adaptable retractor for total hip replacement...
TRANSCRIPT
1
Department of Biomedical Engineering
Design of Biomedical Engineering Devices and Systems
Adaptable Retractor for Total Hip Replacement Surgery
Team Members Trey DeLong (BME)
Lacey Gorochow (BME) Brian Rappa (BME)
Adam Vandergriff (BME) Sandra Wadeer (BME)
Advisors
Dave Martinez Dr. Michael Christie
Dr. Paul H. King
Submission April 26, 2011
Vanderbilt University, Nashville TN
2
Table of Contents
Abstract .................................................................................................................................................... 3
Introduction ............................................................................................................................................ 4
Methodology ........................................................................................................................................... 6
Results ..................................................................................................................................................... 12
Conclusion ............................................................................................................................................. 17
Recommendations .............................................................................................................................. 18
References ............................................................................................................................................. 19
Appendix A: Design Safe Results .................................................................................................... 21
Appendix B: Innovation Work Bench ........................................................................................... 24
3
Abstract
The Journal of Orthopedics states that 24 to 36 percent of patients who have undergone
total hip replacement surgery are overweight. Overweight patients have excess adipose tissue,
and multiple retractors are needed in surgery to displace the tissue to gain clear sight of the
hip. Two undesirable consequences stem from this situation: less available workroom for the
surgeon to operate, and more cost for the hospital included in the cost of the retractors, and
the cost of the surgical technicians to hold these retractors. The goal of this project was to
design an adaptable retractor that eliminates one retractor during total hip replacement
surgery in order to increase the viewing capabilities for the surgeon and decrease surgical costs.
In addition, the designed hip retractor should be able to be simply manufactured out of an
inexpensive, easily sterilized material, and have the ability to adequately retract adipose tissue.
Our final design consists of a retractor and connecting adapter piece. In order to attach the
adapter to the retractor, we designed a clip on the adapter, and guide rails on the retractor,
that would hold the adapter in place. In order to accommodate varying patient sizes, we
designed a round top adapter, lofted adapter, double-sided versions, and mirror versions of
each type of adapter. We analyzed the mechanics of our device using MATLAB and Finite
Element Method analysis, and observed that the device would be strong enough to withstand
tissue loads. After performing a cost benefit analysis, we estimated that implementation of our
device would save hospitals $2.8 million a year. Further analysis with a stainless steel
prototype would allow us to gain insight into the ability for the device to be sterilized, and its
physical application in surgery. Our design concept is considered a success because of its
simplicity, and ability to be adapted for use in other types of surgeries.
4
Introduction
Total hip replacement surgery is a medical procedure that involves removing a diseased
hip joint and replacing it with an artificial joint (Mayo Clinic 2011). The procedure requires the
use of a retractor, which is a stainless steel surgical instrument available in multiple shapes and
sizes (Figure 1), that function to hold back adipose tissue and increase the incision window
(Conditions 2011).
Currently, there are
more than 193,000
total hip
replacement
surgeries performed each year in the United States (Total 2009). People who are overweight
have a high risk of hip arthritis and the Journal of Orthopedics claims that 24 to 36 percent of
patients who have undergone total hip
replacement surgery are overweight (Wegner et
al 2009). Overweight patients have excess
adipose tissue, and in order to gain clear sight of
the hip, up to five retractors are required (Figure
2). Two undesirable consequences stem from this
situation: less available workroom for the
surgeon to operate, and more cost for the
hospital included in the cost of the retractors, and the cost of the surgical technicians to hold
these retractors.
Figure 2. 5 retractors used to hold back adipose tissue in a total hip replacement surgery for an obese patient
Figure 1. Various hip retractors: Hibbs (left), Sofield (middle), and Ischium (right)
5
In order to gain better understanding of the problems faced during a surgical procedure
our design team observed a total hip replacement surgery performed by Dr. Michael Christie,
an orthopedic surgeon at St. Thomas Hospital. First-hand experience of the difficulties faced in
the hip replacement surgeries was very informative and shaped our overall design process.
During the procedure Dr. Christie identified several obstacles, which hindered the overall
efficiency of the surgery. The operation is
conducted via the surgical window, an
incision approximately 12 to 16 cm in
length, depending on patient size, and can
be stretched to 7 to 8 cm in width. This
window is maintained using several surgical
retractors that pull and stretch the tissue
giving the surgeon a dynamic window, which
can be slightly shifted during the operation to change the surgeon’s visual orientation to the
hip. In obese patients this surgical flexibility becomes compromised as the amount of tissue
needed to be displaced to gain clear sight to the hip increases. Contemporary surgical
retractors are not wide enough to sufficiently hold back excess adipose tissue, and as a result
the tissue wraps around the retractor and interferes in the surgery. Therefore additional
retractors are needed to hold back the excess tissue, decreasing the flexibility of the surgical
window. Furthermore, additional surgical technicians, who are paid $20 an hour, are needed to
operate the retractors, crowding the surgery area (Figure 3), and reducing the surgeon’s overall
flexibility in the procedure (Overview of BLS 2011).
Figure 3. Surgeon’s workroom obstructed by crowding surgical technicians holding retractors in place
6
Dr. Christie’s solution to the problem would be to develop a new type of surgical
retractor, which would be able to sufficiently hold back the excess adipose tissue found in
obese patients, preventing the tissue from falling into the surgical window. Such a retractor
must be robust enough to endure the strenuous use in a surgical environment, non-disposable
to limit needless material waste, and simple enough to use without compromising surgical
flexibility.
A previous design team created a single adjustable retractor prototype that could not be
used in surgery. Additionally, their original design was complex and consisted of multiple small
pieces, which is impractical for total hip replacement surgery. As a result, the aim of the
present project is to improve the design created by the previous team, and to create a device
that is more effective in total hip replacement surgery.
Specifically, the goal is to design an adaptable retractor that eliminates one retractor
during total hip replacement surgery in order to increase the viewing capabilities for the
surgeon and decrease surgical costs. In addition, the designed hip retractor should be able to
be simply manufactured out of an inexpensive, easily sterilized material, and have the ability to
adequately retract adipose tissue in total hip replacement surgery.
Methodology
Initial Design Phase
To address our design requirements, we first brainstormed concept ideas. Each
member of the team constructed a sketch of an ideal design, and presented it to the rest of the
team. By each person presenting his or her own idea, we were able to collaborate on different
concepts. Our first design concept was to use design a system similar to a cheek retractor, and
7
keep the retractor inside the incision from beginning to end of the surgery (Figure 4). This
design would be made out of a plastic disposable material, and would be a hands-free device,
allowing the surgeon ample work room. Another design concept was to attach a wing-shaped
piece to the retractor through a sliding method. The retractor would have two guides attached
to it, and the attachment piece would have two slots that could glide along the retractor, and
allow the surgeon to rotate the attachment piece along the guides on the retractor (Figure 5).
This design would be made out of stainless steel, and not be disposable.
After analyzing these designs further, and discussing the concepts with our advisor, and
Dr. Christie, we decided there were several things wrong with each design. According to Dr.
Christie, the first design would not be strong enough to hold back the adipose tissue because it
would be made out of a disposable plastic. In addition, since this design would be stationery
throughout the surgery, it would not allow the surgeon to move the incision window around, as
necessary. The second design concept was flawed because it of the slots in the adapter piece.
These slots would cause concentrated stress at these areas, and would not allow for optimal
strength in the design.
Figure 4. Design idea one: based off cheek retractor.
Figure 5. Design idea two: consisting of sliding mechanism. The guides are on the back of the retractor.
8
Although there were flaws involved in these two designs, some of the concepts within
the design were beneficial. The first design included curvature, which would easily hold back
adipose tissue. The second design offered a way to attach the adapter piece through guide
rails, and offered the surgeon to easily move the incision window around. We used these
beneficial concepts in our final design.
Final Design
Our final design consists of a retractor and connecting adapter piece (Figure 6). In order
to attach the adapter to the retractor, we designed a clip on the adapter, and guide rails on the
retractor, that would hold the adapter in place, yet allow it to be easily removed from the
retractor, once the surgeon is done with the surgery. The retractor has five rails on the front
side, away from the tissue, which hold the adapter in place vertically (Figure 7). The dimensions
of the retractor are based on the incision depth and current hip retractors. The flat part of the
retractor is 14 cm long and the handle is 17 cm long to allow the surgeon to have ample
leverage when retracting the tissue. The ending tip of the retractor has a 2 cm radius to allow
the surgeon to hook the retractor into the pelvic bone.
The clip on the adapter fits onto the retractor very closely in order to prevent any
twisting movement. To prevent the adapter from sliding off of the retractor, there will be a
small dimple placed in the retractor and a complementary bump placed on the adapter. These
additions will work since the metal clip flexes slightly under loads, but will be small due to the
forces necessary to cause significant strain. This feature is not on the plastic retractors since it is
too small for the fabrication process and could cause the plastic prototypes to break.
9
To design the curvature of the adapter, we considered the length, width and depth of
the incision size of a total hip replacement surgery. Using the video from our observation of
total hip replacement surgery with Dr. Christie, we measured the length of the incision, as well
as the dimensions created by using the retractor to pull back the skin (Figure 8). The retractor’s
pull on the incision creates an ellipse, as
seen in Figure 8. We calculated the major
(14.8 cm) and minor axes (8 cm) and then
used the created ellipse as a path for the
adapter to be swept across.
In order to accommodate different
patient sizes, the adapters are made in
different shapes. We designed two different shapes, the round top adapter and the lofted
adapter. The round top adapter curves away from the retractor, at a radius of 1.2 cm, at the
top to envelop and hold back adipose tissue (Figure 9). The lofted adapter is flush with the
retractor, but curves outward with increasing distance from the retractor (Figure 10). The
feature of the lofted adapter allows the adapter piece to not pinch the skin of the patient when
the retractor pulls back on the assembly. The dimensions of the adapters were also based on
the incision size. The length, height, and thickness of each adapter are 9 cm, 6 cm and 0.3 cm
respectively. To accommodate very obese patients who require an incision size of 16 cm, the
retractors are made in double-sided styles (Figure 11). The double sided lofted adapter extends
to a 14 cm length, and the double sided round top adapter extends to a 15.5 cm length, while
keeping the height and curvature of the pieces the same as the one sided adapters. The one
Figure 8. Incision window of THR. Length of incision: 12-16 cm, Width: 7-8 cm, Depth: 4-15 cm. Ellipse over incision window represents curvature of adapter piece. (Major axis: 14.8 cm, minor axis: 8 cm)
10
sided style also requires that mirrored versions be made since the procedure occurs from
different directions for the right hip compared to the left hip (Figure 12). Along with the
different styles, different sizes can be made. The choice of which adapter will be used is left up
to the surgeon. There are slight differences in the procedure for each surgery, so this will allow
for the surgeon to use the adapter that best fits the patient and his style. With different sets of
adapter pieces, the surgeon can choose any type of adapter piece, and slide it onto the
retractor, at varying spots on the retractor. The different levels of guides on the retractor also
allow the surgeon to connect multiple adapter pieces at one time. With this system of devices,
many combinations are possible, which gives the surgeon greater flexibility in his or her choice
of tools for the procedure.
In order to develop a better understanding of our design, we developed an ABS plastic
prototype of the retractor and all connecting adapter pieces. Eventually we will make our
design out 17-4 Precipitation Hardening (17-4 PH) stainless steel. This material is composed of
15.5% chromium, 4.5% nickel, and 3.5% copper (Product Data 2007). It is beneficial to be used
in surgery because it is highly corrosion resistant, and it has a high ultimate tensile strength of
1000 to 1340 MPa (Product Data 2007). In addition, it can maintain its strength up to 600°F,
which is important when sterilizing the device before surgery (Product Data 2007).
11
Figure 9. Lofted adapter. Flush against retractor, and increasing curvature to envelop tissue. Length: 9 cm, Height: 6 cm, Thickness: 0.3 cm.
Figure 10. Round top adapter. Fully rounded across top to envelop tissue. Same length, height, thickness as Figure 9. Top curvature: 1.2 cm radius.
Figure 7. Retractor with five guide rails to allow for varying heights of adapter location, or addition of multiple adapters. Flat region with rails: 14 cm, Handle: 17cm.
Figure 12. Left: mirrored version of lofted adapter. Right: mirrored version of round top adapter.
Figure 11. Left: Double sided version of lofted adapter (14 cm length). Right: Double sided version of round top adapter (15.5 length).
Figure 6. Assembly of retractor and lofted adapter.
12
Results
Mechanical Analysis
In order to analyze whether our design was strong enough to hold back adipose tissue,
we first used MATLAB to determine the forces that would be applied to the device by the
tissue. We then applied these forces in Finite Element Method (FEM) analysis to determine the
stresses and displacement of the device when used in surgery.
The tissue was modeled to determine the forces applied to the retractor. The MATLAB
PDE Tool Box was used to determine the approximate stress required to retract the tissue
enough for adequate viewing for the surgeon. The MATLAB program uses partial differential
equations and stress-strain equations with the tissues’ mechanical properties to create stress-
strain distributions based on boundary condition. The tissue itself was modeled as a 30 cm by
30 cm square fixed on all sides with 0
strain. This will produce the maximum
load on the retractor as generally tissue
will deform and reduce stress. A whole
was created 14 cm long to simulate the
incision (Figure 13). A set strain was
applied to one side to open the incision
to 8 cm, simulating an applied retractor. These values were based on our observations in
surgery. The Young’s modulus of the tissue was assumed to be 200 Pa and the Poisson’s ratio
of .495 from experiments done with breast tissue (Krousko 1998). After running the model, the
Figure 13. Stress distribution based on tissue modeling
13
maximum stress was found to be 300 Pa applied to the retractor piece. Assuming this maximum
stress across the whole adapter piece, a maximum force of 1.5N was obtained.
We used these results, to apply appropriate pressures and forces to the retractor
system. Using FEM analysis in Autodesk Inventor, we applied 300 Pa pressure to the adapter
piece, and a 1.5 N force on the retractor handle. The assembly of retractor and adapter piece
was constrained at the bottom surface of the retractor to simulate the retractor being held in
position by the pelvic bone. The loads simulate a surgeon holding back the retractor in the
incision. As shown in Figure 14, the maximum Von Misses stress, 20.93 MPa, occurred below
the location of where the adapter piece connects to the retractor. The addition of the adapter
piece onto the retractor piece actually strengthens the retractor. The minimum Von Misses
Stress was 0 MPa, and occurs where
the retractor is constrained, and along
the retractor where the adapter piece
is placed, and along the adapter piece.
Above and below the attachment site,
8.37 MPa stress occurs.
Figure 15 depicts the amount
of displacement when the appropriate
loads are applied. The maximum displacement occurred at the tip of the retractor where the
1.5 N load was applied. No displacement occurred at the bottom of the retractor or directly
above the connection site between adapter piece and retractor. A gradual increase of
Figure 14. Maximum Von Misses stress is 20.93 MPa.
Figure 15. Maximum displacement is 1.226 mm.
14
displacement occurred from the point of bending in the retractor (the beginning of the handle)
to the tip of the handle.
Although the maximum stress did occur on the retractor near the adapter piece, 20.93
MPa is a negligible amount of stress for 17-4 PH stainless steel. The ultimate tensile strength of
17-4 PH is 1000-1340 MPa (Product Data 2007). The maximum displacement, 1.226 mm, is also
negligible. Both the stress and displacement results show limited effect on the adapter piece
and retractor. Therefore, our design will be strong enough to hold back adipose tissue.
Safety Considerations Safety is a main concern for our design because our retractor system will be used in
surgery. Appendix A outlines the safety analysis of our design using Design Safe. Three of the
main safety concerns include: the device’s ability to puncture the patient or surgeon, the ability
for the adapter piece to come apart from the retractor in surgery, and the device’s capability of
causing infection in the patient or surgeon. The retractor has the ability to puncture the patient
because it is a heavy piece of metal with a tapering end. When the surgeon places the retractor
in the incision, it could potentially puncture the patient’s muscle or adipose tissue if not
properly used. To avoid severing of any blood vessels, our design does not feature any sharp
edges or corners. All of the edges are rounded with fillets. The surgeon himself could be hurt
by the retractor if the surgeon does not properly assemble the adapter piece and retractor
together. His or her fingers could be pinched if somehow they were caught between the clip of
the adapter and the retractor. To prevent this from occurring, an instruction manual will be
provided with the packaging of the retractor system.
15
While in surgery, the retractor and adapter piece could potentially come apart. To
prevent this from occurring, a small dimple will be made in the retractor, along with a small
bump in the clip of the adapter piece (as explained earlier in the methodology). When the clip
slides over the retractor, the bump will catch into the indentation, and snap into place. Adding
this small detail into the steel retractor will ensure a secure connection between adapter piece
and retractor.
Another major safety concern is the risk of infecting the patient during surgery. The
patient could be infected with another patient’s blood borne disease if the device is not
properly sterilized after and before surgery. The current procedure for sterilizing surgical
instruments involves autoclaving. Autoclaving consists of subjecting the surgical instrument to
a high pressurized steam at 273° C for two minutes (VWR 2011). This pressurized heat kills all
of the bacteria, fungi, viruses and prions that could inhabit the retractor system. To ensure that
our device could be properly sterilized, the material that we will use for the retractor and
adapter piece is 17-4 PH stainless steel. This type of stainless steel is able to maintain its
ultimate tensile strength up to 315.5° C. Therefore, during autoclave, the device will be able to
be sterilized without falling apart or weakening the device.
FDA Standards In order for our device to be used for surgery, it must be approved by the Food and Drug
Administration (FDA). According to the FDA, a retractor is a Class 1 device, and is classified as,
“a manual surgical instrument that is a nonpowered, hand-held, or hand-manipulated device,
wither reusable or disposable, intended to be used in various general surgical procedures”
(FDA, 2010). The FDA also classifies a retractor as being exempt from premarket notification
16
procedures, but not exempt from Good Manufacturing Practice (GMP). A premarket
notification application, or 510K submission is not required before marketing the device in the
U.S., but the manufacturers are required to register their establishment (FDA 2011). In order
for our retractor device to be manufactured, it must follow FDA regulations of GMPs, which
represents a quality assurance program that evaluates the manufacturing, packaging, storage,
distribution, and installation of the adaptable retractor (King 2009).
Economic analysis. In order to determine if our implemented device would eventually save hospitals
money, we performed a cost benefit analysis. Using the Bureau of Labor Statistics, the average
wage for a surgical tech is $20 per hour (Overview of BLS 2011). Given that surgery generally
takes 2 to 4 hours, every additional surgical tech costs $40-80 extra per surgery. Also, the
average retractor used in total hip replacement surgery costs $1150. Assuming each retractor is
used once a week for five years, the expected life for a retractor is approximately 250 uses.
This results in a cost of $4.60 per retractor per surgery. The estimate for the number of
retractors used for soft tissue retraction in an obese patient’s surgery is 3 with 2 techs having to
hold the retractors. This brings the total cost for factors involved with the surgery to $93.80 per
surgery.
Our advisor has estimated the retail of our devise to $1400 based on
production/distribution costs and desired return. However, we expect to reduce the number of
retractors used to two, and the surgical technician to one per surgery. This reduces the prices of
the effected factors from $93.80 to $51.20 per surgery; this is a savings of $42.60 per surgery.
17
Given the large number of surgeries a year, this has potential to a cumulate savings
quickly. Earlier we assumed our devise would be used an average of once a week per year.
Therefore one devise would save $2,130.00 per devise for every year. Using our estimated life
of five years, the total savings from one purchase of the device would be $10,650. Nationwide
there are 193,000 total hip replacement surgeries a year. Using the NY Times estimate of an
adult obesity rate of 34%, this brings the number of total hip replacements on obese patients to
65,620 surgeries. Taking the general population of obese patients and the savings of $42.60
per surgery, the total industry wide savings would total $2.8 million/year. Also, our devise is
highly adaptable to multiple forms of surgery, allowing it to be customized to a variety of
surgeries and increasing the potential savings dramatically.
Conclusion
Advisors’ Opinion After completing our design, we once again met with Dr. Christie for him to observe our
device and receive feedback. Dr. Christie was pleased with our design, and said that our device
was the “best one yet.” He commented that our design was flexible enough to be used in
different types of surgeries. For example, the design could be adapted for larger surgeries, such
as abdominal surgeries, or it could also be adapted for smaller surgeries, such as brain
surgeries. Dave Martinez also expressed satisfaction with our retractor design. Specifically he
said it took a fresh pair of eyes to solve the design problems. Dr. Christie also focused on the
idea that the retractor system could be customized for each different type of surgery. The idea
of customization would limit the number of retractors needed for surgery, and ultimately save
the hospital money.
18
Final Analysis
Based off of the opinions of both our advisors and the computer simulations, we have
determined the prototype design meets our original goals for a simple and adaptable design.
The simplicity of the design will also allow it to be used in surgeries beyond the scope of our
project. Using the stress modeling results, we can establish that the design will be able to
withstand the forces in surgery and can be safely used without failure. Since the model was not
produced in stainless steel, due to financial complications, it remains untested in surgery.
Therefore its sterilization and retraction of soft tissue could not be validated. Also, the general
costs of the device were based on our advisor’s opinion. The cost benefit analysis is only an
estimate because the exact cost saving potential is subject to change. However, given that it is
a widely adaptable design to multiple surgeries, the design has a variety of medical markets and
therefore has a high likelihood of developing several if not many profitable products. Therefore
design rights would be considered valuable and the goal of cost reduction has been meet.
Ultimately, the adapter design concept is considered a success, but its physical application still
remains unproven in surgery.
Recommendations
Future improvements may be made to the original design in order to increase the
device’s efficiency in surgery. The next step in the design process is to manufacture a
completed stainless steel device which could be used in a surgical environment. Additional
attachment pieces can be manufactured with alterations in shape and size. With a set of
different retractor attachments, the surgeon will have the flexibility to choose which piece will
be most appropriate given the patient’s specific body type. This will allow the surgical staff to
19
reduce the number of retractors prepared for surgery, and instead have only a few customized
instruments ready for use which fit the patient’s specific needs. Given the potential for great
variability and customization, the retractor adapter design is not limited to total hip
replacement procedures but can be implemented in many different types of surgery as well.
Lastly, a future a step would be to patent our design. After conducting an extensive patent
search online, there were no similar designs that were patented that were similar to our design.
Since no patents were similar to our design, our design has a great potential to be patented and
manufactured in the future.
References
Conditions, Diagnostic. "Surgical Retractors, Medical Retractors, Hand Held Retractor, Surgical
Retractor Manufacturers." Surgical Instruments, Surgical Medical Instruments, Surgical
Instruments Manufacturers, Medical Instruments Manufacturer. 2011.
<http://www.surgicalsindia.com/surgical-retractors.html>.
FDA. “Code of Federal Regulations Title 21.” U.S. Department of Health and Human Services.
2010.http://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfcfr/CFRSearch.cfm?fr=878.4
800.
FDA. “Product Classification.” U.S. Department of Health and Human Services. 2011.
http://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfPCD/classification.cfm?ID=4886
Ilizaliturri, Victor et al. Small Incision Total Hip Replacement by the Lateral Approach Using
Standard Instruments. Web Image. Orthopedics April 2004;27(4):377
<http://www.orthosupersite.com/view.aspx?rid=1889>.
Innomed Orthopedic Instruments. Innomed Incorporated. 2010. Web Image. 21 April 2011.
20
<http://www.innomed.net/hip_rets_extra.htm>.
King, Paul and Fries, Richard. Design of Biomedical Devices and Systems. CRC Press, Boca Raton,
FL. 2009.
Krouskop, Thomas A., Thomas M. Wheeler, Faouzi Kallel, Brian S. Garra, and Timothy Hall.
"Elastic Moduli of Breast and Prostate Tissue under Compression." Ultrasonic Imaging
20 (1998): 260-74. Web. 5 Apr. 2011.
<http://www.uth.tmc.edu/schools/med/rad/elasto/download/98/98krouskop.pdf>.
Mayo Clinic. "Hip Replacement - MayoClinic.com." Mayo Clinic. Web. 12 Apr. 2011.
<http://www.mayoclinic.com/health/hip-replacement/MY00235>.
“Overview of BLS Wage Data by Area and Occupation,” Bureau of Labor Statistics. United
States Department of Labor. 2011. http://www.bls.gov/bls/blswage.htmStaff,
“Product Data Bulletin: 17-4 PH Stainless Steel,” AK Steel.
http://www.aksteel.com/pdf/markets_products/stainless/precipitation/17-
4_PH_Data_Bulletin.pdf
"Total Hip Replacement - Your Orthopedic Connection - AAOS." AAOS - Your Orthopedic
Connection. 2009. http://orthoinfo.aaos.org/topic.cfm?topic=a00377.
Wegner et al. Comparison of the BMI of Hip Replacement Patients. J. Orthopedics.
J.Orthopaedics 2009;6(4)e4. 2011. <http://www.jortho.org/2009/6/4/e4/index.htm>.
“VWR Lead Free Autoclave Instruction Sheets,” 2011.
https://www.vwrsp.com/catjpg/stibo/low_res/VWR_Autoclave_Tape_Operation_Manu
al.pdf.
21
Appendix A: Design Safe Results
22
23
24
Appendix B: Innovation Work Bench
Ideation Process Innovation Situation Questionnaire 1. Brief description of the problem Current retractors used in total hip replacement surgery have a singular use that does not provide adequate vision for the surgeon in obese patients. Much of the soft tissue continues to cover the joint, obstructing the operation. The object of the design project is to produce multiple modular adapters to existing retractors for a variety of patient sizes in order to:
Reduce cost
Increase the vision and work room for the surgeon
Produce functional modular adaptations ready for use in the operating room 2. Information about the system
2.1. System name Adaptable Retractor for Total Hip Replacement Surgery
2.2. System structure Handheld retractor with modular adapter which can easily be attached to contemporary retractors.
2.3. Functioning of the system
The function of the device is to retract excess adipose tissue during total hip replacement surgery.
2.4. System environment Total hip replacement surgery, hospital operating room. 3. Information about the problem situation 3.1. Problem that should be resolved
During total hip replacement surgery of obese patients excess adipose tissue obscures the surgeon’s field of vision. Contemporary soft tissue retractors are unable to effectively keep excess tissue from interfering in the surgical procedure and as a result multiple retractors and surgical technicians are needed to alleviate the problem. The design of a modular adapter which can attach to current retractors will
3.2. Mechanism causing the problem
25
Obese patients are difficult to operate on because the excess adipose tissue which limits the surgeon’s field of vision and mobility during surgery.
3.3 Undesired consequences of unresolved problem
Poor surgical field of vision
Additional retractors needed during surgery
Additional surgical technicians required
Increase cost for additional materials and personnel 3.4 History of the problem
Total hip replacement surgery is a common surgical procedure to alleviate hip pain and loss of mobility. Arthritis and traumatic injury are the leading causes for chronic hip pain and joint disability. Currently in the United States more than 193,000 total hip replacements are performed each year (Orthoinfo). Similar surgical procedures are also performed on other joints, such as the knee, shoulder, and ankle. The procedure aims to reduce hip pain and increase joint mobility in order to improve the patient’s ability to perform common daily activities. The surgical procedure involves replacing the damaged femoral head and acetabulum with artificial hip prostheses, consisting of a femoral component and an acetabular component. Current tissue retractors being used in the surgical procedure ensure the surgeon has a clear field of vision, but there are a few complications. The retractors do not provide the surgeon with simple use and flexibility when dealing with excess soft tissue in the surgical area. A retractor adapter for soft tissue protection and retraction is needed to facilitate orthopedic total hip surgical procedures.
3.5 Other systems in which a similar problem exists Surgery on obese patients 3.6. Other problems to be solved Modular adapter that can easily fit all contemporary retractors 4. Ideal vision of solution A simple device that provides a means of retracting excess soft tissue during total hip replacement surgeries which can be easily massed produced, sterilized, held by an individual for an extended period of time with no discomfort, and is cost effective. 5. Available resources Contemporary soft tissue retractors, modeling software, 6. Allowable changes to the system Curvature of modular adapter, attachment mechanism 7. Criteria for selection solution concepts
Design must be simple to allow for easy manufacturing
26
Must be cost effective
Efficiently retracts excess soft tissue
Practical design and ease of use for surgeons 8. Company business environment 9. Project data
Adaptable Retractor for Total Hip Replacement Surgery Project Advisor: Dave Martinez VP of Sales Zimmer, Inc Team members: Jack DeLong [email protected] Brian Rappa [email protected] Lacey Gorochow
[email protected] Sandra Wadeer
[email protected] Adam Vandergriff
27
Timeline:
Problem Formulation 1. Build the diagram
2. Directions for innovation
5/211/186/6
Visit Surgery
Design Sketches
3 Pro/E Design…
Final Pro/E Design
Prototype…
Complete…
Presentation
StartDateCompleted
28
Prioritize Directions Prioritizing Directions 1. Attachment mechanism is simple to attach in surgery, and it attaches to a more types of retractors to simplify the adapter's design functionality. 2. Find a way to use the adapter in surgery without attaching to most retractors or having to be easily sterilized. 3. Find a way to be easily sterilized without being affected by the cheap material. 4. Find a cheap material that does not reduce durability or cause sterilization problems and results in greater reduction in cost. 5. Find a durable material that is not affected by being cheap and lasts longer to result in reduction of maintenance or replacement costs. 6. Develop a simple manufacturing process for a more complex design, and adjust it to further reduce labor or material costs. 7. Find any way to reduce cost in addition to utilizing cheap or durable materials, less personnel, and simple manufacturing techniques or increase the effects of those factors. 8. Find a way to have a device that can be Useful in a variety of patient sizes that enhances the retraction of adipose tissue without relying on a complex design. 9. Find a way to retract adipose tissue that can reduce the number of retractors and increases surgical view. 3. Find way to eliminate complex design but does not compete with simple manufacturing, the ability for the adapter to attach to most current retractors, the ability for it to be useful in a variety of patient sizes. 4. Find a way to have a device with multiple sized adapters which reduces cost but is not affected by complex design 5. Find a way to increase surgical view by reducing personnel and retracts adipose tissue. 6. Find a way to reduce personnel in operating room (OR) by reducing the number of retractors necessary in the OR, thus reduces cost for the hospital. 7. Find a way to reduce the number of retractors used in hip surgery which would reduce personnel in the OR and is still able to retract sufficient adipose tissue.
29
Develop Concepts 1. Combine Ideas into Concepts. After combining all of our ideas during our brainstorming sessions we have decided to design an accessory attachment with hooks that can securely attach to the retractor for use during surgery. The design will allow us to meet the goal of eliminating another retractor in surgery because the attachment will be wide enough to hold back the tissue that the former retractor was holding back. 2. Apply Lines of Evolution to Further Improve Concepts After producing our design of the accessory attachment for the retractor successfully, we will research ways to make the accessory expandable to eliminate even another retractor in the surgery, which will thus eliminate another person in the operating room. Evaluate Results 1) Meet criteria for evaluating concepts
a. Sterilization: i. Make of easy to sterilize metal ii. Make out of disposable/one time use material
b. Cheap material i. Use the most cost effective material that will last the longest ii. Use a cheap material that is one time use
c. Useful for various patient sizes i. Complex design that fits multiple patients in one adapter ii. Make simple design that consists of multiple adapters
2) Potential failures
a. Failure to be properly sterilized before repeated use. b. Failure to last through an entire procedure c. Strong material is too expensive d. Complex design is difficult produce or sterilize e. Simple design with multiple adapters presents too many options for surgeon
3) Plan the Implementation
a. Short term: Develop adapter with necessary properties to retract adipose tissue b. Midterm: Develop multiple adapters for various sizes c. Long term: consider alternative materials to further reduce costs