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Purpose Repair of a lacerated flexor digitorum profundus (FDP) tendon underneath or just distal to the A4 pulley can be technically challenging, and success may 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 six cadaveric hands secured to a rigid frame permitting measurement of tendon excursion, tendon force, and finger range of motion. After control testing, each finger underwent laceration and repair of the FDP tendon at the distal margin of the A4 pulley using a six-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 profundus 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 less than 1 mm to over 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 percent increases in work of flexion (WOF) of 11.5 ± 3.1%, 0.83 ± 2.8%, 2.6 ± 2.4%, and 3.25 ± 2.2%, respectively (p<0.05). Conclusions After FDP laceration and repair in the region of the A4 pulley, WOF did not increase by more than 3% from control conditions after partial or complete A4 pulley release, and WOF was significantly less than performing a repair and leaving the A4 pulley intact.

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