Orthopedist Rob Nelissen: ‘We work on operations that involve high levels of mathematics’

• In 2021, nine extra Medical Delta (MD) professors were inaugurated. These professors work at at least two of the five academic institutions represented within Medical Delta (TU Delft, Erasmus MC, Erasmus University, Leiden University and LUMC). The intake brought the total number of MD professors to 22. How does such a double appointment work in practice? That is the underlying question in this miniseries of research portraits.

Professor of Orthopaedics, Prof. Rob Nelissen believes that if you are a medical practitioner in a university hospital where the most complicated procedures are being done, you have to work with engineers if you want to move with your times. He has worked with engineers at TU Delft for decades. During interviews, the Professor regularly refers to his sounding board partners as “Those crazy TU Delft people” and “my friends at TU Delft”. Shortly after the founding of the Medical Delta in 2006, Nelissen had a double appointment, one at the Leiden University Medical Centre (LUMC) and one at TU Delft.

One of his friends of the first hour was Mechanical Engineer Edward Valstar who passed away in 2017. Nelissen worked with Valstar, who also had a Medical Delta professorship, for years. The pair led the way in the development of minimally invasive procedures to help prevent the loosening of prostheses. This is a big problem: 10% of all prostheses loosen within 10 years.

Fifteen years ago, Nelissen’s LUMC group came up with a plan to use gene therapy to address this shortcoming. “We thought of a system and applied for a patent.” Although the first clinical trials were successful, the general public was nervous about gene therapy. “Venture capitalists did not want to work with us to further develop our plan, so I thought, you know what, I’ll approach my friends at TU Delft again. Maybe they and I can come up with something else. We then developed a technique (Dutch only) in which you inject a sort of cement (polymethylmethacrylate) through a thin needle in the space between the prosthesis and the bone. The cement hardens in about 15 minutes and the prosthesis is attached again.”

 ‘The orthopaedic profession doesn’t really exist anymore’

To Nelissen’s mind, that he needs to work with other disciplines to make progress is obvious. “Engineering and the medical sciences have become completely interwoven in the last 10 years. The orthopaedic profession doesn’t really exist anymore.”

Why not? “Complex medical procedures are done at university hospitals like the LUMC. It is the perfect place where several disciplines converge. I work with neurosurgeons, radiologists and engineers. These professions merge with each other. If one practitioner is removed, you cannot carry out that complicated procedure anymore.”

Backpacking
A big adventure. That is what attracts the orthopedist the most about the partnership. “I used to go backpacking. I loved discovering new cultures. And this is why I enjoy working with engineers. It’s like immersing myself in a different culture. There are many creative minds at TU Delft. By discussing things together, you come up with great original concepts for improved patient care.”

Do you have to have loved backpacking to feel at home at Medical Delta? “Ha ha, not particularly. I do not think that Valstar ever did it, but he did love adventure. He went on long hikes. You need to be curious and be prepared to do things outside your comfort zone.”

Nelissen says that he often went outside his comfort zone. “I was motivated to do this at Medical Delta. I am now working with the TU Delft Professor of Biomechanical Engineering Amir Zadpoor, who had the first Chair in Orthopaedic Implants. We are working on techniques for bone operations that involve high level mathematics. It involves things that an ordinary doctor cannot even imagine.

“We operate on a lot of bone tumours at LUMC. If you remove a piece of bone, it is replaced by a prosthesis. While you want to copy the rigidity and the elasticity of the bone, bone is not equally elastic everywhere. Where the muscles attach to the bone it is more flexible, for example, so that it can give when force is put on it. This reduces the chance that the muscles tear loose. We are trying to design joint replacing prostheses that have these qualities using 3D printing techniques. So we are making implants that have a good strength distribution so that the muscles attach well. That is the future.”

‘It is unavoidable that you will sometimes say something silly’

Accurately sawing away bone also needs high tech. “If a bone tumour needs to be removed from the chest or spine for example, the sawing needs to be done very accurately to avoid damaging the surrounding tissue. So we first made a 3D print of the bone tumour and the surrounding bone, and use it to create a cutting template. We use it to accurately carry out the procedure to the millimetre and degree during the operation.”

Another example: technology to prevent bacterial infections in implants. Earlier this year Mahya Ganjian, from the Biomaterials & Tissue Biomechanics Department, got a doctoral degree for her research into implant coatings with sharp points that break bacteria at the nano scale. “The bacteria were speared,” says Nelissen smiling. He was one of her supervisors. The studies on bacterial infections in implants are led by Nelissen, Bart Pijls (LUMC) and Zadpoor.

Guts
You need guts to work on the interface of technology and medicine. It is unavoidable that you will sometimes say something silly. During a brainstorming session on bacterial infections, one TU Delft engineer offered to incorporate antibiotics in prostheses. That is a bad idea as the bacteria quickly become resistant due to continuous exposure to antibiotics.

“You should not be afraid of saying something stupid. I don’t worry about it anymore. Young researchers may have cold feet more often, but you really should look beyond your own discipline. I always enjoy bringing young researchers to the Medical Delta Cafés (regular get togethers of members, where current issues in healthcare are discussed, and where there is much networking and exchanging of ideas). The meetings are disarming. I get a lot of energy from them. People approach each other easily.

“But not all doctors and engineers are open. Some medical practitioners are happy with what they are doing and do not want to work with other disciplines. It will take time, but if you can interest just 5% of young doctors, that is already a good thing.”