Periprosthetic infections: Investigating the influence of stem design

What influence does implant design have on the incidence of infection? Following initial findings based on EPRD registry data [1], a yet-to-be-published, prospective, and randomized study by Dr. Sebastian Meller of the Charité University Hospital in Berlin is now examining the topic in more depth. The results in brief: The short stem enables more precise reconstruction of the hip geometry, and the minimally invasive implantation technique is reflected in reduced muscle fat deposition and lower laboratory markers for tissue damage. We spoke with Dr. Meller about the details of the study design, the findings from the study, and possible next steps.

The industry has been advertising the equation “short stem = minimally invasive = fewer infections” for almost 20 years. Is that true?

Dr. Meller: This equation is striking, but not entirely unjustified. The design of the short stem allows for a more muscle-sparing and less irritating implantation. Whether this will also lead to fewer infections in the long term remains to be seen.

Your study examines the “influencing factor of the stem” on the infection process. What were your preliminary considerations for the study design?

Dr. Meller: Our goal was to compare the biomechanical and soft tissue-specific behavior of two different stem designs. In the prospective, randomized study, 40 patients were treated by a single surgeon using the minimally invasive anterolateral approach – either with a calcar-guided A2® short stem or with an SL-Plus MIA straight stem (Smith & Nephew). We then analyzed muscle fatty degeneration using MRI, and evaluated the geometry (offset, anteversion, etc.) radiologically and with a 3D MRI analysis, as well as muscle trauma using laboratory methods.

What is the result of your study?

Dr. Meller: After a completed 6-month follow-up, both implants led to very good functional results. However, the short stem enabled more consistent reconstruction of the individual anatomy, less muscular fatty degeneration, particularly of the gluteus medius et minimus muscle, and less variability in the restoration of anteversion and anterior offset.

We used CK and myoglobin levels for objective quantification of intraoperative soft tissue damage. These laboratory values reflect muscle cell damage—lower values therefore potentially mean less soft tissue injury during the surgery. The short stems showed less trauma, with lower CK and myoglobin levels. Clinically, the Harris Hip Score was excellent in both groups (>97 points at 6 months).

What conclusions do you draw from the results?

Dr. Meller: Our results show that the short stem, thanks to its design, enables a more anatomical, consistent reconstruction – with simultaneously less muscular damage. This is demonstrable in laboratory tests through lower CK and myoglobin levels. Less trauma could have a protective effect against infection. In the long term, it could offer advantages in rehabilitation, dislocation behavior, and prosthesis durability. Whether it also leads to fewer infections in the long term has not yet been conclusively clarified. An analysis of the EPRD registry data shows at least a tendency towards lower revision rates for periprosthetic infections with short stem prostheses.[1]

What is your conclusion specifically regarding short stem prostheses?

Dr. Meller: Short stems offer real advantages: bone-sparing, soft-tissue-preserving surgery, improved reconstruction of hip geometry, and reduced muscle fat deposition. In my opinion, it’s a suitable standard stem. The cementless short stems, with which we have extensive experience, are particularly suitable for patients with good bone substance. However, they must be implanted by experienced surgeons. The critical selection of the implant is important: not every hip is the same.

What would be good next steps in short-stem care?

Dr. Meller: Femoral neck-preserving, calcar-guided, and proximally voluminous short stems find their orientation in the femoral neck almost automatically, thus helping to accurately re-establish the three-dimensional reconstruction of the center of rotation. However, since the rotation of the stem can only be influenced to a limited extent, the question of pre- and intraoperative assessment of femoral neck rotation arises in pathological situations. Furthermore, we need multicenter studies with larger cohorts and longer follow-up periods—particularly regarding survival times, infection rates, and clinical endpoints—to confirm the outcome in the long term. Finally, in the spirit of “individualized arthroplasty,” digital 3D planning and intraoperative navigation would be exciting approaches to further increase surgical precision.

The study is expected to be published in the fourth quarter of 2025.

[1] Steinbrück, A., Grimberg, A.W., Elliott, J. et al. Orthopäde 50, 296–305 (2021).
Link: https://doi.org/10.1007/s00132-021-04083-y