Tendon transfer fixation in the foot and ankle: a biomechanical study evaluating two sizes of pilot holes for bioabsorbable screws.

The purpose of this study was to compare the initial fixation strengths of bioabsorbable screws for tendon transfers in the foot and ankle when the pilot hole size varied. A 7 x 20 mm screw was used with 5.5 mm and 6.5 mm drill holes, and a 5 x 20 mm screw was used with 3.9 mm and 4.5 mm drill holes. Biomechanical testing was performed on each tendon transfer in cadaver specimens. A paired t-test showed no significant difference in pullout strength when pilot hole size varied between 79 to 93% of the screw size for the 7 mm screw and 78 to 90% of the screw size for the 5 mm screw. Previous studies have found a critical value of tendon tension equaling 50 N with passive dorsiflexion of the foot. With an average value of approximately 170 N, the 7 mm screw provided three times the requisite strength. The 5 mm screw provided 1.5 times the requisite strength, but the transfer was technically more difficult.