The growing utilization of shoulder arthroplasty procedures has seen a concomitant rise in revision shoulder arthroplasty procedures and increased interest in implant design that can facilitate revision procedures. Convertible platform shoulder arthroplasty carries theoretical advantages in ease of revision component implantation, although these systems are not without their limitations.
In a recent JSES review article, Kelly et al. provide a comprehensive review of the literature on advantages and disadvantages of convertible-platform systems in shoulder arthroplasty. The article summarizes the rationale of convertible-platform systems that allow for partial implant retention during revision surgery, as well as some common modes of implant failure that preclude conversion.
The authors cite a study by Young et al. that demonstrated 55% of patients who have undergone an aTSA develop rotator cuff dysfunction at 15 years post-surgery, which underscores the importance of consideration of future revision procedures at the time of primary implantation. In this setting, RSA is often an excellent revision option, given that deltoid function is typically intact. However, other modes of failure, including implant instability and glenoid failure, require component extraction during revision surgery and can obviate the benefits of a convertible-platform system.
The study does acknowledge that convertible-platform systems can eliminate the need for humeral component extraction, traditionally the most common source of intraoperative complications. Specifically, decreased operative time, less blood loss, shorter recovery times, and lower costs have also been reported in head-to-head comparisons between humeral stem retention versus humeral stem exchange in revision procedures. In addition, one study cited in this review describes improved active external rotation in patients undergoing humeral stem retention during revision surgery, suggesting to me greater preservation of the soft tissue envelope.
On the other hand, convertible-platform systems have also demonstrated intraoperative challenges during revision surgery, with multiple studies citing rates of modular humeral component extraction exceeding 25%. This is often due to excessive soft-tissue tensioning or overstuffing during a conversion surgery that can impair intraoperative reduction or terminal range of motion, requiring extraction of components. Therfore, proper stem positioning and an adequate humeral head resection of convertible-platform systems during the index aTSA procedure is essential not only for preventing implant failure, but also for facilitating possible future RSA revision surgery. Inlay humeral components for RSA also have the potential for decreasing implant tension when stem retention is desired, although this is system specific.
On the glenoid side, modular metal-backed glenoid (MBGs) are potentially advantageous in that these components allow for flexibility in revision surgery planning. If the revision is planned for an aTSA, the polyethylene component can be simply exchanged; if the revision is to an RSA, a glenosphere can be attached to the MBG. However, the study authors are careful to note that MBGs are greater than three times more likely to require revisions than their all-polyethylene counterparts. While the historical failure rate of MBGs may continue to decrease due to improved implant design, the current literature suggests a high rate of complications.
This study comprehensively illustrates the current applicability of convertible-platform systems in the context of common failure modes of total shoulder arthroplasty. Current modular implant designs offer significant perioperative and patient-based advantages when convertible-platform systems can be successfully incorporated into revision total shoulder arthroplasties. Despite this, implant extraction at the time of revision surgery remains high. Ultimately, these factors must all be considered when choosing implants for primary shoulder arthroplasty and indications will continue to evolve as increasing longitudinal data on convertible systems is reported in the literature.