Hand infection and flexor-sheath infection

01OverviewDefinition, clinical context and the essential points that orientate the chapter.

The hand concentrates tendon sheaths, joints, nerves and vessels within small compartments, so a puncture that looks trivial can threaten function within hours. Establish time of injury and deterioration, hand dominance, occupation, antibiotic exposure, tetanus status and contamination by tooth, animal, soil, water or injection. Ask about diabetes, immune suppression, vascular disease, renal impairment and anticoagulation. Human bite history may be concealed; ask how a wound over the knuckle occurred and examine with the fist in the position at injury.

Begin with ABCDE and sepsis observations, then remove rings and constrictive items. Inspect both surfaces, nail folds, web spaces and every wound; mark erythema and photograph according to consent and policy. Observe digital cascade and resting posture. Palpate along each flexor sheath and deep space. Test active isolated tendon movement gently, passive extension, two-point or light-touch sensation, capillary refill, temperature and pulses. Do not repeatedly squeeze a suspected felon, force a sheath or infiltrate local anaesthetic into infected closed tissue before surgical planning.

Pyogenic flexor tenosynovitis is a clinical emergency. The classic features are fusiform swelling, a flexed resting digit, tenderness along the flexor sheath and pain on passive extension. Early cases may lack the complete set, particularly after antibiotics or in immune compromise. The tendon has a vulnerable blood supply and infection raises closed-sheath pressure, so delay causes necrosis, adhesions and rupture. Contact the on-call hand service at suspicion, keep the patient fasting and do not await an outpatient scan.

Initial management is simultaneous. Elevate the hand, use a protective intrinsic-plus or anatomy-specific splint, keep the patient fasting, provide analgesia, update tetanus protection and irrigate gross contamination without high-pressure tissue damage. Start intravenous antibiotics promptly after cultures where safe. A clean-source severe infection needs strong staphylococcal and streptococcal cover; bites need aerobic and anaerobic oral-flora cover; water, farm, injecting and MRSA risks require tailored additions. Obtain microbiology advice for allergy, pregnancy, renal failure, immune compromise or unusual exposure.

Surgical source control is central for a deep-space abscess, pyogenic flexor tenosynovitis, septic joint, necrotic tissue, clenched-fist joint penetration, retained foreign body or progression despite treatment. Exploration identifies the anatomical route, decompresses spaces, irrigates the sheath or joint, excises non-viable tissue and supplies deep samples before lavage. Repeat debridement may be necessary. Superficial paronychia or abscess may need local drainage, but incision placement must protect neurovascular structures and preserve pulp stability.

Recovery protects eradication and movement. Re-examine pain, swelling, passive-extension response, tendon function, sensation and perfusion. Begin protected range when the surgeon permits. Older and immune-compromised patients may lack fever; pregnancy changes antibiotic selection, not source-control urgency, and anticoagulation needs an urgent coordinated plan.

Key points

A hand infection is an anatomical diagnosis: decide whether disease is superficial, abscessed, within a tendon sheath, joint, bone or deep fascial space and whether tissue or perfusion is threatened.
Flexor-sheath infection is suggested by flexed rest posture, fusiform swelling, sheath tenderness and pain on passive extension; absence of one sign does not safely exclude early disease.
First-line assessment is ABCDE plus complete hand examination after removing rings: wounds, spread, posture, active tendon function, passive-stretch pain, sensation, capillary refill and pulses.
Obtain FBC, CRP, renal and liver profile, glucose and lactate according to severity; take blood cultures in sepsis and deep tissue or fluid cultures at surgery, but do not delay antibiotics in an unstable patient.
Plain radiographs are first-line imaging for gas, foreign body, fracture and late bone change; ultrasound may identify fluid, but neither normal imaging nor blood tests excludes early sheath infection.
First-line emergency management is elevation, a safe-position splint, fasting, analgesia, tetanus and bite assessment, immediate hand-surgical review and prompt exposure-appropriate intravenous antibiotics.
Urgent operative irrigation and debridement is the treatment of choice for pyogenic flexor tenosynovitis with progression, deep-space abscess, necrosis, joint penetration or failed very-early supervised treatment; imaging must not postpone theatre.
Human and animal bites require irrigation, exploration when deep penetration is possible and co-amoxiclav unless unsuitable, usually 3 days for prophylaxis or 5 days for treatment, extended after review when tissue destruction or deep structures are involved.
Repeat examination after resuscitation and surgery, track erythema and neurovascular findings, review cultures daily and narrow antibiotics with microbiology while starting protected hand therapy as soon as source control permits.

02AetiologyUnderlying causes, associations and risk factors, with why each one matters.

Skin inoculation

Cuts, punctures, splinters, nail-fold disruption, injections and minor trauma introduce skin flora, particularly Staphylococcus aureus and streptococci, into superficial or closed spaces.

Human and animal bites

Human oral flora, Pasteurella from cats or dogs and mixed anaerobes create polymicrobial risk, while clenched-fist injuries can seed extensor tendon and metacarpophalangeal joint.

Contiguous spread

Paronychia, felon, web-space or cellulitic infection can traverse tendon sheaths, bursae, joints and fascial planes because hand compartments communicate anatomically.

Haematogenous and host factors

Bacteraemia can seed a joint or sheath, while diabetes, immune suppression, vascular disease and injecting drug use increase severity and atypical organisms.

03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.

1
Closed-sheath pressure
Purulent fluid within the flexor sheath raises pressure, impairs tendon nutrition and microvascular perfusion and makes passive extension exquisitely painful.
2
Adhesion and tendon necrosis
Inflammation damages synovial glide, encouraging adhesions, rupture and fixed stiffness even after bacterial clearance when source control is delayed.
3
Deep-space propagation
Infection can extend through thenar, midpalmar, web and Parona spaces or along radial and ulnar bursae, producing extensive disease from a small portal.
4
Joint and bone invasion
Direct bite penetration or contiguous spread seeds septic arthritis and osteomyelitis, requiring longer treatment and often repeated debridement.
5
Systemic inflammatory failure
Toxin and bloodstream spread can cause vasodilation, endothelial leak, tissue hypoperfusion and multiorgan dysfunction, while local swelling threatens nerves and vessels.

04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.

Flexed resting posture

The infected digit rests in flexion because this maximises sheath volume and reduces pressure, while attempted extension markedly worsens pain.

Fusiform digital swelling

Uniform spindle-shaped swelling along the digit differs from a focal nail-fold abscess or isolated joint prominence.

Flexor-sheath tenderness

Tenderness tracks the volar tendon sheath rather than one small skin point and can extend proximally into communicating spaces.

Pain on passive extension

Stretching the pressurised infected sheath produces disproportionate pain and is often the earliest high-yield flexor-tenosynovitis sign.

Clenched-fist bite

A small dorsal metacarpophalangeal wound after punching teeth can conceal extensor-tendon, joint and bone contamination when the hand reopens.

Necrotising progression

Rapid spread, severe disproportionate pain, skin anaesthesia, bullae, dusky necrosis, crepitus or shock requires immediate debridement rather than diagnostic delay.

Deep-space infection

Loss of palmar concavity, dorsal oedema, web-space splaying or pain beyond a superficial lesion suggests thenar, midpalmar or collar-button spread.

Red flags requiring action

The four high-yield flexor-sheath features are a flexed resting digit, fusiform swelling, tenderness along the whole sheath and marked pain on passive extension; incomplete sets still require urgent review.
Hypotension, tachypnoea, altered mental state, mottling, oliguria or raised lactate indicates sepsis and demands immediate resuscitation and antimicrobial treatment.
Pain out of proportion, rapid progression, skin anaesthesia, bullae, dusky change, crepitus or gas on imaging suggests necrotising infection requiring immediate surgical exploration.
A clenched-fist human bite over a metacarpophalangeal joint may penetrate tendon and joint despite a tiny wound and requires urgent specialist washout assessment.
A cool, pale or congested digit, delayed refill, new sensory deficit or tense compartment suggests vascular compromise or compartment syndrome and requires emergency surgery.

05InvestigationsWhat to request, why it matters and how to interpret it.

Investigation order

Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.

01
First-line ABCDE and anatomical hand examinationFirst stepFirst line
Why
Identify sepsis, threatened perfusion and the infected compartment before tests or imaging consume time.
Interpretation and limitations
Flexor-sheath or necrotising features trigger immediate senior surgical action even if observations and early blood tests are normal.
02
First-line blood assessment for significant infectionFirst line
Why
Measure FBC, CRP, renal and liver function, glucose and lactate for severity, host risk and antimicrobial safety.
Interpretation and limitations
Trends support response assessment, but normal inflammatory markers cannot exclude early closed-space infection or justify delayed exploration.
03
Deep tissue, fluid and operative cultures
Why
Provide the most meaningful microbiology for narrowing therapy after source control.
Interpretation and limitations
Send multiple samples before lavage when possible; superficial swabs may reflect colonisation and should not replace deep specimens.
04
First-line plain hand radiographs when penetration or deep disease is possibleFirst line
Why
Detect gas, radiopaque foreign body, fracture, tooth fragment, joint damage and established osteomyelitis.
Interpretation and limitations
Normal radiographs do not exclude early flexor-sheath, joint or necrotising infection and must not postpone surgery.
05
Ultrasound for an immediately available focused question
Why
Locate superficial collection, sheath fluid or radiolucent foreign body when examination is uncertain.
Interpretation and limitations
A negative scan cannot safely clear a convincing clinical sheath infection; use only if it causes no treatment delay.
06
MRI for stable deep or bone mapping
Why
Define osteomyelitis, occult abscess or anatomic spread when the patient is stable and results will alter planned surgery.
Interpretation and limitations
MRI is not the emergency gate before theatre in a deteriorating patient or classic pyogenic flexor tenosynovitis.

06Differential diagnosisRealistic alternatives and the features that help distinguish them.

Crystal or inflammatory arthritis

Gout and inflammatory synovitis can cause acute redness and pain, but aspiration and culture are required because crystals and infection can coexist.

Herpetic whitlow

Grouped vesicles and burning distal pain suggest herpes simplex; incision and drainage is inappropriate unless a bacterial abscess also develops.

Acute calcific periarthritis

Abrupt focal pain and calcification near a joint may mimic infection but lacks a portal, purulence and progressive systemic toxicity.

Traumatic tendon injury

A laceration, altered digital cascade and isolated loss of joint flexion can resemble protective posture but requires direct tendon assessment and repair planning.

Compartment or vascular disorder

Tense swelling, perfusion change and pain on stretch may follow trauma, injection or bleeding and needs emergency decompression even without primary infection.

07ManagementImmediate care, first-line treatment, alternatives and escalation.

01ImmediateResuscitate and protect the handFirst stepA deep hand infection, flexor-sheath infection, necrotising process or sepsis is suspected.

1Use ABCDE, obtain observations and intravenous access, treat shock and check glucose and lactate according to the sepsis pathway.
2Remove rings, elevate, mark spread, apply a safe protective splint, keep the patient fasting and give appropriate analgesia.
3DefinitiveCall senior hand surgery and microbiology immediately and arrange transfer if the receiving site lacks definitive hand cover.
4Take blood and appropriate cultures without delaying antibiotics, then start intravenous exposure-specific treatment promptly.

02Source controlExplore the involved compartmentPyogenic flexor tenosynovitis, deep abscess, necrosis, septic joint, retained foreign body, bite penetration or clinical progression is present.

1Proceed urgently to operative exploration rather than waiting for MRI or a complete set of classic signs.
2Obtain multiple deep samples before irrigation, open and decompress affected sheath, joint or fascial space and excise non-viable tissue.
3Inspect tendon, cartilage, bone, neurovascular structures and connected spaces and plan a second look when viability or clearance is uncertain.
4Document postoperative splint position and start protected hand therapy as soon as infection control and repair permit.

03Bite pathwayTreat the hidden depthA human or animal bite, clenched-fist wound or saliva-contaminated puncture involves the hand.

1Irrigate, assess tendon and joint through full relevant movement, update tetanus and radiograph for tooth, fracture or joint injury.
2Refer clenched-fist, deep, infected, neurovascular or structurally penetrating wounds urgently to hand surgery.
3First lineGive co-amoxiclav first-line when appropriate for 3 days prophylaxis or usually 5 days treatment, extending after review for deep destruction.
4Use microbiology-guided alternatives for penicillin allergy, pregnancy, renal impairment, water exposure or resistant-organism risk.

Key medicines and prescribing safety3 treatments · regimens, roles and cautions

Provides immediate high-dose antistaphylococcal treatment alongside, never instead of, drainage and debridement of closed-space infection.

Intravenous flucloxacillin for severe clean-source infection

For a severe clean-source staphylococcal or streptococcal hand infection, a common adult hospital regimen is flucloxacillin 2 g intravenously every 6 hours after cultures where possible; follow local microbiology advice and narrow to results.

Use a different exposure-specific regimen for bites, water, injecting or MRSA risk; check immediate penicillin allergy, liver history, renal impairment, sodium load and interactions, and obtain specialist pregnancy advice.

Covers common aerobic and anaerobic organisms in human, cat and dog bites while definitive wound assessment and source control proceed.

Co-amoxiclav for adult hand bites

Use co-amoxiclav 250/125 mg or 500/125 mg orally three times daily for 3 days as prophylaxis or 5 days for treatment; extend to 7 days after review for significant tissue destruction or penetration of bone, joint, tendon or vascular structures. Use 1.2 g intravenously three times daily when oral treatment is unsuitable or severity requires admission.

Avoid in serious penicillin allergy and previous co-amoxiclav jaundice or hepatic dysfunction, adjust for renal impairment, check anticoagulant interaction and pregnancy, and seek microbiology alternatives rather than using macrolide monotherapy for a deep bite.

Provides analgesia for examination, splinting and perioperative care without relying on NSAIDs in sepsis, renal injury or impending surgery.

Paracetamol with titrated opioid rescue

Give paracetamol 1 g orally or intravenously every 6 hours, maximum 4 g in 24 hours, reducing the maximum for low weight, frailty, malnutrition or liver risk; add small titrated intravenous opioid doses under monitored acute-care protocols for severe pain.

Check duplicate paracetamol products, respiratory depression, sedation, renal and hepatic function and pregnancy; analgesia must not obscure repeated neurovascular and passive-stretch examination.

08ComplicationsImportant consequences, why they occur and why they matter clinically.

Tendon rupture and adhesions

Ischaemia and enzymatic destruction can rupture flexor tendon, while healed synovitis forms adhesions that permanently reduce differential glide.

Stiffness and amputation

Capsular damage, scar, necrosis and delayed source control can leave a useless painful digit or require partial or complete amputation.

Septic arthritis and osteomyelitis

Joint or bone involvement prolongs antibiotics, often requires repeat surgery and can destroy cartilage or structural stability.

Sepsis and metastatic infection

Bacteraemia can cause shock and seed heart valves or distant sites, particularly with Staphylococcus aureus, immune compromise or delayed treatment.

09Monitoring and follow-upTreatment response, safety checks and longer-term review.

Repeat ABCDE observations, perfusion, mental state, urine output and lactate according to sepsis severity until physiology stabilises.
Re-examine digit posture, fusiform swelling, sheath tenderness, passive-extension pain, active tendon movement, sensation and capillary refill serially.
Review blood, operative and bite cultures daily and narrow antibiotics with microbiology, including clearance cultures for Staphylococcus aureus bacteraemia.
Begin and progress protected hand therapy as instructed, monitoring tendon glide, joint range, oedema, scar and emerging adhesions.
After discharge, provide explicit same-day return criteria for fever, spreading redness, recurrent passive-extension pain, drainage, numbness or reduced perfusion.

10Special situationsVariants, exceptions and circumstances that change the usual approach.

One missing sign does not reassure

Early flexor-sheath infection, partial antibiotic treatment and immune compromise can produce fewer than four classic findings while tendon nutrition is already threatened.

The wound position changes depth

A clenched-fist bite retracts away from the injured joint when the hand opens, hiding the tract and making a tiny dorsal wound deceptively benign.

Normal tests do not clear a sheath

Early blood markers, radiographs and ultrasound can be normal; anatomy, passive-extension pain and trajectory determine emergency action.

Antibiotics cannot drain pressure

Closed-space pus compromises tendon and vessels, so antimicrobial treatment without timely decompression can sterilise blood while function continues to die.

Motion follows source control

Early protected rehabilitation limits adhesions, but the surgeon must define timing around tendon viability, repair, wound and residual infection.

11Common pitfallsFrequent interpretation and management errors.

01
Waiting for all four flexor-sheath signs, raised CRP or positive ultrasound before contacting hand surgery.
02
Treating a clenched-fist bite as superficial cellulitis without examining tendon and joint depth through movement.
03
Allowing MRI to delay exploration of a clinically convincing deep or necrotising infection.
04
Using oral antibiotics alone for a pressurised sheath, deep abscess, septic joint or necrotic tissue.
05
Taking only a superficial swab after antibiotics instead of obtaining deep samples before operative lavage.
06
Leaving rings or a tight splint on a swelling hand and failing to repeat neurovascular examination.