Suture Strength for Robotic Surgery

Ahmad Abiri, MS, Omeed Paydar, BS, Erik Dutson, MD, Bradley Genovese, MD, Usah Khrucharoen, MD, Warren Grundfest, MD. University of California, Los Angeles

Introduction. The goal of this work is to determine the force required to break sutures during robotic surgery. The growing popularity of robotic surgery as an option for gastrointestinal procedures has introduced a need for the availability of tensile strength data for commonly used sutures. Intraoperative suture failures result in surgical delays while post-operative failures could require revisions or create major complications for the patient. Availability of tensile strength data for sutures will improve selection of the proper suture type and gauge for a procedure, specifically in robotic surgical procedures where lack of haptic feedback frequently results in excessive force, causing breakage. A suture’s mechanical strength is both a fundamental material property and a function of gauge (i.e., filament diameter). The increase in prevalence of robotic surgery (Barbash et al., 2014) results in a higher incidence of suture failure during procedures (Cundy et al., 2014), which could be mitigated by software barriers and virtual walls at a nominal fraction of the ultimate tensile strength of the material.

Methods and Procedures. In this study, 3 suture materials, Polydioxane (PDS), Silk, and Vicryl, were pulled to failure/breakage (Tytron, MTS Systems Corporation, Eden Prairie, MN, USA). Gauges 5-0 to 0 USP (United States Pharmacopeia) were chosen because of their ubiquity in gastrointestinal surgeries with robotic surgical systems. The sutures were fixed with graspers and pulled at 50 mm/min until failure (parameters from Fraunhofer et al., 1985). Experiments were repeated in triplicate for every sample and results were reported as mean and standard deviation. Failure loads (in N) and tensile strength (N/cm2) were recorded. When possible, comparisons were made to earlier work for statistically significant changes resulting from manufacturing improvements.

Results. Generally, Vicryl and PDS sutures had the highest mechanical strength ranging from 60,565 (0 USP) to 178,449 (5-0 USP) N/cm2, while silk had the lowest 40,307 (0 USP) to 106,442 (5-0 USP) N/cm2. Larger diameter sutures withstand higher total force, but finer gauges consistently show higher force per unit area. The difference between the materials becomes more significant as the diameters decrease. Comparison of identical suture materials, including gauge, with previous literature (Fraunhofer et al., 1985) show between 27-50% improvement in the tensile strength over data obtained from 1985.

Conclusions. New knowledge of failure loads and tensile strength will guide selection and use of sutures during robotic surgery. While manufacturing improvements have created stronger sutures, surgeons must consciously avoid excessive force to prevent intraoperative failure. Ultimately, implementation of these limits into robotic surgery software could proactively prevent suture breakage. Results from this work may help define software safety protocols capable of alerting a surgeon prior to failure.

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