Pulley System of the Hand

The main components of the flexor pulley system include:

• Long flexor tendons and their associated synovial sheaths.
• Annular pulleys: 5 associated with each finger, 2 associated with the thumb.
• Cruciate pulleys: 3 associated with each finger.
• Oblique pulley: 1 associated with the thumb.

The primary function of the flexor pulley system is to hold the flexor tendons against the phalanges, preventing them from pulling away and bowstringing. This allows for efficient flexion of the individual digits by the long flexor muscles.

There are 5 annular pulleys associated with each finger and 2 annular pulleys associated with the thumb in the flexor pulley system.

The types of pulleys found in the flexor pulley system include:

• Annular pulleys: 5 for each finger, 2 for the thumb.
• Cruciate pulleys: 3 for each finger.
• Oblique pulley: 1 for the thumb.

The long flexor tendons of the fingers arise from the flexor digitorum superficialis (FDS) and flexor digitorum profundus (FDP) forearm muscles.

The long flexor tendons enter the hand via the carpal tunnel, enclosed in a common synovial sheath.

The fibrous flexor sheaths are strong ligamentous tunnels that house the long flexor tendons, allowing them to glide smoothly as the fingers flex.

At the base of the proximal phalanx, the FDS tendon splits into two, with the FDP tendon passing between them.

The split FDS tendons attach to the base of the middle phalanx, while the FDP tendon attaches to the base of the distal phalanx.

The annular pulleys are five thickened areas in the fibrous flexor sheaths that reinforce the structure with circular fibres. They are crucial in preventing bowstringing of the flexor tendons. The specific annular pulleys are:

1. A1 - overlies the metacarpophalangeal joint
2. A2 - overlies the proximal aspect of the proximal phalanx
3. A3 - overlies the proximal interphalangeal joint
4. A4 - overlies the mid-portion of the middle phalanx
5. A5 - overlies the distal interphalangeal joint

The cruciate pulleys are areas reinforced by cruciform fibres located between the annular pulleys:

1. C1 - located between A2 and A3
2. C2 - located between A3 and A4
3. C3 - located between A4 and A5

The long flexor tendon of the thumb arises from the flexor pollicis longus (FPL). It passes into the hand through the carpal tunnel and enters the fibrous flexor sheath of the thumb, attaching to the base of the distal phalanx.

The fibrous flexor sheath of the thumb is reinforced by three pulleys:

1. A1 - overlies the metacarpophalangeal joint
2. Oblique - overlies the proximal half of the proximal phalanx
3. A2 - overlies the distal half of the proximal phalanx

Management options for trigger finger include:

1. Splinting of the affected digit
2. Steroid injections to reduce inflammation
3. Surgical release of the tendon if conservative treatments fail

The A1 pulley is the most frequently involved ligament in trigger finger.

Trigger finger is a condition where a finger becomes locked in a bent position due to a constriction of the flexor tendon within the fibrous digital sheath. This constriction prevents smooth gliding of the tendon, leading to the finger being 'stuck' in flexion, which can cause pain and difficulty in extending the finger.