SHOULDER DISLOCATION SIMULATOR
BACKGROUND
The shoulder joint is the most frequently dislocated joint of the body (usually from a fall or sport-related accident). Medical students and residents primarily learn how to perform a shoulder reduction properly by observing a more experience physician perform the procedure during their rotations or residency program. Because of this "see it, do it" training platform, trainees are not given the opportunity practice shoulder, leading to increased risk of complications; these complications can result in increased pain, hospital time, healthcare costs, and potential surgery for the patient involved.
We developed this shoulder dislocation simulator for our Biomedical Engineering Senior Design course with Dr. John Vozenilek is our client who proposed the project with the goal of addressing this gap in medical training. Dr. Vozenilek requested that our trainer teach the Hennepin technique as that is the shoulder reduction technique that is least likely to result in complications. Our final design won the 1st Place Daniel D. Mickelson Engineering Prize for best design among all submitted projects in the McCormick School of Engineering at Northwestern University in 2012 as well as Second Honorable Mention for the NIH DEBUT Challenge in 2012.
Click on the following link to our write-up submission with more detail and data.
DESIGN CONSIDERATIONS
While designing the device, we first wanted to find out what the most common errors are made while someone is performing a shoulder reduction using the Hennepin technique for the first time in order to give feedback on those items while trainees are using the device for practice. After significant research of journals and in person in the ER of Northwestern Memorial Hospital, we found that the two most common issues are that people apply too much downward traction force at the elbow or rotate the arm too fast. Thus, we wanted to instrument the device with a force sensor and angular measurement device as well as means by which the trainees could be given feedback on those tasks.
In order to make the device be able to dislocate and reduce repeatedly, we designed a bi-stable shoulder mechanism as the shoulder joint is also stable in both the dislocated and reduced positions. We developed a mathematical model to accurately mimic the force profile that the shoulder joint should follow- the input to this model was joint tendon testing that we performed on cadavers; although the cadavers would not give us the exact spring constant for the resistive forces necessary, we knew that the force profile would be the same since the path that the shoulder travels is the same. Thus, a profile was developed to find the force profile, and significant testing was conducted with emergency medicine physicians to see what multiplicative factor of the spring constant would give the "right" feel of an arm and the resistive forces that are felt when the shoulder is being reduced.
MECHATRONICS
The shoulder design, integration of the electronic components into the design, and the programming and board design were my primary contributions to this project. The electronics consisted of an Arduino Mega board, a deconstructed luggage scale used to measure the downward traction force, an encoder, and an LCD screen. This was my first foray into the world of mechatronics, so I learned to solder for this project and how to program a microcontroller.
Furthermore, this project provided an interesting challenge of how to integrate the sensors as the final simulator device was a large, somewhat free-hanging, disembodied arm.