The Hip
Home » Muscles Tendons » Flexor Tendon Pulleys and Sheaths

Flexor Tendon Pulleys and Sheaths



- See:
      - Pulley Reconstruction

- Flexor Tendon Pulleys:
    - A1 pulley:
           - arises from volar plate of MP joint, beginning 5 mm proximal to the MP joint and ending at the base of the proximal phalanx;
           - average length of A1 pulley is 1 cm;
           - proximal edge of the 1st annular pulley lies about 2 cm from the proximal finger crease;
           - distal edge of A1 pulley lies about 1 cm from the proximal finger crease;
           - note that the proximal phalangeal crease which lies over the mid portion of the proximal phalanx, and that the A2 pulley begins and ends in the proximal half of the proximal phalanx;
                  - hence, a tendon sheath incision which extends past the level of the proximal phalangeal crease will probably incise most the A2 pulley;
    - A2 pulley arises from periosteum of proximal half of the proximal phalanx;
           - total length is 20 mm, along the mid portion of the proximal phalanx;
           - of all of the flexor tendon sheaths, this is probably the most important;
    - C1 pulley;
    - A3 pulley arises from volar plate of PIP joint;
           - in the report by Tang JB, et al, the authors studied the effects of the A3 pulley and adjacent sheath integrity on tendon function at the proximal interphalangeal (PIP)
                 joint was investigated in 21 fingers in 7 fresh-frozen cadaver hands;
                 - 11 fingers were tested after incision of the A3 pulley, of the A3 pulley and its distal sheath up to the A4 pulley, and of the sheath from the A3 to A4 pulleys;
                 - tendon bowstringing was 0.3 mm after incision of the A3 pulley, 0.6 mm after incision of the A3 pulley with its distal sheath, 0.8 mm after incision of the pulley with its proximal sheath, 1.4 mm after incision of the sheath from the A3 to A4 pulleys, and 1.6 mm after incision of the sheath between the A2 and A4 pulleys;
                 - results suggest that the sheath adjacent to the A3 pulley plays an important role in restraining tendon bowstringing at the PIP joint, whereas the A3 pulley alone is of little importance;
                 - ref: Effect of A3 pulley and adjacent sheath integrity on tendon excursion and bowstringing
    - C2 pulley;
    - A4 pulley arises from periosteum of mid-portion of middle phalanx;
           - this is the second most important flexor tendon sheath pulley (after the A2);
           - when the FDS tendon is lost, the A4 pulley becomes most essential;
    - C3 pulley;
    - A5 pulley arises from volar plate of the DIP joint;

             

- Flexor Tendon Sheath Biomechanics:
    - in the study by Mitsionis G, et al (1999), it was found that 25% of the A2 or A4 pulleys may be excised either separately or in combination;
          - these authors noted that even excision of up to 75% of the pulley resulted in only minimal decreases in PIP angular ROM
          - Feasibility of partial A2 and A4 pulley excision: effect on finger flexor tendon biomechanics.



Three-loop technique for A2 pulley reconstruction.

Digital flexor tendon sheath: an anatomic study.

Anatomy of the finger flexor tendon sheath and pulley system.

Palmar and digital flexor tendon pulleys.