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The heel: The problem

Dr Peter Chung describes the problem and design that resulted in the creation of a titanium heel.
We’ve met with Professor Peter Choong previously. I’d now like to talk to Peter about a recent case involving a titanium heel implant. Peter, can you give us the background to that. Yes Gordon. We had a gentleman who unfortunately had a cancer of his heel. In the past, the way we would treat this is by amputating his leg below the level of the knee. What 3D printing gave us was an option to actually rebuild the heel, implant it, and therefore spare the patient his leg.
The way we did this was to look at precisely the configuration of the bone that had to be printed, where it would sit, what tissues had to be anchored to it, and precisely the part– the neighbouring bones, for example– that had to rub against it. We then used his other heel as the model and mirror image for the one we had to make. Once we were able to produce something like that, there were a number of steps that we had to take to refine this in terms of the weight, the surface polish, the anchoring points, as well as the overall texture of the device to allow soft tissue, or the tissue around the heel, to actually grow into it.
And was it the fact that it could be totally personalised for that particular case that was the real advantage of 3D printing? Absolutely. These devices actually have to fit right up against several other joints. And to be able to coordinate a structure that matches perfectly would be very, very difficult. So the only way you could actually do that was to make a replica, an absolute replica of the bone that was removed. By doing so, it allowed us to then fit it into the space that the original heel bone had occupied and therefore allowing it to match against its counterparts on the other side of the joint. The design of the heel for Professor Peter Choong was a very iterative process.
Professor Choong came to us with the need to create a replacement part for a patient of his who had cancer in the heel. We got a CT scan from that patient, mirrored it across to from the good side. And from there, we created a part that was an exact replica for the patient’s heel before the actual tumour was there. We presented that to Professor Choong and he designed a few more components to it. He told us which surfaces he wanted to be articulating and also some attachment points for the Achilles tendon and the foot pad and lateral medial muscles.
And from there we went about the design process to make sure that it was strong enough and also that it allowed tissue integration in through the implant. So the initial design was a solid titanium heel, which worked out at around about almost half a kilo in weight. Then we decided to look at the vector forces of the implant, and we were able to reduce the volume of the implant down to a couple of struts internally and then laid a mesh over the top.
Through a risk analysis that we completed, we determined that we weren’t able to remove all of this fine titanium particle from inside the implant, so we opened up the pores of the implant, which virtually halved the weight. What 3D printing allowed us to do was to actually address each of those separate facets of texture, bony surfaces, tissue anchoring points, as well as the internal structure of the device, to ensure that we had something strong enough to take six tonne of weight but yet weigh only 200 grammes.
The beauty of 3D printing for medical applications

Personalised medicine

3D printing makes personalised medicine a reality. The ability for patient’s own scans to inform the design of a device has and will continue to revolutionise the way medical solutions are considered. At the same time 3D printing capabilities allow the function of each device to be personalised taking into account the structural needs of the device.
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