Infections of the Hand and Upper Extremity
Recognition and timing
Superficial. Paronychia is treated with incision and drainage, sometimes with nail plate removal. A felon is a distal pulp abscess drained through a lateral incision to spare the digital vessels and nerves. Herpetic whitlow is viral, presents with grouped vesicles, and must never be drained.
Deep. Flexor tenosynovitis is diagnosed by Kanavel's four signs: fusiform swelling, finger held in slight flexion, tenderness along the sheath, and pain with passive extension. Treatment is IV antibiotics plus urgent sheath irrigation. Thenar and midpalmar space infections follow penetrating trauma and produce swelling with loss of the normal palmar concavity. Septic arthritis of the MCP or PIP joint requires drainage and antibiotics.
Bites and atypical infections. Human and animal bites are polymicrobial - Eikenella corrodens and Pasteurella multocida respectively. A 'fight bite' over the MCP joint inoculates the joint and requires exploration, not just antibiotics. Mycobacterium marinum follows aquarium exposure and causes indolent granulomatous tenosynovitis.
Necrotizing fasciitis. Pain out of proportion, blistering, crepitus, and systemic toxicity demand immediate wide debridement.
Traps: draining a herpetic whitlow; treating a fight bite as a simple laceration; and relying on oral antibiotics alone for tenosynovitis.
Rule of thumb: four Kanavel signs mean operative sheath washout; vesicles mean no knife.