Surgeons have aimed to achieve strong repair so as to begin early active rehabilitation programs for flexor tendon injury. Multi-strand suture techniques were developed to gain improved gap resistance and ultimate force compared with the respective two-strand techniques. In vivo studies indicate that multiple strands may cause ischemia during the intrinsic healing process by decreasing the total cross-sectional area of the injured site, unless the total cross-sectional area of the sutures is not decreased.

The hypothesis was to design an in vitro study to understand the biomechanical relationship between suture calibers of core sutures with increased number of suture strands and peripheral suture on final repair strength.

Sixty fresh sheep forelimb flexor digitorum profundus tendons were randomly placed into three groups (A, B, and C), each containing 20 specimens, for tendon repair. Two-, four-, and eight-strand suture techniques were respectively used in Groups A, B, and C. A simple running peripheral suture technique was used in Subgroups A2, B2, and C2. For each repaired tendon, the 2-mm gap-formation force, 2-mm gap-formation strength, maximum breaking force and maximum breaking strength were determined.

Differences in 2-mm gap-formation force and 2-mm gap-formation strength were found between Subgroups A1 and A2, B1 and B2, and C1 and C2. Between Groups A and B, A and C, and B and C, there was no difference as well.

Both the number of strands and the ratio between the total suture volume and tendon volume at the repair site are important for ideal repair. If the total cross-sectional area of the sutures is equal in 2-strand, 4-strand, and 8-strand procedure, there is no difference in the strength of the repair. A decrease in caliber size suture requires more passes to achieve the same strength. Instead, it is much better to use peripheral suture techniques to improve the strength of the repair with larger diameter 2-strand core sutures.