Finger Infections

Finger infections are common soft tissue and deep space infections of the hand, usually arising from minor trauma, bites, nail manipulation or foreign bodies. The hand's compartmentalised anatomy confines pus under pressure, so delayed treatment risks tendon necrosis, stiffness, osteomyelitis and loss of function.

Principal entities

• Paronychia: infection of the nail fold. Acute paronychia follows nail biting, manicure or hangnail, usually Staphylococcus aureus (including MRSA) and streptococci. Chronic paronychia (over 6 weeks) is an irritant and allergic dermatitis with Candida colonisation in people with prolonged wet work (bartenders, cleaners, dishwashers).
• Felon: abscess of the distal pulp. The pulp is divided into 15 to 20 fibrous septa that tether skin to the distal phalanx, so swelling raises pressure, compromises blood supply and can cause osteomyelitis or pulp necrosis. Usually S. aureus after a puncture wound.
• Herpetic whitlow: HSV-1 or HSV-2 infection of the pulp or nail fold, in healthcare and dental workers, children with gingivostomatitis and people with genital herpes. Mistaken for a felon, and incision is harmful.
• Pyogenic flexor tenosynovitis: infection of the flexor tendon sheath, a surgical emergency. Pus within the closed sheath raises pressure and causes tendon ischaemia within 24 to 48 hours.
• Deep palmar space infections: thenar, midpalmar and hypothenar spaces. Parona space (forearm) can link the radial and ulnar bursae via horseshoe abscess.
• Septic arthritis of interphalangeal or metacarpophalangeal joints, and osteomyelitis of the phalanx.
• Bite infections: human bite (fight bite over the metacarpophalangeal joint from a clenched fist striking teeth), polymicrobial with Eikenella corrodens, streptococci, S. aureus and anaerobes. Cat and dog bites carry Pasteurella multocida. Fight bites often involve the extensor tendon and joint capsule.
• Others: erysipeloid (Erysipelothrix, fish and meat handlers), Mycobacterium marinum (fish tank granuloma), sporotrichosis (rose thorn), orf and milker's nodule, Vibrio and Aeromonas in water injuries.
• Risk factors: diabetes, immunosuppression, injection drug use, peripheral vascular disease, nail biting, occupational moisture exposure and delayed presentation.

• Acute paronychia: painful erythema and swelling of the lateral nail fold, with pus collecting under the fold, sometimes extending around the nail (eponychia) or beneath it.
• Chronic paronychia: boggy, thickened nail fold, loss of cuticle, nail ridging and discoloration, with periodic acute flares.
• Felon: throbbing, tense, tender swollen pulp, intense pain worse at night, with loss of normal pulp compressibility.
• Herpetic whitlow: grouped clear vesicles on an erythematous base, burning pain, and sometimes lymphangitis and fever. Pus is absent and the swelling is soft.
• Flexor tenosynovitis (Kanavel signs):
  • Finger held in slight flexion.
  • Fusiform swelling of the whole digit.
  • Tenderness along the flexor tendon sheath.
  • Pain on passive extension, worst at the proximal part of the finger.
• Deep space infections: dorsal hand swelling out of proportion to palmar swelling (lymphatics drain dorsally), loss of the palmar concavity, fever, and pain on finger movement. Thenar space abscess abducts the thumb.
• Septic arthritis: diffuse joint swelling, pain on gentle movement, held in flexion.
• Fight bite: small laceration over the knuckle, which may look trivial, with pain on movement, swelling and later cellulitis.
• Spreading infection: lymphangitic streaking, epitrochlear or axillary lymphadenopathy, systemic features.

Red flags: Kanavel signs, severe pain with passive extension, crepitus, necrosis, systemic sepsis, diabetes with rapid spread, bite wounds over joints, and failure to improve within 24 to 48 hours.

• Diagnosis is clinical. Early imaging and cultures guide management when depth is uncertain.
• Laboratory: CBC, CRP, ESR, glucose or HbA1c, creatinine, blood cultures if febrile. Culture of pus, Gram stain, and fungal or mycobacterial cultures in chronic or atypical infections. HSV PCR from vesicle fluid for suspected whitlow.
• Radiographs: foreign body, gas, fracture (fight bite tooth fragments), osteomyelitis (lucency after 10 to 14 days), joint space change, periosteal reaction.
• Ultrasound: fluid collection within the tendon sheath or pulp, foreign body, and guide for aspiration.
• MRI: suspected osteomyelitis, tenosynovitis, or deep space abscess when diagnosis is unclear.
• Joint aspiration for septic arthritis (white cell count over 50,000/µL, Gram stain, culture, crystals).
• Operative findings confirm diagnosis in tenosynovitis with purulent fluid.
• Tetanus status and immunisation history in all bites and penetrating wounds.

Acute paronychia

• Early cellulitis without abscess: warm soaks 15 minutes three to four times daily, with cefalexin 500 mg four times daily or flucloxacillin 500 mg four times daily for 5 to 7 days. Use trimethoprim-sulfamethoxazole 160/800 mg twice daily or doxycycline 100 mg twice daily if MRSA is likely.
• Abscess: drain after digital block with lidocaine 1% (no adrenaline in classical teaching is no longer required, but use small volumes). Lift the nail fold with a blade or needle along the nail edge, without cutting. Remove the involved nail portion if pus is under the nail. Pack lightly for 24 to 48 hours.

Chronic paronychia

Avoid wet work and irritants, gloves with cotton liners, keep the hands dry, topical corticosteroid (betamethasone valerate 0.1% or mometasone 0.1%) twice daily for 3 to 4 weeks, with topical antifungal (clotrimazole 1% or miconazole 2%) or topical tacrolimus 0.1%. Oral itraconazole 200 mg daily for 1 to 2 weeks is used when this fails. Surgical eponychial marsupialisation or nail fold excision for refractory disease.

Felon

Incise and drain early under digital block. Use a longitudinal volar incision over the point of maximal tenderness, or a lateral incision on the ulnar side of the finger (radial for the thumb and little finger is avoided where contact is needed), dividing the septa. Avoid the fish-mouth incision and keep clear of the flexor sheath. Pack loosely. Antibiotics for 5 to 7 days (cefalexin 500 mg four times daily or MRSA cover). Pulp necrosis or osteomyelitis needs debridement, and amputation of the distal tip if nonviable.

Herpetic whitlow

Do not incise. Protect and dress. Valaciclovir 1 g twice daily for 7 to 10 days, or aciclovir 400 mg three times daily for 7 to 10 days. Occlusive dressing, avoid patient contact until resolved. Suppression (valaciclovir 500 mg daily) for frequent recurrences. Treat secondary bacterial infection.

Flexor tenosynovitis

• Early (within 24 hours) mild cases without prior treatment: IV antibiotics, elevation, splinting and close observation over 12 to 24 hours. If no marked improvement, proceed to drainage.
• Surgical drainage: proximal (A1 pulley) and distal incisions with catheter irrigation of the sheath with saline, or open drainage with a midaxial or Bruner incision. Early active motion postoperatively.
• Antibiotics: ampicillin-sulbactam 3 g IV every 6 hours, or ceftriaxone 2 g daily with clindamycin 600 mg every 8 hours, adding vancomycin 15 to 20 mg/kg every 8 to 12 hours for MRSA risk, narrowed to cultures. Total course 2 to 3 weeks (oral step down when improved).

Deep space abscess

Urgent surgical drainage, debridement, irrigation and IV antibiotics. Hand therapy, elevation and early motion.

Septic arthritis and osteomyelitis

Surgical washout of the joint, bone debridement, and 4 to 6 weeks of antibiotics (2 weeks IV then oral for joint, 6 weeks for osteomyelitis).

Bite wounds

• Irrigation, debridement, no primary closure, and tetanus prophylaxis. Prophylactic amoxicillin-clavulanate 875/125 mg twice daily for 3 to 5 days for fresh moderate to high-risk bites (hand, joint). Established infection or fight bites: ampicillin-sulbactam 3 g IV every 6 hours (or ceftriaxone with metronidazole). Penicillin allergy: doxycycline 100 mg twice daily with metronidazole 500 mg three times daily, or trimethoprim-sulfamethoxazole with clindamycin. Surgical exploration of joints and tendon for fight bites.
• Consider rabies prophylaxis for animal bites and hepatitis B, HIV postexposure prophylaxis for human bites.

Atypical infections

M. marinum: clarithromycin 500 mg twice daily with ethambutol 15 mg/kg, or doxycycline 100 mg twice daily, for 3 to 6 months (at least 1 to 2 months after resolution). Sporotrichosis: itraconazole 200 mg daily for 3 to 6 months. Erysipeloid: penicillin V 500 mg four times daily for 7 days.

Supportive care and rehabilitation

• Elevation, immobilise in the safe position initially, analgesia (paracetamol 1 g, ibuprofen 400 mg), glucose control in diabetes, and early hand therapy to prevent stiffness.
• Prevention: avoid nail biting and aggressive manicure, protect hands during wet work, prompt care of puncture wounds.

Follow-up

Review at 24 to 48 hours after drainage. Persistent stiffness, tendon adhesions, or chronic pain need hand therapy and reconstruction. Review for recurrence and nail deformity.