Blog Post

May 28, 2013 Samuel Hamner

Behind the Scenes: v3 ReMotion Knee

As I write this blog post, Vin and I are en route to Indonesia to deliver the first 40 units of the v3 ReMotion Knee. We will be working with two prosthetic clinics, the Jakarta School of Prosthetics and Orthotics (JSPO) and PUSPADI Bali (formerly Yakkum Bali), to fit the first patients with the knee and launch a 6 month follow-up study. Our goal is to learn about the effectiveness of the new design, what features need tweaking before full scale production, and how the knee impacts the lives of the patients we are remobilizing. We’re also looking for vital feedback from our other key users—the prosthetists fitting the knee—whose opinions and adoption of the knee are just as critical for success as those of the patients.

ReMotion map

Sites for the 2013 ReMotion field trials

As I reflect on our journey to get to this point in the ReMotion project, I want to acknowledge the tremendous support from groups and individuals outside of D-Rev. As Vin highlighted in our last blog post, this new version of the ReMotion Knee represents a radical shift in look, feel, and production. One of the biggest technical challenges in developing the new knee was modifying the design for mass production. Since its inception, every ReMotion Knee has been manufactured using computer numerical-controlled (CNC) milling machines. This process can be a time consuming, as each feature is cut step by step.


v3 ReMotion Knee

CNC was great for when we are prototyping and trying new designs, but we always knew it wasn’t going to cut it (yes, pun intended!) for D-Rev long-term. We want the ReMotion knee to scale for global production and have global impact. CNC is fine when you have low volumes and only need one machine, but scaling up with it would mean many machines, in many locations, and an impossible challenge for managing quality. So we looked for a process that could produce lots of parts very quickly and in one place, allowing us to centrally control quality. This naturally led us to injection modeling. To help make this transition, we were grateful to work with Scott Bowie and Dana Ung at Zao Technology Innovations. A world leader in design and manufacturing with offices in Silicon Valley and Shenzen, Zaotech helped us adapt the design for injection molding. From snap fits to coring to injection gate locations, Zaotech’s expertise with injection molding design was key.

Before we invested time and resources in building parts for the knee, we also wanted to have confidence that it would have the strength and durability to endure the 3 million steps that we estimate each patient will take over 3 years. Before we cut the first mold, we worked with Dr. Paul Briant at Exponent to conduct a thorough finite element analysis (FEA), which simulates the loading conditions each knee will endure. From heel strike to toe-off to a 1 meter drop test, the simulations provided us with an in-depth look at the forces and stresses acting on each component of the knee in various scenarios. This virtual analysis was a critical part of the design process, as it let us identify any “hot spots” where stresses were likely to be high, and then modify the design before going into production.

As the v3 design shifted to injection molding, we also had to design and source custom hardware components for the knee—that is, the nuts and bolts. These components are critical and require precision machining so that the knee swings smoothly. We also switched to standardized connections for prosthetic systems, using a universal pyramid connection at the top of the knee. We’d like to thank Accurate Manufactured Products Group (AMPG), who donated custom hardware for the first 500 units. We also worked with JWP Manufacturing and Silicon Valley Laser to custom fabricate parts for the v3 knee. Special thanks to Carl Madau at JWP Manufacturing for his advice on finding suppliers and discussions on manufacturing methods.

Injection molds

Vin and Garrett unpacking our first shipment of injection molded parts from Protolabs

Our next step in producing the first units of v3 was to find an injection molding manufacturer. We were honored that ReMotion was selected for the Protolab’s Cool Idea! Award. This award provided us with free tooling and supplies for the first 100 units for our field trials. Protolabs is incredible with their quick turn around on parts; we were able to have parts in less than two weeks after we uploaded the final design. We were also impressed with the automated quoting and part advisory system, which allowed us to see all the variations of materials that were available, the different textures and surface finishes, and instantly see how different options affected cost. The system also identified manufacturing issues, like drafting, undercuts, and texture, while the Protolabs technical staff was always available for in-person feedback. It was amazing to upload a part to the Protolabs website at the end of the workday, and then come back the next morning to see feedback on the design.

Vin and Rina

Vin working with Rina, from Hexagon Metrology, to measure each spec of the knee

After months of work, we finally had all of the pieces that would be put together to build the v3 ReMotion Knee! But another aspect of the v3 design process was implementing a rigorous quality control system—and we are proud to say that v3 knees have been manufactured with a fully traceable quality plan. We performed incoming inspections on every component to ensure it matched our engineering specifications. Through generous support from Hexagon Metrology, we were able to work with the incredible Rina Molari for two weeks to inspect every feature—each nook and cranny—of the v3 knees. Using a sophisticated device called a portable coordinate measuring machine or CMM—which looks a lot like a big robot arm—Rina was able to accurately measure each feature that was critical to the design, down to the micron. This inspection allowed us to have confidence that once we started assembly, all the pieces would fit together and function properly!

v3 stress test

The first v3 ReMotion Knee enduring stress testing on our Instron machine

Once we had the knees inspected, we put them together! It was a glorious day when we assembled that first knee. But that wasn’t the last step in the process of getting the knees ready to fit on patients. At D-Rev, we like to say that we’re user-obsessed. Most of the time we are referring to understanding user needs through empathy and the context in which the user lives his or her life; but it also means we’re obsessed with user safety! So before we fit the first patient, we needed to perform physical tests to verify the strength and durability that we simulated with FEA. Thanks to David Maltz and generous donations from Novartis and Instron, D-Rev now has full mechanical testing capabilities. The Instron machine allows us to apply forces to the knee that are similar to those it will undergo with each step, and see how the knee performs before we put it on a patient. This final step is incredibly important for us to have complete confidence in the safety of our design!

And now we are on a plane with our suitcases full of knee joints, waiting eagerly to fit the first patients with the v3 knee this week.

It has been an incredible journey over the last year to get to this point, and none of it could have happened without the support, expert input, and guidance of so many individuals, including everyone who has donated time and resources to us. Thank you especially to the Lemelson Foundation, Focusing Philanthropy and everyone who donated through our 1,000 Knees Campaign. We are grateful. And be on the lookout for more blog posts from the field as patients start wearing our knees.

Back To Posts