Mid-term results (4–8 years) with the stemless Simpliciti shoulder system

The study was reviewed by the local ethics committee (study number AZ-319/17) and informed consent was obtained from all individual participants included in the study.

A single-center, retrospective, single-arm study was performed. The first consecutive 105 patients (110 shoulders) with implantation of the Simplicti shoulder system between April 2011 and December 2014 were assessed.

From April 2011 to December 2014, 110 Simpliciti prosthesis were implanted in 105 patients. During follow-up, four patients died, three patients were lost to follow-up, four patients had to be excluded from this study because of neurological illness, and one patient did not want to participate. Due to the COVID-19 pandemic in 2020, not all patients could be examined clinically, but the SSV and QDASH scores were collected from four patients in telephone interviews.

In total, follow-up of 89.1% of patients was achieved. Data from 98 (98/110) Simpliciti shoulder prostheses in 93 patients (38 men, 55 women) were evaluated for this study. Specifically, 10 HSA and 88 TSA were analyzed. The mean age at surgery was 66.7 years (32–83 years). At follow-up the mean age was 72.7 years (36–90 years). A mean follow-up of 71.5 months (49–106 months) was achieved. Patients with primary omarthrosis, posttraumatic omarthrosis, primary humeral head necrosis, secondary humeral head necrosis after fracture, omarthrosis in glenoid defect, and omarthrosis in glenoid dysplasia were included in the analysis.

Stemless shoulder prostheses have been available since the early 2000s but mid- and long-term results are still scarce [18]. Beck et al. [1] showed good clinical and radiographic results for the stemless TESS (Biomet, Warsaw, IN, USA) with a follow-up of 94.7 months and an average CS of 68.8 points. Currently the Eclipse (Arthrex, Naples, FL, USA) prosthesis is the stemless shoulder prosthesis with the longest evaluated follow-up of 108 months; with an average CS of 62 points, good clinical and functional results were achieved [7]. For the Simpliciti shoulder system, Churchill et al. [3] demonstrated good short-term results with a 2-year follow-up. The CS improved from 44.3 to 80.7 points and a gain in the nCS from 55% to 104% was achieved. Collin et al. [4] showed good results for the Simpliciti with a mean follow-up of 35 months. The current study is the first to report mid-term results for the Simpliciti shoulder system.

It is under debate whether TSA or HSA provides more reliable outcomes. In our study, TSA achieved statistically significantly better postoperative results only in QDASH and nCS compared to HSA, but in no other measured parameter. This could be because the HSA group, with an average age of 63.7 years, consisted of younger patients than the TSA group, with an average age of 73.7 years. Furthermore, the gender distribution in the HSA group was a balanced gender ratio between women and men, whereas there were 54 women and 34 men in the TSA group. Both age and sex have a great influence on the nCS, because the mean CS is significantly higher in male patients than in female patients, and the nCS is also significantly different in each age group [15]. Therefore, it is easier to achieve a high nCS for older, female patients.

In the observation period, no lysis around the nucleus or displacement of the Simpliciti was detected on the X‑ray images and the prosthesis showed good bony ingrowth. There was no loosening of the implant in any patient.

Bone resorption occurred in the marginal areas of the prosthesis, where the humeral head protrudes over the nucleus and no direct contact or force transmission between the prosthesis head and the bone exists (areas S, I, V, D; Figs. 2 and 3). According to Wolff’s law [20], the missing load transmission leads to bone resorption. All bone resorptions detected were without clinical relevance and all Simpliciti prostheses were firmly anchored in the humeral bone. Similar findings were reported by Churchill et al. [3]. They also reported on bone resorption around the humeral medial calcar up to the neck of the nucleus in about 50% of their patients without any signs of prosthetic loosening or clinical relevance.

In our study, a mean deviation of the postoperative COR from the preoperative COR of 3.7 mm ± 1.9 mm was determined. Overall, 39.3% of the measured shoulders showed a deviation of less than 3 mm. The postoperative ROC, which is determined by the prosthesis design, differed by 3.1 mm ± 1.3 mm from the preoperative anatomical ROC. No significant correlation was determined between the deviation in the COR and the ROC with the collected scores. Gallacher et al. [5] reported a deviation in the postoperative COR of less than 3 mm in 76% of cases with the Eclipse, whereas Kadum et al. [8] reported a deviation of less than 3 mm in 82% of the cases using the stemless TESS. A possible explanation for the fact that the reconstruction with a deviation in the COR of less than 3 mm was only achieved in 39.3% of the cases in our study may be found in the prosthesis design of the Simpliciti. When choosing the humeral head component, surgeons orient themselves at the resected bony humeral head and the resection level. When implanting the prosthesis head, care is taken to ensure that the prosthesis does not protrude beyond the resection level and is flush with the metaphyseal bone. The Simpliciti humeral head has rounded edges (Fig. 4a). The surgeon uses this edge to check the size of the prosthesis. Due to the rounded edges, the actual measured diameter of the prosthesis head does not correspond to the printed prosthesis size (Fig. 4b). The printed prosthesis size results from the curvature of the surface of the prosthesis and is achieved when the curvature of the prosthesis surface is continued and intersects the undersurface of the prosthesis with a sharp edge (Fig. 4c). The postoperative measurements of the COR and the ROC on the X‑ray image were carried out similar to Fig. 4c by a best-fitting circle that runs through three points on the prosthesis surface and thus corresponds to the completion of the surface curvature. Due to the rounded edges of the Simpliciti, which intraoperatively merge flush into the humeral bone, an apparently too large ROC is measured on the postoperative X‑ray image. The Eclipse and the TESS do not have rounded edges like the Simpliciti. Here, the printed diameter corresponds to the measured diameter. It is therefore questionable whether this method of measuring the COR and the ROC is equally suitable for the Simpliciti as for the TESS or Eclipse prosthesis.

No intraoperative complications occurred in the present study. Three patients developed secondary shoulder stiffness, which is a rather rare complication of shoulder prostheses. In the affected patients, all implant- and patient-specific factors were excluded and an arthroscopic 360° arthrolysis was performed. It can be assumed that in these cases that the scarring found in the sliding layers was the cause of the stiffness, since none of the patients reported any complaints in the subsequent course, which is also consistent with the results reported by Thorsness et al. [16].

In two of the prostheses examined (2/98), a periprosthetic fracture occurred postoperatively as a result of a fall. One of these fractures could be treated conservatively; in the second, osteosynthesis was performed using an angle-stable plate. Primary implant removal was not necessary in any case. Incidence rates of 1.6–2.8% for postoperative periprosthetic humeral fractures are reported in the literature [12]. Thus, our incidence of 2.0% is within the range described in the literature. Periprosthetic humeral fractures represent a major surgical challenge. The design of the Simpliciti offers more space for the insertion of osteosynthesis material during osteosynthesis and in the event of a fracture with prosthesis loosening, the small implant enables revisions using a stemmed implant.

Radiological signs of loosening of the cemented glenoid were detected in two patients. One of the patients was lost to follow-up. The second patient underwent revision surgery due to glenoid loosening. The Simpliciti was found to be firmly anchored intraoperatively and well integrated with the humeral bone. The metaphyseal anchorage of the Simpliciti and the minimal loss of bone substance during explantation enabled implantation of a standard cemented RSA. Cancellous bone from the metaphysis and cancellous bone that had grown into the nucleus could be used to fill the glenoid defect, eliminating the need for cancellous bone harvest from the iliac crest or the use of allogeneic bone material.

The complication rate of 7.1% (7/98) and the revision rate of 5.1% (5/98) observed here correspond to those reported in the literature for stemless shoulder prostheses [10, 18, 19].

Wiater et al. [17] demonstrated no significant functional or clinical difference between stemmed and stemless shoulder prostheses in their prospective, blinded, randomized controlled trial. So do several current meta-analyses [11, 13, 14]. These data are also in line with the data collected in our study, showing the Simpliciti shoulder system to perform as well as stemmed prostheses at mid-term follow-up.