Medical Device Ergonomic Evaluation & Usability Testing

Medical Device User Testing

At this research project, another student researcher and I, on behalf of the UMN's Human Dimensioning Lab, partnered with a start-up medical device company based in Canada. We designed and carried out usability tests on their finger scanning device in order to report to the company on its current ergonomic state. We ran the test on 10 participants which had them manipulate the device to their comfort level, taking photos of their preferred positions, and taking 3D scans of their hands with and without the devices so we could take measurements.

In order to run this project successfully, we first conducted a literature review examining ergonomics of the wrist and affects of diabetes, which was relevant to the finger scanning device. We also had to write and present our Standard Operation Procedure on how we planned to conduct the usability testing. Once this was approved, we moved forward with the testing.

We wrote a report for the company explaining our findings, as well as offered recommendations on how the company can improve the ergonomics of their device. We also gave them measurements of our participants' hands and fingers, as well as general recommendations from national anthropometric databases such as ANSUR in order to inform their design decisions of the device.

This is the literature review we conducted. Once we gathered and synthesized relevant literature, we presented our initial findings with the start-up team. They gave us feedback on what they believed was relevant to their device.

This is a 3D printed prototype of the medical device that we tested. The idea is that this device would sit flat on a table and the user would sit still while the device scanned their finger. Some of the initial objectives from the start-up team were as follows:

Find the most comfortable hand position as reported by the usability test participants
Report the digits (fingers) that participants prefer to use in the device
Recommend and provide measurements of what the finger hole should be given the measurements of the test participants and standards reported by anthropometric databases
Recommend angle and height measurements of the device from the table

This shows how a general participant might hold the device. One of the first issues that arose was that the participants instinctively wanted to wrap their hand around it. This would interfere with the device and was something my partner and I addressed early on.

This provides and x-ray view of how the finger rests inside the device. Another factor we had to consider, was the length of the finger. Ideally, the participants finger would rest on a pulp inside the device. The pulp needs to be central to the device and has little room to move. However, if the pulp was too far away, it could be too big for some users.

This is an example of the hand position of the participant without the obstruction of the device. This view was important for us to use to take various measurements of the hand.

Another issue we ran into was wrist support. We noticed that participants wanted to rest their wrist on the table but the natural orientation of their wrist did not allow for this. This position was also supported by our research of literature that suggests that the wrist needs to be supported because flexed wrists cause long-term harm by pinching the median nerve.

Our fix to the hand wrapping problem was to crate a plate that participants could not wrap their fingers around. Shown here is how that impacts the users interaction with the device.

This is the station we set up for the test participants to complete the usability testing.

This is the rig we set up that we had participants put their arm through. We used this rig and positioning to take 3D scans of their hands. We took scans of the participants holding the device as well as with a splayed hand. The purpose of the splayed hand was to take computerized measurements of the participants hands.

In order to capture measurements of the participants hands, we created pin-points on various areas of their hands called landmarks. We used these landmarks to digitally capture various hand measurements that we recorded to use in our sizing recommendations.

This is an example of some of the measurements we took of our participants hands.

Here are more measurements. You can see how we used the landmarks to plot these measurements.

This measurement was important for determining if participants could reach the pulp or not.

This was a particularly important set of measurements because it gave us information about the clearance the device needed from the table.

This is a slide from a presentation I made with our final findings. I presented this to the start-up team with our recommendations. This slide shows what each participant's preferred hand position was.

This graphic is meant to illustrate how we classified hand positions.

This information was particularly useful, though surprising. We found that a lot of our participants preferred to hold their thumb in the device. The start-up team anticipated that most users would prefer to scan the index finger. This finding means that in regards to the prototype, the finger hole would need entirely new dimensions to accommodate the much larger thumb.

These are recommendations to the start-up. Most notably, I recommend that this device should be made big enough to scan the four fingers as a whole. This would eliminate discomfort and the inclination to wrap fingers around the device. Secondly, I recommend an arm rest so that users do not need to flex their wrist.

This shows our recommendations for the finger hole measurements. These recommendations are based in our findings from our usability study in conjunction with anthropometric databases.

This shows our recommendations for the finger hole width.

This shows how our participant's measurements compared to the existing anthropometric database of the Human Dimensioning Lab.

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