Comparing the Biomechanical Characteristics of Manual and Powered Laparoscopic Stapler Designs

Donald R Peterson, PhD, Drew R Seils, BS, Tarek Tantawy, BS, Angela S Kueck, MD, M Kurt E Roberts, MD. University of Connecticut Health Center, Yale University

INTRODUCTION: The incidence of musculoskeletal disorders among laparoscopic surgeons is increasing and may be a result of an increase in surgical procedures performed and the biomechanical risks associated with manually-operated laparoscopic instrument use. The introduction of battery-powered surgical instruments may alleviate some of the biomechanical stressors experienced with their manual counterparts and provide an increase in surgical accuracy and efficiency. To better understand and compare the biomechanical risks associated with the use of manual and powered laparoscopic surgical staplers, the physical characteristics and the forces required to activate the various functions of a stapler, including staple firing and blade retraction, were measured for two manual designs (Covidien Endo GIA Ultra, Ethicon Echelon Flex 60) and one powered design (Covidien iDrive Ultra). Measurements included the identification of key ergonomic features such as handle shape and contour, handle angle, hand and finger reach, and grip spans.

METHODS AND PROCEDURES: All physical dimensions were measured using precision calipers and an image analysis software protocol, configured for linear and angular metrics, was used to characterize high-resolution photographs taken of each stapler from various perspectives. The forces required to activate the various functions of the stapler were measured using strain gage force transducers. Four stacked layers of 4 mm thick foam were used as a tissue surrogate for all clamping and firing operations.

RESULTS: The physical dimensions varied between staplers and direct correlations were difficult because of the inherent differences in design and functionality. Except for the finger reach associated with staple firing for the Echelon, the dimensions of each stapler were observed to fall within published anthropometric limits for males and females. The clamping lever motion of the two manual staplers favorably traverses a grip span ranging from 2 to 4.5 inches, which allows for the greatest use of grip strength in both male and female users. The activation forces for each of the stapler components also varied and considerable differences in force levels were observed between the stapler designs. Both manual staplers subject its users to repeated grip forces in excess of 20 pounds during staple firing and blade retraction functions, while published literature indicates that maximum grip force levels should not exceed 25 pounds when designing a hand tool for use by 95 percent of the female population.

CONCLUSION: Although the physical characteristics of the three stapler designs were generally within the recommended anthropometric limits for males and females, the dimensions of the manual staplers are not adequately suited for use by male or female surgeons having a glove size less than 6.5, as reported in the literature. The presence of high activation force levels generates significant biomechanical risks to the surgeon, especially if coupled with awkward postures, strained movements, and/or one-handed operations. The slightly-heavier powered stapler demonstrated negligible staple firing and blade retraction forces when compared to the manual staplers, which may increase instrument stability and decrease surgeon fatigue. If properly designed, powered instruments may help to control, and possibly eliminate, some of the musculoskeletal issues inherent to minimally-invasive surgeries.
 

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