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ERGONOMIC REDESIGN OF A SURGICAL STAPLING

DEVICE

Preliminary Report - BME Design 200/300

October 19, 2016

TEAM MEMBERS:

Project Leader: Madelyn Goedland

Communicator: Justin DeShaw

BSAC: Gregory Wolf

BWIG: Alexander Babinski

BPAG: Jacob Andreae

ADVISOR:

Dr. Thomas Yen, University of Wisconsin, Department of Biomedical Engineering

CLIENT:

Dr. Amy Liepert, University of Wisconsin School of Medicine and Public Health, Department of

Surgery

ABSTRACT

Laparoscopic surgery is a type of minimally invasive procedure conducted through a

small incision in the abdomen. Through this port, entire operations can be performed. Cutting

and stapling functions are often needed throughout the course of the surgery and specialized

staplers have been designed for this purpose. The first surgical stapler was invented in 1908 and

since then, hundreds of redesigns have been made, from fully mechanical to battery-powered

models. Despite years of redesign, many problems still exist with these devices. More recently,

the general population of surgeons has shifted to an aging and more women inclusive

demographic. The size and function of current surgical staplers make them difficult to use for

those with a smaller hand size and/or less powerful grip strength; this is the main problem our

client, a young female surgeon, has with these devices. In mechanical designs, the force required

to physically fire the staples is too great, sometimes requiring two-handed operation. While this

particular problem is solved by battery-powered models, it subsequently adds additional weight

and bulk to the device, making it uncomfortable during use. Many surgical staplers currently on

the market contain these drawbacks. While our client uses solely Ethicon brand surgical staplers,

other companies and products do exist. Our proposed solution is an attachment to a current

mechanical model, in order to decrease the force required for firing the staples. Additionally,

with this solution, a single product could ideally function with and improve multiple

brands/models of surgical staplers.

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TABLE OF CONTENTS

I. Introduction………………………………………………...…………….. 3

A. Motivation

B. Existing Devices

C. Problem Statement

II. Background…………………………………………..………………….. 5

A. Background Research

B. Client Information

C. Design Specifications

III. Preliminary Designs……………………………………………………. 6

A. Design 1: Mechanical Redesign

B. Design 2: Attachment to an Existing Device

C. Design 3: Powered Variant-CO2

D. Design 4: Powered Variant-Capacitors

IV. Preliminary Design Evaluation……………………………………….... 9

A. Design Matrix

B. Summary of Design Matrix

C. Proposed Final Design

V. References..……….……………………………………………………... 11

VI. Appendix: Product Design Specifications……………………………... 11

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I. INTRODUCTION

A. Motivation

The 2014 Orthopaedic Practice in the United States (OPUS) Survey

conducted by the American Academy of Orthopaedic Surgeons found that the

average surgeon age has been steadily increasing since 2008. The majority of full-

time employed orthopaedic surgeons range between the ages of 40 to 59 years

old. The majority of part-time employed orthopaedic surgeons are over 60 years

of age. The census also found an a steady increase in the percentage of females

orthopaedic surgeons than in previous decades. These changes in the orthopaedic

surgeon demographic influence the surgeon’s interaction with their tools [1].

A decrease in the quality of surgeon-device interaction has become

apparent in laparoscopic surgical procedures. Laparoscopic surgery is a minimally

invasive technique in which several sub-centimeter sized incisions are used to

access the body cavity of a patient [2]. A laparoscopic surgical stapling device is

often used during these procedures to close off and separate portions of tissue.

The device is composed of a handle, a long insertion rod, and a clamping

head. The rod is inserted through the patient’s abdominal incision and the head is

clamped around the target tissue. Triggers on the device handle are compressed to

dispense staples into the tissue while a blade cuts the tissue between the staples.

The device allows surgeons to resection (remove), transection (cut through), or

anastomosis (create connections between) tissues [3].

In the opinion of our client, traditional surgical staplers are designed

primarily for a middle aged male surgeon with a size 9 hand. However, the

change in surgeon demographic has made operation of this device increasingly

difficult, since an older and more female surgeon population in general has a

smaller hand size and decreased grip strength. This project hopes to overcome

these demographic changes to improve the surgeon user experience with

laparoscopic surgical stapling devices.

B. Existing Devices

1. Endopath ETS-Flex45

Figure 1: Endopath ETS-Flex45. The Endopath ETS-Flex45 surgical stapler is

a model designed and produced by Ethicon, a subsidiary of Johnson & Johnson. It

is completely mechanically operated with a dual clamping/firing lever

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mechanism. The first lever clamps the stapling head. The second lever drives the

staples via a single pull. It also provides five angle increments to either side of the

head via a head joint, delivering greater articulation options to help enable a more

precise approach. Image taken from:

http://www.ethicon.com/healthcare-professionals/products/staplers

2. Echelon 45

Figure 2: Echelon 45. The Echelon 45 surgical stapler is designed and produced

by Ethicon. It is mechanically operated with a dual clamping/firing lever

mechanism. The first lever clamps the stapling head. The second lever drives the

staples via a ratcheting mechanism, typically requiring the user to pull the lever

four times. Image taken from: http://www.ethicon.com/healthcare-

professionals/products/staplers

3. Echelon Flex Powered Endopath

Figure 3: Echelon Flex Powered Endopath. The Echelon Flex Powered

Endopath surgical stapler is designed and produced by Ethicon. It utilizes a

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manual head clamping lever and a battery powered firing trigger. This decreases

manual strain for one aspect of device operation. The head includes an

articulating joint for greater precision. Image taken from: http://www.ethicon.com/healthcare-professionals/products/staplers

4. iDrive Ultra Powered Stapling System

Figure 4: iDrive Ultra Powered Stapling System. The Covidien iDrive Ultra

Powered Stapling System is a fully rechargeable, battery-powered device that can

last up to a minimum of 300 procedures. The battery is placed below the handle of

the device to provide better balance of weight. iDrive utilizes push button

operation for both clamping and firing mechanisms to decrease manual strain on

the user. It also includes an autoclavable, detachable rod that can accommodate

multiple staple reload sizes. The head includes an articulating joint for greater

precision. Image taken from: http://www.medtronic.com/covidien/products/surgical-

stapling/idrive-ultra-powered-stapling-system

C. Problem Statement

Surgical staplers have undergone many design modifications including the

recent addition of powered devices. Stapling devices are used both for intestinal

resections and anastomoses, as well as for vascular control. With the increase in

female surgeons and an aging surgeon population these devices must be fit to a

wider demographic. We will be focusing specifically on staplers designed for

laparoscopic surgery.

II. BACKGROUND

A. Background Research

The population of surgeons potentially using our device includes males

and females between a range of ages. Additionally, surgeons may use a surgical

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stapler in either their dominant or nondominant hand. Therefore, data on the

average hand size and average grip strength is important in developing our

designs.

In order to accommodate the largest population possible, we decided to

model our designs to fit hand sizes of a 5th percentile female up to a 95th

percentile male. According to multiple sources [4,5], the 5th percentile female

hand size is around 16 cm, and the 95th percentile male hand size is around 20.5

cm.

A study performed by V. Mathiowetz et al. collected data on pinch and

grip strength from 310 adult males and 328 adult females, ranging from 20 to 94

years old. Since we are aiming to accommodate the largest portion of the

population, and the data was lowest in the female population while using the left

hand, we will only focus on these values. The mean grip strength for females in

the left hand was 24.4 kg with a standard deviation of 6.8 kg. However, one

drawback of this study is that it is aimed at maximum force output. A surgical

stapler must be fired multiple times and thus should be designed to use a lower

fraction of the maximum force[6].

B. Client Information

Dr. Amy Liepert is an assistant professor at the University of Wisconsin

School of Medicine and Public Health. She practices in acute care surgery, the

trauma and burn program, and surgical critical care programs.

C. Design Specifications

We will be designing and manufacturing either a prototype surgical stapler

or prototype attachment to an existing device. There are two main types of

models that are in need of a redesign, mechanical and battery-powered.

According to our client, the existing mechanical models are too large, and require

too much grip force to fire the staples. The battery-powered models are too bulky

and heavy, which causes strain in our client’s hands when used. Therefore, our

design must improve on the weight, force, or hand size accommodation of these

models while retaining the accuracy and reliability of the stapling mechanism. For

more, less substantial design considerations, see the Appendix.

III. PRELIMINARY DESIGNS

A. Design 1: Mechanical Redesign

Our first model is a complete redesign of the existing mechanical surgical

staplers. Our main goal in this design is to reduce the force required to depress

each lever and to decrease the angle between the levers and the hand grip, as

shown in the figure below. This model would include an improved ratcheting

mechanism, which utilizes multiple hand squeezes to drive the staples.

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Figure 5: Mechanical Redesign. This diagram depicts the internal

workings of a surgical stapler most similar to the Endopath ETS-Flex45. Our

ratcheting mechanism would help to reduce θ2 and make the grip more

manageable for users with a smaller hand size.

B. Design 2: Attachment to an Existing Device

Our second, and top rated design is an attachment that will be compatible

with an existing device that we have access to. Ideally, we would like to create a

product that is compatible with any device. This model will include adding an

ergonomic grip to the handle to improve comfort and aesthetic, as well as a

powered mechanism, such as a servo motor, that will assist the operator in

depressing the lever and driving the staples.

Figure 6: Attachment to an Existing Device. An example of an

ergonomic handle attachment. Image taken from: https://www.evanscycles.com/specialized-women-s-bg-contour-locking-grip-EV163242

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Figure 7: Attachment to an Existing Device. An example of a motorized

attachment controlling lever movement. Image taken from: https://www.sparkfun.com/products/9065

C. Design 3: Powered Variant-CO2

Our third design idea is a variant that will be a pneumatic pressure based

device. We will essentially be using CO2 cartridges to deliver a force. This will

eliminate any sort of manual force required to thrust the internal mechanism. The

CO2 cartridge is small, lightweight, and can supply enough thrust to drive the

internal mechanism.

Figure 8: Powered Variant-CO2. An example of a CO2 cartridge to be

used in a CO2 powered device. Image taken from: http://www.ebay.com/itm/12G-

Non-THREADED-Co2-CARTRIDGE-100-pack-12-gram-charger-airgun-airsoft-

paintball-/190601595596

D. Design 4: Powered Variant-Capacitors

Our fourth and final design is another variant of the powered surgical

stapler models. We will be using capacitors as an alternative to a battery pack in

an attempt to reduce the weight of the device. When designing this product, we

will incorporate a cycling mechanism to allow the operator to fire staples and cut

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tissue more than once during a single procedure. Relative to a battery, capacitors

are more environmentally friendly in the sense that they do not contain any

chemical elements. Capacitors are also cheaper than batteries. Both of these

attributes are beneficial, considering the entire device will be disposed of after

each procedure.

Figure 9: Powered Variant-Capacitors. Small electrolytic capacitors are

lightweight, simple circuit elements that would replace the battery pack on the

powered stapler. Each capacitor could be calculated to hold enough charge to fire

staples once, and a pack of capacitors with a cycling mechanism could allow for a

given number of discrete fires per pack. Image taken from: http://geoffg.net/Measuring_ESR.html

IV. PRELIMINARY DESIGN EVALUATION

A. Design Matrix

Criteria (weight)

Mechanical Redesign

Attachment to Existing Device

Powered Variant - CO2

Electrical Variant -

Capacitors

Ease of use (50 total)

• Weight of device (20) 3/5 12 1/5 4 4/5 16 4/5 16

• Minimize grip force (15) 2/5 6 4/5 12 5/5 15 5/5 15

• Grip size (15) 3/5 9 4/5 12 4/5 12 4/5 12

Ease of fabrication (30) 1/5 6 5/5 30 0/5 0 1/5 6

Manufacturing cost 2/5 16 5/5 20 3/5 12 3/5 16

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(20)

Total (100) 49 78 55 65

Table 1: Design Matrix. Each design idea was rated based on weighted criteria for the project.

An attachment to an existing device scored the highest based off of these criteria.

B. Summary of Design Matrix

The fully mechanical redesign of the stapler would be very difficult to

fabricate. Many of the internal workings of the device rely on gears and toothed

tracks to generate enough mechanical advantage to make it easy to clamp the

trigger. If the current models are not generating enough mechanical advantage,

that would mean we would need to adapt their system, incorporating different

gears or pulleys. This would be very difficult with the time that we are allowed

and with the skill levels of our team members.

The attachment design seems easier to fabricate, as we will only need to

be making some sort of new handle that adapts the old version. This handle will

have any features we choose to put in it, including, but not limited to, more

ergonomic grip, smaller gripping angle, and assistive motors for clamping the

triggering mechanism. The attachment would also be able to work with the

existing Ethicon brand devices that our client is currently using and would prevent

them from having to go through the process to approve and buy a new brand of

stapler. It would make the existing product more usable without requiring

hospitals to all switch to the brand which they think has the best product. All

hospitals will never be able to use just one brand, so the ability to make any

device more user friendly could be beneficial for hospitals locked into contracts

with stapler companies already.

The CO2 variant has a lot of safety concerns. Whenever pressurized gas is

being used there is difficulty in designing failsafes. If too much gas is released to

the stapling head, it could drive the staples with too much force and cause extra

bleeding. Likewise if it had a leak in the handle, it could build up pressure in the

unit itself and explode in the surgeon’s hand, or at least damage itself enough to

prevent further use. Likewise, utilization of CO2 would require a complete

redesign of the internals to use gas to drive the gears. Thus, it would be

impractical to design a safe enough model in the time we are given.

Capacitors are meant to store charge and then rapidly discharge. This

means that when the circuit closes its switch and the capacitor is able to

discharge, it will release all its charge at once. Initially we thought the staples

were fired more like they are in a stapling gun, where it’s an all or nothing

response. After more research, it is evident that they are in fact driven in a much

more controlled fashion. This would be difficult to do with capacitors. On top of

that, it would require the design of a cycling system that changes out the

capacitors in the pack so that each one is only used for one fire. This system

would likely be bulky and would not fit the design requirements.

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C. Proposed Final Design

We have elected to build an attachment to the existing devices. This would

address our client’s need regardless of device and would allow them to continue

using the Ethicon brand of surgical stapler which is already being used by

hospital. This will address many of the client’s problems, and give them an

alternative to buying the Covidien stapler.

V. REFERENCES

[1] H. Oreluk and J. Cherf, "Orthopaedic workforce trends," 1995. [Online].

Available: http://www.aaos.org/AAOSNow/2015/Sep/managing/managing1/?ssopc=1.

Accessed: Oct. 16, 2016.

[2] "Laparoscopic surgery - what is it?,". [Online]. Available:

https://www.fascrs.org/patients/disease-condition/laparoscopic-surgery-what-it.

Accessed: Oct. 16, 2016.

[3] U.S. Food and Drug Administration, “Surgical stapler information,” 2015.

[Online]. Available:

http://www.fda.gov/MedicalDevices/ProductsandMedicalProcedures/

GeneralHospitalDevicesandSupplies/ucm110739.htm. Accessed: Oct. 16, 2016.

[4] R. M. White, “Comparative anthropometry of the hand,” United States Army, pp.

1–186, 1981.

[5] G. I. of Technology, "Hand anthropometry," 2007. [Online]. Available:

http://usability.gtri.gatech.edu/eou_info/hand_anthro.php. Accessed: Oct. 16, 2016.

[6] V. Mathiowetz, Nancy Kashman, G. Volland, K. Weber, M. Dowe, and S. Rogers,

“Grip and pinch strength: Normative data for adults,” pp. 69–74.

VI. APPENDIX: Product Design Specifications:

Ergonomic Redesign of a Laparoscopic Surgical Stapler

Team Members:

Project Leader: Madelyn Goedland

Communicator: Justin DeShaw

BSAC: Gregory Wolf

BWIG: Alexander Babinski

BPAG: Jacob Andreae

Date of most recent update: October 16, 2016

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Function:

Surgical staplers have undergone many design modifications including the recent addition of

powered devices. Stapling devices are used both for intestinal resections and anastomoses, as

well as for vascular control. With the increase in female surgeons and an aging surgeon

population these devices must be fit to a wider demographic. We will be focusing specifically on

staplers designed for laparoscopic surgery.

Client requirements:

● Battery powered design adds a lot of weight and bulkiness; in general minimize weight.

● Have overall weight be balanced.

● Make both firing and closing triggers adaptable to multiple hand sizes. Current triggers

are designed for a size 9 hand, client has size 6 hand.

● Decrease the overall difficulty of using triggers (necessary grip power) and have device

remain easy to fire despite changing angles of use.

● Minimize wrist strain

Design requirements:

● We have access to limited manufacturing processes

● Our limited knowledge of medical surgical equipment protocols

1. Physical and Operational Characteristics:

a. Performance requirements:

The device should be able to withstand repeated use on one patient, allowing for

procedures involving multiple staples. The device should be reliable.

b. Safety:

The main concern with the device is the mechanical safety hazard of the clamping

and stapling mechanism. This mechanism must have proper safety features to ensure it

does not snap shut unless intended to.

c. Accuracy and Reliability:

Since surgical staplers are used to close vessels, the device has to be accurate in

staple placement, staggering them to prevent leakage.

d. Life in Service:

Each stapler is for single patient use. This lifespan would remain the same in any

new design, unless we devise a way to sterilize the device following all existing hospital

and surgical protocols. The amount of time the stapler is physically in use during surgery

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depends widely upon the specific type of surgery being performed, however laparoscopic

surgeries generally last approximately one hour.

e. Shelf Life:

The stapler comes in a sealed, sterile wrapper. There are no perishable

components to the device, so shelf it can be stored for long periods of time. Typical

storage conditions in the hospital are monitored and constant.

f. Operating Environment:

The operating environment of the device would be highly monitored, since

surgery conditions are kept very stable and sterile to ensure the quality of the procedure

and general safety of the patient. Surgical room standards include a temperature between

68-75°F, and humidity between 50-60%[1]. Surgeons are the only intended users of the

device. Variability in surgeon demographic would include hand strength, and hand size.

g. Ergonomics:

The device will hopefully be designed to accommodate a 5th percentile female to

the 95th percentile male hand size, which includes a range of 16 cm to 20.5 cm [2]. The

device will also be designed to limit the amount of force required to clamp the triggers,

factoring in average grip strength of female and elderly populations. Limiting the amount

of force will also reduce hand muscle fatigue, and eliminate the need for two handed

operation.

h. Size:

Stapler size should not be increased significantly from current models. Ethicon

models measure approximately 55cm long, with a 10cm long and 8cm thick handle.

i. Weight:

Our surgical stapler should not be significantly heavier than current models. An

attachment should be as light as possible. We have not yet had access to a scale to

measure provided staplers.

j. Materials:

The device should be made of metal and plastic. The materials should be durable,

and if possible sterilizable.

k. Aesthetics, Appearance, and Finish:

This device will be used during surgery; aesthetics and appearance are not

important when compared to proper function. Any part of the appearance or finish that

contribute to the overall ergonomic design of the stapler is important. The final shape and

function of the trigger and the gripping material used on the outer portion of it are the

primary ergonomic concerns.

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2. Production Characteristics:

a. Quantity:

Only one prototype surgical stapler or stapler attachment is necessary for this

project.

b. Target Product Cost:

Products are currently priced around $600 per unit, and these units are only used

for one surgery. Additionally, the cost of each staple cartridge costs roughly $100.

Therefore, the goal is to reduce both of these costs to make the device highly marketable.

If an attachment is designed, minimal cost is ideal.

3. Miscellaneous:

a. Standards and Specifications:

Since this device will be used for human surgery, it must comply with all relevant

FDA standards for human practice.

b. Customer:

Surgeons are the only customers of this product. Preferences expressed by our

client have been listed in previous sections.

c. Patient-related concerns:

The surgical stapler does not need to be sterilized since it is discarded after each

surgery. Allowing our device to be properly sterilized would allow for it to be reused and

reduce the cost.

d. Competition:

Surgical staplers were first invented in 1908 and have undergone many redesigns

since[3]. As a result, hundreds of patents on both staplers and specific stapler parts exist.

Modifications and attachments generally target the stapling end, and don’t assist with

grip diameter or gripping force.

References:

[1] F. P. Ellis and B. N. Staff, “THE CONTROL OF OPERATING-SUITE

TEMPERATURES ,” Br. J. Ind. Med., vol. 20, pp. 284–287, 1963.

[2] R. M. White, “Comparative Anthropometry Of The Hand,” United States Army, pp. 1–186,

1981.

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[3] F. Robicsek, "THE BIRTH OF THE SURGICAL STAPLER," (in English),

Surgery Gynecology & Obstetrics, Article vol. 150, no. 4, pp. 579-583, 1980.