✋ Trigger Finger A1 Pulley Injection Simulator

Normal Flexor Tendon Gliding Through the A1 Pulley

A healthy flexor tendon glides freely beneath the A1 pulley ring.

• MCP joint: A1 pulley location (palmar plate level)
• ~1 cm: Pulley width (fibro-osseous band)
• ~2.5 cm: Tendon excursion (full finger flexion)
• 2: Synovial sheath layers (visceral + parietal)

The flexor tendon system

Flexor digitorum superficialis and profundus glide through one shared sheath.

The pulley system

Five annular pulleys (A1–A5) hold tendons close against bone.

Frictionless motion

Synovial fluid lets tendon and pulley slide with almost no resistance.

Nodule Formation on the Flexor Tendon

Repetitive gripping causes microtrauma and a fibrocartilaginous nodule.

• Stenosing tenosynovitis: Condition name (a.k.a. trigger finger)
• 50–60 yrs: Peak age (most common onset)
• 6:1: Female:male ratio (higher in women)
• ~10×: Diabetic risk increase (strong association)

Repetitive strain

Gripping tools or handles overloads the A1 pulley zone repeatedly.

Nodule biology

Chronic friction thickens tendon fibers into a fibrocartilage nodule.

Risk factors

Diabetes, rheumatoid arthritis, and repetitive hand labor raise risk.

Catching Mechanism at the Pulley Edge

An enlarged nodule catches on the A1 pulley during extension.

• Pulley edge: Catch trigger point (proximal margin)
• Yes: Palpable nodule (at distal palmar crease)
• Common: Pain on catching (localized to palm)
• Green–Quinnell: Grading system (stages I–IV)

The bottleneck

The nodule is wider than the pulley opening allows to pass.

Painful snap

Forcing the tendon through produces an audible or felt snap.

Grading severity

Green-Quinnell grading tracks catching from mild to fixed.

Locking Episode — Finger Fixed in Flexion

The finger locks in flexion and needs manual force to extend.

• Grade III–IV: Locking grade (Green-Quinnell scale)
• Painful: Passive extension (needs assistance)
• Grade IV: Fixed contracture risk (cannot passively extend)
• ~50%: Conservative failure rate (progresses to injection)

Mechanical lock

The nodule jams against the pulley, blocking tendon glide entirely.

Functional impact

Grip strength and daily hand tasks become difficult and painful.

Next steps

Persistent locking prompts corticosteroid injection or surgical release.

Corticosteroid Injection Restores Smooth Gliding

Injected corticosteroid reduces inflammation and shrinks the nodule.

• ~57–90%: First-injection success (symptom resolution)
• Triamcinolone: Typical agent (or dexamethasone)
• Days–2 wks: Onset of relief (progressive improvement)
• ~86%: Second injection benefit (combined success rate)

Injection technique

Corticosteroid is placed into the flexor tendon sheath at A1.

Anti-inflammatory action

Steroid suppresses inflammatory swelling around the nodule over days.

Restored function

Smaller nodule glides freely, ending catching and locking.