21.06.2023
Dr. Dirk Ganzer on the anniversary
of the RM cups by Mathys
«Reason to celebrate: RM cups have been convincing for years with long service lives»
The development of the monoblock RM cups is a success story that has been going on for many years. Low abrasion and optimal distribution of forces in the pelvic bone ensure low risks of osteolysis and stress shielding1. As a result, service lives are long, and satisfaction is high – for patients and operating surgeons. Chief physician Dr. Ganzer reports on his experiences.
Dr. Dirk Ganzer
Dr. Dirk Ganzer is chief physician at the Hospital for Orthopaedics and Trauma Surgery at the Dietrich Bonhoeffer Hospital at the Altentreptow and Neubrandenburg locations and head of the EndoProthetikZentrum (EPZ). The hospital focuses on primary and replacement endoprosthetics of the hip and knee joints, as well as surgery of all large joints. The hospital performs about 1700 endoprosthetic procedures a year.
Interview
Dr. Ganzer, Mathys’s titanium-coated RM cups are celebrating their 40th anniversary. How long have you been using them?
Dr. Ganzer: It was about 18 years ago that we implanted the RM Classic cup in our hospital for the first time. At that time, we were looking for an adequate replacement for cemented polyethylene (PE) cups. We were no longer satisfied with the medium-term results of these PE cups. After work shadowing with a key user of RM Classic cups and a short learning curve, we were convinced.
Specifically what was it that convinced you to introduce the RM cup in your hospital?
Dr. Ganzer: It was clearly the clinical results of the RM Classic cup combined with a wealth of very good biomechanical data. Then the easy handling of the RM Pressfit cup and the RM Pressfit vitamys cup represented a clear improvement over the predecessor model, even though this completely changed the anchoring mechanism. Acceptance of this cup implant among the endoprosthetic surgeons at our hospital has increased significantly over the years. Today, the RM Pressfit vitamys is our cup of choice.
So you have remained loyal to the RM cups after their next evolutionary step?
Dr. Ganzer: Yes, we have. Upon the market launch of the RM Pressfit cup, we were among the first users of this new implant. Initially, we were somewhat critical of this innovation. For in terms of shape, this cup lacks the two anchoring pins. However, the principle of isoelasticity was integrated here as well. Our initial concerns that the RM Pressfit cup might lead to poorer clinical results compared to the RM Classic cup turned out baseless. Even now, the RM Pressfit made of conventional polyethylene (UHMWPE) already has a 13A* rating from the Orthopaedic Data Evaluation Panel (ODEP)2, which means very good clinical results after 13 years. The latest cup, RM Pressfit vitamys, already has an ODEP 7A* rating.
“The RM cups are broadly applicable, offer good clinical results, wear little, and have long service lives”
What are the advantages of the RM cup, from your point of view?
Dr. Ganzer: There are very good clinical results for all acetabular cups of the RM family. I would like to emphasise their longevity in particular. In addition, the RM family can be used for many indications. For example, due to the pin anchorage the RM Classic cup is suitable as a cement-free primary implant in cases of less-than-optimal bone quality. It is appropriate for simple revision cases as well. The RM Pressfit cup made of UHMWPE and the RM Pressfit vitamys cup made of highly cross-linked and vitamin-E-enriched PE are monoblock cups for the primary treatment of virtually any indication. Their special advantage is the isoelasticity with the pelvic bone. As a result, the forces acting on the hip are uniformly transmitted to the bone. Stress shielding, as it occurs with conventional cup implants, is reduced.
What about wear and tear?
Dr. Ganzer: The RM Pressfit vitamys cup has very low in vivo wear, with head penetration rates between 0.020 and 0.036 mm/year. PE particles produced by wear and tear are known to be able to cause osteolyses of the pelvic bone as well as of the femoral bone around the stem implant. Model calculations for osteolysis-free periods of a cup implant are based on this. Due to the low PE abrasion of the RM Pressfit vitamys cup, osteolysis-free periods of over 20 years were calculated for it. I find the result impressive, so I put my trust in RM implants.
“Not only the longevity of the implant convinces the patients, but also the quick remobilisation”
Long-established prosthesis models likewise show good clinical results, which are also documented in registries. At what points do the RM cups make the difference, from your point of view?
Dr. Ganzer: Without any question, there are long-established modular cup systems that perform excellently in terms of registry data. From my point of view, the benefits of the RM Pressfit vitamys cup come into their own in the long-term results. In addition to the already mentioned low abrasion and the resulting reduced probability of osteolyses, the low stress shielding has an effect on achieving long service lives as well. This can be a decisive advantage. In addition, it should be mentioned as a special feature of the implant that in the medium term the already low PE abrasion of the RM Pressfit vitamys cup is not influenced by the diameter of the femoral head used.
What are the benefits for the patients, from your point of view?
Dr. Ganzer: For patients, the most important question is how long an implant will last and when it may need to be replaced in its turn. Here the reasons given before provide us with very strong arguments that enable us to convince the patients. A concluding sentence is frequently heard from us: Your hip will run as reliably as a Swiss watch. That convinces even the hesitant. What is crucial, however, is that both the RM Pressfit vitamys cup and the optimys stem are ideally suited for “fast-track surgery3“. Patients benefit enormously from this in terms of very fast convalescence.
“Experienced surgeons can implant the RM cups without any difficulty”
Where do you see the limits of application for the RM cups?
Dr. Ganzer: Acceptable bone quality is a prerequisite for using an RM Pressfit cup. Implantation is possible up to mild osteopenia. As the RM Classic cup is part of our repertoire as well, we can cover also moderately osteopenic situations of the acetabulum and mild revision cases with the RM cup family. I consider severe dysplastic changes of the acetabulum, disturbed integrity of the acetabular ring or manifest osteoporosis as contraindications. However, high individual experience of an experienced operating surgeon with these implants allows their use even in this borderline area.
What is your recommendation to colleagues who are new to the RM Pressfit vitamys implant?
Dr. Ganzer: For an experienced arthroplasty specialist, use of the RM Pressfit vitamys cup is definitely not a challenge. I personally consider the implantation behaviour in the acetabulum to be gentler than insertion of a metal base is. The counter-argument for a monoblock cup is occasionally the impossibility to replace the inlay, should an early septic situation occur. For this case, which is rare in my experience, it should be mentioned that the complete cup change can be done in a very bone preserving manner – usually with a cup of the same size or one size larger. Furthermore, the lack of control over the implantation depth of the cup is sometimes mentioned. In my view, both arguments are largely without merit. They should not be overrated.
Dr. Ganzer, thank you for this interview!
References
- Reduction in bone density due to implantation of an endoprosthesis or other metallic connecting elements, e.g. bone screws or plates
- ODEP is an independent panel of experts that provides objective assessments of the strength of evidence for medical implants.
- Fast-track surgery means a therapeutic concept for multimodal perioperative patient care. By trying to avoid complications after surgeries, convalescence is to be accelerated and the patient’s autonomy preserved.
