Comparison of Tissue Response to Flat and Stepped Design Linear Stapler Cartridges

Marisha L Godek, PhD, MS, Elizabeth M Contini, Jennifer M Diederich, MS, Vit Novacek, PhD, Frederic Turquier, PhD, Dwight G Bronson, MS

Covidien Surgical Solutions

OBJECTIVE: This study examined the effects of stapler cartridge design on tissue deformation and correlated these observations to an existing finite element analysis model.

DESCRIPTION AND METHODS (1): Upon closure, linear surgical staplers apply uniform compression to tissue with the potential for high shear levels, especially when the device is used in thick or dense tissue. This phenomenon occurs along the outer edges of the anvil and cartridge where serosal tearing is sometimes observed. Significantly, a novel stepped cartridge was designed to reduce the relative level of tissue compression at the row farthest from the cut line; this may reduce shear stress along the outer edge of the stapler. An investigation was undertaken to examine acute tissue response to the compression profile applied by each cartridge (stepped versus flat).

Briefly, canine bowel was compressed utilizing commercially available linear surgical staplers, held in compression with custom retention rings placed at the distal tip, and fixed (in place) in 10% buffered formalin. Tissue was removed from the device, sectioned and stained with hematoxylin and eosin or with a modified elastic tri-chrome stain. Sections were examined microscopically, and tissue thickness measurements taken. The acute tissue response was then compared to a previously developed finite element analysis (FEA) soft tissue model which utilized the same anvil and cartridge profiles.

PRELIMINARY RESULTS: Histological results demonstrate different tissue responses based upon stapler design (Figure 1). Tissue that was compressed by a flat cartridge exhibited a more pronounced response to compressive forces as demonstrated by tissue bending or wrapping around the outer edge of the anvil (Figure 1A, 1B) whereas the tissue compressed by the stepped cartridge face displayed a more symmetrical response (Figure 1C, 1D). Superposing stress plots from the FEA model and microscopic images (Figures 1B, 1D) reveals the relationship between the tissue response and the calculated stresses. This study confirmed clear differences between acute tissue responses to compression placed upon tissues by flat and stepped stapler cartridges. The flat cartridge appeared to produce a more uniform tissue response over the area captured between the jaws of the stapler; however, this uniform distribution may not be ideal with the sharp transition at the edge of the stapler.

CONCLUSIONS: Tissue deformation observed via histology and FEA modeling suggest that high stress concentrations present at the edges of the stapler could negatively impact tissues. In contrast, the stepped stapler cartridge results showed tissue which appeared to be slightly thicker (less compressed) as the outer edge of the stapler was approached, correlating to a more gradual transition and lower acute stress. These subtle changes in the appearance of the tissue should correlate to improved tissue health which may translate to improved patient outcomes.

Figure 1. Photomicrograph of a cross section of compressed tissue, fixed and stained with H and E; flat stapler cartridge (A) with FEA stress overlay (B) and stepped cartridge (C) with FEA stress overlay (D).

Session: Poster Presentation

Program Number: ETP063

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