10 Years of the A2® Short Stem: An Assessment Balancing Evidence and Further Development

From Niche to Mainstream Treatment Option

PD Dr. Thomas Randau provided the historical context. The concept of the short-stem implant dates back to 1978, when Pipino introduced the first anatomically preconfigured design. The category now known as “calcar-guided short stems”—which has included the A2® short stem since 2016—began to gain a foothold in 2004 with the introduction of the Nanos stem.

The shifts that have occurred over the past decade are reflected in the EPRD (German Arthroplasty Registry) data presented by Dr. Randau: while short stems accounted for approximately 5 percent of primary hip arthroplasties in 2014, that figure has risen to 23.3 percent according to the latest report. In his presentation, Prof. Dr. Sascha Gravius ​​(Mannheim) also highlighted the frequency of this treatment approach; with more than 170,000 primary hip arthroplasties performed annually in Germany—and a significant expansion in the range of indications—the question arises: is there scientific evidence to support the use of short stems as a standard treatment option?

The cemented short stem provides an answer to a real clinical challenge

A significant further development is the cemented version of the A2® stem. Dr. Bertram Regenbrecht (Lilienthal) placed this innovation within a clear clinical context: data from the German Arthroplasty Registry (EPRD) indicate poorer outcomes for cementless short stems in patients over the age of 75, as well as in cases involving Dorr type B and C femurs—specifically, a higher incidence of periprosthetic fractures. This aligns with the general EPRD recommendation to use cemented fixation for patients aged 75 and older. According to Dr. Regenbrecht, the cemented short stem effectively fills this gap in treatment options. Since its initial implantation in December 2020, the cemented A2® short stem has been used in approximately 7,000 cases across 85 hospitals, as reported by Dr. Regenbrecht.

Prof. Dr. Budde and Dr. Regenbrecht presented data from a multicenter study on the cemented short stem. Among the 147 patients (mean age 78.5 ± 5.2 years [range 66–94]; 72.8% female; mean BMI 26.1 ± 3.5), the following adverse events were recorded: one stem revision due to aseptic subsidence (occurring approximately 2 months postoperatively) and one Vancouver type B2 periprosthetic fracture after approximately 3.2 years (requiring conversion to a Revitan stem). No dislocations occurred. The incidence rate for revisions was 0.71 per 100 patient-years (95% CI 0.18–2.84; based on 281.5 patient-years of observation). Regenbrecht emphasized the importance of correct cementing technique as a decisive factor for the outcome. Prof. Dr. Budde further highlighted the particular responsibility borne by surgeons—given that the A2® short stem is currently the only cemented short stem available on the market—and urged caution when determining indications.

Prof. Dr. Johannes Zeichen (Minden) contextualized the use of the cemented short stem in fracture management. In his own study (n=403, 2021–2024), 69 percent of cases involved fracture patients with an average age of 83; of these, 88 percent had Dorr type B femurs and 8.1 percent had Dorr type C femurs. According to Prof. Dr. Zeichen, the cemented short stem makes it possible to extend the core short-stem philosophy—bone preservation and soft-tissue sparing—to a patient group that previously fell largely outside the classic range of indications: the primary demographic for joint replacement, namely those over the age of 75.

Individualizing Patient Care

Another key focus of the day was the increasingly nuanced approach to assessing and addressing individual anatomy. PD Dr. Tilman Graulich (Oldenburg) introduced the CPAH (Coronal Plane Alignment of the Hip) classification—a new planning tool developed from over 2,300 cases. It categorizes patients into nine morphological groups based on a combination of Dorr type, femoral neck anatomy, and femoral offset. The goal is to identify, at an early stage, complex cases where a mismatch exists between a patient’s anatomy and a standard implant.

The practical relevance of this was highlighted in several presentations on borderline anatomical cases. Dr. Harald Kuhn (Lohne) and Dr. Jens Peters (Sulingen) independently explained that cases involving a narrow medullary canal (Dorr type A) combined with a high offset are particularly challenging to manage using standard or shortened straight stems. In such instances, a calcar-guided short stem—like the A2® system—offers greater flexibility, thanks to its variable offset and the ability to customize the resection level. Dr. Peters described the short stem as a “workhorse” for Dorr type A femurs.

PD Dr. Lothar Seefried (Würzburg) demonstrated the full extent to which such individualization can be applied. As an osteologist and specialist in rare musculoskeletal disorders, he pointed out that what appears to be an atypical case of osteoarthritis may actually be a rare metabolic or endocrine bone disease (such as Paget’s disease, osteopetrosis, Gaucher’s disease, or X-linked hypophosphatemia). Recognizing these conditions is crucial, as they can directly influence the choice between a cemented or cementless implant and may necessitate specific pre-operative treatment. His personal credo: taking just “three seconds longer” to examine medical imaging can often spare one from significant problems in the operating room.

Further, methodologically robust evidence for anatomical adaptability was provided by a randomized controlled trial presented by Dr. Jan-Philipp Imiolczyk from Berlin. The study included 40 patients, randomized to receive either the A2® stem (n=19) or a conventional straight stem (SL-Plus MIA by Smith & Nephew; n=21). Due to the absence of postoperative MRI scans, complete datasets for imaging-based endpoints were available for 18 patients in each group. Based on this cohort (n=18:18), the A2® short stem reconstructed the native femoral antetorsion with significantly greater precision (anatomy-tracking slope 0.88 vs. 0.46; β=-0.42, p=0.048) and demonstrated a significantly smaller postoperative increase in fatty infiltration of the tensor fasciae latae, gluteus medius, and gluteus minimus muscles (p<0.001 for each). Regarding clinical outcomes at six months—measured using the Harris Hip Score—there was no significant difference between the groups (96.6 vs. 94.7; p=0.374).

Functional Planning Instead of a “Safe Zone”

Regarding acetabular component positioning, the prevailing trend has shifted away from rigid target values ​​toward individualized planning. Dr. Frank Horst (Sendenhorst) advocated for adjusting the acetabular anteversion based on the actual anteversion achieved in the femoral stem, rather than aiming for a fixed “safe zone” (as defined by Lewinnek). He suggested that a combined anteversion of 25 to 45 degrees is a more practical target, given that the acetabulum and the femur function as a single system. This approach is particularly well-suited for short-stem implants, where stem torsion varies significantly from patient to patient, allowing the acetabular position to be tailored to the specific placement of the stem. In contrast, standard stems often necessitate certain compromises.

Prof. Dr. Peter Schräder (Seeheim-Jugenheim) approached the same topic from a technological perspective, focusing on robot-assisted hip arthroplasty. He offered a critical assessment of the current trend toward robotics: while international literature consistently indicates improved radiological precision in implant positioning, any additional clinical benefit—in terms of patient-reported outcome measures (PROMs) or revision rates—remains statistically tenuous and potentially confounded by other variables. Prof. Dr. Schräder argued that the true value of robotics lies less in the tool itself and more in a shift in methodology—an “intellectual approach to implantation”—which accounts for spinopelvic imbalance and utilizes a functional, combined anteversion rather than adhering to a rigid safe zone. He cited a study (Iorio et al. 2025) showing that when the acetabular position is planned functionally and tailored to the individual patient, 92 percent of the components fall outside the traditional Lewinnek “safe zone.”

Regarding surgical technique itself, the focus has also shifted toward tissue preservation and individualization. Prof. Dr. Timm Filler (Düsseldorf) added an anatomical perspective: since proprioception is primarily located within the connective tissue and is part of the pain-signaling system, there are sound anatomical reasons to preserve as much tissue as possible and to employ a minimally invasive approach.

PD Dr. Peter Prodinger (Hausham) supplemented the discussion on surgical access by introducing a practical modification for obese patients: instead of making a longitudinal incision through the abdominal and inguinal folds—as is typical for an anterior approach—he utilized a transverse skin incision, following the Langer’s lines of skin tension (a technique known as a “bikini incision”). The objective was to prevent wound-healing complications at the junctions of these skin folds; however, he noted that the cosmetic outcome was, in fact, the primary motivation for developing this approach.

PD Dr. Peter Prodinger