The results afforded by new shoulder implant systems must be compared with the good results obtained using the existing concepts for shoulder arthroplasty. The use of modern anatomically designed shoulder implant systems in combination with glenoid resurfacing provides significant pain relief and improvement of function over the long term [25]. However, the clinical outcome and the long-term survival of the prosthesis in existing modern shoulder prosthesis systems can be affected in particular by problems with the soft tissue and complications with the glenoid component [16, 26, 27]. In contrast, complications relating to the humeral component (such as loosening and malpositioning of the humeral stem or periprosthetic fractures) are much less common (an incidence of approximately 1 % according to the literature); however, given the rising numbers of shoulder implants that are being performed, they are clinically relevant [16]. Another problem with the use of a standard stemmed shoulder prosthesis can occur in patients with posttraumatic situations of the proximal humerus (fracture sequelae). These cases are often associated with deformities of the proximal humerus, especially in the area of the humeral metaphysis. Therefore, the correct positioning of the humeral stem can be challenging and technically demanding [28, 29], which is clearly reflected in the complication rate of 25–32 % [30–32]. A frequent complication after total shoulder arthroplasty is postoperative tearing of the rotator cuff, which may also result in revision of the anatomical total shoulder replacement and the implantation of a reversed shoulder arthroplasty [16]. In these cases, the removal of the humeral stem is also associated with potential problems like fractures with the need for a new massive humeral stem [16]. An alternative that avoids these typical humeral problems is the use of humeral head resurfacing. Nevertheless, surface replacement arthroplasty is also potentially associated with typical problems, such as the potential risk of “overstuffing” the humeral head component; the use of a glenoid component is also technically demanding as the humeral head is left in situ [33].
Due to these specific problems, the anatomic stemless shoulder prosthesis was developed in the mid-1990s. The characteristic feature of this type of prosthesis is the cementless metaphyseal fixation of the implant by some mechanism. The essential advantage of this concept is the fixation of the humeral component without the need to prepare the humeral diaphysis. Therefore, the humeral head can be positioned regardless of the shape of the humeral diaphysis. Aside from patients with primary OA, this fixation technique is particularly useful in patients with posttraumatic OA of the shoulder and deformities in the metaphyseal region.
Another advantage of the stemless shoulder prosthesis is the preservation of the humeral bone stock. This potentially results in better starting conditions if any revision surgery is needed, and reduces the potential risk of typical complications such as intraoperative humeral fracture in cases requiring removal of the humeral stem. Furthermore, in comparison with humeral head resurfacing, adequate exposure of the glenoid to allow the implantation of a glenoid component is much easier to achieve.
In this study, we compared the clinical and radiological results of patients with primary OA of the shoulder who were surgically treated with either a standard stemmed shoulder prosthesis or an anatomical stemless shoulder prosthesis. To our knowledge, this is the first study to be age, gender, and follow-up matched in order to allow the results obtained with both types of prosthesis in patients with primary OA of the shoulder to be compared. In accordance with several other studies [25, 34], our results show significant improvement in shoulder function and pain relief across the entire investigation series. In particular, the clinical results noted here for the stemless shoulder prosthesis were comparable with those reported by other authors [19–21]. However, we did not detect a significant difference in the range of movement, DASH score, and Constant score between both types of prosthesis within the follow-up period. Otherwise, with respect to the intra- and perioperative data, their shorter operative times and reduced loss of blood represent potential advantages of the patient group treated with stemless shoulder prosthesis.
However, another possible reason for the shorter operative time and the minor blood loss seen when using the stemless shoulder prosthesis could be that this is due to the use of different implant fixation techniques in both treatment groups. In contrast to the cementless fixation of the stemless shoulder prosthesis, all conventional humeral stems in the other treatment group were inserted with cement, which necessitated additional operative time for the cement to harden. In addition, patients receiving a standard anatomic shoulder prosthesis (group 1) required more extensive preparation of the humerus, which can lead to higher blood loss. Despite this potential benefit of the stemless shoulder prosthesis, no clinical consequences of it, such as blood transfusion or a higher revision rate in group 1 due to perioperative complications, were observed: the results of radiological investigations and the complication rates in both groups were comparable.
Therefore, we can conclude that the stemless shoulder prosthesis provides good clinical results in patients with patients with OA of the shoulder without the need for a humeral stem. This surgical technique offers a reliable method for the anatomic restoration of the proximal humerus. The metaphyseal anchorage of the humeral implant used in this study was achieved using a specially designed fixation device with six fins coated with hydroxyapatite of different sizes. The impaction of this fixation system with automatic centering in the metaphyseal region of the humerus is appropriate in the normal bone structure as well as in the soft bone structure. Beside the configuration of the spongiosa, the humeral head must be cut precisely such that a plane and stable surface of the bone is obtained for sufficient osteointegration of the implant. If required, an additional bone graft from the resected humeral head can be placed below the prosthetic head, improving the primary stability of the implant. If primary stability of the humeral implant cannot be realized, the placement of a stemmed shoulder prosthesis is mandatory during the surgery as an alternative option. If necessary, a preoperative CT investigation may be helpful for assessing the bone quality of the proximal humerus with respect to the implantation of a stemless shoulder prosthesis.
Although investigating the influence of the factor age on the clinical results was not a main aim of our study, the results presented here indicate that the implantation of a stemless shoulder prosthesis represents a reliable option for surgical treatment, even in elderly patients with potentially decreased bone osseous mineral density. Another influence on the functional results after total shoulder arthroplasty is the status of the rotator cuff [3], which also often shows considerable lesions, particularly in elderly patients. Therefore, when necessary, an additionally MRI investigation was carried out in these patients to exclude massive rotator cuff tears. We were also able to demonstrate [35] that the implantation of a stemless shoulder prosthesis as a hemiarthroplasty can also yield reasonable results in a patient with a rotator cuff tear arthropathy and low functional demands.
One limitation of our study was the duration of our follow-up. Our assessment at 32 months prevents any conclusion from being drawn regarding the long-term results, especially those for the new anatomical stemless shoulder prosthesis. We cannot exclude the possibility that our follow-up was too short to detect possible differences in the survivorship of this prosthesis.
In conclusion, this study demonstrates good midterm results following the placement of an anatomically designed stemless shoulder implant system in the treatment of OA of the shoulder. In addition, the technical aspect of the metaphysal fixation allows precise and simple reconstruction of the proximal humerus with preservation of the humeral bone stock and adequate exposure of the glenoid. Further investigations are needed to determine the long-term performance of this prosthesis.