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.