Redesigning the Powered SurgicalStapler to Accommodate GrowingDiversity in the Surgeon Population

Surgical InnovationXX(X):1–??c©The Author(s) 2016

Reprints and permission:sagepub.co.uk/journalsPermissions.navDOI: 10.1177/ToBeAssignedwww.sagepub.com/

Jamie Spellman1, Srinidhi Emkay1, Kelsey Linsmeier1, Yaniv Sadka1, Connor Sheedy1

AbstractThe current design of powered laparoscopic surgical staplers limits the number of surgeons that can use the staplerto a fraction of the modern surgeon demographics. From 1994 to 2004, women, who on average have hands oneinch shorter in length than men, have doubled in number to 38.3% of all general surgery trainees.2 Based on anergonomic analysis of existing devices and relevant anthropometric data, a novel ergonomic redesign that adjustsseveral of the key elements of this surgical device has been developed and tested. The redesign of the prototypeused anthropometric data to determine the reach distance to pull the clamping lever and the relative strength giventhe average procedural posture. The analysis compared the final design metrics to those for the Ethicon Echelon FlexPowered Stapler, specifically focusing on the reach necessary to pull the clamping lever, and the orthogonal orientationof the device which puts tremendous strain on the forearm of the user. The final ergonomic testing showed that the newdesign increases the percent of females accommodated from 11% to 71% and the percent of males accommodatedfrom 50% to 95%.

KeywordsErgonomic, anthropometry, surgical stapler, laparoscopic, biomedical engineering, medical device

Introduction

According to hand anthropometric calculations, the currentdesign of Ethicons Echelon Flex Powered Stapler accom-modates only 34% of the current surgeon population. Thisseverely limits the number of surgeons who can use thedevice effectively, safely, and comfortably. The ingenuityand utility of the staplers simultaneous slice and seal func-tionality is hindered by the handles ergonomics, which do notaccommodate the smaller hand sizes and lower grip strengthsfound in the diverse surgeon population. An ergonomicredesign and optimization of the surgical stapler shouldincrease the percent of the surgeon population accommo-dated. There are two features in the current device that limitthe design. The first is the orientation of the handle relative tothe body of the stapler, which causes uncomfortable strain onthe wrist of the user. The second is the position and shape ofthe clamping lever relative to the body of the device, whichmakes engaging the lever difficult for those with smallerhand sizes. The redesign focuses on developing a prototypeto address these limitations and improve the accommodationfor the changing diversity of surgeons.

Several other instruments in this class of devices have beendeveloped. The only other powered stapler is the iDrive UltraPowered Stapling System (Medtronic Corp. Minneapolis,MN). The iDrive, however, does not have the tactile responseclosing mechanism, a critical feature because the surgeonneeds to have control over closing the jaws on tissues whichare often inflamed.

Materials and MethodsThis engineering project involves conducting anthropometricand ergonomics research to evaluate a new inline designwhich changes the wrist angle from an orthogonal orientationto a linear orientation, with respect to the forearm. Primaryoutcome measures include reach to pull the clamping lever,percent of the population accommodated, ease of use, andcost. The initial testing evaluated the existing design forhow effectively it could be used by the growing diversity insurgeon populations through both quantitative and qualitativeanalysis. This includes anthropometric measurements, andposture and strength calculations. The results of this analysisinformed the redesign of two key components of the device:

(1.) Orientation of the handle relative to the body of thedevice

(2.) The position & shape of the clamping lever.

EquipmentThe new ergonomic redesign of the stapler system is amodification of Ethicons Echelon Flex Powered Stapleran inline rather than orthogonal design. The new designincorporates a curved body, a safety and fire button on theleft-hand side, a clamping lever beneath the body, and an

1 Bachelor of Science in Biomedical Engineering, University of Wiscon-sin - Madison, Department of Biomedical Engineering, Wisconsin, USA.

Corresponding author:Jamie Spellman, 1550 Engineering Drive, Madison, WI, 53706, USA.Email: spellman3@wisc.edu

2 Surgical Innovation XX(X)

articulating head as seen in the echelon flex. The designimproves wrist posture and decreases strength necessary foruse.

The internal components of Ethicons powered staplerinclude a clamping mechanism that manipulates the jawsof the device using a lever action, and a gear system thatboth drives the knife forward and staples the tissue. The newlinear design utilizes a modified bevel gear system to rotatethe motor gearbox assembly to a more in-line orientation.This rotation does not alter the mechanical function and isspecifically designed to generate the same amount of force atthe end effector of the device.

Figure 1. Internal components of the new drive systemfeaturing a bevel gear assembly

Figure 2. Final design featuring an ergonomic casing

Hand ErgonomicsAnthropometric data from the US Army database, specifi-cally digit length measurements, was used to determine thepercent of the surgeon population that is accommodated bythe device according to reach calculations. Three primarymovements were evaluated, including reach to pull the gripcontroller with the pinky finger, reach to push the Releasewith the thumb, and reach to pull the articulation head withthe pointer finger. The movement that accommodated thesmallest percentage of surgeons was considered the limitingfactor and served as the focus for the new design. The anthro-pometric data was specifically used to develop a new designthat would accommodate a larger percentage of surgeons.

Wrist Ergonomics - Effects of Posture3DSSPP, a software that predicts static strength requirementsto aid in the evaluation of the physical demands of a job, wasused to perform further ergonomic testing. Invented at theUniversity of Michigan, 3DSSPP was used in this setting todetermine the static strength of the individual while holding

Figure 3. The limitations of the Ethicons devices hand andwrist ergonomics

the redesigned stapler. The model used was determined basedon the average body measurements of the surgeon populationfor a combined male and female population. Measurementsof the wrist strength at a given surgery posture could be takenby assigning the appropriate force vectors on the modelswrist. This strength calculation has a number of limitationssuch as the assumptions based on posture of the surgeon andspecificity in terms of localized forces.

These limitations are reconciled by calculations basedon the final designs dimensions and mass using freebody diagrams. Wrist and hand size were based upon theanthropometric data on average female and male sizes, thencalculations for both the Ethicon Echelon Flex and the finalprototype were based upon postures utilized in the 3DSSPPanalysis. An evaluation of the force generation necessaryto conduct this job as intended characterized the strengthaccommodation for surgeons.

Focus GroupThe focus group gauged the tractability of the final design.The study size was expected to include 4-8 surgeons for UWHospital. The goal was to pull some qualitative evaluationsof the devices key characteristics through a short surveycomparing the final prototype alongside Ethicons. However,due to the availability of the surgeons, and the stage of thedesign, the focus group included only two surgeons, one ofwhich was the client, Dr. Liepert. Although the discussionwith Dr. Liepert and her colleague was productive andallowed us to explore other design ideas, it was unable toprovide us a means of measuring the larger market for thisdevice. Further studies would require a much greater samplesize of surgeons, specifically those with diverse hand sizesand experience with surgical staplers. In addition, it wouldbenefit this evaluation of the design greatly if the device wasfunctional in regards to the clamping mechanism because ofits importance to the design work.

Results

AnthropometricsFor each of the primary movements evaluated, meanand standard deviation values were used to calculate theproportion of surgeon hands that fit within the designedreach distance. Values were collected from digit 2, digit 4,and digit 5 length measurements from the US Army HandAnthropometry survey.

Spellman et al 3

From these calculations, it was determined that reachingto pull the grip controller accommodated the fewest numberof surgeons, proving to be the limiting factor as only 34% ofthe studied population is able to wrap the pinky finger aroundthe clamping lever. The other two movements, reaching topush the release and reach to push the articulation head,accommodated a larger portion of surgeons with valuesof 54% and 46% respectively. All percentages represent amixed female/male population with a 60:40 ratio of males tofemales.

The reach to pull the clamping mechanism was determinedby taking the distance from the handle to the lowest pointof the lever. The results from Ethicons device showed adistance of 4.65 inches compared to the 4.1 inches of thenew prototype. The new design allowed an accommodationof 86% of the population, a significant improvement overEthicons design. This is a startling improvement since manysurgeons prior were not able to utilize their entire handto engage the lever. This mechanical clamping system isintegral to the design. Devices such as Medtronics fullymotorized IDrive mechanism is disliked in part becauseit doesnt allow the surgeon the tactile control of thestapler. By increasing the amount of surgeon hand sizesthat can comfortably utilize the device improves the overallergonomics of its design.

The results from the 3DSSPP software, showed that atthe given posture the user would have an improved strengthin their wrist through the inline design. Again, the averagehand size for males and females was compared and usedto provide a model of a surgeon in a posture representativeof a procedure. The results showed that the female strengthimproved from 41% to 99% and males improved from88% to 100%. The cocked position of Ethicons handle isuncomfortable and creates strain in the surgeons wrist whenholding the device. This is further emphasized in proceduressuch as appendectomies which causes the surgeon to holdthe device down by their hip. Although this analysis haslimitations discussed previously, it allow some insight intohow the device may perform in a procedure.

Conclusion

Current medical devices need to be iterated upon toaccommodate the increasing diversity in the surgeonpopulation. By linearizing the drive system on the poweredlaparoscopic surgical stapler and designing a new handlearound the linearized drive system, the surgeon populationaccommodated by the stapling device increased from 34%to 86%. The new shape of the handle decreases stresses andstrains on the forearm and wrist, thus reducing the likelihoodof repetitive strain injuries. Moreover, from a qualitativeperspective, surgeons who participated in the focus groupsresponded positively to the new ergonomic design of thestapler, and showed a willingness to try the new device intheir surgical practice. Overall, this work exemplifies thesignificance of ergonomically redesigning medical devicesalready in practice, not just accounting for occupationalergonomics in new medical devices.

Acknowledgements

The authors would like to acknowledge the help and mentor shipfrom Mitchell E. Tyler MS, and Amy E. Liepert MD

Declaration of conflicting interests

The authors declared no potential conflicts of interest with respectto the research, authorship, and/or publication of this article.

Funding

The authors received no financial support for the research,authorship, and/or publication of this article.

References

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Appendix

Product Design Specifications: Ergonomic Redesign of a Surgical Stapling Device

February 9, 2018

Client: Dr. Amy Liepert, liepert@surgery.wisc.edu Advisor: Mitchell Tyler, mitchell.tyler@wisc.edu Team:

● Jamie Spellman, spellman3@wisc.edu, Team Leader ● Kelsey Linsmeier, klinsmeier@wisc.edu, Communicator ● Connor Sheedy, cjsheedy@wisc.edu, BPAG ● Srinidhi Emkay, emkay@wisc.edu, BSAC ● Yaniv Sadka, sadka@wisc.edu, BWIG

Function:

Despite recent design modifications to surgical staplers, surgical staplers still fail to accommodate even half of the surgeon population. Laparoscopic stapling devices are used both for intestinal resections and anastomoses as well as for vascular control. Dr. Liepert performs laparoscopic surgeries and utilizes Ethicon’s Echelon Flex Powered Endopath surgical stapler to separate and seal tissues simultaneously. Ethicon’s Echelon Flex Powered Endopath Stapler ergonomically accommodates only 33% of a mixed female and male surgeon population.

For the purposes of this engineering design project, ergonomic accommodation is defined as the ability for a surgeon to hold and use the device in the hand as is intended, without overextension of the soft tissues in the wrist, elbow, and shoulder. New electronic surgical staplers, such as Medtronic’s iDrive™ Ultra Powered Stapling System, attempt to fix the ergonomic failures of surgical staplers, but in doing so eliminate the tactical control required for surgeons to comfortably perform accurate procedures. The design specifications outlined below are aimed to increase the percentage of a mixed population accommodated by the handle of the laparoscopic stapler. This project provides the opportunity for lab based and field study investigation of the ergonomic implications for the device users as well as potential for novel design modifications and/or solutions.

This project is now in the fourth semester of BME design work. Previous designs explored moving the handle from the pistol grip to an inline handle design. The most recent design has yielded an 89% ergonomic accommodation when tested using the same method as the current device. The goal for this semester is to not only continue to defend the previous design, but also introduce novel and improved ideas. This semester will also focus on the inner mechanism of the device to present a feasible design.

Client Requirements:

● Redesign the Ethicon Echelon Flex Stapler, including all functions of the current model ● Fabricate a prototype to present and gain feedback from multiple surgeons ● Focus design on reducing stress and strain on wrist and elbow upon firing during

procedures such as an appendectomy ● Increase accomodation percentage from current model

Design requirements:

1. Physical and Operational Characteristics a. Performance requirements:

The stapler will be designed to be disposable after one surgery, designed for a maximum of ten staples. It is not feasible to design a device that can be sterilized and reused.

b. Safety: i. Patient Safety:

1. The stapler will puncture the desired tissue without harming any surrounding tissue of the patient. The ISO standards focus on the physical implant, the staplers, which will not be augmented by the team.

ii. Surgeon Safety: 1. The device aims to minimize the strain on the clinician’s wrist and

elbow, minimizing injury such as Musculoskeletal Disorders from repeated use.

c. Accuracy and Reliability: The ergonomic redesign will not affect the accuracy or reliability of the existing device, the Ethicon Echelon Flex.

d. Life in Service: The stapler will only be employed once before disposal. The single use will supply a maximum of 10 staples. It is not within the specifications of the project to design a device that can be autoclaved for multiple surgical uses.

e. Shelf Life:

The shelf life of the prototype will be 5 years. The electronics within the device will remain viable for the entirety of the shelf life. The device will be sterilized during the manufacturing process and cannot be contaminated before it is used in the operating room.

f. Operating Environment: The device will remain in the original packaging until use. Therefore, the device should be stored at room temperature, away from any liquids, and handled with care until the packaging is opened in the operating room. For this reason set-up and opening of the package must be fast and simple so as to not hold up the surgery. The stapler can be reused multiple times on the same patient during a single operation, but must be disposed of as hazardous material following the operation.

g. Ergonomics: The goal of the project is to improve the ergonomics of the Ethicon Echelon Flex Endopath Stapler. Currently, the grip of the device is too large for not only our client’s hand, but also for 67% of the mixed male and female surgeon population. The prototype will be compatible with Dr. Liepert’s grip. The device will also be designed to be held in a comfortable position by the surgeon during operations, minimizing strain on the user’s wrist and elbow. The force required to fire a staple will be minimized.

Figures 1 and 2: Hand dimensions from US Army Anthropometry tables

Dr. Liepert’s hand measurements are as follows: palm length (61) is 4in, hand breadth from digitizer (62) is 3.25in, wrist-center of grip length (66) is 2.5in, and hand length from digitizer (58) is 7in.

h. Size:

Portability and storage space are not primary concerns of the design of the tool or of the tool itself. Ideally, the product will be smaller than the Ethicon Echelon Flex and will be comfortably held in one hand.

i. Weight:

While no specific weight was set by Dr. Liepert, the weight of the stapler is one of the key aspects of the design that must be considered. The product must weigh less than the current surgical stapler used by Dr. Liepert and, ideally, have a more even distribution of weight for more comfortable and convenient operation and handling with one hand.

j. Materials: The product will likely be made of a plastic alloy; this is in keeping with the designs of current disposable surgical staplers on the market. The material should comply with current FDA guidelines and other relevant requirements.

k. Aesthetics, Appearance, and Finish: Dr. Liepert did not specify a preference of aesthetic, appearance, or finish. The example surgical stapler shown featured a standard white and blue plastic color scheme and finish; many surgical staplers seen on the market feature a similar appearance and style.

2. Production Characteristics a. Quantity:

The goal of the semester is to create one working prototype.

b. Target Product Cost: In the current market the going rate for a laparoscopic surgical stapler ranges from $600-800. For our purposes this semester, we will work with a budget of $100.

c. Standards and Specifications: ISO standards regulate specifications for the implanted device (the staples), but not the stapler.1 We will not be augmenting the staples, therefore this is not a concern for our project.

d. Customer:

Our customer would prefer a small and easy to pick up machine. The design is for a customer with a smaller hand size or weaker grip strength. Eventually this product could be marketed not only to female surgeons but surgeons who are losing hand strength and dexterity to age-related problems.

e. Patient-related concerns: The product will be used on a one per procedure basis. The product will be delivered to the Operating Room sterile, and be disposed of post procedure, therefore sterilization is not a concern. Stapler malfunction, however, is a concern for the patient. Every year, there are 8000-9000 adverse events reported to the FDA as a result of stapler malfunction, approximately 1% of which result in death. The primary patient problems as a result of a stapler malfunction are prolonged surgery, excess bleeding, and infection.2

f. Competition:

The market of surgical staplers is quite large and diverse, as evidenced by searches through online marketplaces. Available staplers vary wildly in price, design, quality, sophistication, and application; staplers of nearly all shapes, sizes, and colors are available with a wide variety of options and design considerations, including how the device is powered, if it is reusable, and several other key factors. These staplers range from $10 for a single, plastic, disposable device to several hundred dollars for metal alloy, reusable staplers. Additionally, each disposable Ethicon stapler used by Dr. Liepert and the UW Hospital costs between $500 and $600.

Sources: [1] “Implants for surgery -- Staples with parallel legs for orthopaedic use -- General requirements ISO 8827:1988,” International Organization for Standardization. [Online]. Available: http://www.iso.org/iso/catalogue_detail.htm?csnumber=16301. [Accessed: 02-Feb-2017]. [2] "Surgical Staplers," in US Food and Drug Administration, Center for Devices and Radiological Health, 2015. [Online]. Available: http://www.fda.gov/MedicalDevices/ProductsandMedicalProcedures/GeneralHospitalDevicesandSupplies/ucm110739.htm. Accessed: Feb. 3, 2017.