Effects of using a surgical clamp to hold tension while tying knots with commonly used orthopedic sutures

Purpose: Tendon repairs are often performed under some degree of tension, and in these instances the use of a clamp to temporarily secure a knot following the first throw can lessen gap formation while subsequent suture throws are made. The effect of clamping on the ultimate tensile load, stiffness, elongation, and mechanism of failure of suture loops has not been investigated for several commonly used orthopedic sutures, and it was the purpose of this study to investigate this issue. Methods: Seven different types/sizes of braided nylon or polyblend (PB) suture were uniformly tied around an isolated 35-mm glass cylinder in a laboratory setting using no clamp, a smooth needle holder, or a serrated clamp to hold a surgeon's knot following the first throw. Knots were secured with four alternating half-hitches with reversed posts, and the suture loops were then loaded on custom hooks in an MTS axial loading frame, preloaded, cycled, and loaded to failure. Elongation, ultimate tensile load (UTL), stiffness, and mechanism of failure were recorded. Results: Six of seven suture loops tied with either clamp showed statistically significant but clinically minimal (<1 mm) increased elongation following cycling. The UTL of No. 2 ForceFiber suture loops tied with serrated clamps were reduced approximately 21% compared to those tied with no clamp (227 N vs. 289 N, P = 0. 003) and approximately 18% compared to those tied with a smooth clamp (227 N vs. 278 N, P = 0. 016). The use of clamps did not affect the UTL for the other six sutures. Clamp use also had no effect on suture loop stiffness for four suture types/sizes, but decreased stiffness for three. Suture loops tied with a serrated clamp were more likely to fail by untying compared to those tied without a clamp, but showed no difference in mechanism of failure from those tied with a smooth clamp. Conclusions: Biomechanical parameters of suture loops were not significantly affected when clamped during tying. Surgeons wishing to temporarily clamp a knot to keep it from slipping during the tying process may do this without concern for weakening the suture.