Approach to the Flexor Sheath and A1 Pulley (Trigger Finger Release)

What it exposes. This approach exposes the fibro-osseous canal of the flexor tendons at the metacarpophalangeal (MCP) joint so that the thickened A1 pulley can be divided completely while the A2 pulley and the flexor tendons are preserved. It is the index operation for trigger finger and trigger thumb that have failed non-operative management. The problem it solves. Trigger finger is a stenosing tenosynovitis in which the A1 pulley thickens and narrows at the mouth of the fibro-osseous canal, while the flexor tendons develop a fusiform swelling or nodule just distal to it. The swollen tendon catches beneath the tight pulley on flexion and then snaps, locks, or cannot actively re-extend. The definitive mechanical solution is surgical enlargement of the canal by complete division of the A1 pulley; the tendon then glides freely and the catching stops. The approach is therefore an approach to the A1 pulley at the MCP joint. Primary indications:

• Trigger finger (trigger digit) that has failed an adequate trial of non-operative management (splintage plus one or more corticosteroid injections)
• Trigger thumb in adults (acquired) that is recurrent or locked and has not responded to injection
• Paediatric trigger thumb (Notta node) that has not resolved spontaneously, typically around four years of age
• Symptomatic locking interfering with function, pain at the A1 pulley, or a fixed flexion deformity Relative indications (same exposure):
• Flexor tenosynovectomy for rheumatoid synovitis localised to the A1 region
• Excision of a symptomatic tendon nodule or a partial flexor digitorum superficialis slip
• Open drainage of localised flexor sheath sepsis in selected cases (a more extensile, multi-incision approach is used for diffuse pyogenic flexor tenosynovitis) Contraindications:
• Active infection of the overlying skin (delay until settled, or use a different incision)
• Mild, intermittent triggering that has not had a fair trial of non-operative care
• Uncontrolled systemic disease (for example poorly controlled diabetes) where the higher recurrence rate should first be discussed with the patient
• A fixed metacarpophalangeal or proximal interphalangeal contracture that will not correct with pulley release alone Alternative management:
• Corticosteroid injection into the sheath — first-line for most adult trigger fingers
• Splintage and activity modification — mild early disease
• Percutaneous A1 pulley release — needle or blade technique, avoiding an open wound but without direct visualisation of the nerve
• Open release — the gold standard described here, with direct visualisation and nerve protection

Position and Landmarks Position: supine on a hand table. Confirm the correct patient, side and digit (mark the digit with an arrow at the MCP joint), document pre-operative active flexion and any locking, and apply and test an upper-arm tourniquet (preferred over a forearm tourniquet for a bloodless, comfortable field). The arm is abducted onto a hand table; the limb is exsanguinated with an Esmarch bandage and the tourniquet inflated. The hand lies supine or pronated so the volar MCP joint crease is uppermost and accessible. Loupe magnification is used throughout, particularly in the thumb where the digital nerves are most at risk.

Surface landmarks (fingers):

• The metacarpophalangeal joint — the joint around which the A1 pulley lies
• The distal palmar crease — overlies the MCP joints and marks the proximal part of the A1 pulley
• The proximal digital flexion crease — lies just distal to the MCP joint
• The flexor tendon mass — palpable in the palm; asking the patient to actively flex the digit localises the tendon and the MCP joint precisely Surface landmarks (thumb):
• The thumb metacarpophalangeal flexion crease — the transverse crease over the thumb MCP joint, where the A1 pulley lies
• The thenar eminence and the radial border of the thumb
• The flexor pollicis longus tendon — localised by active thumb interphalangeal flexion Incision planning:
• Fingers: a short transverse incision about one and a half centimetres long, centred over the MCP joint, lying in or just proximal to the distal palmar crease. An oblique incision along the crease is an alternative.
• Thumb: a short transverse incision in the thumb MCP flexion crease, centred on the flexor pollicis longus tendon.
• Extensile option: a longitudinal or Bruner-type incision if tenosynovectomy or more distal work is planned.
• All incisions are centred strictly on the tendon axis so dissection stays in the midline, away from the neurovascular bundles.

The Internervous Plane There is no true internervous plane. This is an approach to a fibro-osseous tendon sheath rather than a dissection between two muscles. The flexor digitorum superficialis and profundus are both supplied by the median nerve (via the anterior interosseous branch), and the sheath itself is relatively avascular connective tissue overlying the volar plate of the MCP joint. The safety of the approach therefore depends not on an internervous interval but on staying strictly in the midline, on the tendon, so that the digital neurovascular bundles on either side are not encountered.

Work straight down onto the tendon sheath at the MCP joint, staying strictly in the midline to protect the digital neurovascular bundles, define the limits of the A1 pulley, and divide it completely while preserving A2. ### The Flexor Tendon Sheath Pulley System The flexor tendons to each digit are constrained within a fibro-osseous canal by a series of annular and cruciform pulleys that prevent the tendons bowstringing away from the digit during flexion. From proximal to distal the annular pulleys are A1, A2, A3, A4 and A5, interspersed with the cruciform pulleys C1, C2 and C3.

The pathology. The A1 pulley thickens and its entrance narrows, while the flexor digitorum superficialis and profundus tendons develop a constriction ring and a fusiform swelling just distal to the pulley. The swollen segment of tendon is drawn proximally under the tight A1 mouth during flexion but cannot return smoothly, producing catching, snapping and finally locking in flexion. Division of the A1 pulley enlarges the entrance of the canal and abolishes the mechanical obstruction.

Structures at risk, by layer

The four structures you must protect

Extensile Options Proximal extension. The transverse release incision can be converted to a Bruner-type zig-zag or longitudinal incision extending proximally into the palm. This is used when a flexor tenosynovectomy for rheumatoid disease is required, or when releasing a long segment of thickened sheath. Extension across the palm toward the carpal tunnel must respect the superficial palmar arch and the common digital nerves. Distal extension. A Bruner incision can be continued distally onto the finger to address a proximal interphalangeal contracture, to inspect A2, or to deal with a distal tendon nodule — useful in complex or revision cases where pathology extends beyond A1. Combined approach for rheumatoid disease. In rheumatoid flexor tenosynovitis the disease is often extensive, and a limited A1 release is inadequate. A longitudinal extensile incision allows a thorough synovectomy around both flexor tendons from the palm onto the finger, and may need to be combined with a carpal tunnel release if median nerve compression coexists. ### Closure - Haemostasis: release the tourniquet before closure, achieve meticulous haemostasis with bipolar diathermy, and confirm capillary refill and digital perfusion.

• Sheath and pulley: the divided A1 pulley and the sheath are left open. No deep closure is performed — leaving the sheath open is deliberate, as it enlarges the entrance to the canal, which is the whole point of the operation.
• Skin: close the skin only, with simple interrupted non-absorbable sutures, or with an absorbable subcuticular suture in children to avoid later suture removal.
• Dressing: a non-adherent dressing and a light supportive bandage that permits early active mobilisation of all digits. ### Complications Intra-operative and early complications

Late complications

Post-operative Care - Immediate post-operative: neurovascular check of the digit (capillary refill and digital sensation), elevation of the hand, and simple oral analgesia.

• Rehabilitation: early active mobilisation of all digits, usually from the first post-operative day; wound check and dressing change at one to two weeks; suture removal at ten to fourteen days (sooner if an absorbable subcuticular suture was used); return to light activities within days and to heavier or manual tasks over a few weeks.
• Follow-up: one review at two to three weeks is generally sufficient for an uncomplicated release; diabetic, rheumatoid and revision cases may need closer hand-therapy input.

• Flexor tenosynovectomy for rheumatoid or other inflammatory synovitis
• Excision of a symptomatic tendon nodule or a partial flexor digitorum superficialis slip
• Removal of a flexor sheath ganglion arising at the A1 level
• Localised drainage of early, localised flexor sheath infection (diffuse pyogenic tenosynovitis requires the standard extensile approach with mid-lateral incisions)

At a Glance The approach to the flexor sheath and A1 pulley exposes the fibro-osseous canal of the flexor tendons at the metacarpophalangeal joint so that the thickened A1 pulley can be divided completely. It is the index operation for trigger finger and trigger thumb that have failed non-operative management. The patient is positioned supine on a hand table with an upper-arm tourniquet and loupe magnification. There is no true internervous plane — this is an approach to a tendon sheath — so safety depends on staying strictly in the midline on the tendon, because the radial and ulnar digital neurovascular bundles lie only a few millimetres to either side. In the thumb the radial digital nerve crosses the field obliquely and superficially and is the classic structure injured, demanding explicit identification and protection. The A1 pulley, which overlies the MCP joint and is roughly a centimetre long, is divided completely from its proximal to its distal end while A2 is preserved to prevent bowstringing. The sheath is left open and only the skin is closed, allowing early active motion.

Guidelines, Registries and Global Practice Trigger finger and trigger thumb are managed worldwide, and the principles are convergent across the examination systems. A trial of non-operative care — corticosteroid injection and splintage — precedes surgery in the great majority of adults, with open A1 pulley release the standard definitive operation when that fails. Side-by-side principles (where guidance converges): | Body | Position on trigger finger |

|------|----------------------------| | American Academy of Orthopaedic Surgeons / ASSH | Corticosteroid injection is first-line; open or percutaneous A1 release for failure, locking, or recurrence; percutaneous release generally avoided in the thumb because the digital nerve is not visualised | | British Society for Surgery of the Hand / BOA | Splintage and injection first; surgical release for refractory or locked digits; diabetes counselled about higher recurrence | | FESSH (European) | Echoes staged non-operative to operative care; emphasises protection of the digital nerves and complete A1 division at surgery | | EFORT / AO Foundation | Single-stage open release is safe and effective; percutaneous release acceptable in experienced non-thumb cases | Population evidence:

• Trigger digit has a lifetime risk of a few percent in the general population, with a female predominance and a peak in middle age.
• Diabetes markedly increases incidence (up to around one in ten diabetics), with multiple-digit involvement and higher recurrence after both injection and surgery. Global practice variation: Open A1 release is performed with comparable technique worldwide; percutaneous needle release is used more widely in some regions for finger trigger because it avoids an open wound, but open release remains standard where direct nerve visualisation is required, particularly in the thumb. Consent (globally applicable): discuss recurrence (higher in diabetes), digital nerve injury (especially the thumb radial digital nerve), infection, a tender scar, temporary stiffness, and the rare risk of bowstringing if A2 is injured.