Square not a running knot.

BACKGROUND: The tensile strength of running monofilament polypropylene sutures anchored with square knots was compared with the strength of the same size sutures anchored with half hitches. STUDY
DESIGN: Polypropylene (Prolene; Ethicon) 0, 2-0, 3-0, 4-0, and 5-0 sutures were secured to a tensionometer with either square knots or half hitches. As tension was applied to the running suture end, the force required to break the suture and the point at which the break occurred were recorded.
RESULTS: The sutures anchored with square knots showed only 75% of the strength of the sutures secured with half hitches (p=<0.001). Every suture tied with square knots broke precisely at the point where the last two squared throws invariably tumbled into half hitches with increased tension on the running end. The resulting stress transformation distorted and weakened the suture, as documented by electron microscopy scanning. The sutures secured with half hitches did not show any surface defects, and none of the running sutures tied down with half hitches broke at the knots.
CONCLUSIONS: A running polypropylene suture initially anchored with half hitches is stronger and safer than a running suture tied down with square knots.