ERGONOMIC REDESIGN OF A SURGICAL STAPLING DEVICE

Transcription

1 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. 1

2 TABLE OF CONTENTS I. Introduction A. Motivation B. Existing Devices C. Problem Statement II. Background 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-CO 2 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 VI. Appendix: Product Design Specifications

3 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 The majority of fulltime 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 3

4 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: 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: 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 4

5 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: 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: 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 5

6 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. 6

7 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 θ 2 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: 7

8 Figure 7: Attachment to an Existing Device. An example of a motorized attachment controlling lever movement. Image taken from: C. Design 3: Powered Variant-CO 2 Our third design idea is a variant that will be a pneumatic pressure based device. We will essentially be using CO 2 cartridges to deliver a force. This will eliminate any sort of manual force required to thrust the internal mechanism. The CO 2 cartridge is small, lightweight, and can supply enough thrust to drive the internal mechanism. Figure 8: Powered Variant-CO 2. An example of a CO 2 cartridge to be used in a CO 2 powered device. Image taken from: Non-THREADED-Co2-CARTRIDGE-100-pack-12-gram-charger-airgun-airsoftpaintball-/ 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 8

9 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: IV. PRELIMINARY DESIGN EVALUATION A. Design Matrix Mechanical Redesign Attachment to Existing Device Powered Variant - CO2 Electrical Variant - Capacitors Criteria (weight) 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 9

10 (20) Total (100) 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 CO 2 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 CO 2 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. 10

11 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," [Online]. Available: Accessed: Oct. 16, [2] "Laparoscopic surgery - what is it?,". [Online]. Available: Accessed: Oct. 16, [3] U.S. Food and Drug Administration, Surgical stapler information, [Online]. Available: GeneralHospitalDevicesandSupplies/ucm htm. Accessed: Oct. 16, [4] R. M. White, Comparative anthropometry of the hand, United States Army, pp , [5] G. I. of Technology, "Hand anthropometry," [Online]. Available: Accessed: Oct. 16, [6] V. Mathiowetz, Nancy Kashman, G. Volland, K. Weber, M. Dowe, and S. Rogers, Grip and pinch strength: Normative data for adults, pp 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,

12 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 12

13 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 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. 13

14 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 , [2] R. M. White, Comparative Anthropometry Of The Hand, United States Army, pp ,

15 [3] F. Robicsek, "THE BIRTH OF THE SURGICAL STAPLER," (in English), Surgery Gynecology & Obstetrics, Article vol. 150, no. 4, pp ,