ARM Cast

grabcad

I am currently a student at The University of Alabama in Huntsville and I designed the adjustable, reusable and modular (ARM) cast, a replacement for the modern plaster/fiberglass cast. The plaster/fiberglass cast is the current solution for setting and keeping bones stationary while healing after a major accident or surgery. While being the current solution, the plaster/fiberglass cast has many serious disadvantages.Disadvantages of the Plaster/Fiberglass cast:- Long cast preparation/creation time- Requires a skilled physician- Custom made for each patient- Cannot be adjusted or modified after initially made, this can lead to improper healing if bones are shifted after the cast is made- Patient cannot wash or clean skin inside the cast, this can lead to skin infections or irritations under the cast- The cast must be cut off, cast is destroyed after only one use and if done incorrectly could injure the patientThe ARM cast was designed to improve the current plaster/fiberglass cast and it solves many of the issues surrounding the plaster/fiberglass cast.Advantages of the ARM cast:- Short cast preparation/creation time- Does not require a skilled physician, it is easily done by anyone - even the patient himself- It is both adjustable and modular, so it fits many patients; even if it were to be too small/large in overall diameter for the patient's arm, the ARM cast can be scaled and printed in different size ranges such that it would fit anyone (The ARM cast in this entry has a diameter range of 7 to 3 cm; which would fit most youth)- Can be adjusted during the bone’s healing process, in case the bone is shifted or is initially misaligned- Patient can wash and clean skin inside the cast- To remove the cast, it is just loosened and removed- Once sterilized the cast can be reused for other patientsThe ARM cast consists of 3 basic parts, the modular ring, the adjustable pads, and the elbow joint. The modular ring forms the body of the cast and contains the adjustments for the pads (it is the large white ring in the pictures). The modular ring also is threaded on both ends, which allows it to be connected to other modular rings or the elbow joint in order to increase the length of the total cast. The elbow joint can connect two of the modular rings at a forty-five-degree angle around the patient’s elbow. Finally, the modular ring utilizes FDM printing’s ability to create “in-place” assembly’s as it prints the movable slides inside the ring. This saves assembly time and decreases the unique part count.The adjustment pads are the red “C” shaped pieces inside the modular ring. These pads are responsible for adjusting the inside size and shape of the cast to the patient’s arm. To do this, each pad is connected on both ends to the adjustment slides in the modular ring. To adjust the size of the cast, the slides are slid along the slot in the modular ring and this causes the adjustment pads to move toward the center of the ring. Once the pads are adjusted correctly, locking pins are inserted through the slides and into the matching holes found in the modular ring. The bones in a human’s arm naturally twist along the length of the arm; therefore, the slides can be asymmetrically adjusted and this will allow the adjustment pad to follow the bone’s natural twist. Also, each patient’s arm has a unique curvature, so the pads are designed with a “flex point” in the middle of the “C” shape. This flex point is simply a thin section which allows the pads to wrap around the patient’s arm in order to best fit the patient’s arm. The adjustment pads also utilize the FDM printer’s ability to create “in-place” assemblies, since it consists of a three-part moving assembly.The ARM Cast was printed with ABS plastic on a FDM 3D printer. ABS was used as it is far stronger than other common types of FDM filament like PLA. The ARM Cast utilizes a FDM printer’s capabilities to create in place assembly’s as seen in both the modular ring and adjustment pad. Printing "in-place" assemblies increases production and manufacturing efficiency since it decreases both the unique part count and post-manufacturing preparation time. When using an FDM printer (a Makerbot Replicator Mini) to create “in-place” assemblies, a gap of .7mm was left between moving parts (See picture). This gap was enough for the parts to be printed without support and still maintain accuracy and post-print movement.The ARM Cast also utilizes the printer’s layer thickness attributes in the design of the adjustment pads. The “flex-point” of the adjustment pad is designed to be 1.4mm wide, which is approximately 3-4 horizontal layers wide. This is thin enough that the ABS plastic is both strong and flexible. The rest of the adjustment pad is 3.4mm wide, which does not flex at all, rather it remains rigid in order to keep the patient’s bones from moving.For more information, videos of the ARM Cast are available here:- The ARM Cast on a patient: https://www.youtube.com/watch?v=plvG4D_OTr0- ARM Cast fit around different shapes: https://youtu.be/BR-yP8On2TM- Multi-section ARM Cast Assembly: https://youtu.be/d2M21zmt87U- Assembly of the 3D printed parts required to make the ARM Cast: https://youtu.be/T6NEVsAHypYInformation, pictures, and videos are also available on my engineering website: https://goo.gl/7KY0Ss_