Pyogenic flexor tenosynovitis (PFT) is an acute bacterial infection within the closed synovial flexor tendon sheath of a digit. It is a surgical emergency: rising pressure in the confined sheath strangles the tendon's blood supply, causing ischaemia, necrosis, adhesions and, in severe cases, amputation.

• Frequency: roughly 2.5-9.4% of all hand infections across published series.
• Demographics: predominantly working-age adults; reflects the dominant penetrating-trauma mechanism. In children it is rarer and Kanavel signs are less reliable.
• Commonest organism: Staphylococcus aureus, with community-acquired MRSA now a major pathogen; organism varies with exposure (see Investigations & Microbiology).
• Prognosis: excellent with treatment inside 24 h and no purulence/ischaemia; amputation rates rise to around 59% once both subcutaneous purulence and digital ischaemia are present (Pang classification).

The flexor tendon sheath is a closed synovial space with two layers: an outer fibro-osseous tunnel (the annular A1-A5 and cruciate C1-C3 pulleys) and an inner synovial bilaminar sleeve (parietal and visceral) that lubricates and nourishes the FDS and FDP tendons. Infection within this confined space behaves like a compartment syndrome of the digit: as bacteria proliferate, intrasheath pressure rises, and once pressure exceeds the perfusion pressure of the vincular vessels the tendon becomes ischaemic, then necrotic. This is why PFT is a true surgical emergency rather than a simple soft-tissue infection.

Routes of inoculation (in descending frequency): penetrating trauma to the volar aspect of the digit (most common), bites, and haematogenous seeding (classically Neisseria gonorrhoeae in a sexually active patient with no penetrating injury). The most frequent organism overall is Staphylococcus aureus; community-acquired MRSA is now a major pathogen, and polymicrobial or atypical organisms follow specific exposures (soil/plant, water, bite).

Extent:

• Index, Middle, Ring: Sheath ends at A1 pulley (distal palmar crease level) proximally, and DIPJ distally.
• Thumb: Sheath continues into Radial Bursa (wrist).
• Little: Sheath continues into Ulnar Bursa (wrist).

Communication:

• The Radial and Ulnar bursae communicate in 50-80% of people via the Space of Parona (deep to flexor tendons in distal forearm).
• Allows spread from Thumb to Little finger (or vice versa) = Horseshoe Abscess.

Blood Supply:

• Vincula (short and long) enter dorsally.
• High pressure in the sheath tamponades these vessels → Necrosis.

PFT is a clinical diagnosis resting on Kanavel's four cardinal signs (see mnemonic above): fusiform "sausage" swelling of the whole digit, the finger held semi-flexed at rest, tenderness along the volar flexor sheath, and pain on passive extension (the most specific sign). Onset is typically 2-5 days after a penetrating volar injury, with progressive throbbing pain, swelling and erythema.

Caveat: the complete quartet is not always present, particularly early or in children (all four in only about a third of paediatric cases). A high index of suspicion and treatment on clinical grounds is essential — do not wait for the full picture.

PFT is fundamentally a clinical diagnosis; investigations support but never delay treatment.

Adjuncts (never delay surgery to obtain them): ultrasound or MRI can confirm fluid within the sheath in equivocal cases; inflammatory markers (WBC, CRP) help track systemic response; plain radiographs exclude radio-opaque foreign body, gas and osteomyelitis. Always send intra-operative fluid/tissue for Gram stain, aerobic and anaerobic culture, and (where exposure suggests) fungal and mycobacterial culture.

Empirical antibiotics (start immediately after taking cultures, then refine on sensitivities):

There is no consensus treatment algorithm for PFT; the following questions are genuinely unresolved and are favourite examiner territory.

• Antibiotics alone vs early surgery. Truly early disease (within roughly 24-48 h, serous Michon I, no purulence) may settle with IV antibiotics, elevation and splinting, with surgery reserved for failure to improve at 24 h. Once purulence or full Kanavel signs are established, antibiotics alone are inadequate. The threshold for non-operative management is not standardised.
• Closed-catheter irrigation vs open drainage. No randomised trial exists. Comparative data (Gutowski) show no significant outcome difference; closed irrigation causes less scarring but risks under-drainage if flow is poor. Stage III or loculated infection mandates open debridement.
• Continuous postoperative irrigation vs single intraoperative washout. Leaving an indwelling irrigation catheter is common practice but unproven; some series report equivalent results with a single thorough intraoperative washout, avoiding catheter-related morbidity.
• Adjuncts. The roles of intrasheath/local antibiotics and adjunctive corticosteroids (to reduce adhesion and stiffness) remain experimental and are not recommended outside study settings.
• Duration and route of antibiotics. Optimal IV duration before oral switch and total course length are not defined; practice ranges widely (often IV for 48-72 h then oral to complete around 10-14 days), guided by clinical response and cultures.

Global epidemiology. PFT accounts for roughly 2.5-9.4% of all hand infections depending on the series; most patients are working-age adults, reflecting the dominant penetrating-trauma mechanism. S. aureus (including community-acquired MRSA in many regions) is the leading pathogen worldwide, with exposure-specific organisms (Pasteurella after bites, atypical mycobacteria/Vibrio after water, gonococcus when no trauma).

Guidance, side by side. There is no single dedicated international society guideline for PFT; management is anchored in hand-surgery literature and general infection principles.

Registry note. No arthroplasty/implant registry applies to PFT; it is a soft-tissue infection, so "registry evidence" is replaced here by published institutional case series (Pang N=75; Gutowski N=47; Brusalis N=32).

High- vs limited-resource practice variation. Where ultrasound/MRI and 24-h theatre access exist, equivocal cases are confirmed on imaging and drained promptly, favouring digit salvage. In limited-resource settings, delayed presentation, restricted theatre access and lack of MRSA-active or atypical-organism cover increase the rate of Michon III disease, tendon necrosis and amputation, mirroring the poor-prognosis groups described by Pang.

1. Kanavel AB. Infections of the Hand. Lea & Febiger; 1912.
2. Pang HN, Teoh LC, Yam AKT, et al. Factors affecting the prognosis of pyogenic flexor tenosynovitis. J Bone Joint Surg Am. 2007;89(8):1742-8. PMID 17671013.
3. Gutowski KA, Ochoa O, Adams WP. Closed-catheter irrigation is as effective as open drainage for treatment of pyogenic flexor tenosynovitis. Ann Plast Surg. 2002;49(4):350-4. PMID 12370638.
4. Gaston RG, Greenberg JA. Use of continuous marcaine irrigation in the management of suppurative flexor tenosynovitis. Tech Hand Up Extrem Surg. 2009;13(4):182-6. PMID 19956043.
5. Brusalis CM, Thibaudeau S, Carrigan RB, et al. Clinical characteristics of pyogenic flexor tenosynovitis in pediatric patients. J Hand Surg Am. 2017;42(5):388.e1-388.e5. PMID 28341068.
6. Chapman T, Ilyas AM. Pyogenic flexor tenosynovitis: evaluation and treatment strategies. J Hand Surg Am. 2019;44(11):981-985. PMID 31272698.