05 Nov MEET THE EXPERT | Report
1 October 2021 | Triple Z | Essen
MEET THE EXPERT | Report
The A2® short shaft on its way to becoming a standard
On the first weekend in October, the scientific directors Dr. Frank Horst, Sendenhorst and PD Dr. Stefan Budde, Bielefeld, the “Friends of the short shaft” to a “Meet the Experts” of the company Artiqo in Essen. In addition to an intensive exchange between the study and reference centers of the A2® socket and a course on preparations, there was plenty of time to discuss the data and the extensive area of application of the versatile socket system, which is becoming more than standard shank applies.
The short stem and especially the A2® stem can point to very good preclinical and clinical data. Budde emphasised that there are, however, different short stem philosophies: “The short stem idealist looks at the proximal force application.” The analysis of the lime-guided A2® stem with the finite element method shows very clearly how reliably the system anchors proximally. This was not at the expense of the primary stability, as Dr Alexander Derksen, Hanover, explained on the basis of the interim evaluation of the two-year radiostereometry analysis. The 6-month data showed good osseointegration of the A2® stem and a promising migration pattern, which indicated a low risk of aseptic loosening.
From the clinic, Budde added the one-year follow-up of a multicentre application observation of the A2® stem. For 153 of the 173 planned patients, the follow-up showed excellent scores (HHS, HOOS-PS, UCLA, Forgotten Joint) with few complications. Thanks to the Endoprosthesis Register Germany (EPRD), convincing data from the reality of care are also available. Prof. Dr. Arnd Steinbrück, Augsburg, spoke of the good experiences and results of the short stem in Germany in the context of the current EPRD evaluations. At 11%, their share in this country is comparatively high; at the same time, short stems perform significantly better than standard stems in terms of early revisions.
Steinbrück reported that the EPRD had dealt with the prejudice that the revision record of the short stem was only good because it was primarily implanted in young and healthy patients and by experts. With the help of the statistical method of propensity score matching, comparable groups were created, adjusted for influencing factors such as patient age, gender and co-morbidities, hospital volume and the bearing couples used. “The short shaft also performs somewhat better in a comparison of the adjusted groups [1],” summarized Steinbrück. Interesting is the statistically significant infection rate, which 5 years after the primary THA in the short sockets at 0.7% (95% CI 0.5-1.0%) is significantly lower than in the standard sockets with 1.0% 95% CI 0.8-1.2%).1 With regard to the balance of the comparison groups, a final explanation for this phenomenon has not yet been found. Among the short sockets, the A2® socket shows an excellent performance with a revision probability of 1.6% after 3 years, which will also be confirmed again by the annual report 2021, which will be published soon, according to Steinbrück.
Videos:
A. Derksen, MD: A2® RSA Study Results and Findings
Prof. Dr. med. A. Steinbrück:
How do short sockets compare to normal sockets in the EPRD?
PD Dr. medical St. Budde: Why short shafts? – The current data situation
The “all-rounder” among short shafts
The breadth and depth of the A2® socket range translates into a wide range of uses – just as you would expect from a standard socket. dr Harald Dinges, Kusel pointed out the variety of individual anatomies – such as coxa vara, valga and norma – that must be addressed by the user. With the “two body” design concept, the A2® range therefore offers two socket types: Type B for more varus and normal femora and Type G for more valgus femora. The A2® socket system has 19 finely tuned socket sizes so that the cortical femoral neck ring on the resection surface can be retained as far as possible.
Mario Frank, member of the management and developer at Artiqo, explained that the A2® stem shows a high degree of adaptability even with different femur morphologies according to Dorr classification types A, B and C. Especially in type A, which accounts for around 56% of cases [2], the unfavorable lever ratio of a normal socket led to an increased complication rate. From his clinical experience with the A2® socket, Dinges confirmed that the Dorr type A is an “excellent indication for the short socket” and that the femoral neck can be largely preserved.
dr Dirk Ganzer, Altentreptow, explained that with the new cemented A2® stem, there is now a short stem solution for Dorr type C morphologies. While the literature for cementless short stems in Dorr type C documents a fracture rate of 22% [3], a calcar-guided, cemented short stem could be a useful addition to a geriatric and osteoporotic patient clientele who would be classically treated with a cemented standard stem. The advantages of a cemented short stem such as the A2® stem lie in the muscle and bone protection and the minimally invasive procedure, the variable positioning and the reduction of intraoperative fractures. However, according to Ganzer, an exact cementing technique is crucial: “The short anchoring distance does not allow any mistakes in the cementing,” says Ganzer. It is important that the implant is homogeneously surrounded by the cement mantle and that the curing time is observed.
Short shaft for old and obese people – is that possible?
How useful is the short shaft for the very old and for people with obesity? Thorsten Hillmann, Cologne, examined these two previous contraindications. The Eduardus Hospital Cologne retrospectively evaluated the hip endoprosthetic treatment of n= 607 over 80-year-old patients between 2012-2019. Of these, n=191 were fitted with a Zweymüller socket and n=414 with a short socket (including an A2® socket). Since the usual scores for surveying very old and partly demented patients were not suitable, the clinic developed a simple “Cologne-Deutz score” with five items for the follow-up. The results showed a slight but non-significant advantage of the short stems for fractures and fissures, while the dislocation rate was significantly better for the short stems (1.19% after follow-up, p=0.003) than for the straight stems (4.71%). . In the short stem group there were a total of 4 complications and 14 revisions. Because of the advantages – shorter surgery time, less blood loss and trauma, fewer dislocations – active patients between the ages of 18 and 100 are supplied with a short stem in Cologne, says Hillmann. Good bone substance (Dorr type A and B) is decisive for this.
Hillmann emphasized that a safe fitting with a short stem is also possible for people with obesity. In a clinical study, the Cologne-based company compared the cement-free short shaft treatment in n=130 patients with a body mass index (BMI) of ≥ 40 kg/m2 and n=120 patients with a BMI of 20-29, 9kg/m2. The obese patients were on average younger and in poorer physical condition at the time of surgery, and the surgeries took significantly longer. It is well known that people with obesity suffer more complications and the risk of dislocation is also higher, regardless of the implant. The Cologne results showed no fractures in the two groups and no differences in the scores (Oxford Hip Score, “Cologne-Deutz-Score”). Dislocations (4 vs. 1) and revisions (8 vs. 4) occurred more frequently in the people with higher BMI, but without significance.
Preserving and reconstructing anatomy
Bone-saving, muscle-sparing, minimally invasive: these basic considerations had originally led to the creation of the short-shaft genre. Budde referred to the “certainly better anatomical reconstruction” of the femoral offset, which he was able to prove, among other things, through an X-ray CT study in his own clinic: While with a straight stem the reconstruction of the anterior offset would be at the expense of the lateral offset, the ante-tilt position of the calcaneally guided short stem would allow the anterior offset to be reconstructed without disadvantages for the lateral offset. Budde and his team validated the assumption that this could also result in higher stability and a more physiological reconstruction of the muscle tension conditions with a study using gait analyses and isokinetic force measurement.
From the anatomist’s point of view, too, there are reasons to preserve as much tissue as possible and to proceed in a minimally invasive way. Prof. Dr. Timm Filler, Düsseldorf, explained that the propriosensory system is essentially located in the connective tissue. In case of traction, pressure or destruction of the connective tissue, the propriosensory changes. However, proprioception is relevant because it is part of the pain system. Incorrect or excessive strain leads to an irritation of the proprioceptors and to the sensation of pain.
Every short shaft fitting begins with good planning
While the introduction of the short stem is considered to be easier with the normal stem, the preoperative planning is considered to be a central component and more demanding. Dinges pointed out that in addition to the shaft size, CCD angle, offset and medullary cavity geometry, the resection line in relation to the fossa piriformis / lesser trochanter should also be planned as digitally as possible. dr Frank Horst, Sendenhorst, who can refer to the extensive experience of 11,000 short-stem prostheses, added that if in doubt, the femur rotation should be planned via the opposite side. All “four dimensions” including rotation and tissue consistency are only known intraoperatively in order to finally determine the sizes. He also had a tip for the other users for the rotation: Horst first prepares the short stem with his “Femur First” technique in order to be able to assess the rotation and antetorsion of the stem before he implants the cup. This procedure results in a combined anteversion from the anteversion of the shaft and the anteversion of the socket, which amounts to approx. 35-40 degrees, concluded Horst.
[1] Steinbrück, A., Grimberg, A.W., Elliott, J. et al. Orthopäde 50, 296–305 (2021). https://doi.org/10.1007/s00132-021-04083-y
[2] Park, CH-W, Eun H-J, Oh, S-H et al. J Arthroplasty 2019 Mar;34(3):527-533. doi: 10.1016/j.arth.2018.11.004. Epub 2018 Nov 13.
[3] Gkagkalis, G., Goetti, P., Mai, S. et al. BMC Geriatr 19, 112 (2019). https://doi.org/10.1186/s12877-019-1123-1