Professor Karl Philipp Kutzner on optimys short-stem prosthesis

Professor Kutzner, the primary aim in the development of short-stem prostheses was bone preservation. Was this target achieved, and if so, how?

Professor Kutzner: Short-stem prosthetics have been around for about 30 years now, and yes, the idea behind them was to preserve bone over an extended time period. In my opinion, this goal is still one of the most important motivations. The optimys short-stem implant, for example, preserves more bone during the operation because the femoral neck is largely left in place. Also, the implant is not as bulky at the top as older models, so the complete operation is therefore already bone-saving. In addition, unlike long-stem prostheses, short-stem prostheses are fixed close to the joint. This means the force is transferred directly to the bone at the bone neck, and the trabeculae are better preserved at that location. In the case of a potential revision, the bone close to the joint is very stable and doesn’t fracture so easily. Implants fixed away from the joint behave quite differently – where the load isn’t transferred, the bone degrades more quickly.

‘Due to their anatomical shape, short-stem prostheses can more efficiently reconstruct the hip joint’s natural anatomy’

What are the further benefits of short-stem prostheses such as optimys compared to conventional prostheses?

Professor Kutzner: The possibility of minimally invasive surgery is especially advantageous. The short stems – and in particular the curved shape, as with optimys – enable individualised reconstruction with less damage to muscles and soft tissue. Currently, in addition to bone preservation, I see that as a key advantage. Short-stem prostheses such as optimys also have a special conical design while alternative stems are slightly flatter. This can ensure good primary stability and prevent the stem from sinking. That in turn favors healing and, in my experience, patients are usually back on their feet quickly.

A special feature of optimys is that the implant can be fixed close to the joint and also in the proximal diaphysis of the tubular bone. It can be used very individually and flexibly, which means the stem is often also suitable for older people with less than optimal bone quality.


What are the limitations of short-stem implants?

Professor Kutzner: The optimys stem in particular fundamentally has the potential to become a standard prosthesis – it can be used for a wide range of applications and is highly variable. The calcar-guided endoprosthesis follows the patient’s individual anatomy and can be positioned in a customized way, as it were. However, this means the surgeon has to have a certain amount of experience with the technique. Each short-stem prosthesis must be planned carefully and individually. The goal should be very clear and the bone quality has to be well assessed. Those who do this can achieve excellent results for patients. However, they shouldn’t be used in people with poor bone quality. They’re contraindicated in cases of insufficient anchoring potential or insufficient bone strength – in these cases the risk of fracture or sintering of the implant is too high.

What advice would you give to colleagues who would like to familiarise themselves with short-stem endoprosthetics?

Professor Kutzner: With every prosthesis, each surgeon has to go through a learning curve, and that also applies to the optimys stem. Mathys thought about that right from the start, and there are good, regular training courses and workshops for gaining the theoretical know-how. I can also thoroughly recommend taking part in cadaver workshops and, if possible, working with experienced colleagues.

‘If everything goes well, today’s implants may not need to be replaced’

What are the most common complications in hip endoprosthetics?

Professor Kutzner: Fortunately, complications are rare nowadays. Infections occur occasionally regardless of the prothesis, even if they’re not common. In the past we had to worry much more about dislocations, but nowadays they occur only rarely. That’s also reflected in the registry data. Short-stems are some of the implants with the lowest revision rates. 


What lifespans can be expected for short-stem implants?

Professor Kutzner: Of course, that varies from case to case. Seen from today’s perspective, I think that there’s hardly any systemic reason to change the prosthesis. Most patients are over 50 when they undergo hip surgery. Unlike earlier materials, for example metal and non-cross-linked polyethylene, there’s hardly any abrasion today. The head is now made of ceramic and moves in a cup made of durable polyethylene. In terms of materials, there have been a lot of improvements over the past 20 years and even the implants that were used around 20 years ago last a very long time on average. So if there are no complications in the beginning, I expect most people will be able to get by with a prosthesis for a very long time without problems, and they may not need a replacement.


Research is continually progressing. In your opinion, what questions are still unanswered?

Professor Kutzner: I’ve been working on the cementable short-stem version of optimys as part of my habilitation. In my opinion, such a philosophy would offer a solution to even more people, and I’m confident that in the future there’ll be further developments in bone-preserving implants.

I also see an exciting future in the philosophy of surface replacement – a cap that’s placed on the existing femoral head. That’s a topic that was already very big 15 years ago. However, caps and cups made of metal were used and the idea was more or less dismissed due to the high level of abrasion. With the experience we have today with ceramic and polyethylene, surface replacement could again become an important topic. That would mainly be an attractive option for athletes.

Professor Kutzner, many thanks for this interesting discussion!