Upper limb
Fibrous flexor sheaths and digital pulley system
Vaginae fibrosae digitorum manus (pulley-systeem)
- Origin
- Dense fibrous tunnels attached to the lateral margins of the phalanges and volar plates of all digits
- Insertion
- Organized into annular (A1–A5) and cruciform (C1–C3) pulleys (thumb: A1, Oblique, A2 pulleys)
- Function
- Prevents tendon bowstringing during flexion, converting linear muscle contraction into efficient joint rotation
- Innervation
- Digital nerve sensory and proprioceptive endings
- Movement & chain
- Maintains close approximation of flexor tendons to the phalangeal shaft throughout full flexion
- Palpation
- Palpable along the palmar phalangeal aspects; A2 and A4 pulleys palpable over proximal and middle phalanges
- Clinical
- Pulley ruptures in rock climbers (especially A2 and A4 pulleys from intense crimp grip loading); results in bowstringing and loss of finger flexion excursion
- Segmental innervation
- C7–T1 roots
- In clinical practice
- Protective H-taping in climbers, thermoplastic ring splints, and micro-reconstruction of A2/A4 pulleys with tendon grafts
- Region in the model
- Upper limb