Effect of suture locking and suture caliber on fatigue strength of flexor tendon repairs.

The objectives of this cadaveric study were 2-fold: to determine the effect of different locking configurations on the cyclical fatigue strength of flexor tendon repairs and to assess the differences between each repair when a 3-0 or 4-0 suture is used. One hundred twenty flexor digitorum profundus tendons were cut and repaired using nonlocked, simple locked, and cross-stitch locked variations of 2- and 4-strand flexor tendon repairs. Using an incremental cyclical loading protocol we performed 10 trials of each repair with both 3-0 and 4-0 sutures and analyzed the number of Newton-cycles to failure using a 3-way ANOVA. The use of a 3-0 suture led to a 2- to 3-fold increase in fatigue strength in all repairs tested and the fatigue strength of the 4-strand repairs was significantly greater than the 2-strand repairs. All repairs performed with 4-0 suture failed by suture rupture. Of the 3-0 suture repairs, the three 2-strand repairs and the 4-strand cross-stitch locked repair failed by suture rupture. In contrast, 6 of 10 of the 4-strand simple locked and nonlocked repairs failed by suture pullout. There was no significant difference in fatigue strength between the 2 locked and the nonlocked 2-strand repairs using either 3-0 or 4-0 suture. There also was no significant difference in holding capacity or fatigue strength between the simple locked or nonlocked 4-strand repairs. However, the 4-strand cross-stitch locked repair with a 3-0 suture had significantly improved fatigue strength and holding capacity compared with the other repairs tested. Based on the consistently inferior biomechanical performance of 4-0 suture, we recommend that 3-0 suture be considered for 2- or 4-strand tendon repairs when early active motion is planned. The orientation of the transverse and longitudinal components of simple locked repairs did not significantly influence their holding capacity or fatigue strength. The cross-stitch type of locked repair provides better holding capacity and fatigue strength compared with simple locked or nonlocked 4-stranded flexor tendon repairs.

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

The purpose of this study was to delineate the contribution of increasing suture 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 variations of a 4- and 8-strand flexor tendon repair. An incremental cyclical 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 withstood before failure was performed using 2-way ANOVA. The 8-strand repairs demonstrated significantly increased fatigue strength compared with the 4-strand repairs, but the number of strands crossing the repair site did not significantly affect gap resistance. The locked repairs demonstrated a significant 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 fatigue strength of a tendon repair but does not alter its gap resistance to cyclic loading. Locking of the repair does provide additional gap resistance at the relatively low cyclical loads anticipated during the early healing period using an active motion rehabilitation protocol.