Effect of pulley excision on flexor tendon biomechanics

Abstract

Flexor tendon function following excision of various portions of the fibro-osseous pulley system was measured biomechanically using a tensile testing machine. The biomechanical parameters measured were tendon excursion (the excursion of the tendon required to fully flex the digit) and work of flexion (the area under the force-excursion curve, representing all the forces that resist tendon flexion). In this experiment, work of flexion included the forces necessary to accomplish full digital flexion against a 15-g counter-weight, as well as the frictional forces that resist tendon gliding. The results indicate that the work of flexion was affected to a greater degree by pulley loss than was tendon excursion, suggesting that it is a more sensitive measurement of tendon function. A2 was found to be the single most important pulley for flexor tendon function, followed by A4. However, both A2 and A4 had to be present if near-normal hand function was to be achieved; sacrificing the A1 pulley was not associated with a significant loss of flexion. The "pulley effect" of the skin and soft tissue as a supplement to the fibro-osseous pulleys in reducing tendon bow-stringing was also noted. Although the parameters of tendon excursion and work of flexion were used in this study to determine the effect of pulley loss on tendon function, they can also be used to evaluate other flexor tendon studies, such as pulley reconstruction.

The influence of concentric and eccentric loading on the finger pulley system

“…Scanning electron microscopy of the human A2 pulley shows the same transverse fiber direction, perpendicular to the forces applied by the tendons as in these animals, leading to a preferential direction for friction because the shape of the tendon and the direction of the fibers changed when the tendon was under tension (Walbeehm and McGrouther, 1995). Friction between pulleys and flexor tendons has been investigated in several studies in order to assess friction of different suture techniques and tendon grafts Nishida et al, 1998;Peterson et al, 1986;Uchiyama et al, 1997Uchiyama et al, , 1995Williams and Amis, 1995;Woo et al, 1981), but these studies focused on concentric movement. Schweizer et al (2003) developed a method for determining the effect of friction between human finger flexor tendons and pulleys in vivo during high load.…”

Ultrasound-guided percutaneous release of the annular pulley in trigger digit

“…Here, its tip is seen transecting the A1 pulley. Note how the operator can ensure that it remains dead centre over the flexor tendon under sonographic guidance during the procedure, particularly the digital nerves which have been shown to have a variable course in cadaveric studies [12][13][14][15][16][17][18][19][20][21][22]. Several studies suggest the variation in digital nerve position in the thumb, index and little finger puts non-image-guided percutaneous release at risk of complications [6,8,12,16,20,[24][25][26].…”

“…The "blind" percutaneous technique uses surface anatomical landmarks [12][13][14][15][16][17][18][19][20][21][22]. Although it has been shown to be safe, it is complicated by incomplete release or the need to convert to an open release, which has been reported in up to 11% of cases [13,16,23].…”

Management of Complications of Flexor Tendon Injuries

“…However, biomechanical studies have shown the A2 pulley to be the most important for flexor tendon function, followed by A4. 55 Proximal partial pulley excision may have a greater effect on digit range of motion than distal partial pulley excision. 56 To avoid the sequelae of A2 resection, reduction flexor tenoplasty has been reported.…”