hours
- No fluctuance
- Cellulitis without abscess formation
- Cooperative patient for close observation
Conservative Protocol
Flucloxacillin 500mg QID PO (or IV 2g QID if toxic). If penicillin allergic: clindamycin 450mg TDS. Cover MRSA if risk factors (vancomycin 15-20mg/kg IV BD).
Strict elevation above heart level. Volar splint in safe position (wrist 30 deg extension, MP 70 deg flexion, IP extended). Ice packs for 20 min every 2 hours.
Review at 12-24 hours. If worsening pain, increasing swelling, or fluctuance develops - proceed immediately to drainage. Success rate under 20% - low threshold for surgery.
Failure Criteria (proceed to drainage):
- Pain not improving at 12h
- Fluctuance develops
- Systemic signs (fever, tachycardia)
- Patient preference for definitive treatment
Low threshold for surgical intervention as conservative success rate is under 20% for established felon.
Surgical Technique - Detailed Approach
Patient Setup
Setup Checklist
Supine with hand table extension. Affected arm abducted 90 degrees on hand table. Tourniquet on upper arm (inflated to 250mmHg for 20-30 minutes maximum).
Digital block preferred (2% lignocaine 2-3ml each side of digit base, no adrenaline). Alternative: wrist block (median, ulnar, radial nerves) or axillary block. GA for children or extensive debridement.
Betadine prep from fingertip to mid-forearm. Drape hand with window exposing finger. Inflate tourniquet after exsanguination with Esmarch or elevation.
Complications
| Complication | Incidence | Risk Factors | Management |
|---|---|---|---|
| Osteomyelitis of distal phalanx | 10-15% (if drainage delayed over 48h) | Delayed presentation, diabetes, immunosuppression | Debride sequestrum, 4-6 weeks IV antibiotics, serial X-rays, may need amputation if extensive |
| Flexor tenosynovitis | 5% (proximal spread) | Inadequate drainage, delayed treatment | Urgent flexor sheath irrigation, IV antibiotics, may need multiple washouts |
| Septic DIP arthritis | 3-5% | Bone involvement, severe infection | Arthrotomy, joint washout, IV antibiotics 4-6 weeks, may need arthrodesis |
| Fingertip necrosis | 2-5% | Fishmouth incision, inadequate drainage, vascular compromise | Debride necrotic tissue, flap coverage if needed, may need revision amputation |
| Chronic draining sinus | 5% | Retained necrotic tissue, inadequate septa breakdown, osteomyelitis | Excise sinus, debride cavity, antibiotics, flap coverage if large defect |
| Neurovascular injury | Under 2% | Incision too dorsal or volar, poor technique | Microsurgical repair if identified, sensory rehabilitation |
Osteomyelitis is the most devastating complication - occurs in 10-15% if drainage delayed beyond 48 hours. High compartment pressure erodes bone. Once established, requires prolonged IV antibiotics (4-6 weeks), repeat debridement, and carries risk of chronic osteomyelitis requiring amputation. Prevention is key: drain within 24-48 hours, break all septa, debride necrotic tissue thoroughly.
Postoperative Care
Postoperative Timeline
Strict elevation above heart. IV antibiotics (flucloxacillin 2g QID or vancomycin 15mg/kg BD if MRSA). Monitoring for neurovascular compromise. Analgesia (paracetamol + codeine or tramadol).
Remove packing at 48h. Inspect wound - should be clean, no pus. Start daily dressing changes with dry gauze. Remove drain if present. Transition to oral antibiotics if afebrile and improving.
Daily dressing changes. Wound granulates and contracts. Gentle range of motion exercises for DIP and PIP joints (prevent stiffness). Continue oral antibiotics for total 7-10 days.
Wound closes by secondary intention. Epithelialization from edges. Dressings reduced to every 2-3 days. Resume light activities.
Complete healing. Scar massage to soften. Full range of motion. Return to work and normal activities.
This standard protocol achieves healing in 95% of cases when drainage performed within 48 hours of symptom onset.
Outcomes and Prognosis
| Scenario | Success Rate | Healing Time | Complications |
|---|---|---|---|
| Early drainage (under 24h) | 98% complete resolution | 3 weeks | 2% osteomyelitis, minimal scarring |
| Standard drainage (24-48h) | 95% complete resolution | 3-4 weeks | 5-8% osteomyelitis, good function |
| Delayed drainage (over 48h) | 80% complete resolution | 6-8 weeks | 15-18% osteomyelitis, 10% chronic issues |
| Complicated (osteomyelitis) | 70% salvage rate | 8-12 weeks | May require amputation (5-10%) |
Good prognosis: Early drainage (under 48h), complete septa breakdown, adequate antibiotics, no bone involvement, immunocompetent patient.
Poor prognosis: Delayed presentation (over 48h), diabetes (3x higher complication rate), immunosuppression, osteomyelitis, inadequate initial drainage, fishmouth incision, MRSA infection.
- Return to work: 4-6 weeks for manual laborers
- Full range of motion: 90% achieve at 8 weeks
- Grip strength: Returns to 95% baseline by 12 weeks
- Sensory recovery: 85% normal 2-point discrimination
- Chronic pain: 5% report persistent fingertip tenderness
- Cold intolerance: 10-15% in first year
- Nail deformity: Rare (under 2%) if nail matrix avoided
- Recurrence: Under 2% with adequate initial treatment
Evidence Base and Key Studies
Fingertip Infections - Contemporary Review of Anatomy and Management
- Narrative review: fingertip is the most frequent site of hand infection (thorns, needles, splinters)
- Felon defined as a closed-space pulp abscess compartmentalized by fibrous septa from periosteum to dermis
- Early diagnosis and prompt drainage are the key determinants of success; delay risks osteomyelitis
- Emphasises numerous mimics (herpetic whitlow, gout, pyogenic granuloma) requiring careful differential
- Infections are more common and more aggressive in immunosuppressed and diabetic patients
Fingertip Infections - Pathophysiology and Evidence for Management
- Reviews unique anatomy of the volar pulp and perionychium underpinning felon and paronychia
- Felon drainage: incision through point of maximal fluctuance, blunt disruption of septa, irrigation
- Cautions against the classic fishmouth incision because of pulp instability and scar morbidity
- Stresses recognising herpetic whitlow, where incision is contraindicated and worsens outcome
- Choice and duration of antibiotics individualised; MRSA coverage where locally prevalent
Pyogenic Flexor Tenosynovitis - Prognostic Classification (Felon Spread Reference)
- Series of 75 patients with pyogenic flexor tenosynovitis - the feared proximal complication of a neglected felon
- Five poor-prognosis factors: age over 43, diabetes/PVD/renal failure, subcutaneous purulence, digital ischaemia, polymicrobial infection
- Group I (no purulence/ischaemia): no amputations, mean 80% total active motion
- Group II (purulence, no ischaemia): 8% amputation, 72% total active motion
- Group III (purulence plus ischaemia): 59% amputation, 49% total active motion
Epidemiology and Microbiology of Acute Hand Infections
- Review of 2,287 admissions with hand/finger infection; 1,507 incision and drainage procedures over 6 years
- 458 patients (30%) had culture-positive infection across 39 bacterial species
- MRSA was the single commonest isolate (53% of positive cultures), MSSA next (23%)
- Polymicrobial in 19%; IV drug use and diabetes strongly predicted polymicrobial infection
- Volar hand infections had the highest positive-culture rate; paronychia the lowest
Community-Associated MRSA in Hand Infections
- Prospective study of community-acquired hand infections in an urban hospital over 9 months
- After excluding nosocomial infections and fight bites, 52 patients were analysed
- 38 of 52 (73.1%) were MRSA-positive on culture and sensitivity testing
- Community-associated MRSA rate was far higher than previously suspected
- Empiric anti-staphylococcal choice must account for this when treating routine hand infections
Upper Extremity Infections in Patients with Diabetes Mellitus
- Retrospective review of 45 diabetic patients with 46 surgically debrided upper-limb infections
- 27 of 46 infections were deep (fascia, tendon, muscle or bone), 19 superficial
- 23 infections (50%) required more than one operation
- 18 infections (39%) culminated in amputation, with 3 infection-related deaths
- Amputation associated with deep infection, renal failure and gram-negative/anaerobic/polymicrobial cultures (46% polymicrobial)
Exam Viva Scenarios
Practise clinical reasoning and management decisions out loud
“A 35-year-old carpenter presents to ED with 48 hours of severe right index fingertip pain. He recalls a splinter injury 5 days ago. On examination, the pulp is tense, erythematous, and exquisitely tender. There is no proximal swelling. How would you assess and manage this patient?”
“Walk me through your surgical technique for drainage of a felon. Compare and contrast the lateral incision versus volar longitudinal incision. What are the anatomical structures at risk?”
“A 55-year-old diabetic presents 5 days after felon drainage with persistent pain, purulent drainage from the wound, and a foul odor. X-ray shows erosion of the distal phalanx with a sequestrum. How do you manage this complication?”
MCQ Practice Points
Q: How many vertical fibrous septa compartmentalize the pulp space of the distal phalanx, and what is their clinical significance in felon? A: 15-20 vertical fibrous septa run from the periosteum of the distal phalanx to the skin, creating multiple closed compartments. This anatomy is clinically critical because infection in these compartments cannot decompress - pressure builds rapidly causing microvascular thrombosis, tissue necrosis, and bone erosion. All septa must be broken down during surgical drainage to achieve complete decompression.
Q: How do you distinguish between a felon and herpetic whitlow clinically, and why is this distinction critical? A: Felon presents with severe throbbing pain, tense erythematous pulp, and purulent discharge. Herpetic whitlow presents with burning pain, multiple clear vesicles, and history of HSV exposure. The distinction is CRITICAL because incision of herpetic whitlow spreads virus, worsens infection, and can cause permanent nerve damage. Herpetic whitlow requires conservative management (antiviral medication) while felon requires surgical drainage.
Q: Why is the fishmouth incision contraindicated in felon drainage? A: The fishmouth incision (transverse incision across the fingertip) causes pulp necrosis by devascularizing the central pulp tissue and creates an unstable painful fingertip. Studies show 25% complication rate with fishmouth compared to 3% with lateral hockey-stick incision. The lateral or volar longitudinal approach provides adequate drainage while preserving pulp vascularity and avoiding tender scars.
Q: What is the critical time window for drainage of a felon, and what happens if drainage is delayed? A: 24-48 hours is the critical window. Drainage within 24h has 2% osteomyelitis risk. Delayed beyond 48h, osteomyelitis risk increases to 10-18%. Each 24-hour delay triples the risk of bone involvement. High compartment pressure erodes bone and allows proximal spread to flexor sheath (5%) and DIP joint (3-5%).
Q: What is the most common causative organism in felon, and when should you cover MRSA? A: S. aureus is most common (70% of cases). Empiric flucloxacillin 2g QID IV is first-line. Cover MRSA with vancomycin if: healthcare exposure, prior antibiotics, diabetes, IV drug use, or endemic area. MRSA prevalence has increased from 8% to 22% over past decade in community-acquired hand infections.
Q: A patient develops persistent purulent drainage 3 weeks after felon drainage. What is the most likely diagnosis and management? A: Most likely chronic draining sinus (5% incidence) due to retained necrotic tissue, inadequate septa breakdown, or underlying osteomyelitis. Management: First, obtain X-ray to exclude osteomyelitis (sequestrum). Second, sinogram to delineate tract if needed. Third, surgical excision of sinus tract with debridement of cavity and any dead bone. Fourth, prolonged antibiotics if osteomyelitis present. May require flap coverage if large soft tissue defect after excision.
Controversies and Areas of Uncertainty
The "best" incision is expert opinion, not trial-based. Lateral/longitudinal volar and high-lateral incisions all feature; the only point of broad agreement is that the transverse fishmouth incision should be abandoned. No randomised data compare incision types for functional outcome.
Whether a very early cellulitic felon can be aborted with antibiotics and elevation without drainage is debated. Most authorities accept a short, closely monitored trial only before fluctuance develops, with a low threshold to drain - established pulp abscess is a drainage diagnosis.
There is no universal empiric regimen. The decision to add anti-MRSA cover at the outset depends on local prevalence and patient risk, with reported community-MRSA rates varying from a minority to the majority of isolates between regions.
Packing versus simple drainage, drain use, and timing of dressing change are based on tradition rather than evidence. Tight packing can cause pressure necrosis; many now favour minimal packing or a small drain with early review.
Guidelines, Registries & Global Practice
- Fingertip is the most common site of hand infection worldwide (thorns, splinters, needlestick)
- Felon and paronychia together account for the majority of hand abscesses presenting acutely
- Predominantly affects manual workers and the immunosuppressed; rising incidence with diabetes prevalence
- Most managed as day-case or emergency-department drainage - inpatient admission reserved for systemic sepsis, osteomyelitis, or comorbidity
- S. aureus dominates globally; community-associated MRSA now a major isolate in many urban regions
- Empiric choice should follow the local antibiogram, not a single national guideline
- Polymicrobial flora in bite injuries, IV drug use and diabetes
- Anti-MRSA empiric cover advised where community MRSA prevalence is high
| Source | Region | Position on Felon Management |
|---|---|---|
| ASSH / hand surgery texts (Green's, Wolfe) | US / international | Prompt incision and drainage at point of maximal fluctuance; longitudinal/lateral incision; avoid fishmouth; disrupt septa |
| BSSH / BOA principles | UK | Surgical drainage of established pulp abscess; anti-staphylococcal antibiotics; image and debride if bone involved |
| IDSA skin and soft-tissue infection guidance | US / international | Drainage is primary therapy for a localised abscess; empiric MRSA cover where community prevalence is high; tailor to culture |
High-resource settings: digital-block drainage with operating microscope availability for complications, ready MC&S and MRSA testing, hand-therapy referral for scar and stiffness, and early imaging where osteomyelitis is suspected.
Limited-resource settings: clinical diagnosis predominates; bedside incision and drainage under digital block; empiric anti-staphylococcal therapy guided by local resistance patterns rather than routine culture; plain radiography may be the only imaging available, raising the threshold to act early before bone involvement.
Universal principles: drain established pulp abscesses promptly, disrupt all septa, never use a transverse fishmouth incision, exclude herpetic whitlow before incising, document neurovascular status before and after, and arrange review at 48 hours.
Key Anatomy
- 15-20 vertical fibrous septa from periosteum to skin = closed compartments
- Neurovascular bundles at radial and ulnar borders (avoid during drainage)
- Flexor digitorum profundus volar to DIP joint (do not extend incision proximal to DIP crease)
- High pressure (30-40 mmHg) causes vascular thrombosis and bone erosion
Diagnosis
- Felon = pulp space infection (vs paronychia = nail fold)
- Tense tender pulp + erythema + history of penetrating trauma
- No Kanavel signs (distinguishes from flexor tenosynovitis)
- X-ray if over 48h or bony tenderness (check for osteomyelitis)
Management Algorithm
- Under 12h + no fluctuance = trial of IV antibiotics (low success, low threshold for drainage)
- 24-48h or fluctuant = URGENT drainage (standard)
- Over 48h + bone erosion = drainage + sequestrectomy + prolonged antibiotics
- All cases: Flucloxacillin 2g QID IV (or vancomycin if MRSA risk)
Surgical Pearls
- Lateral (hockey-stick) incision PREFERRED: 5mm distal to DIP crease, extend to tip with curve
- NEVER fishmouth (causes pulp necrosis and painful unstable tip)
- MUST break down ALL 15-20 septa with blunt forceps (key step)
- Leave open, pack lightly, drain if large cavity, remove at 48h
Complications
- Osteomyelitis 10-15% if drained over 48h (debride sequestrum, 4-6 weeks IV antibiotics)
- Flexor tenosynovitis 5% (proximal spread - urgent sheath irrigation)
- Septic DIP arthritis 3-5% (arthrotomy, may need fusion)
- Fingertip necrosis 2-5% (from fishmouth incision or inadequate drainage)