Medical Device Link.

ENGINEERING INSIGHT

An injection pen with a side trigger makes it easier for osteoporosis patients lacking strength and dexterity in their hands to self-administer medication.

Empowering patients to take charge of their medical condition, and thus improve their quality of life, is a welcome trend. This requires a shift in thinking among design engineers, who may not be accustomed to developing devices for home use by patients who are impaired. That is the challenge that faced Swedish company Ergonomidesign (Stockholm; www.ergonomidesign.com) when it was asked to design an injection device that would allow patients to self-administer medication that controls osteoporosis. By adopting what it calls an inclusive approach during the design cycle, the company was able to develop a breakthrough product. Described as the first reusable injection pen with a side trigger, the Preotact Pen received a 2008 International Forum (IF) Design Award.

When Ergonomidesign took on the Preotact Pen job, the industrial designers attached to the project concurred that an inclusive approach was needed. The majority of patients who would benefit from this product are elderly women with very little strength in their hands. Moreover, many patients with osteoporosis are often diagnosed with rheumatological disorders. As a result, many potential Preotact users experience pain and dexterity problems in their hands and fingers. These conclusions led the design team to focus on the function and placement of the injection device’s actuator.

“Our objective was to develop a pen that is really easy to use,” explains Maria Benktzon, one of three industrial designers who worked on this project. “It needed a flexible grip that would allow the patient to use the fingers that were the most comfortable.” The device should not require a great deal of strength to operate, she adds, and its design should be intuitive and reassuring. “Many people have a negative attitude toward self-injection,” she notes, “so it was important for it [to have] a friendly look.” The design team built five different prototypes and tested the various concepts with patients diagnosed with osteoporosis and, in some cases, rheumatoid arthritis.
The five design concepts were as follows:

1. A traditional top-trigger design that requires the user to have a flexible thumb joint and appreciable residual thumb and hand strength.
2. A top-trigger design that required less strength to activate than the traditional pen. This pen did not address thumb-joint flexibility issues, however.
3. A pen with a side button that is engaged vertically. This design was more flexible than the first two, since either the thumb or forefinger can be used to operate the pen. The high demand placed on flexibility and strength in the selected finger was a major drawback.
4. A pen with a side trigger and a large stroke key. This design offered a natural hand and finger position in combination with considerable flexibility in the use of fingers or thumb. Very little strength was required because of the high gearing built into the design.
5. The fifth design involved a preloaded concept with top button and side actuator. The device is preloaded by pushing the top button with the thumb, against the other hand, or another surface. The injection is released with a light push on the side actuator.

Concept four got high marks from users: 75% thought it was “easy” or “very easy” to use. Concept five also scored well, but it was very complex to manufacture. The other concepts would have excluded a large number of potential users.

Following the concept tests, the design team channeled its efforts into improving the concept associated with prototype four. Of particular importance was the needle guard.

The needle guard shields the needle from sight and, importantly, assists at the time of injection by increasing the stability of the pen when it is held against the abdomen. A permanent feature, the needle guard is pushed back to safely and easily load a new needle package before each injection. The design team determined that the needle guard should be large with small protrusions to remove as much as possible the sensation associated with needle-based injections. Its contour was inspired by the reassuring shape of the daisy.

The pen device uses a dual-chamber cartridge containing the lyophilized Preotact powder in one side and a liquid in the other. The device includes a dose counter and a colour-coding system that confirms to the patient that the pen is loaded with the correct dose prior to administration.

Britt-Marie Nyhäll-Whålin, a Swedish physician and rheumatologist, describes the positive effects of the final design. “I always study the patients’ hands and fingers and there have been times when I have doubted their ability to use the Preotact Pen because of impairment. Yet it has always worked, and I have been po­sitively surprised.”

Preotact has been available in most European markets since the end of 2007.