Anatomic stemless shoulder arthroplasty and related outcomes: a systematic review

Six different canal-sparing respectively stemless humeral implants are presently available on the market, four of which are described in published studies. The canal-sparing respectively stemless shoulder prosthesis with metaphyseal anchoring is a relatively new concept that reportedly provides good outcomes that are comparable to stemmed designs in short and midterm evaluations [19, 21‐23, 27]. All of the presently reviewed studies demonstrated substantial improvement after replacement. Moreover, the studies that compared the canal-sparing respectively stemless design to stemmed implants showed no differences in outcomes related to the humeral component [21‐23].

The indications for canal-sparing respectively stemless prosthesis are the same as for stemmed systems. Canal-sparing respectively stemless implants cannot be used in cases with poor bone quality, metaphyseal cysts, osteopenia, osteoporosis, or other metabolic bone diseases [29], or in cases with fractures in the metaphyseal area that disturb adequate bony in-growth or primary implant stability. However, there is not yet any test available to objectively determine bone quality pre- or intraoperatively [29]. Churchill et al. [18] described the use of a “thumb test” in which bone quality is intraoperatively assessed by compressing the surface of the neck cut with the thumb. Overall, the presently reviewed studies reported only a few isolated cases of loosening of the stemless component.

Among the various investigated canal-sparing respectively stemless prostheses, the main difference in design is that the Eclipse is inserted over a screw, while the TESS, the Simpliciti, and the Affinis prostheses are inserted using an impaction technique. It appears that the mechanism of force transmission when the Eclipse prosthesis is inserted over a screw differs from that during impaction implantation of the corolla of the TESS, the wings of the Affinis, or the Simpliciti prosthesis. This difference may explain the observed differences in the surrounding humeral bone, with changed bone mineral density seen on radiographs, which could be interpreted as stress shielding beneath the trunnion with the Eclipse prosthesis. These findings are not correlated with any negative clinical symptoms, and seem to be purely a radiographic phenomenon, at least at the midterm follow-up. Subgroup analysis of these patients reported by Habermeyer et al. [27] revealed no statistical significance in the patient cohort, with a minimum follow-up of 5 years.

One major advantage of the canal-sparing respectively stemless prosthesis design is that it can potentially be used in post-traumatic and deformity cases regardless of the humeral head–shaft configuration. Restoration of the glenohumeral center of rotation independently from the shaft is a key goal in secondary shoulder arthroplasty for fracture sequelae treatment [30]. Malunion resulting in metaphyseal–diaphyseal malalignment can make it difficult or even impossible to implant a stemmed or even a short-stemmed prosthesis. In such cases, corrective osteotomies are associated with poor results [31]. Reports of these types of special cases are limited to only rare single cases within the studies. Other advantages of the canal-sparing respectively stemless prosthesis are that it can preserve bone stock of the proximal humerus, as well as avoid humeral stem-related complications in revision cases requiring stem removal. In a commentary, Athwal summarized the advantages of the canal-sparing respectively stemless implant as a theoretically decreased surgical time, less blood loss, bone preservation, and lower risk of intraoperative and potentially postoperative periprosthetic fractures. Canal-sparing respectively stemless prostheses are also suitable for posttraumatic joint reconstruction and, when needed, explantation is easier compared to with the stemmed version. Following explantation, a stemless prosthesis can be replaced by a standard-length primary implant [29].

For the purpose of this review, we chose to include all available literature evaluating anatomic canal-sparing respectively stemless humeral components in shoulder arthroplasty. This review article refers to only implant designs with metaphyseal fixation, and excludes humeral head resurfacing. It is much easier to achieve glenoid exposure for glenoid component implantation using canal-sparing respectively stemless implants compared to with humeral head resurfacing [3, 20].

It must be noted that, all reviewed studies provide only short or midterm results, and include only a limited number of patients. Additionally, some studies were reported by the designer or co-developer of the investigated implant, which suggests the possibility of a certain bias. There are presently ongoing IDE trials, which will provide more robust and high-quality data on this topic.