Flexor Tenosynovitis

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.

Who gets it. PFT accounts for roughly 2.5-9.4% of all hand infections across published series. Most patients are working-age adults, reflecting the dominant penetrating-trauma mechanism. In children it is rarer and Kanavel's signs are less reliable.

Outcome. The prognosis is excellent with treatment inside 24 h and no purulence or ischaemia. Once both subcutaneous purulence and digital ischaemia are present, amputation rates rise to around 59% (Pang classification).

Where the sheaths end. The proximal extent differs by digit.

• Index, middle and ring - the sheath typically ends proximally at the A1 pulley, at the level of the distal palmar crease, and distally at the DIPJ. It does not extend into the wrist.
• Thumb - the sheath continues into the radial bursa at the wrist.
• Little finger - the sheath continues into the ulnar bursa at the wrist.

The horseshoe abscess. The radial and ulnar bursae communicate through the Space of Parona, a deep forearm space lying deep to the flexor tendons in the distal forearm, in a substantial minority of people. Cadaveric series disagree widely on the proportion, so treat communication as common enough to expect rather than as a fixed percentage. This is the anatomical basis of the horseshoe abscess: infection can spread from the thumb to the little finger, or the reverse.

A closed synovial space. The flexor tendon sheath has two layers. The outer fibro-osseous tunnel is formed by the annular (A1-A5) and cruciate (C1-C3) pulleys; the inner synovial sleeve is bilaminar, parietal and visceral, and lubricates and nourishes the FDS and FDP tendons.

A compartment syndrome of the digit. As bacteria proliferate, the pressure inside the sheath rises. The tendon's blood supply comes through the vincula, short and long, which enter dorsally; once sheath pressure exceeds their perfusion pressure these vessels are tamponaded, and the tendon becomes ischaemic, then necrotic. This is why PFT is a true surgical emergency rather than a simple soft-tissue infection.

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Routes of inoculation. In descending frequency, these are penetrating trauma to the volar aspect of the digit (the most common), bites, and haematogenous seeding. Haematogenous infection is classically Neisseria gonorrhoeae in a sexually active patient with no penetrating injury.

Organisms. The most frequent organism overall is Staphylococcus aureus, and community-acquired MRSA is now a major pathogen. Polymicrobial or atypical organisms follow specific exposures (soil or plant, water, bite); they are matched to empirical cover under Investigations and Microbiology.

PFT is fundamentally a clinical diagnosis. Investigations support it; never delay treatment or surgery to obtain them.

Adjuncts. Ultrasound or MRI can confirm fluid within the sheath in equivocal cases. Inflammatory markers (WBC, CRP) help track the systemic response, and plain radiographs exclude a radio-opaque foreign body, gas and osteomyelitis.

Cultures. Always send intra-operative fluid and tissue for Gram stain and aerobic and anaerobic culture, and, where the exposure suggests it, for fungal and mycobacterial culture.

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Empirical antibiotics. Start immediately after taking cultures, then refine on sensitivities. The exposure history predicts the atypical organism. The paediatric evidence card below goes further than the first row of the table: with MRSA the commonest isolate in Brusalis's series, it treats MRSA-active empirical cover as mandatory.

Michon (severity). The Michon classification stages severity at operation and guides treatment, which is set out by stage under Management.

• Stage I - sheath distended with serous exudate (early)
• Stage II - purulent fluid, granulations intact
• Stage III - septic necrosis of tendon, sheath and pulleys

Pang's poor-prognosis factors. Pang et al. (JBJS Am 2007) identified five factors predicting a poor outcome, meaning amputation or stiffness:

• Age over 43 years
• Diabetes (or peripheral vascular disease or renal failure)
• Subcutaneous purulence
• Ischaemia of the digit
• Polymicrobial infection

Pang's clinical groups. Purulence and ischaemia then stratify prognosis into three groups. The groups were derived from the same 75 patients and have not been prospectively validated, a limitation set out in the evidence card below.

History. Onset is typically 2-5 days after a penetrating volar injury, with progressive throbbing pain, swelling and erythema.

Kanavel's four cardinal signs. PFT is a clinical diagnosis, and it rests on these:

• Fusiform swelling of the whole digit, the "sausage digit" - the most sensitive and earliest sign
• Flexed posture - the finger is held semi-flexed at rest to reduce sheath pressure
• Tenderness along the volar flexor sheath, on percussion
• Pain on passive extension - the most specific sign, because it stretches the inflamed sheath directly

When the signs are incomplete. The complete quartet is not always present, particularly early or in children, where all four are found in only about a third of cases. A high index of suspicion and treatment on clinical grounds is essential; do not wait for the full picture.

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Other hand infections. The shape of the swelling, the site of tenderness and the response to motion separate PFT from cellulitis and a felon.

Mimics you must not incise. Just as important, for the exam and for patient safety, are the mimics in which incision and drainage is the wrong answer. Taking one of these to theatre causes harm.

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The decision to operate is clinical. Established Kanavel signs or any purulence mandate theatre, and once they are present antibiotics alone are inadequate. Truly early disease, within roughly 24-48 h, serous (Michon I) and without purulence, may settle with IV antibiotics, elevation and splinting, but only with very close review. The threshold for non-operative management is not standardised.

Closed-catheter irrigation is first line for established disease:

• Proximal incision: mid-lateral or zig-zag over the A1 pulley in the palm
• Distal incision: mid-lateral over the distal phalanx, or at the DIPJ crease
• Insert a fine catheter (16G cannula or paediatric feeding tube) proximally and irrigate copiously, proximal to distal, with saline (500 mL or more)

Leaving the catheter in for continued postoperative irrigation is optional and controversial (see Controversies). Closed irrigation causes less scarring than open drainage but risks under-drainage if flow is poor.

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Open washout. Convert to open drainage if minimal fluid flows or Stage III is suspected; Stage III or loculated infection mandates open debridement. Pang's data concentrate the risk in the finger with subcutaneous purulence or ischaemia, which needs aggressive open debridement rather than closed irrigation alone. Use a full mid-lateral incision or Bruner (zig-zag) exposure, debride necrotic synovium and any non-viable tendon, and leave the wound open for a planned re-look at 48 h.

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After surgery.

• Splint in a safe (intrinsic-plus) position and elevate the limb
• Continue IV antibiotics, de-escalating to oral on clinical response and cultures. The optimal IV duration and total course are not defined and practice ranges widely, often IV for 48-72 h then oral to complete around 10-14 days in total
• Hand-therapy referral and close wound review; repeat the washout if not improving

Early active motion. Start early active range of motion once the drains are removed, at 24-48 h, to prevent adhesions and stiffness. It is the single biggest determinant of final function.

Everything above describes acute pyogenic flexor tenosynovitis. A separate, easily missed entity is chronic granulomatous flexor tenosynovitis, caused by slow-growing organisms. These are mycobacteria, both atypical species (classically Mycobacterium marinum after water or fish exposure, also M. kansasii) and M. tuberculosis, and fungi (Sporothrix schenckii, and regionally Histoplasma and Coccidioides). The same exposure organisms flagged in the microbiology table behave completely differently in the sheath.

Diagnosis. It mimics a ganglion, a sprain or rheumatoid tenosynovitis, and so demands a high index of suspicion. Send tissue for histology and for prolonged culture; MRI shows the tenosynovial thickening and the rice bodies.

• Histology: granulomatous synovitis, caseating in TB and non-caseating with atypical mycobacteria
• Mycobacterial culture is held for weeks, and M. marinum needs lower incubation temperatures (around 30-32°C); fungal cultures are held similarly long
• PCR speeds identification

Management is not emergency irrigation. The cornerstone is open tenosynovectomy, debulking the granulomatous synovium, combined with prolonged organism-specific therapy. That means multidrug antimycobacterial treatment (for example clarithromycin with rifampicin/ethambutol for M. marinum, or standard antituberculous therapy for TB tenosynovitis, typically months) or appropriate antifungals. Surgery debulks; the medical therapy cures, and stopping early invites recurrence. The detailed antimicrobial regimens and systemic atypical-mycobacterial disease are developed in the dedicated atypical-mycobacterial-infection topic.

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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.

There is no consensus treatment algorithm for PFT. Beyond the undefined thresholds for non-operative treatment and antibiotic duration covered under Management, these questions are genuinely unresolved:

• Closed-catheter irrigation vs open drainage. No randomised trial exists. Gutowski's comparison showed no significant difference, but in 47 retrospective patients that falls short of showing the two are equivalent.
• Continuous postoperative irrigation vs a 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 or local antibiotics and adjunctive corticosteroids (to reduce adhesion and stiffness) remain experimental, and they are not recommended outside study settings.

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.