The role of multiple strands and locking sutures on cap formation of flexor tendon repairs during cyclical loading

The purpose of this study was to delineate the contribution of increasing s uture strands and locking repair design in the prevention of gap formation using a cadaveric model for linear cyclical loading. Forty flexor digitorum profundus tendons were lacerated and repaired using locked and nonlocked v ariations of a 4- and 8-strand flexor tendon repair. An incremental cyclica l loading protocol from 25 N to 65 N was used. Comparison of the amount of Newton-cycles to reach 1, 2, 3, and 4 mm of gap and the Newton-cycles withs tood before failure was performed using 2-way ANOVA. The 8-strand repairs d emonstrated significantly increased fatigue strength compared with the 4-st rand repairs, but the number of strands crossing the repair site did not si gnificantly affect gap resistance. The locked repairs demonstrated a signif icant increase in gap resistance to 1 and 2 mm compared with the nonlocked repairs, but the difference was not sustained at higher load cycles. There was no association between gap resistance and fatigue strength. We conclude that an increase in the number of strands significantly increases the fati gue strength of a tendon repair but does not alter its gap resistance to cy clic loading. Locking of the repair does provide additional gap resistance at the relatively low cyclical loads anticipated during the early healing p eriod using an active motion rehabilitation protocol. (J Hand Surg 2000;25A :714-720. Copyright (C) 2000 by the American Society for Surgery of the Han d).