Hand Infections
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Direct answer
Pus in a closed fascial compartment of the hand destroys tendon and cartilage within hours, which is why hand infections are surgical emergencies rather than prescriptions. Acute suppurative flexor tenosynovitis announces itself through Kanavel's four cardinal signs — fusiform swelling of the whole digit, a semi-flexed resting posture, tenderness along the entire flexor sheath, and excruciating pain on passive extension of the finger — and needs urgent sheath irrigation. Felons are pulp-space infections requiring lateral decompression; paronychias are drained by elevating the eponychial fold; and the deep thenar, hypothenar and midpalmar spaces are opened along defined incisions. Two exceptions refuse the knife: herpetic whitlow (vesicles, history of contact, self-limiting) and the collar-stud abscess of tuberculous dactylitis, a chronic Indian favourite.
What you must remember
- Kanavel's signs: fusiform swelling, flexed posture, sheath tenderness along the whole digit, and pain on passive extension — all four, or the diagnosis is in doubt.
- Flexor sheath irrigation: two-incision open or closed catheter technique (incision and a small catheter for continuous irrigation) within 24-48 hours preserves the tendon; delay leaves a stiff, necrotic digit.
- Paronychia versus felon: paronychia is the eponychial fold (elevate the cuticle, no incision into pulp); a felon is the closed septate pulp space (deep lateral incision, break the septa, avoid the fish-mouth and volar midline scars).
- Deep spaces: thenar (thumb flexion painful, dorsal swelling), midpalmar (transverse palmar crease tenderness, digits held flexed), hypothenar, and Parona's space — where thumb and little-finger sheaths communicate to create the horseshoe abscess.
- Herpetic whitlow: vesicular, painful, recurrent, in dentists, nurses and thumb-sucking children; no incision — iatrogenic bacterial superinfection is the danger.
- Bite wounds: human bites seed Eikenella corrodens, dog and cat bites Pasteurella multocida; explore, irrigate, delay closure, and cover anaerobes.
- Chronic Indian pattern: tuberculous dactylitis with a collar-stub abscess — a subperiosteal focus bursting into the soft tissues — plus mycetoma and sporotrichosis in the differential of chronic hand swelling.
- Support package: splint in the safe position, elevation, antibiotics against staphylococci and streptococci, glycaemic control, and early physiotherapy — the stiffness that follows rescue is the real morbidity.
Working through a swollen finger at 2 a.m.
A 34-year-old labourer presents with a swollen right middle finger of two days, held slightly flexed, exquisite pain when you extend it, and tenderness you can trace from the distal palm to the fingertip. Three Kanavel signs plus the fourth on extension confirm flexor tenosynovitis, most often after a puncture wound. The clock starts now: within 24-48 hours, the sheath is drained through a midlateral incision at the base of the digit and a second incision distally in the palm, either leaving the sheath open or threading a small catheter for irrigation with saline; antibiotics cover Staphylococcus aureus and streptococci, and the hand is splinted and elevated. Presenting on day five with a tense, dusky digit, the same patient may already have tendon necrosis and is heading for stiffness or amputation — the gap between two stories is purely time.
Contrast the neighbour in the next cubicle: a dentist with a painful, vesicular, coalescing thumb of four days and no fluctuance. Incising her herpetic whitlow would add bacterial infection to a self-limiting herpes simplex infection; treatment is analgesia, dry dressings and wait. A third patient, a diabetic with a trivial scrape, has spreading erythema with crepitus and greydish discharge — necrotising infection of the hand, a surgical emergency of a different order requiring radical debridement and critical care. And the young man with a six-week, painless, boggy swelling over the proximal phalanx and sinus formation has the collar-stud abscess of tuberculosis: drainage of the superficial pocket alone guarantees recurrence unless the deep subperiosteal focus is tracked and antitubercular therapy started.
Where students slip
The routine error is calling every swollen finger a paronychia and incising the pulp for a sheath infection — the Kanavel quartet, not the location of maximum tenderness, separates the two. The second slip is the felon incision: midline volar and fish-mouth incisions are condemned because they scar the tactile surface and destabilise the pulp; the correct incision is lateral, deep, parallel to the digital neurovascular bundle's safe side. Third, candidates forget that a horseshoe abscess explains simultaneous thumb and little-finger signs through the synovial connection at Parona's space. Finally, in chronic disease the reflex diagnosis of "chronic osteomyelitis" without biopsy loses Indian marks: tuberculosis and mycetoma are the two entities a biopsy and culture must separate before months of wrong therapy.
Frequently asked questions
What are Kanavel's cardinal signs of flexor tenosynovitis?
Fusiform swelling of the digit, semi-flexed resting posture, tenderness along the entire flexor sheath, and severe pain on passive extension of the finger.
How is an acute felon drained?
Through a lateral incision deep enough to break the fibrous septa of the pulp, avoiding midline volar and fish-mouth incisions that sacrifice the tactile pulp.
Which hand infection must not be incised?
Herpetic whitlow — vesicular, recurrent, self-limiting — where incision invites bacterial superinfection of a viral lesion.
What is a collar-stub abscess?
The chronic dual compartment of tuberculous dactylitis, where a subperiosteal focus ruptures to create a superficial abscess connected by a narrow neck; both tracks must be laid open.
Why do thumb and little finger swell together in some infections?
Their flexor sheaths communicate through Parona's space in the forearm, producing a horseshoe abscess requiring drainage of both sheaths.