Quantification of partial or complete A4 pulley release with FDP repair in cadaveric tendons

Abstract

Purpose: Repair of a lacerated flexor digitorum profundus (FDP) tendon underneath or just distal to the A4 pulley can be technically challenging, and success can be confounded by tendon triggering and scarring to the pulley. The purpose of this study was to quantify the effect of partial and complete A4 pulley release in the context of a lacerated and repaired FDP tendon just distal to the A4 pulley.

Methods: Tendon biomechanics were tested in 6 cadaveric hands secured to a rigid frame, permitting measurement of tendon excursion, tendon force, and finger range of motion. After control testing, each finger had laceration and repair of the FDP tendon at the distal margin of the A4 pulley using a 6-strand core suture technique and epitendinous repair. Testing was then repeated after the following interventions: (1) intact A4 pulley, (2) release of the distal half of the A4 pulley, (3) complete release of the A4 pulley, and (4) continued proximal release of the sheath to the distal edge of A2 (release of C2, A3, and C1 pulleys). Release of the pulleys was performed by incision; no tissue was removed from the specimens.

Results: From full extension to full flexion, average FDP tendon excursion for all intact digits was 37.9 ± 1.5 mm, and tendon repair resulted in average tendon shortening of 1.6 ± 0.4 mm. Flexion lag increased from <1 mm to >4 mm with venting of the A4 pulley, complete A4 release, and proximal sheath release, respectively. Compared to the intact state, repair of the tendon with an intact A4 pulley, release of half the A4 pulley, complete A4 release, and proximal sheath release resulted in percentage increases in work of flexion of 11.5 ± 3.1%, 0.83 ± 2.8%, 2.6 ± 2.4%, and 3.25 ± 2.2%, respectively.

Conclusions: After FDP laceration and repair in the region of the A4 pulley, work of flexion did not increase by more than 3% from control conditions after partial or complete A4 pulley release, and work of flexion was significantly less than that achieved by performing a repair and leaving the A4 pulley intact.

Figure 1

Mechanical testing apparatus. The cadaveric hand was disarticulated proximal to the base of the metacarpals, and skin was removed proximal to the level of the proximal wrist crease. Two Steinman pins were drilled through at least 3 metacarpals and securely fixed to a custom brace. The tendon was then clamped to a dual-servo motor for excursion/force testing.

Figure 2

Excursion represented as the percent change from the control condition for all fingers. Error bars represent the SEM. *signifies p<0.05 across all conditions.

Figure 3

Work of flexion represented as the percent change from the repaired condition with A4 pulley intact. Error bars represent the SEM. *signifies p<0.05 across all conditions.

Figure 4

Flexion lag under each pulley/sheath condition for each of the four fingers. Data are represented as a mean for each type of finger and error bars represent the SEM.