Pediatric Splints
Progress Report
BME 401A Group 16
Yoon Kim, Kearsten Miller, Kaitlin Donlon
12/1/22
Table of Contents
1. Background and Project Updates
1.1: Updated Need Statement
1.2: Updated Project Scope
1.3: Updated Design Specification
1.4: Updated Team Responsibilities
2. Design Alternatives
2.1: Circumference Adjustable Using Velcros and Elastic Bands
- 2.1.1: Velcro Straps
- 2.1.2: Elastic Bands
2.2: Circumference Adjustable Using Screws and Knobs
- 2.2.1: Screws
- 2.2.2: Knobs
2.3: Circumference Adjustable Using Flexible Material
- 2.3.1: Bendable Plastic
- 2.3.2: Elastic Sleeve
- 2.3.3: Expandable Fabric
2.4: Circumference Adjustable Using Inflation
3. Analysis of Solutions
3.1: Pugh Chart
3.2: Analysis of Pugh Chart
4. Overview of Chosen Solution
5. Proposed Budget
5.1 Estimated Cost
5.2 Funds Request
6. References
Appendix A: Revised Need Statement
Appendix B: Revised Project Scope
Appendix C: Revised Design Specifications
Appendix D: Revised Team Responsibilities
1. Background and Project Updates
The primary objective of this project is to develop a size-adjustable arm splint that covers from the forearm to above the elbow and is suitable for pediatric patients from 18 months to 13 years old. Such a splint will significantly reduce the time spent creating a unique splint for every pediatric patient. This progress report outlines the changes made to the initial project scope, need statement, and design specifications, analyzes alternative solutions, highlights the ideal design alternative, and provides an overview of the chosen solution and an estimated proposed budget.
1.1. Updated Need Statement
The need statement was revised, as shown in Appendix A, to clarify the number of pediatric patients per year that need arm splints and the target area where they are most needed to address feedback received on the preliminary report.
1.2. Updated Project Scope
The project scope was rephrased based on feedback. Unnecessary components not part of the scope were removed, as shown in Appendix B.
1.3. Updated Design Specifications
Slight adjustments were made to the original list of design specifications based on instructor feedback and further discussion with the client regarding materials. The updated list can be found in Appendix C.
1.4. Updated Team Responsibilities
Updates were made to the original team responsibilities, as shown in Appendix D.
2. Design Alternatives
A wide range of design options constructed of distinct materials and components was considered to develop a final prototype that best addresses the medical need. After the need for a size-adjustable pediatric splint that fits patients from 18 months to 13 years old had been established, the prototype of potential design alternatives was developed. This is primarily based on different methods to adjust the circumference of the splint: adjustable by using velcro straps, elastic bands, screws or knobs, flexible material, and inflation, with all designs holding the angle of the elbow joint at 90 degrees for maximized healing. Following the development of prototypes corresponding to the categories above, it was determined that the length-adjustable component can be added. This would enable the splint to expand or compress in both width and length. Various methods of adjusting length were determined to be unfolding, sliding and screwing, pinning, twisting, and locking an extra piece on both the forearm and upper arm framework, as well as a flexible material that would harden to the chosen length and width. The general workflow followed to develop the prototypes is depicted in Figure 1 below.
Figure 1. General workflow of prototype development.
Different ideas to adjust length and circumference were combined to develop different prototypes. The choice of material also contributes to the flexibility and adjustability of the splint.
2.1. Circumference Adjustable Using Velcros and Elastic Bands
The first method considered to adjust the splint circumference is using velcro straps and elastic bands to wrap around the splint. The prototype comes in two separate components: the plastic framework of the splint with either velcro straps or elastic bands. The framework of the splint is designed to hold the elbow joint at a 90-degree angle, where the material used for the rigid portion of the splint for the upper arm and the forearm is made of rigid plastic: high-density polyethylene.
2.1.1. Velcro Straps
The first design alternative shown in Figure 2 below utilizes velcro straps to wrap around a patient’s upper arm and forearm above the splint. This allows for adjusting the circumference of the splint by manually varying the tightness of the velcro straps at application. The velcro is attached to the splint by sliding them through the pairs of parallel slits pre-cut on the plastic frame. These pre-made slits are longer than the width of the velcro so that the velcro has enough space to slide up and down accordingly, thus allowing for placement on different areas of the arm as needed. There are four sets of slits on the upper arm and two on the forearm plates, allowing for four velcro straps to wrap around the upper arm and two for the forearm.
Figure 2. Splint design with pre-made slits on the upper arm and forearm plates where velcro can slide through and wrap around the arm. All dimensions shown in the figure are in inches.
2.1.2. Elastic Bands
The second design alternative is based on a similar plastic frame with pre-made slits used for the first design shown in Figure 2 but uses elastic bands to secure the splint onto the arm instead of velcro. The circumference can be adjusted by using sliding in bands of varying elasticity – bands with larger elasticity will result in a smaller circumference. A length-adjustable component was added to the design, by enabling the ends to unfold one at a time to increase the length to fit patients as needed. The length can range from 7.6-17.6 cm for the upper arm support and 11-5-26.5cm for the forearm support. In order to address the client’s feedback regarding the material used in the first design alternative, cotton padding will be placed between the plastic frame and the arm to reduce patient discomfort and avoid the need to pre-wrap the arm with gauze prior to placing the arm on the splint.
Figure 3. Splint design with pre-made slits on the upper arm and forearm plates where elastic bands can slide through and wrap around the arm. Both ends can unfold to increase in length if needed. All dimensions shown in the figure are in inches.
2.2. Circumference Adjustable Using Screws and knobs
The second method considered to adjust the circumference of the splint is utilizing screws and knobs. The prototypes are designed to have either holes where screws are screwed in to decrease the width or pre-attached knobs that can be turned to adjust the width accordingly. The prototypes also consist of slits where velcro can slide through and wrap around the arm to hold the splint in place. A length-adjustable component was also incorporated for this design that allows the length to extend from 11-21 cm of forearm support and 7-12 cm of upper arm support. Both plastic portions for the upper arm and forearm are made of high-density polyethylene (a plastic that has no reaction with the skin) [5] and composed of two overlapping layers, where the inner layer is able to slide up and down to match the desired length to fit patients of varying arm lengths.
2.2.1. Screws
The screw design is displayed in Figures 4.1 and 4.2.
Figures 4.1 and 4.2. The bottom and top diagonal views of the splint framework. Velcros can slide through the premade slits and fasten around the patient’s arm. All dimensions shown in the figure are in inches.
The part on the bottom of the splint that compresses the screw is made of aluminum. When the screw is tightened using a screwdriver, it turns a gear that moves the sides of the aluminum portion of the splint closer together, thus compressing the plastic and decreasing its width both in the horizontal and vertical directions allowing it to fit an arm with a circumference of 12 cm or less. Cotton padding was added for comfort along the edges.
2.2.1. Knobs
An additional design using the identical framework shown in Figures 4.1 and 4.2 was created identical to the previous one except the gear is placed on the outside and covered with a knob that can be turned. Knobs are also used to fasten the extra parts at the appropriate length so that no additional materials and tools are needed to fit the splint.
2.3. Circumference Adjustable by Flexible Material
The second method used to adjust the splint to fit the circumference of the patient’s arm is to use more flexible materials. The first material considered is semi-flexible plastic, made from Smoothcast 300 and KX Flex 40 resin [6], that can bend at thin widths. These plastics are non-toxic once cured but will be covered for extra skin protection and comfort. The second was to use an elastic sleeve made of merino wool which is soft, controls odors, and absorbs moisture from skin [8] to cover the framework of the design and add comfort. These concepts were slightly adjusted with options of increasing length using extra parts that slide in and out of the original framework, twist key, and lock into place or use pins to lock into place. All of the following designs include holes where elastic velcros attach to wrap the arm and can expand to support ranges of 7.3-12.85 cm up the upper arm and 11.9-27.0 cm of the forearm.
2.3.1. Bendable Plastic
Slightly bendable plastic was used in the prototype displayed in Figures 5.1 and 5.2. The flexible frame has three places on each side of the splint where the thickness is significantly decreased to allow for material and splint bending.
Figures 5.1 and 5.2. Top and bottom diagonal views of the splint framework that is made of bendable plastic. All dimensions shown in the figure are in inches.
The width of the thicker center portion of the splint is larger than the outside parts to add extra support and bending resistance, holding the elbow at 90 degrees. The additional pieces slide into the frame to the appropriate length when the knobs are turned to the open position, and lock into place when they are turned to the closed position.
An additional design was created displayed in Figures 6.1 and 6.2 below that bends the framework to properly fit the maximum circumference without additional bending. Larger holes were created to allow for wider elastic and velcro pieces to wrap the arm in order to disperse pressure on the patient’s arm and provide increased comfortability. Cotton padding was added to the inside of the splint and additional length pieces.
Figures 6.1 and 6.2. Top and bottom diagonal views of rounded splint framework made with bendable plastic. All dimensions shown in the figure are in inches.
2.3.2. Elastic Sleeve
An additional way to change the circumference of the splint was to create separate parts of the splint as depicted in Figures 7.1 and 7.2. The plastic material used is identical to the previous design, but instead of thinner areas, the splint is cut into multiple pieces. These parts are then placed and covered by an elastic fabric and merino wool that can absorb moisture, add comfort, and allow for bending between segments.
Figures 7.1 and 7.2. Framework for plastic pieces that would be inserted into the elastic sleeve.
An alternative design is the same as the previous except the very center of the plastic would be made of high-density polyethylene to maintain a rigid 90-degree angle of the elbow, while the outside pieces and the edges of the centerpiece would be made of KX Flex 40 resin in order to allow for even more bend when appropriate, but still, obtain proper resistance and support. The framework for this design is displayed in Figures 8.1 and 8.2. Extra pieces of the high-density polyethylene at a 90-degree angle would be included for an optional insert into the sleeve if extra support is needed.
Figures 8.1 and 8.2. The framework of plastics of varying flexibility covered in an elastic sleeve along with extra support pieces that can be inserted into slits. All dimensions shown in the figure are in inches.
2.3.3. Expandable Fabric
The following prototype was developed based on a similar framework shown in Figures 8.1 and 8.2 but by using an expandable fabric that can be rolled out in water and heat-activated to harden, so it will adjust correspondingly to the patient’s arm dimension. An adjustable portion to be placed at the elbow is 3D printed so it slides and clicks into different size steps, and goes under or on either side of the elbow under the forearm piece to add stability and control the size. The patient’s arm is wrapped with either gauze or ace bandages before being placed in the splint.
2.4. Circumference Adjustable by Inflation
The final method considered to adjust the circumference of the splint is inflation. The prototype shown in Figures 10.1 and 10.2 was developed to hold a maximum range of circumference while utilizing hard plastic for the material. A flexible bag that holds air sits between the long bars shown in the figures and the framework so that when air is pumped in inflates the bag to an appropriate circumference of a patient’s arm. A safety lock is placed on the air pump to prevent unnecessary air from flowing in or out to change the circumference from what is desired, and the cap on the air pump is used to deflate the air. The prototype was also designed to be length-adjustable by shifting the adjustable pieces on both the forearm and upper arm held by pins. Like all other designs, the angle of the elbow joint is held at 90 degrees.
Figures 10.1 and 10.2. Top and bottom diagonal views of the splint framework where the circumference is adjustable by inflation. All dimensions shown in the figure are in inches.
3. Analysis of Solutions
3.1. Pugh Chart
A pugh chart was created in order to comprehensively analyze the design alternatives stated above in Section 2. Values were determined for each design on how closely they fit the design specifications. Keeping the elbow at 90 degrees was weighted as the highest criterion, as it ensures that the patient’s injury heals properly. Comfort was weighted second highest as that is another top concern for patients and parents. If these two criteria are not met, patients and parents may prefer to spend the extra cost and time on custom-made existing solutions. The ranges of length and circumference are of the next importance as they are crucial to finding an adequate solution for the need for adjustable-sized splints. The values are listed in detail in Table 1 below along with a comprehensive score based on weights and values.
Table 1. Pugh chart that analyzes different design alternatives for a pediatric splint. Each design specification criteria was weighted by an integer between 1-10 based on importance. The design alternative with the highest total score was chosen to be developed.
3.2. Analysis of Pugh Chart
Each of the designs was analyzed based on the design specifications in order to determine the best solution. The first design solution utilizes a rigid plastic frame that is not able to be adjusted individually to shape adequately to the patient’s arm. The elastic and velcro straps allow for some size customization but do not allow for any curvature of the base allowing for rotation of the arm. The screw design requires extra tools for the application while both the screw nor knob design do not have the ability to adjust the circumference for the upper arm to a different size from the lower arm. The first bendable plastic design allows for a limited change in the circumference of the arm and fails to properly fit the curvature of the elbow which increases the possibility of the elbow sliding out of place and no longer bending at 90 degrees. The second bendable plastic design accounts for the curvature of maximum circumference as well as allowing for farther bending for smaller arms. The idea of using inflation was expected to be the most effective in adjusting the circumference itself, but other criteria including weight, cost, and durability were not the most ideal when compared to other alternatives such as the elastic sleeves. The design alternative utilizing expandable fabric scored relatively high in circumference range and angle of the elbow joint, but patients having to wait until the material softens or hardens results in a lower score in application time.
Overall, the second elastic sleeve design was concluded to provide the most comfort as well as preferred healing specifications as provided by the client, scoring the highest. Between the healing specifications, client comfort, as well as practitioner benefits this design allows for the closest matches to what is desired for the splint.
4. Overview of Chosen Solution
As described in section 2.3.2 and depicted in Figures 8.2 and 8.1, the second elastic sleeve solution consists of a plastic curved framework where the very center of the plastic would be made of high-density polyethylene to maintain a rigid 90-degree angle of the elbow, while the outside pieces and the edges of the centerpiece would be made of KX Flex 40 resin in order to allow for even more bend when appropriate, but still obtain proper resistance and support. These pieces will be covered and held together by an elastic sleeve. The sleeve will fit tightly around the pieces by allowing for it to bend between to fit circumferences of 15cm to 27.3cm. Two extension pieces will be inserted by the use of pins at the appropriate location to adjust the length of the forearm between 11.9-27.0 cm and the upper arm piece 7.3-12.85 cm. It is made to extend the full length of the forearm and half the length of the upper arm. Overall, only one additional size would be needed to fit the average range of 18 months to 13 years. Elastic velcro will be used to secure the splint in place around the arm. The application time would be approximately two minutes. The steps are simple to ensure that a range of workers can apply the product. Extra features such as cotton and merino wool are attached to the inside allowing for increased padding and comfort as sweat is absorbed and odor is reduced. These materials are a small cost that decreases common patient complaints about many splints.
5. Proposed Budget
While the client has not specified the desired cost of the prototype in particular, it was concluded that having a prototype of preferably under $100 USD so it can be produced relatively easily would be ideal. Sections 5.1 and 5.2 below outline the estimated cost of producing the chosen prototype and the amount that Group 16 requests from the department.
5.1. Estimated Cost
Table 2 below lists the estimated cost for each component needed to build the prototype in detail.
Table 2. Estimated cost for the initial prototype of the chosen design alternative.
| Material | Size | Quantity | Estimated cost |
| High-density Polyethylene | 12x8x1cm Sheet | 1 | $22.03 [3] |
| KX Flex 40 Plastic | 0.35 Liters | 1 | $31.56 [4] |
| Elastic Fabric | 1250 cm2 | 1 | $16.99 [7] |
| Velcros | 50 cm2 | 1 | $7.88 [9] |
| Merino Wool | 20×30 cm Single Sheet | 1 | $3.25 [1] |
| Cotton | 100×4 cm Roll | 1 | $15.34 [2] |
| Total cost | $97.65 |
5.2. Funds Request
The prices listed in Table 2 were determined based on the amount of material needed to build one prototype. Some values are for volumes larger than needed, but no lower quantity was sold. The estimated total cost to produce a single prototype is $97.65, but taking into account possible failures while creating the prototype, students Yoon Kim, Kearsten Miller, and Kaitlin Donlon are requesting $200, so that $195.30 can be spent to develop two prototypes and the rest potentially accounting for additional costs that may arise in the process of development.
6. References
[1] Amazon.com: Holland Felt – 100% Merino Wool Felt – Neutrals and Browns … https://www.amazon.com/Holland-Felt-Merino-Neutrals-Black-40/dp/B083JM8RLX.
[2] BSN 9043 3 in. x 4 Yard 100 Percentage Cotton Specialist Cast Padding … https://www.amazon.com/Percentage-Cotton-Specialist-Padding-Rolls/dp/B012XHODEG.
[3] Buyplastic Natural White HDPE Plastic Sheet 1 1/2″ x 6″ x 6″, High … https://www.amazon.com/BuyPlastic-Natural-Plastic-Thickness-Polyethylene/dp/B08PVZGVVK.
[4] “KX Flex™ 40.” Smooth, https://shop.smooth-on.com/kx-flextm-40.
[5] “Polymers: HDPE: LLDPE: High & Low Density Polyethylene: UHMWPE: Homopolymer: Repol: Relpipe: Petrochemical Companies in India.” Reliance Industries Limited, https://www.ril.com/OurBusinesses/Petrochemicals/Polymers.aspx.
[6] Smooth-Cast™ 300 Series. https://www.smooth-on.com/tb/files/Smooth-Cast_300q,_300,_305___310.pdf.
[7] Strapcrafts 6-Inch Wide by 2-Yard Black Heavy Stretch Knit Elastic 74060. https://www.amazon.com/iCraft-6-Inch-2-Yard-Stretch-Elastic/dp/B01A39TTBS.
[8] Sylvest, Julie. “Merino Wool: Advantages, Origin and Care.” Dagsmejan, Dagsmejan, 23 Feb. 2022, https://dagsmejan.com/blogs/sleep/merino-advantages?gclid=Cj0KCQiAvqGcBhCJARIsAFQ5ke6goF3JOtRvNZFzoKKJyeF0lqO0-qdUGfuhylUZJBMxAl6lLSnht70aAlE9EALw_wcB.
[9] Velcro Brand Heavy Duty Fasteners | 4×2 Inch Strips with Adhesive 8 … https://www.amazon.com/VELCRO-Brand-Fasteners-Industrial-VEL-30703-USA/dp/B09BNPX3XJ.
[10] Okubo, H., et al. “Epidemiology of Paediatric Elbow Fractures: A Retrospective Multi-Centre Study of 488 Fractures.” Journal of Children’s Orthopaedics, vol. 13, no. 5, 2019, pp. 516–521., https://doi.org/10.1302/1863-2548.13.190043.
Appendix A. Revised Need Statement
The most common type of fracture identified among pediatric patients is elbow fractures – a study conducted in Okinawa suggests that 488 patients younger than 15 years old were treated for elbow fractures across 11 hospitals throughout the year [10]. A pre-formed arm splint that is quickly applicable and adjustable in size so that it fits pediatric patients of age ranging from 18 months to 13 years old that fully supports the elbow at a desired angle is needed. The client, Dr. Linda Wu (a Clinical Instructor in Pediatrics at Washington University School of Medicine in St. Louis), is looking for a size-adjustable splint for pediatric patients that will firmly hold the fractured area at an appropriate angle for healing. The client expects that the primary target of the developed prototype will be ER and urgent care where X-ray machines can diagnose elbow fractures, while it is also possible that it can be used at orthopedics clinics.
Appendix B. Revised Project Scope
Students Yoon Kim, Kearsten Miller, and Kaitlin Donlon are aiming to provide the prototype of a size-adjustable splint that can properly fit patients of the target age range yet still holds the fractured area firmly at an appropriate angle for healing to the client at the completion of the product in April of 2023.
Appendix C. Updated Design Specifications
The following design specifications were finalized based on input from the client, feedback from the instructor, guidelines that existing solutions follow, and studies supporting properties of splints that lead to proper and maximized healing.
Table C1. Final design specifications for the prototype
| Design Specification | Metric |
| Operation | Can be operated by one person on one patient |
| Target | Pediatric patients of age 18 months to 13 years |
| Coverage | Covers the patient’s arm from the forearm to the wrist |
| Arm orientation | Holds the elbow flexed at a 90-degree angle Forearm held at a neutral rotation |
| Size | Accommodates patients of various sizes within the range specified below while available in no more than three size variations |
| Weight | Should not exceed 0.5 kg |
| Material | Hypoallergenic materials No use of materials with sharp edges or pressure points Rigid when applied – the yield load should be approximately 1.1 N/g |
| Range of motion allowed | Less than 31% supination of the forearm (from the baseline measurement with no immobilization) Less than 34% pronation of the forearm (from the baseline measurement with no immobilization) |
| Cost | Total cost should not exceed $200 |
| Time | Applicable in approximately 5 minutes Holds duration for more than one week |
| Comfort | Comfortable for daily wear |
Appendix D. Updated Team Responsibilities
Table D1 lists the responsibilities of each individual for successful completion of the project.
Table D1. responsibilities of each group member over the course of the project.
| Student | Responsibility |
| Yoon Kim | Communicate with the client, schedule meetings as needed Take meeting notes, make updates on LabArchives Perform analysis of design alternatives |
| Keasten Miller | Use CAD to model design alternativesCommunicate with course instructors on behalf of the group Test mechanical aspects of the prototype |
| Kaitlin Donlon | Organize the lab notebook |