Jan 8, 2016 | By Alec
3D printing is quickly making a name for itself in the academic medical world as a tool for creating high quality surgical models, but a new breakthrough by Stratasys reminds everyone that we’re only at the beginning of a medical 3D printing revolution. Together with biomedical specialists DamaMed, they have developed the Pathfinder, a 3D printed metal tool that is set to revolutionize the treatment methods for damaged anterior cruciate ligaments (ACLs) – the most important ligaments in the body that are responsible for regular knee movement. This tool is essentially a biocompatible surgical device that will enable surgeons to reconstruct partially or fully torn ACLs and even reduce the risk of re-tearing.
This is very important as an ACL injury is one of the most widespread ligament issues in the world and, until now, is something you tend to suffer from your entire life. The anterior cruciate ligament (ACL) plays the crucial role of connecting the tibia (shin bone) to the femur (thigh bone), and by doing so stabilizes the knee and enables regular movement. However, around 200,000 people in the US alone tear their ACLs partially or fully every year. While some treatment options are possible, the ACL replacements are very prone to tears and see people going in and out of surgery every year or so. ACL damage is known as a killer of athlete careers, and especially affects runners and other athletes who put a lot of stress on their knees.
Dr. Dana Piasecki, an orthopedic surgeon from OrthoCarolina Sports Medicine, in Charlotte, N.C., set out to improve the success rate of ACL reconstruction surgeries, and after some experiments found that alternative tools could offer the solution. The key, he discovered, would be a surgical tool shaped to match the anatomy of the knee, which would greatly improve the placement accuracy of the grafts put into knees to replace ACLs. For the current surgical technique has trouble reaching the exact location within the knee, resulting in a misplacement of the graft by as much as 5 to 10 mm. This results in more biomechanical strain on the graft than on a regular ACL, increasing the likelihood of failure.
“The main problem is doctors are using a straight drill to create the tibia and femur attachment points for the graft, but instrumenting through the rigid tibial tunnel limits where you can get on the femur. I realized I needed a procedure in which the drill is flexible and could be bent to follow the ligament’s normal path to impact the femur at the location and angle that anatomically mimics native ACL positioning. I then needed a tool that could be inserted into the inner knee space to grasp the flexible drill, steer it to the proper spot on the femur and hold it during the drilling process,” Piasecki explained. Among others, to match the organic structure of the knee, the tool would need a slotted groove that holds a 2.2 mm diameter flexible drill and a curvilinear head section. Several different sizes with surface variations were also needed, as knee anatomy is not always consistent in all patients.
Piasecki and DanaMed, with whom he was working, realized that they were in need of a manufacturing process that could efficiently produce the complex surgical instrument affordably. Most importantly, the tool had to be sterilizable and biocompatible, as it would be actively in contact with the human body, while its exact function and proximity to bone required a strong, durable and flexible solution. Metal 3D printing through Stratasys was thus an obvious choice, especially because it also presented them with the ability to make quick design changes in a moment’s notice.
Fortunately, Piasecki and DanaMed were already working with plastic 3D printed models and CAD design techniques, with the help from Minnesota-based Laser Design, which scanned the initial hand-made prototype and helped with CAD development. “With 3D scanning and 3D printing technologies, we are able to turn the hand-whittled design into a functional CAD file and a 3D printed model within hours,” said Larry Carlberg from Laser Design. This resulted in a pretty good FDM 3D printed model made in PC-ISO thermoplastic, which proved to be an excellent model for Stratasys to work with.
To give life to this complex tool, Stratasys used their Direct Metal Laser Sintering (DMLS) 3D printing technology, with Inconel 718 material. They say it’s the only manufacturing process capable of building such intricate geometry at a price point that is realistic for low-volume production. The surface finish, oil resistance and mechanical properties are all absolutely perfect. “Manufacturing the part with DMLS took some fine-tuning. We worked closely with Laser Design to refine our method for this particular application,” said Stratasys project engineer John Self. While already looking perfect right off the machine, the team realized that some shrinkage took place upon cooling, so this had to be taken into account. Some minimal material removal was also necessary.
But the results are fantastic and Stratasys identified the process controls necessary for a repeatable design within a +/- 0.005” tolerance – which is checked with a few custom Nylon 12 PA fixtures, made with laser sintering 3D printing. “Pathfinder illustrates how 3D printing is uniquely capable of enabling breakthroughs in medical technology that otherwise would not be possible,” Self said of the breakthrough “And by offering DanaMed 97 percent cost savings over conventional manufacturing methods, 3D printing has demonstrated its business value in bringing complex, high-quality parts to market.”
What’s more, DanaMed are wasting no time in getting this invaluable tool to patients. The Pathfinder has already been registered with the FDA, which have given it a Class 1 Medical Device certification, classifying it as a biocompatible tool fit for an initial market release. While already in the hands of orthopedic surgeons across the US, DanaMed is keeping a close eye on feedback to ensure continuous improvement through Stratasys -something also impossible without 3D printing. “Being able to make design changes and 3D print new tools within days was extremely important to helping us perfect the design. We could get feedback from a doctor, make design adjustments and send an updated Pathfinder within a week – something we wouldn’t be able to do with investment casting or injection molding,” said Jim Duncan.
This is excellent news for patients and athletes everywhere, though it will take some time before the actual results come in. However, initial feedback has already shown that doctors are overwhelmingly positive. Numbers show a 95 success rate in anchoring the graft in the right place, so this 3D printed tool is set to make a real difference. “This surgical tool has turned our vision of transforming ACL reconstruction into a reality faster and someday will hopefully eliminate repeat knee injuries to keep more athletes off the bench and on the field,” said Dr. Piasecki. For more information, check out the Pathfinder patent.
Posted in 3D Printing Application
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Stratasys don't use dmls. it is EOS technology
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