Quantitative Ergonomics Assessment of NOTES Techniques: A Study of Physical Workload, Body Movement and Posture

Introduction: This study investigates through biomechanical analyses NOTES and laparoscopic physical workloads. Research confirms that surgeons experience physical symptoms due to the unfavorable ergonomics of MIS performance. The ergonomics of NOTES—potentially the next evolutionary surgical step—is only now being quantitatively and systematically assessed

Methods and Procedures: Six surgeons with varying MIS experience were recruited for this IRB-approved study. Each participant performed two tasks 1) transferring rings between two sets of pegs by using two graspers; 2) transferring a triangle with attached eyelet between two circles by using a needle held by a needle driver. These tasks were performed using two surgical platforms: 1) traditional laparoscopy employing rigid instruments; 2) NOTES employing a dual-working channel flexible endoscope. With NOTES, the surgeon instructed an assistant in opening and closing the graspers. The NOTES approach was simulated by an upper torso mannequin placed at the trainer box front; an endoscope was introduced through the mannequin’s mouth. Motion capture, sixteen-channel electromyography (EMG), and force plate systems recorded biomechanical data. Integrated percentage maximum voluntary contraction (%MVC) obtained from EMG data collected throughout performance permitted identification of accumulated muscular workload. Mean %MVC was calculated for average muscular activation level. The postural stability demand (PSD) and the sway areas calculated from center of mass (COM) and center of pressure (COP) allowed postural sway quantification. A parallel study investigated surgical grasper force transfer mechanisms. Six electrodes placed on each subject’s forearm muscle groups and a force sensor located between each instrument’s jaws acquired data. Participants performed an opening/closing task using 1) two different-sized hemostats, 2) Maryland and Park laparoscopic graspers, and 3) endo-graspers and biopsy forceps. Force transfer was calculated by dividing &MVC by maximum tip force.

Results: Integrated %MVC was substantially higher with NOTES performance (1305 %MVC) than with laparoscopy (375 %MVC) (p<.05). Average muscular workload was also higher with NOTES (8.2 %MVC, laparoscopy: 6.9 %MVC, p<.05). Analysis of motion capture data showing greater increased elbow flexion and wrist flexion/extension and increased finger movements supported this result by demonstrating that the higher muscle activations exhibited specifically by biceps, wrist flexors/extensors, and thenar compartments during NOTES performance could be attributed to scope holding/navigation and the in and out movements of endoscopic instruments (significant Platform x Muscle interaction, p<.05). During NOTES the postural sway area was demonstrated to be 6 to 7 times greater and PSD in the anterior-posterior direction shown to be significantly higher [NOTES (43.3mm), laparoscopy (17mm) (p<.05)]. Force transfer with endoscopic instruments (.06~.08 %MVC/Newton) was found to be significantly less than with laparoscopic instruments (0.31~3.56 %MVC/Newton).

Conclusions: This study demonstrated the ergonomics of NOTES to be significantly more challenging to surgeons than laparoscopic performance. Based on the strength of our results, we propose an alternative NOTES platform design, coupling the laparoscopic paradigm with the NOTES approach to overcome the awkward operational mechanism of the dual-working channel flexible endoscope. Given the inadequacy of endoscopic instruments’ force transfer, we also propose the endoscopic surgical platform used in NOTES incorporate alternative mechanisms, e.g. motor-driven control.

Session: Podium Presentation

Program Number: S043

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