Distally Based Flexor Digitorum Superficialis (FDS) Slip Flap as a Vascularized Alternative to Double-Loop Tendon Grafting in A4 Pulley Reconstruction

BACKGROUND: Zone II flexor tendon injuries involving the loss of the A3 and A4 pulleys present a reconstructive challenge due to the critical role of these structures in tendon gliding and digital function. Traditional A4 pulley reconstruction using autologous double-loop tendon grafts requires donor site harvesting and additional dissection. This study introduces a modified distally based flexor digitorum superficialis (FDS) slip flap as a vascularized, local alternative that preserves anatomic alignment and may reduce surgical morbidity. METHODS: This retrospective study evaluated 34 fingers from 31 patients who underwent primary flexor tendon repair with concurrent A3 and A4 pulley reconstruction. Patients were allocated into 2 groups: Group 1 (n=15) received a transverse double-loop graft using the palmaris longus tendon, and Group 2 (n=19) underwent reconstruction using a distally based FDS slip flap, sutured to the contralateral slip at its insertion. FDP tendons were repaired using the 6-strand M-Tang technique. Outcomes were assessed using total active motion (TAM) and QuickDASH scores at 1 and 6 months. Group 2 underwent high-frequency ultrasonographic evaluation at 6 months to assess neo-pulley integrity. RESULTS: TAM at 1 month was similar between groups (Group 1: 149.33±17.40 degrees; Group 2: 150.26±17.27 degrees; P =0.848), with significant improvement by 6 months (Group 1: 235.00±31.39 degrees; Group 2: 239.21±42.07 degrees; P =0.363). QuickDASH scores also improved comparably in both groups. Ultrasonography in Group 2 confirmed the presence of an intact, anatomically positioned neo-pulley. Donor site complications occurred only in Group 1. CONCLUSION: The modified FDS slip flap provides functional outcomes comparable to traditional grafting techniques while eliminating the need for donor site harvesting. Its vascularized design, anatomic replication of the native A4 pulley, and operative simplicity make it a valuable reconstructive option in acute injuries with pulley loss.