Finger pulleys !

The finger pulleys are fibrous rings along each finger that keep the flexor tendons close to the bones, so the fingers curl strongly.

Official name: Flexor tendon sheaths and pulleys

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What it is

Tunnels of bands along the palm side of each finger that guide the flexor tendons.

What it does

Stop the tendons bowstringing so the fingers curl strongly.

Key facts

Attaches: Fibrous digital sheath: A1 (MCP), A2 (proximal phalanx), A3 (PIP), A4 (middle phalanx), A5 (DIP); cruciform C1–C3 between
Function: Hold the flexor tendons against the bones; A2 and A4 most important (bowstringing if torn); A1 thickens in trigger finger
Tight in: Forceful finger flexion (crimp grip)

Relations

Contents: FDS tendons and FDP tendons (FPL tendon in the thumb) inside their synovial sheath, with the vincula carrying blood to the tendons
Behind: Phalanges and the volar plates of the finger joints
Lateral: Digital nerves and digital arteries along each side of the sheath, held by Grayson (palmar) and Cleland (dorsal) ligaments
In front: Thin palmar skin; the flexion creases lie very close to the sheath, so a small cut or puncture there can enter it

How to find it

Not felt one by one; skin creases are the guide. A1 sits under the distal palmar crease (ring and little fingers) or the proximal palmar crease (index), A2 under the proximal half of the proximal phalanx, A3 at the PIP crease, A4 over the middle of the middle phalanx and A5 at the DIP crease.

Examination

Bowstringing on resisted finger flexion: the tendon lifts away from the proximal phalanx; visible or palpable bowstringing suggests rupture of A2, often with A3 or A4

On imaging

Dynamic ultrasound during resisted flexion measures the distance between the flexor tendon and the bone at the A2 and A4 levels; a widened gap means rupture. MRI in forced flexion shows the same and grades injuries of several pulleys.

Clinical notes

Flexor tendon repair in zone II, where FDS and FDP share the tight sheath, is the classic difficult zone; A2 and A4 are kept, or only partly vented, so the repair can glide
Pulley reconstruction uses a tendon graft looped around the phalanx, often the palmaris longus tendon
Infection of the sheath spreads along its length; from the little finger and thumb it can reach the ulnar and radial bursae

Anatomical variants

The ulnar bursa usually continues into the little finger sheath, while the index, middle and ring finger sheaths end before the palm; the thumb sheath continues as the radial bursa
The two bursae can communicate at the wrist, letting an infection spread between thumb and little finger (horseshoe abscess)

Memory aid

Odd over joints, even over bones: A1, A3 and A5 on the joints; A2 and A4 on the shafts.

Test yourself

Think of the answer, then tap the question to see it.

Which annular finger pulleys lie over joints and which over bone shafts?

Odd-numbered A1, A3 and A5 over the joints (from the volar plates); even A2 and A4 on the proximal and middle phalanx shafts.

Which finger pulleys matter most, and what happens if they are lost?

A2 and A4; without them the tendons bowstring, costing flexion range and grip strength.

Which finger pulley injury is the commonest in rock climbers?

A2 pulley rupture, usually in the ring finger, from the crimp grip.

Which thumb pulley matters most for the flexor pollicis longus?

The oblique pulley, between the A1 and A2 pulleys of the thumb.

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Educational information, not medical advice. For any symptom, see a health professional.

Its names

Official Latin (TA2): vaginae fibrosae digitorum manus TA2 2584
Official Spanish (DeCS): Vainas fibrosas de los dedos de la mano (porciones anulares y cruciformes)
English (TA2): Flexor tendon sheaths and pulleys
Also called: flexor pulleys · A and C pulleys

Sources: Terminologia Anatomica (TA2); Anatomy, Shoulder and Upper Limb, Hand Long Flexor Tendons and Sheaths; Anatomy, Shoulder and Upper Limb, Hand Ulnar Bursa.

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Representative model, for educational purposes only.

Finger pulleys highlighted on the Durgical 3D model