Customized Implants cover bones optimally

Interview with Prof. Christian Lüring, Director of the Orthopaedic Clinic in Dortmund

It may fits, but somewhere it still tweaks. Although a suit off the rack serves its purpose, it is still far from being an ideal solution. With a custom made heart it is different: Here everything fits perfectly. It is similar with implants. Often patients complain about the fact that those implants feel strange. 3D printing is on the best way to change this. Here, the implants are adapted to the carrier. However, as with a suit, quality also has its price.


Photo: Christian Lüring

Prof. Christian Lüring with a knee implant in his hands; © Christian Lüring

On Prof. Christian Lüring, Director of the Orthopaedic Clinic in Dortmund, explains how the 3D procedure works, the use of cobalt-chromium alloys and why the future of 3D printing can be compared to motor sports.

Prof. Lüring, what differentiates 3D printing from the standard process?

Christian Lüring: The implant production is different. With 3D printing, the prosthesis is made with a printer while conventional prosthetics are manufactured using a die casting process.

What does the 3D printing process look like?

Lüring: Prior to the surgery, we need a computed tomography (CT) scan to be able to measure the patient’s knee joint. The knee replacement is generated on the computer using this CT scan. After checking whether everything is accurate and fits the bone exactly, the prosthetic is then printed and manufactured. The implant is subsequently returned to the hospital where we are able to ultimately use it. This process takes about eight weeks.

Why the specific use of cobalt-chromium alloys?

Lüring: The advantage is that they have a high flexural strength. Most implant components we insert into patients are made of cobalt-chromium because the material is also very biocompatible. There are also implants made of titanium for example but the drawback here is that they are not as hard as they need to be, especially when they need to be inserted into the femur.
Photo: Cobalt-chromium knee implant

Cobalt-chromium alloys have a high flexural strength and are also very biocompatible; © Christian Lüring

What are the advantages of this process in your opinion?

Lüring: You achieve a very accurate fit since the implant is directly customized to the individual bone structure. You might compare this with a suit. Even though a suit also fits if you buy it off the rack, it does not fit as well as a custom-made one. It is definitely an advantage that the bone is optimally covered by the prosthetic. The drawback is that we don’t have any long-term experience with this relatively new process yet. Whether it works as well as a standard prosthesis remains to be seen.

How many of these types of implants are you and your team inserting each year?

Lüring: We implant approximately 100 of these types of customized knee replacements each year. In a nationwide comparison, this definitely makes us one of those hospitals that implant the majority of these prosthetics. However, compared to the standard, only about 25 percent of patients receive this type of prosthetic.

Why is the percentage still comparatively small compared to the standard process?

Lüring: These implants are a lot more expensive than the conventional ones. Plus they are not suitable for all patients. If we have extremely bowlegged patients, that is their legs have a pronounced X-shaped or O-shaped curvature, you can no longer use this implant. In many of these cases, the three components we have available are not able to correct the leg alignment.

How do you rate the future of this process?

Lüring: As is often the case, I think when you have technological progress, it rarely triumphs on a broader basis. It will end up being more like things are in motorsports or with cars. Many innovations that make their way into motorsports can, later on, become standard practice. Many insights we gain from customized knee implants and the 3D printing process can find their way into standard operations. That said, I can almost not imagine that we would only use those special implants going forward. To do this, we would first need to gather long-term experiences and results. Since those are not available yet, it’s hard to predict what the future holds. Things would be very different if we find out that these implants will last forever. But that remains to be seen.


The interview was conducted by Kilian Spelleken and translated by Elena O'Meara.