“There is so much knowledge in the algorithm”

Interview Prof. Schroeder-Boersch

“There is so much knowledge in the algorithm”

Interview with Prof. Dr. Henrik Schroeder-Boersch

“There’s so much knowledge in the algorithm”

Artiqo spoke to Prof. Dr. Henrik Schroeder-Boersch, Wiesbaden, why he thinks mechanical alignment of the knee joint is no longer up-to-date, why he advocates an anatomical reconstruction and what role the 4-Motion® knee system plays in this.

Prof. Dr. med. Schroeder-Boersch

Artiqo: They stand for an anatomical reconstruction of the knee. Why?

Schroeder-Boersch: It is simply out of date to do a mechanical reconstruction as has been advocated for the past four decades simply because of a desire to simplify the technique. Many knee systems stand for a specific technique, be it aligning at right angles or always taking 3 degrees. However, as we now know, this does not correspond to the range of possible anatomies of the patients. I hope that an anatomical reconstruction will result in a better functioning knee due to less irritation of the structures involved.

Artiqo: What makes anatomical reconstruction easier today than it was then?

Schroeder-Boersch: The installation of a knee prosthesis is still complex. At the same time, knee replacements are being performed in large numbers, including by surgeons in smaller centers with fewer cases and less experience. We can make this easier today because we have patient-specific cutting blocks at our disposal. Anatomical reconstruction is therefore a procedure that can prevent potential errors.

Artiqo: What does a knee prosthesis system have to offer that can consistently be called anatomical?


Schroeder-Boersch: Two things are important: the implant has to be suitable for it and I have to have a surgical technique that allows me to personalize it.

The components must be able to technically follow the individual and anatomical positioning. There are implant systems that are always installed with a three-degree inclination. However, we know that in a third of patients this does not correspond to their own anatomical axis. An anatomical system must have an implant design that is variable within the allowed range of 90° to 87° in the frontal plane.

I also need an instrument system that allows me to consciously implant at an angle. That sounds banal in the age of lasers, microprocessors and high-performance milling, but the reality at the operating table is different. It is worked with rough saws, hammer and chisel. Installing a targeted two-degree incline is most reliable if I have pre-produced individual cutting blocks.

Artiqo: With the 4-Motion® knee system, we still have the planning algorithm that significantly simplifies the whole process…

Schroeder-Boersch: The 3 degree inclined joint line is 3 degrees oblique if we look at the front of the knee in extension. However, the knee is often in some flexed position in between. That means: I also have to adjust the knee in flexion. This is the process that can be difficult for the surgeon when standing at the operating table.

Planning based on a predetermined algorithm helps enormously. You should already have understood the algorithm and also understand the result of the planning. But in reality you often have little time and a lot of pressure. It is very valuable if you can really rely on the basic principle of planning. This algorithm contains so much knowledge and experience from the literature and so much mechanical understanding that I call the planning algorithm of the 4-Motion® knee system mature planning.

And I have the opportunity not only to work purely on the bones, but also to give the algorithm additional information in special cases – when ligaments are particularly short and contracted. This makes it easier for me to balance my knees, as I can already create space in the bones during the planning and don’t have to loosen the ligaments. This also means intraoperatively: simply do, simply implement. Therefore, I believe that the system is also a good support for surgeons with lower case numbers.

Artiqo: They recently said personalized anatomical alignment could be a way to increase patient satisfaction. What did you mean?

Schroeder-Boersch: Incorporating a new surface into the knee involves a tremendous amount of disruption to the surrounding soft tissue. On the operating table, patients can fully extend and bend 145 degrees, but after six weeks or three months they are sometimes missing 10 degrees of extension and can only bend 100 degrees. That’s enough for cycling, but not for more.

If a joint was previously set to some degree of inclination, all the ligaments and capsules work beautifully with that degree of inclination, and then I put in a standard knee the old-fashioned way, I can cause irritation because the axes of rotation aren’t perfectly aligned, the ligaments in extension and flexion tightened differently and because the knee was installed differently than the old surface. It is possible that this chronic stimulus leads to postoperative scarring.

Therefore, the reverse conclusion: If I manage to prevent this disruptive factor by anatomically fitting the knee and the ligaments run smoothly, then I hope for less post-operative scarring, less warm knees and fewer knees that need an adjustment period.

Artiqo: What are your user experiences with the 4-Motion® knee system?


Schroeder-Boersch: Good. I can just sum it up like this. The planning is delivered with the individual cutting blocks and is hanging on my operating room wall. Before I begin, I find out about the planned bony incisions. I feel very comfortable because I know so much about the knee before the operation. I find that crucial. And if I only know: It’s a pretty standard knee. But you’re also prepared when it’s a difficult anatomy.

In addition, the implants are well thought out. The tibia is designed for variable positions, the fit is good and there is the option of using high-quality PE inlays. There are many points.

As with all new techniques, it takes a bit of patience at the beginning and getting used to it, e.g. when it comes to the exact placement of the cutting blocks. With the 4-Motion® knee system, we need the bony axes from the CT. In the operating theater I often have the knee still with cartilage in front of me. However, the cutting blocks must rest on the bare bone. I now have to learn to thoroughly remove the cartilage where the cutting block rests. That’s the learning curve you have. But there are always control options in the system. And that’s why courses and internships are important, as well as tips from surgeon to surgeon.

Artiqo: Some manufacturers have patient-specific instruments. Can one say that the cutting blocks in the 4-Motion® knee system make sense for the first time?

Schroeder-Boersch: Exactly that. There’s more to it here because it means anatomical reconstruction in extension, in flexion, and in the positions in between.

Without the PSI system, I can skew the joint line a little, resect the femur and tibia a little differently. But then I would have to adjust the femur rotation correctly. Do I need to rotate more? Or not? Do I follow the tapes? The whole thing takes on a degree of complexity that can become difficult in the usual surgical procedure – under time pressure, the patient is bleeding, the next operation is pending, it’s noisy.

This is where it helps to put the thought process in front of the surgery, with an algorithm that tells me, “From what we know about knee replacement, the best thing you can do is operate on this knee.” And of course you can still adjust it. This outsourcing of mental work makes the PSI so valuable with the 4-Motion® knee system. You no longer operate in a standard way, like all instruments can do, but you operate individually.

Other PSI systems go to the mechanical axes 90°/90° and the inclination comes into the system by making the femur a bit smaller laterally and the inlay a bit higher laterally. That only fits for two thirds of the patients. I have no variability there.

Artiqo: The planning and creation of the patient-specific instruments takes about 6-7 weeks today. How can this be communicated to patients, how is the acceptance?

Schroeder-Boersch: The waiting time is due to technical reasons. When things really get urgent, Artiqo is able to shorten the waiting time by two weeks. They’re very helpful there.

Patients want their doctor to take them seriously and treat them individually. By that I don’t mean an individual knee replacement at all, but about recognition as a person with special features. They don’t feel accepted if I say, “Your knee, that’s standard – I’ve done that 1,000 times. It will be good for them too.” At least with a differentiated audience, as I often have in Wiesbaden, it is difficult.

In my experience, patients are grateful when I explain to them that their knee has angles and inclinations and that we have the opportunity here to take these special features into account in the prosthetics. For this we need precise cutting blocks from the 3D printer, which have to be sterilized and securely packaged. For those who understand that there is an individual solution, waiting is an argument.


Read more on this topic:

Consistently anatomical
Lecture EKB Endokongress | ARTIQO Knee Symposium

4-motion® knee system