Experimental Characterization and Numerical Simulations of Surgical Knots

Abstract

INTRODUCTION: Suture strength and knot topology are two of the several factors impacting the strength of surgical repairs in soft tissue such as a tendon and skin. The measurement and comparison of the strength of knotted suture is complicated by the lack of consensus test methods. Several prior studies assess FiberWire and others sutures, however, they evaluate or compare only the gross structural response of specific sutures or their knots without direct investigation of the governing mechanics. Little has been reported about the constituents of the suture, the core and jacket separately, nor their impact on the knot strength and failure mechanisms. PURPOSE: To develop a 3D finite element model of a surgical knot in order to determine the influence of knot topology and other factors governing the mechanics of surgical suture. MATERIAL & METHODS: An experimental study No.2 FiberWire was performed to observe the governing mechanics and to obtain data for finite element model validation. FiberWire suture is composed of a core covered with a jacket; each was tested separately and together as manufactured. A finite element model was created consisting of one knot throw. RESULTS: The maximum load of the core and jacket are approximately 65 N and 210 N respectively, and the maximum strain is 2.6% for the core and 9% for the jacket. The as-manufactured suture exhibited a failure mechanism akin to a child’s “finger trap” toy, that is, the core failed several times prior to complete failure of the suture. The finite element results were consistent with the experiments. They explain that the knot’s ~50% strength reduction relative to suture is due to the stresses from bending, twisting, and the stress concentrations from knot frictional contact. CONCLUSIONS: Under tension, the braided jacket lengthens and narrows while the angle between the warp and weft threads changes. Therefore, the circumference shrinks with increases in tension and “traps” the core with compression. This permits shear load transferred between the core and the jacket after core failure. The finite element of the knot is qualitatively consistent with experimental results. Thus, the model can be used in additional investigations