Direct metal laser sintering (DMLS) is an industrial 3D printing process, increasingly put to use in applications such as the manufacture of car parts. But EOS recently used its DMLS technology to manufacture parts for something much smaller than a car – a handsome cat from Virginia, named Mr. Cyrano L. Catte II. After being cured of cancer, the cat nearly had one of his legs amputated, but his loving owners, veterinary surgeons, and 3D printing technology all worked together to keep him on four legs.

Cyrano is the first feline in the US to receive a Total Knee Arthroplasty (TKA).  [Image: NC State University]

Cyrano developed bone cancer in his left hind leg, and was the first cat to receive stereotactic radiation therapy, where focused beams are aimed right at the tumor. After two rounds of radiation, Cyrano was considered in remission, but an unfortunate side effect of the life-saving treatment was bone deterioration of his distal femur, along with some deterioration of his tibia. As Cyrano is a heftier cat of 26 lbs, the normal solution of amputating his leg was not recommended – it would be too hard for him to move on just three legs. So his owners looked into another option, and another first for a cat in the US: completely replacing his knee with an artificial one.

Cyrano was then taken to the veterinary facility at North Carolina State University, where veterinary surgeon and orthopedic professor Dr. Denis Marcellin-Little and Professor Ola Harrysson, with the university’s Industrial and Systems Engineering department, determined that Cyrano’s implants would need to be very small, and that they would need to manufacture stems to anchor the components with his bones. It was also decided that they would use DMLS technology from EOS to make the artificial knee’s two main components.

The stems would need to be very precisely made, as its features would have to match up with custom drilling and cutting guides. Using DMLS would allow them to manufacture the metal components into shapes that aren’t possible to achieve through conventional molding or subtractive cutting processes. Additionally, the two wanted to include multiple surface types in the device.

Professor Harrysson explained, “The EOS technology not only gives us design freedom for orthopedic implants, it also offers the means to build osseointegrated surfaces directly into the part.”

3D data was taken from CT scans of both of Cyrano’s hind legs, and the team made 3D design models of the components using Materialise Mimics software.

Dr. Denis Marcellin-Little

“We started from one of BioMedtrix‘s knee implants for dogs and miniaturized it. We added the stems, the bolts that hold the stems in place, and other features unique to this design,” said Dr. Marcellin-Little.

We’ve seen stories of 3D printed prosthetic legs for cats before, but we don’t often hear of 3D printed feline implants like Cyrano’s. It was difficult to make the implants small enough for a cat, but eventually the metal component models were 3D printed using DMLS technology at EOS’ headquarters in Germany, finished at BioMedtrix, and then delivered to the surgical team.

Typically when we’re talking about 3D printed medical implants and devices, they’re made of titanium, which is excellent for bone ingrowth, but Cyrano’s team decided it was too soft for the job.

“The loads on a titanium femoral head would wear the metal down eventually,” Dr. Marcellin-Little explained. “Because the implant components would already be thin in some places, they might be subject to breaking or cracking if they eroded still further. Cobalt chromium was our best choice.”

Thanks to the precise nature of EOS’ DMLS technology, the density, layout, and pore size of the porous section of the implants were able to be specified. The stems that extended inside the cat’s hollowed-out femur and tibia were textured, in order to promote bone ingrowth, and there was also an area of porous mesh further up the stems, to make strong osseointegration possible; these textured and meshed surfaces will help promote long-term stability of the implant. In addition, the bearing surface at the end of each piece was polished so smooth motion was possible against the implant’s polyethylene tibial mobile bearing surface, which rotates when the leg moves.

The assembled implant shows the stems that insert into the leg bones and the bolts that fix them in place. [Image: NC State University]

 “This kind of implant had never been made before, and this surgery never attempted,” Dr. Marcellin-Little said.

“The main change this technology has brought is that the manufacturing process is no longer a barrier to the imagination of an orthopedic clinician who needs to create something very specific.”

The six-hour surgery went off without a hitch, and Dr. Marcellin-Little said that without the 3D printed stems, the femoral component would not have been stable enough, due to the cat’s poor bone quality. Cyrano does walk with a limp now, but he is able to comfortably use his leg and joint, an outcome that would not have been possible without 3D printing technology.

“What we learned from the Cyrano project is transferable to other animals and even to human medicine,” said Professor Harrysson. “Now that we know how to miniaturize a joint this sophisticated there are a number of potential applications, in hands or jaws, for example.”

Let us know what you think of Cyrano’s implant in the DMLS Cat Implants forum thread at 3DPB.com.

[Source: EOS]
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